text:
A computationally efficient aerosol nucleation/condensation method: Pseudo-steady state gas phase sulfuric acid
NASA Astrophysics Data System (ADS)
Adams, P. J.; Pierce, J. R.
Aerosol nucleation and condensation are two processes that compete for gas phase sulfuric acid when it is formed in the atmosphere. Without approximations, accurate numerical integration of aerosol microphysics requires time steps on the order of seconds or less when nucleation is occurring, significantly shorter than the time steps required by other processes governing aerosol microphysics. This computational burden makes the explicit numerical simulation burdensome in 3-dimensional atmospheric models. We have developed an efficient method for simulating nucleation/condensation by assuming that gas phase sulfuric acid is at a pseudo- steady state (PSS) concentration determined by chemical generation and its loss by nucleation and condensation. The time step for nucleation/condensation is then governed by 1) the change in the condensation sink, 2) the change in the generation rate of sulfuric acid, 3) the coagulation timescale, or 4) a master time step in the model. The PSS assumption fails only when the time for sulfuric acid to reach its PSS state concentration is not significantly shorter than the four timescales above. This may occur when the following conditions are met 1) the condensation sink is less than 10-3-10-4 s-1, 2) nucleation is not occurring, and 3) the gas phase production rate is changing. These conditions are not frequently met for a long period of time in the atmosphere. The PSS assumption allows for time step increases of two to three orders of magnitude during nucleation events in typical atmospheric conditions and has been shown to reduce the nucleation/condensation computational time by a factor of 10-100.
Onset conditions for gas phase reaction and nucleation in the CVD of transition metal oxides
NASA Technical Reports Server (NTRS)
Collins, J.; Rosner, D. E.; Castillo, J.
A combined experimental/theoretical study is presented of the onset conditions for gas phase reaction and particle nucleation in hot substrate/cold gas CVD of transition metal oxides. Homogeneous reaction onset conditions are predicted using a simple high activation energy reacting gas film theory. Experimental tests of the basic theory are underway using an axisymmetric impinging jet CVD reactor. No vapor phase ignition has yet been observed in the TiCl4/O2 system under accessible operating conditions (below substrate temperature Tw = 1700 K). The goal of this research is to provide CVD reactor design and operation guidelines for achieving acceptable deposit microstructures at the maximum deposition rate while simultaneously avoiding homogeneous reaction/nucleation and diffusional limitations.
The effect of carrier gas pressure on vapor phase nucleation experiments using a thermal diffusion cloud chamber
D. Kane; S. P. Fisenko; M. Rusyniak; M. S. El-Shall
Recent measurements of critical supersaturations for the vapor phase homogeneous nucleation of several substances using a diffusion cloud chamber technique exhibit a dependence on the pressure of the carrier gas used in the experiments. A model of droplet growth and motion in a diffusion cloud chamber, combined with the density and temperature profiles of the chamber is presented to explain
Modeling gas-phase nucleation in inductively coupled silane-oxygen S.-M. Suh, S. L. Girshick,a)
Zachariah, Michael R.
Modeling gas-phase nucleation in inductively coupled silane-oxygen plasmas S.-M. Suh, S. L. An inductively coupled plasma reactor was modeled in a one-dimensional multicomponent two-temperature framework while also having the capability of anisotropic deep etching. Inductively coupled plasmas ICPs
Phase nucleation in curved space
NASA Astrophysics Data System (ADS)
G¾mez, Leopoldo R.; GarcĒa, Nicolßs A.; Vitelli, Vincenzo; Lorenzana, Josķ; Vega, Daniel A.
Nucleation and growth is the dominant relaxation mechanism driving first-order phase transitions. In two-dimensional flat systems, nucleation has been applied to a wide range of problems in physics, chemistry and biology. Here we study nucleation and growth of two-dimensional phases lying on curved surfaces and show that curvature modifies both critical sizes of nuclei and paths towards the equilibrium phase. In curved space, nucleation and growth becomes inherently inhomogeneous and critical nuclei form faster on regions of positive Gaussian curvature. Substrates of varying shape display complex energy landscapes with several geometry-induced local minima, where initially propagating nuclei become stabilized and trapped by the underlying curvature.
Phase nucleation in curved space.
G¾mez, Leopoldo R; GarcĒa, Nicolßs A; Vitelli, Vincenzo; Lorenzana, Josķ; Vega, Daniel A
Nucleation and growth is the dominant relaxation mechanism driving first-order phase transitions. In two-dimensional flat systems, nucleation has been applied to a wide range of problems in physics, chemistry and biology. Here we study nucleation and growth of two-dimensional phases lying on curved surfaces and show that curvature modifies both critical sizes of nuclei and paths towards the equilibrium phase. In curved space, nucleation and growth becomes inherently inhomogeneous and critical nuclei form faster on regions of positive Gaussian curvature. Substrates of varying shape display complex energy landscapes with several geometry-induced local minima, where initially propagating nuclei become stabilized and trapped by the underlying curvature. PMID:25896725
Pore-scale interfacial dynamics during gas-supersaturated water injection in porous media - on nucleation, growth and advection of disconnected fluid phases (Invited)
NASA Astrophysics Data System (ADS)
Or, D.; Ioannidis, M.
Degassing and in situ development of a mobile gas bubbles occur when injecting supersaturated aqueous phase into water-saturated porous media. Supersaturated water injection (SWI) has potentially significant applications in remediation of soils contaminated by non-aqueous phase liquids and in enhanced oil recovery. Pore network simulations indicate the formation of a region near the injection boundary where gas phase nuclei are activated and grow by mass transfer from the flowing supersaturated aqueous phase. Ramified clusters of gas-filled pores develop which, owing to the low prevailing Bond number, grow laterally to a significant extent prior to the onset of mobilization, and are thus likely to coalesce. Gas cluster mobilization invariably results in fragmentation and stranding, such that a macroscopic region containing few tenuously connected large gas clusters is established. Beyond this region, gas phase nucleation and mass transfer from the aqueous phase are limited by diminishing supply of dissolved gas. New insights into SWI dynamics are obtained using rapid micro-visualization in transparent glass micromodels. Using high-speed imaging, we observe the nucleation, initial growth and subsequent fate (mobilization, fragmentation, collision, coalescence and stranding) of CO2 bubbles and clusters of gas-filled pores and analyze cluster population statistics. We find significant support for the development of invasion-percolation-like patterns, but also report on hitherto unaccounted for gas bubble behavior. Additionally, we report for the first time on the acoustic emission signature of SWI in porous media and relate it to the dynamics of bubble nucleation and growth. Finally, we identify the pore-scale mechanisms associated with the mobilization and subsequent recovery of a residual non-aqueous phase liquid due to gas bubble dynamics during SWI.
Investigation of metal and metal oxide clusters small enough to constitute the critical size for gas phase nucleation in combustion processes. Final report, 1 October 1975-30 June 1979
Over the course of this contract a variety of techniques have been employed to study the properties of small atomic and molecular clusters formed in the gas phase via homogeneous nucleation. The clustering occurs either in an adiabatic expansion of a condensable species (e.g. argon, krypton, xenon, or sulfur hexafluoride) in an inert carrier gas (e.g. helium), or as a
Analysis of urban gas phase ammonia measurements from the 2002 Atlanta Aerosol Nucleation and Real-Time Characterization Experiment (ANARChE)
NASA Astrophysics Data System (ADS)
Nowak, J. B.; Huey, L. G.; Russell, A. G.; Tian, D.; Neuman, J. A.; Orsini, D.; Sjostedt, S. J.; Sullivan, A. P.; Tanner, D. J.; Weber, R. J.; Nenes, A.; Edgerton, E.; Fehsenfeld, F. C.
Gas phase ammonia (NH3) measurements were made in July and August 2002 during the Atlanta Aerosol Nucleation and Real-Time Characterization Experiment with two different chemical ionization mass spectrometry techniques. Correlations between the 1 min data from both instruments yielded a slope of 1.17 and an intercept of -0.295 ppbv, with a linear correlation coefficient (r2) of 0.71. Ambient NH3 mixing ratios ranged from 0.4 to 13 ppbv. NH3 observations were compared to the Community Multiscale Air Quality (CMAQ) modeling system as well as a thermodynamic equilibrium model, ISORROPIA, used by CMAQ to predict NH3 partitioning. A morning rise in both observed and modeled NH3 mixing ratios strongly suggests a regional influence due to automobile emissions. However, at midday the predicted NH3 decreased to less than 0.5 ppbv, while the observations remained around 3 ppbv. Both observed and modeled ammonium nitrate levels were too low to support the observed midday NH3 mixing ratios. ISORROPIA calculations of NH3 constrained by the total measured ammonia mass (NH3 + ammonium (NH4+)) agreed well with the observations (slope of 1.25 and r2 of 0.75). For times when the net aerosol charge was near zero the agreement was excellent (slope of 1.22 and r2 of 0.88). These results indicate that for most of the observed conditions, ISORROPIA could accurately predict NH3 partitioning. The observations suggest that local sunlight- or temperature-driven NH3 sources, such as soil emissions, may be responsible for the discrepancy between the model results and measured values.
Nucleation kinetics of phase separation in a sodium silicate glass
Zoe Ann Osborne
This study was undertaken with the goal of comparing the calculated nucleation rate for phase separation with experimental measurements for a simple glass system. The magnitude and the temperature dependence of the nucleation rate for a sodium silicate glass composition in the binodal regime was calculated. These calculations used a minimum of assumptions in order to determine the limits on
Nucleation and growth of Nb nanoclusters during plasma gas condensation
Bray, K. R.; Jiao, C. Q. [UES, Inc., 4401 Dayton-Xenia Rd, Dayton, Ohio 45432 (United States)] [UES, Inc., 4401 Dayton-Xenia Rd, Dayton, Ohio 45432 (United States); DeCerbo, J. N. [Air Force Research Laboratory, AFRL/RQQE, 1950 Fifth St., WPAFB, Ohio 45433 (United States)] [Air Force Research Laboratory, AFRL/RQQE, 1950 Fifth St., WPAFB, Ohio 45433 (United States)
Niobium nanoclusters were produced using a plasma gas condensation process. The influence of gas flow rate, aggregation length, and source current on the nanocluster nucleation and growth were analyzed. Nanoclusters with an average diameter from 4 nm to 10 nm were produced. Cluster size and concentration were tuned by controlling the process inputs. The effects of each parameter on the nucleation zone, growth length, and residence time was examined. The parameters do not affect the cluster formation and growth independently; their influence on cluster formation can be either cumulative or competing. Examining the nucleation and growth over a wide combination of parameters provided insight into their interactions and the impact on the growth process. These results provide the opportunity for a broader understanding into the nucleation and growth of nanoclusters and some insights into how process parameters interact during deposition. This knowledge will enhance the ability to create nanoclusters with desired size dispersions.
Simulation and Kinetics of Grain-Boundary Nucleated Phase Transformations
Cambridge, University of
Simulation and Kinetics of Grain-Boundary Nucleated Phase Transformations E.A. Jõgle1, E fields overlap e.g. Phase-Field simulations1 1 Bruna et al., J. Appl. Phys. 100 (2006) 054907 / 2 violated e.g. if diffusion fields overlap e.g. Phase-Field simulations1 equiaxed growth violated e
Vekilov, Peter G.
Crystallization starts with nucleation and control of nucleation is crucial for the control of the number, size, perfection, polymorphism and other characteristics of crystalline materials. This is particularly true for crystallization in solution, which is an essential part of processes in the chemical and pharmaceutical industries and a major step in physiological and pathological phenomena. There have been significant recent advances in the understanding of the mechanism of nucleation of crystals in solution. The foremost of these are the two-step mechanism of nucleation and the notion of the solution¢crystal spinodal. According to the two-step mechanism, the crystalline nucleus appears inside pre-existing metastable clusters of size several hundred nanometers, which consist of dense liquid and are suspended in the solution. While initially proposed for protein crystals, the applicability of this mechanism has been demonstrated for small molecule organic materials, colloids, polymers, and biominerals. This mechanism helps to explain several long-standing puzzles of crystal nucleation in solution: nucleation rates which are many orders of magnitude lower than theoretical predictions, the significance of the dense protein liquid, and others. At high supersaturations typical of most crystallizing systems, the generation of crystal embryos occurs in the spinodal regime, where the nucleation barrier is negligible. The solution-crystal spinodal helps to understand the role of heterogeneous substrates in nucleation and the selection of crystalline polymorphs. Importantly, these ideas provide powerful tools for control of the nucleation process by varying the solution thermodynamic parameters. PMID:21132117
Gas-Phase Polymerization: Ultraslow Chemistry
Howard Reiss
The mechanism of formation of polymer molecules in the gas phase is difficult to study because the involatile polymers tend to condense out of that phase. However, new techniques, involving the use of cloud chambers, have enabled workers to use the nucleation of liquid drops in supersaturated monomer vapors to detect single polymer molecules and therefore to work with so
Nucleation of the diamond phase in aluminium-solid solutions
NASA Technical Reports Server (NTRS)
Hornbogen, E.; Mukhopadhyay, A. K.; Starke, E. A., Jr.
Precipitation was studied from fcc solid solutions with silicon, germanium, copper and magnesium. Of all these elements only silicon and germanium form diamond cubic (DC) precipitates in fcc Al. Nucleation of the DC structure is enhanced if both types of atom are dissolved in the fcc lattice. This is interpreted as due to atomic size effects in the prenucleation stage. There are two modes of interference of fourth elements with nucleation of the DC phase in Al + Si, Ge. The formation of the DC phase is hardly affected if the atoms (for example, copper) are rejected from the (Si, Ge)-rich clusters. If additional types of atom are attracted by silicon and/or germanium, DC nuclei are replaced by intermetallic compounds (for example Mg2Si).
Observing classical nucleation theory at work by monitoring phase transitions with molecular precision.
Sleutel, Mike; Lutsko, Jim; Van Driessche, Alexander E S; Durßn-Olivencia, Miguel A; Maes, Dominique
It is widely accepted that many phase transitions do not follow nucleation pathways as envisaged by the classical nucleation theory. Many substances can traverse intermediate states before arriving at the stable phase. The apparent ubiquity of multi-step nucleation has made the inverse question relevant: does multistep nucleation always dominate single-step pathways? Here we provide an explicit example of the classical nucleation mechanism for a system known to exhibit the characteristics of multi-step nucleation. Molecular resolution atomic force microscopy imaging of the two-dimensional nucleation of the protein glucose isomerase demonstrates that the interior of subcritical clusters is in the same state as the crystalline bulk phase. Our data show that despite having all the characteristics typically associated with rich phase behaviour, glucose isomerase 2D crystals are formed classically. These observations illustrate the resurfacing importance of the classical nucleation theory by re-validating some of the key assumptions that have been recently questioned. PMID:25465441
Observing classical nucleation theory at work by monitoring phase transitions with molecular precision
Sleutel, Mike; Lutsko, Jim; Van Driessche, Alexander E.S.; Durßn-Olivencia, Miguel A.; Maes, Dominique
It is widely accepted that many phase transitions do not follow nucleation pathways as envisaged by the classical nucleation theory. Many substances can traverse intermediate states before arriving at the stable phase. The apparent ubiquity of multi-step nucleation has made the inverse question relevant: does multistep nucleation always dominate single-step pathways? Here we provide an explicit example of the classical nucleation mechanism for a system known to exhibit the characteristics of multi-step nucleation. Molecular resolution atomic force microscopy imaging of the two-dimensional nucleation of the protein glucose isomerase demonstrates that the interior of subcritical clusters is in the same state as the crystalline bulk phase. Our data show that despite having all the characteristics typically associated with rich phase behaviour, glucose isomerase 2D crystals are formed classically. These observations illustrate the resurfacing importance of the classical nucleation theory by re-validating some of the key assumptions that have been recently questioned. PMID:25465441
Observing classical nucleation theory at work by monitoring phase transitions with molecular precision
NASA Astrophysics Data System (ADS)
Sleutel, Mike; Lutsko, Jim; van Driessche, Alexander E. S.; Durßn-Olivencia, Miguel A.; Maes, Dominique
It is widely accepted that many phase transitions do not follow nucleation pathways as envisaged by the classical nucleation theory. Many substances can traverse intermediate states before arriving at the stable phase. The apparent ubiquity of multi-step nucleation has made the inverse question relevant: does multistep nucleation always dominate single-step pathways? Here we provide an explicit example of the classical nucleation mechanism for a system known to exhibit the characteristics of multi-step nucleation. Molecular resolution atomic force microscopy imaging of the two-dimensional nucleation of the protein glucose isomerase demonstrates that the interior of subcritical clusters is in the same state as the crystalline bulk phase. Our data show that despite having all the characteristics typically associated with rich phase behaviour, glucose isomerase 2D crystals are formed classically. These observations illustrate the resurfacing importance of the classical nucleation theory by re-validating some of the key assumptions that have been recently questioned.
Nucleation and phase selection in undercooled Fe-Cr-Ni melts. Part 1: Theoretical analysis of nucleation behavior
Volkmann, T.; Herlach, D.M. [German Aerospace Research Establishment, Koeln (Germany). Inst. for Space Simulation; Loeser, W. [Inst. for Solid State and Materials Research, Dresden (Germany). Inst. for Metallic Materials
The selection of the primary solidifying phase in undercooled stainless steel melts is theoretically analyzed in terms of nucleation theory. Nucleation phenomena are considered using different models for the solid-liquid interface energy. The classical nucleation theory for sharp interfaces and an improved modification, the diffuse interface theory, are applied. The influence of deviations of the nucleus composition from the overall alloy composition is also revealed. A preferred nucleation of the metastable bcc phase in fcc equilibrium solidification-type alloys is predicted. The critical undercooling of metastable crystallization as a function of alloy composition is calculated for an isoplethal section at 69 at. pct Fe of Fe{sub 69}Cr{sub 31{minus}x}Ni{sub x} alloys. The results are summarized in a phase selection diagram predicting the primary solidification mode as a function of undercooling and melt composition.
Toward a complete description of nucleation and growth in liquid-liquid phase separation
Paris-Sud XI, Universitķ de
Toward a complete description of nucleation and growth in liquid-liquid phase separation Short separation mechanism of a binary liquid mixture off-critically quenched in its miscibility gap is nucleation separates in two phases. This liquid-liquid phase separation gives the opportunity to observe the pathway
Application of classical nucleation theory to phase selection and composition of nucleated nanocrystals during crystallization
Laughlin, David E.
online 11 June 2010 Abstract Classical steady-state nucleation theory is applied to Co-rich Fe,Co reserved. Keywords: Crystallization; Nucleation; FeCo; Co-rich; Nanocomposite 1. Motivation and relevant) crystallization of an initially amorphous precursor to form a composite microstructure of Fe,Co-based nanocrystals
Homogeneous and heterogeneous nucleations in the surface phase transition: Si(111)4 ū 1-In
NASA Astrophysics Data System (ADS)
Shim, Hyungjoon; Jeon, Youjin; Yeo, Jonghoon; Lee, Geunseop
Homogeneous and heterogeneous nucleations in a reduced-dimensional system undergoing a first-order structural phase transition were examined by using low electron energy diffraction and scanning tunneling microscopy. The high-temperature 4 ū 1 phase of a Si(111)-In surface was supercooled at temperatures below the transition temperature ({T}{{c}}) and evolved slowly into a low-temperature 8 ū 2 phase with time. The transition rate decreased significantly as the temperature approached {T}{{c}}. The kinetics of the observed homogeneous nucleation was analyzed by classical nucleation theory. The introduction of oxygen atoms reduced the hysteresis and accelerated nucleation significantly, showing that the {T}{{c}}-raising oxygen impurity plays the role of a nucleation seed for heterogeneous nucleation.
Gas Phase Nanoparticle Synthesis
NASA Astrophysics Data System (ADS)
Granqvist, Claes; Kish, Laszlo; Marlow, William
This book deals with gas-phase nanoparticle synthesis and is intended for researchers and research students in nanomaterials science and engineering, condensed matter physics and chemistry, and aerosol science. Gas-phase nanoparticle synthesis is instrumental to nanotechnology - a field in current focus that raises hopes for environmentally benign, resource-lean manufacturing. Nanoparticles can be produced by many physical, chemical, and even biological routes. Gas-phase synthesis is particularly interesting since one can achieve accurate manufacturing control and hence industrial viability.
Heterogeneous Nucleation of the T1 Phase on Dispersoids in Al-Cu-Li Alloys
NASA Astrophysics Data System (ADS)
Tsivoulas, Dimitrios
The major strengthening phase of modern Al-Cu-Li alloys, T1, is so far known to nucleate on a number of sites in the microstructure. However, its preferential nucleation on Al20Cu2Mn3 dispersoids has never been reported with strong evidence up to now. The present work suggests that such heterogeneous nucleation is possible and performs a comparison with the precipitates distributed homogeneously in the matrix. This phenomenon is shown to promote a particle decohesive fracture mode.
Multiscale approach to CO2 hydrate formation in aqueous solution: phase field theory and molecular dynamics. Nucleation and growth.
Tegze, Gy÷rgy; Pusztai, Tamßs; T¾th, Gyula; Grßnßsy, Lßszl¾; Svandal, Atle; Buanes, Trygve; Kuznetsova, Tatyana; Kvamme, Bjorn
A phase field theory with model parameters evaluated from atomistic simulations/experiments is applied to predict the nucleation and growth rates of solid CO(2) hydrate in aqueous solutions under conditions typical to underwater natural gas hydrate reservoirs. It is shown that under practical conditions a homogeneous nucleation of the hydrate phase can be ruled out. The growth rate of CO(2) hydrate dendrites has been determined from phase field simulations as a function of composition while using a physical interface thickness (0.85+/-0.07 nm) evaluated from molecular dynamics simulations. The growth rate extrapolated to realistic supersaturations is about three orders of magnitude larger than the respective experimental observation. A possible origin of the discrepancy is discussed. It is suggested that a kinetic barrier reflecting the difficulties in building the complex crystal structure is the most probable source of the deviations. PMID:16821944
Propandiol vapor nucleation rates
NASA Astrophysics Data System (ADS)
Anisimov, M. P.; Nasibulin, A. G.; Timoshina, L. V.; Koropchak, J. A.
Consideration of vapor-gas nucleation as binary vapor nucleation (instead widely used the one component approximation for nucleation of this system now) may lead the progress in the development of nucleation theory. Observations of phase transitions initiated by the carrier gas in the critical embryos of condensate can be a sufficiently convincing argument in this discussion. In order to confirm the role of the carrier gases received in the recent research1, in present study 1,2-propanediol and 1,3-propanediol vapor nucleation rates were measured. Carbon dioxide (Tc=304.2 K,Pc=7.39 MPa) and sulfur hexafluoride (Tc=318.7 K,Pc=3.75 MPa) were chosen as the carrier gases, because of their low and convenient critical temperatures, Tc, and critical pressures, Pc. Analysis of the experimental data shows that gas-carrier molecules are involved in new phase embryo formation. Vapor nucleation of investigated substances in a carrier gas atmosphere can be considered as nucleation of binary system.
1,2-propanediol and 1,3-propanediol homogeneous nucleation rates and phase transitions in the new phase critical embryos
NASA Astrophysics Data System (ADS)
Anisimov, M. P.; Koropchak, J. A.; Nasibulin, A. G.; Timoshina, L. V.
Nucleation rates of supersaturated vapors near the conditions for the critical line for each pair of 1,2- or 1,3-propanediol and carbon dioxide or sulfur hexafluoride at total system pressures of P=0.10, 0.20, and 0.30 MPa have been measured in a flow diffusion chamber. Critical parameters, i.e., temperatures and pressures, of the binary systems versus compositions were semiempirically evaluated. It was found experimentally that there is an area of parameters in the PTx phase diagram, for each pair of vapor and carrier gas investigated in the present research, for which critical embryo phase transitions of the first order take place (where P, T, and x are pressure, temperature, and embryo composition, respectively). The nucleation rate surface singularity and a gap in the number of molecules in critical embryos reflect this area. Shifts of the phase transition temperatures can be initiated by increasing the pressure (or concentration) of the carrier gas. This behavior is peculiar for binary systems. It is well-known that no liquid-liquid phase transitions can exist for a one-component system. At least a binary solution is required for liquid-liquid phase transitions. This means that vapor nucleation of the investigated substances in the carrier gas atmosphere can be considered as nucleation of a binary vapor-gas system. A schematic diagram for the possible metastable vapor conditions is presented. On the basis of our experimental results, one can assume that there exists a surface describing the parameters related with a phase transition of the first order in critical embryos. This surface is located within the volume of the possible vapor metastable conditions.
Nucleation of ordered solid phases of proteins via a disordered high-density state: Phenomenological approach
NASA Astrophysics Data System (ADS)
Pan, Weichun; Kolomeisky, Anatoly B.; Vekilov, Peter G.
Nucleation of ordered solid phases of proteins triggers numerous phenomena in laboratory, industry, and in healthy and sick organisms. Recent simulations and experiments with protein crystals suggest that the formation of an ordered crystalline nucleus is preceded by a disordered high-density cluster, akin to a droplet of high-density liquid that has been observed with some proteins; this mechanism allowed a qualitative explanation of recorded complex nucleation kinetics curves. Here, we present a simple phenomenological theory that takes into account intermediate high-density metastable states in the nucleation process. Nucleation rate data at varying temperature and protein concentration are reproduced with high fidelity using literature values of the thermodynamic and kinetic parameters of the system. Our calculations show that the growth rate of the near-critical and supercritical ordered clusters within the dense intermediate is a major factor for the overall nucleation rate. This highlights the role of viscosity within the dense intermediate for the formation of the ordered nucleus. The model provides an understanding of the action of additives that delay or accelerate nucleation and presents a framework within which the nucleation of other ordered protein solid phases, e.g., the sickle cell hemoglobin polymers, can be analyzed.
In Situ Spectroscopic Investigation of Gas Phase Chemistry During Silicon Chemical Vapor Deposition
James E. Maslar; Wilbur S. Hurst
During silicon thermal chemical vapor deposition, reactions occurring in the gas phase above the wafer surface can strongly influence the deposited film quality. Depending on the process conditions, e.g., temperature, silicon precursor, carrier gas, pressure, etc., gas phase reactions can include not only precursor decomposition but also nucleation of silicon nanoparticles above the wafer surface. Optical diagnostics were employed to
Role of Dynamic Nucleation at Moving Boundaries in Phase and Microstructure Selection
NASA Technical Reports Server (NTRS)
Karma, Alain; Trivedi, Rohit
Solidification microstructures that form under steady-state growth conditions (cells, dendrites, regular eutectics, etc.) are reasonably well understood in comparison to other, more complex microstructures, which form under intrinsically non-steady-state growth conditions due to the competition between the nucleation and growth of several phases. Some important practical examples in this latter class include microstructures forming in peritectic systems in highly undercooled droplets, and in strip cast stainless steels. Prediction of phase and microstructure selection in these systems has been traditionally based on (1) heterogeneous nucleation on a static interface, and (2) comparing the relative growth rate of different phase/microstructures under steady-state growth conditions. The formation of new phases, however, occurs via nucleation on, or ahead of, a moving boundary. In addition, the actual selection process is controlled by a complex interaction between the nucleation process and the growth competition between the nuclei and the pre-existing phase under non-steady-state conditions. As a result, it is often difficult to predict which microstructure will form and which phases will be selected under prescribed processing conditions. This research addresses this critical role of nucleation at moving boundaries in the selection of phases and solidification microstructures through quantitative experiments and numerical modeling in peritectic systems. In order to create a well characterized system in which to study this problem, we focus on the directional solidification of hypo- and hyper-peritectic alloys in the two-phase region, imposing a large enough ratio of temperature gradient/growth rate (G/V(sub p)) to suppress the morphological instability of both the parent (alpha) and peritectic (Beta) phases, i.e. each phase alone would grow as a planar front. Our combined experimental and theoretical results show that, already in this simplified case, the growth competition of these two phases leads to a rich variety of microstructures that depend sensitively upon the relative importance of nucleation, diffusion, and convection.
Heterogeneous nucleation of/on nanoparticles: a density functional study using the phase-field crystal model
Lßszl¾ Grßnßsy; Frigyes Podmaniczky; Gyula I. T¾th; Gy÷rgy Tegze; Tamßs Pusztai
Crystallization of supersaturated liquids usually starts by heterogeneous nucleation. Mounting evidence shows that even homogeneous nucleation in simple liquids takes place in two steps; first a dense amorphous precursor forms, and the crystalline phase appears via heterogeneous nucleation in/on the precursor cluster. Herein, we review recent results by a simple dynamical density functional theory, the phase-field crystal model, for (precursor-mediated) homogeneous and heterogeneous nucleation of nanocrystals. It will be shown that the mismatch between the lattice constants of the nucleating crystal and the substrate plays a decisive role in determining the contact angle and nucleation barrier, which were found to be non-monotonic functions of the lattice mismatch. Time dependent studies are essential as investigations based on equilibrium properties often cannot identify the preferred nucleation pathways. Modeling of these phenomena is essential for designing materials on the basis of controlled nucleation and/or nano-patterning.
Nucleation of the CO2 hydrate from three-phase contact lines.
Bai, Dongsheng; Chen, Guangjin; Zhang, Xianren; Wang, Wenchuan
Using molecular dynamics simulations on the microsecond time scale, we investigate the nucleation and growth mechanisms of CO(2) hydrates in a water/CO(2)/silica three-phase system. Our simulation results indicate that the CO(2) hydrate nucleates near the three-phase contact line rather than at the two-phase interfaces and then grows along the contact line to form an amorphous crystal. In the nucleation stage, the hydroxylated silica surface can be understand as a stabilizer to prolong the lifetime of adsorbed hydrate cages that interact with the silica surface by hydrogen bonding, and the adsorbed cages behave as the nucleation sites for the formation of an amorphous CO(2) hydrate. After nucleation, the nucleus grows along the three-phase contact line and prefers to develop toward the CO(2) phase as a result of the hydrophilic nature of the modified solid surface and the easy availability of CO(2) molecules. During the growth process, the population of sI cages in the formed amorphous crystal is found to increase much faster than that of sII cages, being in agreement with the fact that only the sI hydrate can be formed in nature for CO(2) molecules. PMID:22551251
Free-energy landscape of nucleation with an intermediate metastable phase studied using capillarity approximation
Masao Iwamatsu
Capillarity approximation is used to study the free-energy landscape of nucleation when an intermediate metastable phase exists. The critical nucleus that corresponds to the saddle point of the free-energy landscape as well as the whole free-energy landscape can be studied using this capillarity approximation, and various scenarios of nucleation and growth can be elucidated. In this study we consider a model in which a stable solid phase nucleates within a metastable vapor phase when an intermediate metastable liquid phase exists. We predict that a composite critical nucleus that consists of a solid core and a liquid wetting layer as well as pure liquid and pure solid critical nuclei can exist depending not only on the supersaturation of the liquid phase relative to that of the vapor phase but also on the wetting behavior of the liquid surrounding the solid. The existence of liquid critical nucleus indicates that the phase transformation from metastable vapor to stable solid occurs via the intermediate metastable liquid phase, which is quite similar to the scenario of nucleation observed in proteins and colloidal systems. By studying the minimum-free-energy path on the free-energy landscape, we can study the evolution of the composition of solid and liquid within nuclei not limited to the critical nucleus.
Two-step nucleation mechanism in solid-solid phase transitions.
Peng, Yi; Wang, Feng; Wang, Ziren; Alsayed, Ahmed M; Zhang, Zexin; Yodh, Arjun G; Han, Yilong
The microscopic kinetics of ubiquitous solid-solid phase transitions remain poorly understood. Here, by using single-particle-resolution video microscopy of colloidal films of diameter-tunable microspheres, we show that transitions between square and triangular lattices occur via a two-step diffusive nucleation pathway involving liquid nuclei. The nucleation pathway is favoured over the direct one-step nucleation because the energy of the solid/liquid interface is lower than that between solid phases. We also observed that nucleation precursors are particle-swapping loops rather than newly generated structural defects, and that coherent and incoherent facets of the evolving nuclei exhibit different energies and growth rates that can markedly alter the nucleation kinetics. Our findings suggest that an intermediate liquid should exist in the nucleation processes of solid-solid transitions of most metals and alloys, and provide guidance for better control of the kinetics of the transition and for future refinements of solid-solid transition theory. PMID:25218059
Two-step nucleation mechanism in solid¢solid phase transitions
NASA Astrophysics Data System (ADS)
Peng, Yi; Wang, Feng; Wang, Ziren; Alsayed, Ahmed M.; Zhang, Zexin; Yodh, Arjun G.; Han, Yilong
The microscopic kinetics of ubiquitous solid¢solid phase transitions remain poorly understood. Here, by using single-particle-resolution video microscopy of colloidal films of diameter-tunable microspheres, we show that transitions between square and triangular lattices occur via a two-step diffusive nucleation pathway involving liquid nuclei. The nucleation pathway is favoured over the direct one-step nucleation because the energy of the solid/liquid interface is lower than that between solid phases. We also observed that nucleation precursors are particle-swapping loops rather than newly generated structural defects, and that coherent and incoherent facets of the evolving nuclei exhibit different energies and growth rates that can markedly alter the nucleation kinetics. Our findings suggest that an intermediate liquid should exist in the nucleation processes of solid¢solid transitions of most metals and alloys, and provide guidance for better control of the kinetics of the transition and for future refinements of solid¢solid transition theory.
The influence of additives and metal rods on the nucleation and growth of gas hydrates.
Li, Jinping; Liang, Deqing; Guo, Kaihua; Wang, Ruzhu
A major technical issue in industrial applications of the gas hydrate storage process is to develop a practical means for rapid hydrate formation. In this paper, the formation processes of HCFC141b (CH(3)CCl(2)F) gas hydrate in a column of water with additives and with an iron rod that was placed in the center of the column have been studied to reveal the influence of the additives and the iron rod on the nucleation and growth of the gas hydrate. The water solution column, in a cylindrical glass container, was placed in a thermostatic bath at 274.15-280.15 K and under atmospheric pressure. The experimental results show that, compared to the pure water and the HCFC141b system, the properly placed iron rod combined with proper concentrations of lauryl sodium sulfonate, lauryl sodium sulfate, and sodium dodecylbenzenesulfonate-6 considerably reduces the hydrate nucleation time and promotes formation speed. The formation rate of HCFC141b gas hydrate increases with increasing concentration of sodium dodecylbenzenesulfonate-6 in the water solution, while the addition of potassium oxalate monohydrate in water has shown no effect on the nucleation and growth of HCFC141b gas hydrate. Under the experimental conditions, both the anion surfactants and the iron rod strongly induce the first nucleation of HCFC141b gas hydrate, while the following growth of the HCFC141b gas hydrate is primarily influenced by the anion surfactant. This experiment suggests a new way of fast formation of clathrate hydrate, which may be much easier for practical application of the gas hydrate for cold storage in air conditioning systems. PMID:15694442
Experimental studies of the vapor phase nucleation of refractory compounds. VI. The condensation of sodium
Daniel M. MartĒnez; Frank T. Ferguson; Richard H. Heist; Joseph A. Nuth
In this paper we discuss the condensation of sodium vapor and the formation of a sodium aerosol as it occurs in a gas evaporation condensation chamber. A one-dimensional model describing the vapor transport to the vapor\\/aerosol interface was employed to determine the onset supersaturation, in which we assume the observed location of the interface is coincident with a nucleation rate
Computer Simulation Study of the Nucleation of Rotator Phases in Hard Polyhedral Particles
NASA Astrophysics Data System (ADS)
Thapar, Vikram; Escobedo, Fernando
The nucleation kinetics of the rotator phase in hard cuboctahedra, truncated octahedra, and rhombic dodecahedra is simulated via a combination of forward flux sampling and umbrella sampling. We compute the degrees of supersaturation at their corresponding pressures by improving upon the interfacial method used to estimate the liquid-rotator coexistence pressure. The nucleation rates are obtained by calculating the mean first passage time from liquid to rotator phase using forward flux sampling, and the free-energy barriers are estimated using umbrella sampling. For comparable degrees of supersaturation, the polyhedra are found to have significantly lower free-energy barriers and faster nucleation rates than hard spheres. This difference primarily stems from localized orientational ordering, which steers polyhedral particles to pack more efficiently. Orientational order hence fosters here the growth of orientationally disordered nuclei. The results are compared to preliminary data for the disorder-to-order transition for other polyhedral systems including systems pinned on a 2D interface.
Grain boundary filtration by selective nucleation and solid phase epitaxy of Ge through planar constrictions
Atwater, Harry
Grain boundary filtration by selective nucleation and solid phase epitaxy of Ge through planar for publication 24 October 2000 We have proposed and experimentally demonstrated a grain boundary filtration- ary filtration technique by using planar constrictions in pat- terned films during SNSPE of Ge. Large
NASA Astrophysics Data System (ADS)
Meyer, Erich
A simple adiabatic nucleation model, based on an extended Mollier (enthalpy-entropy) diagram, predicts a definite stability limit for the liquid-solid phase transition and is in good agreement with the lowest known experimental supercooling temperatures of low viscosity liquids. In the case of liquid gallium this model also correctly predicts that, at maximum supercooling, the metastable phase Ga ? will nucleate rather than the stable phase Ga ? or the metastable phase Ga ?.
Polymer + Solvent Systems: Phase Diagrams, Interface Free Energies, and Nucleation
Kurt Binder; Marcus M³ller; Peter Virnau; Luis Gonzßlez MacDowell
Some theoretical concepts on polymer + solvent systems and Monte Carlo simulations of corresponding coarse-grained models are briefly reviewed. While the phase diagram of polymers in bad solvents invoking the incompressibility approximation for the polymer solution has been a standard problem of polymer science for a long time, a more complete understanding of compressible polymer solutions, where liquid-liquid phase separation
;es a critical value of f at an incipient phase boundary. We then incorporate inertial eects, and we of longitudinal motions of an elastic bar, one considers a pair of conservation laws in one space dimension in dynamics, but in the theory of phase transitions in quasi-static motions as well. In [2], we viewed
Quantized hard-x-ray phase vortices nucleated by aberrated nanolenses
Pavlov, Konstantin M. [School of Science and Technology, University of New England, Armidale, New South Wales 2351 (Australia); School of Physics, Monash University, Victoria 3800 (Australia); Paganin, David M. [School of Physics, Monash University, Victoria 3800 (Australia); Vine, David J. [ARC Centre of Excellence for Coherent X-ray Science, School of Physics, The University of Melbourne, Parkville, Victoria 3010 (Australia); Schmalz, Jelena A. [School of Science and Technology, University of New England, Armidale, New South Wales 2351 (Australia); Suzuki, Yoshio; Uesugi, Kentaro; Takeuchi, Akihisa; Yagi, Naoto [SPring-8/JASRI (Japan Synchrotron Radiation Research Institute), Hyogo 679-5198 (Japan); Kharchenko, Alexander; Blaj, Gabriel [PANalytical B.V., P.O. Box 13, 7600 AA Almelo (Netherlands); Jakubek, Jan [Institute of Experimental and Applied Physics, Czech Technical University in Prague, 166 36 Prague 6 (Czech Republic); Altissimo, Matteo [Melbourne Centre for Nanofabrication, 151 Wellington Road, Clayton, Victoria 3168 (Australia); Materials Science and Engineering, Commonwealth Scientific and Industrial Research Organisation, Clayton South, Victoria 3169 (Australia); Clark, Jesse N. [London Centre for Nanotechnology, University College, Gower St, London WC1E 6BT (United Kingdom)
Quantized x-ray phase vortices, namely, screw-type topological defects in the wave fronts of a coherent monochromatic scalar x-ray wave field, may be spontaneously nucleated by x-ray lenses. Phase retrieval is used to reconstruct the phase and amplitude of the complex disturbance created by aberrated gold nanolenses illuminated with hard x rays. A nanoscale quantized x-ray vortex-antivortex dipole is observed, manifest both as a pair of opposite-helicity branch points in the Riemann sheets of the multivalued x-ray phase map of the complex x-ray field and in the vorticity of the associated Poynting vector field.
specifies a critical value of f at an incipient phase boundary. We then incorporate inertial effects, and we of longitudinal motions of an elastic bar, one considers a pair of conservation laws in one space dimension in quasiŁstatic motions as well. In [2], we
Underbarrier nucleation kinetics in a metastable quantum liquid near the liquid-gas spinodal line
Burmistrov, S.N. [Kurchatov Institute, 123182, Moscow, Russia (Russian Federation); Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro, Tokyo 152-8551 (Japan); Dubovskii, L.B. [Kurchatov Institute, 123182, Moscow (Russian Federation); Okuda, Y. [Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro, Tokyo 152-8551 (Japan)
We develop a theory that incorporates the relaxation properties of a condensed medium into the quantum decay of a metastable liquid near the liquid-gas spinodal line at low temperatures. We find that both the regime and the rate of quantum nucleation strongly depend on the relaxation time and its temperature behavior. The quantum nucleation rate slows down with decreasing relaxation time. We also discuss the low-temperature experiments on cavitation in normal {sup 3}He and superfluid {sup 4}He at negative pressures. It is the drastic distinctions in the properties of the high-frequency sound mode and in the temperature behavior of the relaxation time that make the quantum cavitation kinetics in {sup 3}He and {sup 4}He completely different.
Nucleation of (He-3)-B from the A phase - A cosmic-ray effect?
NASA Technical Reports Server (NTRS)
Leggett, A. J.
When He-3 is liquified and subsequently cooled, it undergoes, at a temperature of approximately 2.0-2.5 mK, a second-order transition into the so-called A phase. On further cooling, a first-order transition occurs, and the liquid passes into the B phase. Supercooling occurs with respect to the second transition, and the problem of nucleation arises. In connection with the experimental interest in studying metastable (He-3)-A down to the lowest temperatures in weak magnetic fields, the understanding of the mechanism of this transition and the feasibility of its inhibition is of some importance. The present investigation is concerned with the possibility that the transition is nucleated by the passage of a cosmic ray through the sample cell.
Investigation on phase separation, nucleation and crystallization in bioactive glass-ceramics containing fluorophlogopite and fluorapatite
Xiaofeng Chen; Larry L. Hench; David Greenspan; Jipin Zhong; Xiaokai Zhang
Apatite and mica-containing glass-ceramics in the system K2O?MgOCaO?Al2O3?B2O3 SiO2?P2O5?F can be used to repair and reconstruct diseased or damaged bones and teeth, due to their biocompatibility and bioactivity. Like other glass-ceramics, the properties of these machinable glass-ceramics depend on composition, size and volumetric ratios of the crystalline phases in the materials. Phase separation, nucleation and crystallisation of these multi-phase glass-ceramics
Nucleation and phase selection in undercooled Fe-Cr-Ni melts. Part 2: Containerless solidification experiments
Volkmann, T.; Herlach, D.M. [German Aerospace Research Establishment, Koeln (Germany). Inst. for Space Simulation; Loeser, W. [Inst. for Solid State and Materials Research, Dresden (Germany). Inst. for Metallic Materials
The solidification behavior of undercooled Fe-Cr-Ni melts of different compositions is investigated with respect to the competitive formation of {delta}-bcc (ferrite) and {gamma}-fcc phase (austenite). Containerless solidification experiments, electromagnetic levitation melting and drop tube experiments of atomized particles, show that {delta} (bcc) solidification is preferred in the highly undercooled melt even at compositions where {delta} is metastable. Time-resolved detection of the recalescence events during crystallization at different undercooling levels enable the determination of a critical undercooling for the transition to metastable bcc phase solidification in equilibrium fcc-type alloys. Measurements of the growth velocities of stable and metastable phases, as functions of melt undercooling prior to solidification, reveal that phase selection is controlled by nucleation. Phase selection diagrams for solidification processes as function of alloy composition and melt undercooling are derived from two types of experiments: X-ray phase analysis of quenched samples and in situ observations of the recalescence events of undercooled melts. The experimental results fit well with the theoretical predictions of the metastable phase diagram and the improved nucleation theory presented in an earlier article. In particular, the tendency of metastable {delta} phase formation in a wide composition range is confirmed.
Assisted nucleation of ?? phase in Al¢Cu¢Sn: the modified crystallography of tin precipitates
L. Bourgeois; J. F. Nie; B. C. Muddle
The formation of particles of elemental tin in association with the nucleation of the precipitate phase ?? in an Al¢1.7?at.%?Cu¢0.01?at.%?Sn alloy has been investigated by high resolution transmission electron microscopy. Analysis of lattice images has demonstrated that these tin particles associated with ?? platelets formed during short-term ageing (typically 3?min at 200░C) exhibit a crystallographic form that is distinctly different
Optimization of crystal nucleation close to a metastable fluid-fluid phase transition
Wedekind, Jan; Xu, Limei; Buldyrev, Sergey V.; Stanley, H. Eugene; Reguera, David; Franzese, Giancarlo
The presence of a metastable fluid-fluid critical point is thought to dramatically influence the crystallization pathway, increasing the nucleation rate by many orders of magnitude over the predictions of classical nucleation theory. We use molecular dynamics simulations to study the kinetics of crystallization in the vicinity of this metastable critical point and throughout the metastable fluid-fluid phase diagram. To quantitatively understand how the fluid-fluid phase separation affects the crystal nucleation, we evaluate accurately the kinetics and reconstruct the thermodynamic free-energy landscape of crystal formation. Contrary to expectations, we find no special advantage of the proximity of the metastable critical point on the crystallization rates. However, we find that the ultrafast formation of a dense liquid phase causes the crystallization to accelerate both near the metastable critical point and almost everywhere below the fluid-fluid spinodal line. These results unveil three different scenarios for crystallization that could guide the optimization of the process in experiments PMID:26095898
Microphysical Consequences of the Spatial Distribution of Ice Nucleation in Mixed-Phase Stratiform Clouds
Yang, Fan; Ovchinnikov, Mikhail; Shaw, Raymond A.
Mixed-phase stratiform clouds can persist even with steady ice precipitation fluxes, and the origin and microphysical properties of the ice crystals are of interest. Vapor deposition growth and sedimentation of ice particles along with a uniform volume source of ice nucleation, leads to a power law relation between ice water content wi and ice number concentration ni with exponent 2.5. The result is independent of assumptions about the vertical velocity structure of the cloud and is therefore more general than the related expression of Yang et al. [2013]. The sensitivity of the wi-ni relationship to the spatial distribution of ice nucleation is confirmed by Lagrangian tracking and ice growth with cloud-volume, cloud-top, and cloud-base sources of ice particles through a time-dependent cloud field. Based on observed wi and ni from ISDAC, a lower bound of 0.006 m^3/s is obtained for the ice crystal formation rate.
Heterogeneous ice nucleation on phase-separated organic-sulfate particles: effect of liquid vs. glassy coatings
NASA Astrophysics Data System (ADS)
Schill, G. P.; Tolbert, M. A.
Atmospheric ice nucleation on aerosol particles relevant to cirrus clouds remains one of the least understood processes in the atmosphere. Upper tropospheric aerosols as well as sub-visible cirrus residues are known to be enhanced in both sulfates and organics. The hygroscopic phase transitions of organic-sulfate particles can have an impact on both the cirrus cloud formation mechanism and resulting cloud microphysical properties. In addition to deliquescence and efflorescence, organic-sulfate particles are known to undergo another phase transition known as liquid-liquid phase separation. The ice nucleation properties of particles that have undergone liquid-liquid phase separation are unknown. Here, Raman microscopy coupled with an environmental cell was used to study the low temperature deliquescence, efflorescence, and liquid-liquid phase separation behavior of 2 : 1 mixtures of organic polyols (1,2,6-hexanetriol and 1 : 1 1,2,6-hexanetriol + 2,2,6,6-tetrakis(hydroxymethyl)cyclohexanol) and ammonium sulfate from 240-265 K. Further, the ice nucleation efficiency of these organic-sulfate systems after liquid-liquid phase separation and efflorescence was investigated from 210-235 K. Raman mapping and volume-geometry analysis indicate that these particles contain solid ammonium sulfate cores fully engulfed in organic shells. For the ice nucleation experiments, we find that if the organic coatings are liquid, water vapor diffuses through the shell and ice nucleates on the ammonium sulfate core. In this case, the coatings minimally affect the ice nucleation efficiency of ammonium sulfate. In contrast, if the coatings become semi-solid or glassy, ice instead nucleates on the organic shell. Consistent with recent findings that glasses can be efficient ice nuclei, the phase-separated particles are nearly as efficient at ice nucleation as pure crystalline ammonium sulfate.
Heterogeneous ice nucleation on phase-separated organic-sulfate particles: effect of liquid vs. glassy coatings
NASA Astrophysics Data System (ADS)
Schill, G. P.; Tolbert, M. A.
Atmospheric ice nucleation on aerosol particles relevant to cirrus clouds remains one of the least understood processes in the atmosphere. Upper tropospheric aerosols as well as sub-visible cirrus residues are known to be enhanced in both sulfates and organics. The hygroscopic phase transitions of organic-sulfate particles can have an impact on both the cirrus cloud formation mechanism and resulting cloud microphysical properties. In addition to deliquescence and efflorescence, organic-sulfate particles are known to undergo another phase transition known as liquid-liquid phase separation. The ice nucleation properties of particles that have undergone liquid-liquid phase separation are unknown. Here, Raman microscopy coupled with an environmental cell was used to study the low temperature deliquescence, efflorescence, and liquid-liquid phase separation behavior of 2:1 mixtures of organic polyols (1,2,6-hexanetriol, and 1:1 1,2,6-hexanetriol +2,2,6,6-tetrakis(hydroxymethyl)cycohexanol) and ammonium sulfate from 240-265 K. Further, the ice nucleation efficiency of these organic-sulfate systems after liquid-liquid phase separation and efflorescence was investigated from 210-235 K. Raman mapping and volume-geometry analysis indicates that these particles contain solid ammonium sulfate cores fully engulfed in organic shells. For the ice nucleation experiments, we find that if the organic coatings are liquid, water vapor diffuses through the shell and ice nucleates on the ammonium sulfate core. In this case, the coatings minimally affect the ice nucleation efficiency of ammonium sulfate. In contrast, if the coatings become semi-solid or glassy, ice instead nucleates on the organic shell. Consistent with recent findings that glasses can be efficient ice nuclei, the phase separated particles are nearly as efficient at ice nucleation as pure crystalline ammonium sulfate.
Vortex nucleation in phase-slippage experiments in ultrapure superfluid 4 He below 0.5 K
Packard, Richard E.
Vortex nucleation in phase-slippage experiments in ultrapure superfluid 4 He below 0.5 K E is thought to involve quantum tunneling. The critical velocity data obtained in phase- slippage experiments an analysis of the experimental data on phase slippage in ultrapure 4 He at tem- peratures from 400 mK down
Detached Melt Nucleation during Diffusion Brazing of a Technical Ni-based Superalloy: A Phase-Field Study
NASA Astrophysics Data System (ADS)
B÷ttger, B.; Apel, M.; Laux, B.; Piegert, S.
Advanced solidification processes like welding, soldering, and brazing are often characterized by their specific solidification conditions. But they also may include different types of melting processes which themselves are strongly influenced by the initial microstructures and compositions of the applied materials and therefore are decisive for the final quality and mechanical properties of the joint. Such melting processes are often not well- understood because - compared to other fields of solidification science - relatively little research has been done on melting by now. Also, regarding microstructure simulation, melting has been strongly neglected in the past, although this process is substantially different from solidification due to the reversed diffusivities of the involved phases. In this paper we present phase-field simulations showing melting, solidification and precipitation of intermetallic phases during diffusion brazing of directionally solidified and heat-treated high-alloyed Ni- based gas turbine blade material using different boron containing braze alloys. Contrary to the common belief, melting of the base material is not always planar and can be further accompanied by detached nucleation and growth of a second liquid phase inside the base material leading to polycrystalline morphologies of the joint after solidification. These findings are consistent with results from brazed laboratory samples, which were characterized by EDX and optical microscopy, and can be explained in terms of specific alloy thermodynamics and inter-diffusion kinetics. Consequences of the gained new understanding for brazing of high- alloyed materials are discussed.
Gas phase atmospheric bromine photochemistry
D. J. Lary
This paper reviews the current knowledge of gas phase bromine photochemistry and presents a budget study of atmospheric bromine species. The effectiveness of the ozone catalytic loss cycles involving bromine is quantified by considering their chain length and effectiveness. The chain effectiveness is a new variable defined as the chain length multiplied by the rate of the cycle's rate-limiting step.
Report on the Implementation of Homogeneous Nucleation Scheme in MARMOT-based Phase Field Simulation
Li, Yulan; Hu, Shenyang Y.; Sun, Xin
In this report, we summarized our effort in developing mesoscale phase field models for predicting precipitation kinetics in alloys during thermal aging and/or under irradiation in nuclear reactors. The first part focused on developing a method to predict the thermodynamic properties of critical nuclei such as the sizes and concentration profiles of critical nuclei, and nucleation barrier. These properties are crucial for quantitative simulations of precipitate evolution kinetics with phase field models. Fe-Cr alloy was chosen as a model alloy because it has valid thermodynamic and kinetic data as well as it is an important structural material in nuclear reactors. A constrained shrinking dimer dynamics (CSDD) method was developed to search for the energy minimum path during nucleation. With the method we are able to predict the concentration profiles of the critical nuclei of Cr-rich precipitates and nucleation energy barriers. Simulations showed that Cr concentration distribution in the critical nucleus strongly depends on the overall Cr concentration as well as temperature. The Cr concentration inside the critical nucleus is much smaller than the equilibrium concentration calculated by the equilibrium phase diagram. This implies that a non-classical nucleation theory should be used to deal with the nucleation of Cr precipitates in Fe-Cr alloys. The growth kinetics of both classical and non-classical nuclei was investigated by the phase field approach. A number of interesting phenomena were observed from the simulations: 1) a critical classical nucleus first shrinks toward its non-classical nucleus and then grows; 2) a non-classical nucleus has much slower growth kinetics at its earlier growth stage compared to the diffusion-controlled growth kinetics. 3) a critical classical nucleus grows faster at the earlier growth stage than the non-classical nucleus. All of these results demonstrated that it is critical to introduce the correct critical nuclei into phase field modeling in order to correctly capture the kinetics of precipitation. In most alloys the matrix phase and precipitate phase have different concentrations as well as different crystal structures. For example, Cu precipitates in FeCu alloys have fcc crystal structure while the matrix Fe-Cu solid solution has bcc structure at low temperature. The WBM model and KimS model, where both concentrations and order parameters are chosen to describe the microstructures, are commonly used to model precipitations in such alloys. The WBM and KimS models have not been implemented into Marmot yet. In the second part of this report, we focused on implementing the WBM and KimS models into Marmot. The Fe-Cu alloys, which are important structure materials in nuclear reactors, was taken as the model alloys to test the models.
Aerosol Inflluence on Ice Nucleation via the Immersion Mode in Mixed-Phase Arctic Stratiform Clouds
NASA Astrophysics Data System (ADS)
de Boer, G.; Hashino, T.; Tripoli, G. J.; Eloranta, E. W.
Mixed-phase stratiform clouds are commonly observed at high latitudes (e.g. Shupe et al., 2006; de Boer et al., 2009a). Herman and Goody (1976), as well as Curry et al. (1996) present summaries of Arctic cloud climatologies that show low altitude stratus frequencies of up to 70% during transitional seasons. In addition to their frequent occurrence, these clouds have significant impacts on the near-surface atmospheric radiative budget, with estimates of wintertime reductions in net surface cooling of 40-50 Wm-2 (Curry et al., 1996) due predominantly to liquid in the mixed-phase layer. Both observational and modeling studies (e.g. Harrington et al., 1999; Jiang et al., 2000; Shupe et al., 2008; Klein et al., 2008) show a strong connection between the amount of ice present and the lifetime of the liquid portion of the cloud layer. This is thought to occur via the Bergeron-Findeissen mechanism (Pruppacher and Klett, 1997) in which ice grows at the expense of liquid due to its lower saturation vapor pressure. Unfortunately, the mechanisms by which ice is nucleated within these mixed-phase layers are not yet fully understood, and therefore an accurate depiction of this process for mixed-phase stratiform clouds has not yet been characterized. The nucleation mechanisms that are active in a given environment are sensitive to aerosol properties. Insoluble particles are typically good nuclei for ice particle formation, while soluble particles are typically better at nucleating water droplets. Aerosol observations from the Arctic often show mixed aerosol particles that feature both soluble and insoluble mass (Leaitch et al., 1984). Soluble mass fractions for these particles have been shown to be high, with estimates of 60-80% and are often made up of sulfates (Zhou et al., 2001; Bigg and Leck, 2001). It is believed that a significant portion of this sulfate mass comes from dimethyl sulfide (DMS) production in the Arctic Ocean and subsequent atmospheric oxidation. Since these mixed particles may initially nucleate liquid droplets that then contain the remaining insoluble mass, immersion freezing has been theorized to contribute to ice nucleation in these clouds (de Boer et al., 2009b). In this work, we present a numerical study focusing on immersion freezing in mixed-phase stratiform clouds. We investigate the effects of aerosol properties such as soluble mass fraction, insoluble mass type and aerosol concentration on cloud liquid water fraction and lifetime. The high-resolution simulations used are based on the current GEWEX Cloud System Study (GCSS)/World Meteorological Organization (WMO) mixed-phase stratus model intercomparison (Morrison and Zuidema, 2008) and are completed using the University of Wisconsin Non-Hydrostatic Modeling System (UW-NMS, Tripoli, 1992) in combination with an advanced bin microphysical scheme (AMPS, Hashino and Tripoli, 2008). Immersion freezing is represented using a parameterization from Diehl and Wurzler (2004), which accounts for the freezing point depression due to the concentration of soluble mass within the water droplet.
Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystals and Polytetrahedral-Phase-Forming Alloys
NASA Technical Reports Server (NTRS)
Kelton, K. F.; Gangopadhyay, A. K.; Lee, G. W.; Hyers, R. W.; Rogers, J. R.; Robinson, M. B.; Rathz, T. J.; Krishnan, S.; Curreri, Peter A. (Technical Monitor)
The local atomic structures of undercooled liquid metals are presumed to be icosahedral; this order is incompatible with translational periodicity, constituting a barrier to the nucleation of the crystal phase. The extended atomic structure of the icosahedral quasicrystal (i-phase) is similar to that presumed in the undercooled liquid. Therefore, a comparison of the maximum undercooling in alloys that form the i-phase with those that form crystal phases provides a probe of the liquid structure.
Cluster nucleation and growth from a highly supersaturated adatom phase: silver on magnetite.
Bliem, Roland; Kosak, Rukan; Perneczky, Lukas; Novotny, Zbynek; Gamba, Oscar; Fobes, David; Mao, Zhiqiang; Schmid, Michael; Blaha, Peter; Diebold, Ulrike; Parkinson, Gareth S
The atomic-scale mechanisms underlying the growth of Ag on the (?2ū?2)R45░-Fe3O4(001) surface were studied using scanning tunneling microscopy and density functional theory based calculations. For coverages up to 0.5 ML, Ag adatoms populate the surface exclusively; agglomeration into nanoparticles occurs only with the lifting of the reconstruction at 720 K. Above 0.5 ML, Ag clusters nucleate spontaneously and grow at the expense of the surrounding material with mild annealing. This unusual behavior results from a kinetic barrier associated with the (?2ū?2)R45░ reconstruction, which prevents adatoms from transitioning to the thermodynamically favorable 3D phase. The barrier is identified as the large separation between stable adsorption sites, which prevents homogeneous cluster nucleation and the instability of the Ag dimer against decay to two adatoms. Since the system is dominated by kinetics as long as the (?2ū?2)R45░ reconstruction exists, the growth is not well described by the traditional growth modes. It can be understood, however, as the result of supersaturation within an adsorption template system. PMID:24945923
Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystal and Polytetrahedral-Phase Forming Alloys
NASA Technical Reports Server (NTRS)
Kelton, K. F.; Gangopadhyay, Anup K.; Lee, G. W.; Hyers, Robert W.; Rathz, T. J.; Robinson, Michael B.; Rogers, Jan R.
From extensive ground based work on the phase diagram and undercooling studies of Ti-Zr-Ni alloys, have clearly identified the composition of three different phases with progressively increasing polytetrahedral order such as, (Ti/Zr), the C14 Laves phase, and the i-phase, that nucleate directly from the undercooled liquid. The reduced undercooling decreases progressively with increasing polytetrahedral order in the solid, supporting Frank s hypothesis. A new facility for direct measurements of the structures and phase transitions in undercooled liquids (BESL) was developed and has provided direct proof of the primary nucleation of a metastable icosahedral phase in some Ti-Zr-Ni alloys. The first measurements of specific heat and viscosity in the undercooled liquid of this alloy system have been completed. Other than the importance of thermo-physical properties for modeling nucleation and growth processes in these materials, these studies have also revealed some interesting new results (such as a maximum of C(sup q, sub p) in the undercooled state). These ground-based results have clearly established the necessary background and the need for conducting benchmark nucleation experiments at the ISS on this alloy system.
Controlled Nucleation Aerosol Reactors: Production of Bulk Silicon
M. K. Alam; R. C. Flagan
A new type of aerosol reactor is described. By controlling the rate of gas phase reactions such that vapor diffusion to existing particles is favored over homogeneous nucleation, a small number of seed particles can be grown to supermicron sizes. A model for the influence of growing particles on the rate of homogeneous nucleation has been used to design a
Electroweak phase transition nucleation with the MSSM and electromagnetic field creation
Henley, Ernest M.; Johnson, Mikkel B.; Kisslinger, Leonard S. [Department of Physics, University of Washington, Seattle, Washington 98195 (United States); Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 (United States)
Using EW-MSSM field theory, so the electroweak phase transition (EWPT) is first order, we derive the equations of motion (e.o.m.) for the gauge fields. With an isospin ansatz we derive e.o.m. for the electrically charged W fields uncoupled from all other fields. These and the lepton currents serve as the current for the Maxwell-like e.o.m. for the electromagnetic field. The electromagnetic field arising during EWPT bubble nucleation without leptons is found. We then calculate the electron current contribution, which is seen to be quite large. This provides the basis for determining the magnetic field created by EWPT bubble collisions, which could seed galactic and extragalactic magnetic fields.
Experimental studies on nucleation, nanoparticle's formation and polymerization from the vapor phase
NASA Astrophysics Data System (ADS)
Abdelsayed, Victor Maher
This research is divided into three major parts. In part I, the critical supersaturations required for the homogeneous nucleation of 2,2,2-trifluorothanol (TFE) vapor have been measured over a temperature range (266-296 K) using an upward thermal diffusion cloud chamber (DCC). The measured supersaturations are in agreement with the predictions of both the classical and the scaled theory of nucleation. Moreover, the condensation of supersaturated TFE vapor on laser-vaporized magnesium nanoparticles has been studied under different experimental conditions, such as the supersaturation, the pressure and the electric field. In part II, the laser vaporization controlled condensation (LVCC) technique was used to prepare Au-Ag alloy nanoparticles in the vapor phase using designed targets of compressed Au and Ag micron-sized powder mixtures of selected composition. The results showed that the optical properties of these nanoparticles could be tuned depending on the alloy composition and the laser wavelength. Different intermetallic nanoparticles (FeAl and NiAl) from the vapor phase has also been prepared, using the same approach. In this work, the fraction of the charged particles generated during the laser vaporization process was used to prepare a new class of nanoparticle assemblies in the LVCC chamber under the influence of an electric field. The results showed that the electric field required to induce the formation of these nanoassemblies is material and field dependent. By coupling the LVCC chamber with the differential mobility analyzer, size-selected nanoparticles have been prepared in the vapor phase. The prepared nanoparticles were characterized by different techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-visible spectroscopy. In part III, new methods were developed to prepare nanoparticle-polymer composites from the vapor phase. In the first method, the LVCC method was used to prepare a carbonaceous cross-linked resin, with different nanoparticles (Ni, Pt and FeAl) embedded inside. In the second method, free radical-thermally initiated polymerization was used to polymerize a monomer vapor of styrene on the surfaces of activated Ni nanoparticles.
Studies of Nucleation, Growth, Specific Heat, and Viscosity of Undercooled Melts of Quasicrystals and Polytetrahedral-Phase-Forming Alloys
NASA Technical Reports Server (NTRS)
Kelton, K. F.; Croat, T. K.; Gangopadhyay, A.; Holland-Moritz, D.; Hyers, Robert W.; Rathz, Thomas J.; Robinson, Michael B.; Rogers, Jan R.
Undercooling experiments and thermal physical property measurements of metallic alloys on the International Space Station (ISS) are planned. This recently-funded research focuses on fundamental issues of the formation and structure of highly-ordered non-crystallographic phases (quasicrystals) and related crystal phases (crystal approximants), and the connections between the atomic structures of these phases and those of liquids and glasses. It extends studies made previously by us of the composition dependence of crystal nucleation processes in silicate and metallic glasses, to the case of nucleation from the liquid phase. Motivating results from rf-levitation and drop-tube measurements of the undercooling of Ti/Zr-based liquids that form quasicrystals and crystal approximants are discussed. Preliminary measurements by electrostatic levitation (ESL) are presented.
NASA Technical Reports Server (NTRS)
Hansen, C. F.
Reaction-rate theory and experiment are given a critical review from the engineers' point of view. Rates of heavy-particle, collision-induced reaction in gas phase are formulated in terms of the cross sections and activation energies for reaction. The effect of cross section function shape and of excited state contributions to reaction both cause the slope of Arrhenius plots to differ from the true activation energy, except at low temperature. The master equations for chemically reacting gases are introduced, and dissociation and ionization reactions are shown to proceed primarily from excited states about kT from the dissociation or ionization limit. Collision-induced vibration, vibration-rotation, and pure rotation transitions are treated, including three-dimensional effects and conservation of energy, which have usually been ignored. The quantum theory of transitions at potential surface crossing is derived, and results are found to be in fair agreement with experiment in spite of some questionable approximations involved.
Effect of an alpha-phase nucleating agent on the crystallization kinetics of a propylene/ethylene random copolymer at largely different supercooling
NASA Astrophysics Data System (ADS)
Androsch, Renķ; Monami, Andrea; Kucera, Jaroslav
The effect of addition of 0.1 wt% phosphate-ester based alpha-phase nucleating agent on the crystallization of a random propylene-based copolymer with 3.9 mol% ethylene has been investigated by fast scanning chip calorimetry (FSC). Main purpose of the work was the evaluation of the effect of the nucleating agent on the bimodal temperature dependence of the crystallization rate of propylene-based polymers caused by a change of the nucleation mechanism from heterogeneous to homogeneous nucleation on lowering the temperature to below about 60 ░C. Presence of the nucleation agent in the copolymer of the present study accelerates crystallization only in the high-temperature range of predominant heterogeneous nucleation, but does not affect the crystallization rate in the low-temperature range of homogeneous nucleation. The observed decrease of the minimum crystallization half-time due to the addition of the nucleation agent, from 0.2 s in case of the unmodified copolymer to 0.04 s in case of the copolymer containing the nucleating agent, is paralleled by an increase of the critical cooling rate required to inhibit crystallization on continuous cooling to below the glass transition temperature from 102 to 103 K s-1. The study is completed by an analysis of the effect of addition of the nucleation agent on the spherulitic superstructure.
Transient nucleation in glasses
NASA Technical Reports Server (NTRS)
Kelton, K. F.
Nucleation rates in condensed systems are frequently not at their steady state values. Such time dependent (or transient) nucleation is most clearly observed in devitrification studies of metallic and silicate glasses. The origin of transient nucleation and its role in the formation and stability of desired phases and microstructures are discussed. Numerical models of nucleation in isothermal and nonisothermal situations, based on the coupled differential equations describing cluster evolution within the classical theory, are presented. The importance of transient nucleation in glass formation and crystallization is discussed.
Order and phase nucleation in non-equilibrium nanocomposite Fe-Pt thin films with perpendicular magnetic anisotropy.
Clavero, C.; Skuza, J. R.; Garcia-Martin, J. M.; Cebollada, A.; Walko, D. A.; Lukaszew, R. A.; Coll. of William and Mary; Inst. de Microelectronica de Madrid
We report on the time evolution of mass transport upon annealing nonequilibrium Fe-Pt nanocomposite films, leading to nucleation of L1{sub 0} chemically ordered phase. The nonequilibrium nanocomposite films were fabricated by applying Fe{sup +} ion implantation to epitaxial Pt films grown on (001) MgO substrates, yielding Fe nanoclusters embedded in a Pt matrix at a tailored penetration depth. Time-resolved x-ray diffraction studies were carried out using synchrotron radiation, allowing determination of the activation energy for nucleation of the FePt L1{sub 0} phase within the segregated nanoclusters during annealing. The growth of the segregated L1{sub 0} ordered phase was modeled using ideal grain-size law and found to be dominated by strain-driven surface nucleation. The activation energies were found to correlate with the nanocluster size. Magnetic characterization of selected annealed samples indicates perpendicular magnetic anisotropy with high coercive field coincident with high value of the chemical order parameter of the ordered phase within the magnetic nanoclusters.
Nucleation mechanism of nano-sized NaZn13-type and ?-(Fe,Si) phases in La-Fe-Si alloys during rapid solidification
NASA Astrophysics Data System (ADS)
Hou, Xue-Ling; Xue, Yun; Liu, Chun-Yu; Xu, Hui; Han, Ning; Ma, Chun-Wei; Phan, Manh-Huong
The nucleation mechanism involving rapid solidification of undercooled La-Fe-Si melts has been studied experimentally and theoretically. The classical nucleation theory-based simulations show a competitive nucleation process between the ?-(Fe,Si) phase (size approximately 10 to 30 nm) and the cubic NaZn13-type phase (hereinafter 1:13 phase, size approximately 200 to 400 nm) during rapid solidification, and that the undercooled temperature change ? T plays an important factor in this process. The simulated results about the nucleation rates of the ?-(Fe,Si) and 1:13 phases in La-Fe-Si ribbons fabricated by a melt-spinner using a copper wheel with a surface speed of 35 m/s agree well with the XRD, SEM, and TEM studies of the phase structure and microstructure of the ribbons. Our study paves the way for designing novel La-Fe-Si materials for a wide range of technological applications.
Influence of ferrite nanoparticle type and content on the crystallization kinetics and electroactive phase nucleation of poly(vinylidene fluoride).
Sencadas, Vitor; Martins, Pedro; PitŃes, Alexandre; Benelmekki, Maria; G¾mez Ribelles, Josķ Luis; Lanceros-Mendez, Senentxu
This work reports on the nucleation of the ?-phase of poly(vinylidene fluoride) (PVDF) by incorporating CoFe(2)O(4) and NiFe(2)O(4) nanoparticles, leading in this way to the preparation of magnetoelectric composites. The fraction of filler nanoparticles needed to produce the same ?- to ?-phase ratio in crystallized PVDF is 1 order of magnitude lower in the cobalt ferrite nanoparticles. The interaction between nanoparticles and PVDF chains induce the all-trans conformation in PVDF segments, and this structure then propagates in crystal growth. The nucleation kinetics is enhanced by the presence of nanoparticles, as corroborated by the increasing number of spherulites with increasing nanoparticle content and by the variations of the Avrami's exponent. Further, the decrease of the crystalline fraction of PVDF with increasing nanoparticle content indicates that an important fraction of polymer chains are confined in interphases with the filler particle. PMID:21545124
Order and phase nucleation in non-equilibrium nanocomposite Fe-Pt thin films with perpendicular magnetic anisotropy
C. Clavero; J. R. Skuza; J. M. Garcia-Martin; A. Cebollada; D. A. Walko; R. A. Lukaszew
We report on the time evolution of mass transport upon annealing nonequilibrium Fe-Pt nanocomposite films, leading to nucleation of L1 chemically ordered phase. The nonequilibrium nanocomposite films were fabricated by applying Fe{sup +} ion implantation to epitaxial Pt films grown on (001) MgO substrates, yielding Fe nanoclusters embedded in a Pt matrix at a tailored penetration depth. Time-resolved x-ray diffraction
Control of protein crystal nucleation around the metastable liquidliquid phase boundary
Vekilov, Peter
Galkin and Peter G. Vekilov¦ Center for Microgravity and Materials Research, and Department of Chemistry. On further cooling below Tcrit , the enhancement of nucleation tapers off. Both parts of this prediction have conditions or may take labora- tory or technolo
Experimental studies on nucleation, nanoparticle's formation and polymerization from the vapor phase
Victor Maher Abdelsayed
This research is divided into three major parts. In part I, the critical supersaturations required for the homogeneous nucleation of 2,2,2-trifluorothanol (TFE) vapor have been measured over a temperature range (266-296 K) using an upward thermal diffusion cloud chamber (DCC). The measured supersaturations are in agreement with the predictions of both the classical and the scaled theory of nucleation. Moreover,
The effects of hygroscopicity on ice nucleation of fossil fuel combustion aerosols in mixed-phase clouds
NASA Astrophysics Data System (ADS)
Yun, Y.; Penner, J. E.; Popovicheva, O.
Fossil fuel black carbon and organic matter (ffBC/OM) are often emitted together with sulfate, which coats the surface of these particles and changes their hygroscopicity. Observational studies at cirrus temperatures (?-40 ░C) show that the hygroscopicity of soot particles can modulate their ice nucleation ability. Here, we implement a scheme for 3 categories of soot (hydrophobic, hydrophilic and hygroscopic) on the basis of laboratory data and specify their ability to act as ice nuclei at mixed-phase temperatures by extrapolating the observations using a published deposition/condensation/immersion freezing parameterization. The new scheme results in significant changes to anthropogenic forcing in mixed-phase clouds. The net forcing in our offline model studies varies from 0.111 to 1.059 W m-2 depending on the ice nucleation capability of hygroscopic soot particles. The total anthropogenic cloud forcing and whole-sky forcing with the new scheme are 0.06 W m-2 and -2.45 W m-2, respectively, but could be more positive (by about 1.17 W m-2) if hygroscopic soot particles are allowed to nucleate ice particles. The change in liquid water path dominates the anthropogenic forcing in mixed-phase clouds.
Mechanisms for the deposition of thin metallic films by laser driven gas phase reactions
Jervis, T.R.; Menon, S.K.; Joyce, E.L.; Carroll, D.W.
Gas phase processing makes laser deposition over large areas possible but homogeneous nucleation of large atomic clusters must be avoided if films are to be produced. Clusters can be highly variable in size from a few atoms to significant fractions of a micrometer. If conditions do not allow for complete quenching of the clusters produced in the gas phase, these clusters can arrive at the substrate with sufficient energy to self sinter into homogeneous films which are substantially different from metallic films grown by thermal techniques. Using transmission electron microscopy (TEM), we have characterized the microstructure of thin metallic films deposited by laser breakdown chemical vapor deposition and identified a range of deposition conditions which can lead from powders to homogeneous polycrystalline films and mixed phase materials. Gas phase nucleation is dependent on reactant partial pressures and the gas phase quench rate which can be varied in part by adjusting the H/sub 2/ content of the source gas. Manipulation of these parameters can vary powder size from about one micrometer to less than 2 nanometers. Variation of the quench rate during the deposition of polycrystalline films varies the grain size in the films. Heating the substrate drastically changes the conditions under which the film is formed and as a consequence, can radically alter the microstructure of the film itself. 6 refs., 2 figs.
Effects of strain on phonon interactions and phase nucleation in several semiconductor and nano particle systems
NASA Astrophysics Data System (ADS)
Tallman, Robert E.
Raman scattering is utilized to explore the effects of applied pressure and strain on anharmonic phonon interactions and nucleation of structural transitions in several bulk and nanoparticle semiconductor systems. The systems investigated are bulk ZnS and ZnSe in several isotopic compositions, InP/CdS core/shell nanoparticles exhibiting confined and surface optical Raman modes, and amorphous selenium films undergoing photo-induced crystallization. The anharmonic decay of long-wavelength optical modes into two-phonon acoustic combinations modes is studied in 64Zn32S, 64Zn34S, natZnatS bulk crystals by measuring the TO(Gamma) Raman line-shape as a function of applied hydrostatic pressure. The experiments are carried out at room temperature and 16K for pressures up to 150 kbars using diamond-anvil cells. The most striking effects occur in 68Zn32S where the TO(Gamma) peak narrows by a factor of 10 and increases in intensity at pressures for which the TO(Gamma) frequency has been tuned into a gap in the two-phonon density of states (DOS). In all the isotopic compositions, the observed phonon decay processes can be adequately explained by a second order perturbation treatment of the anharmonic coupling between TO(Gamma) and TA + LA combinations at various critical points, combined with an adiabatic bond-charge model for the phonon DOS and the known mode Gruneisen parameters. Bulk ZnSe crystals exhibit very different behavior. Here we find that anharmonic decay alone can not explain the excessive (ś 60 cm-1 ) broadening in the TO(Gamma) Raman peak observed as the pressure approaches to within 50kbar of the ZB -> B1 phase transition (at P ś 137 kbar). Rather the broadening appears to arise from antecedent nucleation of structural changes within nanoscopic domains, with the mechanism for line-shape changes being mode mixing via localization and disorder instead of anharmonicity. To sort out these contributions, pressure experiments on natural ZnSe and on isotopically pure 68Zn76Se are compared. Again we use an appropriate bond-charge model to obtain the phonon DOS. It is concluded that the antecedent nucleation mechanism is much more important in ZnSe than in ZnS. In order to further investigate interactions of vibrational modes in spatially confined systems, pressure-Raman experiments are carried out on InP/CdS core/shell nanoparticles. This system differs from most other core/shell nanoparticles systems, in that the near degeneracy of the bulk InP TO(Gamma) and CdS LO(Gamma) phonons leads to possible cross-interface mode coupling. Different confined and surface (or interface) optical modes are studied as a function of pressure up 65 kbar at 373 and 230 K. The results are compared with the predictions of dielectric continuum theory using a phenomenological macroscopic approach (PMA) to include the pressure dependence. Three different pressure media are employed, and the effects on the surface modes of their different static dielectric constants are investigated. The pressure-shifts of the observed confined and surface modes are well accounted for without the need to include cross-interface coupling. We conclude that the conventional boundary condition, of vanishing phonon amplitude at the heterointerface, remains valid in the InP/CdS nanoparticle system, in spite of the near degeneracy of the bulk optical phonons. Photo-induced crystallization in amorphous selenium (a-Se) was also explored in this dissertation, as another example of a nanoscopic nucleation process influenced by strain, in this case internal strain. In order to observe photo-crystallization, the Raman spectra of commercial a-Se films used as targets in high-gain avalanche rushing photodetectors (HARP) cameras was studied at temperatures in the range 260 - 330 K. We find a rich temperature behavior that reflects the competition of changes in viscosity and strain, and defines four distinct regimes. These results are in qualitative accord with a theory by R.B.Stephens treating the effects of local strain on the secondary growth of crystalline nuclei in a-Se. W
Nucleation mechanisms in microcellular polymer foams
NASA Astrophysics Data System (ADS)
Kweeder, James A.
Existing models for microcellular foam nucleation fail to predict observed experimental results. Experimental results were compared to classical nucleation models and revealed irreconcilable differences. Based on the knowledge that microscopic defects exist in polymer systems, a new physical mechanism for foam cell formation is proposed which is consistent with experimental results. Rather than nucleating a new gas phase during foaming, one is instead trying to grow microscopic voids and cracks into the bubbles. From this concept, a thermodynamic model has been proposed for the activation of microvoids into viable foam cells. Study of the resulting model reaffirms the validity of the microvoid mechanism; but, it also demonstrates that foam cell nucleation can no longer be treated separately from the bubble growth phenomena.
Probabilistic breakdown phenomenon at on-ramp bottlenecks in three-phase traffic theory: Congestion nucleation in spatially non-homogeneous traffic
NASA Astrophysics Data System (ADS)
Kerner, Boris S.; Klenov, Sergey L.
A nucleation model for the breakdown phenomenon in an initial non-homogeneous free traffic flow that occurs at an on-ramp bottleneck is presented. This model is in the context of three-phase traffic theory. In this theory, the breakdown phenomenon is associated with a first-order phase transition from the ōfree flowö phase to the ōsynchronized flowö phase. In contrast with many other nucleation models for phase transitions in different systems of statistical physics in which random precluster emergence from fluctuations in an initial homogeneous system foregoes subsequent cluster evolution towards a critical cluster (critical nuclei), random precluster occurrence in free flow at the bottleneck is not necessary for traffic breakdown. In the model, the breakdown phenomenon can also occur if there were no fluctuations in free flow. This is because there is a permanent and motionless non-homogeneity that can be considered a deterministic vehicle cluster localized in a neighborhood of the bottleneck. The presented nucleation model and a nucleation rate of traffic breakdown that follows from the model exhibit qualitatively different features in comparison with previous results. In the nucleation model, traffic breakdown nucleation occurs through a random increase in vehicle number within the deterministic vehicle cluster, if the amplitude of the resulting random vehicle cluster exceeds some critical amplitude. The mean time delay and the associated nucleation rate of traffic breakdown at the bottleneck are found and investigated. The nucleation rate of traffic breakdown as a function of the flow rates to the on-ramp and upstream of the bottleneck is studied. Boundaries for traffic breakdown in the diagram of congested patterns at the bottleneck are found. These boundaries are qualitatively correlated with numerical results of simulation of microscopic traffic flow models in the context of three-phase traffic theory.
Gas-Phase Infrared; JCAMP Format
National Institute of Standards and Technology Data Gateway
SRD 35 NIST/EPA Gas-Phase Infrared; JCAMP Format (PC database for purchase)ĀĀ This data collection contains 5,228 infrared spectra in the JCAMP-DX (Joint Committee for Atomic and Molecular Physical Data "Data Exchange") format.
Project ARGO: Gas phase formation in simulated microgravity
NASA Technical Reports Server (NTRS)
Powell, Michael R.; Waligora, James M.; Norfleet, William T.; Kumar, K. Vasantha
The ARGO study investigated the reduced incidence of joint pain decompression sickness (DCS) encountered in microgravity as compared with an expected incidence of joint pain DCS experienced by test subjects in Earth-based laboratories (unit gravity) with similar protocols. Individuals who are decompressed from saturated conditions usually acquire joint pain DCS in the lower extremities. Our hypothesis is that the incidence of joint pain DCS can be limited by a significant reduction in the tissue gas micronuclei formed by stress-assisted nucleation. Reductions in dynamic and kinetic stresses in vivo are linked to hypokinetic and adynamic conditions of individuals in zero g. We employed the Doppler ultrasound bubble detection technique in simulated microgravity studies to determine quantitatively the degree of gas phase formation in the upper and lower extremities of test subjects during decompression. We found no evidence of right-to-left shunting through pulmonary vasculature. The volume of gas bubble following decompression was examined and compared with the number following saline contrast injection. From this, we predict a reduced incidence of DCS on orbit, although the incidence of predicted mild DCS still remains larger than that encountered on orbit.
Molecular dynamics investigation of homogeneous nucleation and cluster growth of platinum clusters from supersaturated vapour
N. L³mmen; T. Kraska
The formation of platinum nanoparticles from a supersaturated vapour phase is investigated by molecular dynamics simulations. Argon is added as carrier gas, removing the condensation heat from the nucleating system. The interactions between the platinum atoms are modelled by the multi-body embedded atom method. The nucleation rates in highly supersaturated systems are estimated as well as properties of the critical
Nucleation Behavior of Oxygen-Acetylene Torch-Produced Diamond Films
NASA Technical Reports Server (NTRS)
Roberts, F. E.
A mechanism is presented for the nucleation of diamond in the combustion flame environment. A series of six experiments and two associated simulations provide results from which the mechanism was derived. A substantial portion of the prior literature was reviewed and the data and conclusions from the previous experimenters were found to support the proposed mechanism. The nucleation mechanism builds on the work of previous researchers but presents an approach to nucleation in a detail and direction not fully presented heretofore. This work identifies the gas phase as the controlling environment for the initial formation steps leading to nucleation. The developed mechanism explains some of the difficulty which has been found in producing single crystal epitaxial films. An experiment which modified the initial gas phase precursor using methane and carbon monoxide is presented. Addition of methane into the precursor gases was found to be responsible for pillaring of the films. Atomic force microscopy surface roughness data provides a reasonable look at suppression of nucleation by carbon monoxide. Surface finish data was taken on crystals which were open to the nucleation environment and generally parallel to the substrate surface. The test surfaces were measured as an independent measure of the instantaneous nucleation environent. A gas flow and substrate experiment changed the conditions on the surface of the sample by increasing the gas flow rate while remaining on a consistent point of the atomic constituent diagram, and by changing the carbide potential of the substrate. Two tip modification experiments looked at the behavior of gas phase nucleation by modifying the shape and behavior of the flame plasma in which the diamond nucleation is suspected to occur. Diamond nucleation and growth was additionally examined using a high-velocity oxygen fuel gun and C3H6 as the fuel gas phase precursor with addition of carbon monoxide gas 01 addition of liquid toluene.
Phases and phase transitions in a dipolar ferromagnetic spinor gas
NASA Astrophysics Data System (ADS)
Stamper-Kurn, Dan
In the regime of quantum degeneracy, a gas of spin-1 rubidium atoms is predicted to become simultaneously superfluid and magnetically ordered. We have studied such a gas using dispersive imaging to measure the complete vector magnetization in situ. I will present three main findings from our work. First, we have studied the dynamics of a gas that is suddenly quenched across a symmetry-breaking phase transition, characterizing the spectrum of dynamic instabilities and quantifying the symmetry-breaking seed that is predicted to arise due to quantum spin fluctuations. Second, we have ascertained that magnetic dipole interactions are an important influence on this spin-1 gas. Third, we have explored the equilibrium phase diagram for this gas, finding that a robust inhomogeneous but spatially structured spin texture arises in steady state below the apparent Bose-Einstein condensation transition temperature.
Effects of strain on phonon interactions and phase nucleation in several semiconductor and nano particle systems
Robert E. Tallman
Raman scattering is utilized to explore the effects of applied pressure and strain on anharmonic phonon interactions and nucleation of structural transitions in several bulk and nanoparticle semiconductor systems. The systems investigated are bulk ZnS and ZnSe in several isotopic compositions, InP\\/CdS core\\/shell nanoparticles exhibiting confined and surface optical Raman modes, and amorphous selenium films undergoing photo-induced crystallization. The anharmonic
Thermodynamics and kinetics of binary nucleation in ideal-gas mixtures
Alekseechkin, Nikolay V
The nonisothermal single-component theory of droplet nucleation (Alekseechkin, 2014) is extended to binary case; the droplet volume V, composition x, and temperature T are the variables of the theory. An approach based on macroscopic kinetics (in contrast to the standard microscopic model of nucleation operating with the probabilities of monomer attachment and detachment) is developed for the droplet evolution and results in the derived droplet motion equations in the space (V,x,T) - equations for V_dot, x_dot, and T_dot. The work W(V,x,T) of the droplet formation is calculated; it is obtained in the vicinity of the saddle point as a quadratic form with diagonal matrix. Also the problem of generalizing the single-component Kelvin equation for the equilibrium vapor pressure to binary case is solved; it is presented here as a problem of integrability of a Pfaffian equation. The equation for is shown to be the first law of thermodynamics for the droplet, which is a consequence of Onsagers reciprocal relations an...
Thermal phases of interstellar and quasar gas
NASA Technical Reports Server (NTRS)
Lepp, S.; Mccray, R.; Shull, J. M.; Woods, D. T.; Kallman, T.
Interstellar gas may be in a variety of thermal phases, depending on how it is heated and ionized; here a unified picture of the equation of state of interstellar and quasar gas is presented for a variety of such mechanisms over a broad range of temperatures, densities, and column densities of absorbing matter. It is found that for select ranges of gas pressure, photoionizing flux, and heating, three thermally stable phases are allowed: coronal gas (T above 100,000 K); warm gas (T about 10,000 K); and cold gas (T less than 100 K). With attenuation of ultraviolet and X-ray radiation, the cold phase may undergo a transition to molecules. In quasar broad-line clouds, this transition occurs at column density N(H) = about 10 to the 23rd/sq cm and could result in warm molecular cores and observable emission from H2 and OH. The underlying atomic physics behind each of these phase transitions and their relevance to interstellar matter and quasars are discussed.
Two-step nucleation of the g-phase in a Ti-45Al-18Nb alloy
Goyel, Sonalika [University of Florida, Gainesville; Rios, Orlando [ORNL; Kesler, Michael [University of Florida, Gainesville; Ebrahimi, Fereshteh [University of Florida, Gainesville
Phase transformations in a high Nb TieAleNb alloy (Ti-45Al-18Nb at%) upon cooling were studied. This alloy solidifies as single b-phase, which upon cooling under equilibrium conditions, is expected to follow the b / b g / b g s / g s transformation path. The DTA analysis confirmed two transformation events as manifested by two peaks upon cooling. However, compositional and structural characterization of samples with different heat treatment schedules, including slow cooling (9 C/min), revealed that the s-phase did not form upon cooling. The two DTA peaks observed in the cooling cycle of the alloy are proven to be associated with the two-stage formation of the g-phase. Detailed microstructural evaluations showed that the g-phase nucleated in two discrete stages and exhibited two different morphologies. The absence of the s-phase is believed to be due to the lack of enough driving force at high temperatures. The aging of a fast cooled sample, yielding an equilibrated microstructure, substantiated the presence of the s-phase.
Sublimating comets as the source of nucleation seeds for grain condensation in the gas outflow from AGB stars
NASA Technical Reports Server (NTRS)
Whitmire, D. P.; Matese, John J.; Reynolds, R. T.
A growing amount of observational and theoretical evidence suggests that most main sequence stars are surrounded by disks of cometary material. The dust production by comets in such disks is investigated when the central stars evolve up the red giant and asymptotic giant branch (AGB). Once released, the dust is ablated and accelerated by the gas outflow and the fragments become the seeds necessary for condensation of the gas. The origin of the requisite seeds has presented a well known problem for classical nucleation theory. This model is consistent with the dust production observed in M giants and supergiants (which have increasing luminosities) and the fact that earlier supergiants and most WR stars (whose luminosities are unchanging) do not have significant dust clouds even though they have significant stellar winds. Another consequence of the model is that the spatial distribution of the dust does not, in general, coincide with that of the gas outflow, in contrast to the conventional condensation model. A further prediction is that the condensation radius is greater that that predicted by conventional theory which is in agreement with IR interferometry measurements of alpha-Ori.
Probabilistic breakdown phenomenon at on-ramp bottlenecks in three-phase traffic theory: Congestion nucleation in spatially non-homogeneous traffic
Boris S. Kerner; Sergey L. Klenov
A nucleation model for the breakdown phenomenon in an initial non-homogeneous free traffic flow that occurs at an on-ramp bottleneck is presented. This model is in the context of three-phase traffic theory. In this theory, the breakdown phenomenon is associated with a first-order phase transition from the ōfree flowö phase to the ōsynchronized flowö phase. In contrast with many other
Probabilistic breakdown phenomenon at on-ramp bottlenecks in three-phase traffic theory: Congestion nucleation in spatially non-homogeneous traffic
Boris S. Kerner; Sergey L. Klenov
A nucleation model for the breakdown phenomenon in an initial non-homogeneous free traffic flow that occurs at an on-ramp bottleneck is presented. This model is in the context of three-phase traffic theory. In this theory, the breakdown phenomenon is associated with a first-order phase transition from the ``free flow'' phase to the ``synchronized flow'' phase. In contrast with many other
Liquid-gas phase transition in hypernuclei
NASA Astrophysics Data System (ADS)
Mallik, S.; Chaudhuri, G.
The fragmentation of excited hypernuclear systems formed in heavy ion collisions has been described by the canonical thermodynamical model extended to three-component systems. The multiplicity distribution of the fragments has been analyzed in detail and it has been observed that the hyperons tend to get attached to the heavier fragments. Another important observation is the phase coexistence of the hyperons, a phenomenon which is linked to the liquid-gas phase transition in strange matter.
Dynamics of Arctic Mixed Phase Clouds: A focus on the effects of ice crystal habits and nucleation
NASA Astrophysics Data System (ADS)
Komurcu, M.; Harrington, J. Y.
The Arctic is warming significantly; this warming is greater than any other region on Earth. To understand the future atmospheric state of the Arctic, climate models are typically run through different climate scenarios. The common conclusion of all climate model simulations is that a warming in Arctic will occur. The degree of warming for the same scenarios, however, is inconsistent among the climate models. Clouds are ubiquitous over the Arctic and they strongly affect the surface radiative and energy budget. This result makes clouds a key component of the Arctic climate. Recent studies using regional climate models show that models are not capable of reproducing the supercooled liquid observed in clouds during the cold season. Large discrepancies exist in the partitioning of phase between ice and liquid water among different models. It is currently thought that these discrepancies are due to the way ice crystal habits are parameterized and the way ice is nucleated in models. However, the evolution of ice within clouds, and ice nucleation, depend critically on the dynamics that drive cloud scale motions. We will present results that attempt to separate the influences of microphysics and dynamics, with a view to understanding how dynamic processes affect the production and maintenance of supercooled liquid within Arctic cloud systems.
Tetragonal Lysozyme Nucleation and Crystal Growth: The Role of the Solution Phase
NASA Technical Reports Server (NTRS)
Pusey, Marc L.; Forsythe, Elizabeth; Sumida, John; Maxwell, Daniel; Gorti, Sridhar
Lysozyme, and most particularly the tetragonal form of the protein, has become the default standard protein for use in macromolecule crystal nucleation and growth studies. There is a substantial body of experimental evidence, from this and other laboratories, that strongly suggests this proteins crystal nucleation and growth is by addition of associated species that are preformed by standard reversible concentration-driven self association processes in the bulk solution. The evidence includes high resolution AFM studies of the surface packing and of growth unit size at incorporation, fluorescence resonance energy transfer measurements of intermolecular distances in dilute solution, dialysis kinetics, and modeling of the growth rate data. We have developed a selfassociation model for the proteins crystal nucleation and growth. The model accounts for the obtained crystal symmetry, explains the observed surface structures, and shows the importance of the symmetry obtained by self-association in solution to the process as a whole. Further, it indicates that nucleation and crystal growth are not distinct mechanistically, but identical, with the primary difference being the probability that the particle will continue to grow or dissolve. This model also offers a possible mechanism for fluid flow effects on the growth process and how microgravity may affect it. While a single lysozyme molecule is relatively small (M.W. = 14,400), a structured octamer in the 4(sub 3) helix configuration (the proposed average sized growth unit) would have a M.W. = 115,000 and dimensions of 5.6 x 5.6 x 7.6 nm. Direct AFM measurements of growth unit incorporation indicate that units as wide as 11.2 nm and as long as 11.4 nm commonly attach to the crystal. These measurements were made at approximately saturation conditions, and they reflect the sizes of species that both added or desorbed from the crystal surface. The larger and less isotropic the associated species the more likely that it will be oriented to some degree in a flowing boundary layer, even at the low flow velocities measured about macromolecule crystals. Flow-driven effects resulting in misorientation upon addition to and incorporation into the crystal need only be a small fraction of a percentage to significantly affect the resulting crystal. One Earth, concentration gradient driven flow will maintain a high interfacial concentration, i.e., a high level (essentially that of the bulk solution) of solute association at the interface and higher growth rate. Higher growth rates mean an increased probability that misaligned growth units are trapped by subsequent growth layers before they can be desorbed and try again, or that the desorbing species will be smaller than the adsorbing species. In microgravity the extended diffusive boundary layer will lower the interfacial concentration. This results in a net dissociation of aggregated species that diffuse in from the bulk solution, i.e., smaller associated species, which are more likely able to make multiple attempts to correctly bind, yielding higher quality crystals.
Liang Hu
A new process called phase enhanced gas-liquid absorption has been developed in its early stage. It was found that adding another phase into the absorption system of gas/aqueous phase could enhance the absorption rate. A system with three phases was studied. In the system, gas phase was carbon dioxide. Two liquid phases were used. One was organic phase. Another was aqueous phase. By addition of organic phase into the absorption system of CO{sub 2}-aqueous phase, the absorption rate of CO{sub 2} was increased significantly. CO{sub 2} finally accumulated into aqueous phase. The experimental results proved that (1) Absorption rate of carbon dioxide was enhanced by adding organic phase into gas aqueous phase system; (2) Organic phase played the role of transportation of gas solute (CO{sub 2}). Carbon dioxide finally accumulated into aqueous phase.
On radiative forcing of sulphate aerosol produced from ion-promoted nucleation mechanisms in an atmospheric global model
Hashmi FatimaH; H. C. Upadhyaya; S. N. Tripathi; O. P. Sharma; Fangqun Yu
A significant fraction of the total number of particles present in the atmosphere is formed by nucleation in the gas phase.\\u000a Nucleation and the subsequent growth process influence both number concentration of particles and their size distribution\\u000a besides chemical and optical properties of atmospheric aerosols. Sulphate aerosol nucleation mechanisms promoted by ions have\\u000a been evaluated here in a tropospheric interactive
From gas-phase oxidation of SO2 by SO4- to the formation of sulfuric acid
NASA Astrophysics Data System (ADS)
Tsona, Narcisse; Bork, Nicolai; Vehkamõki, Hanna
One of the difficulties to predict atmospheric nucleation is related to inaccurate measure of the total sulfuric acid concentration. We present a density functional theory investigation of the SO2 gas phase oxidation by SO4-. In the immediate product, SO2.SO4- cluster, SO2 is subsequently oxidized and SO3SO3- is formed at 1.7 ū 10-7 s-1 reaction rate. SO3SO3- interacts with O2 molecule to form SO3 and SO5-, which are important species in the gas phase chemistry of sulfur and in the formation mechanism of sulfuric acid.
Gas-phase synthesis of l-leucine-coated micrometer-sized salbutamol sulphate and sodium chloride particles
Janne Raula; Annukka Kuivanen; Anna Lõhde; Esko I. Kauppinen
Coating of micrometer-sized particles of salbutamol sulphate or sodium chloride with the amino acid l-leucine in the gas phase is described. A novel method to synthesize core particles and coat them with l-leucine simultaneously was carried out in an aerosol flow reactor. The coating was prepared via temperature-induced heterogeneous nucleation of l-leucine vapor on the 0.6¢1.0ĀĄm core particles, and subsequent
Nonextensive nuclear liquid-gas phase transition
NASA Astrophysics Data System (ADS)
Lavagno, A.; Pigato, D.
We study an effective relativistic mean-field model of nuclear matter with arbitrary proton fraction at finite temperature in the framework of nonextensive statistical mechanics, characterized by power-law quantum distributions. We investigate the presence of thermodynamic instability in a warm and asymmetric nuclear medium and study the consequent nuclear liquid-gas phase transition by requiring the Gibbs conditions on the global conservation of baryon number and electric charge fraction. We show that nonextensive statistical effects play a crucial role in the equation of state and in the formation of mixed phase also for small deviations from the standard Boltzmann-Gibbs statistics.
Gas-phase separations of protease digests.
Valentine, S J; Counterman, A E; Hoaglund, C S; Reilly, J P; Clemmer, D E
A mixture of peptides from a complete tryptic digest of ubiquitin has been analyzed by ion mobility/time-of-flight mass spectrometry techniques. All components of the mixture were electrosprayed and ions were separated in the gas phase based on differences in their mobilities through helium before being dispersed into a time-of-flight mass spectrometer for mass-to-charge analysis. The data show that ions separate into families primarily according to differences in their charge states and, to a lesser extent, differences in conformation. This approach reduces spectral congestion typically associated with electrosprayed mixtures and provides charge assignments for mass-to-charge ratio data. Gas-phase separations of ions appear to provide a new physical basis for characterizing components of biological mixtures. PMID:9794086
Ultrafast gas-phase electron diffraction
Joseph Charles Williamson
The temporal resolution of pump-probe, gas-phase electron diffraction (GED) has been extended to the picosecond time scale, a three order-of-magnitude improvement. With such resolution, GED can now be applied to structural studies of fundamental chemical dynamics, providing complementary information to conventional time-resolved spectroscopy techniques. This thesis gives a thorough theoretical and experimental treatment of ultrafast GED. Simulations of coherent chemical
Substrate-Free Gas-Phase Synthesis of Graphene Sheets
Frenklach, Michael
Substrate-Free Gas-Phase Synthesis of Graphene Sheets Albert Dato,*, Velimir Radmilovic, Zonghoon in the gas phase, and the entire synthesis process took place in fractions of a second, in an atmospheric graphene sheets in the gas phase using a substrate-free, atmospheric-pressure microwave plasma reactor
Fuel Performance Experiments and Modeling: Fission Gas Bubble Nucleation and Growth in Alloy Nuclear Fuels
McDeavitt, Sean; Shao, Lin; Tsvetkov, Pavel; Wirth, Brian; Kennedy, Rory
Advanced fast reactor systems being developed under the DOE's Advanced Fuel Cycle Initiative are designed to destroy TRU isotopes generated in existing and future nuclear energy systems. Over the past 40 years, multiple experiments and demonstrations have been completed using U-Zr, U-Pu-Zr, U-Mo and other metal alloys. As a result, multiple empirical and semi-empirical relationships have been established to develop empirical performance modeling codes. many mechamistic questions about fission as mobility, bubble coalescience, and gas release have been answered through industrial experience, reearch, and empirical understanding. The advent of modern computational materials science, however, opens new doors of development such that physics-based multi-scale models may be developed to enable a new generation of predictive fuel performance codes that are not limited by empiricism.
Isothermal nucleation and growth kinetics of Pd/Ag alloy phase via in-situ time-resolved high-temperature x-ray diffraction (HTXRD) analysis
Ayturk, Mahmut Engin [Worcester Polytechnic Institute; Payzant, E Andrew [ORNL; Speakman, Scott A [ORNL; Ma, Yi Hua [Worcester Polytechnic Institute
Among several different approaches to form Pd/Ag alloys for hydrogen separation applications, ex-situ studies carried by conventional X-ray point scanning detectors might fail to reveal the key aspects of the phase transformation between Pd and Ag metals. In this respect, in-situ time-resolved high temperature X-ray diffraction (HTXRD) was employed to study the Pd/Ag alloy phase nucleation and growth kinetics. By the use of linear position sensitive detectors, advanced optics and profile fitting with the use of JADE-6.5 software, isothermal phase evolution of the Pd/Ag alloy at 500 C, 550 C and 600 C under hydrogen atmosphere were quantified to elucidate the mechanistic details of the Pd/Ag alloy phase nucleation and growth pattern. Analysis of the HTXRD data by the Avrami model indicated that the nucleation of the Pd/Ag alloy phase was instantaneous where the growth mechanism was through diffusion-controlled one-dimensional thickening of the Pd/Ag alloy layer. The value of the Avrami exponent, n, was found to increase with temperature with the values of 0.34, 0.39 and 0.67 at 500oC, 550oC and 600oC, respectively. In addition, parabolic rate law analysis suggested that the nucleation of the Pd/Ag alloy phase was through a heterogeneous nucleation mode, in which the nucleation sites were defined as the non-equilibrium defects. The cross-sectional SEI micrographs indicated that the Pd/Ag alloy phase growth was strongly dependent upon the deposition morphology of the as-synthesized Pd and Ag layers formed by the electroless plating. Based on the Avrami model and the parabolic rate law, the estimated activation energies for the phase transformation were 236.5 and 185.6 kJ/mol and in excellent agreement with the literature values (183-239.5 kJ/mol).
Initiation of the ice phase by marine biogenic surfaces in supersaturated gas and supercooled aqueous phases.
Alpert, Peter A; Aller, Josephine Y; Knopf, Daniel A
Biogenic particles have the potential to affect the formation of ice crystals in the atmosphere with subsequent consequences for the hydrological cycle and climate. We present laboratory observations of heterogeneous ice nucleation in immersion and deposition modes under atmospherically relevant conditions initiated by Nannochloris atomus and Emiliania huxleyi, marine phytoplankton with structurally and chemically distinct cell walls. Temperatures at which freezing, melting, and water uptake occur are observed using optical microscopy. The intact and fragmented unarmoured cells of N. atomus in aqueous NaCl droplets enhance ice nucleation by 10-20 K over the homogeneous freezing limit and can be described by a modified water activity based ice nucleation approach. E. huxleyi cells covered by calcite plates do not enhance droplet freezing temperatures. Both species nucleate ice in the deposition mode at an ice saturation ratio, S(ice), as low as ~1.2 and below 240 K, however, for each, different nucleation modes occur at warmer temperatures. These observations show that markedly different biogenic surfaces have both comparable and contrasting effects on ice nucleation behaviour depending on the presence of the aqueous phase and the extent of supercooling and water vapour supersaturation. We derive heterogeneous ice nucleation rate coefficients, J(het), and cumulative ice nuclei spectra, K, for quantification and analysis using time-dependent and time-independent approaches, respectively. Contact angles, ?, derived from J(het)via immersion freezing depend on T, a(w), and S(ice). For deposition freezing, ? can be described as a function of S(ice) only. The different approaches yield different predictions of atmospheric ice crystal numbers primarily due to the time evolution allowed for the time-dependent approach with implications for the evolution of mixed-phase and ice clouds. PMID:21912788
Bursts of particle nucleation in storm outflows.
NASA Astrophysics Data System (ADS)
Ford, I. J.; Clement, C. F.; Twohy, C. H.; Weinheimer, A.; Campos, T.
Nucleation of atmospheric aerosol is an inherently intermittent process. The concentrations of gas phase precursors are unevenly distributed in the atmosphere, and the ambient temperature varies too, leading to localised regions where nucleation is favoured thermodynamically. The non-linear dependence of the nucleation rate on the thermodynamic driving forces causes particle production be even more localised. Furthermore, the nucleation of particles depletes the concentration of precursor, so that production can quickly terminate. Together, these features of the system and process cause nucleation to occur in localised bursts. We have developed simple models of nucleation bursts, and recently were able to test the model predictions by analysing measurements of particles produced when precursor-bearing air flows out of the tops of large scale storm clouds. These flows are very favourable for particle production since existing aerosol, which competes for condensation, has been scavenged within the cloud. Also, the temperatures are very low at the top of the troposphere. Estimates show that storm outflows could constitute a very significant source of atmospheric particles. While the nucleation bursts are indeed localised, on the spatial scales associated with major storms they can be viewed as operating rather uniformly across a large part of the atmosphere. We are then able to apply a simple analysis of the production and transport. As part of the SUCCESS campaign, the concentrations of atmospheric gases and condensation nuclei in the outflow of a major storm were measured aboard a NASA DC-8 aircraft. The data provide an excellent opportunity to study nucleation, growth and coagulation of particles. The data are consistent with the binary nucleation of droplets of water and sulphuric acid produced in the storm outflow by the oxidation of sulphur dioxide. We conclude that a 5 minute burst of nucleation was followed by growth and coagulation over a period of about 5 hours until measured by the aircraft. Both the mass and number concentrations of the observed aerosol can be reproduced by this analysis within a timescale consistent with that of the storm. Somewhat surprisingly, our models suggest that the final particle number concentration is very insensitive to the initial sulphur dioxide concentration, which might have implications in considering the effect of increases in atmospheric pollution on particle production.
Nucleation and temperature-driven phase transitions of silicene superstructures on Ag(1?1?1).
Grazianetti, C; Chiappe, D; Cinquanta, E; Fanciulli, M; Molle, A
Silicene grown on Ag(1?1?1) is characterized by several critical parameters. Among them, the substrate temperature plays a key role in determining the morphology during growth. However, an unexpected important role is also equally played by the post-deposition annealing temperature which determines the self-organization of silicene domains even in the submonolayer coverage regime and consecutive transitions between silicene with different periodicity. These temperature-driven phase transitions can be exploited to select the desired majority silicene phase, thus allowing for the manipulation of silicene properties. PMID:26020358
Infrared spectroscopy of homogeneously nucleated hydrazine aerosols - Disordered and crystalline phases
NASA Astrophysics Data System (ADS)
Dunder, T.; Clapp, M. L.; Miller, R. E.
It is shown that aerosols generated at low temperatures and high condensation rate spontaneously form in a highly crystalline state. The resonant absorption bands in the IR spectra of these highly crystalline particles are much sharper than any reported previously in the bulk, and reveal details in the N-H vibrational bands that have not been previously observed. A disordered phase is also observed at somewhat higher temperatures. These results are consistent with this being a supercooled liquid. The fact that the spectra associated with these two aerosol phases are quite different is important to any future attempts at detecting hydrazine aerosols in planetary atmospheres by remote sensing techniques.
Loitering Phase in Brane Gas Cosmology
Robert Brandenberger; Damien A. Easson; Dagny Kimberly
Brane Gas Cosmology (BGC) is an approach to M-theory cosmology in which the initial state of the Universe is taken to be small, dense and hot, with all fundamental degrees of freedom near thermal equilibrium. Such a starting point is in close analogy with the Standard Big Bang (SBB) model. The topology of the Universe is assumed to be toroidal in all nine spatial dimensions and is filled with a gas of p-branes. The dynamics of winding modes allow, at most, three spatial dimensions to become large, thus explaining the origin of our macroscopic 3+1-dimensional Universe. Here we conduct a detailed analysis of the loitering phase of BGC. We do so by including into the equations of motion that describe the dilaton gravity background some new equations which determine the annihilation of string winding modes into string loops. Specific solutions are found within the model that exhibit loitering, i.e. the Universe experiences a short phase of slow contraction during which the Hubble radius grows larger than the physical extent of the Universe. As a result the brane problem (generalized domain wall problem) in BGC is solved. The initial singularity and horizon problems of the SBB scenario are solved without relying on an inflationary phase.
On the nucleation and propagation of phase transformation fronts in a NiTi alloy
J. A. Shaw; S. Kyriakides
In this paper we present an experimental methodology for simultaneous full field monitoring of the deformation and thermal changes in NiTi during mechanically unstable regimes associated with the pseudoelastic material response. The deformation history is established by photographically recording surface changes of a brittle coating as austenite-martensite phase transition fronts traverse the specimen. Temperature changes are monitored by infrared thermal
Homogeneous nucleation of droplets from a supersaturated vapor phase Michael P. Moody and Phil Attard
Attard, Phil
Attard Ian Wark Research Institute, University of South Australia, Mawson Lakes SA 5095 Australia are compared for the case where the vapor phase forms a reservoir constant supersaturation . In the case and will in all likelihood evaporate. As a result of this energy barrier, the system can exist in a metastable
Homogeneous Crystal Nucleation Near a Metastable Fluid-Fluid Phase Transition Sergey V. Buldyrev,2
Stanley, H. Eugene
. Buldyrev,2 H. Eugene Stanley,3 and Giancarlo Franzese4 1 International Center for Quantum Materials, Peking-fluid phase separation below the solubility line. Based on computations, it was proposed that the fluid but widespread pathologies, such as eye cataracts--a common cause of blindness. The repercussions of protein
Giddings Austin chalk enters deep lean-gas phase
Moritis, G.
Deep lean gas is the latest phase in the growth of the Giddings field Austin chalk play. The first phase involved drilling vertical oil and gas wells. Next came the horizontal well boom in the shallower Austin chalk area, which is still continuing. And now this third phase places horizontal laterals in the Austen chalk at about 14,000--15,000 ft to produce lean gas. The article describes the producing wells and gas gathering.
Normal Phase of an Imbalanced Fermi Gas
Mora, Christophe [Laboratoire Pierre-Aigrain, Ecole Normale Superieure, CNRS and Universite Paris 7 Diderot, 24 rue Lhomond, 75005 Paris (France); Chevy, Frederic [Laboratoire Kastler-Brossel, Ecole Normale Superieure, CNRS and UPMC, 24 rue Lhomond, 75005 Paris (France)
Recent experiments on imbalanced Fermi gases have raised interest in the physics of an impurity immersed in a Fermi sea, the so-called Fermi polaron. In this Letter, a simple theory is devised to describe dilute Fermi-polaron ensembles corresponding to the normal phase of an imbalanced Fermi gas. An exact formula is obtained for the dominant interaction between polarons, expressed solely in terms of a single-polaron parameter. The physics of this interaction is identified as a signature of the Pauli exclusion principle.
Gas phase thermochemistry of organogermanium compounds
Engel, J.P.
A variety of silyl- and alkyl-germylene precursors have been synthesized and subsequently pyrolyzed in the gas phase. Arrhenius parameters were obtained employing a pulsed-stirred flow reactor for these unimolecular decompositions. These precursors are divided into two major categories by mechanism of germylene extrusion: {alpha}-elimination precursors and germylacetylenes. The extrusion of germylenes from germylacetylene precursors is of primary interest. A mechanism is proposed employing a germacyclopropene intermediate. Evidence supporting this mechanism is presented. In the process of exploring germylacetylenes as germylene precursors, an apparent dyatropic rearrangement between germanium and silicon was observed. This rearrangement was subsequently explored.
Gas phase and surface reactions in subatmospheric chemical vapor deposition of tetraethylorthosilicate-ozone
Gill, W.N.; Ganguli, S. [Department of Chemical Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180-3590 (United States)] [Department of Chemical Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180-3590 (United States)
A new physical-chemical model, which applies over a wide range of operating pressures, describes the gas phase and surface reactions in subatmospheric chemical vapor deposition of silicon dioxide for producing inter-layer dielectrics in a cold-wall reactor. Tetraethylorthosilicate (TEOS) reacts in the gas phase to form an intermediate which is adsorbed and reacts on the surface to produce a silicon dioxide film. The results compare favorably with experimental data over a pressure range of 100{endash}600 Torr and a temperature range of 370{endash}500{degree}C. The concentration distributions of TEOS, intermediate and ozone in the gas phase and their ratios at the surface of the wafer are determined to study gas phase nucleation and the relationship between composition distributions and film quality. Previous models based on low pressure data in the range of 30{endash}90 Torr need to be modified to predict accurately the rates of deposition from 100 Torr to atmospheric pressure. Gas phase reactions cause the maximum in the deposition rates to shift to higher pressures at lower deposition temperatures, both in the model and experiments. At higher pressures, particulates are formed by the gas phase reactions which must be included to represent properly the chemical dynamics of the process. The deposition rate increases up to an asymptotic value as the TEOS flow rate is increased; above this level no further increase in growth rate occurs. This is a consequence of the basic mechanism of the surface reaction which predicts the asymptotic behavior observed. {copyright} {ital 1997 American Vacuum Society.}
Nucleation pathways in partially disordered lattice models
NASA Astrophysics Data System (ADS)
Quigley, David; Lifanov, Yuri; Vorselaars, Bart
Simple lattice models are attractive for the study of non-classical nucleation and growth from solution, a phenomenon still largely inaccessible to atomistic simulation. We have extended the Potts Lattice Gas (PLG) model of Duff and Peters to include a metastable partially ordered precursor phase, mimicking the common mineral calcium carbonate. Using a combination of multicanonical Monte Carlo and equilibrium path sampling, we demonstrate that thermodynamically favourable pathways between a metastable solution state and the fully ordered lattice proceed via formation of partially ordered nuclei. By comparing the activation energy associated with the ordering of these nuclei to that needed to nucleate the ordered phase directly, we demonstrate dissolution and re-precipitation as an emergent growth phenomenon of our model.
