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Collective thermodiffusion of colloidal suspensions - JuSER
Collective thermodiffusion of colloidal suspensions
Daniel Lüsebrink and Marisol Ripoll
Citation: J. Chem. Phys. 137, 194904 (2012); doi: 10.1063/1.4767398
View online: http://dx.doi.org/10.1063/1.4767398
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Collective thermodiffusion of colloidal suspensions
Daniel Lüsebrink and Marisol Ripoll a)
Theoretical Soft-Matter and Biophysics, Institute of Complex Systems, Forschungszentrum Jülich,
52425 Jülich, Germany
(Received 1 August 2012; accepted 25 October 2012; published online 21 November 2012)
The thermophoretic behavior of concentrated colloidal suspensions can be understood as the sum
of single particle and collective effects. Here, we present a simulation model to investigate the particularities
of the collective thermodiffusive effects in concentrated uncharged solutions, where the
influence of different colloid-colloid interactions is analyzed. The concentration dependence found
in our simulations qualitatively agrees with experimental results. Colloids with repulsive interactions
are found to accumulate more effectively than the solvent in the warm areas, such that the
corresponding Soret coefficients are negative and decrease with increasing concentration. The accumulation
of colloids in the cold regions is facilitated by attraction, such that colloids with attractive
interactions have larger values of the Soret coefficient. A thermodynamic argument that explains
our results from equilibrium quantities is discussed as well. © 2012 American Institute of Physics.
The transport of mass as a response to a temperature
gradient is known as thermodiffusion or Soret effect. 1 This
phenomenon has found a large number of applications in
general and, in particular, when applied to soft matter systems
such as colloidal or polymeric dispersions. Examples range
from separation techniques 2, 3 to microfluidic applications. 4–6
Moreover, thermodiffusion might even have facilitated
conditions for the origin of life. 7, 8 Most of the existing work
on thermodiffusion of colloidal systems is performed in the
regime of dilute systems, 9–15 where the interactions between
macromolecules are not important. The scarce theoretical and
experimental investigations have mainly focused on strongly
interacting systems and have concluded that there is a pronounced
concentration dependence of the thermodiffusive behavior.
We briefly summarize various aspects of these studies.
Experiments with micellar systems 16 display a linear dependence
of the inverse Soret coefficient on concentration, which
is reversed with the addition of surfactant. Measurements on
polystyrene solutions 17 show a strong dependence of some
thermodiffusive properties as the system approaches the glass
transition, while the Soret coefficient decreases slowly with
the concentration, insensitive to the glass transition. Concentrated
charged colloidal systems have been investigated
experimentally and theoretically. 18, 19 In all presented cases,
these systems are characterized by a negative Soret coefficient
that increases with concentration. Using a microscopic
approach at low volume fractions, the contribution of colloidcolloid
interactions to the thermal diffusion coefficient has
been studied theoretically. 20, 21 The temperature dependence
of the potential of mean-force has shown to give rise to sign
changes of the Soret coefficient upon changing temperature
and/or concentration under appropriate conditions. Recent
experiments 22 have investigated the thermophoretic properties
of concentrated colloidal suspensions in which the
a) Electronic mail: email@example.com.
interactions between the colloids were varied from purely
repulsive to short ranged attractive. Results in the low concentration
regime show a reasonable agreement with theory, although
at larger concentrations a significant change of behavior
is observed. At low concentrations, the contribution of the
colloid-colloid interactions or collective contribution is found
to be much less important than the contribution of the colloidsolvent
interaction or single particle contribution. However,
not much is known about the origin of the behavioral change
at larger concentrations. A detailed study of the collective
contribution to the thermodiffusion of colloidal systems by
means of computer simulations can, therefore, importantly
contribute to the deeper understanding of these systems.
In this work, simulations of concentrated systems are performed
with different colloid-colloid interaction potentials.
The model used here essentially disregards single particle effects
becoming an ideal candidate to study the importance of
collective interactions in the thermodiffusion phenomena. The
paper is organized as follows. After a brief introduction of the
main theoretical concepts, we present and reinterpret the experimental
results of Ning et al. 22 to display more clearly the
importance of the collective contribution. Then, the simulation
model and the procedure to perform the measurements
is introduced, and the simulation results are presented afterwards.
The influence of the different characteristics of the interaction
potentials are analyzed separately, such as the effect
of the steepness of the repulsive potential, the range, or
the strength of the attractive interaction. Finally, we present a
simple thermodynamic argument that allows us to express the
Soret coefficient of the dispersion in terms of the thermal expansion
of its components, which explains some of our results
very satisfactorily.