The effect of lattice and grain boundary diffusion on the redistribution of Xe in metallic nuclear fuels: Implications for the use of ion implantation to study fission-gas-bubble nucleation mechanisms
Wayne E. King; Scott J. Tumey; Jeffrey Rest; George H. Gilmer
A multi-atom gas bubble-nucleation mechanism has been proposed as part of a predictive fission-gas release model for metallic nuclear fuels. Validation of this mechanism requires experimental measurement of fission-gas bubble-size distributions at well-controlled gas concentrations and temperatures. There are advantages to carrying out such a study using ion implantation as the source of gas atoms compared with neutron irradiations. In
Loitering Phase in Brane Gas Cosmology
Brandenberger, R H; Kimberly, D M; Brandenberger, Robert; Easson, Damien A.; Kimberly, Dagny
Brane Gas Cosmology (BGC) is an approach to M-theory cosmology in which the initial state of the Universe is taken to be small, dense and hot, with all fundamental degrees of freedom near thermal equilibrium. Such a starting point is in close analogy with the Standard Big Bang (SBB) model. The topology of the Universe is assumed to be toroidal in all nine spatial dimensions and is filled with a gas of p-branes. The dynamics of winding modes allow, at most, three spatial dimensions to become large, thus explaining the origin of our macroscopic 3+1-dimensional Universe. Here we conduct a detailed analysis of the loitering phase of BGC. We do so by including into the equations of motion that describe the dilaton gravity background some new equations which determine the annihilation of string winding modes into string loops. Specific solutions are found within the model that exhibit loitering, i.e. the Universe experiences a short phase of slow contraction during which the Hubble radius grows larger than the phys...
Molecular Ice Nucleation Activity of Birch Pollen
NASA Astrophysics Data System (ADS)
Felgitsch, Laura; Bichler, Magdalena; Hõusler, Thomas; Weiss, Victor U.; Marchetti-Deschmann, Martina; Allmaier, G³nter; Grothe, Hinrich
Heterogeneous ice nucleation plays a major part in ecosystem and climate. Due to the triggering of ice cloud formation it influences the radiation balance of the earth, but also on the ground it can be found to be important in many processes of nature. So far the process of heterogeneous ice nucleation is not fully understood and many questions remain to be answered. Biological ice nucleation is hereby from great interest, because it shows the highest freezing temperatures. Several bacteria and fungi act as ice nuclei. A famous example is Pseudomonas syringae, a bacterium in commercial use (Snomax«), which increases the freezing from homogeneous freezing temperatures of approx. -40░ C (for small volumes as in cloud droplets) to temperatures up to -2░ C. In 2001 it was found that birch pollen can trigger ice nucleation (Diehl et al. 2001; Diehl et al. 2002). For a long time it was believed that this is due to macroscopic features of the pollen surface. Recent findings of Bernhard Pummer (2012) show a different picture. The ice nuclei are not attached on the pollen surface directly, but on surface material which can be easily washed off. This shows that not only the surface morphology, but also specific molecules or molecular structures are responsible for the ice nucleation activity of birch pollen. With various analytic methods we work on elucidating the structure of these molecules as well as the mechanism with which they trigger ice nucleation. To solve this we use various instrumental analytic techniques like Nuclear Magnetic Resonance spectroscopy (NMR), Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry (MALDI-MS), and Gas-phase Electrophoretic Mobility Molecular Analysis (GEMMA). Also standard techniques like various chromatographic separation techniques and solvent extraction are in use. We state here that this feature might be due to the aggregation of small molecules, with agglomerates showing a specific surface structure. Our results indicate that the substance is amphiphilic in character leading finally to micelle formation. Diehl, K., Quick, C., Matthias-Maser, S., Mitra, S. K., and Jaenicke, R.: The ice nucleation ability of pollen, part I, Atmos. Res., 58, 75-87, 2001. Diehl, K., Matthias-Maser, S., Jaenicke, R., and Mitra, S. K.: The ice nucleation ability of pollen, part II, Atmos. Res., 61, 125-133, 2002. Pummer, B., Bauer, H., Bernardi, J., Bleicher, S., Grothe, H.; Suspendable macromolecules are responsible for ice nucleation activity of birch and conifer pollen; Atmos. Chem. Phys., 12, 2541 - 2550, 2012.
Gas-phase helical peptides mimic solution-phase behavior.
Morrison, Lindsay J; Wysocki, Vicki H
In solution, ?-helices are stabilized at the termini by a variety of different capping interactions. Study of these interactions in the gas phase provides a unique means to explore the intrinsic properties that cause this stabilization. Evidence of helical and globular conformations is presented here for gas-phase, doubly charged peptides of sequence XAnK, wherein X is D, N, Q, or L. The relative abundance of the helical conformation is found to vary as a function of peptide length and the identity of the first amino acid, consistent with solution phase studies that have looked at the identity of the first amino acid. The N-terminal, b ion fragments of the doubly charged precursor peptides are shown to form helical and globular conformations. The stability of the helical fragments is examined as a function of fragment length, N-terminal amino acid, precursor conformation, and the activation energy used to generate the fragment. At lower collision energies, helical b ions preferentially form, particularly from helical precursors. The abundance of the helical b ion population is observed to dramatically decrease for NAn and DAn b ions smaller than the b10; simulations suggest this feature is due to the b10 having two complete turns of the helix, while the b9 and smaller ions have only a partial second turn, suggesting the b10 is the lower limit for stable helical conformations in b ions. Use of higher collision energies promotes the formation of globular structures in the b ions. This characteristic is attributed to increased conformational dynamics and subsequently improved proton transfer kinetics from the b ion's C-terminal oxazolone ring to the N-terminus. PMID:25203898
Calculation of two-phase flow in gas turbine combustors
A. K. Tolpadi
A method is presented for computing steady two-phase turbulent combusting flow in a gas turbine combustor. The gas phase equations are solved in an Eulerian frame of reference. The two-phase calculations are performed by using a liquid droplet spray combustion a model and treating the motion of the evaporating fuel droplets in a Lagrangian frame of reference. The numerical algorithm
Fundamentals of gas phase plasmas for treatment of human tissue.
Kushner, Mark J; Babaeva, Natalia Yu
The use of gas phase plasmas for treating human tissue is at the intersection of two disciplines - plasma physics and engineering, and medicine. In this paper, a primer will be provided for the medical practitioner on the fundamentals of generating gas phase plasmas at atmospheric pressure in air for the treatment of human tissue. The mechanisms for gas phase plasmas interacting with tissue and biological fluids will also be discussed using results from computer modeling. PMID:21335808
Gas: A Neglected Phase in Remediation of Metals and Radionuclides
Denham, Miles E.; Looney, Brian B
The gas phase is generally ignored in remediation of metals and radionuclides because it is assumed that there is no efficient way to exploit it. In the literal sense, all remediations involve the gas phase because this phase is linked to the liquid and solid phases by vapor pressure and thermodynamic relationships. Remediation methods that specifically use the gas phase as a central feature have primarily targeted volatile organic contaminants, not metals and radionuclides. Unlike many organic contaminants, the vapor pressure and Henry's Law constants of metals and radionuclides are not generally conducive to direct air stripping of dissolved contaminants. Nevertheless, the gas phase can play an important role in remediation of inorganic contaminants and provide opportunities for efficient, cost effective remediation. The objective here is to explore ways in which manipulation of the gas phase can be used to facilitate remediation of metals and radionuclides.
Gas phase hyper-Rayleigh scattering measurements
NASA Astrophysics Data System (ADS)
Shelton, David P.
Measurements of hyper-Rayleigh scattering intensities and polarization ratios are presented for nine small molecules in the gas phase [CH4, CF4, CCl4, N2O, NH3, D2O, SO2, CF2Cl2, and (CH3)2CO]. In four cases [CH4, CF4, CCl4, and N2O] all molecular hyperpolarizability tensor components can be determined from the measurements. The results of this experiment are compared with the results of previous ab initio calculations, finding discrepancies up to 60%. Including vibrational contributions decreases the discrepancies for CH4 and CF4 and increases them for CCl4, D2O, and NH3.
Phase transitions in a gas of anyons
MacKenzie, R.; Nebia-Rahal, F.; Paranjape, M. B. [Groupe de physique des particules, Departement de physique, Universite de Montreal, C.P. 6128, Succ. Centre-ville, Montreal, Quebec, H3C 3J7 (Canada); Richer, J. [Reseau quebecois de calcul de haute performance, DGTIC, Universite de Montreal, C.P. 6128, Succ. Centre-ville, Montreal, Quebec, H3C 3J7 (Canada)
We continue our numerical Monte Carlo simulation of a gas of closed loops on a 3 dimensional lattice, however, now in the presence of a topological term added to the action which corresponds to the total linking number between the loops. We compute the linking number using a novel approach employing certain notions from knot theory. Adding the topological term converts the particles into anyons. Interpreting the model as an effective theory that describes the 2+1-dimensional Abelian Higgs model in the asymptotic strong-coupling regime, the topological linking number simply corresponds to the addition to the action of the Chern-Simons term. The system continues to exhibit a phase transition as a function of the vortex mass as it becomes small. We find the following new results. The Chern-Simons term has no effect on the Wilson loop. On the other hand, it does effect the 't Hooft loop of a given configuration, adding the linking number of the 't Hooft loop with all of the dynamical vortex loops. We find the unexpected result that both the Wilson loop and the 't Hooft loop exhibit a perimeter law even though there are no massless particles in the theory, in both phases of the theory. It should be noted that our method suffers from numerical instabilities if the coefficient of the Chern-Simons term is too large; thus, we have restricted our results to small values of this parameter. Furthermore, interpreting the lattice loop gas as an effective theory describing the Abelian Higgs model is only known to be true in the infinite coupling limit; for strong but finite coupling this correspondence is only a conjecture, the validity of which is beyond the scope of this article.
Transferring pharmaceuticals into the gas phase
NASA Astrophysics Data System (ADS)
Christen, Wolfgang; Krause, Tim; Rademann, Klaus
The dissolution of molecules of biological interest in supercritical carbon dioxide is investigated using pulsed molecular beam mass spectrometry. Due to the mild processing temperatures of most supercritical fluids, their adiabatic expansion into vacuum permits to transfer even thermally very sensitive substances into the gas phase, which is particularly attractive for pharmaceutical and biomedical applications. In addition, supercritical CO2constitutes a chemically inert solvent that is compatible with hydrocarbon-free ultrahigh vacuum conditions. Here, we report on the dissolution and pulsed supersonic jet expansion of caffeine (C8H10N4O2), the provitamin menadione (C11H8O2), and the amino acid derivative l-phenylalanine tert-butyl ester hydrochloride (C6H5CH2CH(NH2)COOC(CH3)3[dot operator]HCl), into vacuum. An on-axis residual gas analyzer is used to monitor the relative amounts of solute and solvent in the molecular beam as a function of solvent densityE The excellent selectivity and sensitivity provided by mass spectrometry permits to probe even trace amounts of solutes. The strong density variation of CO2 close to the critical point results in a pronounced pressure dependence of the relative ion currents of solute and solvent molecules, reflecting a substantial change in solubility.
Buckyball Nucleation of HiPco Tubes
NASA Technical Reports Server (NTRS)
Smalley, Richard E.
The purpose of this innovation is to enhance nucleation of single-wall nanotubes (SWNTs) in the HiPco process, selectively producing 10,10 tubes, something which until now has not been thought possible. This is accomplished by injecting C60, or a derivative of C60, solubilized in supercritical CO2 together with a transition metal carboneal cocatalyst into the HiPco reactor. This is a variant on the supercritical disclosure. C60 has never been used to nucleate carbon nanotubes in the gas phase. C60 itself may not have adequate solubility in supercritical CO2. However, fluorinated C60, e.g., C60F36, is easy to make cheaply and should have much enhanced solubility.
Onset of runaway nucleation in aerosol reactors
NASA Technical Reports Server (NTRS)
Wu, Jin Jwang; Flagan, Richard C.
The onset of homogeneous nucleation of new particles from the products of gas phase chemical reactions was explored using an aerosol reactor in which seed particles of silicon were grown by silane pyrolysis. The transition from seed growth by cluster deposition to catastrophic nucleation was extremely abrupt, with as little as a 17 percent change in the reactant concentration leading to an increase in the concentration of measurable particles of four orders of magnitude. From the structure of the particles grown near this transition, it is apparent that much of the growth occurs by the accumulation of clusters on the growing seed particles. The time scale for cluster diffusion indicates, however, that the clusters responsible for growth must be much smaller than the apparent fine structure of the product particles.
Design Considerations on Three Phase Enclosure Type Gas Insulated Substation
K. Azumi; H. Kuwahara; I. Sakon; T. Marutani; H. Niwa
A series of three phase enclosure type gas insulated substations is developed at the voltage ratings from 72 kV up to 204 kV. All the substation equipments, not only the switchgears and bus works but measuring transformers, surge arresters and the connections to transformers and cables are enclosed three phases in a common enclosure in the gas insulated substation (GIS).
SHORT COMMUNICATION Gas-Phase Separations of Protease Digests
Clemmer, David E.
SHORT COMMUNICATION Gas-Phase Separations of Protease Digests Stephen J. Valentine, Anne E University, Bloomington, Indiana, USA A mixture of peptides from a complete tryptic digest of ubiquitin has and identify peptides from a tryptic digest of ubiquitin. The mixture was electrosprayed into the gas phase
Pressure Dependence of Gas-Phase Reaction Rates
ERIC Educational Resources Information Center
De Persis, Stephanie; Dollet, Alain; Teyssandier, Francis
It is presented that only simple concepts, mainly taken from activated-complex or transition-state theory, are required to explain and analytically describe the influence of pressure on gas-phase reaction kinetics. The simplest kind of elementary gas-phase reaction is a unimolecular decomposition reaction.
Instabilities in Lean Gas-Phase Combustion
NASA Astrophysics Data System (ADS)
Schneider, K.; Bockhorn, H.; Eigenbrod, Ch.; Emerson, D.; Haldenwang, P.; Hoffmann, F.; Roekaerts, D.; Ronney, P.; Triebel, W.; Tummers, M.
Lean burning is the burning of fuel-air mixtures with less than the chemically- balanced (stoichiometric) mixture. It produces a significant increase in fuel efficiency and reduction in pollution. However, the limits and control of lean burning are still not well understood.This is the motivation behind the study of instabilities in lean gas-phase combustion under microgravity conditions via direct numerical simulations and comparison of the results with experimental data.The goal is to gain fundamental insights in order to identify and understand the intrinsic chemical and fluid dynamical mechanisms responsible for these instabilities.The potential of this microgravity combustion research includes the development of technology that would reduce pollution and fire and explosion hazards, improve hazardous waste incineration and increase efficiency of the conversion of chemical energy to electric power or motive force.The results from this fundamental research will thus benefit chemical engineering and power generation. Its wide range of applications in industry includes lean-burning car engines.
Noble metal alloy clusters in the gas phase derived from protein templates: unusual recognition of palladium by gold.
Baksi, Ananya; Pradeep, T
Matrix assisted laser desorption ionization of a mixture of gold and palladium adducts of the protein lysozyme (Lyz) produces naked alloy clusters of the type Au24Pd(+) in the gas phase. While a lysozyme-Au adduct forms Au18(+), Au25(+), Au38(+) and Au102(+) ions in the gas phase, lysozyme-Pd alone does not form any analogous cluster. Addition of various transition metal ions (Ag(+), Pt(2+), Pd(2+), Cu(2+), Fe(2+), Ni(2+) and Cr(3+)) in the adducts contributes to drastic changes in the mass spectrum, but only palladium forms alloys in the gas phase. Besides alloy formation, palladium enhances the formation of specific single component clusters such as Au38(+). While other metal ions like Cu(2+) help forming Au25(+) selectively, Fe(2+) catalyzes the formation of Au25(+) over all other clusters. Gas phase cluster formation occurs from protein adducts where Au is in the 1+ state while Pd is in the 2+ state. The creation of alloys in the gas phase is not affected whether a physical mixture of Au and Pd adducts or a Au and Pd co-adduct is used as the precursor. The formation of Au cores and AuPd alloy cores of the kind comparable to monolayer protected clusters implies that naked clusters themselves may be nucleated in solution. PMID:24146135
[On road particle emission characteristics of a Chinese phase IV natural gas bus].
Lou, Di-Ming; Cheng, Wei; Feng, Qian
An on-road experimental research was made on a Chinese phase IV natural gas bus using a Portable Emission Measurement System (PEMS), and particle emission characteristics under different vehicle speed, acceleration and vehicle specific power were investigated. The results show that particle number and mass emission rates increase and their emission factors decrease while the speed of the bus rises. Particle number concentration of different sizes shows multimodal logarithmic distribution pattern when the bus runs on all operation conditions (idle, low speed, medium speed and high speed), and nucleation mode particle account for a large proportion in the total particle number. With the increase of acceleration, particle emission rate rises, and it is lower when the bus runs at constant speed or slow deceleration condition than that at the fast acceleration condition. Furthermore, particle emission rate increases against the absolute value of the vehicle specific power (VSP). PMID:24881371
Gamma-ray spectra of hexane in gas phase and liquid phase
Xiaoguang Ma; Feng Wang
Theoretical gamma-ray spectra of molecule hexane have been calculated and compared with the experimental results in both gas (Surko et al, 1997) and liquid (Kerr et al, 1965) phases. The present study reveals that in gas phase not all valence electrons of hexane exhibit the same probability to annihilate a positron. Only the positrophilic electrons in the valence space dominate the gamma-ray spectra, which are in good agreement with the gas phase measurement. When hexane is confined in liquid phase, however, the intermolecular interactions ultimately eliminate the free molecular orientation and selectivity for the positrophilic electrons in the gas phase. As a result, the gamma-ray spectra of hexane become an averaged contribution from all valence electrons, which is again in agreement with liquid phase measurement. The roles of the positrophilic electrons in annihilation process for gas and liquid phases of hexane have been recognized for the first time in the present study.
Metadynamics studies of crystal nucleation
Giberti, Federico; Salvalaglio, Matteo; Parrinello, Michele
Crystallization processes are characterized by activated events and long timescales. These characteristics prevent standard molecular dynamics techniques from being efficiently used for the direct investigation of processes such as nucleation. This short review provides an overview on the use of metadynamics, a state-of-the-art enhanced sampling technique, for the simulation of phase transitions involving the production of a crystalline solid. In particular the principles of metadynamics are outlined, several order parameters are described that have been or could be used in conjunction with metadynamics to sample nucleation events and then an overview is given of recent metadynamics results in the field of crystal nucleation. PMID:25866662
[Effect of inert gas xenon on the functional state of nucleated cells of peripheral blood during freezing].
Laptev, D S; Polezhaeva, T V; Zaitseva, O O; Khudyakov, A N; Utemov, S V; Knyazev, M G; Kostyaev, A A
A new method of preservation of nucleated cells in the electric refrigerator with xenon. After slow freezing and storage is even one day at -80 ░C persists for more than 60% leukocytes. Cell membranes are resistant to the vital dye. In 85% of granulocytes stored baseline lysosomal-cationic protein, reduced lipid peroxidation and antioxidant activity. Cryopreservation of biological objects in inert gases is a promising direction in the practice of medicine and can be an alternative to the traditional method using liquid nitrogen. PMID:26027341
Aerosol formation from the reaction of {alpha}pinene and ozone using a gas-phase kinetics-aerosol partitioning model
Kamens, R.; Jang, M.; Chien, C.J.; Leach, K. [Univ. of North Carolina, Chapel Hill, NC (United States). Dept. of Environmental Sciences and Engineering] [Univ. of North Carolina, Chapel Hill, NC (United States). Dept. of Environmental Sciences and Engineering
As a result of new aerosol compositional information, the authors have implemented an exploratory model for predicting aerosol yields from the reaction of {alpha}-pinene with ozone in the atmosphere. This new approach has the ability to embrace a range of different atmospheric chemical conditions, which bring about biogenic aerosol formation. A kinetic mechanism was used to describe the gas-phase reactions of {alpha}-pinene with ozone. This reaction scheme produces low vapor pressure reaction products that distribute between gas and particle phases. Some of the products have subcooled liquid vapor pressures which are low enough to initiate self-nucleation. More volatile products such as pinonic acid and pinonaldehyde will not self-nucleate but will partition onto existing particle surfaces. Partitioning was treated as an equilibrium between the rate of particle uptake and rate of particle loss of semivolatile terpene reaction products. Given estimated liquid vapor pressures and activation energies of desorption, it was possible to calculate gas-particle equilibrium constants with aerosol desorption rate constants at different temperatures. This permitted an estimate of the rate of absorption from the gas phase. Gas- and aerosol-phase reactions were linked together in one chemical mechanism, and a chemical kinetics solver was used to predict reactant and product concentrations over time. Aerosol formation from the model was then compared with aerosol production observed from outdoor chamber experiments.
Bubble nucleation in stout beers.
Lee, W T; McKechnie, J S; Devereux, M G
Bubble nucleation in weakly supersaturated solutions of carbon dioxide-such as champagne, sparkling wines, and carbonated beers-is well understood. Bubbles grow and detach from nucleation sites: gas pockets trapped within hollow cellulose fibers. This mechanism appears not to be active in stout beers that are supersaturated solutions of nitrogen and carbon dioxide. In their canned forms these beers require additional technology (widgets) to release the bubbles which will form the head of the beer. We extend the mathematical model of bubble nucleation in carbonated liquids to the case of two gases and show that this nucleation mechanism is active in stout beers, though substantially slower than in carbonated beers and confirm this by observation. A rough calculation suggests that despite the slowness of the process, applying a coating of hollow porous fibers to the inside of a can or bottle could be a potential replacement for widgets. PMID:21728549
Bubble nucleation in stout beers
NASA Astrophysics Data System (ADS)
Lee, W. T.; McKechnie, J. S.; Devereux, M. G.
Bubble nucleation in weakly supersaturated solutions of carbon dioxideŚsuch as champagne, sparkling wines, and carbonated beersŚis well understood. Bubbles grow and detach from nucleation sites: gas pockets trapped within hollow cellulose fibers. This mechanism appears not to be active in stout beers that are supersaturated solutions of nitrogen and carbon dioxide. In their canned forms these beers require additional technology (widgets) to release the bubbles which will form the head of the beer. We extend the mathematical model of bubble nucleation in carbonated liquids to the case of two gases and show that this nucleation mechanism is active in stout beers, though substantially slower than in carbonated beers and confirm this by observation. A rough calculation suggests that despite the slowness of the process, applying a coating of hollow porous fibers to the inside of a can or bottle could be a potential replacement for widgets.
Equilibrium structures from gas-phase electron-diffraction dataĀ
McCaffrey, Philip D
For the past 75 years gas-phase electron diffraction (GED) has remained the most valuable technique for determining structures of small molecules, free from intermolecular interactions. Throughout this period many ...
Mixed Stationary Liquid Phases for Gas-Liquid Chromatography.
ERIC Educational Resources Information Center
Koury, Albert M.; Parcher, Jon F.
Describes a laboratory technique for use in an undergraduate instrumental analysis course that, using the interpretation of window diagrams, prepares a mixed liquid phase column for gas-liquid chromatography. A detailed procedure is provided. (BT)
History-dependent nucleation and growth of the martensitic phase in the magnetic shape memory alloy Ni45Co5Mn38Sn12
NASA Astrophysics Data System (ADS)
Banerjee, A.; Chaddah, P.; Dash, S.; Kumar, Kranti; Lakhani, Archana; Chen, X.; Ramanujan, R. V.
We study through the time evolution of magnetization the low-temperature (T) dynamics of the metastable coexisting phases created by traversing different paths in magnetic field H and T space in a shape memory alloy system, Ni45Co5Mn38Sn12. It is shown that these coexisting phases consisting of a fraction of kinetically arrested austenite phase and a remaining fraction of low-T equilibrium martensitic phase undergo a slow relaxation to low magnetization (martensitic) state but with very different thermomagnetic history-dependent rates at the same T and H. We discovered that, when the nucleation of the martensitic phase is initiated at much lower T through the de-arrest of the glasslike arrested state contrasted with the respective first-order transformation (through supercooling at much higher T), the long-time relaxation rate scales with the nonequilibrium phase fraction but has a very weak dependence on T. This is explained on the basis of the H-T path dependent size of the critical radii of the nuclei and the subsequent growth of the equilibrium phase through the motion of the interface.
Comparison of catalytic ethylene polymerization in slurry and gas phase
Majid Daftaribesheli
Polyethylene (PE) with the annual consumption of 70 million tones in 2007 is mostly produced in slurry, gas-phase or combination of both processes.\\u000aThis work focuses on a comparison between the slurry and gas phase processes. Why does PE produced in theses two processes can show extremely different properties and extremely different reaction behaviour even if the same Ziegler-Natta (ZN)
Investigating the Microphysics of Arctic Mixed-Phase Clouds using Large Eddy Simulations: The Importance of Liquid-Dependent Ice Nucleation
NASA Astrophysics Data System (ADS)
Young, Gillian; Connolly, Paul J.; Jones, Hazel M.; Choularton, Thomas W.; Gallagher, Martin W.; Crosier, Jonathan; Lloyd, Gary; Bower, Keith N.
Our ability to comprehend and accurately model the Arctic climate is currently hindered by a lack of observations of the atmospheric processes unique to this region. A significant source of uncertainty in such models may be found in our representation of aerosol-cloud interactions [1]: for example, there are unanswered questions concerning the relationship between the ice-nucleating Arctic aerosol and the unique cloud microphysics observed in this region [2]. In an effort to address this issue, the Aerosol-Cloud Coupling and Climate Interactions in the Arctic (ACCACIA) campaign of 2013 was conducted in the vicinity of the Svalbard archipelago, carrying out in-situ airborne observations of the mixed-phase clouds in this region. This campaign was split into two segments - one in spring, the other in summer - with airborne- and surface-based measurement platforms utilised in each. During the spring campaign, a range of microphysics and remote-sensing instruments were active on board the Facility for Airborne Atmospheric Measurements' (FAAM) BAe146 aircraft to produce a detailed record of the observed Arctic atmosphere. These data were used to conduct a modelling investigation with a focus on ice nucleation: the Large Eddy Model (LEM) - a cloud-resolving model developed by the UK Met Office - was initialised from these observations and simulations were performed to allow the resultant cloud evolution, structure and microphysics to be examined. Models on various scales notoriously have issues with reproducing persistent, mixed-phase Arctic clouds [2,3] and, upon first inspection, the LEM was no different: the modelled cloud dissipated quickly, thus inaccurately replicating the long-lived, mixed-phase clouds observed. However, by considering the discrepancies between the model output and aircraft observations, the treatment of cloud microphysics within the LEM has been developed to improve the simulation of the observed clouds. A long-lived, mixed-phase cloud of similar microphysical properties to those observed is achieved, providing an indication that the realistic simulation of Arctic clouds is strongly dependent on the ice nucleus parameterisation used. References: [1] Curry, J. A. et al., 1996. Overview of Arctic Cloud and Radiation Characteristics. Journal of Climate, 9, 1731-1764. [2] Prenni, A. J. et al., 2007. Can Ice-Nucleating Aerosols Affect Arctic Seasonal Climate? Bulletin of the American Meteorological Society, 88, 541-550. [3] Morrison, H. et al., 2012. Resilience of persistent Arctic mixed-phase clouds. Nature Geoscience, 5, 11-17.
Nucleation and growth studies of polycrystalline covalent materials
NASA Astrophysics Data System (ADS)
Yun, Jungheum
The chemical vapor deposition of different covalent polycrystalline materials---including diamond, silicon carbide, and carbon nitride---in stagnation flow reactors was rigorously simulated to determine the nucleation and growth mechanisms of these materials. Kinetic models were used to predict the rates of gas-phase and surface chemistry, the temperature and velocity profiles, potential gaseous film growth precursors, the time evolution of nucleation and intermediate layer formation, and the morphological evolution of continuous polycrystalline films. Numerical studies were also carried out to determine the dependence of the kinetics of nucleation and subsequent polycrystalline film growth on operating conditions. The calculated results for carbon nitride deposition indicate that the experimentally measured bond types in the carbon nitride films must result from chemical bond rearrangement occurring on the deposition surface or in the bulk phase once gaseous film growth precursors, including C, CH2 , CH3, C2H2, N, NH, NH2, HCN, and H2CN, are adsorbed. Of these precursors, C and CH 3 dominate the carbon contribution to carbon nitride film growth, and atomic nitrogen is the principal nitrogen bearing species. When the evolution rates of a silicon carbide intermediate layer and diamond clusters are calculated by accounting for gas-phase and surface reactions, surface and bulk diffusion, the mechanism for intermediate layer formation, and heterogeneous diamond nucleation kinetics, it is predicted that higher adsorption energies, in the range of 3.7 to 4.5 eV, lead to larger surface adatom densities, lower saturated nucleation densities, and larger silicon carbide intermediate layer thicknesses. The intermediate layer thickness becomes saturated while the growing diamond nuclei still cover a very small fraction of the silicon carbide. Reports of heteroepitaxial diamond nucleation without silicon carbide intermediate layer formation may be readily explained by a significant decrease in the intermediate layer thickness at lower substrate temperatures and at higher diamond nucleation densities. Further, the results of the morphology evolution model reveal that the crystallographic texture and surface morphology---surface roughness, film texture, and grain size---of polycrystalline silicon carbide films, as well as diamond films deposited on the silicon carbide layer, are strongly dependent upon the saturated nucleation density, the deposition condition, and film thickness.
Gas phase antimony\\/magnesium\\/oxygen clusters
H. T. Deng; Y. Okada; M. Foltin; A. W. Jr. Castleman
Antimony\\/magnesium\\/oxygen clusters are produced by a gas aggregation source, in which a mixture of antimony and magnesium is vaporized and reacted with N[sub 2]O introduced in helium carrier gas. The resulting product distribution is detected by a time-of-flight mass spectrometer following ionization with a KrF excimer laser. Four types of cluster products are observed: Sb[sub x][sup +], Sb[sub x]Mg[sub y]O[sub
Printing nanoparticles from the liquid and gas phases using nanoxerography
Chad R Barry; Michael G Steward; Nyein Z Lwin; Heiko O Jacobs
This paper reports on the directed self-assembly of nanoparticles onto charged surface areas with a resolution of 200 nm from the liquid phase and 100 nm from the gas phase. The charged areas required for this type of nanoxerographic printing were fabricated using a parallel method that employs a flexible, electrically conductive, electrode to charge a thin-film electret. As electrodes,
Simulation Approach for Microscale Noncontinuum Gas-Phase Heat Transfer
NASA Astrophysics Data System (ADS)
Torczynski, J. R.; Gallis, M. A.
In microscale thermal actuators, gas-phase heat transfer from the heated beams to the adjacent unheated substrate is often the main energy-loss mechanism. Since the beam-substrate gap is comparable to the molecular mean free path, noncontinuum gas effects are important. A simulation approach is presented in which gas-phase heat transfer is described by Fourier's law in the bulk gas and by a wall boundary condition that equates the normal heat flux to the product of the gas-solid temperature difference and a heat transfer coefficient. The dimensionless parameters in this heat transfer coefficient are determined by comparison to Direct Simulation Monte Carlo (DSMC) results for heat transfer from beams of rectangular cross section to the substrate at free-molecular to near-continuum gas pressures. This simulation approach produces reasonably accurate gas-phase heat-transfer results for wide ranges of beam geometries and gas pressures. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Para-Hydrogen-Enhanced Gas-Phase Magnetic Resonance Imaging
Bouchard, Louis-S.; Kovtunov, Kirill V.; Burt, Scott R.; Anwar,M. Sabieh; Koptyug, Igor V.; Sagdeev, Renad Z.; Pines, Alexander
Herein, we demonstrate magnetic resonance imaging (MRI) inthe gas phase using para-hydrogen (p-H2)-induced polarization. A reactantmixture of H2 enriched in the paraspin state and propylene gas is flowedthrough a reactor cell containing a heterogenized catalyst, Wilkinson'scatalyst immobilized on modified silica gel. The hydrogenation product,propane gas, is transferred to the NMR magnet and is spin-polarized as aresult of the ALTADENA (adiabatic longitudinal transport and dissociationengenders net alignment) effect. A polarization enhancement factor of 300relative to thermally polarized gas was observed in 1D1H NMR spectra.Enhancement was also evident in the magnetic resonance images. This isthe first demonstration of imaging a hyperpolarized gaseous productformed in a hydrogenation reaction catalyzed by a supported catalyst.This result may lead to several important applications, includingflow-through porous materials, gas-phase reaction kinetics and adsorptionstudies, and MRI in low fields, all using catalyst-free polarizedfluids.
Gas-phase diffusion in porous media: Comparison of models
Webb, S.W.
Two models are commonly used to analyze gas-phase diffusion in porous media in the presence of advection, the Advective-Dispersive Model (ADM) and the Dusty-gas Model (DGM). The ADM, which is used in TOUGH2, is based on a simple linear addition of advection calculated by Darcy`s law and ordinary diffusion using Fick`s law with a porosity-tortuosity-gas saturation multiplier to account for the porous medium. Another approach for gas-phase transport in porous media is the Dusty-Gas Model. This model applies the kinetic theory of gases to the gaseous components and the porous media (or dust) to combine transport due to diffusion and advection that includes porous medium effects. The two approaches are compared in this paper.
Constant volume gas cell optical phase-shifter
Phillion, Donald W. (Dublin, CA)
A constant volume gas cell optical phase-shifter, particularly applicable for phase-shifting interferometry, contains a sealed volume of atmospheric gas at a pressure somewhat different than atmospheric. An optical window is present at each end of the cell, and as the length of the cell is changed, the optical path length of a laser beam traversing the cell changes. The cell comprises movable coaxial tubes with seals and a volume equalizing opening. Because the cell is constant volume, the pressure, temperature, and density of the contained gas do not change as the cell changes length. This produces an exactly linear relationship between the change in the length of the gas cell and the change in optical phase of the laser beam traversing it. Because the refractive index difference between the gas inside and the atmosphere outside is very much the same, a large motion must be made to change the optical phase by the small fraction of a wavelength that is required by phase-shifting interferometry for its phase step. This motion can be made to great fractional accuracy.
A transmission electron microscopy and X-ray photoelectron spectroscopy study of annealing induced ?-phase nucleation, clustering, and interfacial dynamics in reactively sputtered amorphous alumina thin films
NASA Astrophysics Data System (ADS)
Kumar, A. K. Nanda; Prasanna, S.; Subramanian, B.; Jayakumar, S.; Rao, G. Mohan
Pure ?-Al2O3 exhibits a very high degree of thermodynamical stability among all metal oxides and forms an inert oxide scale in a range of structural alloys at high temperatures. We report that amorphous Al2O3 thin films sputter deposited over crystalline Si instead show a surprisingly active interface. On annealing, crystallization begins with nuclei of a phase closely resembling ?-Alumina forming almost randomly in an amorphous matrix, and with increasing frequency near the substrate/film interface. This nucleation is marked by the signature appearance of sharp (400) and (440) reflections and the formation of a diffuse diffraction halo with an outer maximal radius of ?0.23 nm enveloping the direct beam. The microstructure then evolves by a cluster-coalescence growth mechanism suggestive of swift nucleation and sluggish diffusional kinetics, while locally the Al ions redistribute slowly from chemisorbed and tetrahedral sites to higher anion coordinated sites. Chemical state plots constructed from XPS data and simple calculations of the diffraction patterns from hypothetically distorted lattices suggest that the true origins of the diffuse diffraction halo are probably related to a complex change in the electronic structure spurred by the a-? transformation rather than pure structural disorder. Concurrent to crystallization within the film, a substantially thick interfacial reaction zone also builds up at the film/substrate interface with the excess Al acting as a cationic source.
Gas phase radiative effects in diffusion flames
Hasan Bedir
Several radiation models are evaluated for a stagnation point diffusion flame of a solid fuel in terms of accuracy and computational time. Narrowband, wideband, spectral line weighted sum of gray gases (SLWSGG), and gray gas models are included in the comparison. Radiative heat flux predictions by the nongray narrowband, wideband, and SLWSGG models are found to be in good agreement
Loitering Phase in Brane Gas Cosmology
R H Brandenberger; D A Easson; D M Kimberly
Brane Gas Cosmology (BGC) is an approach to M-theory cosmology in which the initial state of the Universe is taken to be small, dense and hot, with all fundamental degrees of freedom near thermal equilibrium. Such a starting point is in close analogy with the Standard Big Bang (SBB) model. The topology of the Universe is assumed to be toroidal
Loitering phase in brane gas cosmology
Robert Brandenberger; Damien A. Easson; Dagny Kimberly
Brane gas cosmology (BGC) is an approach to M-theory cosmology in which the initial state of the Universe is taken to be small, dense and hot, with all fundamental degrees of freedom near thermal equilibrium. Such a starting point is in close analogy with the standard big bang (SBB) model. The topology of the Universe is assumed to be toroidal
ATALANTE 2004 Nmes (France) June 21-25, 2004 1 Control of nucleation and crystal growth of a silicate apatitic phase in a glassy matrix
Paris-Sud XI, Universitķ de
P39 ATALANTE 2004 NŅmes (France) June 21-25, 2004 1 Control of nucleation and crystal firstname.lastname@example.com Abstract Ł Nucleation and growth of crystal in an oxide glass was studied in a Si B Al Zr Nd Ca Na O system the crystal nucleation and growth from the parent glass is crucial. In this work, trivalent minor actinides
Gas-phase self-assembly of endohedral metallofullerenes
NASA Astrophysics Data System (ADS)
Clemmer, David E.; Shelimov, Konstantin B.; Jarrold, Martin F.
METALLOFULLERENES1,2consist of metal atoms trapped inside closed fullerene cages. Virtually nothing is known about the mechanism of metallofullerene synthesis, although the possibility of a condensed-phase mechanism has been suggested in recent studies3,4. Here we show that laser vaporization of a La2O3/graphite rod produces a number of LaC60 + isomers, including the endohedral metallofullerene and a variety of different isomers in which lanthanum seems to be bound to polycyclic polyyne rings. When heated, nearly all of the different ring isomers convert spontaneously into metallofullerenes, trapping the metal atom inside the fullerene cage with remarkably high efficiency (>98%). We suggest that in the first step of this annealing process the lanthanum atom acts as a nucleation centre and the carbon rings arrange themselves around the lanthanum atom before converting into a fullerene cage.
Communication: Fourier-transform infrared probing of remarkable quantities of gas trapped in cold homogeneously nucleated nanodroplets.
Uras-Aytemiz, Nevin; Devlin, J Paul
Studies of catalyzed all-vapor gas-hydrate formation on a sub-second timescale have been extended with a special focus on liquid-droplet compositions at the instant of hydrate crystallization. This focus has been enabled by inclusion of methanol in the all-vapor mixture. This slows droplet to gas-hydrate conversion near 200 K to a time scale suited for standard FTIR sampling. Such droplet data are sought as a guide to ongoing efforts to reduce the amount of guest catalyst required for instant formation of the gas hydrates. For the same reason, all-vapor sampling has also been extended to the generation of long-lived liquid droplets with reduced or no water content. Observations of single-solvent droplets show that surprising quantities of gas molecules are trapped during rapid droplet growth. For example, CO2 is trapped at levels near 50 mol. % in droplets of acetone, tetrahydrofuran, or trimethylene oxide formed under CO2 pressures of several Torr in a cold-chamber at 170 K. Less but significant amounts of gas are trapped at higher temperatures, or in methanol or water-methanol droplets. The droplet metastability appears to commonly lead to formation of bubbles larger than the original nanodroplets. Besides serving as a guide for the all-vapor gas-hydrate studies, the semiquantitative evidence of extensive trapping of gases is expected to have a role in future studies of atmospheric aerosols. PMID:23862921
SVOC partitioning between the gas phase and settled dust indoors
NASA Astrophysics Data System (ADS)
Weschler, Charles J.; Nazaroff, William W.
Semivolatile organic compounds (SVOCs) are a major class of indoor pollutants. Understanding SVOC partitioning between the gas phase and settled dust is important for characterizing the fate of these species indoors and the pathways by which humans are exposed to them. Such knowledge also helps in crafting measurement programs for epidemiological studies designed to probe potential associations between exposure to these compounds and adverse health effects. In this paper, we analyze published data from nineteen studies that cumulatively report measurements of dustborne and airborne SVOCs in more than a thousand buildings, mostly residences, in seven countries. In aggregate, measured median data are reported in these studies for 66 different SVOCs whose octanol-air partition coefficients ( Koa) span more than five orders of magnitude. We use these data to test a simple equilibrium model for estimating the partitioning of an SVOC between the gas phase and settled dust indoors. The results demonstrate, in central tendency, that a compound's octanol-air partition coefficient is a strong predictor of its abundance in settled dust relative to its gas phase concentration. Using median measured results for each SVOC in each study, dustborne mass fractions predicted using Koa and gas-phase concentrations correlate reasonably well with measured dustborne mass fractions ( R2 = 0.76). Combined with theoretical understanding of SVOC partitioning kinetics, the empirical evidence also suggests that for SVOCs with high Koa values, the mass fraction in settled dust may not have sufficient time to equilibrate with the gas phase concentration.
Off-gas recycle for long-term low temperature gas phase uranium decontamination
R. D. Bundy; D. H. Bunch; E. B. Munday; D. W. Simmons
In situ long-term low-temperature (LTLT) gas phase decontamination is being developed and demonstrated at the K-25 site as a technology that has the potential to substantially lower these costs while reducing criticality and safeguards concerns and worker exposure to hazardous and radioactive materials. The objective of gas phase decontamination is to employ a gaseous reagent to fluorinate nonvolatile uranium deposits
Effects of nuclei concentrations, ice nucleation mechanisms and crystal habits on the dynamics and microphysics of Arctic mixed-phase clouds
NASA Astrophysics Data System (ADS)
Komurcu, Muge
There is a significant warming in the Arctic that is evident in both observations and in the future climate predictions. The Arctic warming is greater than any other region on Earth, however, the degree of warming is inconsistent among the climate models even for the same emission scenarios. Clouds, especially low-level clouds, are a prevailing feature of the Arctic atmosphere. They strongly affect the surface radiative and energy budgets, which make them a key component of the Arctic climate. Recent inter-comparison studies using regional climate models show that models are incapable of reproducing the supercooled liquid water observed in clouds during the cold season. Large discrepancies exist in the partitioning of phase between ice and liquid water among different models. It is currently thought that these discrepancies are due to the uncertainties in ice nuclei concentrations, ice nucleation, and ice crystal habits used in models. Predicting these physical processes controls the partitioning between liquid and ice, and hence the impact of mixed-phase clouds on the surface energy budget. There is a need to improve model cloud predictions in the Arctic, however, the microphysical uncertainties mentioned above are tied directly to the cloud dynamics that help maintain persistent mixed-phase clouds. Therefore, this dissertation analyzes and inter-compares the impacts of different ice nuclei concentrations, ice nucleation mechanisms and ice crystal habits on mixedphase cloud dynamics. Separate simulations using different ice nuclei concentrations, ice nucleation mechanisms, and crystal habits are performed. It is found that the choice of habits in models alters the water paths and cloud dynamics strongly. Next, the relative importance of and interactions among the processes that influence the dynamics of the cloud, such as the radiative cooling at cloud top, and the ice precipitation induced cloudbase stabilization are investigated. To examine these processes in detail, sensitivity studies are performed by fixing the radiative cooling, and the diabatic influences of ice precipitation. In addition, simulations with increasing ice nuclei concentrations, different nucleation mechanisms, and crystal habits are repeated with surface fluxes and largescale forcing included. The influence of surface fluxes is important as it can compensate for the water mass that is lost through ice precipitation if the ice precipitation is weak. Surface fluxes can also lead to the coupling of the liquid cloud layer with the sub-cloud layer. The cloud-base stability is diminished with the inclusion of the surface fluxes, and the effect of entrainment is enhanced. Sensitivity tests are also repeated with the added surface fluxes. Using the results of the sensitivity analysis, a ratio identifying the decoupling of the cloud and subcloud layers is generated, and also with the sensitivity analysis cloud dynamic and microphysical interactions within Arctic mixed-phase clouds are explained.
Phase-separation induced homogeneous nucleation and growth of Cs{sub 3}LaCl{sub 6} nanoparticles in chalcohalide glass
Yang, Anping [State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China); Lin, Hang, E-mail: firstname.lastname@example.com [Key Laboratory of Design and Assembly of Functional Nanostructures, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China); Chen, Daqin; Yu, Yunlong [Key Laboratory of Design and Assembly of Functional Nanostructures, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China); Wang, Yuansheng, E-mail: email@example.com [State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China)
Graphical abstract: The phase-separation induced nucleation and growth of Cs{sub 3}LaCl{sub 6} nanocrystals has been studied for the first time. It is experimentally evidenced that the doped active rare earth ions are incorporated into the Cs{sub 3}LaCl{sub 6} nanocrystals, resulting in the intensified down- and up-conversion emissions. - Highlights: Ģ A novel transparent glass ceramic containing Cs{sub 3}LaCl{sub 6} nanocrystals was fabricated. Ģ Crystallization behaviors of Cs{sub 3}LaCl{sub 6} nanophase are systematically investigated. Ģ The up-/down-conversion emissions are greatly intensified after crystallization. - Abstract: The phase-separation induced nucleation and growth of Cs{sub 3}LaCl{sub 6} nanocrystals has been studied in the GeS{sub 2}-Ga{sub 2}S{sub 3}-La{sub 2}S{sub 3}-LaCl{sub 3}-CsCl system for the first time. Remarkably, the precipitated chloride nanocrystals are spherical and distributed homogeneously in the glass matrix. Benefiting from the uniform structure, high transparency of the glass ceramic is maintained after heat treatment by reducing adverse optical scattering. As revealed by the absorption spectra and Judd¢Ofelt calculations, the doped active rare earth ions are partially partitioned into the low-phonon-energy Cs{sub 3}LaCl{sub 6} nanocrystals, resulting in the decrease of the non-radiative transition probabilities and therefore intensified photoluminescence emission of Nd{sup 3+} and up-conversion one of Er{sup 3+}.
Microfabricated Gas Phase Chemical Analysis Systems
A portable, autonomous, hand-held chemical laboratory ({micro}ChemLab{trademark}) is being developed for trace detection (ppb) of chemical warfare (CW) agents and explosives in real-world environments containing high concentrations of interfering compounds. Microfabrication is utilized to provide miniature, low-power components that are characterized by rapid, sensitive and selective response. Sensitivity and selectivity are enhanced using two parallel analysis channels, each containing the sequential connection of a front-end sample collector/concentrator, a gas chromatographic (GC) separator, and a surface acoustic wave (SAW) detector. Component design and fabrication and system performance are described.
Microfabricated Gas Phase Chemical Analysis Systems
Casalnuovo, Stephen A.; Frye-Mason, Gregory C; Heller, Edwin J.; Hietala, Vincent M.; Kottenstette, Richard J.; Lewis, Patrick R.; Manginell, Ronald P.; Matzke, Carolyn M.; Wong, C. Channy
A portable, autonomous, hand-held chemical laboratory ({mu}ChemLab{trademark}) is being developed for trace detection (ppb) of chemical warfare (CW) agents and explosives in real-world environments containing high concentrations of interfering compounds. Microfabrication is utilized to provide miniature, low-power components that are characterized by rapid, sensitive and selective response. Sensitivity and selectivity are enhanced using two parallel analysis channels, each containing the sequential connection of a front-end sample collector/concentrator, a gas chromatographic (GC) separator, and a surface acoustic wave (SAW) detector. Component design and fabrication and system performance are described.
Nucleated deliquescence of salt
NASA Astrophysics Data System (ADS)
Cantrell, Will; McCrory, Charles; Ewing, George E.
We have studied deliquescence on the (001) face of single crystals of NaCl and find that it is a nucleated phenomenon. The phase transition occurs only after the relative humidity exceeds that found over the saturated solution by at least 5%. The contrast between our observations and previous measurements using salt powders or crystallites leads us to the conclusion that deliquescence is controlled by the differences in energy required to solvate ions from the smooth (001) face and from the defect-rich surfaces of particulate samples.
Gas-phase dissociation pathways of a tetrameric protein complex
NASA Astrophysics Data System (ADS)
Sobott, Frank; McCammon, Margaret G.; Robinson, Carol V.
The gas-phase dissociation of the tetrameric complex transthyretin (TTR) has been investigated with tandem-mass spectrometry (tandem-MS) using a nanoflow-electrospray interface and a quadrupole time-of-flight (Q-TOF) mass spectrometer. The results show that highly charged monomeric product ions dissociate from the macromolecular complex to form trimeric products. Manipulating the pressure conditions within the mass spectrometer facilitates the formation of metastable ions. These were observed for the transitions from tetrameric to monomeric and trimeric product ions and additionally for losses of small molecules associated with the protein complex in the gas phase. These results are interpreted in the light of recent mechanisms for the electrospray process and provide insight into the composition and factors governing the stability of macromolecular ions in the gas phase.
Gas phase chemical detection with an integrated chemical analysis system
Microfabrication technology has been applied to the development of a miniature, multi-channel gas phase chemical laboratory that provides fast response, small size, and enhanced versatility and chemical discrimination. Each analysis channel includes a sample preconcentrator followed by a gas chromatographic separator and a chemically selective surface acoustic wave detector array to achieve high sensitivity and selectivity. The performance of the components, individually and collectively, is described.
Gas purification in the dense phase at the CATS terminal
Openshaw, P.J.; Carnell, P.J.H.; Rhodes, E.F.
The purification and transportation of natural gas at very high pressures can help to minimize the capital cost of pipelines and processing equipment. However, complex mixtures of hydrocarbons undergo unusual phase changes, such as retrograde condensation, as the temperature and pressure are altered. The Central Area Transmission System (CATS) is a joint venture of Amoci, BG, Amerada Hess, Phillips, Agip and Fina operated by Amoco on behalf of the owners. The design of the CATS terminal has provided an interesting processing challenge. The terminal receives a total of 1.6 Bscf/d of rich gas from a number of offshore fields. All are relatively sweet but the small amounts of H{sub 2}S and Hg are removed. Fixed bed technology was selected as the most economic purification process, while minimizing hydrocarbon loss and operator involvement. Conventionally, the raw gas would be split into the different hydrocarbon fractions and each would be processed separately. This would require the installation of a large number of reactors. A more elegant solution is to treat the gas on arrival at the terminal in the dense phase. This option raised questions around whether a fixed bed would be prone to fouling, could the pressure drop be kept low enough to avoid phase separation and would inadvertent wetting by condensation cause problems. Details are given of the test work carried out to prove the viability of using fixed bed technology for dense phase gas processing, the eventual design adopted and the performance over the first year of service.
Collision-induced gas phase dissociation rates
NASA Technical Reports Server (NTRS)
Hansen, C. Frederick
The Landau-Zener theory of reactive cross sections was applied to diatomic molecules dissociating from a ladder of vibrational states. The result predicts a dissociation rate that is quite well duplicated by an Arrhenius function having a preexponential temperature dependence of about T(sub -1/2), at least for inert collision partners. This relation fits experimental data reasonably well. The theory is then used to calculate the effect of vibrational nonequilibrium on dissociation rate. For Morse oscillators, the results are about the same as given by Hammerling, Kivel, and Teare in their analytic approximation for harmonic oscillators, though at very high temperature a correction for the partition function limit is included. The empirical correction for vibration nonequilibrium proposed by Park, which is a convenient algorithm for CFD calculations, is modified to prevent a drastic underestimation of dissociation rates that occurs with this method when vibrational temperature is much smaller than the kinetic temperature of the gas.
ICA and Its Application in the Phase Information Extraction of Oil-Gas-Water Three-Phase Flow
Kong Lingfu; Gao Fan; Li Yingwei; Liu Xingbin; Hu JinHai
The independent component analysis(ICA)is applied to studying the oil-gas-water three-phase flow noisy signals responded by conductance sensor, and extracting the flow signals which characterized the gas and liquid phase respectively so as to obtain gas\\/liquid phase information. The algorithm of FastICA which based on kurtosis is applied to separating the field simulation well logging oil-gas-water three-phase signals responded by multi-channel
Decay Pathways of Pyrimidine Bases: From Gas Phase to Solution
Wei Kong; Yonggang He; Chengyin Wu
We use a variation of the pump-probe technique to unravel the photodynamics of nucleic acid bases and their water complexes.\\u000a Our work aims at bridging studies from the gas phase with those in the solution phase. Our results indicate that the intrinsic\\u000a properties of the pyrimidine bases can be dramatically modified by the surrounding environment. As isolated species, the bases
Gas-phase dissociation pathways of multiply charged peptide clusters
John C. Jurchen; David E. Garcia; Evan R. Williams
Numerous studies of cluster formation and dissociation have been conducted to determine properties of matter in the transition\\u000a from the condensed phase to the gas phase using materials as diverse as atomic nuclei, noble gasses, metal clusters, and amino\\u000a acids. Here, electrospray ionization is used to extend the study of cluster dissociation to peptides including leucine enkephalin\\u000a with 7¢19 monomer
Proceedings of the Symposium on Fundamental Gas-Phase and Surface Chemistry of Vapor-Phase Materials Synthesis,
Taylor, James H.
Proceedings of the Symposium on Fundamental Gas-Phase and Surface Chemistry of Vapor-Phase Materials Synthesis, PV98-28, p. 153,The Electrochemical Society, 1998. IN SITU STUDIES OF TEOS/OZONE CVD, gas chromatographic and other evidence (5-9) supports the participation of transient gas phase
Investigation of condensed and early stage gas phase hypergolic reactions
NASA Astrophysics Data System (ADS)
Dennis, Jacob Daniel
Traditional hypergolic propellant combinations, such as those used on the space shuttle orbital maneuvering system first flown in 1981, feature hydrazine based fuels and nitrogen tetroxide (NTO) based oxidizers. Despite the long history of hypergolic propellant implementation, the processes that govern hypergolic ignition are not well understood. In order to achieve ignition, condensed phase fuel and oxidizer must undergo simultaneous physical mixing and chemical reaction. This process generates heat, intermediate condensed phase species, and gas phase species, which then may continue to react and generate more heat until ignition is achieved. The process is not well understood because condensed and gas phase reactions occur rapidly, typically in less than 200 ?s, on much faster timescales than traditional diagnostic methods can observe. A detailed understanding of even the gas phase chemistry is lacking, but is critical for model development. Initial research has provided confidence that a study of condensed phase hypergolic reactions is useful and possible. Results obtained using an impinging jet apparatus have shown a critical residence time of 0.3 ms is required for the reaction between monomethylhydrazine (MMH) and red fuming nitric acid (RFNA, ~85% HNO3 + 15% N2O4) to achieve conditions favorable for ignition. This critical residence time spans the time required for liquid phase reactions to occur at the fuel/oxidizer interface and can give some insight into the reaction rates for this propellant combination. Experiments performed in a forced mixing constant volume reactor have demonstrated that the chamber pressurization rate for MMH/RFNA can be significantly reduced by diluting the MMH with deionized water. This result indicates that propellant dilution can slow the chemical reaction rates to occur over observable time scales. The research described in this document consists of two efforts that contribute knowledge to the propulsion community regarding the hypergolic liquid propellant combination of MMH and RFNA or pure nitric acid. The first and most important effort focuses on furthering the understanding of condensed phase reactions between MMH and nitric acid. To accomplish this goal diluted MMH and nitric acid were studied in a Fourier transform infrared spectrometer. By tracking the generation or destruction of specific chemical species in the reacting fluid we can measure the reaction progress as a function of reactant concentration and temperature. This work provides the propulsion community with a quantitative global condensed phase reaction rate equation for MMH/nitric acid. The second effort focuses on improving understanding the recently proposed gas phase hypergolic reaction mechanisms using a streak camera based ultraviolet and visible spectrometer. The time resolution on the streak camera system allows for detailed investigation of the pre-ignition and early stage gas phase species present during the reaction between MMH and RFNA.
Statistical and Microscopic Approach to Gas Phase Chemical Kinetics.
ERIC Educational Resources Information Center
Perez, J. M.; Quereda, R.
Describes advanced undergraduate laboratory exercise examining the dependence of the rate constants and the instantaneous concentrations with the nature and energy content in a gas-phase complex reaction. Computer program (with instructions and computation flow charts) used with the exercise is available from the author. (Author/JN)
Autoxidation of MMH at Room Temperature in the Gas Phase
Laurent Catoire; Claude Paillard
The objective of this study is to characterize the lifetime of monomethylhydrazine mixed with O2, both in the gas phase, at 298 K. A detailed kinetic model has been built to allow a numerical study of the homogeneous MMH\\/O2 reactivity.
Gas-phase terpene oxidation products: a review
A. Calogirou; B. R. Larsen; D. Kotzias
Terpenes are emitted in large quantities from vegetation into the troposphere, where they react readily with ozone, OH and NO3 radicals leading to a number of oxidation products. The current knowledge about gas-phase terpene oxidation products is reviewed. Their formation and decomposition pathways, their products and their relevance for the troposphere, and their chemical analysis are discussed. Data on oxidation
Gas phase pulse radiolysis. [Reaction with hydroxyl radical
Jonah, C.D.; Andong Liu; Mulac, W.A.
Gas phase pulse radiolysis, a technique which can be used to study many different phenomena in chemistry and physics, is discussed. As a source of small radicals, pulse radiolysis is important to the field of chemistry, particularly to combustion and atmospheric kinetics. The reactions of 1,3-butadiene, allene, ethylene and acetylene with OH are presented. 52 refs., 1 fig., 1 tab.
Extended sugar synthesis from a gas phase formose reaction
Abraham F. Jalbout; Leif Abrell; Ludwik Adamowicz; Robin Polt; L. M. Ziurys
The prebiotic possibilities for the synthesis of interstellar ribose through a protic variant of the formose reaction under gas phase conditions were studied with the use of a proton source as a known catalyst. Mass spectrometry was sought as a method to probe the synthesis of higher order sugars. Ab initio calculations were used to evaluate protic formose mechanism possibilities
Sugar Synthesis from a Gas-Phase Formose Reaction
Abraham F. Jalbout; Leif Abrell; Ludwik Adamowicz; Robin Polt; A. J. Apponi; L. M. Ziurys
Prebiotic possibilities for the synthesis of interstellar ribose through a protic variant of the formose reaction under gas-phase conditions were studied in the absence of any known catalyst. The ion-molecule reaction products, diose and triose, were sought by mass spectrometry, and relevant masses were observed. Ab initio calculations were used to evaluate protic formose mechanism possibilities. A bilateral theoretical and
The paper presents data on the effect of ozone on both vegetative and spore-forming fungi as well as on spore-forming bacteria. (NOTE: Despite the wide use of ozone generators in indoor air cleaning, there is little research data on ozone's biocidal activity in the gas phase.) Dr...
Selected examples of gas-phase ion chemistry studies.
Nibbering, Nico M M
Gas-phase ion chemistry is an area in mass spectrometry that has received much research interest since the mid fifties of the last century. Although the focus of mass spectrometric research has shifted the last twenty years largely to life science studies, including proteomics, genomics and metabolomics, there are still several groups in the world active in gas-phase ion chemistry of both positive and negative ions, either unimolecularly and/or bimolecularly. In this tutorial lecture the formation and determination of tautomeric ion structures and intra-ionic catalyzed tautomerization in the gas phase will be discussed. In addition, an example of formation of different tautomeric structures in protic and aprotic solvents under electrospray ionization conditions will be given, as established by gas-phase infrared multiphoton dissociation spectroscopy. This will be followed by presenting an example of time-resolved MS/MS which enables to identify the structure of an ion, generated at a particular molecular ion lifetime. At the end of the lecture the power of ion mobility will be shown in elucidating the mechanism of epimerization of bis-Tr÷ger bases having chiral nitrogen centers. PMID:24349921
Printing nanoparticle building blocks from the gas phase using nanoxerography
Chad R. Barry; Nyein Z. Lwin; Wei Zheng; Heiko O. Jacobs
This letter reports on the electrostatic driven self-assembly of nanoparticles onto charged surface areas ~receptors! from the gas phase for nanoparticle based device fabrication. The charged areas were generated by a parallel technique that uses a ?exible, conductive electrode to pattern electrons and holes in a thin film electret. Samples, 1 cm, in size, were patterned with charge in 10
Photodissociation and spectroscopy of gas phase bimetallic clusters
Focus of the research program is the study of gas phase metal clusters for modeling fundamental interactions on metal surfaces. We characterize the chemical bonding between component atoms in clusters as well as the bonding in adsorption on cluster surfaces. Electronic spectra, vibrational frequencies and bond dissociation energies are measured for both neutral and ionized clusters with laser\\/mass spectrometry techniques.
Ion-Molecule Reactions in Gas Phase Radiation Chemistry.
ERIC Educational Resources Information Center
Willis, Clive
Discusses some aspects of the radiation chemistry of gases, focusing on the ion-molecule and charge neutralization reactions which set study of the gas phase apart. Uses three examples that illustrate radiolysis, describing the radiolysis of (1) oxygen, (2) carbon dioxide, and (3) acetylene. (CS)
Nucleation of electroactive beta-phase poly(vinilidene fluoride) with CoFe2O4 and NiFe2O4 nanofillers: a new method for the preparation of multiferroic nanocomposites
P. Martins; C. M. Costa; S. Lanceros-Mendez
Multiferroic and magnetoelectric materials show enormous potential for technological developments. Multiferroic composites are more attractive for applications due to their enhanced properties with respect to single-phase multiferroic materials. In this paper we report on the nucleation of the electroactive beta-phase of poly(vinylidene fluoride), PVDF, by the addition of CoFe2O4 and NiFe2O4 nanoparticles in order to prepare poly(vinylidene fluoride)\\/ferrite nanocomposite for
Measurements of the Aerosol Size Distribution Down to 1 Nanometer to Investigate Aerosol Nucleation and Initial Growth During the GoAmazon Campaign
NASA Astrophysics Data System (ADS)
Kuang, C.; Artaxo, P.; Backman, J.; Kim, S.; Kulmala, M. T.; Martin, S. T.; Petõjõ, T.; Seco, R.; Smith, J. N.; Souza, R. A. F. D.
Atmospheric particle nucleation is an important environmental nano-scale process, with field measurements and modeling studies indicating that freshly nucleated particles are a significant source of global cloud condensation nuclei. However, our understanding of atmospheric nucleation and its influence on climate is limited as few ambient measurements have been made of either the nucleation rate (at 1 nm) or the initial growth rate of newly formed clusters (from 1 to 3 nm), both of which are necessary to constrain and investigate the nucleation mechanism and to develop process-level models. Aerosol nucleation and initial growth were investigated during the Green Ocean Amazon (GoAmazon) campaign spanning the wet and dry seasons of 2014 downwind of the city of Manaus, Brazil. Aerosol measurement was accomplished through the deployment of a condensation particle counter-based electrical mobility spectrometer, optimized for the detection of aerosol down to 1 nm in diameter. An electrometer-based neutral air ion spectrometer was also deployed at the same location to measure the neutral and charged fraction of aerosol down to 1.5 nm in diameter. From these size distribution measurements, periods of nucleation will be identified, and the resulting nucleation rates and initial growth rates will be presented. Concurrent and co-located measurements of gas-phase sulfuric acid will provide the opportunity to investigate the functional contribution of sulfuric acid to the observed nucleation rate and initial growth rate.
Gas Phase Reactivity of Carboxylates with N-Hydroxysuccinimide Esters
NASA Astrophysics Data System (ADS)
Peng, Zhou; McGee, William M.; Bu, Jiexun; Barefoot, Nathan Z.; McLuckey, Scott A.
N-hydroxysuccinimide (NHS) esters have been used for gas-phase conjugation reactions with peptides at nucleophilic sites, such as primary amines (N-terminus, ?-amine of lysine) or guanidines, by forming amide bonds through a nucleophilic attack on the carbonyl carbon. The carboxylate has recently been found to also be a reactive nucleophile capable of initiating a similar nucleophilic attack to form a labile anhydride bond. The fragile bond is easily cleaved, resulting in an oxygen transfer from the carboxylate-containing species to the reagent, nominally observed as a water transfer. This reactivity is shown for both peptides and non-peptidic species. Reagents isotopically labeled with O18 were used to confirm reactivity. This constitutes an example of distinct differences in reactivity of carboxylates between the gas phase, where they are shown to be reactive, and the solution phase, where they are not regarded as reactive with NHS esters.
Nucleation and early stage growth in phase-separating liquid mixtures under weak time-dependent supersaturation
S. Buil; J. P. Delville; A. Ducasse
: ĀĀIn the standard description of phase separation, quenching from an initial equilibrium state to a final metastable state in\\u000a the two-phase region is usually assumed to be instantaneous. Such an artificial situation is nevertheless intrinsically at\\u000a variance with experiments because the quench rate is finite due to the continuous changes in thermodynamic parameters between\\u000a the initial and final states.
Star formation via the phase transition of an adiabatic gas
NASA Technical Reports Server (NTRS)
Tohline, Joel E.; Christodoulou, Dimitris M.
An analytic model based on a second-order accurate global virial analysis is used to describe two stable equilibrium states for rotating gas clouds: a pressure-supported, diffuse state and a rotationally supported, compact state. Diffuse and compact equilibrium sequences are identified along which slow, secular evolution of a gas cloud can occur. A virial analysis provides analytic expressions for the limiting masses of gas clouds at points of dynamical instability. The minimum mass below which external triggers of any amplitude cannot effectively induce star formation is identified for adiabatic gas clouds. It is suggested that fluctuations in the ISM of some galaxies may actually cause star formation to proceed primarily via a phase transition, rather than via the classical Jeans instability.
Gas phase hydroformylation of propylene and allyl alcohol with immobilized rhodium complexes
Munck, N.A.D.
Contents: Introduction--(Carbon monoxide as a chemical feedstock, hydroformylation of alkenes, immobilization of homogeneous catalysts, synthesis of 1,4-butanediol, and scope of this thesis); Gas phase hydroformylation of propylene with porous resin anchored rhodium complexes--(Methods of catalyst preparation and characterization); Gas phase hydroformylation of propylene with porous resin anchored rhodium complexes--(The catalytic performance); Gas phase hydroformylation of propylene with immobilized rhodium complex monolayer catalysts; Gas phase hydroformylation of allyl alcohol with supported liquid phase catalysts.
Preconceptual design of the gas-phase decontamination demonstration cart
Munday, E.B.
Removal of uranium deposits from the interior surfaces of gaseous diffusion equipment will be a major portion of the overall multibillion dollar effort to decontaminate and decommission the gaseous diffusion plants. Long-term low-temperature (LTLT) gas-phase decontamination is being developed at the K-25 Site as an in situ decontamination process that is expected to significantly lower the decontamination costs, reduce worker exposure to radioactive materials, and reduce safeguard concerns. This report documents the preconceptual design of the process equipment that is necessary to conduct a full-scale demonstration of the LTLT method in accordance with the process steps listed above. The process equipment and method proposed in this report are not intended to represent a full-scale production campaign design and operation, since the gas evacuation, gas charging, and off-gas handling systems that would be cost effective in a production campaign are not cost effective for a first-time demonstration. However, the design presented here is expected to be applicable to special decontamination projects beyond the demonstration, which could include the Deposit Recovery Program. The equipment will therefore be sized to a 200 ft size 1 converter (plus a substantial conservative design margin), which is the largest item of interest for gas phase decontamination in the Deposit Recovery Program. The decontamination equipment will allow recovery of the UF{sub 6}, which is generated from the reaction of ClF{sub 3} with the uranium deposits, by use of NaF traps.
Homogeneous nucleation and growth in supersaturated zinc vapor investigated by molecular dynamics simulation.
R÷mer, F; Kraska, T
Homogeneous nucleation and growth of zinc from supersaturated vapor are investigated by nonequilibrium molecular dynamics simulations in the temperature range from 400 to 800 K and for a supersaturation ranging from log S=2 to 11. Argon is added to the vapor phase as carrier gas to remove the latent heat from the forming zinc clusters. A new parametrization of the embedded atom method for zinc is employed for the interaction potential model. The simulation data are analyzed with respect to the nucleation rates and the critical cluster sizes by two different methods, namely, the threshold method of Yasuoka and Matsumoto [J. Chem. Phys. 109, 8451 (1998)] and the mean first passage time method for nucleation by Wedekind et al. [J. Chem. Phys. 126, 134103 (2007)]. The nucleation rates obtained by these methods differ approximately by one order of magnitude. Classical nucleation theory fails to describe the simulation data as well as the experimental data. The size of the critical cluster obtained by the mean first passage time method is significantly larger than that obtained from the nucleation theorem. PMID:18154402
Characterizing protein crystal nucleation
NASA Astrophysics Data System (ADS)
Akella, Sathish V.
We developed an experimental microfluidic based technique to measure the nucleation rates and successfully applied the technique to measure nucleation rates of lysozyme crystals. The technique involves counting the number of samples which do not have crystals as a function of time. Under the assumption that nucleation is a Poisson process, the fraction of samples with no crystals decays exponentially with the decay constant proportional to nucleation rate and volume of the sample. Since nucleation is a random and rare event, one needs to perform measurements on large number of samples to obtain good statistics. Microfluidics offers the solution of producing large number of samples at minimal material consumption. Hence, we developed a microfluidic method and measured nucleation rates of lysozyme crystals in supersaturated protein drops, each with volume of ś 1 nL. Classical Nucleation Theory (CNT) describes the kinetics of nucleation and predicts the functional form of nucleation rate in terms of the thermodynamic quantities involved, such as supersaturation, temperature, etc. We analyzed the measured nucleation rates in the context of CNT and obtained the activation energy and the kinetic pre-factor characterizing the nucleation process. One conclusion is that heterogeneous nucleation dominates crystallization. We report preliminary studies on selective enhancement of nucleation in one of the crystal polymorprhs of lysozyme (spherulite) using amorphous mesoporous bioactive gel-glass te{naomi06, naomi08}, CaO.P 2O5.SiO2 (known as bio-glass) with 2-10 nm pore-size diameter distribution. The pores act as heterogeneous nucleation centers and claimed to enhance the nucleation rates by molecular confinement. The measured kinetic profiles of crystal fraction of spherulites indicate that the crystallization of spherulites may be proceeding via secondary nucleation pathways.
Gas Phase Chemical Detection with an Integrated Chemical Analysis System
Baca, Albert G.; Casalnuovo, Stephen A.; Frye-Mason, Gregory C.; Heller, Edwin J.; Hietala, Susan L.; Hietala, Vincent M.; Kottenstette, Richard J.; Lewis, Patrick R.; Manginell, Ronald P.; Matzke, Carloyn M.; Reno, John L.; Sasaki, Darryl Y.; Schubert, W. Kent
Microfabrication technology has been applied to the development of a miniature, multi-channel gas phase chemical laboratory that provides fast response, small size, and enhanced versatility and chemical discrimination. Each analysis channel includes a sample concentrator followed by a gas chromatographic separator and a chemically selective surface acoustic wave detector array to achieve high sensitivity and selectivity. The performance of the components, individually and collectively, is described. The design and performance of novel micromachined acoustic wave devices, with the potential for improved chemical sensitivity, are also described.
Simulating gas-aerosol-cirrus interactions: Process-oriented microphysical model and applications
Deutsches Zentrum
This work describes a process-oriented, microphysical-chemical model to simulate the formation and evolution of aerosols and ice crystals under the conditions prevailing in the upper troposphere and lower stratosphere. The model can be run as a box model or along atmospheric trajectories, and considers mixing, gas phase chemistry of aerosol precursors, binary homogeneous aerosol nucleation, homogeneous and heterogeneous ice nucleation,
Nucleation at macroscopic steps
NASA Astrophysics Data System (ADS)
Mederos, L.; Quintana, A.; Navascuķs, G.
The classical heterogeneous nucleation theory is used to study nucleation at macroscopic steps. Line tension effects are included to give a correct description of the phenomena within the known limits of the theory. A criterion of preferential nucleation at steps (decoration criterion) is given. The expected behavior of the system for low macroscopic contact angles is found.
Timescales in Bubble Nucleation Events for the Formation of Microcellular Biodegradable Foams
NASA Astrophysics Data System (ADS)
Iannace, Salvatore; Di Maio, Ernesto
In this work, the nucleating ability of different micro and nano sized nucleating agents for the foaming of thermoplastic biodegradable semi-crystalline polymer will be reviewed. In particular, the efficiency of the nucleating agent in inducing the formation of the gaseous phase will be compared to the efficiency in inducing the formation of the crystalline phase. In effect, in foaming of semi crystalline polymers, bubble nucleation and crystal nucleation are concurrent and somehow conflicting phenomena.
Nucleation of 1Pentanol Using a Thermal Diffusion Cloud Chamber
Anne Bertelsmann; Richard H. Heist
We report results of new nucleation experiments involving 1-pentanol with hydrogen as the background gas obtained from constant pressure critical supersaturation measurements and from constant temperature critical supersaturation experiments utilizing the high-pressure diffusion cloud chamber. We continue to observe significant background gas effects upon nucleation that we have reported previously; and we briefly discuss the important issue of stability (the
Terahertz wave generation from gas plasma using a phase compensator with attosecond phase-control accuracy
Dai Jianming; Zhang, X.-C. [Center for Terahertz Research, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)
We report the use of a precise phase compensator for the generation of intense terahertz waves from laser-induced gas plasma excited by a femtosecond pulse ({omega}) and its second harmonic (2{omega}) at both close contact and standoff distances. The attosecond accuracy phase-control capability of the device enables further optimization of the terahertz emission from gas plasma and elimination of the temporal walkoff between the {omega} and 2{omega} pulses traveling in dispersive media, resulting in intense terahertz generation at a distance of over 100 m by sending the optical beams far away and focusing them locally.
Kinetic analysis of the gas-phase pyrolysis of carbohydrates
Eun-Jae Shin; Mark R. Nimlos; Robert J. Evans
Cellulose-derived pyrolysis products and selected primary products, 5-hydroxymethyl furfural (5-HMF), levoglucosan and hydroxyacetaldehyde (HAA) were used as starting materials for kinetic studies of gas-phase pyrolysis by using flow tube reactors and product detection with molecular beam mass spectrometry (MBMS). Multivariate data analysis was used to identify major product classes for lumped product kinetic analysis. The methodology employed in this work
Molecular dynamics of gas phase hydrogen-bonded complexesĀ
Wofford, Billy Alan
of rovibrational bands in hydrogen- bonded complexes have been recorded. Static gas phase infrared spec- troscopic analysis of fundamental, overtone, combination and hot bands in the common and some isotopically substituted species have been per- formed using a... necessitates rovibrational analysis of a plethora of vibrational bands. Observa- tion of the 2vl overtone band in the hydrogen-bonded complex HCN---HF permits evaluation of the anharmonicity constant Xll ? -116. 9(1) cm and determination...
Gas phase fractionation method using porous ceramic membrane
Peterson, Reid A. (Madison, WI); Hill, Jr., Charles G. (Madison, WI); Anderson, Marc A. (Madison, WI)
Flaw-free porous ceramic membranes fabricated from metal sols and coated onto a porous support are advantageously used in gas phase fractionation methods. Mean pore diameters of less than 40 .ANG., preferably 5-20 .ANG. and most preferably about 15 .ANG., are permeable at lower pressures than existing membranes. Condensation of gases in small pores and non-Knudsen membrane transport mechanisms are employed to facilitate and increase membrane permeability and permselectivity.
Photodissociation of condensed carbon dioxide below the gas phase thresholds
J. M. Coquel; L. Siller; J. Wilkes; R. Carrapa; C. L. A. Lamont; T. Almeida Gasche; R. E. Palmer; A. M. C. Moutinho
We have investigated photodesorption from condensed carbon dioxide for photon energies ranging from 13 to 35 eV using synchrotron radiation. We report the desorption of O2+ ions at energies as low as 13 eV, and discuss this behaviour in terms of ion¢molecule reactions. The desorbed CO+ ion yield shows resonances at ?15.4 and ?17 eV, below the gas-phase thermodynamic threshold
V. ELECTRON GAS, RANDOM PHASE APPROXIMATION Markus Holzmann
a kak (2) V = 1 2 q=0 vq k,k a k+qa k -qak ak (3) = 1 2 q=0 vq [q-q - 0] (4) where a k (ak) are creation. In the Heisenberg picture, the time evolution of the creation operator a k with |k| > kF is given by -i d dt a k = HV. ELECTRON GAS, RANDOM PHASE APPROXIMATION Markus Holzmann LPMMC, Maison de Magist`ere, Grenoble
Preconceptual design of the gas-phase decontamination demonstration cart
Removal of uranium deposits from the interior surfaces of gaseous diffusion equipment will be a major portion of the overall multibillion dollar effort to decontaminate and decommission the gaseous diffusion plants. Long-term low-temperature (LTLT) gas-phase decontamination is being developed at the K-25 Site as an in situ decontamination process that is expected to significantly lower the decontamination costs, reduce worker
Gas-phase dissociation reactions of protonated saxitoxin and neosaxitoxin
Lekha Sleno; Dietrich A. Volmer; Borislav Kova?evi?; Zvonimir B. Maksi?
The aim of this study was to investigate the behavior of the protonated paralytic shellfish poisons saxitoxin (STX) and neosaxitoxin\\u000a (NEO) in the gas-phase after ion activation using different tandem mass spectrometry techniques. STX and NEO belong to a group\\u000a of neurotoxins produced by several strains of marine dinoflagellates. Their chemical structures are based on a tetrahydropurine\\u000a skeleton to which
Determination of the Gas-phase Acidities of Oligopeptides
Ren, Jianhua; Sawhney, Ashish; Tian, Yuan; Padda, Bhupinder; Batoon, Patrick
Amino acid residues located at different positions in folded proteins often exhibit different degrees of acidities. For example, a cysteine residue located at or near the N-terminus of a helix is often more acidic than that at or near the C-terminus 1-6. Although extensive experimental studies on the acid-base properties of peptides have been carried out in the condensed phase, in particular in aqueous solutions 6-8, the results are often complicated by solvent effects 7. In fact, most of the active sites in proteins are located near the interior region where solvent effects have been minimized 9,10. In order to understand intrinsic acid-base properties of peptides and proteins, it is important to perform the studies in a solvent-free environment. We present a method to measure the acidities of oligopeptides in the gas-phase. We use a cysteine-containing oligopeptide, Ala3CysNH2 (A3CH), as the model compound. The measurements are based on the well-established extended Cooks kinetic method (Figure 1) 11-16. The experiments are carried out using a triple-quadrupole mass spectrometer interfaced with an electrospray ionization (ESI) ion source (Figure 2). For each peptide sample, several reference acids are selected. The reference acids are structurally similar organic compounds with known gas-phase acidities. A solution of the mixture of the peptide and a reference acid is introduced into the mass spectrometer, and a gas-phase proton-bound anionic cluster of peptide-reference acid is formed. The proton-bound cluster is mass isolated and subsequently fragmented via collision-induced dissociation (CID) experiments. The resulting fragment ion abundances are analyzed using a relationship between the acidities and the cluster ion dissociation kinetics. The gas-phase acidity of the peptide is then obtained by linear regression of the thermo-kinetic plots 17,18. The method can be applied to a variety of molecular systems, including organic compounds, amino acids and their derivatives, oligonucleotides, and oligopeptides. By comparing the gas-phase acidities measured experimentally with those values calculated for different conformers, conformational effects on the acidities can be evaluated. PMID:23851399
Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystals and Polytetrehedral-Phase-Forming Alloys
NASA Technical Reports Server (NTRS)
By investigating the properties of quasicrystals and quasicrystal-forming liquid alloys, we may determine the role of ordering of the liquid phase in the formation of quasicrystals, leading to a better fundamental understanding of both the quasicrystal and the liquid. A quasicrystal is solid characterized by a symmetric but non-periodic arrangement of atoms, usually in the form of an icosahedron (12 atoms, 20 triangular faces). It is theorized that the short-range order in liquids takes this same form. The degree of ordering depends on the temperature of the liquid, and affects many of the liquid s properties, including specific heat, viscosity, and electrical resistivity. The MSFC role in this project includes solidification studies, phase diagram determination, and thermophysical property measurements on the liquid quasicrystal-forming alloys, all by electrostatic levitation (ESL). The viscosity of liquid quasicrystal-forming alloys is measured by the oscillating drop method, both in the stable and undercooled liquid state. The specific heat of solid, undercooled liquid, and stable liquid are measured by the radiative cooling rate of the droplets.
Wooldridge, Margaret S.
DEMONSTRATION OF GAS-PHASE COMBUSTION SYNTHESIS OF NANOSIZED PARTICLES USING A HYBRID BURNER) Abstract--A new approach for gas-phase combustion synthesis of nanosized particles using a novel hybrid. Introduction Gas-phase combustion synthesis is an important methodology for the production of nanosized
The partitioning of ketones between the gas and aqueous phases
NASA Astrophysics Data System (ADS)
Betterton, Eric A.
Most ketones are not significantly hydrated; they therefore retain their chromophore and they could be photolytically degraded in solution yielding a variety of products including carboxylic acids, aldehydes and radicals. It is difficult to accurately model the partitioning of ketones between the gas phase and aqueous phase because of the lack suitable estimates of the Henry's Law constants; consequently the fate and environmental effects of ketones cannot be confidently predicted. Here we report the experimental determination of the Henry's Law constants of a series of ketones that has yielded a simple straight line equation to predict the Henry's Law constants of simple aliphatic ketones: log H ? =0.23?? ? + 1.51; where H ? is the effective Henry's Law constant (M atm -1, and ?? ? is the Taft polar substituents constants. The results for 25░C are (M atm -1) CH 3COCH 3, 32; C 6H 5COCH 3, 110; CH 2ClCOCH 3, 59; CH 3COCOCH 3, 74; CF 3COCH 3, 138. Acetophenone appears to have an abnormally high H ?. Most low molecular weight aliphatic ketones are predicted to characterized by H ??30 M atm -1 and therefore they are expected to be found in the aqueous phase at concentrations of ?5 - 0.5 ?M (given a typical gas-phase concentration range of 1-10 ppbv). The expected rate of decomposition of ketones due to photolysis in hydrometers is briefly discussed.
Gas-phase chemistry of technetium carbonyl complexes.
Wang, Yang; Qin, Zhi; Fan, Fang-Li; Haba, Hiromitsu; Komori, Yukiko; Cao, Shi-Wei; Wu, Xiao-Lei; Tan, Cun-Min
Gas-phase chemical behaviors of short-lived technetium carbonyl complexes were studied using a low temperature isothermal chromatograph (IC) coupled with a (252)Cf spontaneous fission (SF) source. Fission products recoiled from the (252)Cf SF source were thermalized in a mixed gas containing CO, and then technetium carbonyl complexes were formed from reactions between CO gas and various technetium isotopes. A gas-jet system was employed to transport the volatile carbonyl complexes from a recoil chamber to the IC. Short IC columns made of Fluorinated Ethylene Propylene (FEP) Teflon and quartz were used to obtain chemical information about the technetium carbonyl complexes. The results for the (104)Tc-(106)Tc carbonyl complexes were found to be strongly influenced by the precursors, and showed the chemical behaviors of (104)Mo-(106)Mo carbonyl complexes, respectively. However, (107)Tc and (108)Tc could represent the chemical information of the element technetium due to their high independent yields and the very short half-lives of their precursors (107)Mo and (108)Mo. An adsorption enthalpy of about ?Hads = -43 kJ mol(-1) was determined for the Tc carbonyl complexes on both the Teflon and quartz surfaces by fitting the breakthrough curves of the (107)Tc and (108)Tc carbonyl complexes with a Monte Carlo simulation program. Chemical yields of around 25% were measured for the Tc carbonyl complexes relative to the transport yields obtained with the gas-jet transport of KCl aerosol particles with Ar carrier gas. Furthermore, the influence of a small amount of O2 gas on the yields of the Mo and Tc carbonyl complexes was studied. PMID:25920667
Nucleation and growth of Ag nanoparticles on amorphous carbon surface from vapor phase formed by vacuum evaporation
NASA Astrophysics Data System (ADS)
Gromov, Dmitry G.; Pavlova, Lydia M.; Savitsky, Andrey I.; Trifonov, Alexey Yu.
We present the results of experimental study of Ag nanoparticle arrays on thin film of amorphous carbon. The arrays were formed by means of vapor phase deposition on non-heated substrate. The investigation was carried out using TEM technique. It has been found that the size of the particles and their surface density significantly depend on the amount of condensing substance. In particular, increasing the portion of evaporating Ag material from 5.1 to 47.5 mg results in drastic reduction of surface density of the particles from ~8,000 to ~40 Ąm-2, whereas the predominant particle size changes from ~7 to ~60 nm. We present phenomenological description of the process: directed flow of silver atoms to growing Ag particles takes place during condensation.
Specific, trace gas induced phase transition in copper(II)oxide for highly selective gas sensing
NASA Astrophysics Data System (ADS)
Kneer, J.; W÷llenstein, J.; Palzer, S.
Here, we present results on the investigation of the percolation phase transition in copper(II)oxide (CuO) and show how it may be used to determine trace gas concentrations. This approach provides a highly selective sensing mechanism for the detection of hydrogen sulfide even in oxygen depleted atmospheres. In real-world applications, this scenario is encountered in biogas plants and natural gas facilities, where reliable H2S sensing and filtering are important because of the destructive effects H2S has on machinery. As opposed to gas detection via standard metal-oxide reaction routes, the percolation dynamics are demonstrated to be independent of the surface morphology in accordance with the universality of phase transitions. The sensing behavior of ink-jet printed CuO layers was tested for a large set of parameters including layer temperature, hydrogen sulfide (H2S) and oxygen concentration, as well as the sensitivity towards other gas species. The electrical percolation of the sensing layer is heralded by a dramatic drop in the overall resistivity of the CuO layer for temperatures below 200 ░C. The observed percolation phenomena in this temperature regime are unique to H2S even in comparison with related volatile thio-compounds making the sensing mechanism highly selective. At elevated temperatures above 300 ░C, the phase transition does not occur. This enables two distinct operational modes which are tunable via the sensor temperature and also allows for resetting the sensing layer after an electrical breakthrough.
Ice Nucleation in Deep Convection
NASA Technical Reports Server (NTRS)
Jensen, Eric; Ackerman, Andrew; Stevens, David; Gore, Warren J. (Technical Monitor)
The processes controlling production of ice crystals in deep, rapidly ascending convective columns are poorly understood due to the difficulties involved with either modeling or in situ sampling of these violent clouds. A large number of ice crystals are no doubt generated when droplets freeze at about -40 C. However, at higher levels, these crystals are likely depleted due to precipitation and detrainment. As the ice surface area decreases, the relative humidity can increase well above ice saturation, resulting in bursts of ice nucleation. We will present simulations of these processes using a large-eddy simulation model with detailed microphysics. Size bins are included for aerosols, liquid droplets, ice crystals, and mixed-phase (ice/liquid) hydrometers. Microphysical processes simulated include droplet activation, freezing, melting, homogeneous freezing of sulfate aerosols, and heterogeneous ice nucleation. We are focusing on the importance of ice nucleation events in the upper part of the cloud at temperatures below -40 C. We will show that the ultimate evolution of the cloud in this region (and the anvil produced by the convection) is sensitive to these ice nucleation events, and hence to the composition of upper tropospheric aerosols that get entrained into the convective column.
Mechanisms of the water-gas-shift reaction by iron pentacarbonyl in the gas phase.
Rozanska, Xavier; Vuilleumier, Rodolphe
We analyzed the mechanisms of the water-gas-shift reaction catalyzed by Fe(CO) 5/OH (-) in the gas phase using DFT methods. The systematic analysis of the accessible reaction mechanisms and the consideration of the Gibbs free energies allows for different reaction routes than previously suggested. In the dominant catalytic cycle, the hydride [FeH(CO) 4]- is the important intermediate. Associative reaction mechanisms are not favorable under moderate and low pressures. At high pressure, a side reaction takes over and prevents the conversion of H 2O and CO to H 2 and CO 2 and leads to the formation of HCOOH. PMID:18754658
Gas-phase pyridylamination of saccharides: development and applications.
Nakakita, Shin-ichi; Sumiyoshi, Wataru; Miyanishi, Nobumitsu; Natsuka, Shunji; Hase, Sumihiro; Hirabayashi, Jun
Pyridylamination is a versatile method for fluorescence labeling of oligosaccharides. The technique affords sensitive detection of saccharides with reducing termini and high-resolution separation by high-performance liquid chromatography. The conventional method, based on a liquid-phase reaction, has been extensively used in various aspects of glycobiology and glycotechnology. Unfortunately, the necessity for removing excess 2-aminopyridine makes the technique both laborious and time-consuming. Furthermore, removal of excess reagent can result in a significant loss of short saccharide components. In the present paper, we report an alternative methodology based on a "gas-phase" reaction, in which dried saccharides are reacted with vaporized 2-aminopyridine. The resultant Schiff base was also reduced in the gas phase within the same reaction microtube using a purpose-built device. The newly developed procedure was applied to both monosaccharide (GlcNAc) and oligosaccharides (isomalto-oligosaccharides) at quantitative yields with no requirement to remove excess reagent. The acid-labile sialyl linkages of alpha2-6-disialobiantennary oligosaccharides proved to be fully stable during the procedure. The developed method was also successfully applied to profiling N-linked oligosaccharides liberated from glycoproteins by hydrazinolysis and, thus, should contribute to various fields of glycomics. PMID:17335182
Microcanonical molecular simulations of methane hydrate nucleation and growth: evidence that direct nucleation to sI hydrate is among the multiple nucleation pathways.
Zhang, Zhengcai; Walsh, Matthew R; Guo, Guang-Jun
The results of six high-precision constant energy molecular dynamics (MD) simulations initiated from methane-water systems equilibrated at 80 MPa and 250 K indicate that methane hydrates can nucleate via multiple pathways. Five trajectories nucleate to an amorphous solid. One trajectory nucleates to a structure-I hydrate template with long-range order which spans the simulation box across periodic boundaries despite the presence of several defects. While experimental and simulation data for hydrate nucleation with different time- and length-scales suggest that there may exist multiple pathways for nucleation, including metastable intermediates and the direct formation of the globally-stable phase, this work provides the most compelling evidence that direct formation to the globally stable crystalline phase is one of the multiple pathways available for hydrate nucleation. PMID:25743115
Gas-phase hydrolysis of SOF2 and SOF4
NASA Astrophysics Data System (ADS)
Van Brunt, R. J.; Sauers, I.
The rates for gas-phase hydrolysis of SOF2 (thionylfluoride) and SOF4 (thionyl tetrafluoride) have been measured at a temperature of 298 K. The second order rate constant for SOF2 hydrolysis in SF6 buffer gas was found to have the value (1.2▒0.3)ū10-23 cm3/s which agrees with previous estimates of Sauers et al., but is three orders of magnitude lower than the value obtained by R³egsegger et al. at 340 K. The rate constant for SOF4 hydrolysis has not previously been measured and its value in both SF6 and N2 buffer gases was found here to be (1.0▒0.3)ū10-21 cm3/s.
Homogeneous nucleation and growthin iron-platinum vapour investigated by molecular dynamics simulation
N. L³mmen; T. Kraska
.ĀĀHomogeneous nucleation and growth\\u000a from binary metal vapour is investigated by molecular dynamics simulation. It is focused here mainly on the iron-platinum\\u000a system with a mole fraction of 0.5. The simulations are started in the highly supersaturated vapour phase. Argon is added\\u000a as carrier gas removing the heat of condensation from the forming clusters. The embedded atom method is employed
Contrail formation: Homogeneous nucleation of H2SO4\\/H2O droplets
B. Kaercher; Th. Peter; R. Ottmann
Homogeneous nucleation of sub-nanometer H2SO4\\/H2O germs, their growth and freezing probability in the cooling wake of a subsonic jet aircraft at tropopause altitude are investigated. Heteromolecular condensation, water uptake, and coagulation cause a small subset of the germs to grow into nm-sized solution droplets which overcome the Kelvin barrier. These droplets efficiently take up water vapor from the gas phase,
Experiments on Nucleation in Different Flow Regimes
NASA Technical Reports Server (NTRS)
Bayuzick, Robert J.
The vast majority of metallic engineering materials are solidified from the liquid phase. Understanding the solidification process is essential to control microstructure, which in turn, determines the properties of materials. The genesis of solidification is nucleation, where the first stable solid forms from the liquid phase. Nucleation kinetics determine the degree of undercooling and phase selection. As such, it is important to understand nucleation phenomena in order to control solidification or glass formation in metals and alloys. Early experiments in nucleation kinetics were accomplished by droplet dispersion methods [1-6]. Dilitometry was used by Turnbull and others, and more recently differential thermal analysis and differential scanning calorimetry have been used for kinetic studies. These techniques have enjoyed success; however, there are difficulties with these experiments. Since materials are dispersed in a medium, the character of the emulsion/metal interface affects the nucleation behavior. Statistics are derived from the large number of particles observed in a single experiment, but dispersions have a finite size distribution which adds to the uncertainty of the kinetic determinations. Even though temperature can be controlled quite well before the onset of nucleation, the release of the latent heat of fusion during nucleation of particles complicates the assumption of isothermality during these experiments. Containerless processing has enabled another approach to the study of nucleation kinetics [7]. With levitation techniques it is possible to undercool one sample to nucleation repeatedly in a controlled manner, such that the statistics of the nucleation process can be derived from multiple experiments on a single sample. The authors have fully developed the analysis of nucleation experiments on single samples following the suggestions of Skripov [8]. The advantage of these experiments is that the samples are directly observable. The nucleation temperature can be measured by noncontact optical pyrometry, the mass of the sample is known, and post processing analysis can be conducted on the sample. The disadvantages are that temperature measurement must have exceptionally high precision, and it is not possible to isolate specific heterogeneous sites as in droplet dispersions.
Gas-phase energetics of thorium fluorides and their ions.
Irikura, Karl K
Gas-phase thermochemistry for neutral ThF(n) and cations ThF(n)(+) (n = 1-4) is obtained from large-basis CCSD(T) calculations, with a small-core pseudopotential on thorium. Electronic partition functions are computed with the help of relativistic MRCI calculations. Geometries, vibrational spectra, electronic fine structure, and ion appearance energies are tabulated. These results support the experimental results by Lau, Brittain, and Hildenbrand for the neutral species, except for ThF. The ion thermochemistry is presented here for the first time. PMID:23137388
Neurotransmitters in the Gas Phase: La-Mb Studies
NASA Astrophysics Data System (ADS)
Cabezas, C.; Mata, S.; L¾pez, J. C.; Alonso, J. L.
LA-MB-FTMW spectroscopy combines laser ablation with Fourier transform microwave spectroscopy in supersonic jets overcoming the problems of thermal decomposition associated with conventional heating methods. We present here the results on LA-MB-FTMW studies of some neurotransmitters. Six conformers of dopamine, four of adrenaline, five of noradrenaline and three conformers of serotonin have been characterized in the gas phase. The rotational and nuclear quadrupole coupling constants extracted from the analysis of the rotational spectrum are directly compared with those predicted by ab initio methods to achieve the conclusive identification of different conformers and the experimental characterization of the intramolecular forces at play which control conformational preferences.
Gas phase hydrogen-bonded complexes of aromatic molecules
NASA Astrophysics Data System (ADS)
Mons, Michel; Dimicoli, Iliana; Piuzzi, Franńois
The present review discusses the possibility of measuring the dissociation energy of gas phase complexes from their dissociative photoionization. A compilation of recent results on hydrogen-bonded complexes of aromatic molecules, with a polar solvent molecule (water, alcohol, NH 3 , HCl, etc.), playing the role of either proton donor or proton acceptor is presented. We show that laser experiments begin to provide a consistent set of energetic data that can be considered as benchmarks to assess quantum calculations as well as to parametrize the force field models used in biochemistry.
Nucleation of electroactive ? -phase poly(vinilidene fluoride) withĀCoFe 2 O 4 and NiFe 2 O 4 nanofillers: a new method forĀtheĀpreparation of multiferroic nanocomposites
P. Martins; C. M. Costa; S. Lanceros-Mendez
Multiferroic and magnetoelectric materials show enormous potential for technological developments. Multiferroic composites\\u000a are more attractive for applications due to their enhanced properties with respect to single-phase multiferroic materials.\\u000a In this paper we report on the nucleation of the electroactive ?-phase of poly(vinylidene fluoride), PVDF, by the addition of CoFe2O4 and NiFe2O4 nanoparticles in order to prepare poly(vinylidene fluoride)\\/ferrite nanocomposite for
Gas-phase deposition of tungsten carbide coatings
Roman, O.V.; Kirilyuk, L.M.; Chernousova, S.A.
The object of this work is to investigate the phase composition and the structure of coatings based on tungsten carbide, and also to reveal the factors determining their operational characteristics. The investigations were carried out on a laboratory installation. As metal containing compound we used tungsten hexachloride WC/sub 16/, the carbon containing medium was methane CH/sub 4/. The vapor-gas mixture (WC/sub l6/ + CH/sub 4/) was conveyed by argon to the reaction chamber where the coating was deposited at 723-1023/sup 0/K. Investigation of the effect of the temperature on the phase composition of the forming coating enabled us to subdivide the temperature interval into several ranges in which we obtained layers with the composition W + W/sub 2/C, W/sub 2/C + WC, WC.
Thermally induced evolution of phase transformations in gas hydrate sediment
NASA Astrophysics Data System (ADS)
Zhang, Xuhui; Lu, Xiaobing; Li, Qingping; Yao, Haiyuan
Thermally induced evolution of phase transformations is a basic physical-chemical process in the dissociation of gas hydrate in sediment (GHS). Heat transfer leads to the weakening of the bed soil and the simultaneous establishment of a time varying stress field accompanied by seepage of fluids and deformation of the soil. As a consequence, ground failure could occur causing engineering damage or/and environmental disaster. This paper presents a simplified analysis of the thermal process by assuming that thermal conduction can be decoupled from the flow and deformation process. It is further assumed that phase transformations take place instantaneously. Analytical and numerical results are given for several examples of simplified geometry. Experiments using Tetra-hydro-furan hydrate sediments were carried out in our laboratory to check the theory. By comparison, the theoretical, numerical and experimental results on the evolution of dissociation fronts and temperature in the sediment are found to be in good agreement.
Generalized Gibbs' approach in heterogeneous nucleation
NASA Astrophysics Data System (ADS)
Abyzov, Alexander S.; Schmelzer, J³rn W. P.
Heterogeneous nucleation (condensation and boiling) on planar solid surfaces is described taking into account changes of the state parameters of the critical clusters in dependence on supersaturation. The account of the variation of the state parameters of the cluster phase on nucleation is performed in the framework of the generalized Gibbs' approach. One-component van der Waals fluids are chosen as a model for the analysis of the basic qualitative characteristics of the process. The analysis is performed for both hydrophobic and hydrophilic surfaces and similarities and differences between condensation and boiling processes are discussed for the two different cases. It is shown that, in the generalized Gibbs' approach, contact angle and catalytic factor for heterogeneous nucleation become dependent on the degree of metastability (undercooling or superheating) of the fluid. For the case of formation of a droplet in supersaturated vapor on a hydrophobic surface and bubble formation in a liquid on a hydrophilic surface the solid surface has only a minor influence on nucleation. In the alternative cases of condensation of a droplet on a hydrophilic surface and of bubble formation in a liquid on a hydrophobic surface, nucleation is significantly enhanced by the solid. Effectively, the existence of the solid surface results in a significant shift of the spinodal to lower supersaturations as compared with homogeneous nucleation. Qualitatively the same behavior is observed now near the new (solid surface induced) limits of instability of the fluid as compared with the behavior near to the spinodal curve in the case of homogeneous nucleation.
Gas phase reaction of sulfur trioxide with water vapor
Kolb, C.E.; Molina, M.J.; Jayne, J.T.; Meads, R.F.; Worsnop, D.R.
Sulfur trioxide (SO3) has long been known to react with water to produce sulfuric acid (H2S04). It has been commonly assumed that the gas phase reaction in the Earth`s atmosphere between SO3 and water vapor to produce sulfuric acid vapor is an important step in the production of sulfuric acid aerosol particles. The kinetics of the gas phase reaction of SO3 with water vapor have previously been studied by Castleman and co-workers, Wang et al and Reiner and Arnold. Each of these studies was carried out in a flow reactor, with the first two studies performed at low pressure (1-10 Torr) and the latter from approx. 30 to 260 Torr. Each of these studies measured SO3 decays over a range of H2O vapor levels, obtaining data consistent with interpreting the reaction of gaseous SO3 and H2O as a bimolecular process. It is not clear why previous experimental studies failed to observe a nonlinear dependence of SO3 consumption on water vapor concentration. It is probable that sufficient water dimer exists in much of the Earth`s atmosphere to allow dimer reactions to participate in sulfuric acid vapor formation.
Electron scattering from gas-phase glycine molecules.
Tashiro, Motomichi
Low-energy electron collisions with gas-phase glycine molecules have been studied using the fixed-nuclei R-matrix method based on state-averaged complete-active-space self-consistent-field orbitals. A total of 40 electronic states of neutral glycine, including 3s and 3p Rydberg excited states, are included in the R-matrix model. A large peak is observed in the A(") partial elastic cross section around 3.4 eV, which originates from the pi( *) shape resonance. In addition, many sharp narrow peaks coming from core excited resonances are seen in the elastic and inelastic cross sections at energies above 5 eV. Although the effect of the Rydberg orbitals on the elastic cross section is insignificant, these orbitals are crucial to represent core excited resonances in the inelastic cross sections. In previous experiments on dissociative electron attachment to gas-phase glycine, noticeable product ion peaks have been observed at electron collision energies around 1-2 and 5-10 eV. The resonance positions obtained in our calculations are generally close to these experimental results. PMID:19045267
Probing Guanine and Cytosine Tautomers in the Gas Phase
NASA Astrophysics Data System (ADS)
Pena, I.; Vaquero, V.; L¾pez, J. C.; Alonso, J. L.
Using laser ablation molecular beam Fourier transform microwave spectroscopy (LA-MB-FTMW) we have recently studied the nucleic acid bases uracil and thymine. We have now successfully probed in isolation conditions in the gas phase cytosine and guanine which are solids with high melting points (m.p.>300░C) and a low vapour pressure, and consequently, they are elusive to gas-phase rotational studies. Five rotational species have been detected in the supersonic expansion of cytosine. The unambiguous assignment of the observed species to the various tautomer/conformer structures is based on the markedly different values of the quadrupole coupling constants of the three ^{14}N nuclei, which act as fingerprints for the identification of the various species. Four species have been observed in the rotational spectra of Guanine. The comparison between the experimental rotational constants and those calculated ab initio provide a definitive test for the identification of the four lowest energy forms. The planarity of the tautomers is discussed on the basis of the inertial defect values (?=I_c-I_a-I_b). V. Vaquero, M.E. Sanz, J.C. L¾pez and J.L. Alonso, J. Phys. Chem. A 111, 3443 (2007) J.C. L¾pez, M.I. Pe±a, M.E. Sanz and J.L. Alonso, J. Chem. Phys. 126, 191103 (2007)
Nucleation Pathways of CO2 Condensation under Mesoporous Templated Glass
NASA Astrophysics Data System (ADS)
Wang, Bo; Byran, Matthew S.; Warren, Garfield T.; Sokol, Paul E.; Indiana University Team; NIST Collaboration
Carbon capture and storage (CCS) are important elements in reducing greenhouse gas emission and combating global warming. The adsorption behavior of CO2 under mesoporous confinement at room temperature is particularly relevant. , Small Angle Scattering of X-ray (SAXS) and Neutron (SANS) were used to probe the adsorption process of CO2 under such mesoporous confinement MCM-41 and details of nucleation pathways were mapped out by fitting the scattering intensities with adsorption models. From both experiments, the nucleation of CO2 on the inner pore surface of MCM-41 is found to be a two-step process; high density liquid phase CO2 first forms uniform layers following the long range translational symmetry of the porous matrix, above one CO2 filling, determined by the pore size and temperature, capillary condensation initiates. The nucleation sites formed during capillary condensation start to separate the long range symmetry from the one at uniform layers. Finally, SAXS and SANS techniques are compared and they both showed their unique properties of probing the filling-dependent structures of adsorbed CO2 under such mesoporous system.
Engine exhaust particulate and gas phase contributions to vascular toxicity.
Campen, Matthew; Robertson, Sarah; Lund, Amie; Lucero, Joann; McDonald, Jacob
Cardiovascular health effects of near-roadway pollution appear more substantial than other sources of air pollution. The underlying cause of this phenomenon may simply be concentration-related, but the possibility remains that gases and particulate matter (PM) may physically interact and further enhance systemic vascular toxicity. To test this, we utilized a common hypercholesterolemic mouse model (Apolipoprotein E-null) exposed to mixed vehicle emission (MVE; combined gasoline and diesel exhausts) for 6?h/d?ū?50?d, with additional permutations of removing PM by filtration and also removing gaseous species from PM by denudation. Several vascular bioassays, including matrix metalloproteinase-9 protein, 3-nitrotyrosine and plasma-induced vasodilatory impairments, highlighted that the whole emissions, containing both particulate and gaseous components, was collectively more potent than MVE-derived PM or gas mixtures, alone. Thus, we conclude that inhalation of fresh whole emissions induce greater systemic vascular toxicity than either the particulate or gas phase alone. These findings lend credence to the hypothesis that the near-roadway environment may have a more focused public health impact due to gas-particle interactions. PMID:24730681
Campen, Matthew; Robertson, Sarah; Lund, Amie; Lucero, Joann; McDonald, Jacob
Cardiovascular health effects of near-roadway pollution appear more substantial than other sources of air pollution. The underlying cause of this phenomenon may simply be concentration-related, but the possibility remains that gases and particulate matter (PM) may physically interact and further enhance systemic vascular toxicity. To test this, we utilized a common hypercholesterolemic mouse model (Apolipoprotein E-null) exposed to mixed vehicular emissions (MVE; combined gasoline and diesel exhausts) for 6 h/d ū 50 days, with additional permutations of removing PM by filtration and also removing gaseous species from PM by denudation. Several vascular bioassays, including matrix metalloproteinase 9 (MMP9) protein, 3-nitrotyrosine, and plasma-induced vasodilatory impairments, highlighted that the whole emissions, containing both particulate and gaseous components, was collectively more potent than MVE-derived PM or gas mixtures, alone. Thus, we conclude that inhalation of fresh whole emissions induce greater systemic vascular toxicity than either the particulate or gas phase alone. These findings lend credence to the hypothesis that the near-roadway environment may have a more focused public health impact due to gas-particle interactions. PMID:24730681
Feasibility of gas-phase decontamination of gaseous diffusion equipment
Munday, E.B.; Simmons, D.W.
The five buildings at the K-25 Site formerly involved in the gaseous diffusion process contain 5000 gaseous diffusion stages as well as support facilities that are internally contaminated with uranium deposits. The gaseous diffusion facilities located at the Portsmouth Gaseous Diffusion Plant and the Paducah Gaseous Diffusion Plant also contain similar equipment and will eventually close. The decontamination of these facilities will require the most cost-effective technology consistent with the criticality, health physics, industrial hygiene, and environmental concerns; the technology must keep exposures to hazardous substances to levels as low as reasonably achievable (ALARA). This report documents recent laboratory experiments that were conducted to determine the feasibility of gas-phase decontamination of the internal surfaces of the gaseous diffusion equipment that is contaminated with uranium deposits. A gaseous fluorinating agent is used to fluorinate the solid uranium deposits to gaseous uranium hexafluoride (UF{sub 6}), which can be recovered by chemical trapping or freezing. The lab results regarding the feasibility of the gas-phase process are encouraging. These results especially showed promise for a novel decontamination approach called the long-term, low-temperature (LTLT) process. In the LTLT process: The equipment is rendered leak tight, evacuated, leak tested, and pretreated, charged with chlorine trifluoride (ClF{sub 3}) to subatmospheric pressure, left for an extended period, possibly > 4 months, while processing other items. Then the UF{sub 6} and other gases are evacuated. The UF{sub 6} is recovered by chemical trapping. The lab results demonstrated that ClF{sub 3} gas at subatmospheric pressure and at {approx} 75{degree}F is capable of volatilizing heavy deposits of uranyl fluoride from copper metal surfaces sufficiently that the remaining radioactive emissions are below limits.
Microporous hydrophobic hollow fiber modules for gas-liquid phase separation in microgravity
Gary Noyes
Gas-liquid interphase mass transfer operations, such as gas-liquid phase separation, gas absorption into liquid or dissolved gas separation from liquid, gas humidification and drying via liquid contact, and evaporative cooling are readily accomplished on the Earth with settling\\/spray chambers, packed towers, or bubble columns. This paper reports on gas-water mass transfer tests performed utilizing microporous hydrophobic Hollow Fiber Modules (HFMs)
Diamond Nucleation Using Polyethene
NASA Technical Reports Server (NTRS)
Morell, Gerardo (Inventor); Makarov, Vladimir (Inventor); Varshney, Deepak (Inventor); Weiner, Brad (Inventor)
The invention presents a simple, non-destructive and non-abrasive method of diamond nucleation using polyethene. It particularly describes the nucleation of diamond on an electrically viable substrate surface using polyethene via chemical vapor deposition (CVD) technique in a gaseous environment.
Nucleation of protein crystals
Juan Manuel Garc??a-Ruiz
This paper introduces nucleation theory applied to crystallizing protein solutions. It is shown that the classical approach explains the available nucleation data under most conditions used for growing protein crystals for structural studies and for industrial crystallization. However, it fails to explain most experimental data on the structure of the critical clusters. It is also shown that for open systems
Diamond nucleation using polyethene
Morell, Gerardo; Makarov, Vladimir; Varshney, Deepak; Weiner, Brad
The invention presents a simple, non-destructive and non-abrasive method of diamond nucleation using polyethene. It particularly describes the nucleation of diamond on an electrically viable substrate surface using polyethene via chemical vapor deposition (CVD) technique in a gaseous environment.
Musculoskeletal-induced Nucleation in Altitude Decompression Sickness
NASA Technical Reports Server (NTRS)
Pollock, N. W.; Natoli, M. J.; Conkin, J.; Wessel, J. H., III; Gernhardt, M. L.
Musculoskeletal activity has the potential to both improve and compromise decompression safety. Exercise enhances inert gas elimination during oxygen breathing prior to decompression (prebreathe), but it may also promote bubble nuclei formation (nucleation), which can lead to gas phase separation and bubble growth and increase the risk of decompression sickness (DCS). The timing, pattern and intensity of musculoskeletal activity and the level of tissue supersaturation may be critical to the net effect. There are limited data available to evaluate cost-benefit relationships. Understanding the relationship is important to improve our understanding of the underlying mechanisms of nucleation in exercise prebreathe protocols and to quantify risk in gravity and microgravity environments. Data gathered during NASA's Prebreathe Reduction Program (PRP) studies combined oxygen prebreathe and exercise followed by low pressure (4.3 psi; altitude equivalent of 30,300 ft [9,235 m]) microgravity simulation to produce two protocols used by astronauts preparing for extravehicular activity. Both the Phase II/CEVIS (cycle ergometer vibration isolation system) and ISLE (in-suit light exercise) trials eliminated ambulation to more closely simulate the microgravity environment. The CEVIS results (35 male, 10 female) serve as control data for this NASA/Duke study to investigate the influence of ambulation exercise on bubble formation and the subsequent risk of DCS.
Gas-Phase Dissociation Pathways of Multiply Charged Peptide Clusters
Jurchen, John C.; Garcia, David E.; Williams, Evan R.
Numerous studies of cluster formation and dissociation have been conducted to determine properties of matter in the transition from the condensed phase to the gas phase using materials as diverse as atomic nuclei, noble gasses, metal clusters, and amino acids. Here, electrospray ionization is used to extend the study of cluster dissociation to peptides including leucine enkephalin with 7¢19 monomer units and 2¢5 protons, and somatostatin with 5 monomer units and 4 protons under conditions where its intramolecular disulfide bond is either oxidized or reduced. Evaporation of neutral monomers and charge separation by cluster fission are the competing dissociation pathways of both peptides. The dominant fission product for all leucine enkephalin clusters studied is a proton-bound dimer, presumably due to the high gas-phase stability of this species. The branching ratio of the fission and evaporation processes for leucine enkephalin clusters appears to be determined by the value of z2/n for the cluster where z is the charge and n the number of monomer units in the cluster. Clusters with low and high values of z2/n dissociate primarily by evaporation and cluster fission respectively, with a sharp transition between dissociation primarily by evaporation and primarily by fission measured at a z2/n value of ~0.5. The dependence of the dissociation pathway of a cluster on z2/n is similar to the dissociation of atomic nuclei and multiply charged metal clusters indicating that leucine enkephalin peptide clusters exist in a state that is more disordered, and possibly fluid, rather than highly structured in the dissociative transition state. The branching ratio, but not the dissociation pathway of [somatostatin5 + 4H]4+ is altered by the reduction of its internal disulfide bond indicating that monomer conformational flexibility plays a role in peptide cluster dissociation. PMID:14652186
Spectroscopic studies of molecular iodine emitted into the gas phase by seaweed
NASA Astrophysics Data System (ADS)
Ball, S. M.; Hollingsworth, A. M.; Humbles, J.; Leblanc, C.; Potin, P.; McFiggans, G.