The thermodiffusion phenomena of a two component
mixture can be characterized phenomenologically by the
0021-9606/2012/137(19)/194904/11/$30.00 137, 194904-1
© 2012 American Institute of Physics
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194904-2 D. Lüsebrink and M. Ripoll J. Chem. Phys. 137, 194904 (2012)
quantification of the particle flux J of one of the components
in the direction of a temperature gradient ∇T, 23
J =−ñD m ∇x − ñD T x(1 − x)∇T, (1)
where ñ = n + n ′ is the averaged total number density, with n
and n ′ are the density of the two components, x = n/ñ is the
molar fraction of component one, D m is the mutual diffusion
coefficient, and D T is the thermal diffusion coefficient. The
so-called Soret coefficient is defined as the ratio of the two
diffusion coefficients
D m
and indicates how strongly the two components separate. In
the stationary state, the particle flux vanishes, and the Soret
coefficient can be obtained from the molar fraction and temperature
1 ∇x
x(1 − x) ∇T . (3)
Note that by convention, a positive S T indicates that the relative
accumulation of component one is higher in the cold
side, while a negative S T will display a reverse behavior.
Equation (3) constitutes the standard method to quantify
the thermodiffusion phenomena in concentrated mixtures.
Recently, 24 an alternative expression of the Soret coefficient
has been proposed in terms of the difference of mechanical
driving forces exerted on the particles. These forces are
induced by the presence of temperature inhomogeneities on
the constituent particles, namely, the thermophoretic forces f
and f ′ ,
S T = (f ′ 1
− f )
k B T ∇T . (4)
In the case of a large size separation between the components,
as is the case of a colloidal suspension, the force on the small
component f ′ can be neglected.
When investigating the thermodiffusion properties of a
colloidal suspension with the volume fraction φ, the behavior
can be understood to include two main contributions. The
single particle contribution is determined by the particular
characteristics of the local interactions of the colloid with
the surrounding solvent and can be characterized in the limit
of diluted solutions. The collective contribution appears
when the number of colloids in the solution increases and
will be determined by both the interactions among colloids
and eventually also by the interactions of the colloid with
the surrounding solvent. The single particle contribution
13, 25–27
of the Soret coefficient has shown a pronounced
dependence on the average temperature, particle size, or
nature of the surface interactions.
The collective interactions have been studied theoretically
by Dhont. 20, 21 This theory predicts that colloids with
hard sphere interactions in an incompressible solvent, display
at low concentrations, an approximately linear decay of the
Soret coefficient with the volume fraction φ that can be described
by the expression
low (φ) = 1 T
1 − 0.35φ
(1 − φ)(1 + 1.45φ) + D T,sing
D 0 (1 + 1.45φ) , (5)
≃ 1 T (1 − 0.80φ) + S T,sing(1 − 1.45φ), (6)
where D 0 is the translational diffusion coefficient in the limit
infinite dilution. Here, D T,sing and S T,sing refer to the single
particle contribution of the thermal diffusion and the Soret
coefficients, respectively. The difference between S T,sing and
(φ = 0) corresponds to the ideal gas contribution. 28 Comparison
of this theory with experimental results in the low
concentration regime is discussed in Sec. III. For larger volume
fractions, there is to our best knowledge no available theory
for uncharged colloidal systems.
20, 21
In the theoretical approach of Dhont, single
particle and the collective contributions to the thermal diffusion
coefficient are assumed to be independent of each
other, this is D T = D T,sing + D T, coll , and similarly for the
mutual diffusion coefficient. Considering the definition of
the Soret coefficient in Eq. (2), it can be easily inferred
that the single particle contribution can be defined as S T,sing
= D T,sing /D 0 . This is not the case for the collective contribution,
S T, coll , which will be, in general, dependent on both
D T,sing and D T, coll . Alternatively, it could be assumed that
S T,sing and S T, coll are independent of each other, which would
imply that the two components of D T would not be independent
then. This assumption can be justified considering that
the related thermophoretic forces in Eq. (4) in a concentrated
suspension could be considered as the sum of two independent
contributions. Simulations and experiments considering
different interactions between colloids and solvent as well as
different colloid-colloid interactions at varying concentration
can help us to understand this point better.
The thermal diffusion behavior of coated colloids in
toluene as a function of the volume fraction has been experimentally
investigated by Ning et al. 22 The coating consists of
octadecyl alcohol, which are chains with a length of 18 carbon
groups. They can be thought of as a thin brush covering
the colloid core. The core interactions are essentially attractive
(van der Waals interactions) and, the coating of the colloids
is typically employed to stabilize the suspension. The
brush hair has a length roughly 1% of the colloid size, and
a temperature dependent behavior that can change the colloid
properties. At low temperatures, the attached brushes are
in a collapsed state, such that the colloid-colloid interactions
are attractive at short distances. 29, 30 At high temperatures, the
brushes tend to be extended, and therefore the colloid-colloid
interactions are close to a hard spherelike behavior.
Experiments at different temperatures and volume fractions
of colloids are performed by Ning et al. 22 The experimental
results of the Soret coefficient are summarized in
Fig. 1(a). The range of concentrations goes from the very dilute
solutions with about 1% volume fraction of colloids up to
30% volume fraction. In the range below 10% the magnitude
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194904-3 D. Lüsebrink and M. Ripoll J. Chem. Phys. 137, 194904 (2012)
S T - S T (φ=0)
T = 15 0 C (higher attrac.)
T = 15 0 C (higher attrac.)
1 10
φ / %
φ / %
S T (φ=0,T)
S T,sing (T)
10 20 30 40 50 60
10 20 30 40 50 60
FIG. 1. (a) Soret coefficient for octadecyl coated silica particles in toluene
as a function of the volume fraction φ for different values of the average
temperature. Solid lines are a fit to Eq. (5) for low φ, and dashed lines a
fit to Eq. (7) for high φ. (b) Values of the Soret coefficient at the limit of
zero volume fraction, and the single particle contribution as a function of
the temperature, obtained from the fit of the data to Eq. (5). (c) Temperature
dependence contribution of S T at high φ values are obtained from a fit of
the data to Eq. (7). (a) Reprinted with permission from J. Chem. Phys. 125,
204911 (2006). Copyright 2006 American Institute of Physics.
of the Soret coefficient decreases slightly in all cases. In this
regime, the experimental data are compared to the theoretical
results in Eq. (5) shown as solid lines. This comparison allows
them to determine the values of the single particle contribution
S T,sing in Eq. (6). The extrapolation to zero concentration
S T (φ = 0) can also be straightforwardly obtained from Eq. (6).
Both values are presented in Fig. 1(b), where a strong increase
FIG. 2. Displaced Soret coefficient as a function φ, corresponding to the
collective contribution. Lines correspond to those in Fig. 1. The arrow indicates
increasing colloid-colloid attraction. (Inset) Difference between the
"zero concentration extrapolated Soret coefficients" at low concentration in
Eq. (6) and high concentration in Eq. (7).
of S T with temperature can be observed. Similar behavior is
experimentally observed for colloids in aqueous solutions 27
in the limit of very low concentrations.
For larger volume fractions, the dependence of S T with
concentration changes significantly, and the theory of Dhont
is not longer valid. In Fig. 1(a), it can be seen that for volume
fractions larger than 10% S T becomes a decreasing function in
all cases, eventually even displaying a sign change. Furthermore,
the functional form of this decay can be empirically
described by a universal logarithmic decay 31
S high
=−0.01 ln φ + S high
The extrapolated value at zero concentration S high
for a constant displacement including all the temperature dependence
of S high
. This extrapolated value is noticeably different
from the limit at vanishing concentration of ST
low as displayed
in Fig. 1(c).
As shown in Fig. 1, single particle effects have a very
strong contribution to the Soret coefficient for all volume fractions.
It is interesting though to find a representation in which
these effects are disregarded such that the behavior of the
purely collective effects can be investigated. For this purpose,
Fig. 2 compares the different sets of data displacing them all
to the same vanishing value at limiting zero concentration. At
low volume fractions, the collective contribution to the Soret
coefficient in Fig. 2 decreases with increasing temperature.
This trend follows from the analytical curves in Eq. (5) as
a consequence of the different S T,sing contributions. Within
this representation, the relative error of experimental data is
magnified in the low concentration regime as can be seen in
Fig. 2. On the other hand, increasing the temperature of the
system employed in Ref. 22 affects also the colloid-colloid interactions
that vary from hard-sphere type of repulsion at high
temperature (50 ◦ C), to strong short-ranged attractive interactions
at low temperatures (15 ◦ C). From the data at low concentrations
in Fig. 2 it can then be understood that increasing
the strength of the attraction increases the value of the Soret
coefficient, or similarly, that with increasing attraction the colloids
accumulate more effectively in the cold areas. Moreover,
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194904-4 D. Lüsebrink and M. Ripoll J. Chem. Phys. 137, 194904 (2012)
the collective contribution to the Soret coefficient is typically
negative for purely repulsive colloids and positive for colloids
with a short-range attraction.