Time profiles of molecular iodine emissions from seven species of seaweed have been measured at high time resolution (7.5 s) by direct spectroscopic quantification of the gas phase I2 using broadband cavity enhanced absorption spectroscopy. Substantial differences were found between species, both in the amounts of I2 emitted when the plants were exposed to air and in the shapes of their emission time profiles. Two species of kelp, Laminaria digitata and Laminaria hyperborea, were found to be the most potent emitters, producing an intense burst of I2 when first exposed to air. I2 was also observed from Saccharina latissima and Ascophyllum nodosum but in lower amounts and with broader time profiles. I2 mixing ratios from two Fucus species and Dictyopteris membranacea were at or below the detection limit of the present instrument (25 pptv). A further set of experiments investigated the time dependence of I2 emissions and aerosol particle formation when fragments of L. digitata were exposed to desiccation in air, to ozone and to oligoguluronate stress factors. Particle formation occurred in all L. digitata stress experiments where ozone and light were present, subject to the I2 mixing ratios being above certain threshold amounts. Moreover, the particle number concentrations closely tracked variations in the I2 mixing ratios, confirming the results of previous studies that the condensable particle-forming gases derive from the photochemical oxidation of the plant's I2 emissions. This work also supports the theory that particle nucleation in the coastal atmosphere occurs in "hot-spot" regions of locally elevated concentrations of condensable gases: the greatest atmospheric concentrations of I2 and hence of condensable iodine oxides are likely to be above plants of the most efficiently emitting kelp species and localised in time to shortly after these seaweeds are uncovered by a receding tide.
Spectroscopic studies of molecular iodine emitted into the gas phase by seaweed
NASA Astrophysics Data System (ADS)
Ball, S. M.; Hollingsworth, A. M.; Humbles, J.; Leblanc, C.; Potin, P.; McFiggans, G.
Time profiles of molecular iodine emissions from seven species of seaweed have been measured at high time resolution (7.5 s) by direct spectroscopic quantification of the gas phase I2 using broadband cavity enhanced absorption spectroscopy. Substantial differences were found between species, both in the amounts of I2 emitted when the plants were exposed to air and in the shapes of their emission time profiles. Two species of kelp, Laminaria digitata and Laminaria hyperborea, were found to be the most potent emitters, producing an intense burst of I2 when first exposed to air. I2 was also observed from Saccharina latissima and Ascophyllum nodosum but in lower amounts and with broader time profiles. I2 mixing ratios from two Fucus species and Dictyopteris membranacea were at or below the detection limit of the present instrument (25 pptv). A further set of experiments investigated the time dependence of I2 emissions and aerosol particle formation when fragments of L. digitata were exposed to desiccation in air, to ozone and to oligoguluronate stress factors. Particle formation occurred in all L. digitata stress experiments where ozone and light were present, subject to the I2 mixing ratios being above certain threshold amounts. Moreover, the particle number concentrations closely tracked variations in the I2 mixing ratios, confirming the results of previous studies that the condensable particle-forming gases derive from the photochemical oxidation of the plant's I2 emissions. This work also supports the theory that particle nucleation in the coastal atmosphere occurs in "hot-spot" regions of locally elevated concentrations of condensable gases: the greatest atmospheric concentrations of I2 and hence of condensable iodine oxides are likely to be above plants of the most efficiently emitting kelp species and localised in time to shortly after these seaweeds are uncovered by a receding tide.
Phase separation in a polarized Fermi gas with spin-orbit coupling
Yi, W.; Guo, G.-C. [Key Laboratory of Quantum Information, University of Science and Technology of China, CAS, Hefei, Anhui, 230026 (China)
We study the phase separation of a spin-polarized Fermi gas with spin-orbit coupling near a wide Feshbach resonance. As a result of the competition between spin-orbit coupling and population imbalance, the phase diagram for a uniform gas develops a rich structure of phase separation involving topologically nontrivial gapless superfluid states. We then demonstrate the phase separation induced by an external trapping potential and discuss the optimal parameter region for the experimental observation of the gapless superfluid phases.
Condensation of water vapor in rarefaction waves. I - Homogeneous nucleation
J. P. Sislian; I. I. Glass
A detailed theoretical investigation has been made of the condensation of water vapor\\/carrier gas mixtures in the nonstationary rarefaction wave generated in a shock tube. It is assumed that condensation takes place by homogeneous nucleation. The equations of motion together with the nucleation rate and the droplet growth equations were solved numerically by the method of characteristics and Lax's method
Navigating Organo-Lead Halide Perovskite Phase Space via Nucleation Kinetics toward a Deeper Understanding of Perovskite Phase Transformations and Structure-Property Relationships.
Williams, Spencer T; Chueh, Chu-Chen; Jen, Alex K-Y
Organo-lead halide perovskite photovoltaics have developed faster than our understanding of the material itself. Using the vast body of work on perovskite processing created in just the past few years, it is possible to create a better picture of this material's complex phase-transformation behavior. This concept paper summarizes and correlates the current understanding of structural intermediates, kinetic controls, and structure-property relationships of organo-lead iodide perovskites. To this end, a new way of graphically relating information is developed, allowing the simultaneous mapping of schematic kinetic relationships between all currently prevailing perovskite deposition and growth techniques. PMID:25760403
Nucleation and growth of combustion flame deposited diamond coatings on silicon nitride
NASA Astrophysics Data System (ADS)
Rozbicki, Robert T.
An investigation has been performed on the kinetics of diamond nucleation on silicon nitride (Si3N4) based materials during oxy-acetylene combustion flame chemical vapor deposition. The deposits were characterized using scanning electron microscopy (SEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) techniques. Kinetic parameters of the nucleation process, such as nucleation rate (I), period of initial nuclei formation (tng), and maximum nucleation density (Nd) were experimentally determined. It was concluded that at low temperatures (Ts < 875░C), the observed nucleation density is due to epitaxial or pseudo-epitaxial growth on residual particles on the substrate surface. At higher temperatures (Ts > 875░C), heterogeneous nucleation of diamond on Si3N4 occurs with an apparent activation energy ( Eahet ) of ś 18 kcal/mol. From an Arrhenius plot of particle growth rate, the activation energy (Ea) for diamond growth was calculated to be ś 9 kcal/mol. These results suggest that the energy barrier associated with the heterogeneous nucleation process ( Eahet > Ea) may in fact be responsible for the observed low nucleation densities on Si3N4 substrates. Consequently, nucleation density on Si3N4 is limited by the concentration of available sites for nuclei formation. As surface diffusion to those sites was determined to be negligible, growth of stable nuclei occurs via direct impingement of gas phase species. Based on these conclusions, a multistage deposition technique was developed to deposit continuous diamond coatings on untreated Si3N4 substrates. This two stage technique consisted of (i) an in situ flame pretreatment of the substrate to enhance nucleation through the formation of SiC and (ii) subsequent growth on the flame pretreated surface under optimized parameters. Using a previously developed compression test for brittle coating/substrate systems, the adhesion of multistage deposited coatings was compared to conventionally deposited coatings. Normalized values of adhesion for the multistage coatings were observed to be the same order of magnitude as the conventionally seeded diamond coatings. However, the failure mechanisms of the two coatings were observed to be significantly different. Multistage coating failure was characterized by partial ( ś typically 5%) delamination while conventionally seeded coatings were observed to completely disintegrate (100% delamination) at failure. Thus, it was projected that the fracture toughness of the multistage deposited coatings may be superior to that of conventionally seeded coatings. Finally, a modified flame technique is introduced to remedy a number of deficiencies and increase the commercial viability of combustion flame synthesis. This technique consists of simple modifications to conventional apparatus which significantly enhances the deposition area and expands the number of candidate substrate materials and geometries that can be coated using combustion flame CVD.
Gas-phase reactions of halogen species of atmospheric importance
NASA Astrophysics Data System (ADS)
Heard, Anne C.
A low-pressure discharge-flow technique, with various optical detection methods, has been used to determine bimolecular rate coefficients for a number of reactions in the gas-phase between OH radicals and organic halogen-containing molecules and between NO3 radicals and the iodine species I2 and I. These experiments have shown that: (1) the reaction of methyl iodide with OH accounts for approximately 2 percent of the removal of CH3I from the troposphere as compared with photolysis; (2) abstraction of I-atoms from a C-I bond by OH is probable in the gas-phase; (3) the halogen-containing anaesthetic substances halothane CF3CClBrH, enflurane CF2HOCF2CFClH, isoflurane CF2HOCClHCF3 and sevoflurane (CF3)2CHOCFH2 have significantly shorter tropospheric lifetimes than the fully halogenated CFCs and halons because of reaction with the OH radical and are thus unlikely to be transported up to the stratosphere where they could contribute to the depletion of ozone. Data obtained for reactions between OH and some 'CFC alternatives' along with measurements of the integrated absorption cross-sections of the compounds in the spectral region 800-1200 cm(exp -1) were used to calculate ozone depletion potentials (ODP) and greenhouse warming potentials relative to CFCl3 for each compound. The study of the reactions between OH and CF3CFBrH and CF2BrH was used to provide a useful first estimate of the environmental acceptability of these compounds in the context of their possible use as replacements for the conventional CFCs. A method was developed to provide a first estimate of the ODP of a halogenated alkane without use of a complicated (and expensive) computer modeling scheme. A reaction between molecular iodine and the nitrate radical in the gas-phase was discovered and the kinetics of this reaction have been studied. No temperature or pressure dependence was observed for the rate of reaction, the rate constant of which was found to be (1.5 +/- 0.5) x 10(exp -12)/cu cm/molecule/s. The reaction between I and NO3 was found to occur at a rate of about 60 percent of the hard-sphere collision frequency for the two species. The rate constant for reaction between I and NO3 was found to be (4.5 +/- 1.9) x 10(exp -10)/cu cm/molecule/s. An upper limit for the heat of formation of IONO2 of (21 +/- 3) kJmol(exp -1) was also derived.
Relating the hygroscopic properties of submicron aerosol to both gas- and particle-phase chemical composition in a boreal forest environment
NASA Astrophysics Data System (ADS)
Hong, J.; Kim, J.; Nieminen, T.; Duplissy, J.; Ehn, M.; ─ijõlõ, M.; Hao, L.; Nie, W.; Sarnela, N.; Prisle, N. L.; Kulmala, M.; Virtanen, A.; Petõjõ, T.; Kerminen, V.-M.
Measurements of the hygroscopicity of 15-145 nm particles in a boreal forest environment were conducted using two Hygroscopicity Tandem Differential Mobility Analyzer (HTDMA) systems during the Pan-European Gas-AeroSOIs-climate interaction Study (PEGASOS) campaign in spring 2013. Measurements of the chemical composition of non-size segregated particles were also performed using a High-Resolution Aerosol Mass Spectrometer (HR-AMS) in parallel with hygroscopicity measurements. On average, the hygroscopic growth factor (HGF) of particles was observed to increase from the morning until afternoon. In case of accumulation mode particles, the main reasons for this behavior were increases in the ratio of sulfate to organic matter and oxidation level (O : C ratio) of the organic matter in the particle phase. Using an O : C dependent hygroscopic growth factor of organic matter (HGForg), fitted using the inverse Zdanovskii-Stokes-Robinson (ZSR) mixing rule, clearly improved the agreement between measured HGF and that predicted based on HR-AMS composition data. Besides organic oxidation level, the influence of inorganic species was tested when using the ZSR mixing rule to estimate the hygroscopic growth factor of organics in the aerosols. While accumulation and Aitken mode particles were predicted fairly well by the bulk aerosol composition data, the hygroscopicity of nucleation mode particles showed little correlation. However, we observed them to be more sensitive to the gas phase concentration of condensable vapors: the more there was sulfuric acid in the gas phase, the more hygroscopic the nucleation mode particles were. No clear dependence was found between the extremely low-volatility organics (ELVOCs) concentration and the HGF of particles of any size.
Model of nucleation and growth of crystals in cooling magmas
Atsushi Toramaru
The nucleation and growth of liquidus phases in cooling magmas at constant rates are modeled taking into account homogeneous\\u000a nucleation, diffusion-limited growth, and depletion of crystallizing component from melt, and the temperature-dependent diffusivity.\\u000a The formulation of governing equations shows that four dimensionless parameters, whose physical meanings are the nucleation\\u000a difficulty, the fusion enthalpy, the ratio of the growth rate to
An approximate method of estimating the maximum saturation, the nucleation rate, and the total number nucleated per second during the laminar flow of a hot vapour¢gas mixture along a tube with cold walls is described. The basis of the approach is that the temperature an...
Assessing nucleation in cloud formation modelling for Brown Dwarf and Exoplanet atmospheres
NASA Astrophysics Data System (ADS)
Lee, Graham; Helling, Christiane; Giles, Helen; Bromley, Stefan
Context. Substellar objects such as Brown Dwarfs and hot Jupiter exoplanets are cool enough that clouds can form in their atmospheres (Helling & Casewell 2014; A&ARv 22)). Unlike Earth, where cloud condensation nuclei are provided by the upward motion of sand or ash, in Brown Dwarf and hot Jupiters these condensation seeds form from the gas phase. This process proceeds in a stepwise chemical reaction of single monomer addition of a single nucleation species, referred to as homogeneous nucleation. The rate at which these seeds form is determined by the local thermodynamic conditions and the chemical composition of the local gas phase. Once the seed particles have formed, multiple materials are thermally stable and grow almost simultaneously by chemical surface reactions. This results in the growth of the condensation seeds to macroscopic particles of ?m size. At the same time, the gas phase becomes depleted. Once temperatures become too high for thermal stability of the cloud particle, it evaporates until its constituents return to the gas phase. Convection from deeper atmospheric layers provides element replenishment to upper, cooler layers allowing the cloud formation process to reach a stationary state (Woitke & Helling 2003; A&A 399). Aims. The most efficient nucleation is a 'winner takes all' process as the losing molecules will condense on the surface of the faster nucleating seed particle. We apply new molecular (TiO2)N-cluster and SiO vapour data to our cloud formation model in order to re-asses the question of the primary nucleation species. Methods. We apply density functional theory (B3LYP, 6-311G(d)) using the computational chemistry package GAUSSIAN 09 to derive updated thermodynamical data for (TiO2)N-clusters as input for our TiO2 seed formation model. We test both TiO2 and SiO as primary nucleates assuming a homogeneous nucleation process and by solving a system of dust moment equations and element conservation for a pre-scribed Brown Dwarf/hot Jupiter DRIFT-PHOENIX atmospheric model temperature-pressure structure. Results. We present updated Gibbs free energies for the new (TiO2)N-clusters. We discuss the effect of this new data on the resulting cloud structure and cloud properties like particle number density, grain sizes and grain composition. We find SiO to be the more efficient nucleation species. However, subsequent SiO condensation onto seed particle mantles result in element depletion, reducing the number density of gaseous SiO and reducing the efficiency of nucleation. Therefore, TiO2 remains therefore the primary nucleation species (Lee et al. 2014; arXiv:1410.6610).
Simulations of strongly phase-separated liquid-gas systems
A. J. Wagner; C. M. Pooley
Lattice Boltzmann simulations of liquid-gas systems are believed to be restricted to modest density ratios of less than 10. In this article we show that reducing the speed of sound and, just as importantly, the interfacial contributions to the pressure allows lattice Boltzmann simulations to achieve high density ratios of 1000 or more. We also present explicit expressions for the limits of the parameter region in which the method gives accurate results. There are two separate limiting phenomena. The first is the stability of the bulk liquid phase. This consideration is specific to lattice Boltzmann methods. The second is a general argument for the interface discretization that applies to any diffuse interface method.
Silicon Nanowire-Based Devices for Gas-Phase Sensing
Cao, Anping; Sudh÷lter, Ernst J.R.; de Smet, Louis C.P.M.
Since their introduction in 2001, SiNW-based sensor devices have attracted considerable interest as a general platform for ultra-sensitive, electrical detection of biological and chemical species. Most studies focus on detecting, sensing and monitoring analytes in aqueous solution, but the number of studies on sensing gases and vapors using SiNW-based devices is increasing. This review gives an overview of selected research papers related to the application of electrical SiNW-based devices in the gas phase that have been reported over the past 10 years. Special attention is given to surface modification strategies and the sensing principles involved. In addition, future steps and technological challenges in this field are addressed. PMID:24368699
Synthesis and Gas Phase Thermochemistry of Germanium-Containing Compounds
Nathan Robert Classen
The driving force behind much of the work in this dissertation was to gain further understanding of the unique olefin to carbene isomerization observed in the thermolysis of 1,1-dimethyl-2-methylenesilacyclobutane by finding new examples of it in other silicon and germanium compounds. This lead to the examination of a novel phenylmethylenesilacyclobut-2-ene, which did not undergo olefin to carbene rearrangement. A synthetic route to methylenegermacyclobutanes was developed, but the methylenegermacyclobutane system exhibited kinetic instability, making the study of the system difficult. In any case the germanium system decomposed through a complex mechanism which may not include olefin to carbene isomerization. However, this work lead to the study of the gas phase thermochemistry of a series of dialkylgermylene precursors in order to better understand the mechanism of the thermal decomposition of dialkylgermylenes. The resulting dialkylgermylenes were found to undergo a reversible intramolecular {beta} C-H insertion mechanism.
Molecular ions of ionic liquids in the gas phase.
Gross, J³rgen H
Ionic liquids form neutral ion pairs (CA) upon evaporation. The softness of the gas-phase ionization of field ionization has been used to generate "molecular ions," CA(+*), of ionic liquids, most probably by neutralization of the anion. In detail, 1-ethyl-3-methylimidazolium-thiocyanate, [C(6)H(11)N(2)](+) [SCN](-), 1-butyl-3-methylimidazolium-tricyanomethide, [C(8)H(15)N(2)](+) [C(4)N(3)](-), N-butyl-3-methylpyridinium-dicyanamide, [C(10)H(16)N](+) [C(2)N(3)](-), and 1-butyl-1-methylpyrrolidinium-bis[(trifluormethyl)sulfonyl]amide, [C(9)H(20)N](+) [C(2)F(6)NO(4)S(2)](-) were used. The assignment as CA(+*) ions, which has been confirmed by accurate mass measurements and misassignments due to thermal decomposition of the ionic liquids, has been ruled out by field desorption and electrospray ionization mass spectrometry of the residues. PMID:18650101
Spin effects in gas-phase organometallic chemistry
Armentrout, P.B.; Wight, C.A.; Dalleska, N.; Schultz, R.H. [Univ. of Utah, Salt Lake City, UT (United States)
Recent work providing evidence of spin-effects on organometallic chemistry in the gas-phase will be presented. The authors` studies have found such effects in three areas. First, different electronic states of atomic transition metal ions can exhibit very different reactivity with small molecules. Second, sequential bond dissociation energies for cationic metal ligand complexes are found to vary nonmonotonically, an observation that has been explained in terms of changes in spin as ligands are removed. Studies that vary the ligand field strength by changing the ligand support this explanation. Third, in the multiphoton dissociation multiphoton ionization (MPD-MPI) spectroscopy of a series of cobalt complexes, the authors have found that increasing the complexity of the ligands or decreasing the photon flux increases the likelihood that the cobalt atom is formed in an excited electronic state. This counterintuitive result can be explained in terms of a propensity for spin-conservation.
Infrared photodissociation spectroscopy of protonated neurotransmitters in the gas phase
NASA Astrophysics Data System (ADS)
MacLeod, N. A.; Simons, J. P.
Protonated neurotransmitters have been produced in the gas phase via a novel photochemical scheme: complexes of the species of interest, 1-phenylethylamine, 2-amino-1-phenylethanol and the diastereo-isomers, ephedrine and pseudoephedrine, with a suitable proton donor, phenol (or indole), are produced in a supersonic expansion and ionized by resonant two photon ionization of the donor. Efficient proton transfer generates the protonated neurotransmitters, complexed to a phenoxy radical. Absorption of infrared radiation, and subsequent evaporation of the phenoxy tag, coupled with time of flight mass spectrometry, provides vibrational spectra of the protonated (and also hydrated) complexes for comparison with the results of quantum chemical computation. Comparison with the conformational structures of the neutral neurotransmitters (established previously) reveals the effect of protonation on their structure. The photochemical proton transfer strategy allows spectra to be recorded from individual laser shots and their quality compares favourably with that obtained using electro-spray or matrix assisted laser desorption ion sources.
Regenerable Air Purification System for Gas-Phase Contaminant Control
NASA Technical Reports Server (NTRS)
Constantinescu, Ileana C.; Finn, John E.; LeVan, M. Douglas; Lung, Bernadette (Technical Monitor)
Tests of a pre-prototype regenerable air purification system (RAPS) that uses water vapor to displace adsorbed contaminants from an adsorbent column have been performed at NASA Ames Research Center. A unit based on this design can be used for removing trace gas-phase contaminants from spacecraft cabin air or from polluted process streams including incinerator exhaust. During the normal operation mode, contaminants are removed from the air on the column. Regeneration of the column is performed on-line. During regeneration, contaminants are displaced and destroyed inside the closed oxidation loop. In this presentation we discuss initial experimental results for the performance of RAPS in the removal and treatment of several important spacecraft contaminant species from air.
Regenerable Air Purification System for Gas-Phase Contaminant Control
NASA Technical Reports Server (NTRS)
Constantinescu, Ileana C.; Qi, Nan; LeVan, M. Douglas; Finn, Cory K.; Finn, John E.; Luna, Bernadette (Technical Monitor)
A regenerable air purification system (RAPS) that uses water vapor to displace adsorbed contaminants from an. adsorbent column into a closed oxidation loop is under development through cooperative R&D between Vanderbilt University and NASA Ames Research Center. A unit based on this design can be used for removing trace gas-phase contaminants from spacecraft cabin air or from polluted process streams including incinerator exhaust. Recent work has focused on fabrication and operation of a RAPS breadboard at NASA Ames, and on measurement of adsorption isotherm data for several important organic compounds at Vanderbilt. These activities support the use and validation of RAPS modeling software also under development at Vanderbilt, which will in turn be used to construct a prototype system later in the project.
Sugar synthesis from a gas-phase formose reaction.
Jalbout, Abraham F; Abrell, Leif; Adamowicz, Ludwik; Polt, Robin; Apponi, A J; Ziurys, L M
Prebiotic possibilities for the synthesis of interstellar ribose through a protic variant of the formose reaction under gas-phase conditions were studied in the absence of any known catalyst. The ion-molecule reaction products, diose and triose, were sought by mass spectrometry, and relevant masses were observed. Ab initio calculations were used to evaluate protic formose mechanism possibilities. A bilateral theoretical and experimental effort yielded a physical model for glycoaldehyde generation whereby a hydronium cation can mediate formaldehyde dimerization followed by covalent bond formation leading to diose and water. These results advance the possibility that ion-molecule reactions between formaldehyde (CH(2)O) and H(3)O(+) lead to formose reaction products and inform us about potential sugar formation processes in interstellar space. PMID:17630839
Tautomeric properties and gas-phase structure of acetylacetone.
Belova, Natalya V; Oberhammer, Heinz; Trang, Nguen Hoang; Girichev, Georgiy V
The tautomeric and structural properties of acetylacetone, CH3C(O)CH2C(O)CH3, have been studied by gas-phase electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 approximation with different basis sets up to aug-cc-pVTZ). The analysis of GED intensities resulted in the presence of 100(3)% of the enol tautomer at 300(5) K and 64(5)% of the enol at 671(7) K. The enol tautomer possesses Cs symmetry with a planar ring and strongly asymmetric hydrogen bond. The diketo form possesses C2 symmetry. The experimental geometric parameters of both tautomeric forms are reproduced very closely by B3LYP/aug-cc-pVTZ and MP2/cc-pVTZ methods. PMID:24758690
Diamond nucleation under bias conditions
NASA Astrophysics Data System (ADS)
St÷ckel, R.; Stammler, M.; Janischowsky, K.; Ley, L.; Albrecht, M.; Strunk, H. P.
The so-called bias pretreatment allows the growth of heteroepitaxial diamond films by plasma chemical vapor deposition on silicon (100) surfaces. We present plan-view and cross-sectional transmission electron micrographs of the substrate surface at different phases of the bias pretreatment. These observations are augmented by measurements of the etch rates of Si, SiC, and different carbon modifications under plasma conditions and the size distribution of oriented diamond crystals grown after bias pretreatment. Based on these results a new model for diamond nucleation under bias conditions is proposed. First, a closed layer of nearly epitaxially oriented cubic SiC with a thickness of about 10 nm is formed. Subplantation of carbon into this SiC layer causes a supersaturation with carbon and results in the subcutaneous formation of epitaxially oriented nucleation centers in the SiC layer. Etching of the SiC during the bias pretreatment as well as during diamond growth brings these nucleation centers to the sample surface and causes the growth of diamonds epitaxially oriented on the Si/SiC substrate.
NASA Astrophysics Data System (ADS)
Vali, G.; DeMott, P.; M÷hler, O.; Whale, T. F.
Progress in the understanding of ice nucleation is being hampered by the lack of uniformity in how some terms are used in the literature. This even extends to some ambiguity of meanings attached to some terms. Suggestions are put forward here for common use of terms. Some are already well established and clear of ambiguities. Others are less engrained and will need a conscious effort in adoption. Evolution in the range of systems where ice nucleation is being studied enhances the need for a clear nomenclature. The ultimate limit in the clarity of definitions is, of course, the limited degree to which ice nucleation processes are understood.
Interfacial process of nucleation and molecular nucleation templator
NASA Astrophysics Data System (ADS)
Liu, X. Y.
Interfacial effects of nucleation inhibition and promotion were identified from the nucleation of paracetamol. Unlike the classic interfacial effects, which are caused by the change in nucleation barrier, the nonepitaxial interfacial effects are only associated with kink integration kinetics. Methylparaben inhibits nucleation by increasing the desolvation free energy barrier, which is revealed as the nonepitaxial interfacial effect of nucleation inhibition. Polysaccharide revealed its nonepitaxial interfacial effects of nucleation promotion by lowering the conformation entropic barrier via liquid molecule preordering. Polysaccharide can be regarded as an example of molecular nucleation promoter based on the nonepitaxial interfacial effects.
Dissipative transformation of non-nucleated dwarf galaxies into nucleated systems
Kenji Bekki; Warrick J. Couch; Yasuhiro Shioya
Recent photometric observations by the {\\it Hubble Space Telescope (HST)} have revealed the physical properties of stellar galactic nuclei in nucleated dwarf galaxies in the Virgo cluster of galaxies. In order to elucidate the formation processes of nucleated dwarfs, we numerically investigate gas dynamics, star formation, and chemical evolution within the central 1 kpc of gas disks embedded within the galactic stellar components of non-nucleated dwarfs. We find that high density, compact stellar systems can be formed in the central regions of dwarfs as a result of dissipative, repeated merging of massive stellar and gaseous clumps developed from nuclear gaseous spiral arms as a result of local gravitational instability. The central stellar components are found to have stellar masses which are typically $~$5% of their host dwarfs and show very flattened shapes, rotational kinematics, and central velocity dispersions significantly smaller than those of their host dwarfs. We also find that more massive dwarfs can develop more massive, more metal-rich, and higher density stellar systems in their central regions, because star formation and chemical enrichment proceed more efficiently owing to the less dramatic suppression of star formation by supernovae feedback effects in more massive dwarfs. Based on these results, we suggest that gas-rich, non-nucleated dwarfs can be transformed into nucleated ones as a result of dissipative gas dynamics in their central regions. We discuss the origin of the observed correlations between physical properties of stellar galactic nuclei and those of their host galaxies.
Comparison of photoluminescence of carbon nanotube/ZnO nanostructures synthesized by gas- and solution-phase transport
NASA Astrophysics Data System (ADS)
Jin, Changhyun; Lee, Seawook; Kim, Chang-Wan; Park, Suyoung; Lee, Chongmu; Lee, Dongjin
Multiwalled carbon nanotubes (MWCNTs)/ZnO heterostructures were synthesized by two different processes: (1) gas-phase transport (GPT) and nucleation of Zn powders and (2) solution-phase transport (SPT) chemical reaction of zinc nitrate solution on the MWCNTs. Transmission electron microscopy and X-ray diffraction analysis indicated that the ZnO nanostructures on the MWCNTs from the GPT and SPT processes were poly- and single-crystal hexagonal wurtzite structure, respectively. The major photoluminescence (PL) spectra of our MWCNT/ZnO hybrid, excited at 380 nm and 550 nm, were presented. The PL intensity of the MWCNT/ZnO coaxial nanostructures behaves differently depending on the ZnO synthesis methods on the MWCNTs. The MWCNT/ZnO heterostructures synthesized using the GPT process were more efficient than those synthesized by SPT process in enhancing the PL intensity around the near-band-edge emission region. However, the emission enhancement around defect region was mostly attributed to increase in the O vacancy concentration in the ZnO on the MWCNTs during the SPT process.
Atomic and molecular physics in the gas phase.
Toburen, L H
The spatial and temporal distributions of energy deposition by high-linear-energy-transfer radiation play an important role in the subsequent chemical and biological processes leading to radiation damage. Because the spatial structures of energy deposition events are of the same dimensions as molecular structures in the mammalian cell, direct measurements of energy deposition distributions appropriate to radiation biology are infeasible. This circumstance has led to the development of models of energy transport based on a knowledge of atomic and molecular interactions that enable one to simulate energy transfer on an atomic scale. Such models require a detailed understanding of the interactions of ions and electrons with biologically relevant material. During the past 20 years, there has been a great deal of progress in our understanding of these interactions, much of it coming from studies in the gas phase. These studies provide information on the systematics of interaction cross sections, and lead to knowledge of the regions of energy deposition where molecular and phase effects are important-knowledge that guides development in appropriate theory. In this report, studies of the doubly differential cross sections, which are crucial to the development of stochastic energy deposition calculations and track structure simulation, are reviewed. We discuss areas of understanding and address directions for future work. Particular attention is given to experimental and theoretical findings that have changed the traditional view of secondary electron production for charged-particle interactions with atomic and molecular targets. PMID:1811483
Full field gas phase velocity measurements in microgravity
NASA Technical Reports Server (NTRS)
Griffin, Devon W.; Yanis, William
Measurement of full-field velocities via Particle Imaging Velocimetry (PIV) is common in research efforts involving fluid motion. While such measurements have been successfully performed in the liquid phase in a microgravity environment, gas-phase measurements have been beset by difficulties with seeding and laser strength. A synthesis of techniques developed at NASA LeRC exhibits promise in overcoming these difficulties. Typical implementation of PIV involves forming the light from a pulsed laser into a sheet that is some fraction of a millimeter thick and 50 or more millimeters wide. When a particle enters this sheet during a pulse, light scattered from the particle is recorded by a detector, which may be a film plane or a CCD array. Assuming that the particle remains within the boundaries of the sheet for the second pulse and can be distinguished from neighboring particles, comparison of the two images produces an average velocity vector for the time between the pulses. If the concentration of particles in the sampling volume is sufficiently large but the particles remain discrete, a full field map may be generated.
Processes forming Gas, Tar, and Coke in Cellulose Gasification from Gas-Phase Reactions of Levoglucosan as Intermediate.
Fukutome, Asuka; Kawamoto, Haruo; Saka, Shiro
The gas-phase pyrolysis of levoglucosan (LG), the major intermediate species during cellulose gasification, was studied experimentally over the temperature range of 400-900?░C. Gaseous LG did not produce any dehydration products, which include coke, furans, and aromatic substances, although these are characteristic products of the pyrolysis of molten LG. Alternatively, at >500?░C, gaseous LG produced only fragmentation products, such as noncondensable gases and condensable C1 -C3 fragments, as intermediates during noncondensable gas formation. Therefore, it was determined that secondary reactions of gaseous LG can result in the clean (tar- and coke-free) gasification of cellulose. Cooling of the remaining LG in the gas phase caused coke formation by the transition of the LG to the molten state. The molecular mechanisms that govern the gas- and molten-phase reactions of LG are discussed in terms of the acid catalyst effect of intermolecular hydrogen bonding to promote the molten-phase dehydration reactions. PMID:26099988
Dislocation nucleation: Diffusive origins
NASA Astrophysics Data System (ADS)
Li, Ju
A growing body of evidence suggests that nucleation of a first dislocation in a pristine crystal is associated with a diffusion-controlled process. Understanding this is critical for strain-engineered devices at ultrahigh stresses.
Simulation of the transfer of water with a fine-disperse gas phase in porous media
NASA Astrophysics Data System (ADS)
Dem'yanov, A. Yu.; Dinariev, O. Yu.; Ivanov, E. N.
The problem on the transfer of a three-phase water-gas-oil mixture in a porous medium was solved for the case where the water contains a fine-disperse gas phase in the form of microsized or nanosized bubbles. It was suggested that the transfer of bubbles is mainly due to the flow of the disperse phase (water). In this case, the large aggregates of the gas phase in the porous space, in the water, and in the oil are transferred in accordance with the modified Darcy law for multiphase mixtures. A mathematical model of movement of the indicated mixture has been constructed for the case where the main phases (water, gas, and oil) adhere to the filtration equations and the fine-disperse gas phase is defined by a kinetic equation like the Boltzmann equation. Some one-dimensional numerical solutions of the indicated problem were analyzed.
Gas-Phase Reactions of Halogen Species of Atmospheric Importance.
NASA Astrophysics Data System (ADS)
Heard, Anne C.
Available from UMI in association with The British Library. Requires signed TDF. A low-pressure discharge-flow technique, with various optical detection methods, has been used to determine bimolecular rate coefficients for a number of reactions in the gas-phase between OH radicals and organic halogen -containing molecules and between NO_3 radicals and the iodine species I_2 and I. These experiments have shown that: (i) the reaction of methyl iodide with OH accounts for approximately 2% of the removal of CH_3I from the troposphere as compared with photolysis; (ii) abstraction of I-atoms from a C-I bond by OH is probable in the gas -phase; (iii) the halogen-containing anaesthetic substances halothane CF_3CCl BrH, enflurane CF_2HOCF _2CFClH, isoflurane CF_2HOCClHCF _3 and sevoflurane (CF_3) _2CHOCFH_2 have significantly shorter tropospheric lifetimes than the fully halogenated CFCs and halons because of reaction with the OH radical and are thus unlikely to be transported up to the stratosphere where they could contribute to the depletion of ozone. Data obtained for reactions between OH and some 'CFC alternatives' along with measurements of the integrated absorption cross -sections of the compounds in the spectral region 800-1200 cm^{-1} were used to calculate ozone depletion potentials (ODP) and greenhouse warming potentials relative to CFCl_3 for each compound. The study of the reactions between OH and CF_3CFBrH and CF _2BrH was used to provide a useful first estimate of the environmental acceptability of these compounds in the context of their possible use as replacements for the conventional CFCs. A method was developed to provide a first estimate of the ODP of a halogenated alkane without use of a complicated (and expensive) computer modeling scheme. A reaction between molecular iodine and the nitrate radical in the gas-phase was discovered and the kinetics of this reaction have been studied. No temperature or pressure dependence was observed for the rate of reaction, the rate constant of which was found to be (1.5 +/- 0.5) times 10 ^{-12}cm^{ -3}molecule^{-1}s ^{-1}. The reaction between I and NO_3 was found to occur at a rate of about 60% of the hard-sphere collision frequency for the two species. The rate constant for reaction between I and NO_3 was found to be (4.5 +/- 1.9) times 10^{-10}cm^3 molecule^{-1}s ^{-1}. An upper limit for the heat of formation of IONO_2 of (21 +/- 3) kJmol^ {-1} was also derived. (Abstract shortened by UMI.).
Energetics of Selected Gas Phase Ion-Molecule Reactions
NASA Astrophysics Data System (ADS)
Paul, Gary John Charles
The energetics of the gas phase negative ion-molecule association reactions M + X^{-} = McdotX^ {-}, where M are substituted benzenes, quinones and ethylenes and X^{-} are the halide ions (F^{-} , Cl^{-}, Br ^{-} and I^{ -}), were determined by equilibrium measurements with the pulsed electron high pressure mass spectrometer (PHPMS). Evaluation of the equilibrium constants for the halide association (XA) reactions leads directly to absolute bond free energy determinations, -DeltaG _sp{XA}{circ}, in McdotX^{- }. Under conditions where halide association equilibria could not be measured directly, relative bond free energies, -DeltaDeltaG _sp{XA}{circ}, were obtained by measurements of the transfer equilibria McdotX^{-} + M^' = M + cdotM^'cdot X^{-}. Combining -DeltaDeltaG_sp {XA}{circ} values with directly determined -DeltaG _sp{XA}{circ} values leads to further absolute bond free energy determinations. The hydrogen bond free energies in the singly substituted phenol complexes YPhOHcdotBr ^{-}, combined with previous data for X^{-} = Cl ^{-} and I^{ -} from this laboratory, are used to examine the substituent effects on hydrogen bonding. The dominant contribution to YPhOHcdotBr ^{-} stabilization, where the extent of proton transfer from YPhOH to Br^{ -} is small, is due to the field effects of the substituents with pi delocalization playing only a small part. Thus, the correlation with the acidity of YPhOH, where pi delocalization is important, is not very close. Substituent effect analysis of experimentally determined bond free energies and quantum mechanical calculations are used to gain structural information on the complexes McdotX^{-} where M does not possess substituents with protic hydrogens. The results indicate the complexes M cdotX^{-} have a variety of structures, depending on X^ {-} and the nature of the substituents. The temperature dependence of the equilibrium constants for the gas phase reactions HO^ - + HOH = HO^-cdotHOH and CH_3O^- + HOCH_3 = CH_3O ^-cdotHOCH_3 was measured with the PHPMS. The enthalpy and entropy changes were obtained from van't Hoff plots of the equilibrium constants. The enthalpy changes were found to be in good agreement with experimentally determined values reported by Meot-Ner and Sieck and recent theoretical results. The agreement for the entropy changes is found not to be as good. The electron affinities of 20 cyclic diones, mostly substituted maleic and phthalic anhydrides and maleimides and phthalimides, were determined with the PHPMS by measuring gas phase electron transfer equilibria A^ {-} + B = A + B^{ -} involving these compounds and reference compounds whose electron affinities were determined previously. The effects of substituents on electron affinities are similar to those observed previously for other groups of organic compounds.
Nucleation of protein fibrillation by nanoparticles.
Linse, Sara; Cabaleiro-Lago, Celia; Xue, Wei-Feng; Lynch, Iseult; Lindman, Stina; Thulin, Eva; Radford, Sheena E; Dawson, Kenneth A
Nanoparticles present enormous surface areas and are found to enhance the rate of protein fibrillation by decreasing the lag time for nucleation. Protein fibrillation is involved in many human diseases, including Alzheimer's, Creutzfeld-Jacob disease, and dialysis-related amyloidosis. Fibril formation occurs by nucleation-dependent kinetics, wherein formation of a critical nucleus is the key rate-determining step, after which fibrillation proceeds rapidly. We show that nanoparticles (copolymer particles, cerium oxide particles, quantum dots, and carbon nanotubes) enhance the probability of appearance of a critical nucleus for nucleation of protein fibrils from human beta(2)-microglobulin. The observed shorter lag (nucleation) phase depends on the amount and nature of particle surface. There is an exchange of protein between solution and nanoparticle surface, and beta(2)-microglobulin forms multiple layers on the particle surface, providing a locally increased protein concentration promoting oligomer formation. This and the shortened lag phase suggest a mechanism involving surface-assisted nucleation that may increase the risk for toxic cluster and amyloid formation. It also opens the door to new routes for the controlled self-assembly of proteins and peptides into novel nanomaterials. PMID:17485668
Gas Phase Nanomaterial Integration Lead P.I. Heiko O. Jacobs*
Jacobs, Heiko O.
1 Gas Phase Nanomaterial Integration Lead P.I. Heiko O. Jacobs* University of Minnesota Engineering Abstract: This letter reports on a new gas phase printing approach to deposit nanomaterials the assembly of nanomaterials into the openings. Directed assembly was observed due to a naturally occurring
Spectroscopic Evidence for Gas Phase Formation of Successive -turns in a Three-Residue Peptide Chain
Paris-Sud XI, Universitķ de
Spectroscopic Evidence for Gas Phase Formation of Successive -turns in a Three-Residue Peptide MN Nieuwegein, The Netherlands Author E-mail : email@example.com Gas phase studies of small biomolecules1 between secondary structures such as -strands, -turns, 27 ribbons, - and 310 helices. In the present
Protein Structure in Vacuo: Gas-Phase Conformations of BPTI and Cytochrome c
Clemmer, David E.
Protein Structure in Vacuo: Gas-Phase Conformations of BPTI and Cytochrome c Konstantin B. Shelimov pancreatic trypsin inhibitor) and cytochrome c ions in the gas phase, as a function of charge. For BPTI into place by three covalent disulfide bridges. For cytochrome c, geometries with cross sections close
Nuclear symmetry energy effects on liquid-gas phase transition in hot asymmetric nuclear matter
Bharat K. Sharma; Subrata Pal
The liquid-gas phase transition in hot asymmetric nuclear matter is investigated within relativistic mean-field model using the density dependence of nuclear symmetry energy constrained from the measured neutron skin thickness of finite nuclei. We find symmetry energy has a significant influence on several features of liquid-gas phase transition. The boundary and area of the liquid-gas coexistence region, the maximal isospin asymmetry and the critical values of pressure and isospin asymmetry all of which systematically increase with increasing softness in the density dependence of symmetry energy. The critical temperature below which the liquid-gas mixed phase exists is found higher for a softer symmetry energy.
Vapor liquid solid-hydride vapor phase epitaxy (VLS-HVPE) growth of ultra-long defect-free GaAs nanowires: Ab initio simulations supporting center nucleation
Andrķ, Yamina, E-mail: email@example.com; Lekhal, Kaddour; Hoggan, Philip; Avit, Geoffrey; Rķda Ramdani, M.; Monier, Guillaume; Colas, David; Ajib, Rabih; Castelluci, Dominique; Gil, Evelyne [Clermont Universitķ, Universitķ Blaise Pascal, Institut Pascal, BP 10448, F-63000 Clermont-Ferrand (France); CNRS, UMR6602, Institut Pascal, F-63171 AubiĶre (France); Cadiz, Fabian; Rowe, Alistair; Paget, Daniel [Physique de la matiĶre condensķe, Ecole Polytechnique CNRS, Palaiseau (France); Petit, Elodie [Clermont Universitķ, Universitķ Blaise Pascal, Institut de Chimie de Clermont-Ferrand, BP 10448, F-63000 Clermont-Ferrand (France); CNRS, UMR 6296, ICCF, F-63171 AubiĶre (France); Leroux, Christine [Universitķ de Toulon, IM2NP, BŌt. R, B.P. 20132, 83957 La Garde Cedex (France); CNRS, UMR 7334, 83957 La Garde Cedex (France); Trassoudaine, AgnĶs [Clermont Universitķ, Universitķ Blaise Pascal, Institut Pascal, BP 10448, F-63000 Clermont-Ferrand (France); CNRS, UMR6602, Institut Pascal, F-63171 AubiĶre (France); Clermont Universitķ, Universitķ dÆAuvergne, BP 10448, F-63000 Clermont-Ferrand (France)
High aspect ratio, rod-like and single crystal phase GaAs nanowires (NWs) were grown by gold catalyst-assisted hydride vapor phase epitaxy (HVPE). High resolution transmission electron microscopy and micro-Raman spectroscopy revealed polytypism-free zinc blende (ZB) NWs over lengths of several tens of micrometers for a mean diameter of 50 nm. Micro-photoluminescence studies of individual NWs showed linewidths smaller than those reported elsewhere which is consistent with the crystalline quality of the NWs. HVPE makes use of chloride growth precursors GaCl of which high decomposition frequency after adsorption onto the liquid droplet catalysts, favors a direct and rapid introduction of the Ga atoms from the vapor phase into the droplets. High influxes of Ga and As species then yield high axial growth rate of more than 100 ?m/h. The diffusion of the Ga atoms in the liquid droplet towards the interface between the liquid and the solid nanowire was investigated by using density functional theory calculations. The diffusion coefficient of Ga atoms was estimated to be 3 ū 10{sup ?9} m{sup 2}/s. The fast diffusion of Ga in the droplet favors nucleation at the liquid-solid line interface at the center of the NW. This is further evidence, provided by an alternative epitaxial method with respect to metal-organic vapor phase epitaxy and molecular beam epitaxy, of the current assumption which states that this type of nucleation should always lead to the formation of the ZB cubic phase.
Establishment phase greenhouse gas emissions in short rotation woody biomass plantations
Turner, Monica G.
Establishment phase greenhouse gas emissions in short rotation woody biomass plantations February 2014 Keywords: SRWC Populus Salix Greenhouse gas balance Bioenergy Land use change a b s t r a c t Uncertainty exists over the magnitude of greenhouse gas (GHG) emissions associated with open land conversion
Importance of the gas phase role to the prediction of energetic material behavior: An experimental study
Ali, A.N.; Son, S.F.; Asay, B.W.; Sander, R.K. [Los Alamos National Laboratory, MS C920, Los Alamos, New Mexico 87544 (United States)
Various thermal (radiative, conductive, and convective) initiation experiments are performed to demonstrate the importance of the gas phase role in combustion modeling of energetic materials (EM). A previously published condensed phase model that includes a predicted critical irradiance above which ignition is not possible is compared to experimental laser ignition results for octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 2,4,6-trinitrotoluene (TNT). Experimental results conflict with the predicted critical irradiance concept. The failure of the model is believed to result from a misconception about the role of the gas phase in the ignition process of energetic materials. The model assumes that ignition occurs at the surface and that evolution of gases inhibits ignition. High speed video of laser ignition, oven cook-off and hot wire ignition experiments captures the ignition of HMX and TNT in the gas phase. A laser ignition gap test is performed to further evaluate the effect of gas phase laser absorption and gas phase disruption on the ignition process. Results indicate that gas phase absorption of the laser energy is probably not the primary factor governing the gas phase ignition observations. It is discovered that a critical gap between an HMX pellet and a salt window of 6 mm{+-}0.4 mm exists below which ignition by CO{sub 2} laser is not possible at the tested irradiances of 29 W/cm{sup 2} and 38 W/cm{sup 2} for HMX ignition. These observations demonstrate that a significant disruption of the gas phase, in certain scenarios, will inhibit ignition, independent of any condensed phase processes. These results underscore the importance of gas phase processes and illustrate that conditions can exist where simple condensed phase models are inadequate to accurately predict the behavior of energetic materials.
Gas Phase Dissociation Behavior of Acyl-Arginine Peptides
McGee, William M.; McLuckey, Scott A.
The gas phase dissociation behavior of peptides containing acyl-arginine residues is investigated. These acylations are generated via a combination of ion/ion reactions between arginine-containing peptides and N-hydroxysuccinimide (NHS) esters and subsequent tandem mass spectrometry (MS/MS). Three main dissociation pathways of acylated arginine, labeled Paths 1-3, have been identified and are dependent on the acyl groups. Path 1 involves the acyl-arginine undergoing deguanidination, resulting in the loss of the acyl group and dissociation of the guanidine to generate an ornithine residue. This pathway generates selective cleavage sites based on the recently discussed ōornithine effectö. Path 2 involves the coordinated losses of H2O and NH3 from the acyl-arginine side chain while maintaining the acylation. We propose that Path 2 is initiated via cyclization of the ?-nitrogen of arginine and the C-terminal carbonyl carbon, resulting in rapid rearrangement from the acyl-arginine side chain and the neutral losses. Path 3 occurs when the acyl group contains ?-hydrogens and is observed as a rearrangement to regenerate unmodified arginine while the acylation is lost as a ketene. PMID:24465154
Surface plasmon sensing of gas phase contaminants using optical fiber.
Thornberg, Steven Michael; White, Michael I.; Rumpf, Arthur Norman; Pfeifer, Kent Bryant
Fiber-optic gas phase surface plasmon resonance (SPR) detection of several contaminant gases of interest to state-of-health monitoring in high-consequence sealed systems has been demonstrated. These contaminant gases include H{sub 2}, H{sub 2}S, and moisture using a single-ended optical fiber mode. Data demonstrate that results can be obtained and sensitivity is adequate in a dosimetric mode that allows periodic monitoring of system atmospheres. Modeling studies were performed to direct the design of the sensor probe for optimized dimensions and to allow simultaneous monitoring of several constituents with a single sensor fiber. Testing of the system demonstrates the ability to detect 70mTorr partial pressures of H{sub 2} using this technique and <280 {micro}Torr partial pressures of H{sub 2}S. In addition, a multiple sensor fiber has been demonstrated that allows a single fiber to measure H{sub 2}, H{sub 2}S, and H{sub 2}O without changing the fiber or the analytical system.
Application of modified moments method for kinetics description of nano-, micro-particles formation in gas phase
A. Durov; M. Deminsky; M. Strelkova; B. V. Potapkin
The description of dynamics of particles size distribution function (PDF) in processes of new phase formation is important task in various technologies. Moments method is one of modern approaches which meet demands of accuracy and moderate usage of computer resources. Modified moments method which permits one to describe correctly both particles growth (in results of nucleation, coagulation and surface reactions)
Crystal nucleation and cluster-growth kinetics in a model glass under shear
Paris-Sud XI, Universitķ de
Crystal nucleation and cluster-growth kinetics in a model glass under shear Anatolii V. Mokshin1, 2010) Crystal nucleation and growth processes induced by an externally applied shear strain in a model The study of phase transformation between liquid and crystal through a nucleation and subsequent growth
A comparison of heterogeneous ice nucleation parameterizations using a parcel model framework
Trude Eidhammer; Paul J. DeMott; Sonia M. Kreidenweis
A liquid-phase Lagrangian parcel model was expanded to include nucleation and growth of ice crystals. Intercomparisons between three heterogeneous ice nucleation parameterizations that link aerosol type and number to ice crystal concentration were conducted. Results indicate large differences in the prediction of ice formation in modestly supercooled clouds and in the susceptibility of cirrus to heterogeneous ice nucleation for the
Binary nucleation and condensation in associated vapors
NASA Astrophysics Data System (ADS)
Studzi?ski, W.; Spiegel, G. H.; Zahoransky, R. A.
The binary nucleation theory is extended to include vapor phase association. Similar to the effects found for pure vapors, two opposite influences due to stable association complexes have been derived. A kinetic one increases the nucleation rate and a larger, thermodynamic effect acts contradictory. The developed theory is applied to the water-acetic acid system. Extensive experiments were performed in the unsteady rarefaction wave of a preheated shock tube. The variation of the measured critical supersaturation as a function of mixture composition was found to agree well with the predictions of the theory.
In previous publications (McMurry and Wilson, 1982; McMurry et al., 1981), techniques for determining the relative contributions of gas phase and liquid phase reactions to secondary ambient aerosol formation have been described. In this paper these methods are applied to more rec...
Carrier Gas Dependent Evaporation Energy of GaN Estimated from Spiral Growth Rates in Selective-Area Metalorganic Vapor Phase Epitaxy
NASA Astrophysics Data System (ADS)
Akasaka, Tetsuya; Kobayashi, Yasuyuki; Kasu, Makoto; Yamamoto, Hideki
GaN was grown in spiral growth mode by metalorganic vapor phase epitaxy in selective areas having screw-type dislocations. Relationships between the growth rate and supersaturation provide a novel way to estimate the evaporation energy of GaN, which turns out to be carrier gas dependent: 4.3▒0.9 eV for N2 and 2.1▒0.4 eV for H2. The latter is significantly smaller, probably due to enhanced etching by H2. Suppression of excessive nucleation by etching in H2 may be responsible for the formation of step-free GaN surfaces at low temperatures in selective areas free from screw-type dislocations.
Source apportionment of wintertime gas-phase and particle-phase air pollutants using organic compounds as tracers
James J. Schauer; Glen R. Cass
Two chemical mass balance receptor models are developed which can determine the source contributions to atmospheric pollutant concentrations using organic compounds as tracers. The first model uses particle-phase organic compounds to apportion the primary source contribution to atmospheric fine particulate organic carbon concentrations and fine particle mass concentrations. The second receptor model simultaneously uses both volatile gas-phase hydrocarbon and particle-phase
Fragile-to-fragile liquid transition at Tg and stable-glass phase nucleation rate maximum at the Kauzmann temperature TK
NASA Astrophysics Data System (ADS)
Tournier, Robert F.
An undercooled liquid is unstable. The driving force of the glass transition at Tg is a change of the undercooled-liquid Gibbs free energy. The classical Gibbs free energy change for a crystal formation is completed including an enthalpy saving. The crystal growth critical nucleus is used as a probe to observe the Laplace pressure change ?p accompanying the enthalpy change -Vmū?p at Tg where Vm is the molar volume. A stable glass-liquid transition model predicts the specific heat jump of fragile liquids at T?Tg, the Kauzmann temperature TK where the liquid entropy excess with regard to crystal goes to zero, the equilibrium enthalpy between TK and Tg, the maximum nucleation rate at TK of superclusters containing magic atom numbers, and the equilibrium latent heats at Tg and TK. Strong-to-fragile and strong-to-strong liquid transitions at Tg are also described and all their thermodynamic parameters are determined from their specific heat jumps. The existence of fragile liquids quenched in the amorphous state, which do not undergo liquid-liquid transition during heating preceding their crystallization, is predicted. Long ageing times leading to the formation at TK of a stable glass composed of superclusters containing up to 147 atom, touching and interpenetrating, are evaluated from nucleation rates. A fragile-to-fragile liquid transition occurs at Tg without stable-glass formation while a strong glass is stable after transition.
Fragile-to-fragile Liquid Transition at Tg and Stable-Glass Phase Nucleation Rate Maximum at the Kauzmann Temperature TK
Robert Felix Tournier
An undercooled liquid is unstable. The driving force of the glass transition at Tg is a change of the undercooled-liquid Gibbs free energy. The classical Gibbs free energy change for a crystal formation is completed including an enthalpy saving. The crystal growth critical nucleus is used as a probe to observe the Laplace pressure change Dp accompanying the enthalpy change -Vm *Dp at Tg where Vm is the molar volume. A stable glass-liquid transition model predicts the specific heat jump of fragile liquids at temperatures smaller than Tg, the Kauzmann temperature TK where the liquid entropy excess with regard to crystal goes to zero, the equilibrium enthalpy between TK and Tg, the maximum nucleation rate at TK of superclusters containing magic atom numbers, and the equilibrium latent heats at Tg and TK. Strong-to-fragile and strong-to-strong liquid transitions at Tg are also described and all their thermodynamic parameters are determined from their specific heat jumps. The existence of fragile liquids quenched in the amorphous state, which do not undergo liquid-liquid transition during heating preceding their crystallization, is predicted. Long ageing times leading to the formation at TK of a stable glass composed of superclusters containing up to 147 atoms, touching and interpenetrating, are evaluated from nucleation rates. A fragile-to-fragile liquid transition occurs at Tg without stable-glass formation while a strong glass is stable after transition.
Homogeneous crystal nucleation in binary metallic melts
NASA Technical Reports Server (NTRS)
Thompson, C. V.; Spaepen, F.
A method for calculating the homogeneous crystal nucleation frequency in binary metallic melts is developed. The free energy of crystallization is derived from regular solution models for the liquid and solid and is used, together with model-based estimates of the interfacial tension, to calculate the nucleation frequency from the classical theory. The method can account for the composition dependence of the maximum undercooling observed in a number of experiments on small droplet dispersions. It can also be used to calculate the driving force for crystal growth and to obtain more precise estimates of the homogeneous crystal nucleation frequency in glass-forming alloys. This method, although approximate, is simple to apply, and requires only knowledge of the phase diagram and a few readily available thermodynamic quantities as input data.
Microgravity nucleation and particle coagulation experiments support
NASA Technical Reports Server (NTRS)
Lilleleht, L. U.; Lass, T. J.
A hollow sphere model is developed to predict the range of supersaturation ratio values for refractory metal vapors in a proposed experimental nucleation apparatus. Since the experiments are to be carried out in a microgravity environment, the model neglects the effects of convection and assumes that the only transfer of vapors through an inert gas atmosphere is by conduction and molecular diffusion. A consistent set of physical properties data is assembled for the various candidate metals and inert ambient gases expected to be used in the nucleation experiments. Transient partial pressure profiles are computed for the diffusing refractory species for two possible temperature distributions. The supersaturation ratio values from both candidate temperature profiles are compared with previously obtained experimetnal data on a silver-hydrogen system. The model is used to simulate the diffusion of magnesium vapor through argon and other inert gas atmospheres over ranges of initial and boundary conditions. These results identify different combinations of design and operating parameters which are liekly to produce supersaturation ratio values high enough to induce homogeneous nucleation in the apparatus being designed for the microgravity nucleation experiments.