The logarithmic decay described in Eq. (7) in the regime
of large concentrations is independent of the temperature.
Nevertheless, the relative displacement of these curves with
respect to each other shows to be non-monotonic with temperature.
This can be seen directly in the data in Fig. 2, and in
the differences of the Soret coefficients extrapolated to zero
concentration for low concentrations in Eq. (6) and high concentrations
in Eq. (7), as displayed in the inset of Fig. 2. This
non-monotonic behavior will be most likely overruled by the
experimental error when determining the contribution to the
Soret coefficient in the limit of zero concentration, since these
values were not the main goal of the experiments in Ref. 22.
More precise experimental data, and/or simulation results, can
contribute to clarify whether the behavior at high concentrations
depends on the interaction, and in that case if it has the
same, or opposite trend as in the low concentration regime.
This is, whether increasing attractive interactions facilitate the
effective accumulation of colloids in the cold areas.
Existing simulations of colloids in temperature
gradients 32–34 are performed with molecular dynamics
(MD) of both the colloidal and solvent particles. The typical
experimental sizes of colloids and solvent particles can
be separated by several orders of magnitude. This largely
hinders simulations that explicitly account for the solvent
particles such as MD or Monte Carlo. Alternatively, several
methods to coarse grain the solvent dynamics have been developed
in the last decades. Outstanding examples are lattice
Boltzmann (LB) 35 or dissipative particle dynamics (DPD). 36
Both these methods are isothermal in their most extended
implementations, although corresponding modifications to
these models have been proposed in order to be able to
37, 38
sustain temperature inhomogeneities both for LB and
In the present work, we employ a relatively new
coarse-grained method known as multiparticle collision dynamics
(MPC) 42 or stochastic rotation dynamics. 43, 44 This
technique has shown to include properly hydrodynamic
interactions, 45, 46 and furthermore to be able to sustain temperature
gradients. 47 Colloidal dynamics are simulated by MD,
where the interactions between colloids is considered by explicit
potentials. Apart from the explicit and efficient implementation
of the non-isothermal solvent, the employed MPC
method offers us the possibility of strongly tune the solvent
colloid interactions.
A. MPC solvent
The mesoscopic MPC fluid consists in N point particles
of constant mass m i (with i the particle index) in a box of volume
V . The particle state is described by its position r i and
velocity v i which vary continuously in phase space. Two alternating
steps determine the system dynamics. In the streaming
step, particles evolve ballistically during a certain collision
time h, r i (t + h) = r i (t + h) + hv i (t). In the collision step,
particles are sorted into cubic collision boxes. All particles j
within the collision box of particle i at a certain time step, interact
with each other through the center-of-mass velocity of
the collision box
v cm,i (t) =
∑ i,t
m j v j (t)
∑ i,t
. (8)
m j
The actual collision considers a rotation of the relative velocity
to the center-of-mass velocity by an angle α, around a
random orientation,
v i (t + h) = v cm,i (t) + R(α)[v i (t) − v cm,i (t)], (9)
with R(α) the stochastic rotation matrix. This simple collision
rule imposes conservation of mass, linear momentum,
and kinetic energy at the collision box level. This ensures the
presence of hydrodynamic interactions, together with the sustainability
of temperature gradients, and thermal fluctuations.
In order to preserve Galilean invariance, and to enhance collisional
transport, random shift of the collision box grid is additionally
considered. 43 The reference units are chosen to be
the particle mass m, the collision box size a, and a reference
system temperature T, that are set to one. This corresponds
to measure length as ˆx = x/a and time as ˆt = t √ k B T/ma 2 ,
with k B the Boltzmann constant. The transport properties of
the MPC fluid have been very successfully related to the
MPC parameters by means of kinetic theory calculations. 48–50
These MPC parameters are the collision time h, the rotation
angle α, and the particle density ρ = N/V. The MPC solvent
is characterized by the ideal gas equation of state due
to the absence of an explicit interaction potential among its
constituent particles. Nevertheless, the range of parameters
with large values of α and small values of h has shown to
display a liquidlike behavior characterized by large values of
the Schmidt number Sc = ν/D with ν the kinematic viscosity
and D the diffusion coefficient. 46, 51 In this work, we use a
unique set of parameters to describe the MPC solvent, these
are h = 0.1, α = 120 ◦ , and ρ = 5, which in three dimensions
corresponds to Sc = 9.6. The averaged temperature has been
set to T 0 = 2 in all simulations, unless stated otherwise.