Molecular Dynamics Simulation of Homogeneous Crystal Nucleation in Polyethylene
Yi, Peng
Using a realistic united-atom force field, molecular dynamics simulations were performed to study homogeneous nucleation of the crystal phase at about 30% supercooling from the melts of n-pentacontahectane (C150) and a ...
The Relative Importance of Aqueous-Phase and Gas-Phase Phenol Oxidation as Sources of SOA (Invited)
NASA Astrophysics Data System (ADS)
Anastasio, C.; Smith, J.
The oxidation of phenols is a source of secondary organic aerosol (SOA) in the gas phase as well as in aqueous phases (e.g., cloud and fog drops and water-containing aerosol particles). The relative importance of the gas- and aqueous-phase pathways depends largely on three factors: (1) the partitioning of phenols between the gaseous and condensed phases, (2) the rates of reaction in each phase, and (3) the yields of SOA in each phase. Our goal in this work is to determine the relative importance of these two pathways as sources of SOA. Using previously published rate constants, as well as newly determined kinetics and SOA yield data in the aqueous phase, we find that in a cloudy atmosphere both aqueous- and gas-phase sinks are significant for phenols with high vapor pressures (e.g., phenol itself), but that aqueous-phase sinks can dominate for phenols with lower vapor pressures (e.g., phenols with multiple hydroxy or methoxy substituents). In regions with wood combustion (a major source of phenols), our calculations indicate that destruction of phenols within wood smoke particles is very important and that reaction with particulate triplet excited states is a major sink.
Methane-to-Methanol Conversion by Gas-Phase Transition Metal Oxide Cations: Experiment and Theory
Metz, Ricardo B.
Methane-to-Methanol Conversion by Gas-Phase Transition Metal Oxide Cations: Experiment and Theory-phase transition metal oxide cations can convert methane to methanol. Methane activation by MO+ is discussed-phase transition metal oxides with methane are thus a simple model system for the direct conversion of methane
Proton irradiation of DNA nucleosides in the gas phase.
Poully, Jean-Christophe; Miles, Jordan; De Camillis, Simone; Cassimi, Amine; Greenwood, Jason B
The four DNA nucleosides guanosine, adenosine, cytidine and thymidine have been produced in the gas phase by a laser thermal desorption source, and irradiated by a beam of protons with 5 keV kinetic energy. The molecular ions as well as energetic neutrals formed have been analyzed by mass spectrometry in order to shed light on the ionization and fragmentation processes triggered by proton collision. A range of 8-20 eV has been estimated for the binding energy of the electron captured by the proton. Glycosidic bond cleavage between the base and sugar has been observed with a high probability for all nucleosides, resulting in predominantly intact base ions for guanosine, adenosine, and cytidine but not for thymidine where intact sugar ions are dominant. This behavior is influenced by the ionization energies of the nucleobases (G < A < C < T), which seems to determine the localization of the charge following the initial ionization. This charge transfer process can also be inferred from the production of protonated base ions, which have a similar dependence on the base ionization potential, although the base proton affinity might also play a role. Other dissociation pathways have also been identified, including further fragmentation of the base and sugar moieties for thymidine and guanosine, respectively, and partial breakup of the sugar ring without glycosidic bond cleavage mainly for adenosine and cytidine. These results show that charge localization following ionization by proton irradiation is important in determining dissociation channels of isolated nucleosides, which could in turn influence direct radiation damage in DNA. PMID:25691342
IV-VI semiconductor lasers for gas phase biomarker detection
NASA Astrophysics Data System (ADS)
McCann, Patrick; Namjou, Khosrow; Roller, Chad; McMillen, Gina; Kamat, Pratyuma
A promising absorption spectroscopy application for mid-IR lasers is exhaled breath analysis where sensitive, selective, and speedy measurement of small gas phase biomarker molecules can be used to diagnose disease and monitor therapies. Many molecules such as nitric oxide, ethane, formaldehyde, acetaldehyde, acetone, carbonyl sulfide, and carbon disulfide have been connected to diseases or conditions such as asthma, oxidative stress, breast cancer, lung cancer, diabetes, organ transplant rejection, and schizophrenia. Measuring these and other, yet to be discovered, biomarker molecules in exhaled breath with mid-IR lasers offers great potential for improving health care since such tests are non-invasive, real-time, and do not require expensive consumables or chemical reagents. Motivated by these potential benefits, mid-IR laser spectrometers equipped with presently available cryogenically-cooled IV-VI lasers mounted in compact Stirling coolers have been developed for clinical research applications. This paper will begin with a description of the development of mid-IR laser instruments and their use in the largest known exhaled breath clinical study ever performed. It will then shift to a description of recent work on the development of new IV-VI semiconductor quantum well materials and laser fabrication methods that offer the promise of low power consumption (i.e. efficient) continuous wave emission at room temperature. Taken together, the demonstration of compelling clinical applications with large market opportunities and the clear identification of a viable pathway to develop low cost mid-IR laser instrumentation can create a renewed focus for future research and development efforts within the mid-IR materials and devices area.
Gas-Phase Combustion Synthesis of Nonoxide Nanoparticles in Microgravity
NASA Technical Reports Server (NTRS)
Axelbaum, R. L.; Kumfer, B. M.; Sun, Z.; Chao, B. H.
Gas-phase combustion synthesis is a promising process for creating nanoparticles for the growing nanostructure materials industry. The challenges that must be addressed are controlling particle size, preventing hard agglomerates, maintaining purity, and, if nonoxides are synthesized, protecting the particles from oxidation and/or hydrolysis during post-processing. Sodium-halide Flame Encapsulation (SFE) is a unique methodology for producing nonoxide nanoparticles that addresses these challenges. This flame synthesis process incorporates sodium and metal-halide chemistry, resulting in nanoparticles that are encapsulated in salt during the early stages of their growth in the flame. Salt encapsulation has been shown to allow control of particle size and morphology, while serving as an effective protective coating for preserving the purity of the core particles. Metals and compounds that have been produced using this technology include Al, W, Ti, TiB2, AlN, and composites of W-Ti and Al-AlN. Oxygen content in SFE synthesized nano- AlN has been measured by neutron activation analysis to be as low as 0.54wt.%, as compared to over 5wt.% for unprotected AlN of comparable size. The overall objective of this work is to study the SFE process and nano-encapsulation so that they can be used to produce novel and superior materials. SFE experiments in microgravity allow the study of flame and particle dynamics without the influence of buoyancy forces. Spherical sodium-halide flames are produced in microgravity by ejecting the halide from a spherical porous burner into a quiescent atmosphere of sodium vapor and argon. Experiments are performed in the 2.2 sec Drop Tower at the NASA-Glenn Research Center. Numerical models of the flame and particle dynamics were developed and are compared with the experimental results.
Gas-Phase Combustion Synthesis of Aluminum Nitride Powder
NASA Technical Reports Server (NTRS)
Axelbaum, R. L.; Lottes, C. R.; Huertas, J. I.; Rosen, L. J.
Due to its combined properties of high electrical resistivity and high thermal conductivity aluminum nitride (AlN) is a highly desirable material for electronics applications. Methods are being sought for synthesis of unagglomerated, nanometer-sized powders of this material, prepared in such a way that they can be consolidated into solid compacts having minimal oxygen content. A procedure for synthesizing these powders through gas-phase combustion is described. This novel approach involves reacting AlCl3, NH3, and Na vapors. Equilibrium thermodynamic calculations show that 100% yields can be obtained for these reactants with the products being AlN, NaCl, and H2. The NaCl by-product is used to coat the AlN particles in situ. The coating allows for control of AlN agglomeration and protects the powders from hydrolysis during post-flame handling. On the basis of thermodynamic and kinetic considerations, two different approaches were employed to produce the powder, in co-flow diffusion flame configurations. In the first approach, the three reactants were supplied in separate streams. In the second, the AlCl3 and NH3 were premixed with HCl and then reacted with Na vapor. X-ray diffraction (XRD) spectra of as-produced powders show only NaCl for the first case and NaCl and AlN for the second. After annealing at 775 C tinder dynamic vacuum, the salt was removed and XRD spectra of powders from both approaches show only AlN. Aluminum metal was also produced in the co-flow flame by reacting AlCl3 with Na. XRD spectra of as-produced powders show the products to be only NaCl and elemental aluminum.
Dissociative electron attachment to the gas-phase nucleobase hypoxanthine
NASA Astrophysics Data System (ADS)
Dawley, M. Michele; Tanzer, Katrin; Carmichael, Ian; Denifl, Stephan; Ptasi?ska, Sylwia
We present high-resolution measurements of the dissociative electron attachment (DEA) to isolated gas-phase hypoxanthine (C5H4N4O, Hyp), a tRNA purine base. The anion mass spectra and individual ion efficiency curves from Hyp were measured as a function of electron energy below 9 eV. The mass spectra at 1 and 6 eV exhibit the highest anion yields, indicating possible common precursor ions that decay into the detectable anionic fragments. The (Hyp - H) anion (C5H3N4O-) exhibits a sharp resonant peak at 1 eV, which we tentatively assign to a dipole-bound state of the keto-N1H,N9H tautomer in which dehydrogenation occurs at either the N1 or N9 position based upon our quantum chemical computations (B3LYP/6-311+G(d,p) and U(MP2-aug-cc-pVDZ+)) and prior studies with adenine. This closed-shell dehydrogenated anion is the dominant fragment formed upon electron attachment, as with other nucleobases. Seven other anions were also observed including (Hyp - NH)-, C4H3N4-/C4HN3O-, C4H2N3-, C3NO-/HC(HCN)CN-, OCN-, CN-, and O-. Most of these anions exhibit broad but weak resonances between 4 and 8 eV similar to many analogous anions from adenine. The DEA to Hyp involves significant fragmentation, which is relevant to understanding radiation damage of biomolecules.
Dissociative electron attachment to the gas-phase nucleobase hypoxanthine.
Dawley, M Michele; Tanzer, Katrin; Carmichael, Ian; Denifl, Stephan; Ptasi?ska, Sylwia
We present high-resolution measurements of the dissociative electron attachment (DEA) to isolated gas-phase hypoxanthine (C5H4N4O, Hyp), a tRNA purine base. The anion mass spectra and individual ion efficiency curves from Hyp were measured as a function of electron energy below 9 eV. The mass spectra at 1 and 6 eV exhibit the highest anion yields, indicating possible common precursor ions that decay into the detectable anionic fragments. The (Hyp - H) anion (C5H3N4O(-)) exhibits a sharp resonant peak at 1 eV, which we tentatively assign to a dipole-bound state of the keto-N1H,N9H tautomer in which dehydrogenation occurs at either the N1 or N9 position based upon our quantum chemical computations (B3LYP/6-311+G(d,p) and U(MP2-aug-cc-pVDZ+)) and prior studies with adenine. This closed-shell dehydrogenated anion is the dominant fragment formed upon electron attachment, as with other nucleobases. Seven other anions were also observed including (Hyp - NH)(-), C4H3N4 (-)/C4HN3O(-), C4H2N3 (-), C3NO(-)/HC(HCN)CN(-), OCN(-), CN(-), and O(-). Most of these anions exhibit broad but weak resonances between 4 and 8 eV similar to many analogous anions from adenine. The DEA to Hyp involves significant fragmentation, which is relevant to understanding radiation damage of biomolecules. PMID:26049525
Quantum phases of a one-dimensional dipolar Fermi gas
NASA Astrophysics Data System (ADS)
Mosadeq, Hamid; Asgari, Reza
We quantitatively obtain the quantum ground-state phases of a Fermi system with on-site and dipole-dipole interactions in one-dimensional lattice chains within the density matrix renormalization group. We show, at a given spin polarization, the existence of six phases in the phase diagram and find that the phases are highly dependent on the spin degree of freedom. These phases can be constructed using available experimental techniques.
Clear evidence of fluorescence resonance energy transfer in gas-phase ions.
Dashtiev, Maxim; Azov, Vladimir; Frankevich, Vladimir; Scharfenberg, Ludwig; Zenobi, Renato
Fluorescence resonance energy transfer (FRET) is a distance-sensitive method that correlates changes in fluorescence intensity with conformational changes, for example, of biomolecules in the cellular environment. Applied to the gas phase in combination with Fourier transform ion cyclotron resonance mass spectrometry, it opens up possibilities to define structural/conformational properties of molecular ions, in the absence of solvent, and without the need for purification of the sample. For successfully observing FRET in the gas phase it is important to find suitable fluorophores. In this study several fluorescent dyes were examined, and the correlation between solution-phase and gas-phase fluorescence data were studied. For the first time, FRET in the gas phase is demonstrated unambiguously. PMID:16023366
Stages of homogeneous nucleation in solid isotopic helium mixtures.
Poole, M; Saunders, J; Cowan, B
We have made pressure and NMR measurements during the evolution of phase separation in solid helium isotopic mixtures. Our observations indicate clearly all three stages of the homogeneous nucleation-growth process: (1) creation of nucleation sites; (2) growth of the new-phase component at these nucleation sites; and (3) coarsening: the dissolution of subcritical droplets with the consequent further late-stage growth of the supercritical droplets. The time exponent for the coarsening, a=1/3, is consistent with the conserved order parameter Lifshitz-Slezov evaporation-condensation mechanism. PMID:18352566
Parameter identification in non-isothermal nucleation and growth processes
NASA Astrophysics Data System (ADS)
H÷mberg, Dietmar; Lu, Shuai; Sakamoto, Kenichi; Yamamoto, Masahiro
We study non-isothermal nucleation and growth phase transformations, which are described by a generalized Avrami model for the phase transition coupled with an energy balance to account for recalescence effects. The main novelty of our work is the identification of temperature dependent nucleation rates. We prove that such rates can be uniquely identified from measurements in a subdomain and apply an optimal control approach to develop a numerical strategy for its computation.
Application of gamma densitometry and statistical signal analysis to gas phase velocity measurements in pipeline hydrotransport
NASA Astrophysics Data System (ADS)
Zych, Marcin; Hanus, Robert; Petryka, Leszek; ?wisulski, Dariusz; Strz?powicz, Anna; Zych, Piotr
The work presents selected methods of signal analysis used in the processing of data obtained from radiometric probes. The used data came from an exemplary study of a two-phase liquid-gas flow at the laboratory installation. In such rigs many possible transport types may be observed, i.e. slug, plug and bubble flow, and each of them gives different signal-to-noise ratio of recorded data. Therefore, available radiometric methods of gas phase velocity measurements give diverse accuracies. Authors consider several improvements of data acquisition and processing which increase possibility of the flow type recognition and higher accuracy of the gas phase velocity estimation.
The gas-phase thermal chemistry of tetralin and related model systems
Malandra, J.
The thesis is divided into 5 papers: gas-phase thermal decomposition of tetralin; flash vacuum pyrolysis of 3-benzocycloheptenone and 1,3, 4,5-tetrahydro-2-benzothiepin-2,2-dioxide (model systems for gas-phase pyrolysis of tetralin); high-temperature gas-phase reactions of o-allylbenzyl radicals generated by flash vacuum pyrolysis of is(o-allylbenzyl) oxalate; flash vacuum pyrolysis of 1,4-diphenylbutane; and flash vacuum pyrolysis of o-allyltoluene, o-(3-butenyl)toluene and o-(pentenyl)toluene were also used.
Kenneth C. Russell
The homogeneous nucleation theory of Lothe and Pound is extended to condensation on ions. A rate equation is derived that gives the frequency of droplet formation on an attenuated concentration of gaseous ions in supersaturated unary vapors. This treatment predicts little catalytic effect of ions in contrast to the classical theories of Volmer and of Becker and Doering, which predict
Steady-State and Dynamic Modeling of Gas-Phase Polypropylene Processes Using Stirred-Bed Reactors
Liu, Y. A.
Steady-State and Dynamic Modeling of Gas-Phase Polypropylene Processes Using Stirred-Bed Reactors for the continuous gas-phase synthesis of polypropylene using stirred-bed reactors. The model considers the important and techniques used to develop a comprehensive model for a gas-phase polypropylene process using stirred
An Experimental Investigation of Gas-Phase Combustion Synthesis of SiO2 Nanoparticles Using a Multi-Element
Wooldridge, Margaret S.
An Experimental Investigation of Gas-Phase Combustion Synthesis of SiO2 Nanoparticles Using a Multi of an experimental investigation of gas-phase combustion synthesis of silica (SiO2) particles using a multi of the MEDB in providing a controlled environment for fundamental studies of gas-phase combustion synthesis
On the ice nucleation spectrum
NASA Astrophysics Data System (ADS)
Barahona, D.
This work presents a novel formulation of the ice nucleation spectrum, i.e. the function relating the ice crystal concentration to cloud formation conditions and aerosol properties. The new formulation relies on a statistical view of the ice nucleation process and explicitly accounts for the dependency of the ice crystal concentration on temperature, supersaturation, cooling rate, and particle size, and, in the case of heterogeneous ice nucleation, on the distributions of particle area and surface composition. The new formulation is used to generate ice nucleation parameterizations for the homogeneous freezing of cloud droplets and the heterogeneous deposition ice nucleation on dust and soot ice nuclei. For homogeneous freezing, it was found that by increasing the dispersion in the droplet volume distribution the fraction of supercooled droplets in the population increases. For heterogeneous ice nucleation it was found that ice nucleation on efficient ice nuclei (IN) shows features consistent with the singular hypothesis (characterized by a lack of temporal dependency of the ice nucleation spectrum) whereas less efficient IN tend to display stochastic behavior. Analysis of empirical nucleation spectra suggested that inferring the aerosol heterogeneous ice nucleation properties from measurements of the onset supersaturation and temperature may carry significant error as the variability in ice nucleation properties within the aerosol population is not accounted for. This work provides a simple and rigorous ice nucleation framework were theoretical predictions, laboratory measurements and field campaign data can be reconciled, and that is suitable for application in atmospheric modeling studies.
Experimental Tests of Nucleation Theory
Jack Yuen Dea
In recent years there has been controversy surrounding experimental nucleation data that did not conform to classical nucleation theory. More recent data, however, suggest good agreement between theory and experiment. At the Desert Research Institute (DRI), it was decided to perform sensitive tests of nucleation in soluble aerosol particles using newly developed instruments and techniques. Very steady aerosol generation was
An investigation into the flow behavior of a single phase gas system and a two phase gas/liquid system in normal gravity with nonuniform heating from above
NASA Technical Reports Server (NTRS)
Disimile, Peter J.; Heist, Timothy J.
The fluid behavior in normal gravity of a single phase gas system and a two phase gas/liquid system in an enclosed circular cylinder heated suddenly and nonuniformly from above was investigated. Flow visualization was used to obtain qualitative data on both systems. The use of thermochromatic liquid crystal particles as liquid phase flow tracers was evaluated as a possible means of simultaneously gathering both flow pattern and temperature gradient data for the two phase system. The results of the flow visualization experiments performed on both systems can be used to gain a better understanding of the behavior of such systems in a reduced gravity environment and aid in the verification of a numerical model of the system.
Energetics of protein nucleation on rough polymeric surfaces.
Curcio, Efrem; Curcio, Valerio; Di Profio, Gianluca; Fontananova, Enrica; Drioli, Enrico
Metropolis Monte Carlo (MC) algorithm of the two-dimensional Ising model is used to study the heterogeneous nucleation of protein crystals on rough polymeric surfaces. The theoretical findings are compared to those obtained from classical nucleation theory (CNT), and to experimental data from protein model hen egg white lysozyme (HEWL) crystallized on poly(vinylidene fluoride) or PVDF, poly(dimethylsiloxane) or PDMS and Hyflon homemade membranes. The reduction of the activation energy for the nucleation process on polymeric membranes, predicted to occur at increasing surface roughness, results in a nucleation kinetics that is many orders of magnitude faster than in homogeneous phase. In general, MC stochastic dynamics offers the unique opportunity to investigate the effects of collective molecular aggregation at site level on the nucleation rate and, consequently, allows to identify optimal morphological and structural properties of polymeric membranes for a fine control of the crystallization kinetics. PMID:20939543
Structures and Aggregation States of Fluoromethyllithium and Chloromethyllithium Carbenoids in the Gas Phase and in Ethereal
Ramachandran, Bala (Ramu)
in the gas-phase structures. At the most complete level of theory the 173 K standard-state free energy species is the carbenoid, free carbene liberated from the carbenoid, or both. Seebach and co-workers were
Gas Phase Studies of N-Heterocyclic Carbene-Catalyzed Condensation Reactions.
Tian, Yuan; Lee, Jeehiun K
N-Heterocyclic carbenes (NHCs) catalyze Umpolung condensation reactions of carbonyl compounds, including the Stetter reaction. These types of reactions have not heretofore been examined in the gas phase. Herein, we explore the feasibility of examining these reactions in the absence of solvent. A charge-tagged thiazolylidene catalyst is used to track the reactions by mass spectrometry. We find that the first Umpolung step, the addition of the NHC catalyst to a carbonyl compound to form the "Breslow intermediate", does not readily proceed in the gas phase, contrary to the case in solution. The use of acylsilanes in place of the carbonyl compounds appears to solve this issue, presumably because of a favorable Brook rearrangement. The second addition reaction, with enones, does not occur under our gas phase conditions. These reactions do occur in solution; the differential reactivity between the condensed and gas phases is discussed, and calculations are used to aid in the interpretation of the results. PMID:26066314
An analytical method has been developed to determine the chloroethene series, tetrachloroethene (PCE), trichloroethene (TCE),cisdichloroethene (cis-DCE) andtransdichloroethene (trans-DCE) in environmental biotreatment studies using gas chromatography coupled with a solid phase mi...
Partitioning of formaldehyde between gas phase and particles (PM2.5) in Mķxico City
An annular denuder\\/filter-pack sampling technique has been employed to get an insight of the formaldehyde partitioning between gas phase and particles (PM2.5) in Mķxico City using short time sampling periods. Formaldehyde was trapped using DNPH derivatives and analyzed by HPLC\\/UV. One annular denuder was used to trap formaldehyde from the gas phase followed by a Teflon filter to trap PM2.5,
The Nuclear Liquid-Gas Phase Transition: Q.E.D
V. E. Viola
For the past decade, intense experimental effort has been devoted to the search for a liquid-gas phase transition in highly excited nuclei. Now, synthesis of the large body of existing multifragmentation data provides a strong case for identification of this phenomenon. In this presentation we discuss several salient features of the data that support their interpretation in terms of a spinodal liquid-gas phase transition.
The determination of compressibility factors of gaseous butane-nitrogen mixtures in the gas phaseĀ
Evans, Robert Buckner
THE DETERMINATION OF COMPRESSIBILITY FACTORS OF GASEOUS BUTANE-NITROGEN MIXTURES IN THE GAS PHASE A D issertation By Robert Buckner Evans, III Approved as to style and content by: (Chairman of Committee) (Head of^ 'ent Advisor) June 1955... ?-; i'i i ; A R y ? 'A 'Gi- Or- T EX AS THE DETERMINATION OF COMHIESSIBILITI FACTORS OF GASEOUS BUTANE-NITROGEN MIXTURES IN THE GAS PHASE A D issertation By ROBERT BUCKNER EVANS, III Submitted' to the Graduate School of the Agricultural...
Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species
Hall, G.E.
This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. Chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry are investigated by high resolution spectroscopic tools. Production, reaction, and energy transfer processes are investigated by transient, double resonance, polarization and saturation spectroscopies, with an emphasis on technique development and connection with theory, as well as specific molecular properties.
An atmospheric pressure flow reactor: Gas phase kinetics and mechanism in tropospheric conditions without wall effects
NASA Technical Reports Server (NTRS)
Koontz, Steven L.; Davis, Dennis D.; Hansen, Merrill
A new type of gas phase flow reactor, designed to permit the study of gas phase reactions near 1 atm of pressure, is described. A general solution to the flow/diffusion/reaction equations describing reactor performance under pseudo-first-order kinetic conditions is presented along with a discussion of critical reactor parameters and reactor limitations. The results of numerical simulations of the reactions of ozone with monomethylhydrazine and hydrazine are discussed, and performance data from a prototype flow reactor are presented.
Simulation of Gas-Phase Kinetics in CHF3:H2: O2 Mixtures
Dmitry G. Voloshin; Konstantin S. Klopovskiy; Yuri A. Mankelevich; Nikolay A. Popov; Tatyana V. Rakhimova; Alexander T. Rakhimov
A gas-phase reaction model for and mixtures was developed. Self-consistent electron impact cross-section set for was introduced. The original total and partial dissociation cross sections were received. A developed gas-phase kinetic scheme was tested on the experimental data. An important role of the chain reactions in the kinetics of F and H atoms and radicals was revealed.
The determination of compressibility factors of gaseous butane-nitrogen mixtures in the gas phase
Evans, Robert Buckner
THE DETERMINATION OF COMPRESSIBILITY FACTORS OF GASEOUS BUTANE-NITROGEN MIXTURES IN THE GAS PHASE A D issertation By Robert Buckner Evans, III Approved as to style and content by: (Chairman of Committee) (Head of^ 'ent Advisor) June 1955... ?-; i'i i ; A R y ? 'A 'Gi- Or- T EX AS THE DETERMINATION OF COMHIESSIBILITI FACTORS OF GASEOUS BUTANE-NITROGEN MIXTURES IN THE GAS PHASE A D issertation By ROBERT BUCKNER EVANS, III Submitted' to the Graduate School of the Agricultural...
Formation of complex organic molecules in cold objects: the role of gas-phase reactions
NASA Astrophysics Data System (ADS)
Balucani, Nadia; Ceccarelli, Cecilia; Taquet, Vianney
While astrochemical models are successful in reproducing many of the observed interstellar species, they have been struggling to explain the observed abundances of complex organic molecules. Current models tend to privilege grain surface over gas-phase chemistry in their formation. One key assumption of those models is that radicals trapped in the grain mantles gain mobility and react on lukewarm ( ? 30 K) dust grains. Thus, the recent detections of methyl formate (MF) and dimethyl ether (DME) in cold objects represent a challenge and may clarify the respective role of grain-surface and gas-phase chemistry. We propose here a new model to form DME and MF with gas-phase reactions in cold environments, where DME is the precursor of MF via an efficient reaction overlooked by previous models. Furthermore, methoxy, a precursor of DME, is also synthesized in the gas phase from methanol, which is desorbed by a non-thermal process from the ices. Our new model reproduces fairly well the observations towards L1544. It also explains, in a natural way, the observed correlation between DME and MF. We conclude that gas-phase reactions are major actors in the formation of MF, DME and methoxy in cold gas. This challenges the exclusive role of grain-surface chemistry and favours a combined grain-gas chemistry.
Degradation of phenol in water using a gas¢liquid phase pulsed discharge plasma reactor
Jie Li; Masayuki Sato; Takayuki Ohshima
In this paper, a gas¢liquid phase pulsed discharge plasma reactor was used to dispose phenol in aqueous solutions. The effect of pulsed peak voltage and energy, solution conductivity, solution pH, and additive gas varieties on degradation efficiency of phenol was reviewed in the research. The observed results showed that degradation efficiency of phenol increased with the increase of pulsed peak
Photocatalytic destruction of toluene and xylene at gas phase on a titania based monolithic catalyst
J. Blanco; P. Avila; A. Bahamonde; E. Alvarez; B. Sßnchez; M. Romero
Toluene and xylene were subjected to gas-solid heterogeneous photocatalytic oxidation on a titania based monolithic catalyst, in order to investigate the potential of solar-driven detoxification as a clean and safe method for air purification and gas phase waste destruction. Thus, gaseous streams with toluene or xylene were conducted through a monolithic catalysts based on titania dispersed on a fibrous silicate
This report details the Superfund Innovative Technology Evaluation of Eco Logic International's gas-phase chemical reduction process, with an emphasis on their Reactor System. he Eco Logic process employees a high temperature reactor filled with hydrogen gas as the means to destr...
The patented Eco Logic Process employs a gas-phase reduction reaction of hydrogen with organic and chlorinated organic compounds at elevated temperatures to convert aqueous and oily hazardous contaminants into a hydrocarbon-rich gas product. After passing through a scrubber, the ...
Magnetizabilities and Nuclear Shielding Constants of the Fluoromethanes in the Gas Phase and Solution
Helgaker, Trygve
Magnetizabilities and Nuclear Shielding Constants of the Fluoromethanes in the Gas Phase and Solution Per-Olof A░ strand,*,, Kurt V. Mikkelsen,, Kenneth Ruud,¦ and Trygve Helgaker¦ Department are discussed, and it is demonstrated that they must be included in order to reproduce the experimental gas
ORIGINAL PAPER Gas-Phase Hydroformylation of Propene over Silica-Supported
Iglesia, Enrique
ORIGINAL PAPER Gas-Phase Hydroformylation of Propene over Silica-Supported PPh3-Modified Rhodium Hydroformylation ┴ Butanal ┴ Heterogeneous ┴ Rhodium ┴ Silica ┴ Supported 1 Introduction Aldehydes are produced industrially by hydroformylation of olefins with synthesis gas. Homogeneous complexes of Rh and Co
A High Phase-Space-Density Gas of Polar Molecules
K.-K. Ni; S. Ospelkaus; M. H. G. de Miranda; A. Pe'er; B. Neyenhuis; J. J. Zirbel; S. Kotochigova; P. S. Julienne; D. S. Jin; J. Ye
A quantum gas of ultracold polar molecules, with long-range and anisotropic interactions, not only would enable explorations of a large class of many-body physics phenomena but also could be used for quantum information processing. We report on the creation of an ultracold dense gas of potassium-rubidium (40K87Rb) polar molecules. Using a single step of STIRAP (stimulated Raman adiabatic passage) with
Two-stage coal liquefaction without gas-phase hydrogen
Stephens, H.P.
A process is provided for the production of a hydrogen-donor solvent useful in the liquefaction of coal, wherein the water-gas shift reaction is used to produce hydrogen while simultaneously hydrogenating a donor solvent. A process for the liquefaction of coal using said solvent is also provided. The process enables avoiding the use of a separate water-gas shift reactor as well as high pressure equipment for liquefaction. 3 tabs.
Ionic liquids as stationary phases in gas chromatography--an LSER investigation of six commercial phases and some applications.
Weber, Waldemar; Andersson, Jan T
The separation properties of six novel stationary phases for gas chromatography, commercially available from Sigma-Aldrich (Supelco) and based on ionic liquids (ILs), were investigated. The linear solvation energy relationship model (LSER) was used to describe the molecular interactions between these stationary phases and 30 solutes. The solutes belong to different groups of compounds, like haloalkanes, alcohols, ketones, aromatics, aliphatics, and others. A good description of different interactions, as described by the LSER model, could be achieved. The calculated values of system constants for the ionic liquid phases were compared with constants of commonly used standard phases like a 5Ā% phenyl/95Ā% dimethyl siloxane and a polyethylene glycol phase. The solute descriptors are in good agreement with those found by previous authors who have used the LSER model for 44 different ionic liquids as stationary phase. The experiments were carried out at two temperatures to evaluate the influence on the phase parameters and separation characteristics. The interactions of different functional groups with the IL phases are discussed. These novel IL phases are a promising replacement of or an addition to common polar phases. Based on the evaluated phase properties, several possibilities for applications of these novel phases are shown. PMID:24965162
Phase transitions in the two-dimensional electron-hole gas
NASA Astrophysics Data System (ADS)
Kezerashvili, Roman; Berman, Oleg; Ziegler, Klaus
For a gas of spatially separated electrons and holes with tunable Coulomb interaction and variable density a first order phase transition between a Bardeen-Cooper-Schrieffer (BCS) phase and an insulating Mott phase is predicted. The phase diagram is obtained in the framework of a BCS-like mean-field approach and a Landau expansion in terms of the pairing order parameter. This phase diagram indicates several phases and phase transitions, including an electron-hole plasma at low density and weak interaction, an intermediate BCS phase with Cooper pairs and an electron-hole plasma at high density and weak interaction. The insulating Mott phase appears for the strong interaction and low temperatures. The possibilities to realize these phases in realistic systems such as coupled quantum wells and graphene double layers are discussed.
Microgravity nucleation and particle coagulation experiments support
NASA Technical Reports Server (NTRS)
Lilleleht, L. U.; Ferguson, F. T.; Stephens, J. R.
Modifications to the nucleation apparatus suggested by our first microgravity flight campaign are complete. These included a complete 'repackaging' of the equipment into three racks along with an improved vapor spout shutter mechanism and additional thermocouples for gas temperature measurements. The 'repackaged' apparatus was used in two KC-135 campaigns: one during the week of June 3, 1991 consisting of two flights with Mg and two with Zn, and another series consisting of three flights with Zn during the week of September 23, 1991. Our effort then was focused on the analysis of these data, including further development of the mathematical models to generate the values of temperature and supersaturation at the observed points of nucleation. The efforts to apply Hale's Scaled Nucleation Theory to our experimental data have met with only limited success, most likely due to still inadequate temperature field determination. Work on the development of a preliminary particle collector system designed to capture particles from the region of nucleation and condensation, as well as from other parts of the chamber, are discussed.
Nucleation in Synoptically Forced Cirrostratus
NASA Technical Reports Server (NTRS)
Lin, R.-F.; Starr, D. OC.; Reichardt, J.; DeMott, P. J.
Formation and evolution of cirrostratus in response to weak, uniform and constant synoptic forcing is simulated using a one-dimensional numerical model with explicit microphysics, in which the particle size distribution in each grid box is fully resolved. A series of tests of the model response to nucleation modes (homogeneous-freezing-only/heterogeneous nucleation) and heterogeneous nucleation parameters are performed. In the case studied here, nucleation is first activated in the prescribed moist layer. A continuous cloud-top nucleation zone with a depth depending on the vertical humidity gradient and one of the nucleation parameters is developed afterward. For the heterogeneous nucleation cases, intermittent nucleation zones in the mid-upper portion of the cloud form where the relative humidity is on the rise, because existent ice crystals do not uptake excess water vapor efficiently, and ice nuclei (IN) are available. Vertical resolution as fine as 1 m is required for realistic simulation of the homogeneous-freezing-only scenario, while the model resolution requirement is more relaxed in the cases where heterogeneous nucleation dominates. Bulk microphysical and optical properties are evaluated and compared. Ice particle number flux divergence, which is due to the vertical gradient of the gravity-induced particle sedimentation, is constantly and rapidly changing the local ice number concentration, even in the nucleation zone. When the depth of the nucleation zone is shallow, particle number concentration decreases rapidly as ice particles grow and sediment away from the nucleation zone. When the depth of the nucleation zone is large, a region of high ice number concentration can be sustained. The depth of nucleation zone is an important parameter to be considered in parametric treatments of ice cloud generation.
High GVF and low pressure gas¢liquid two-phase flow measurement based on dual-cone flowmeter
Fusheng Zhang; Feng Dong; Chao Tan
Parameter measurement of gas¢liquid two-phase flows with a high gas volume fraction (GVF) has received great attention in the research field of multiphase flow. The cone meter, as a new proposed differential pressure (DP) meter, is increasingly being applied in flowrate measurement of gas¢liquid two-phase flow. A dual-parameter measurement method of gas¢liquid two-phase flow based on a dual-cone meter is
Influence of the carrier gas molar mass on the particle formation in a vapor phase.
Braun, S; R÷mer, F; Kraska, T
The influence of the molar mass of a carrier gas on the formation of nanoparticles in the vapor phase is investigated. The function of the carrier gas atmosphere is the regulation of the particle temperature by collisions with the cluster surface. The aim of this work is to optimize the carrier gas in a simulation in order to mimic a large amount of carrier gas atoms by few gas atoms with effective parameters. In this context the efficiency of the heat exchange with the carrier gas depending on its molar mass is analyzed. As a result one finds for varying molar masses and unchanged interaction parameters a competition between the efficiency and the number of the collisions. For too small molar masses the energy exchange per collision is too small while for too high masses the carrier gas atoms become very slow, decreasing the number of collisions. PMID:19691389
Influence of the carrier gas molar mass on the particle formation in a vapor phase
NASA Astrophysics Data System (ADS)
Braun, S.; R÷mer, F.; Kraska, T.
The influence of the molar mass of a carrier gas on the formation of nanoparticles in the vapor phase is investigated. The function of the carrier gas atmosphere is the regulation of the particle temperature by collisions with the cluster surface. The aim of this work is to optimize the carrier gas in a simulation in order to mimic a large amount of carrier gas atoms by few gas atoms with effective parameters. In this context the efficiency of the heat exchange with the carrier gas depending on its molar mass is analyzed. As a result one finds for varying molar masses and unchanged interaction parameters a competition between the efficiency and the number of the collisions. For too small molar masses the energy exchange per collision is too small while for too high masses the carrier gas atoms become very slow, decreasing the number of collisions.
Control of gas phase nanoparticle shape and its effect on MRI relaxivity
NASA Astrophysics Data System (ADS)
Akta?, S?tk?; Thornton, Stuart C.; Binns, Chris; Lari, Leonardo; Pratt, Andrew; Kr÷ger, Roland; Horsfield, Mark A.
We have used a sputtering gas aggregation source to produce Fe@FeO nanoparticles with different shapes, by annealing them at different temperatures in the gas phase. Without annealing, the most common shape found for the nanoparticles is cubic but annealing the nanoparticles at 1129 ░C transforms the cubes into cuboctahedra. Measurements of the MRI relaxivity show that the cubic nanoparticles have a higher performance by a factor of two, which is attributed to a higher saturation magnetization for this shape. This indicates that the shape-control enabled by gas-phase synthesis is important for obtaining optimal performance in applications.
A pressure cell for nonresonant inelastic x-ray scattering studies of gas phases
Minzer, M.; Bradley, J. A.; Musgrave, R.; Seidler, G. T. [Physics Department, University of Washington, Seattle, Washington 98195 (United States); Skilton, A. [Mechanical Engineering Department, University of Washington, Seattle, Washington 98195 (United States)
We report the design and performance of a gas-phase sample cell for measurements of momentum transfer (q) dependent nonresonant inelastic x-ray scattering (NRIXS). NRIXS measurements from He gas at 2 MPa (20 bars) readily demonstrate dipole-allowed and dipole-forbidden final states for two-electron excitations. Direct comparison of gas-phase NRIXS measurements with the corresponding nonresonant electron energy loss spectroscopy results (EELS) will be a valuable method for characterizing systematic errors in either technique for studies that require absolute normalization of the double differential cross section.
Separation of gas from liquid in a two-phase flow system
NASA Technical Reports Server (NTRS)
Hayes, L. G.; Elliott, D. G.
Separation system causes jets which leave two-phase nozzles to impinge on each other, so that liquid from jets tends to coalesce in center of combined jet streams while gas phase is forced to outer periphery. Thus, because liquid coalescence is achieved without resort to separation with solid surfaces, cycle efficiency is improved.
Investigation of the formation of iron nanoparticles from the gas phase by molecular dynamics simulation
N. L³mmen; T. Kraska
The formation of iron particles from the supersaturated gas phase is investigated by molecular dynamics simulation. The atomic interaction is modelled with a recent parameterization of the embedded atom method which is able to describe the bcc phase of bulk iron. The influence of the state conditions such as temperature and density on the growth mechanisms of the iron particles
Molecular Orbital Studies of Zinc Oxide Chemical Vapor Deposition: Gas-Phase Radical Reactions
Schlegel, H. Bernhard
Molecular Orbital Studies of Zinc Oxide Chemical Vapor Deposition: Gas-Phase Radical Reactions-phase reactions involved in the radical mechanism for zinc oxide chemical vapor deposition have been examined in the radical and closed shell mechanisms for zinc oxide chemical vapor deposition shows that the barrier
Simultaneous study of gas phase and secondary organic aerosols' chemical composition
Paris-Sud XI, Universitķ de
of oxygenated Semi-Volatile Organic Compounds (SVOCs). SVOCs partition between gas and particulate phases or biogenic Volatile Organic Compounds (VOCs) with atmospheric oxidants (OH, O3, NO3) leading to the formation and particulate phases simultaneously and allowing : - Characterization of secondary compounds partitioning
Supplemental Information The potential for organic compounds to partition from the gas phase to the condensed phase
Meskhidze, Nicholas
. As an example, we calculate July 2003 averages for aqueous partitioned organic aerosol concentrations Supplemental Information The potential for organic compounds to partition from the gas phase that arise when a simplified Henry's Law approach is used. Equation S1 Where: CJ
Development of techniques for measurement of gas-phase hydrogen peroxide
Shen, J.; Tanner, R.L.; Kelly, T.J.
The techniques of measuring gas-phase hydrogen peroxide by impinger and diffusion scrubber have been extensively investigated. The mass transfer of collected peroxide in a diffusion scrubber is discussed. The equation describing collection of soluble substances by diffusion scrubber is given for low and high gas flow rates. Gaseous hydrogen peroxide in ambient air can be collected by impinger or scrubber without artifact formation of hydrogen peroxide if O/sub 3/ is first removed by gas-phase reaction with nitric oxide. Losses of gas-phase hydrogen peroxide in the sampling tubing and in the scrubber have been quantified. In sampling of gas-phase H/sub 2/O/sub 2/ in ambient air at Brookhaven National Laboratory and in Los Angeles, a total of 180 samples were collected by impinger and 330 by diffusion scrubber. The ambient levels and the diurnal variation of gas-phase H/sub 2/O/sub 2/ are discussed and perhaps indicate the range of observed H/sub 2/O/sub 2/ levels. Data collected simultaneously by impinger and scrubber collection methods are compared, and the causes of lower than predicted recovery efficiency from the scrubber are discussed. 24 refs., 15 figs., 11 tabs.
The Vaguries of Pyroxene Nucleation and the Resulting Chondrule Textures
NASA Technical Reports Server (NTRS)
Lofgren, G. E.; Le, L.
Pyroxene is a major phase in chondrules, but often follows olivine in the crystallization sequence and depending on the melting temperature and time may not nucleate readily upon cooling. Dynamic crystallization experiments based on total or near total melting were used to study PO (porphyritic olivine) and PP (Porphyritic pyroxene) compositions as defined by. The experiments showed that pyroxene nucleated only at subliquidus temperatures in the PP melts and rarely in the PO melts. Porphyritic chondrules with phenocrysts of both olivine and pyroxene (POP chondrules) were not easily produced in the experiments. POP chondrules are common and it is important for deciphering their formation that we understand pyroxene nucleation properties of chondrule melts.
On the ice nucleation spectrum
NASA Astrophysics Data System (ADS)
Barahona, D.
This work presents a novel formulation of the ice nucleation spectrum, i.e. the function relating the ice crystal concentration to cloud formation conditions and aerosol properties. The new formulation is physically-based and explicitly accounts for the dependency of the ice crystal concentration on temperature, supersaturation, cooling rate, and particle size, surface area and composition. This is achieved by introducing the concepts of ice nucleation coefficient (the number of ice germs present in a particle) and nucleation probability dispersion function (the distribution of ice nucleation coefficients within the aerosol population). The new formulation is used to generate ice nucleation parameterizations for the homogeneous freezing of cloud droplets and the heterogeneous deposition ice nucleation on dust and soot ice nuclei. For homogeneous freezing, it was found that by increasing the dispersion in the droplet volume distribution the fraction of supercooled droplets in the population increases. For heterogeneous ice nucleation the new formulation consistently describes singular and stochastic behavior within a single framework. Using a fundamentally stochastic approach, both cooling rate independence and constancy of the ice nucleation fraction over time, features typically associated with singular behavior, were reproduced. Analysis of the temporal dependency of the ice nucleation spectrum suggested that experimental methods that measure the ice nucleation fraction over few seconds would tend to underestimate the ice nuclei concentration. It is shown that inferring the aerosol heterogeneous ice nucleation properties from measurements of the onset supersaturation and temperature may carry significant error as the variability in ice nucleation properties within the aerosol population is not accounted for. This work provides a simple and rigorous ice nucleation framework where theoretical predictions, laboratory measurements and field campaign data can be reconciled, and that is suitable for application in atmospheric modeling studies.
On the Ice Nucleation Spectrum
NASA Technical Reports Server (NTRS)
Barahona, D.
This work presents a novel formulation of the ice nucleation spectrum, i.e. the function relating the ice crystal concentration to cloud formation conditions and aerosol properties. The new formulation is physically-based and explicitly accounts for the dependency of the ice crystal concentration on temperature, supersaturation, cooling rate, and particle size, surface area and composition. This is achieved by introducing the concepts of ice nucleation coefficient (the number of ice germs present in a particle) and nucleation probability dispersion function (the distribution of ice nucleation coefficients within the aerosol population). The new formulation is used to generate ice nucleation parameterizations for the homogeneous freezing of cloud droplets and the heterogeneous deposition ice nucleation on dust and soot ice nuclei. For homogeneous freezing, it was found that by increasing the dispersion in the droplet volume distribution the fraction of supercooled droplets in the population increases. For heterogeneous ice nucleation the new formulation consistently describes singular and stochastic behavior within a single framework. Using a fundamentally stochastic approach, both cooling rate independence and constancy of the ice nucleation fraction over time, features typically associated with singular behavior, were reproduced. Analysis of the temporal dependency of the ice nucleation spectrum suggested that experimental methods that measure the ice nucleation fraction over few seconds would tend to underestimate the ice nuclei concentration. It is shown that inferring the aerosol heterogeneous ice nucleation properties from measurements of the onset supersaturation and temperature may carry significant error as the variability in ice nucleation properties within the aerosol population is not accounted for. This work provides a simple and rigorous ice nucleation framework where theoretical predictions, laboratory measurements and field campaign data can be reconciled, and that is suitable for application in atmospheric modeling studies.
Organic hydrogen gas sensor with palladium-coated ?-phase poly(vinylidene fluoride) thin films
NASA Astrophysics Data System (ADS)
Imai, Yuji; Kimura, Yasuo; Niwano, Michio
We have proposed an organic hydrogen gas sensor in which palladium (Pd)-coated ?-phase poly(vinylidene fluoride) (PVDF) films are utilized. Volume expansion of the Pd thin film caused by absorption of hydrogen gas is monitored by a piezoelectric thin film of PVDF attached to the Pd films. We have developed a simple method of synthesizing ?-phase PVDF films from ?-phase PVDF powder by using a wet process in which a mixture of acetone and hexamethylphosphoric triamide is used as the solvent for the PVDF powder. The sensor works by itself at room temperature without a power source.
Gas phase effect on characteristics of a precessing vortex in the axisymmetric hydrodynamic chamber
NASA Astrophysics Data System (ADS)
Vinokurov, A. P.; Shtork, S. I.; Alekseenko, S. V.
The work deals with the experimental study of precessing vortex in the gas-liquid swirl flow. The data on flow visualization are presented, dependences of precession frequency and pressure drop on the gas flow rate are determined, and correlation between these characteristics, which undergo abrupt changes at low gas contents, is determined. The main effect determining the nature of evolution of the flow parameters relates to the fact that due to strong flow swirl, phase separation with formation of a hollow vortex with the gas core occurs.
A FIRE-ACE/SHEBA Case Study of Mixed-Phase Arctic Boundary Layer Clouds: Entrainment Rate Limitations on Rapid Primary Ice Nucleation Processes
Shupe, Matthew
sink is sedimentation. Large-eddy simu- lations with size-resolved microphysics are initializedA FIRE-ACE/SHEBA Case Study of Mixed-Phase Arctic Boundary Layer Clouds: Entrainment Rate, in final form 2 August 2011) ABSTRACT Observations of long-lived mixed-phase Arctic boundary layer clouds
Phenolic oxime copper complexes: a gas phase investigationĀ
Roach, Benjamin David
This thesis explores the use of mass spectrometry to define the strengths, and understand solution phase speciation of phenolic oxime-based solvent extractants of the types used in the hydrometallurgical recovery of ...
The development of an instrument for continuously monitoring SO2 levels in flue gas is proposed. The SO2 will be detected by means of an electrochemical sensor cell, which operates in a three-electrode potentiostatic mode. The proposed innovation is develop-ment of an advan...
Integrated gasification combined cycle (IGCC) is a new coal gasification technique that efficiently uses the hot (900-1500░C) generated syngas to power both steam and gas turbines. Due to regulations, this syngas must be free of sulfur and purification is normally carried ...
Abatement of Gas-Phase MercuryŚRecent Developments
Benjaram M. Reddy; Naga Durgasri; Thallada Vinod Kumar; Suresh K. Bhargava
Among various pollutants, mercury has a significant impact on the environment, human beings, and wildlife with its different forms, namely, elemental mercury (Hg), oxidized mercury (Hg), and particle-bound mercury (Hgp). Mercury dispersions mainly occur from coal burning, which is the world's major energy source. Among the three forms, Hg and Hgp are relatively easy to remove from the flue gas
Development and Evaluation of Gold-Centered Monolayer Protected Nanoparticle Stationary Phases for Gas Chromatography
Gross, Gwen M.; Grate, Jay W.; Synovec, Robert E.
The current status for the development of novel open-tubular gas chromatography (GC) stationary phases consists of thin films of gold-centered monolayer protected nanoparticles (MPNs) is reported. Dodecanethiol MPNs, in which the monolayer is dodecanethiol linked to the gold nanoparticle, have shown great promise as a GC stationary phase with efficient columns having been produced in a variety of capillary i.d.'s with stationary phase film depths ranging from 10-60 nm, +/- 2 nm at a given film depth. Stationary phase operational parameters are discussed including maximum operating temperature, sample capacity, and stationary phase lifetime and robustness.
Nucleation of silicon nanocrystals in a remote plasma without subsequent coagulation
NASA Astrophysics Data System (ADS)
Do?an, Ilker; Weeks, Stephen L.; Agarwal, Sumit; van de Sanden, Mauritius C. M.
We report on the growth mechanism of spherical silicon nanocrystals in a remote expanding Ar plasma using a time-modulated SiH4 gas injection in the microsecond time range. Under identical time-modulation parameters, we varied the local density of the SiH4 gas by changing its stagnation pressure on the injection line over the range of 0.1-2.0 bar. We observed that nanocrystals were synthesized in a size range from ś2 to ś50 nm with monocrystalline morphology. Smaller nanocrystals (ś2-6 nm) with narrower size distributions and with higher number densities were synthesized with an increase of the SiH4 gas-phase density. We related this observation to the rapid depletion of the number density of the molecules, ions, and radicals in the plasma during nanocrystal growth, which can primarily occur via nucleation with no significant subsequent coagulation. In addition, in our remote plasma environment, rapid cooling of the gas in the particle growth zone from ś1500 to ś400 K significantly reduces the coalescence rate of the nanoparticles, which makes the coagulation process highly unlikely. Our observations on nanocrystal formation via nucleation indicated that subsequent coagulation for further growth is not always an essential step on nanoparticle formation.
Excitations and Stripe Phase Formation in a Two-Dimensional Dipolar Bose Gas with Tilted Polarization
NASA Astrophysics Data System (ADS)
Macia, A.; Hufnagl, D.; Mazzanti, F.; Boronat, J.; Zillich, R. E.
We present calculations of the ground state and excitations of an anisotropic dipolar Bose gas in two dimensions, realized by a nonperpendicular polarization with respect to the system plane. For sufficiently high density, an increase of the polarization angle leads to a density instability of the gas phase in the direction where the anisotropic interaction is strongest. Using a dynamic many-body theory, we calculate the dynamic structure function in the gas phase which shows the anisotropic dispersion of the excitations. We find that the energy of roton excitations in the strongly interacting direction decreases with increasing polarization angle and almost vanishes close to the instability. Exact path integral ground state Monte Carlo simulations show that this instability is indeed a quantum phase transition to a stripe phase, characterized by long-range order in the strongly interacting direction.
Identification of Ice Nucleation Active Sites on Silicate Dust Particles
NASA Astrophysics Data System (ADS)
Zolles, Tobias; Burkart, Julia; Hõusler, Thomas; Pummer, Bernhard; Hitzenberger, Regina; Grothe, Hinrich
Mineral dusts originating from Earth's crust are known to be important atmospheric ice nuclei. In agreement with earlier studies, feldspar was found as the most active of the tested natural mineral dusts [1-3]. Nevertheless, among those structures K-feldspar showed by far the highest ice nucleation activity. In this study, the reasons for its activity and the difference in the activity of the different feldspars were investigated in closer details. Conclusions are drawn from scanning electron microscopy, X-ray powder diffraction, infrared spectroscopy, and oil-immersion freezing experiments. We give a potential explanation of the increased ice nucleation activity of K-feldspar. The ice nucleating sites are very much dependent on the alkali ion present by altering the water structure and the feldspar surface. The higher activity of K-feldspar can be attributed to the presence of potassium ions on the surface and surface bilayer. The alkali-ions have different hydration shells and thus an influence on the ice nucleation activity of feldspar. Chaotropic behavior of Calcium and Sodium ions are lowering the ice nucleation potential of the other feldspars, while kosmotropic Potassium has a neutral or even positive effect. Furthermore we investigated the influence of milling onto the ice nucleation of quartz particles. The ice nucleation activity can be increased by mechanical milling, by introducing more molecular, nucleation active defects to the particle surface. This effect is larger than expected by plane surface increase. [1] Atkinson et al. The Importance of Feldspar for Ice Nucleation by Mineral Dust in Mixed-Phase Clouds. Nature 2013, 498, 355-358. [2] Yakobi-Hancock et al.. Feldspar Minerals as Efficient Deposition Ice Nuclei. Atmos. Chem. Phys. 2013, 13, 11175-11185. [3] Zolles et al. Identification of Ice Nucleation Active Sites on Feldspar Dust Particles. J. Phys. Chem. A 2015 accepted.
Third-order gas-liquid phase transition and the nature of Andrews critical Tian Ma and Shouhong Wang
Wang, Shouhong
Third-order gas-liquid phase transition and the nature of Andrews critical point Tian Ma-order gas-liquid phase transition and the nature of Andrews critical point Tian Ma1 and Shouhong Wang2 1 is to study the nature of the Andrews critical point in the gas-liquid transition in a physical
Liquid to solid nucleation via onion structure droplets
NASA Astrophysics Data System (ADS)
Barros, Kipton; Klein, W.
We study homogeneous nucleation from a deeply quenched metastable liquid to a spatially modulated phase. We find, for a general class of density functional theories, that the universally favored nucleating droplet in dimensions d ? 3 is spherically symmetric with radial modulations resembling the layers of an onion. The existence of this droplet has important implications for systems with effective long-range interactions, and potentially applies to polymers, plasmas, and metals.
Transient nucleation in condensed systems
NASA Technical Reports Server (NTRS)
Kelton, K. F.; Greer, A. L.; Thompson, C. V.
Using classical nucleation theory we consider transient nucleation occurring in a one-component, condensed system under isothermal conditions. We obtain an exact closed-form expression for the time dependent cluster populations. In addition, a more versatile approach is developed: a numerical simulation technique which models directly the reactions by which clusters are produced. This simulation demonstrates the evolution of cluster populations and nucleation rate in the transient regime. Results from the simulation are verified by comparison with exact analytical solutions for the steady state. Experimental methods for measuring transient nucleation are assessed, and it is demonstrated that the observed behavior depends on the method used. The effect of preexisting cluster distributions is studied. Previous analytical and numerical treatments of transient nucleation are compared to the solutions obtained from the simulation. The simple expressions of Kashchiev are shown to give good descriptions of the nucleation behavior.
Numerical Computation of Flame Spread over a Thin Solid in Forced Concurrent Flow with Gas-phase Radiation
NASA Technical Reports Server (NTRS)
Jiang, Ching-Biau; T'ien, James S.
Excerpts from a paper describing the numerical examination of concurrent-flow flame spread over a thin solid in purely forced flow with gas-phase radiation are presented. The computational model solves the two-dimensional, elliptic, steady, and laminar conservation equations for mass, momentum, energy, and chemical species. Gas-phase combustion is modeled via a one-step, second order finite rate Arrhenius reaction. Gas-phase radiation considering gray non-scattering medium is solved by a S-N discrete ordinates method. A simplified solid phase treatment assumes a zeroth order pyrolysis relation and includes radiative interaction between the surface and the gas phase.
Nova Dust Nucleation: Kinetics and Photodissociation
D. J. Johnson; M. W. Friedlander; J. I. Katz
Dust is observed to form in nova ejecta. The grain temperature is determined by the diluted nova radiation field rather than the gas kinetic temperature, making classical nucleation theory inapplicable. We used kinetic equations to calculate the growth of carbon nuclei in these ejecta. For expected values of the parameters too many clusters grew, despite the small sticking probability of atoms to small clusters, and the clusters only reached radii of about 100\\AA\\ when the carbon vapor was depleted. We then included the effects of cluster photodissociation by ultraviolet radiation from the nova. This suppresses nucleation, but too well, and no grains form at all. Finally we suggest that a few growing carbon nuclei may be protected from photodissociation by a sacrificial surface layer of hydrogen.
Gas phase condensation of superparamagnetic iron oxide-silica nanoparticles - control of the intraparticle phase distribution
NASA Astrophysics Data System (ADS)
St÷tzel, C.; Kurland, H.-D.; Grabow, J.; M³ller, F. A.