B. Colloid-solvent interactions
In this work, we employ a simplified model for simulating
the interaction of the colloids with the surrounding solvent.
The interaction of solvent particles and colloids occurs
in the collision step, in which the colloids are considered as
point particles of different mass than the fluid particles in
the calculation of the collision box center-of-mass velocity in
Eq. (8). This is the MPC coupling. The fact that colloidsolvent
interactions do not have any exclude volume potential
implies that the solvent particles can penetrate the volume of
the colloids since they perceive them only as heavy point particles.
A consequence is that local effects are mostly not taken
into account.
In a recent study, performed in parallel to the present one,
colloids interacting with MPC solvent and non-penetrating
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194904-5 D. Lüsebrink and M. Ripoll J. Chem. Phys. 137, 194904 (2012)
solvent-colloid interactions 52, 53 have been investigated in the
limit of an infinitely dilute solution. In this case, the single
particle contribution to thermodiffusion shows an important
dependence on the solvent-colloid interactions which can
even change direction. Simulations with MD solvent and colloids
have also investigated different features of their behavior
in the presence of temperature gradients, 32–34 but have so far
been only employed in the dilute regime.
In the present work, we restrict ourselves to the MPC
coupling for colloid solvent interactions. In spite of its
drawbacks, this coupling has shown to capture the dynamics
of solute particles 51 and has been used in similar fashion to
correctly describe some aspects of the dynamics of concentrated
colloidal solutions. One of the most successful
51, 54
characteristics of the method and this coupling is that hydrodynamic
interactions are properly taken into account. This
has been verified in dilute polymer solutions 46, 55 simulated
with this coupling, and it has been frequently employed in
systems such as rodlike colloids, 56–59 star polymers, 60–62 or
self-propelled structures. 63–65
More interestingly, the MPC coupling provides a very
useful opportunity to investigate the collective contribution
to the thermodiffusion effect in colloidal suspensions, since
the single particle contribution is strongly suppressed, as will
be precisely shown in Sec. VA1. Additionally, this coupling
is computationally very efficient, given the fact that explicit
solvent-colloid forces do not need to be calculated.
C. Colloid-colloid interactions
A pair interaction potential between colloids is considered
by means of MD. This means that although the
colloids take part in the MPC collision step, they do not follow
the MPC streaming step. 45 The colloids positions are updated
with the MD integration algorithm, velocity-Verlet in
our case, where the potential interactions are considered. The
MD integration time step t should be small enough to integrate
the corresponding potential, although there is no further
dependence on it. Typical values are h/t = 50, 100, 200 depending
on the potential.
The colloid-colloid pair potentials are varied to analyze
the influence of attractive and repulsive interactions, and the
effects of softness or attraction strength. Two functional forms
for the potentials are employed in this work. One is the
Lennard-Jones (LJ) type potentials 66
[ (σ ) 2n ( σ
U(r) = 4ɛ −
r r
) n
+ C, r < r c (10)
with r the distance between two colloid centers. The potential
depth is by default chosen to be ɛ/k B T = 1, with k B T the
reference temperature. The colloidal diameter is fixed to σ
= 1, and the mass is m c = 5.0; this is the value that matches
the mass of the fluid in one collision box which has shown
to be an appropriate value to enhance the effect of hydrodynamic
interactions. 51 The repulsive potential (rLJ) is characterized
by C = ɛ, and the attractive (LJ) by C = 0. The value
of the exponent n determines the softness and range of the
interaction. The cut-off radius for rLJ is simply r c = 2 1/n σ
and for the attractive LJ interaction is matched at the point
where the potential is as small as the standard LJ n = 6 potential.
In this way, we define Ũ = U n=6 (r = 2.5 σ ), such that
r c = [2/(1 − √ 1 + Ũ)] 1/6 σ .
The second functional form of the potential is intended
to more accurately match the experimental interactions in
Ref. 22, which are very short ranged. To this potential we refer
as sticky potential, U stk (r), in correspondence to the sticky
spheres in experiments. Similar to the Lennard-Jones potential,
the sticky potential is composed by two terms, a repulsive
core and an attractive tail. The repulsive core is given by
U stk
r (r ij ) = λ r
( σ
r ij
) 48
and the attractive part that is chosen to reproduce the functional
form of depletion interactions, 67–69
U stk
a (r ij ) =−λ a
1 − 3 4
( rij
+ 1 ( rij
) ] 3
. (12)
2 2a
The coefficients λ r and λ a determine the relative strength of
the two contributions. The colloid diameter is estimated by
σ , and the range of the attractive part of the potential is independently
determined by a. The total potential is given by
U stk (r ij ) = ɛ [ U stk
(r ij ) + Ua
stk (r ij ) − Ur stk (r c ) ] , (13)
where ɛ is the strength of the potential, and r c is the cutoff
radius. The parameters employed in the simulations in Sec. V
are specified in Table I.
In the simulations, the number of colloids N c in the simulation
box of size V is varied to account for concentration
effects. The volume fraction of colloids is defined as
φ c = N c πσ 3 /6V . The effective diameter is not taken into account,
although this should not have a big effect, since the
estimation of the effective diameter with an expression, such
as Barker-Henderson, 70 has shown to increase the diameter
only by 1% with our choice of parameters. 51
D. Temperature gradient establishment
We consider a three-dimensional system with periodic
boundary conditions. In one of the dimensions, the temperature
gradient is realized by defining a cold layer with temperature
T c at one extreme of the box, and a hot layer with
temperature T h > T c at the center of the box. In this way, the
simulation box is divided in two half-boxes with increasing
temperatures towards the center. The temperature at the cold
and hot layers is not directly imposed but a consequence of
an energy flux which is imposed with the so-called velocity
TABLE I. Parameters employed for the sticky potentials in Eq. (13).
r c /σ λ r λ a a/σ
1.0365 4. 1940. 0.522
1.1 1.3 185. 0.55
1.2 1.0 43. 0.6
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194904-6 D. Lüsebrink and M. Ripoll J. Chem. Phys. 137, 194904 (2012)
Δx, Δ ρ
Δx, Δ ρ
Δ ρ coll
Δ ρ solv
φ = 0.2
Δ ρ solv
Δ ρ coll
E. Determination of the Soret coefficient
The Soret coefficient is determined through Eq. (3) by
measuring the temperature and the density distribution profiles
of both colloids and solvent within the simulation box.
The profiles are averaged over simulation steps such that local
fluctuations in temperature and density are reduced. For
further analysis, the first two boundary slabs, where the velocity
exchange is performed, are disregarded.
The average density ρ k , is the density that component k
would have in the absence of a temperature gradient. It is instructive
to show in which percentage each component varies
its density with respect to the average value. The normalized
relative density is then defined as
φ = 0.3
0 5 10 15 20
FIG. 3. Profiles for concentrated colloids suspensions interacting with the
LJ n = 6 potential. Crosses indicate the temperature profile with values in
the right axis. The left axis quantifies the normalized relative density of colloids
(down triangles), solvent particles (up triangles), and the normalized
relative molar fraction of colloids (bullets). Lines correspond to the linear fits
to determine the gradients of temperature and molar fraction. (a) φ c = 0.2 as
example of a positive S T with colloids excess on the cold side. (b) φ c = 0.3
as example of a negative S T .
exchange algorithm. The method was originally introduced in
the framework of MD simulations, 71, 72 and consists in identifying
the hottest solvent particle of the cold layer and the
coldest of the warm layer, and interchange their velocities, as
a type of a Maxwell's demon. More details of this, and other
possible implementations of the temperature gradient within
the MPC fluid can be found in Ref. 47. After a certain time,
the system in contact with the thermal baths reaches a steady
linear temperature profile
T (z) = T c +∇Tz (14)
with ∇T = (T h − T c )/L z the resulting temperature gradient
in the z-direction, and L z the distance between the two baths.
The equation of state of a MPC fluid is the one of an ideal gas
which determines the density distribution as ρ(z) = p/k B T(z),
with p the system pressure. In the limit of small temperature
differences, the density profile can be approximated to a linear
function decreasing in the direction of the increasing temperature.
Typical examples of the temperature and solvent density
profiles are shown in Fig. 3. The size of the simulation box
is L ⊥ in the two directions perpendicular to the temperature
gradient and 2L z in the gradient direction. In this work, we
have fixed L z = 40 for all potentials. For the purely repulsive
interactions we use L ⊥ = 30. For the attractive potentials
we employ the smaller value L ⊥ = 10, in order to reduce
computational costs. Simulations are started by arranging the
colloidal particles on a grid and letting the system relax to a
stationary state. Similar to the experimental values we have
varied the volume fraction of colloids up to φ c = 30%.