Spherical, softly agglomerated and superparamagnetic nanoparticles (NPs) consisting of maghemite (?-Fe2O3) and amorphous silica (SiO2) were prepared by CO2 laser co-vaporization (CoLAVA) of hematite powder (?-Fe2O3) and quartz sand (SiO2). The ?-Fe2O3 portion of the homogeneous starting mixtures was gradually increased (15 mass%-95 mass%). It was found that (i) with increasing iron oxide content the NPs' morphology changes from a nanoscale SiO2 matrix with multiple ?-Fe2O3 inclusions to Janus NPs consisting of a ?-Fe2O3 and a SiO2 hemisphere to ?-Fe2O3 NPs each carrying one small SiO2 lens on its surface, (ii) the multiple ?-Fe2O3 inclusions accumulate at the NPs' inner surfaces, and (iii) all composite NPs are covered by a thin layer of amorphous SiO2. These morphological characteristics are attributed to (i) the phase segregation of iron oxide and silica within the condensed Fe2O3-SiO2 droplets, (ii) the temperature gradient within these droplets which arises during rapid cooling in the CoLAVA process, and (iii) the significantly lower surface energy of silica when compared to iron oxide. The proposed growth mechanism of these Fe2O3-SiO2 composite NPs during gas phase condensation can be transferred to other systems comprising a glass-network former and another component that is insoluble in the regarding glass. Thus, our model will facilitate the development of novel functional composite NPs for applications in biomedicine, optics, electronics, or catalysis.Spherical, softly agglomerated and superparamagnetic nanoparticles (NPs) consisting of maghemite (?-Fe2O3) and amorphous silica (SiO2) were prepared by CO2 laser co-vaporization (CoLAVA) of hematite powder (?-Fe2O3) and quartz sand (SiO2). The ?-Fe2O3 portion of the homogeneous starting mixtures was gradually increased (15 mass%-95 mass%). It was found that (i) with increasing iron oxide content the NPs' morphology changes from a nanoscale SiO2 matrix with multiple ?-Fe2O3 inclusions to Janus NPs consisting of a ?-Fe2O3 and a SiO2 hemisphere to ?-Fe2O3 NPs each carrying one small SiO2 lens on its surface, (ii) the multiple ?-Fe2O3 inclusions accumulate at the NPs' inner surfaces, and (iii) all composite NPs are covered by a thin layer of amorphous SiO2. These morphological characteristics are attributed to (i) the phase segregation of iron oxide and silica within the condensed Fe2O3-SiO2 droplets, (ii) the temperature gradient within these droplets which arises during rapid cooling in the CoLAVA process, and (iii) the significantly lower surface energy of silica when compared to iron oxide. The proposed growth mechanism of these Fe2O3-SiO2 composite NPs during gas phase condensation can be transferred to other systems comprising a glass-network former and another component that is insoluble in the regarding glass. Thus, our model will facilitate the development of novel functional composite NPs for applications in biomedicine, optics, electronics, or catalysis. Electronic supplementary information (ESI) available: Infrared absorption of the raw powders hematite and quartz (section S1), TEM investigation of the spatial distribution of the ?-Fe2O3 inclusions (section S2), particle size distributions of the Fe2O3@SiO2 nanopowder samples (section S3), ?-potentials of aqueous dispersions of all ?-Fe2O3@SiO2 nanopowder samples (section S4), silanization of Fe2O3@SiO2 composite nanopowders with [3-(2,3-epoxypropoxy)-propyl]trimethoxysilane (section S5), and animation composed of TEM micrographs of Fe2O3@SiO2 NPs recorded at incrementally altered tilt angles (``Rotating Fe2O3@SiO2 NP.avi''). See DOI: 10.1039/c5nr00845j
Gas distribution equipment in hydrogen service - Phase II
NASA Technical Reports Server (NTRS)
Jasionowski, W. J.; Huang, H. D.
The hydrogen permeability of three different types of commercially available natural gas polyethylene pipes was determined. Ring tensile tests were conducted on permeability-exposed and as-received samples. Hydrogen-methane leakage experiments were also performed. The results show no selective leakage of hydrogen via Poiseuille, turbulent, or orifice flow (through leaks) on the distribution of blends of hydrogen and methane. The data collected show that the polyethylene pipe is 4 to 6 times more permeable to hydrogen than to methane.
Entropy-driven phase transitions in multitype lattice gas models
H.-O. Georgii; Valentin Zagrebnov
In multitype lattice gas models with hard-core interaction of Widom--Rowlinson type, there is a competition between the entropy due to the large number of types, and the positional energy and geometry resulting from the exclusion rule and the activity of particles. We investigate this phenomenon in four different models on the square lattice: the multitype Widom-Rowlinson model with diamond-shaped resp.
Nonequilibrium Features of the Nuclear Liquid-Gas Phase Transition
NASA Astrophysics Data System (ADS)
Zwieglinski, B.; Odeh, T.; Gross, C.; Schwarz, C.; Bassini, R.; Begemann-Blaich, M.; Blaich, T.; Emling, H.; Ferrero, A.; Fritz, S.; Gaff, S. J.; Imme, G.; Iori, I.; Kleinevoss, U.; Kunde, G. J.; Kunze, W. D.; Lindenstruth, V.; Lynen, U.; Mahi, M.; Moroni, A.; Moehlenkamp, T.; Mueller, W. F. J.; Ocker, B.; Pochodzalla, J.; Raciti, G.; Rubehn, Th.; Sann, H.; Schnittker, M.; Schuettauf, A.; Seidel, W.; Serfling, V.; Stroth, J.; Trautmann, W.; Trzcinski, A.; Verde, G.; Woerner, A.; Xi, H.; Zude, E.
Energy spectra of protons emitted by the target residue in Au + Au collisions at 1 GeV/u were measured for different excitation energy bins. They reveal two components with different slopes attributed to preequilibrium and equilibrium emission. The relative contribution of the latter decreases rapidly with excitation energy, so that its presence becomes not apparent for the highest energy bins. It is argued therefore, that equilibrium may not be reached on the gas branch of the caloric curve.
Nucleation in synoptically forced cirrostratus
R.-F. Lin; D. O. Starr; J. Reichardt; P. J. DeMott
Formation and evolution of cirrostratus in response to weak, uniform, and constant synoptic forcing is simulated using a one-dimensional numerical model with explicit microphysics, in which the particle size distribution in each grid box is fully resolved. A series of tests of the model response to nucleation modes (homogeneous-freezing-only\\/heterogeneous nucleation) and heterogeneous nucleation parameters are performed. In the case studied
Nucleation dynamics of water nanodroplets.
Bhattacharya, Dipanjan; Bosman, Michel; Mokkapati, Venkata R S S; Leong, Fong Yew; Mirsaidov, Utkur
The origin of the condensation of water begins at the nanoscale, a length-scale that is challenging to probe for liquids. In this work we directly image heterogeneous nucleation of water nanodroplets by in situ transmission electron microscopy. Using gold nanoparticles bound to a flat surface as heterogeneous nucleation sites, we observe nucleation and growth of water nanodroplets. The growth of nanodroplet radii follows the power law: R(t)~(t-t 0) ? , where ?~0.2-0.3. PMID:24667092
Measuring Soil-Water Content with Gas-Phase Partitioning Tracers: Mass Transfer Limitations
NASA Astrophysics Data System (ADS)
Li, L.; Imhoff, P. T.
Soil-water content is an important parameter for soil scientists, hydrologists, and engineers studying the movement of water, gas, and pollutants in the vadose zone. Traditionally, soil-water content is characterized with point measurements, which include gravimetric analysis of core samples, time domain reflectrometry, and neutron moderation. More recently, the gas-phase partitioning tracer method has been suggested as an in situ tool for obtaining soil water content over large measurement volumes. Here, two tracers move through the gas phase, one that is non-reactive and one that partitions into the bulk water. Chromatographic separation of the tracers occurs that can be related to the soil-water content in the volume traversed by the tracers. Gas-phase partitioning tracers were previously tested under controlled laboratory conditions in homogeneous porous media with reasonably homogeneous distributions of soil-water content. In natural systems, though, soil-water is often heterogeneously distributed and sometimes moving. In this study, we investigated the utility of gas-phase partitioning tracers for these conditions. Laboratory columns were constructed with homogeneous and heterogeneous distributions of sand, which resulted in homogeneous or heterogeneous distributions of soil-water after water addition. In some experiments, the water infiltrated at a steady rate. Carbon dioxide and difluoromethane were selected as bulk-water partitioning tracers, which are tracers whose predominant mechanism of retention is partitioning into water; helium was the conservative tracer. These tracers were flushed through the experimental systems, varying the tracer slug size and gas-phase velocity. Measured soil water contents where compared with known values to infer the conditions under which mass transfer limitations influence gas-phase tracer measurements.
Efficient and directed peptide bond formation in the gas phase via ion/ion reactions
McGee, William M.; McLuckey, Scott A.
Amide linkages are among the most important chemical bonds in living systems, constituting the connections between amino acids in peptides and proteins. We demonstrate the controlled formation of amide bonds between amino acids or peptides in the gas phase using ion/ion reactions in a mass spectrometer. Individual amino acids or peptides can be prepared as reagents by (i) incorporating gas phase¢labile protecting groups to silence otherwise reactive functional groups, such as the N terminus; (ii) converting the carboxyl groups to the active ester of N-hydroxysuccinimide; and (iii) incorporating a charge site. Protonation renders basic sites (nucleophiles) unreactive toward the N-hydroxysuccinimide ester reagents, resulting in sites with the greatest gas phase basicities being, in large part, unreactive. The N-terminal amines of most naturally occurring amino acids have lower gas phase basicities than the side chains of the basic amino acids (i.e., those of histidine, lysine, or arginine). Therefore, reagents may be directed to the N terminus of an existing ōanchorö peptide to form an amide bond by protonating the anchor peptideÆs basic residues, while leaving the N-terminal amine unprotonated and therefore reactive. Reaction efficiencies of greater than 30% have been observed. We propose this method as a step toward the controlled synthesis of peptides in the gas phase. PMID:24474750
Surface passivation in diamond nucleation
NASA Astrophysics Data System (ADS)
Lee, C. H.; Lin, Z. D.; Shang, N. G.; Liao, L. S.; Bello, I.; Wang, N.; Lee, S. T.
Surface passivation is introduced to suppress the deleterious effect of Si surface oxides and thus enhance diamond heteroepitaxial nucleation. Surface composition and diamond nucleation and growth on H-, Br-, and I-passivated Si surfaces were studied. X-ray photoelectron spectroscopy showed that the passivated Si surfaces were free of silicon oxides and carbides. Remarkable enhancement in nucleation was achieved on passivated surfaces and the nucleation density obtained on a Br-passivated Si surface reached 1010 cm-2. Programmable temperature desorption revealed that the adsorbate desorption temperature increased in the order of H, I, and Br passivation. The same order of increase was also observed in the saturation value of electron emission current from the passivated surfaces, which was related to the degree of nucleation. Nucleation enhancement was shown to be greater when the adsorbate desorption temperature is closer to the nucleation temperature, so that more adsorbate- and oxide-free Si surface area would be available for nucleation. The study established that surface passivation is potentially an effective approach for diamond heteroepitaxial nucleation.
Surface Nanobubbles Nucleate Microdroplets
NASA Astrophysics Data System (ADS)
Zhang, Xuehua; Lhuissier, Henri; Sun, Chao; Lohse, Detlef
When a hydrophobic solid is in contact with water, surface nanobubbles often form at the interface. They have a lifetime many orders of magnitude longer than expected. Here, we show that they even withstand a temperature increase to temperatures close to the boiling point of bulk water; i.e., they do not nucleate larger bubbles ("superstability"). On the contrary, when the vapor-liquid contact line passes a nanobubble, a liquid film remains around it, which, after pinch-off, results in a microdroplet in which the nanobubbles continue to exist. Finally, the microdroplet evaporates and the nanobubble consequently bursts. Our results support that pinning plays a crucial role for nanobubble stability.
Vortex nucleation in Bose-Einstein Condensates subject to light induced effective magnetic fields
D. R. Murray; P ųhberg; Damiß Gomila; Stephen M. Barnett
We numerically simulate vortex nucleation in a Bose-Einstein Condensate (BEC) subject to an effective magnetic field. The effective magnetic field is generated from the interplay between light with a non-trivial phase structure and the BEC, and can be shaped and controlled by appropriate modifications to the phase and intensity of the light. We demonstrate that the nucleation of vortices is
Earthquake nucleation in intact or healed rocks
NASA Astrophysics Data System (ADS)
Brantut, Nicolas; Viesca, Robert C.
Earthquakes are generated because faults lose strength with increasing slip and slip rate. Among the simplest representations of slip-dependent strength is the linear slip-weakening model, characterized by a linear drop to a residual friction. However, healed fault rocks often exhibit some slip strengthening before the onset of weakening. Here we investigate the effect of such a slip-hardening phase on the initial growth of a slip patch and on the nucleation of rupture instabilities. We assume a piecewise linear strength versus slip constitutive relation. We compute stress and slip distributions for in-plane or antiplane rupture configurations in response to an increasing, locally peaked (parabolic with curvature ?) stress profile. In contrast with the strictly linear slip-weakening case, our calculations show that the curvature of the loading profile and the level of background stress strongly influence the nucleation size. Even for small amounts of slip hardening, we find that the critical nucleation size scales with 1/?? for ??0, i.e., crack growth remains stable up to very large crack sizes for sufficiently smooth loading profiles. Likewise, when the background stress ?b is very close to the initial strength ?c, the critical crack size scales with 1/?(?c-?b). An eigenvalue analysis shows that the nucleation length increases as the proportion of the crack undergoing slip hardening increases, irrespective of the details of the loading profile. Overall, our results indicate that earthquake nucleation sizes can significantly increase due to slip hardening (e.g., in healed fault rocks), especially when the background loading is smooth.
Submission PDF Surfactants from the gas phase may enhance aerosol
Nenes, Athanasios
, 17). A continuous flow streamwise thermal gradient CCN chamber (CFSTGC) was used downstream of a 3-phase methylglyoxal and/or acetaldehyde in an aerosol reaction chamber for up to 5 h. For the more atmospherically.5 m3 Teflon reaction chamber or an aerosol
Experimental evidence for seismically initiated gas bubble nucleation and growth in groundwater as a mechanism for coseismic borehole water level rise and remotely triggered seismicity
NASA Astrophysics Data System (ADS)
Crews, Jackson B.; Cooper, Clay A.
Changes in borehole water levels and remotely triggered seismicity occur in response to near and distant earthquakes at locations around the globe, but the mechanisms for these phenomena are not well understood. Experiments were conducted to show that seismically initiated gas bubble growth in groundwater can trigger a sustained increase in pore fluid pressure consistent in magnitude with observed coseismic borehole water level rise, constituting a physically plausible mechanism for remote triggering of secondary earthquakes through the reduction of effective stress in critically loaded geologic faults. A portion of the CO2 degassing from the Earth's crust dissolves in groundwater where seismic Rayleigh and P waves cause dilational strain, which can reduce pore fluid pressure to or below the bubble pressure, triggering CO2 gas bubble growth in the saturated zone, indicated by a spontaneous buildup of pore fluid pressure. Excess pore fluid pressure was measured in response to the application of 0.1-1.0 MPa, 0.01-0.30 Hz confining stress oscillations to a Berea sandstone core flooded with initially subsaturated aqueous CO2, under conditions representative of a confined aquifer. Confining stress oscillations equivalent to the dynamic stress of the 28 June 1992 Mw 7.3 Landers, California, earthquake Rayleigh wave as it traveled through the Long Valley caldera, and Parkfield, California, increased the pore fluid pressure in the Berea core by an average of 36 ▒ 15 cm and 23 ▒ 15 cm of equivalent freshwater head, respectively, in agreement with 41.8 cm and 34 cm rises recorded in wells at those locations.
Development and initial evaluation of a dynamic species-resolved model for gas phase chemistry and size-resolved gas//particle
Dabdub, Donald
biogenic and anthropogenic sources. [3] The gas phase oxidation chemistry of SOA-forming VOCs is complex of the semivolatile or nonvolatile products of VOC oxidation between the gas and particle phases. Chem- ical analysis are presented in which a single salt (either dry or aqueous), a volatile organic compound, and oxides
On radiative forcing of sulphate aerosol produced from ion-promoted nucleation mechanisms in an atmospheric global model
NASA Astrophysics Data System (ADS)
Fatima, Hashmi; Upadhyaya, H. C.; Tripathi, S. N.; Sharma, O. P.; Yu, Fangqun
A significant fraction of the total number of particles present in the atmosphere is formed by nucleation in the gas phase. Nucleation and the subsequent growth process influence both number concentration of particles and their size distribution besides chemical and optical properties of atmospheric aerosols. Sulphate aerosol nucleation mechanisms promoted by ions have been evaluated here in a tropospheric interactive chemistry-aerosol module for mass and number concentration in a global atmospheric model. The indirect radiative forcing of sulphate particles is assessed in this model; indirect radiative forcing is different for ion-induced (IIN) and ion-mediated (IMN) mechanisms. The indirect radiative forcing in 10-year simulation runs has been calculated as -1.42 W/m2 (IIN) and -1.54 W/m2 (IMN). The 5% emission of primary sulphate particles in simulations changes the indirect radiative forcing from -1.42 to -1.44 W/m2 for IIN case, and from -1.54 to -1.55 W/m2 for the IMN case. More precisely, owing to greater nucleation rates, IMN mechanisms produces greater cooling than the IIN mechanisms in the backdrop that both mechanisms produce almost identical distribution of CDNC in their pre-industrial runs. The inclusion of primary particles in simulations with IIN and IMN mechanisms increases both CDNC and the indirect radiative forcing.
Chiral recognition in gas-phase cyclodextrin: Amino acid complexesŚIs the three point interaction still valid in the gas phase?
Seonghee Ahn; Javier Ramirez; Gabriela Grigorean; Carlito B. Lebrilla
The validity of the ōthree-point interactionö model is examined in the guest exchange reaction involving complexes of cyclodextrins\\u000a and amino acids. The amino acid guest is exchanged in the gas phase in the presence of a gaseous alkyl amine. The net reaction\\u000a is proton transfer between the protonated amino acid and the alkyl amine. The amino acid is lost as
Phase diagram of a two-dimensional lattice gas model of a ramp system.
Almarza, Noķ G; Capitßn, Josķ A; Cuesta, Josķ A; Lomba, Enrique
Using Monte Carlo simulation and fundamental measure theory we study the phase diagram of a two-dimensional lattice gas model with a nearest neighbor hard core exclusion and a next-to-nearest neighbor finite repulsive interaction. The model presents two competing ranges of interaction and, in common with many experimental systems, exhibits a low density solid phase, which melts back to the fluid phase upon compression. The theoretical approach is found to provide a qualitatively correct picture of the phase diagram of our model system. PMID:19791893
Formation of 9,10-phenanthrenequinone by atmospheric gas-phase reactions of phenanthrene
NASA Astrophysics Data System (ADS)
Wang, Lin; Atkinson, Roger; Arey, Janet
Phenanthrene is a 3-ring polycyclic aromatic hydrocarbon which exists mainly in the gas-phase in the atmosphere. Recent concern over the presence of 9,10-phenanthrenequinone in ambient particles led us to study the products of the gas-phase reactions of phenanthrene with hydroxyl radicals, nitrate radicals and ozone. The formation yields of 9,10-phenanthrenequinone were measured to be ś3%, 33▒9%, and ś2% from the OH radical, NO 3 radical and O 3 reactions, respectively. Calculations suggest that daytime OH radical-initiated and nighttime NO 3 radical-initiated reactions of gas-phase phenanthrene may be significant sources of 9,10-phenanthrenequinone in ambient atmospheres. In contrast, the ozone reaction with phenanthrene is unlikely to contribute significantly to ambient 9,10-phenanthrenequinone.
Insights into diastereoisomeric characterization of tetrahydropyridazine amino acid derivatives: crystal structures and gas phase ion chemistry.
Giorgi, Gianluca; Favi, Gianfranco; Attanasi, Orazio A
Structural, conformational properties, and gas phase reactivity of two representative diastereoisomeric members of a series of ?,?-tetrahydropyridazine amino acid derivatives have been investigated by using X-ray crystallography, tandem mass spectrometry and theoretical calculations. Both diastereoisomers show an unusual screw-boat conformation of the tetrahydropyridazine ring. While protonated molecules mainly decompose in the gas phase by loss of acetamide, the main reactivity of the [M + Na](+) species consists of loss of PhNCO followed by acetamide and it is strictly dependent upon the stereochemistry of the parent compound. The most stable energy minimized structures obtained by theoretical calculations are in full agreement with the experimental data and allowed us to rationalize the gas phase reaction pathways. PMID:23787961
Oxidation of formic acid on the Pt(111) surface in the gas phase.
Gao, Wang; Keith, John A; Anton, Josef; Jacob, Timo
Formic acid (HCOOH) oxidation on Pt(111) under gas-phase conditions is a benchmark heterogeneous catalysis reaction used to probe electro-catalytic HCOOH conversion in fuel cells, itself an important reaction in energy conversion. We used density functional theory (DFT) calculations to elucidate the fundamental oxidation mechanisms of HCOOH in the gas phase, determining the relative strengths of chemical interactions between HCOOH oxidation intermediates and the Pt(111) surface. We focused on investigating how water and adsorption coverage affects reaction intermediate structures and transition states. Our results show that adsorbed HCOO is a reactive intermediate in gas phase, and co-adsorbed water plays a key role in HCOOH oxidation influencing the structure of reaction intermediates and reaction barriers on Pt(111). The simulations show the preferred catalytic pathway is qualitatively dependent on surface coverage. These results provide a conceptual basis to better interpret its complicated experimental reaction kinetics. PMID:20714626
The Stability of CI02 as a Product of Gas Phase Decontamination Treatments
D. W. Simmons
The gas phase decontamination project is investigating the use of chlorine trifluoride (ClF{sub 3}) to fluorinate nonvolatile uranium deposits to produce uranium hexafluoride (UF{sub 6}) gas. The potential existence of chlorine dioxide (ClO{sub 2}) during gas phase decontamination with ClF{sub 3} has been the subject of recent safety discussions. Some of the laboratory data collected during feasibility studies of the gas phase process has been evaluated for the presence of ClO{sub 2} in the product gas stream. The preliminary evidence to date can be summarized as follows: (1) ClO{sub 2} was not detected in the flow loop in the absence of ClF{sub 3}; (2) ClO{sub 2} was not detected in the static reactors in the absence of both ClF{sub 3} and ClF; and (3) ClO{sub 2} was detected in a static reactor in the absence of all fluorinating gases. The experimental evidence suggests that ClO{sub 2} will not exist in the presence of ClF{sub 3}, ClF, or UF{sub 6}. The data analyzed to date is insufficient to determine the stability of ClO{sub 2} in the presence of ClO{sub 2}F. Thermodynamic calculations of the ClF{sub 3} + H{sub 2}O system support the experimental evidence, and suggest that ClO{sub 2} will not exist in the presence of ClO{sub 2}F. Additional experimental efforts are needed to provide a better understanding of the gas phase ClF{sub 3} treatments and the product gases. However, preliminary evidence to date suggests that ClO{sub 2} should not be present as a product during the normal operations of the gas phase decontamination project.
Polymerization in the gas phase, in clusters, and on nanoparticle surfaces.
El-Shall, M Samy
Gas phase and cluster experiments provide unique opportunities to quantitatively study the effects of initiators, solvents, chain transfer agents, and inhibitors on the mechanisms of polymerization. Furthermore, a number of important phenomena, unique structures, and novel properties may exist during gas-phase and cluster polymerization. In this regime, the structure of the growing polymer may change dramatically and the rate coefficient may vary significantly upon the addition of a single molecule of the monomer. These changes would be reflected in the properties of the oligomers deposited from the gas phase. At low pressures, cationic and radical cationic polymerizations may proceed in the gas phase through elimination reactions. In the same systems at high pressure, however, the ionic intermediates may be stabilized, and addition without elimination may occur. In isolated van der Waals clusters of monomer molecules, sequential polymerization with several condensation steps can occur on a time scale of a few microseconds following the ionization of the gas-phase cluster. The cluster reactions, which bridge gas-phase and condensed-phase chemistry, allow examination of the effects of controlled states of aggregation. This Account describes several examples of gas-phase and cluster polymerization studies where the most significant results can be summarized as follows: (1) The carbocation polymerization of isobutene shows slower rates with increasing polymerization steps resulting from entropy barriers, which could explain the need for low temperatures for the efficient propagation of high molecular weight polymers. (2) Radical cation polymerization of propene can be initiated by partial charge transfer from an ionized aromatic molecule such as benzene coupled with covalent condensation of the associated propene molecules. This novel mechanism leads exclusively to the formation of propene oligomer ions and avoids other competitive products. (3) Structural information on the oligomers formed by gas-phase polymerization can be obtained using the mass-selected ion mobility technique where the measured collision cross-sections of the selected oligomer ions and collision-induced dissociation can provide fairly accurate structural identifications. The identification of the structures of the dimers and trimers formed in the gas-phase thermal polymerization of styrene confirms that the polymerization proceeds according to the Mayo mechanism. Similarly, the ion mobility technique has been utilized to confirm the formation of benzene cations by intracluster polymerization following the ionization of acetylene clusters. Finally, it has been shown that polymerization of styrene vapor on the surface of activated nanoparticles can lead to the incorporation of a variety of metal and metal oxide nanoparticles within polystyrene films. The ability to probe the reactivity and structure of the small growing oligomers in the gas phase can provide fundamental insight into mechanisms of polymerization that are difficult to obtain from condensed-phase studies. These experiments are also important for understanding the growth mechanisms of complex organics in flames, combustion processes, interstellar clouds, and solar nebula where gas-phase reactions, cluster polymerization, and surface catalysis on dust nanoparticles represent the major synthetic pathways. This research can lead to the discovery of novel initiation mechanisms and reaction pathways with applications in the synthesis of oligomers and nanocomposites with unique and improved properties. PMID:18557636
Challenges in Modeling Gas-Phase Flow in Microchannels: From Slip to Transition
Robert W. Barber; David R. Emerson
It has long been recognized that the fluid mechanics of gas-phase microflows can differ significantly from the macroscopic world. Non-equilibrium effects such as rarefaction and gas-surface interactions need to be taken into account, and it is well known that the no-slip boundary condition of the Navier-Stokes equations is no longer valid. Following ideas proposed by Maxwell, it is generally accepted
Amphipols outperform dodecylmaltoside micelles in stabilizing membrane protein structure in the gas phase.
Calabrese, Antonio N; Watkinson, Thomas G; Henderson, Peter J F; Radford, Sheena E; Ashcroft, Alison E
Noncovalent mass spectrometry (MS) is emerging as an invaluable technique to probe the structure, interactions, and dynamics of membrane proteins (MPs). However, maintaining native-like MP conformations in the gas phase using detergent solubilized proteins is often challenging and may limit structural analysis. Amphipols, such as the well characterized A8-35, are alternative reagents able to maintain the solubility of MPs in detergent-free solution. In this work, the ability of A8-35 to retain the structural integrity of MPs for interrogation by electrospray ionization-ion mobility spectrometry-mass spectrometry (ESI-IMS-MS) is compared systematically with the commonly used detergent dodecylmaltoside. MPs from the two major structural classes were selected for analysis, including two ?-barrel outer MPs, PagP and OmpT (20.2 and 33.5 kDa, respectively), and two ?-helical proteins, Mhp1 and GalP (54.6 and 51.7 kDa, respectively). Evaluation of the rotationally averaged collision cross sections of the observed ions revealed that the native structures of detergent solubilized MPs were not always retained in the gas phase, with both collapsed and unfolded species being detected. In contrast, ESI-IMS-MS analysis of the amphipol solubilized MPs studied resulted in charge state distributions consistent with less gas phase induced unfolding, and the presence of lowly charged ions which exhibit collision cross sections comparable with those calculated from high resolution structural data. The data demonstrate that A8-35 can be more effective than dodecylmaltoside at maintaining native MP structure and interactions in the gas phase, permitting noncovalent ESI-IMS-MS analysis of MPs from the two major structural classes, while gas phase dissociation from dodecylmaltoside micelles leads to significant gas phase unfolding, especially for the ?-helical MPs studied. PMID:25495802
Measurements of liquid-phase turbulence in gas-liquid two-phase flows using particle image velocimetry
NASA Astrophysics Data System (ADS)
Zhou, Xinquan; Doup, Benjamin; Sun, Xiaodong
Liquid-phase turbulence measurements were performed in an air-water two-phase flow loop with a circular test section of 50 mm inner diameter using a particle image velocimetry (PIV) system. An optical phase separation method--planar laser-induced fluorescence (PLIF) techniqueŚwhich uses fluorescent particles and an optical filtration technique, was employed to separate the signals of the fluorescent seeding particles from those due to bubbles and other noises. An image pre-processing scheme was applied to the raw PIV images to remove the noise residuals that are not removed by the PLIF technique. In addition, four-sensor conductivity probes were adopted to measure the radial distribution of the void fraction. Two benchmark tests were performed: the first was a comparison of the PIV measurement results with those of similar flow conditions using thermal anemometry from previous studies; the second quantitatively compared the superficial liquid velocities calculated from the local liquid velocity and void fraction measurements with the global liquid flow rate measurements. The differences of the superficial liquid velocity obtained from the two measurements were bounded within ▒7% for single-phase flows and two-phase bubbly flows with the area-average void fraction up to 18%. Furthermore, a preliminary uncertainty analysis was conducted to investigate the accuracy of the two-phase PIV measurements. The systematic uncertainties due to the circular pipe curvature effects, bubble surface reflection effects and other potential uncertainty sources of the PIV measurements were discussed. The purpose of this work is to facilitate the development of a measurement technique (PIV-PLIF) combined with image pre-processing for the liquid-phase turbulence in gas-liquid two-phase flows of relatively high void fractions. The high-resolution data set can be used to more thoroughly understand two-phase flow behavior, develop liquid-phase turbulence models, and assess high-fidelity codes for multi-phase flows.
Plasma-produced phase-pure cuprous oxide nanowires for methane gas sensing
Cheng, Qijin, E-mail: email@example.com; Zhang, Fengyan [School of Energy Research, Xiamen University, Xiamen City, Fujian Province 361005 (China); Yan, Wei [School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales 2052 (Australia); Plasma Nanoscience Laboratories, CSIRO Materials Science and Engineering, Lindfield, New South Wales 2070 (Australia); Randeniya, Lakshman [Plasma Nanoscience Laboratories, CSIRO Materials Science and Engineering, Lindfield, New South Wales 2070 (Australia); Ostrikov, Kostya [Plasma Nanoscience Laboratories, CSIRO Materials Science and Engineering, Lindfield, New South Wales 2070 (Australia); Plasma Nanoscience, School of Physics, The University of Sydney, Sydney, New South Wales 2006 (Australia)
Phase-selective synthesis of copper oxide nanowires is warranted by several applications, yet it remains challenging because of the narrow windows of the suitable temperature and precursor gas composition in thermal processes. Here, we report on the room-temperature synthesis of small-diameter, large-area, uniform, and phase-pure Cu{sub 2}O nanowires by exposing copper films to a custom-designed low-pressure, thermally non-equilibrium, high-density (typically, the electron number density is in the range of 10{sup 11}¢10{sup 13}?cm{sup ?3}) inductively coupled plasmas. The mechanism of the plasma-enabled phase selectivity is proposed. The gas sensors based on the synthesized Cu{sub 2}O nanowires feature fast response and recovery for the low-temperature (?140?░C) detection of methane gas in comparison with polycrystalline Cu{sub 2}O thin film-based gas sensors. Specifically, at a methane concentration of 4%, the response and the recovery times of the Cu{sub 2}O nanowire-based gas sensors are 125 and 147?s, respectively. The Cu{sub 2}O nanowire-based gas sensors have a potential for applications in the environmental monitoring, chemical industry, mining industry, and several other emerging areas.
Direct gas-phase epoxidation of propylene to propylene oxide through radical reactions: A theoretical study
NASA Astrophysics Data System (ADS)
Kizilkaya, Ali Can; Fellah, Mehmet Ferdi; Onal, Isik
The gas-phase radical chain reactions which utilize O 2 as the oxidant to produce propylene oxide (PO) are investigated through theoretical calculations. The transition states and energy profiles were obtained for each path. The rate constants were also calculated. The energetics for the competing pathways indicate that PO can be formed selectively due to its relatively low activation barrier (9.3 kcal/mol) which is in a good agreement with the experimental value (11 kcal/mol) of gas-phase propylene epoxidation. The formation of the acrolein and combustion products have relatively high activation barriers and are not favored. These results also support the recent experimental findings.
Atmospheric chemistry of gas-phase polycyclic aromatic hydrocarbons: formation of atmospheric mutagens.
Atkinson, R; Arey, J
The atmospheric chemistry of the 2- to 4-ring polycyclic aromatic hydrocarbons (PAH), which exist mainly in the gas phase in the atmosphere, is discussed. The dominant loss process for the gas-phase PAH is by reaction with the hydroxyl radical, resulting in calculated lifetimes in the atmosphere of generally less than one day. The hydroxyl (OH) radical-initiated reactions and nitrate (NO3) radical-initiated reactions often lead to the formation of mutagenic nitro-PAH and other nitropolycyclic aromatic compounds, including nitrodibenzopyranones. These atmospheric reactions have a significant effect on ambient mutagenic activity, indicating that health risk assessments of combustion emissions should include atmospheric transformation products. PMID:7821285
Droplet Freezing by Surface Nucleation
Narayan R. Gokhale; James Goold Jr.
Droplet freezing by surface nucleation has been observed during the course of studies of ice nucleation in our laboratories. A constant rate of cooling apparatus and a specially constructed cold chamber were used for this study. Silver iodide particles sprinkled on supercooled, millimeter-size water drops are effective in freezing the drops at 5C. Particles of naturally occurring silicates were found
Molecular simulation of crystal nucleation in n-octane melts
Yi, Peng
Homogeneous nucleation of the crystal phase in n-octane melts was studied by molecular simulation with a realistic, united-atom model for n-octane. The structure of the crystal phase and the melting point of n-octane were ...
Effect of liquid distribution on gas-water phase mass transfer in an unsaturated sand during infiltration
NASA Astrophysics Data System (ADS)
Imhoff, Paul T.; Jaffķ, Peter R.
Gas-water phase mass transfer was examined in a homogeneous sand with both the gas and water phase mobile: water was infiltrated from the top of the sand column while benzene-laden air flowed upward from the bottom. Mass-transfer limitations for this situation may be important for applications of bioventing, where water and nutrients are added at the ground surface simultaneously with induced air movement to carry oxygen and volatile organics to microbial populations. Gas- and water-phase samples indicate that gas-water phase mass transfer was sufficiently fast that equilibrium between gas and water phases was achieved at all sampling locations within the porous medium. Lower-bound estimates for the gas-water mass-transfer rate coefficient show that mass transfer was at least 10-40 times larger than predictions made from an empirical model developed for gas-water phase mass transfer in an identical porous medium. A water-phase tracer test demonstrates that water flow was much more uniform in this study than in those earlier experiments, which is a likely explanation for the differing rates of gas-water phase mass transfer. It is hypothesized that the liquid distribution in previous laboratory experiments was less uniform because of preferential flow paths due to wetting front instabilities. Gas-water phase mass-transfer rate coefficients reported in this investigation are for an ideal situation of uniform water infiltration: mass-transfer rates in field soils are expected to be significantly smaller.
Phase equilibrium of gas hydrate: Implications for the formation of hydrate in the deep sea floor
NASA Astrophysics Data System (ADS)
Zatsepina, Olga Ye.; Buffett, Bruce A.
We calculate the solubility of methane gas over a range of pressure and temperature. The gas is dissolved in liquid water, which coexists with free gas at high temperature or solid hydrate at low temperature and high pressure. We show that solubility is significantly altered by the presence or absence of the hydrate phase. When hydrate is absent at high temperatures, our calculations reproduce experimentally observed increases in solubility with decreasing temperature. When hydrate is present, however, we find that the gas solubility decreases sharply with decreasing temperature. Such an abrupt decrease in solubility permits hydrate to crystallize directly from the aqueous solution, without the need of any free gas. This result has important implications for the formation of gas hydrate in marine environments, where the gas supply may not be sufficient to provide free gas. We apply our calculations at typical pressure and temperature conditions in marine sediments to establish the gas concentration needed to stabilize hydrate. Estimates of the vertical distribution of hydrate in marine sediments and the rate of accumulation are obtained using simple models of hydrate formation.
Role of three-hydrocarbon-phase flow in a gas-displacement process
Mohanty, K.K. [Univ. of Houston, TX (United States); Masino, W.H. Jr.; Ma, T.D. [Arco Alaska Inc., Anchorage, AK (United States); Nash, L.J. [Energy Biosystems Corp., The Woodlands, TX (United States)
The objective of this work is to identify the role of three-hydrocarbon-phase flow in the displacement of a reservoir oil by light-hydrocarbon-gas mixtures (methane through n-butane). Slim-tube displacements were conducted with several hydrocarbon-gas mixtures. A compositional simulator capable of handling three nonaqueous phases was used to simulate these 1D displacements. Slim-tube experiments show that as dilution with lean gas increases, the displacements go from first-contact miscible to multicontact miscible to three-phase, 3{phi}, immiscible to two-phase, 2{phi}, immiscible. Recovery is high (> 85%) at high enrichment, but nonmonotonic with dilution. Simulation results mimic experimental slim-tube recovery and gas-breakthrough behavior qualitatively; especially the increase in oil recovery with increasing methane dilution of the solvent. High oil recoveries in the 3{phi} cases appear to be the result of condensation of solvent into the oil, resulting in (1) low oil viscosity and (2) effective displacement of oil by the second liquid phase that forms.
Nucleating quark droplets in the core of magnetars
Daniel Kroff; Eduardo S. Fraga
To assess the possibility of homogeneous nucleation of quark matter in magnetars, we investigate the formation of chirally symmetric droplets in a cold and dense environment in the presence of an external magnetic field. As a framework, we use the one-loop effective potential of the two-flavor quark-meson model. Within the thin-wall approximation, we extract all relevant nucleation parameters and provide an estimate for the typical time scales for the chiral phase conversion in magnetized compact star matter. We show how the critical chemical potential, critical radius, correlation length and surface tension are affected, and how their combination to define the nucleation time seems to allow for nucleation of quark droplets in magnetar matter even for not so small values of the surface tension.
A three-phase free boundary problem with melting ice and dissolving gas
Maurizio Ceseri; John M. Stockie
We develop a mathematical model for a three-phase free boundary problem in one dimension that involves the interactions between gas, water and ice. The dynamics are driven by melting of the ice layer, while the pressurized gas also dissolves within the meltwater. The model incorporates a Stefan condition at the water-ice interface along with Henry's law for dissolution of gas at the gas-water interface. We employ a quasi-steady approximation for the phase temperatures and then derive a series solution for the interface positions. A non-standard feature of the model is an integral free boundary condition that arises from mass conservation owing to changes in gas density at the gas-water interface, which makes the problem non-self-adjoint. We derive a two-scale asymptotic series solution for the dissolved gas concentration, which because of the non-self-adjointness gives rise to a Fourier series expansion in eigenfunctions that do not satisfy the usual orthogonality conditions. Numerical simulations of the original governing equations are used to validate the series approximations.
Microporous hydrophobic hollow fiber modules for gas-liquid phase separation in microgravity
NASA Astrophysics Data System (ADS)
Noyes, Gary
Gas-liquid interphase mass transfer operations, such as gas-liquid phase separation, gas absorption into liquid or dissolved gas separation from liquid, gas humidification and drying via liquid contact, and evaporative cooling are readily accomplished on the Earth with settling/spray chambers, packed towers, or bubble columns. This paper reports on gas-water mass transfer tests performed utilizing microporous hydrophobic Hollow Fiber Modules (HFMs) of the type currently employed as blood oxygenators in heart-lung machines. In these HFMs, gases are transferrred to and from water or other hydrophilic liquids through the microporous fiber walls; liquid water does not enter the pores of the highly hydrophobic wall material. The experiments included air-water phase separation, absorption of oxygen and carbon dioxide into water and separation of these dissolved gases from water, air humidification and drying by contact with temperature-controlled water, and controlled evaporation of water into a vacuum. In each of these experiments, a small, light HFM sucessfully performed the mass tranfer function, with no leakage of liquid water through the porous walls of the hollow fibers, even with high pressure across the fiber wall for extended periods of time. These results demonstrate that gas-liquid mass transfer unit operations on hydrophilic liquids, implemented with microporous hydrophobic HFM technology, are ready for use in microgravity fluid processing systems.
Experimental on two sensors combination used in horizontal pipe gas-water two-phase flow
NASA Astrophysics Data System (ADS)
Wu, Hao; Dong, Feng
Gas-water two phase flow phenomenon widely exists in production and living and the measurement of it is meaningful. A new type of long-waist cone flow sensor has been designed to measure two-phase mass flow rate. Six rings structure of conductance probe is used to measure volume fraction and axial velocity. The calibration of them have been made. Two sensors have been combined in horizontal pipeline experiment to measure two-phase flow mass flow rate. Several model of gas-water two-phase flow has been discussed. The calculation errors of total mass flow rate measurement is less than 5% based on the revised homogeneous flow model.
The nucleation of Fe-Rich phases on oxide films in Al11.5Si0.4Mg cast alloys
X. Cao; J. Campbell
The microstructures of Al-11.5Si-0.4Mg alloys with various Fe and Mn contents have been studied to investigate the potential\\u000a influence of oxide films on the precipitation of Fe-rich phases from the liquid metal. Oxide films are incorporated into melts\\u000a by an entrainment process. This is an enfolding mechanism of incorporation. Folded oxide films in melts have two sides: the\\u000a dry unbonded
Determination of the nucleation region of Si particles produced by pulsed-laser deposition in Monte Carlo simulation
NASA Astrophysics Data System (ADS)
Qin, Aili; Chu, Lizhi; Deng, Zechao; Zhang, Xiaolong; Wang, Yinglong
The nucleation and growth of Si nanoparticle produced by pulsed laser ablation in helium gas ambient is investigated via direct simulation Monte Carlo method with a real physical scale of target-substrate configuration. The nucleation area is important for the formation of Si nanoparticles, and the average size and size distribution of Si nanoparticles formed in this region depend on its range. The narrower the nucleation area and, therefore, the less the maximum times of collisions between Si atoms in the region, the smaller and the more uniform the Si nanoparticles. A nucleation and growth process is clearly observed. It is shown that the nucleation region and the nucleation growth internal is changing with time. The ambient gas pressure is important to nucleation region. The suitable pressure range under certain conditions is given and our simulated results are approximately in agreement with the previous experimental data.
Nucleation and solidification in static arrays of monodisperse dropså
Edd, Jon F.; Humphry, Katherine J.; Irimia, Daniel; Weitz, David A.; Toner, Mehmet
The precise measurement of nucleation and non-equilibrium solidification are vital to fields as diverse as atmospheric science, food processing, cryopreservation and metallurgy. The emulsion technique, where the phase under study is partitioned into many droplets suspended within an immiscible continuous phase, is a powerful method for uncovering rates of nucleation and dynamics of phase changes as it isolates nucleation events to single droplets. However, averaging the behavior of many drops in a bulk emulsion leads to the loss of any drop-specific information, and drop polydispersity clouds the analysis. Here we adapt a microfluidic technique for trapping monodisperse drops in planar arrays to characterize solidification of highly supercooled aqueous solutions of glycerol. This system measured rates of nucleation between 10 ¢5 and 10 ¢2 pL ¢1 s ¢1, yielded an ice-water interfacial energy of 33.4 mJ m ¢2 between ¢38 and ¢35 ░C, and enabled the specific dynamics of solidification to be observed for over a hundred drops in parallel without any loss of specificity. In addition to the physical insights gained, the ability to observe the time and temperature of nucleation and subsequent growth of the solid phase in static arrays of uniform drops provides a powerful tool to discover thermodynamic protocols that generate desirable crystal structures. PMID:19532960
Using the thermal diffusion cloud chamber to study the ion-induced nucleation by radon decay
Thermal diffusion cloud chamber is steady-state device and has been extensively used for nucleation research. In order to study the ion-induced nucleation by radon decay, a new chamber was designed with improved both upper and bottom plates, the system of circulating fluid, the gasketting, the temperature measurement and the insulation. An alternative method of using oxygen as carrier gas was
In situ measurements of gas/particle-phase transitions for atmospheric semivolatile organic compounds.
Williams, Brent J; Goldstein, Allen H; Kreisberg, Nathan M; Hering, Susanne V
An understanding of the gas/particle-phase partitioning of semivolatile compounds is critical in determining atmospheric aerosol formation processes and growth rates, which in turn affect global climate and human health. The Study of Organic Aerosol at Riverside 2005 campaign was performed to gain a better understanding of the factors responsible for aerosol formation and growth in Riverside, CA, a region with high concentrations of secondary organic aerosol formed through the phase transfer of low-volatility reaction products from the oxidation of precursor gases. We explore the ability of the thermal desorption aerosol gas chromatograph (TAG) to measure gas-to-particle-phase transitioning for several organic compound classes (polar and nonpolar) found in the ambient Riverside atmosphere by using in situ observations of several hundred semivolatile organic compounds. Here we compare TAG measurements to modeled partitioning of select semivolatile organic compounds. Although TAG was not designed to quantify the vapor phase of semivolatile organics, TAG measurements do distinguish when specific compounds are dominantly in the vapor phase, are dominantly in the particle phase, or have both phases present. Because the TAG data are both speciated and time-resolved, this distinction is sufficient to see the transition from vapor to particle phase as a function of carbon number and compound class. Laboratory studies typically measure the phase partitioning of semivolatile organic compounds by using pure compounds or simple mixtures, whereas hourly TAG phase partitioning measurements can be made in the complex mixture of thousands of polar/nonpolar and organic/inorganic compounds found in the atmosphere. PMID:20142511
A review of two-phase gas¢liquid adiabatic flow characteristics in micro-channels
Sira Saisorn; Somchai Wongwises
A literature review of recent research on two-phase flow in micro-channels is provided in this article. Researches on the micro-hydrodynamics concerned with two-phase gas¢liquid adiabatic flow characteristics in both circular and non-circular micro-channels are discussed. This review aims to survey and identify new findings obtained from this attractive area, which may contribute to optimum design and process control of high
Hydrothermal transformation of Chinese privet seed biomass to gas-phase and semi-volatile products
Thomas L. Eberhardt; W. James Catallo; Todd F. Shupe
Hydrothermal (HT) treatment of seeds from Chinese privet (Ligustrum sinense), a non-native and invasive species in the southeastern United States, was examined with respect to the generation of gas-phase and semi-volatile organic chemicals of industrial importance from a lipid-rich biomass resource. Aqueous seed slurries were transformed into biphasic liquid systems comprised of a milky aqueous phase overlain by a black
Surface nanobubbles nucleate microdroplets.
Zhang, Xuehua; Lhuissier, Henri; Sun, Chao; Lohse, Detlef
When a hydrophobic solid is in contact with water, surface nanobubbles often form at the interface. They have a lifetime many orders of magnitude longer than expected. Here, we show that they even withstand a temperature increase to temperatures close to the boiling point of bulk water; i.e., they do not nucleate larger bubbles ("superstability"). On the contrary, when the vapor-liquid contact line passes a nanobubble, a liquid film remains around it, which, after pinch-off, results in a microdroplet in which the nanobubbles continue to exist. Finally, the microdroplet evaporates and the nanobubble consequently bursts. Our results support that pinning plays a crucial role for nanobubble stability. PMID:24765973
Phase-sensitive terahertz emission from gas targets irradiated by few-cycle laser pulses
NASA Astrophysics Data System (ADS)
Wu, Hui-Chun; Meyer-ter-Vehn, J³rgen; Sheng, Zheng-Ming
The effect of the carrier envelope phase (CEP) of few-cycle laser pulses on terahertz (THz) emission from gas targets is investigated by analysis and two-dimensional particle-in-cell simulations. For linearly polarized (LP) light, the THz amplitude depends on the CEP phase sinusoidally. For circularly polarized (CP) light, the THz amplitude is independent of the phase, but its polarization plane rotates with the phase. By measuring the THz amplitude or polarization direction, one can determine the CEP of LP or CP laser pulses, respectively. We find that when the ionization degree of atoms is lower than 10%, the phase dependence of the THz radiation is insensitive to intensity and duration of the laser pulse, which is preferable for the phase determination.
Flow field simulation of gas-water two phase flow in annular channel
NASA Astrophysics Data System (ADS)
Ji, Pengcheng; Dong, Feng
The gas-water two-phase flow is very common in the industrial processes. the deep understanding of the two-phase flow state is to achieve the production equipment design and safe operation. In the measurement of gas-water two-phase flow, the differential pressure sensor is widely used, and some measurement model of multiphase flow have been concluded. The differential pressure is generated when fluid flowing through the throttling components to calculate flow rate. This paper mainly focuses on two points: 1. The change rule of the parameters include velocity, pressure, phase fraction as the change of time, when the phase inlet velocity is given. 2. Analysis the distribution of the parameters above-mentioned at a certain moment under the condition of different water inlet velocity. Three-dimensional computational fluid dynamics (CFD) approach was used to simulate gas-water two-phase flow fluid in the annular channel, which is composed of horizontal pipe and long- waist cone sensor. The simulation results were obtained from FLUENT software.
Energetic Charged Particles Produced in the Gas Phase by Electrolysis
NASA Astrophysics Data System (ADS)
Oriani, R. A.; Fisher, J. C.
CR-39 plastic detector chips suspended in the vapor over the electrolytic solution during electrolysis record the tracks of highly energetic charged particles. The probability that the track densities found in these detector chips and the generally smaller track densities found in controls belong to a common population is 3 ū 10-10 by the Mann-Whitney statistical test. It is therefore concluded that a nuclear reaction that originates in the vapor phase can accompany electrolysis. Occasionally huge numbers of nuclear tracks are recorded by detector chips in the vapor over active electrolysis cells. One such experiment is analyzed in which two contiguous detector chips recorded approximately 40,000 tracks. Analysis of track orientations shows that the shower of charged particles originated in a compact source in the vapor between the chips at about 2 mm from one of the chips. A new type of nuclear reaction is indicated.
Migration of photoinitiators by gas phase into dry foods.
RodrĒguez-Bernaldo de Quir¾s, Ana; Paseiro-Cerrato, Rafael; Pastorelli, Sarah; Koivikko, Riitta; Simoneau, Catherine; Paseiro-Losada, Perfecto
Photoinitiators are components widely used in UV-cured inks for printing food packaging. In the present study, the migration of seven photoinitiators through the vapor phase was investigated. To perform the migration test, an additive enriched polyethylene wax was used as a source to release photoinitiators. The method was applied to evaluate the migration of the photoinitiators into five selected dry foods (cake, bread, cereals, rice and pasta). The highest level of migration was found in the cake. Parameters affecting the migration process were evaluated, and high migration level was found to correlate with both the porosity and the fat content. In addition, the kinetics of migration of the photoinitiators from the additive enriched wax into the cake were studied under accelerated conditions. PMID:19839623
Gas adsorption/absorption heat switch, phase 1. Final report
Chan, C.K.
The service life and/or reliability of far-infrared sensors on surveillance satellites is presently limited by the cryocooler. The life and/or reliability, however, can be extended by using redundant cryocoolers. To reduce parasitic heat leak, each stage of the inactive redundant cryocooler must be thermally isolated from the optical system, while each stage of the active cryocooler must be thermally connected to the system. The thermal break or the thermal contact can be controlled by heat switches. Among different physical mechanisms for heat switching, mechanically activated heat switches tend to have low reliability and, furthermore, require a large contact force. Magnetoresistive heat switches are, except at very low temperatures, of very low efficiency. Heat switches operated by the heat pipe principle usually require a long response time. A sealed gas gap heat switch operated by an adsorption pump has no mechanical motion and should provide the reliability and long lifetime required in long-term space missions. Another potential application of a heat switch is the thermal isolation of the optical plane during decontamination.
Gas adsorption/absorption heat switch, phase 1
NASA Technical Reports Server (NTRS)
Chan, C. K.
The service life and/or reliability of far-infrared sensors on surveillance satellites is presently limited by the cryocooler. The life and/or reliability, however, can be extended by using redundant cryocoolers. To reduce parasitic heat leak, each stage of the inactive redundant cryocooler must be thermally isolated from the optical system, while each stage of the active cryocooler must be thermally connected to the system. The thermal break or the thermal contact can be controlled by heat switches. Among different physical mechanisms for heat switching, mechanically activated heat switches tend to have low reliability and, furthermore, require a large contact force. Magnetoresistive heat switches are, except at very low temperatures, of very low efficiency. Heat switches operated by the heat pipe principle usually require a long response time. A sealed gas gap heat switch operated by an adsorption pump has no mechanical motion and should provide the reliability and long lifetime required in long-term space missions. Another potential application of a heat switch is the thermal isolation of the optical plane during decontamination.
Heaven, Michael C.; Gibson, John K.; Marcalo, Joaquim
In this chapter we review the spectroscopic data for actinide molecules and the reaction dynamics for atomic and molecular actinides that have been examined in the gas phase or in inert cryogenic matrices. The motivation for this type of investigation is that physical properties and reactions can be studied in the absence of external perturbations (gas phase) or under minimally perturbing conditions (cryogenic matrices). This information can be compared directly with the results from high-level theoretical models. The interplay between experiment and theory is critically important for advancing our understanding of actinide chemistry. For example, elucidation of the role of the 5f electrons in bonding and reactivity can only be achieved through the application of experimentally verified theoretical models. Theoretical calculations for the actinides are challenging due the large numbers of electrons that must be treated explicitly and the presence of strong relativistic effects. This topic has been reviewed in depth in Chapter 17 of this series. One of the goals of the experimental work described in this chapter has been to provide benchmark data that can be used to evaluate both empirical and ab initio theoretical models. While gas-phase data are the most suitable for comparison with theoretical calculations, there are technical difficulties entailed in generating workable densities of gas-phase actinide molecules that have limited the range of species that have been characterized. Many of the compounds of interest are refractory, and problems associated with the use of high temperature vapors have complicated measurements of spectra, ionization energies, and reactions. One approach that has proved to be especially valuable in overcoming this difficulty has been the use of pulsed laser ablation to generate plumes of vapor from refractory actinide-containing materials. The vapor is entrained in an inert gas, which can be used to cool the actinide species to room temperature or below. For many spectroscopic measurements, low temperatures have been achieved by co-condensing the actinide vapor in rare gas or inert molecule host matrices. Spectra recorded in matrices are usually considered to be minimally perturbed. Trapping the products from gas-phase reactions that occur when trace quantities of reactants are added to the inert host gas has resulted in the discovery of many new actinide species. Selected aspects of the matrix isolation data were discussed in chapter 17. In the present chapter we review the spectroscopic matrix data in terms of its relationship to gas-phase measurements, and update the description of the new reaction products found in matrices to reflect the developments that have occurred during the past two years. Spectra recorded in matrix environments are usually considered to be minimally perturbed, and this expectation is borne out for many closed shell actinide molecules. However, there is growing evidence that significant perturbations can occur for open shell molecules, resulting in geometric distortions and/or electronic state reordering. Studies of actinide reactions in the gas phase provide an opportunity to probe the relationship between electronic structure and reactivity. Much of this work has focused on the reactions of ionic species, as these may be selected and controlled using various forms of mass spectrometry. As an example of the type of insight derived from reaction studies, it has been established that the reaction barriers for An+ ions are determined by the promotion energies required to achieve the 5fn6d7s configuration. Gas-phase reaction studies also provide fundamental thermodynamic properties such as bond dissociation and ionization energies. In recent years, an increased number of gas-phase ion chemistry studies of bare (atomic) and ligated (molecular) actinide ions have appeared, in which relevant contributions to fundamental actinide chemistry have been made. These studies were initiated in the 1970's and carried out in an uninterrupted way over the course of the past three d
In vivo bubble nucleation probability in sheep brain tissue
NASA Astrophysics Data System (ADS)
Gateau, J.; Aubry, J.-F.; Chauvet, D.; Boch, A.-L.; Fink, M.; Tanter, M.
Gas nuclei exist naturally in living bodies. Their activation initiates cavitation activity, and is possible using short ultrasonic excitations of high amplitude. However, little is known about the nuclei population in vivo, and therefore about the rarefaction pressure required to form bubbles in tissue. A novel method dedicated to in vivo investigations was used here that combines passive and active cavitation detection with a multi-element linear ultrasound probe (4-7 MHz). Experiments were performed in vivo on the brain of trepanated sheep. Bubble nucleation was induced using a focused single-element transducer (central frequency 660 kHz, f-number = 1) driven by a high power (up to 5 kW) electric burst of two cycles. Successive passive recording and ultrafast active imaging were shown to allow detection of a single nucleation event in brain tissue in vivo. Experiments carried out on eight sheep allowed statistical studies of the bubble nucleation process. The nucleation probability was evaluated as a function of the peak negative pressure. No nucleation event could be detected with a peak negative pressure weaker than -12.7 MPa, i.e. one order of magnitude higher than the recommendations based on the mechanical index. Below this threshold, bubble nucleation in vivo in brain tissues is a random phenomenon.