ρ k (z) = ρ k(z) − ρ k
ρ k
. (15)
Figure 3 shows two examples of relative density profiles of the
solvent and colloids together with their corresponding temperature
profiles. The profiles are only shown for the left side
of the bi-periodic simulation box, although the averages consider
both boxes. The density profile of the fluid essentially
does not change due to the presence of the colloids and it is
determined by the ideal gas equation of state. The average
colloidal molar fraction x c = ρ c /(ρ c + ρ s ) and its gradient
can then be determined from the density values. The resulting
normalized relative mass fractions are shown in Fig. 3 for two
values of the colloid volume fraction. These values together
with the temperature gradient and Eq. (3) allows us to determine
the Soret coefficient, as shown in Fig. 3. It is interesting
to note that
ρ c (z) >ρ s (z) ⇔ x c (z) > 0. (16)
This means that if the colloids have a relative density variation
larger than the solvent in the cold part of the system,
the weight fraction decreases with increasing temperature, or
similarly that S T > 0. This is the case displayed in Fig. 3(a),
while the reverse situation can be seen in Fig. 3(b). Therefore,
in this system it is not adequate to say that S T < 0 indicates
that the component is thermophilic or that it goes preferably
to the warm side, as it would happen, for example, in an incompressible
fluid. Both components can accumulate in the
cold side, but one can accumulate less effective than the other
one in the cold side, which would lead to a negative S T .
The values obtained for S T are given in MPC units, as
indicated in Sec. IV A. In order to compare these values
with experimental ones, the LJ values can be referred to
the Argon values, as standardly done with MD simulations.
This choice is ɛ Ar = 999 J/mol, which implies that the
relevant factor to convert the units is ɛ Ar /TR = 60 K with
R = 8.314 J/(K mol) the ideal gas constant, and T = 2the
employed average temperature. The typical values obtained in
our investigation are between S T ≃ 0.2 and S T ≃−0.3inMPC
units which correspond to values between S T ≃ 0.003 K −1
and S T ≃−0.005 K −1 . This gives a reasonable quantitative
agreement with the experimental data in Fig. 2.
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194904-7 D. Lüsebrink and M. Ripoll J. Chem. Phys. 137, 194904 (2012)
10 15
FIG. 4. Temperature gradient induced phase separation of colloids in liquidgas
coexistence regime below critical point with LJ 12-6, ɛ = 1.0, φ c = 0.1,
and T 0 = 1.0. The volume fraction on the cold side of the system is φ c ≃ 0.37
corresponding to a liquid state. On the hot side, φ c ≃ 0.03 corresponding to
a gas phase.
F. Condensation effects
The absolute values of the temperature distribution may
drive the cold and hot sides of the system into different
points of the phase diagram. The Monte Carlo simulations
by Vliegenthart et al. 66 of Lennard-Jones fluids have shown
that the critical point of a LJ n = 6 fluid is at T c = 1.316 and
φ c = 0.165. where φ sc ≈ 0.52 is the simple cubic packing
fraction. Below the critical point, the system is in the liquidgas
coexistence regime and a phase separation due to the temperature
gradient is observed as can be seen in Fig. 4. Inthis
example, where the average temperature is below the critical
temperature the volume fraction profile of the colloids is not
changing linearly, but drops abruptly indicating a liquid phase
of colloids on the cold side and a gas phase on the warm side.
In principle it is also possible that the colloids form clusters
or droplets, structures that might not be easily observed in
density profiles. For simulation parameters below the critical
point (i.e., high attraction strengths or low temperatures), we
have checked that there are no additional colloid accumulations,
besides the one observed in Fig. 4. We assume that this
check is sufficient although a more exhaustive analysis would
require, for instance, to investigate the pair correlation functions.
In any case, for the remaining study of thermodiffusion
effects performed in this work, we chose system parameters
such that the system remains in a single phase.
To study collective effects in the thermodiffusion of
colloidal suspensions, we perform simulations for various
colloid-colloid interactions with varying colloidal volume
fractions. Different characteristics of the interactions and their
effects on the Soret coefficient are investigated. The purely repulsive
or attractive nature of the interaction, the steepness of
the repulsion, the range, and the strength of the attractive interaction
are the effects we analyze.
A. Limiting cases
1. Limit of infinite dilution
In the limit of very low volume fractions, there are no interactions
among colloids, such that the values of S T should
TABLE II. Values of the Soret coefficient for the MPC binary mixture
at various concentrations, and for two potential interactions at very low
Interaction x c φ S T
MPC binary mixture 0.02 0.05 0.033
" 0.04 0.1 0.019
" 0.07 0.2 0.021
" 0.10 0.3 0.017
rLJ n = 6 0.001 0.02
LJ n = 6 0.001 0.01
be independent of the interaction potential. This is the single
particle limit in which S T is determined by the colloid-solvent
interactions. In order to quantify S T with the MPC coupling in
this limit we perform two types of simulations. First, interactions
potential among colloids are not taken into account, and
second the limit of very low volume fraction is investigated.