In vivo bubble nucleation probability in sheep brain tissue.
Gateau, J; Aubry, J-F; Chauvet, D; Boch, A-L; Fink, M; Tanter, M
Gas nuclei exist naturally in living bodies. Their activation initiates cavitation activity, and is possible using short ultrasonic excitations of high amplitude. However, little is known about the nuclei population in vivo, and therefore about the rarefaction pressure required to form bubbles in tissue. A novel method dedicated to in vivo investigations was used here that combines passive and active cavitation detection with a multi-element linear ultrasound probe (4-7 MHz). Experiments were performed in vivo on the brain of trepanated sheep. Bubble nucleation was induced using a focused single-element transducer (central frequency 660 kHz, f-number = 1) driven by a high power (up to 5 kW) electric burst of two cycles. Successive passive recording and ultrafast active imaging were shown to allow detection of a single nucleation event in brain tissue in vivo. Experiments carried out on eight sheep allowed statistical studies of the bubble nucleation process. The nucleation probability was evaluated as a function of the peak negative pressure. No nucleation event could be detected with a peak negative pressure weaker than -12.7 MPa, i.e. one order of magnitude higher than the recommendations based on the mechanical index. Below this threshold, bubble nucleation in vivo in brain tissues is a random phenomenon. PMID:22015981
A microcomputer-controlled gas phase microreactor system
Morris, R.M.
Although automated reactors are effective tools for studying a single type of reaction or optimizing catalyst performance, they may not be well suited for exploratory research. These reactors generally have several shortcomings. First, they may have limited versatility since they are usually designed with a single application in mind. Second, computer systems used for process control and data acquisition are often expensive and complex, so that once they are set up for a given application, it is quite difficult to adapt them for another. Because of these restrictions, experimental reactors are often operated manually, requiring a full-time operator to monitor operations and acquire data. This is a greater problem in laboratories where projects are often short-term, and the costs of setting up an automated reactor may outweigh the benefits of automation. For an automated reactor to be cost-effective in such an environment, both reactor hardware and control software must be versatile enough that they can be easily modified and adapted for different experiments. An automated gas-flow microreactor has been designed and constructed which is both inexpensive and flexible. The reactor is capable of performing three different types of experiments, 1) continuous reagent feed with analysis of the product stream, 2) pulsed-flow experiments, and 3) temperature-programmed desorption (TPD) and reaction (TPR). Conversion of the reactor from one configuration to another requires less than one hour. Process control and data acquisition are performed using an Apple II Plus microcomputer (Apple Computer Corp., Cupertino, Calif.) and an ISAAC interface device (Cyborg Corp., Newton, Mass.).
Effect of surfactants on gas holdup of two-phase bubble columns
Estevez, L.A. (Univ. of Puerto Rico, Dept. of Chemical Engineering (US)); Saez, E. (Univ. Simon Bolivar, Dept. de Termodinamica); Pachino, J.; Cavicchioli, I. (INTEVEP, S. A., Caracas (VE))
Two-phase experiments have been carried out using organic liquids with a surfactant and air in a bubble column 30 (cm) inside diameter and 3 (m) tall. Under the presence of the surfactant, two distinct regions are observed: a bubbling region is the lower part, and a froth zone in the upper part of the column. Intrinsic gas holdups were measured in each region. Results showed that intrinsic gas holdup did not change significantly with surfactant concentration. However, the position of the limiting surface separating the two regions varied considerably with surfactant concentration, thus affecting strongly the overall gas holdup. Based on the described experimental observations, correlations for intrinsic and overall gas holdups have been proposed. Intrinsic gas holdups have been correlated and a function of gas and liquid superficial velocities, and not as functions of surfactant concentration. Overall gas holdups have been expressed in terms of intrinsic gas holdup and of the fraction PHI of the column that is occupied by the froth region. The variable PHI is the one that has been correlated in terms of the surfactant concentration.
Steam generators two phase flows numerical simulation with liquid and gas momentum equations
Paris-Sud XI, Universitķ de
that links the core and the steam generator. It goes through the exchanger inside a U-shaped tube bundleSteam generators two phase flows numerical simulation with liquid and gas momentum equations M Abstract This work takes place in steam generators flow studies and we consider here steady state three
A reference trajectory approach to Langevin equations in gas phase collision dynamics
George C. Schatz; Mark D. Moser
In this paper, a new approach to the development of Langevin-like equations for studying gas phase collisional energy tranfer and other dynamical problems is introduced based on the use of reference trajectories to describe memory effects and nonlinear interactions. In this development, the exact equations of motion are first expressed in terms of the deviations of the coordinates and momenta
Methylation of 2-Naphthol Using Dimethyl Carbonate under Continuous-Flow Gas-Phase Conditions
ERIC Educational Resources Information Center
Tundo, Pietro; Rosamilia, Anthony E.; Arico, Fabio
This experiment investigates the methylation of 2-naphthol with dimethyl carbonate. The volatility of the substrates, products, and co-products allows the reaction to be performed using a continuous-flow gas-phase setup at ambient pressure. The reaction uses catalytic quantities of base, achieves high conversion, produces little waste, andģ
Dynamic digital speckle interferometry applied to optical diagnosis of gas-liquid phase change
Yaozu Song; Hongling Zhang; Wei Zhang; Tianfeng Jiao
In this paper, a Dynamic Digital Speckle Interferometry (DDSI) applied to optical diagnosis of gas-liquid phase change is proposed. The basic principle and experimental system of the DDSI are presented. This technology of flow optical diagnosis has the following three main advantages. First, DDSI uses a CCD camera as record device of a specklegram and a microcomputer, which processes the
Gas phase detection of cyclic B3 : 2 2 A1 electronic origin band
Maier, John Paul
Gas phase detection of cyclic B3 : 2 2 E ]X 2 A1 electronic origin band P. Cias, M. Araki, A in the 2 2 E X 2 A1 electronic spectrum of cyclic B3 has been observed by cavity ring down spectroscopy. EXPERIMENT This consists of a standard cavity ring down setup sam- pling a plasma generated in a pulsed
Humidity independent mass spectrometry for gas phase chemical analysis via ambient proton transfer reaction.
Zhu, Hongying; Huang, Guangming
In this work, a humidity independent mass spectrometric method was developed for rapid analysis of gas phase chemicals. This method is based upon ambient proton transfer reaction between gas phase chemicals and charged water droplets, in a reaction chamber with nearly saturate humidity under atmospheric pressure. The humidity independent nature enables direct and rapid analysis of raw gas phase samples, avoiding time- and sample-consuming sample pretreatments in conventional mass spectrometry methods to control sample humidity. Acetone, benzene, toluene, ethylbenzene and meta-xylene were used to evaluate the analytical performance of present method. The limits of detection for benzene, toluene, ethylbenzene and meta-xylene are in the range of ?0.1 to ?0.3 ppbV; that of benzene is well below the present European Union permissible exposure limit for benzene vapor (5 ?g m(-3), ?1.44 ppbV), with linear ranges of approximately two orders of magnitude. The majority of the homemade device contains a stainless steel tube as reaction chamber and an ultrasonic humidifier as the source of charged water droplets, which makes this cheap device easy to assemble and facile to operate. In addition, potential application of this method was illustrated by the real time identification of raw gas phase chemicals released from plants at different physiological stages. PMID:25813029
This study focuses on the review and evaluation of mechanistic and kinetic data for the gas-phase reactions that lead to the production of acidic substances in the environment. A master mechanism is designed that treats oxides, sulfur dioxide, ozone, hydrogen peroxide, ammonia, t...
Field ionization kinetic and electron impact studies of gas phase transition states - The cyclic bromonium ion
NASA Technical Reports Server (NTRS)
Green, M. M.; Giguere, R. J.; Falick, A. M.; Aberth, W.; Burlingame, A. L.
Cis- and trans-isomers of 4-t-butylcyclohexyl bromide were studied to determine the mechanism of cyclic bromonium ion formation. The field ionization kinetic and electron impact data indicate that the formation of the cyclic structure occurs simultaneously with loss of the neutral fragment. The data also show that little or no gas-phase cis-trans isomerization occurs.
The report gives results of Phase II of a field study to assess the applicability of combustion modification (CM) techniques to control NOx and other pollutant emissions from utility boilers and gas turbines without causing deleterious side effects. Comprehensive, statistically d...
NRMRL-RTP-P- 620 Hays**, M.D., Geron*, C.D., Linna**, K.J., Smith*, N.D., and Schauer, J.J. Speciation of Gas-Phase and Fine Particle Emissions from Burning of Foliar Fuels. Submitted to: Environmental Science & Technology EPA/600/J-02/234, http://pubs.acs.org/journals/esthag/...
Modeling gas phase nitric oxide release in lung epithelial cells Jingjing Jiang a
George, Steven C.
Modeling gas phase nitric oxide release in lung epithelial cells Jingjing Jiang a , Steven C Revised 21 April 2011 Available online xxxx Keywords: Arginase Nitric oxide synthase L-Arginine a b s t r a c t Nitric oxide (NO) is present in exhaled breath and is generally considered to be a noninvasive
Formation of complex organic molecules in cold objects: the role of gas phase reactions
Balucani, Nadia; Taquet, Vianney
While astrochemical models are successful in reproducing many of the observed interstellar species, they have been struggling to explain the observed abundances of complex organic molecules. Current models tend to privilege grain surface over gas phase chemistry in their formation. One key assumption of those models is that radicals trapped in the grain mantles gain mobility and react on lukewarm (>30 K) dust grains. Thus, the recent detections of methyl formate (MF) and dimethyl ether (DME) in cold objects represent a challenge and may clarify the respective role of grain surface and gas phase chemistry. We propose here a new model to form DME and MF with gas phase reactions in cold environments, where DME is the precursor of MF via an efficient reaction overlooked by previous models. Furthermore, methoxy, a precursor of DME, is also synthetized in the gas phase from methanol, which is desorbed by a non-thermal process from the ices. Our new model reproduces fairy well the observations towards L1544. It also...
Gas-phase photoemission with soft x-rays: cross sections and angular distributions
Shirley, D.A.; Kobrin, P.H.; Truesdale, C.M.; Lindle, D.W.; Ferrett, T.A.; Heimann, P.A.; Becker, U.; Kerkhoff, H.G.; Southworth, S.H.
A summary is presented of typical gas-phase photoemission studies based on synchrotron radiation in the 50-5000 eV range, using beam lines at the Stanford Synchrotron Radiation Laboratory. Three topics are addressed: atomic inner-shell photoelectron cross sections and asymmetries, correlation peaks in rare gases, and core-level shape resonances in molecules.
Surface Induced Dissociation: Dissecting Noncovalent Protein Complexes in the Gas phase
Wysocki, Vicki H.
with the native quaternary structure of several protein systems studied, even for a large chaperone protein, GroSurface Induced Dissociation: Dissecting Noncovalent Protein Complexes in the Gas phase Mowei Zhou Avenue, Columbus, Ohio 43210, United States CONSPECTUS: The quaternary structures of proteins are both
Cis-Trans Signatures of Proline-Containing Tryptic Peptides in the Gas Phase
Clemmer, David E.
Cis-Trans Signatures of Proline-Containing Tryptic Peptides in the Gas Phase Anne E. Counterman digest peptide ions obtained from digestion of common proteins. Here, we report a mobility signature that aids in identifying proline-containing peptides containing 4-10 residues. Of 129 peptides (e10 residues
Time Resolved, Phase-Matched Harmonic Generation from Exploding Noble Gas Clusters
Shim Bonggu; Hays, Greg; Fomyts'kyi, Mykhailo; Arefiev, Alex; Breizman, Boris; Ditmire, Todd; Downer, Michael C. [Department of Physics, University of Texas at Austin, Austin, Texas 78712 (United States)
Third-harmonic generation from noble-gas clusters by ultrafast probe pulses is more sharply-enhanced than linear absorption following heating by an ultrafast pump pulse, in good agreement with simulations of cluster expansion and collective electron dynamics with phase matching consideration.
Research Paper Sugar Synthesis from a Gas-Phase Formose Reaction
Prebiotic possibilities for the synthesis of interstellar ribose through a protic variant of the formose reaction under gas-phase conditions were studied in the absence of any known cat- alyst. The ion-molecule reaction products, diose and triose, were sought by mass spectrome- try, and relevant masses were observed. Ab initio calculations were used to evaluate protic formose mechanism possibilities. A bilateral
The isomeric ions produced by the gas phase protonation of HNCO and HCNO
NASA Astrophysics Data System (ADS)
Hop, C. E. C. A.; Holmes, J. L.; Ruttink, P. J. A.; Schaftenaar, G.; Terlouw, J. K.
Ab initio molecular orbital theory calculations combined with mass spectrometric experiments show that the gas phase protonation of HNCO yields [H 2NCO] + (? Hf0=672 kJ mol -1), whereas HCNO produces [HCNOH] + (? Hf0=990 kJ mol -1). The proton affinity of fulminic acid, HCNO, is estimated to be 758 kJ mol -1.
Chemical reactions between cold trapped Ba+ ions and neutral molecules in the gas phase
Schiller, Stephan
Chemical reactions between cold trapped Ba+ ions and neutral molecules in the gas phase B. Roth, D-cooled ion trapping apparatus, we have investigated laser-induced chemical reactions between cold trapped Ba is to investigate chemical reactions between cold atomic and molecular ions trapped in radio-frequency traps
Chemical reaction of metal-fullerene in gas phase (2) >Masamichi Konoa
Maruyama, Shigeo
f18-068 Chemical reaction of metal-fullerene in gas phase (2) Ę>Masamichi Konoa , Syuhei Inoueb structure, formation mechanism, chemical reactivity, and so on. To examine these question, chemical reaction clusters. In order to observe the chemical reaction product on a clean baseline, all clusters except for C
Selective oxidations of various primary and secondary alcohols were studied in a gas phase photochemical reactor using immobilized TiO2 catalyst. An annular photoreactor was used at 463K with an average contact time of 32sec. The system was found to be specifically suited for the...
A Lithium Amide Protected Against Protonation in the Gas Phase: Unexpected Effect of LiCl.
Lesage, Denis; Barozzino-Consiglio, Gabriella; Duwald, Romain; Fressignķ, Catherine; Harrison-Marchand, Anne; Faull, Kym F; Maddaluno, Jacques; Gimbert, Yves
In cold THF and in the presence of LiCl, a lithium pyrrolidinylamide forms a 1:1 mixed aggregate, which is observed directly by ESI-MS. Gas-phase protonation of this species leads to selective transfer of H(+) to the chlorine, suggesting that LiCl shields the amide nitrogen and prevents its direct protonation. PMID:25997158
The ozonizer discharge as a gas-phase advanced oxidation process
In the past several years, there has been increased interest in gas-phase pollution control arising from a larger body of environmental regulations and a greater respect for the environment. One promising class of pollution-control technologies is that called advanced oxidation processes (AOPs). Ozonizers have been used for over a century in water treatment and for about two decades in advanced
Relative rate constants for the gas phase reactions of OH radicals with a series of cycloalkenes have been determined at 298 + or - 2 K, using methyl nitrite photolysis in air as a source of OH radicals. The data show that the rate constants for the nonconjugated cycloalkenes stu...
Photodissociation and spectroscopy of gas phase bimetallic clusters. Annual progress report
Focus of the research program is the study of gas phase metal clusters for modeling fundamental interactions on metal surfaces. We characterize the chemical bonding between component atoms in clusters as well as the bonding in adsorption on cluster surfaces. Electronic spectra, vibrational frequencies and bond dissociation energies are measured for both neutral and ionized clusters with laser\\/mass spectrometry techniques.
Photodissociation and spectroscopy of gas phase bimetallic clusters. Progress report for 1990--1991
The general goals of this research project are (1) to synthesize novel bimetallic clusters in the gas phase; (2) to characterize their geometry, electronic structure, and chemical bonding; and (3) to compare these heterogeneous systems to corresponding pure component clusters. Clusters are synthesized by pulsed laser vaporization of solid metal rods coincident with laser photolysis of volatile metal complexes (e.g.,
Photoelectron spectroscopy and photochemistry of tetracyanoethylene radical anion in the gas phase
Sanov, Andrei
Photoelectron spectroscopy and photochemistry of tetracyanoethylene radical anion in the gas phase photochemistry. ė 2012 Elsevier B.V. All rights reserved. 1. Introduction In the past decades, a considerable and photochemistry using photoelectron imaging and photofragment mass-spectros- copy. We report the first direct
Gas phase hydrogenation of acetonitrile on Raney nickel catalysts: reactive hydrogen
F. Hochard; H. Jobic; J. Massardier; A. J. Renouprez
Catalytic hydrogenation of acetonitrile on Raney nickel has been studied in gas phase. The chemisorption of hydrogen has been followed by TPD and inelastic neutron scattering; these techniques indicate the presence of both weakly and strongly adsorbed hydrogen. Kinetic studies and pulse experiments show that only weakly adsorbed hydrogen, localised on top of the nickel atoms and on C3v symmetry
Lattice gas simulations of one and two-phase fluid flows using the Connection Machine-2
Chen, S. (Los Alamos National Lab., NM (USA) Delaware Univ., Newark, DE (USA). Bartol Research Inst.); Doolen, G.D.; Eggert, K.; Grunau, D. (Los Alamos National Lab., NM (USA)); Loh, E.Y. (Thinking Machines Corp., Cambridge, MA (USA))
In this paper, we report recent lattice gas simulations for single-phase and two-phase flows for two dimensional problems using the Connection Machine-2. For the single-phase fluid problem, we use the standard 7-bit lattice gas model with the maximum collision rules. The velocity and vorticity field of the Kelvin-Helmholtz instability is studied. It is shown that the lattice gas method preserves the main properties of the flow patterns observed in other numerical simulations. Using colored particles and holes, the lattice gas method is extended to simulate immiscible fluids with adjustable surface tension, using a purely local collision scheme. The locality of this model allows us to implement a very fast and parallel algorithm on the Connection Machine-2. Because this new model correctly describes short-range particle-particle interactions between liquids and also particle-solid interactions between the fluid and the wall, cohesion and wettability can be simulated. Applications of the current model to several physical systems including spinodal decomposition, Rayleigh-Taylor flows and wettability in two-phase flows through porous media are discussed. 15 refs., 10 figs.
Review of stationary phases for microelectromechanical systems in gas chromatography: feasibility and separations.
Azzouz, I; Vial, J; Thiķbaut, D; Haudebourg, R; Danaie, K; Sassiat, P; Breviere, J
This review covers the recent development of stationary phases for chip-based gas chromatography (GC). Portable systems for rapid and reliable analysis are urgently needed. One way to achieve this is to miniaturize the entire analysis. Because the column is the central component of the GC system and determines the feasibility and quality of separation, this review focuses on stationary phases reported in the literature and their use in different fields during the last two decades, with emphasis on different methods for introducing the stationary phase into the GC column. PMID:23929190
Nucleation and growth of /sup 3/He-B in /sup 3/He-A
Swift, G.W.; Buchanan, D.S.
The /sup 3/He A ..-->.. B transition is remarkable for a number of reasons. Because of the small bulk free energy difference between the two phases, the probability of homogeneous thermal nucleation of the B phase is vanishingly small. Thus the experimental fact that the B phase nucleates readily from the A phase is not understood. The A ..-->.. B transition is also remarkable in that when it occurs after cooling from above the critical temperature, it occurs in an extreme state of supercooling known as hypercooling. In this situation, the velocity of propagation of the A-B phase interface is controlled by microscopic phenomena rather than by thermal diffusion. We briefly review our recent work on both these topics, including the velocity of propagation of the A-B interface through hypercooled /sup 3/He-A, a search for cosmic-ray-induced B-phase nucleation, and preliminary observations of B-phase nucleation locations and temperatures. 15 refs.
Climate Impacts of Ice Nucleation
NASA Technical Reports Server (NTRS)
Gettelman, Andrew; Liu, Xiaohong; Barahona, Donifan; Lohmann, Ulrike; Chen, Celia
Several different ice nucleation parameterizations in two different General Circulation Models (GCMs) are used to understand the effects of ice nucleation on the mean climate state, and the Aerosol Indirect Effects (AIE) of cirrus clouds on climate. Simulations have a range of ice microphysical states that are consistent with the spread of observations, but many simulations have higher present-day ice crystal number concentrations than in-situ observations. These different states result from different parameterizations of ice cloud nucleation processes, and feature different balances of homogeneous and heterogeneous nucleation. Black carbon aerosols have a small (0.06 Wm(exp-2) and not statistically significant AIE when included as ice nuclei, for nucleation efficiencies within the range of laboratory measurements. Indirect effects of anthropogenic aerosols on cirrus clouds occur as a consequence of increasing anthropogenic sulfur emissions with different mechanisms important in different models. In one model this is due to increases in homogeneous nucleation fraction, and in the other due to increases in heterogeneous nucleation with coated dust. The magnitude of the effect is the same however. The resulting ice AIE does not seem strongly dependent on the balance between homogeneous and heterogeneous ice nucleation. Regional effects can reach several Wm2. Indirect effects are slightly larger for those states with less homogeneous nucleation and lower ice number concentration in the base state. The total ice AIE is estimated at 0.27 +/- 0.10 Wm(exp-2) (1 sigma uncertainty). This represents a 20% offset of the simulated total shortwave AIE for ice and liquid clouds of 1.6 Wm(sup-2).
Nucleation and particle coagulation experiments in microgravity
NASA Technical Reports Server (NTRS)
Nuth, J.
Measurements of the conditions under which carbon, aluminum oxide, and silicon carbide smokes condense and of the morphology and crystal structure of the resulting grains are essential if the nature of the materials ejected into the interstellar medium and the nature of the grains which eventually became part of the proto solar nebular are to be understood. Little information is currently available on the vapor-solid phase transitions of refractory metals and solids. What little experimental data do exist are, however, not in agreement with currently accepted models of the nucleation process for more volatile materials. The major obstacle to performing such experiments in earth-based laboratories is the susceptibility of these systems to convection. Evaporation of refractory materials into a low-pressure environment with a carefully controlled temperature gradient will produce refractory smokes when the critical supersaturation of the system is exceeded. Measurement of the point at which nucleation occurs, via light scattering or extinction, can not only yield nucleation data but also, information on the chemical composition and crystal structure of the condensate. Experimental requirements are presented.
A new model for nucleate boiling heat transfer
P. Stephan; J. Hammer
A new model to calculate heat transfer coefficients in nucleate boiling is presented. Heat transfer and fluid flow around a single bubble are investigated taking into account the influence of meniscus curvature, adhesion forces and interfacial thermal resistance on the thermodynamic equilibrium at the gas-liquid interface. The model requires only bubble site densities and departure diameters. Further quantities except the
J. S. Colton
The nucleation of microcellular foams in amorphous thermoplastics has been performed by supersaturation with gas at an elevated temperature. Pressure and temperature are then carefully reduced in the vicinity of the glass transition temperature of the material. The result is a foam structure with cells on the order of 10 microns. This material exhibits greatly increased impact strength, as well
Roaming-mediated ultrafast isomerization of geminal tri-bromides in the gas and liquid phases.
Mereshchenko, Andrey S; Butaeva, Evgeniia V; Borin, Veniamin A; Eyzips, Anna; Tarnovsky, Alexander N
'Roaming' is a new and unusual class of reaction mechanism that has recently been discovered in unimolecular dissociation reactions of isolated molecules in the gas phase. It is characterized by frustrated bond cleavage, after which the two incipient fragments 'roam' on a flat region of the potential energy surface before reacting with one another. Here, we provide evidence that supports roaming in the liquid phase. We are now able to explain previous solution-phase experiments by comparing them with new ultrafast transient absorption data showing the photoisomerization of gas-phase CHBr3. We see that, upon S0-S1 excitation, gas-phase CHBr3 isomerizes within 100?fs into the BrHCBr-Br species, which is identical to what has been observed in solution. Similar sub-100 fs isomerization is now also observed for BBr3 and PBr3 in solution upon S1 excitation. Quantum chemical simulations of XBr3 (X?=?B, P or CH) suggest that photochemical reactivity in all three cases studied is governed by S1/S0 conical intersections and can best be described as occurring through roaming-mediated pathways. PMID:26100804
Roaming-mediated ultrafast isomerization of geminal tri-bromides in the gas and liquid phases
NASA Astrophysics Data System (ADS)
Mereshchenko, Andrey S.; Butaeva, Evgeniia V.; Borin, Veniamin A.; Eyzips, Anna; Tarnovsky, Alexander N.
æRoamingÆ is a new and unusual class of reaction mechanism that has recently been discovered in unimolecular dissociation reactions of isolated molecules in the gas phase. It is characterized by frustrated bond cleavage, after which the two incipient fragments æroamÆ on a flat region of the potential energy surface before reacting with one another. Here, we provide evidence that supports roaming in the liquid phase. We are now able to explain previous solution-phase experiments by comparing them with new ultrafast transient absorption data showing the photoisomerization of gas-phase CHBr3. We see that, upon S0¢S1 excitation, gas-phase CHBr3 isomerizes within 100?fs into the BrHCBr¢Br species, which is identical to what has been observed in solution. Similar sub-100 fs isomerization is now also observed for BBr3 and PBr3 in solution upon S1 excitation. Quantum chemical simulations of XBr3 (X?=?B, P or CH) suggest that photochemical reactivity in all three cases studied is governed by S1/S0 conical intersections and can best be described as occurring through roaming-mediated pathways.
Sputtered alumina as a novel stationary phase for micro machined gas chromatography columns.
Haudebourg, R; Matouk, Z; Zoghlami, E; Azzouz, I; Danaie, K; Sassiat, P; Thiebaut, D; Vial, J
Silica and graphite sputtering have previously been reported as novel solid stationary phase deposition techniques for micro gas chromatography columns. As a conventional solid stationary phase in gas chromatography, compatible with sputtering yet so far unreported, alumina was evaluated in this study. Alumina sputtered semi-packed micro columns were fabricated (including an activation step) and proved able to separate a mixture of volatile alkanes (C1-C4 with isomers) in less than 1Āmin. Kinetic and a thermodynamic evaluation led to calculation of 4,500 theoretical plates for ethane in 1.1Ām (HETPmin?=?250Ā?m) and a Gibbs free energy for propane of 30.2ĀkJĀmol(-1), making this stationary phase's properties very close to those observed with silica-sputtered micro columns. PMID:23989966
Design and results of a dual-gas quasi-phase matching (QPM) foil target
NASA Astrophysics Data System (ADS)
Hage, Arvid; Landgraf, Bj÷rn; Taylor, Michael; W³nsche, Martin; Prandolini, Mark J.; Yeung, Mark; H÷ppner, Hauke; Schulz, Michael; Riedel, Robert; Tavella, Franz; Dromey, Brendan; Zepf, Matthew
Quasi-phase matching (QPM) can be used to increase the conversion efficiency of the high harmonic generation (HHG) process. We observed QPM with an improved dual-gas foil target with a 1 kHz, 10 mJ, 30 fs laser system. Phase tuning and enhancement were possible within a spectral range from 17 nm to 30 nm. Furthermore analytical calculations and numerical simulations were carried out to distinguish QPM from other effects, such as the influence of adjacent jets on each other or the laser gas interaction. The simulations were performed with a 3 dimensional code to investigate the phase matching of the short and long trajectories individually over a large spectral range.
Observation of the Berezinskii-Kosterlitz-Thouless Phase Transition in an Ultracold Fermi Gas
NASA Astrophysics Data System (ADS)
Murthy, P. A.; Boettcher, I.; Bayha, L.; Holzmann, M.; Kedar, D.; Neidig, M.; Ries, M. G.; Wenz, A. N.; Z³rn, G.; Jochim, S.
We experimentally investigate the first-order correlation function of a trapped Fermi gas in the two-dimensional BEC-BCS crossover. We observe a transition to a low-temperature superfluid phase with algebraically decaying correlations. We show that the spatial coherence of the entire trapped system can be characterized by a single temperature-dependent exponent. We find the exponent at the transition to be constant over a wide range of interaction strengths across the crossover. This suggests that the phase transitions in both the bosonic regime and the strongly interacting crossover regime are of Berezinskii-Kosterlitz-Thouless type and lie within the same universality class. On the bosonic side of the crossover, our data are well described by the quantum Monte Carlo calculations for a Bose gas. In contrast, in the strongly interacting regime, we observe a superfluid phase which is significantly influenced by the fermionic nature of the constituent particles.
Inhibited phase behavior of gas hydrates in graphene oxide: influences of surface and geometric constraints.
Kim, Daeok; Kim, Dae Woo; Lim, Hyung-Kyu; Jeon, Jiwon; Kim, Hyungjun; Jung, Hee-Tae; Lee, Huen
Porous materials have provided us unprecedented opportunities to develop emerging technologies such as molecular storage systems and separation mechanisms. Pores have also been used as supports to contain gas hydrates for the application in gas treatments. Necessarily, an exact understanding of the properties of gas hydrates in confining pores is important. Here, we investigated the formation of CO2, CH4 and N2 hydrates in non-interlamellar voids in graphene oxide (GO), and their thermodynamic behaviors. For that, low temperature XRD and P-T traces were conducted to analyze the water structure and confirm hydrate formation, respectively, in GO after its exposure to gaseous molecules. Confinement and strong interaction of water with the hydrophilic surface of graphene oxide reduce water activity, which leads to the inhibited phase behavior of gas hydrates. PMID:25232710
Disulfide-Intact and -Reduced Lysozyme in the Gas Phase: Conformations and Pathways of Folding and Unfolding
Clemmer, David E.
have been studied in the gas phase using ion mobility mass spectrometry techniques. When solutions-intact and disulfide-reduced lysozyme ions in the gas phase using ion-mobility techniques.11-14 Lysozyme is made up, 1997X The conformations of gaseous lysozyme ions (+5 through +18) produced by electrospray ionization
Development of a direct-injected natural gas engine system for heavy-duty vehicles: Final report phase 2
G. B. Cox; K. A. DelVecchio; W. J. Hays; J. D. Hiltner; R. Nagaraj; C. Emmer
This report summarizes the results of Phase 2 of this contract. The authors completed four tasks under this phase of the subcontract. (1) They developed a computational fluid dynamics (CFD) model of a 3500 direct injected natural gas (DING) engine gas injection\\/combustion system and used it to identify DING ignition\\/combustion system improvements. The results were a 20% improvement in efficiency
Charge Loss in Gas-Phase Multiply Negatively Charged Oligonucleotides Iwona Anusiewicz,,, Joanna Berdys-Kochanska,, Cezary Czaplewski, Monika Sobczyk,,
Simons, Jack
Charge Loss in Gas-Phase Multiply Negatively Charged Oligonucleotides Iwona Anusiewicz,,,¦ Joanna. Introduction A. Review of Experimental Findings on Negative Oli- goucleotides. In recent gas-phase experiments1 on small mul- tiply charged single-strand oligonucleotides,2 the Parks group has observed very slow (e
The mid-IR absorption spectrum of gas-phase clusters of the nucleobases guanine and cytosine
de Vries, Mattanjah S.
The mid-IR absorption spectrum of gas-phase clusters of the nucleobases guanine and cytosine Joost pairs that cross-link the two strands, (ii) the interaction between the nucleobases on one strand the factors that play a role, which can be achieved by studying isolated molecules in the gas phase
Predicting Chemical Fingerprints of Vadose Zone Soil Gas and Indoor Air from NonAqueous Phase Liquid Composition
Allen D. Uhler; Kevin J. McCarthy; Stephen D. Emsbo-Mattingly; Scott A. Stout; Gregory S. Douglas
Complex mixtures of volatile organic chemical (VOC) vapors can exist over subsurface accumulations of non-aqueous phase liquids (NAPLs) and contaminated soils. The ability to predict the relative soil gas chemical composition arising from such NAPLs is relevant to studies of the sources and fate of soil gas, and in assessing the possible intrusion of soil gas chemical constituents to indoor
Computational model and simulations of gas-liquid-solid three-phase interactions
NASA Astrophysics Data System (ADS)
Zhang, Lucy; Wang, Chu
A computational technique to model three-phase (gas-liquid-solid) interactions is proposed in this study. This numerical algorithm couples a connectivity-free front-tracking method that treats gas-liquid multi-fluid interface to the immersed finite element method that treats fully-coupled fluid-solid interactions. The numerical framework is based on a non-boundary-fitted meshing technique where the background grid is fixed where no mesh-updating or re-meshing is required. An indicator function is used to identify the gas from the liquid, and the fluid (gas or liquid) from the solid. Several 2-D and 3-D validation cases are demonstrated to show the accuracy and the robustness of the method. A computational technique to model three-phase (gas-liquid-solid) interactions is proposed in this study. This numerical algorithm couples a connectivity-free front-tracking method that treats gas-liquid multi-fluid interface to the immersed finite element method that treats fully-coupled fluid-solid interactions. The numerical framework is based on a non-boundary-fitted meshing technique where the background grid is fixed where no mesh-updating or re-meshing is required. An indicator function is used to identify the gas from the liquid, and the fluid (gas or liquid) from the solid. Several 2-D and 3-D validation cases are demonstrated to show the accuracy and the robustness of the method. Funding from NRC and CCNI computational facility at Rensselaer Polytechnic Institute are greatly acknowledged.
Gas and particulate phase velocity measurements of a high-speed gas jet into a two-dimensional bubbling fluidized bed
NASA Astrophysics Data System (ADS)
Mychkovsky, Alexander; Ceccio, Steven
A Laser Doppler Velocimetry (LDV) technique was implemented to simultaneously measure the gas and particulate phase velocities in a high-speed jet plume in a two-dimensional (2D) bubbling fluidized bed. The gas and particulate phase velocity profiles are presented and analyzed. This includes similarity profile scaling as well as volume fraction, mass flow, and momentum transport calculations for the two phases. Furthermore, applying the Eulerian equation of motion to the particulate phase with the measured velocity profiles, the bed particle drag coefficient is recovered and is found to be consistent with the established empirical value.
X. Wang; X. Sun; H. Zhao
In modeling gas-liquid two-phase flows, the concept of flow regime has been used to characterize the global interfacial structure of the flows. Nearly all constitutive relations that provide closures to the interfacial transfers in two-phase flow models, such as the two-fluid model, are often flow regime dependent. Currently, the determination of the flow regimes is primarily based on flow regime maps or transition criteria, which are developed for steady-state, fully-developed flows and widely applied in nuclear reactor system safety analysis codes, such as RELAP5. As two-phase flows are observed to be dynamic in nature (fully-developed two-phase flows generally do not exist in real applications), it is of importance to model the flow regime transition dynamically for more accurate predictions of two-phase flows. The present work aims to develop a dynamic modeling strategy for determining flow regimes in gas-liquid two-phase flows through the introduction of interfacial area transport equations (IATEs) within the framework of a two-fluid model. The IATE is a transport equation that models the interfacial area concentration by considering the creation and destruction of the interfacial area, such as the fluid particle (bubble or liquid droplet) disintegration, boiling and evaporation; and fluid particle coalescence and condensation, respectively. For the flow regimes beyond bubbly flows, a two-group IATE has been proposed, in which bubbles are divided into two groups based on their size and shape (which are correlated), namely small bubbles and large bubbles. A preliminary approach to dynamically identifying the flow regimes is provided, in which discriminators are based on the predicted information, such as the void fraction and interfacial area concentration of small bubble and large bubble groups. This method is expected to be applied to computer codes to improve their predictive capabilities of gas-liquid two-phase flows, in particular for the applications in which flow regime transition occurs.
Gas-Phase Lasers - a Historical Perspective in Relation to the GEC
NASA Astrophysics Data System (ADS)
Hays, Gerry
Understanding of gas-phase lasers inevitably involves an expertise in many of the specialties of the GEC community - especially homogenous and heterogeneous kinetics, collision cross-sections, gas breakdown physics and fundamental swarm parameters. The GEC community decided early in the evolution of gas-phase lasers to include papers on this topic and the result was many years of contributions to the evolution of and improvement in our understanding of this important class of lasers. Many of the ground-breaking results in gas laser technology were presented at the GEC over the last 3 decades as the traditional rare-gas atomic physics and low-temperature plasma groups turned their attention to parameters of interest to the laser modelers and experimenters. This paper will trace the development of this field, especially as it pertained to the GEC. Some of the key results will be highlighted, together with some of the unpublished trivia and anecdotal incidents in order to capture the flavor of the rapid developments in the early days. The talk will include speculation as to the direction this field is taking, and some suggestions as to opportunities. This work supported by the United States Department of Energy under Contract DE-AC04-94AL85000. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the United States Department of Energy.
Nucleation and dendritic growth in undercooled melts
Herlach, D.M. [DLR, Koeln (Germany). Inst. fuer Raumsimulation
Techniques of containerless processing are applied to undercool and solidify metals and alloys. These techniques allow direct measurements of both the undercooling and the crystal growth velocity. Experimental results are presented for studies of nucleation of metastable crystalline phases and quasicrystals. Measurements of the dendrite growth velocity as a function of undercooling are exemplified for dilute Ni-based alloys and intermetallics. The results are analyzed within current theories of rapid crystal growth. Their consequences on the formation of grain refined microstructures are highlighted. In addition, recent experiments on the undercooling of magnetic alloys are discussed revealing the existence of long-range magnetic ordering in an undercooled melt.
Conformational composition, molecular structure and decomposition of difluorophosphoryl azide in the gas phase.
Wu, Zhuang; Li, Hongmin; Zhu, Bifeng; Zeng, Xiaoqing; Hayes, Stuart A; Mitzel, Norbert W; Beckers, Helmut; Berger, Raphael J F
The conformational composition, molecular structure and decomposition of difluorophosphoryl azide F2P(O)N3 in the gas phase were studied using gas electron diffraction (GED), matrix isolation IR spectroscopy, and quantum-chemical calculations, respectively. While computational methods predict only minor differences in the total energy between the two possible conformers (syn and anti), the analysis of electron diffraction data reveals the dominating abundance of the syn conformer in the gas phase at room temperature. Ab initio frequency analyses suggest that a low-frequency large-amplitude motion of the N3 group with respect to the P-N-N-N torsion is to be expected for the syn conformer. The large amplitude motion was included explicitly into the GED structure refinement procedure. It presumably contributes to a thermodynamic stabilization of the syn-conformer with respect to the anti-conformer in the gas phase at ambient temperature. Upon flash vacuum pyrolysis, this syn conformer undergoes a stepwise decomposition via the difluorophosphoryl nitrene, F2P(O)N, which features as the first experimentally observed phosphoryl nitrene that can be thermally produced in the gas phase. To reveal the reaction mechanism, quantum-chemical calculations on the potential energy surface (PES) of F2P(O)N3 were performed. Both B3LYP/6-311+G(3df) and CBS-QB3 calculation results strongly support a stepwise decomposition into the singlet F2P(O)N, which prefers intersystem crossing to the thermally persistent triplet ground state instead of a Curtius rearrangement into FP(O)NF. PMID:25740559
Missing gas-phase source of HONO inferred from Zeppelin measurements in the troposphere
NASA Astrophysics Data System (ADS)
Li, Xin; Rohrer, Franz; Hofzumahaus, Andreas; Brauers, Theo; Hõseler, Rolf; Bohn, Birger; Broch, Sebastian; Fuchs, Hendrik; Gomm, Sebastian; Holland, Frank; Jõger, Julia; Kaiser, Jennifer; Keutsch, Frank N.; Lohse, Insa; Tillmann, Ralf; Wegener, Robert; Wolfe, Glenn M.; Mentel, Thomas F.; Kiendler-Scharr, Astrid; Wahner, Andreas
Nitrous acid (HONO) is an important trace gas in the atmosphere due to its contribution to the cycles of nitrogen oxides (NOX) and hydrogen oxides (HOX). In the past decades, ground-based observations of HONO around the world showed much higher daytime concentrations than can be explained by the known gas-phase chemistry (i.e., HONO + h? ? OH + NO, HONO + OH ? NO2 + H2O, OH + NO + M ? HONO + M). Different light-dependent reactions on ground surfaces have been proposed as additional daytime HONO sources. However, due to lack of measurements, little is known about the concentrations of HONO and its sources in the planetary boundary layer (PBL) at higher altitudes above the earth's surface. The airship Zeppelin NT is an ideal platform to investigate the chemistry and dynamics of the PBL. During the PEGASOS field campaigns in 2012 and 2013, HONO and its gas-phase sources and sinks were measured simultaneously on-board the airship Zeppelin NT, for the lowest 1 km of the PBL. In the upper part of the altitude range during morning hours, when the airmass is still isolated from processes at the earth's surface by the remaining nocturnal boundary layer, we find unexpectedly large concentrations of HONO which can neither be explained by heterogeneous reactions on aerosol and ground surfaces, nor by known gas-phase reactions. Our observations show evidence for an unknown gas-phase light-dependent HONO production which dominates the overall HONO formation in the lower troposphere. This new HONO source requires NOX and possibly OH or HO2 radicals. As a result, the general impact of HONO on the OH formation is likely overestimated.
A kinetic mechanism was used to link and model the gas-phase reactions and aerosol accumulation resulting from -pinene reactions in the presence of sunlight, ozone (O3), and oxides of nitrogen (NO ...
Dynamic Nucleation of Ice Induced by a Single Stable Cavitation Bubble
NASA Technical Reports Server (NTRS)
Ohsaka, Kenichi; Trinh, Eugene H.
Dynamic nucleation of ice induced by caviation bubble in undercooled water is observed using an acoustic levitation technique. The observation indicates that a high pressure pulse associated with a collapsing bubble is indeed responsible for the nucleation of a high pressure phase of ice.
Climate Impacts of Ice Nucleation
Gettelman, A.; Liu, Xiaohong; Barahona, Donifan; Lohmann, U.; Chen, Chih-Chieh
Several different ice nucleation parameterizations in two different General Circulation Models are used to understand the effects of ice nucleation on the mean climate state, and the climate effect of aerosol perturbations to ice clouds. The simulations have different ice microphysical states that are consistent with the spread of observations. These different states occur from different parameterizations of the ice cloud nucleation processes, and feature different balances of homogeneous and heterogeneous nucleation. At reasonable efficiencies, consistent with laboratory measurements and constrained by the global radiative balance, black carbon has a small (-0.06 Wm?2) and not statistically significant climate effect. Indirect effects of anthropogenic aerosols on cirrus clouds occur mostly due to increases in homogeneous nucleation fraction as a consequence of anthropogenic sulfur emissions. The resulting ice indirect effects do not seem strongly dependent on the ice micro-physical balance, but are slightly larger for those states with less homogeneous nucleation in the base state. The total ice AIE is estimated at 0.26▒0.09 Wm?2 (1? uncertainty). This represents an offset of 20-30% of the simulated total Aerosol Indirect Effect for ice and liquid clouds.
Computational modeling of soot nucleation
NASA Astrophysics Data System (ADS)
Chung, Seung-Hyun
Recent studies indicate that soot is the second most significant driver of climate change---behind CO2, but ahead of methane---and increased levels of soot particles in the air are linked to health hazards such as heart disease and lung cancer. Within the soot formation process, soot nucleation is the least understood step, and current experimental findings are still limited. This thesis presents computational modeling studies of the major pathways of the soot nucleation process. In this study, two regimes of soot nucleation---chemical growth and physical agglomeration---were evaluated and the results demonstrated that combustion conditions determine the relative importance of these two routes. Also, the dimerization process of polycyclic aromatic hydrocarbons, which has been regarded as one of the most important physical agglomeration processes in soot formation, was carefully examined with a new method for obtaining the nucleation rate using molecular dynamics simulation. The results indicate that the role of pyrene dimerization, which is the commonly accepted model, is expected to be highly dependent on various flame temperature conditions and may not be a key step in the soot nucleation process. An additional pathway, coronene dimerization in this case, needed to be included to improve the match with experimental data. The results of this thesis provide insight on the soot nucleation process and can be utilized to improve current soot formation models.
Nucleated casting for the production of large superalloy ingots
NASA Astrophysics Data System (ADS)
Carter, William T.; Jones, Robin M. Forbes
The gas turbine industry is continuously driven to achieve higher thermodynamic efficiency, higher electrical output, and higher reliability through turbine design improvements. The specific component of interest in this article is the turbine wheel, which is the rotating hub on which turbine blades are mounted. The wheel is mechanically loaded by both axial and centrifugal forces and thermally loaded by heat that is conducted from the turbine blades. Currently, the turbine wheel is forged from an ingot that is triple-melted, but nucleated casting is under development as a long-term option. This article describes the investigation into nucleated casting technology for future turbine wheel production.
A correlation for nucleate flow boiling in small channels
Tran, T.N. [Texas Tech Univ., Lubbock, TX (United States). Dept. of Mechanical Engineering]|[Argonne National Lab., IL (United States); Wambsganss, M.W. [Argonne National Lab., IL (United States); Chyu, M.C. [Texas Tech Univ., Lubbock, TX (United States). Dept. of Mechanical Engineering; France, D.M. [Univ. of Illinois, Chicago, IL (United States). Dept. of Mechanical Engineering
Compact heat exchangers are becoming more attractive for applications in which energy conservation, space saving, and cost are important considerations. Applications exist in the process industries where phase-change heat transfer realizes more compact designs and improved performance compared to single-phase heat transfer. However, there have been only a few studies in the literature reporting on phase-change heat transfer and two-phase flow in compact heat exchangers, and validated design correlations are lacking. Recent data from experiments on flow boiling of refrigerants in small channels have led researchers to conclude that nucleation is the dominant heat transfer mechanism over a broad range of heat flux and wall superheats. Local heat transfer coefficients and overall two-phase pressure drops were measured for three different refrigerants with circular and non-circular channels in a range of pressures. This data base supports the nucleate boiling mechanism, and it was used to develop a new correlation for heat transfer in nucleate flow boiling. The correlation is based on the Rohsenow boiling model, introducing a confinement number defined by Kew and Cornwell. The new correlation predicts the experimental data for nucleate flow boiling of three refrigerants within {+-}15%.
Laboratory investigations of the alpha-pinene/ozone gas-phase reaction
Benner, C.L.
In order to provide more insight into terpene photooxidation or ozonolysis reaction mechanisms, a radiotracer technique was developed. This technique was applied to an investigation of the /sup 14/C-alpha-pinene/ozone reaction. In the first phase of the research, the carbon distribution at the conclusion of the ozonolysis reaction was determined by separating carbon-14-labelled gaseous products from labelled aerosols, and counting each phase by liquid scintillation methods. The resulting carbon balance was 38% to 60% filtered aerosols, 6% to 20% gas phase compounds, and 11% to 29% products absorbed on the reaction chamber walls. Recoveries of the alpha-pinene carbon-14 ranging from 79% to 97% were achieved using this method. The alpha-pinene concentrations in these experiments were close to ambient (1 part per billion), yet the carbon balance was similar to that observed at much higher concentrations (>1 part per million). In the second phase of the alpha-pinene study, both gas and aerosol products of the ozonolysis reaction were collected on cartridges impregnated with 2,4-dinitrophenylhydrazine, then analyzed by HPLC. In the final experiments, alpha-pinene aerosol was reacted with a silylating agent to improve the detection of organic acids and alcohols. The gas chromatographic/mass spectrometric analysis of the silylated aerosol products showed evidence of dimer/polymer formation occurring in the ozonolysis reaction.
The use of gas-phase substrates to study enzyme catalysis at low hydration.
Dunn, Rachel V; Daniel, Roy M
Although there are varying estimates as to the degree of enzyme hydration required for activity, a threshold value of ca. 0.2 g of water per gram of protein has been widely accepted. The evidence upon which this is based is reviewed here. In particular, results from the use of gas-phase substrates are discussed. Results using solid-phase enzyme-substrate mixtures are not altogether in accord with those obtained using gas-phase substrates. The use of gaseous substrates and products provides an experimental system in which the hydration of the enzyme can be easily controlled, but which is not limited by diffusion. All the results show that increasing hydration enhances activity. The results using gas-phase substrates do not support the existence of a critical hydration value below which enzymatic activity is absent, and suggest that enzyme activity is possible at much lower hydrations than previously thought; they do not support the notion that significant hydration of the surface polar groups is required for activity. However, the marked improvement of activity as hydration is increased suggests that water does play a role, perhaps in optimizing the structure or facilitating the flexibility required for maximal activity. PMID:15306385
DFT study on foscarnet as an antiviral drug: Conformer analysis, gas phase acidity, metal ion affinity and influence of metal complexation on gas phase acidity
NASA Astrophysics Data System (ADS)
Khalili, Behzad; Rimaz, Mehdi; Tondro, Tahereh
This work presents a density functional theory study of Foscarnet (FOS), an anti-viral drug. In this study conformational analysis, gas phase acidity and metal ion affinity (MIA) of foscarnet with selected cations from alkalis (Li+, Na+, and K+) and alkaline earths (Ca2+ and Mg2+) were calculated. All of the structure optimizations and frequency calculations were performed at the B3LYP level of theory with 6-311++G(d,p) basis set. The calculations showed the MIA order to be K+ < Na+ < Li+ < Ca2+ < Mg2+, in agreement with increasing gas phase acidity of the foscarnet molecule during complexation. Natural bond orbital theory (NBO) and quantum theory of atoms in molecules (QTAIM) were used to investigate the charge transfer process and the nature of interactions in the formed complexes. The results of the NBO analysis revealed that Mn+ acts as charge acceptor and the amount of charge transfer is in agreement with MIA. The QTAIM analysis shows that (Msbnd O) coordinations are electrostatic in nature, and their strengths are in agreement with electron densities at their bond critical points (BCP).
Photodissociation and spectroscopy of gas phase bimetallic clusters. Final report, September 15, 1990--September 14, 1993
Duncan, M.A.
Focus is the study of gas phase metal clusters to evaluate their potential to model fundamental interactions on metal surfaces. Chemical bonding between component atoms in metal clusters and physisorption on cluster surfaces are studied. Electronic spectra, vibrational frequencies, and bond dissociation energies are measured for both neutral and ionized clusters using laser/mass spectrometry. Interest is on bimetallic cluster systems and how they compare to pure metal clusters. The following were studied: Bi/Cr, Bi/Fe, Pb/Sb, Ag{sub 2}-rare gas, Ag-Al, Ag-K, Ag-Na, Ag-Li, and Ag{sub 3}.
Numerical simulation of unsteady planar ammonium perchlorate flames including detailed gas phase chemistry and fluid-structure interaction
NASA Astrophysics Data System (ADS)
Giovangigli, Vincent; Rahman, Shihab
A one-dimensional unsteady combustion model is presented for ammonium perchlorate flames taking into account a detailed gas phase chemistry with 36 species and 216 reactions, a fully-coupled fluid-structure interaction and allowing for acoustic and elastic waves propagation. The model is used to calculate a wave propagating from the gas phase into the solid phase and reflected by the interface. The interface temporal response shows a linear behavior for the test case of interest in this article.
Determination of local values of gas and liquid mass flux in highly loaded two-phase flow
NASA Technical Reports Server (NTRS)
Burick, R. J.; Scheuerman, C. H.; Falk, A. Y.
A measurement system using a deceleration probe was designed for determining the local values of gas and liquid mass flux in various gas/liquid droplet sprayfields. The system was used to characterize two-phase flowfields generated by gas/liquid rocket-motor injectors. Measurements were made at static pressures up to 500 psia and injected mass flow ratios up to 20. The measurement system can also be used at higher pressures and in gas/solid flowfields.
Laboratory studies of cirrus clouds: the ins and outs of ice nucleation
NASA Astrophysics Data System (ADS)
Tolbert, M. A.; Schill, G. P.; Baustian, K. J.
Although cirrus clouds are ever-present in the upper troposphere, the precise mechanisms governing their formation are still uncertain. Recent field observations suggest that ice nucleation in the atmosphere is often more consistent with a heterogeneous nucleation mechanism than a homogeneous one. In the present work, we use optical microscopy coupled with Raman spectroscopy to examine ice nucleation on individual micron-sized particles. Because upper tropospheric particles as well as sub-visible cirrus residues are enhanced in both sulfates and organics, our focus is on complex particles containing these two species. Particles with well-defined structures were generated by nebulization of solutions containing ammonium sulfate and an organic. As the relative humidity was decreased, the aqueous particles underwent liquid-liquid phase separation forming an organic coating over ammonium sulfate. Lowering the relative humidity further resulted in ammonium sulfate efflorescence to a crystalline solid. Ice nucleation was then studied on the layered particles as a function of temperature and relative humidity. During particle formation and ice nucleation, Raman mapping was used to determine the particle structures. Depending on the organic composition and temperature, ice was sometimes observed to nucleate on the ammonium sulfate core within the particle and sometimes nucleated on the organic outer layer. The combination of Raman and optical microscopy allows visualization of the ice nucleation process for complex particles. These studies reveal that the mechanism of heterogeneous ice nucleation depends not just on particle size, but also on particle composition, phase and mixing state.
Nucleation and growth of quasicrystalline Pd--U--Si from the glassy state
Drehman, A.J.; Pelton, A.R.; Noack, M.A.
A Pd--U--Si metallic glass transforms upon annealing to a quasicrystalline phase of the same composition. Electron diffraction patterns of this material verify its icosahedral symmetry. Differential scanning calorimetry and transmission electron microscopy are used to obtain both the nucleation and growth kinetics of this glass-to-quasicrystal, first-order phase tranformation. The homogeneous nucleation rate of the quasicrystalline phase in the metallic glass achieves a maximum at a temperture where its growth is still relatively slow.
Heterogeneous ice nucleation on simulated secondary organic aerosol.
Schill, Gregory P; De Haan, David O; Tolbert, Margaret A
In this study, we have explored the phase behavior and the ice nucleation properties of secondary organic aerosol made from aqueous processing (aqSOA). AqSOA was made from the dark reactions of methylglyoxal with methylamine in simulated evaporated cloud droplets. The resulting particles were probed from 215 to 250 K using Raman spectroscopy coupled to an environmental cell. We find these particles are in a semisolid or glassy state based upon their behavior when exposed to mechanical pressure as well as their flow behavior. Further, we find that these aqSOA particles are poor depositional ice nuclei, in contrast to previous studies on simple mixtures of glassy organics. Additionally, we have studied the effect of ammonium sulfate on the phase, morphology, and ice nucleation behavior of the aqSOA. We find that the plasticizing effect of ammonium sulfate lowers the viscosity of the aqSOA, allowing the ammonium sulfate to effloresce within the aqSOA matrix. Upon humidification, the aqSOA matrix liquefies before it can depositionally nucleate ice, and the effloresced ammonium sulfate can act as an immersion mode ice nucleus. This change in the mode of nucleation is accompanied by an increase in the overall ice nucleation efficiency of the aqSOA particles. PMID:24410444
A Chain of Modeling Tools For Gas and Aqueous Phase Chemstry
NASA Astrophysics Data System (ADS)
Audiffren, N.; Djouad, R.; Sportisse, B.
Atmospheric chemistry is characterized by the use of large set of chemical species and reactions. Handling with the set of data required for the definition of the model is a quite difficult task. We prsent in this short article a preprocessor for diphasic models (gas phase and aqueous phase in cloud droplets) named SPACK. The main interest of SPACK is the automatic generation of lumped species related to fast equilibria. We also developped a linear tangent model using the automatic differentiation tool named ODYSSEE in order to perform a sensitivity analysis of an atmospheric multi- phase mechanism based on RADM2 kinetic scheme.Local sensitivity coefficients are computed for two different scenarii. We focus in this study on the sensitivity of the ozone,NOx,HOx, system with respect to some aqueous phase reactions and we inves- tigate the influence of the reduction in the photolysis rates in the area below the cloud region.
Gas- and aqueous-phase chemistry of HO/sub 2/ in liquid water clouds
Schwartz, S.E.
A model for reversible mass transport of HO/sub 2/ between the gas and aqueous phases of liquid water clouds is used to examine the coupling of reaction kinetics of this species in the two phases. The Henry's law coefficient of HO/sub 2/ necessary for this analysis is evaluated by means of a thermochemical cycle involving O/sup -//sub 2/(aq) to be (1--3) x 10/sup 3/ M atm/sup -1/. The mass accommodation coefficient ..cap alpha.. for uptake of HO/sub 2/ by liquid water is not known and is treated as an adjustable parameter. Results are expressed in terms of yields of HNO/sub 3/(g),H/sub 2/O/sub 2/(aq) relative to the initial photochemical generation rate of OH(g). For large values of ..cap alpha..(> or approx. =10/sup -3/) aqueous-phase H/sub 2/O/sub 2/ formation may be a major radical sink process, but the rate of aqueous-phase H/sub 2/O/sub 2/ production decreases strongly with ..cap alpha..< or approx. =10/sup -3/. Substantial difference, e.g., a factor of as much as 50 in gas-phase HO/sub 2/ concentraiton, is found between kinetic calculations where uptake of HO/sub 2/ by cloud droplets is treated reversibly versus irreversibly. Such differences demonstrate the need to treat the dissolution process as reversible, even for reactive free-radical species.