In case colloids without interaction potential are considered,
the colloids are reduced to be heavy particles, thisis
MPC particles of larger mass than the solvent particles, such
that the system is a binary mixture of MPC particles. Values
computed for S T in such MPC binary mixture, and various
concentrations are shown in Table II. The concentrations
are expressed in terms of the heavy particle molar fraction
x c = N c /(N c + N). For the sake of better comparison, we
also refer to the volume fraction of N c colloids of diameter
σ = 1. Apart from statistical precision, worse with small
numbers of colloids, the concentration dependence shows to
be practically negligible. It is furthermore noticeable that the
values of S T are always positive. This agrees with the well
described mass effect for Lennard-Jones mixtures, 73–75 which
shows that for a binary mixture of particles of different mass,
the heavier particle will accumulate more effectively in the
cold areas.
In order to have a reference value for the low volume
fraction limit, simulations with φ c = 0.001 have been performed
with two LJ potentials. Values in Table II show, as expected,
to be very similar in spite of the very different interaction
among colloids. The S T values are positive and one order
of magnitude smaller than those at higher volume fractions in
Secs. VB–VD. We can conclude that in the simulations with
potential interactions shown in the rest of this work, the mass
effect is always present, although it is weak and does not dependent
on the volume fraction.
2. Closed packed limit
In the limit of very high volume fraction of colloids the
system will crystallize. In that case, the colloid positions are
not really affected by the temperature and their density is
practically constant along the temperature gradient. The separation
comes then only from how the solvent still adapts to
the temperature gradient. The experiments performed by Ning
et al. 22 are far away from that limit. Experimental results of
highly concentrated solutions of polymers, 76, 77 show a strong
decay of the Soret coefficient to vanishing values for concentrations
approaching the gelation density. In our simulations,
and given the nature of the MPC solvent, the separation be-
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194904-8 D. Lüsebrink and M. Ripoll J. Chem. Phys. 137, 194904 (2012)
S T 1 n=6
φ c
1.0 1.1
0.0 0.1 0.2 0.3
0.0 0
1 2
0.0 0.1 φ
0.2 0.3
FIG. 5. Soret coefficient S T for different mean volume fractions φ c for colloids
with rLJ potentials in Eq. (10) with n = 6 bullets, n = 12 up-triangles,
and n = 24 down-triangles. The inset displays the employed potentials.
FIG. 6. Soret coefficients S T as a function of the volume fraction φ c for LJ
potentials in Eq. (10) with n = 6 squares, n = 12 up-triangles. The inset
displays the employed potentials.
tween solvent and colloids remains also in the case of colloid
concentration at the close packing value S T,cp . As it will be
justified in Sec. VI S T, cp ≃−1/T 0 , value that constitutes the
a minimum threshold. For the simulations presented in this
work then S T, cp =−0.50.
B. Effect of repulsion and repulsion softness
With the exception of very low average volume fractions,
simulations with repulsive colloid-colloid interactions show
a colloid density gradient smaller than the solvent, such that
the Soret coefficient is always negative, as can be seen in
Fig. 5. This can be understood since the excluded volume
interactions do not facilitate an inhomogeneous distribution
of the colloids with the temperature gradient. Increasing
concentration translates in smaller density gradients which
differentiate stronger from the solvent and therefore have
more negative Soret coefficients.
The repulsive interaction between colloids can range
from a completely hard to very soft interactions. We investigate
the effect of the repulsion softness by repulsive Lennard-
Jones type potentials in Eq. (10). An increase of the exponent
n is equivalent to an increase of the steepness of repulsion, or
decrease of softness, as illustrated in the inset of Fig. 5. Results
in Fig. 5 show a very small dependence in the repulsion
softness. Although, the softer potential with n = 6 shows magnitudes
of S T slightly larger for all mean volume fractions than
for the other two potentials, the differences are very small, and
they could account for a different effective colloidal radius.
C. Effect of attraction and attraction range
Attractive interactions favor that colloids are on average
closer to each other than colloids with purely repulsive interactions.
The cold area is then more favorable since they
can approach to each other decreasing their potential energy.
This explains that the relative density of colloids in the cold
area can eventually be higher than the solvent, which translates
into a positive Soret coefficient as can be seen in Fig. 6.
At low volume fractions, increasing concentration may then
increase the value of S T from the limit of low volume fractions.
Increasing the volume fraction, the repulsive part of the
potential becomes progressively more important, and the colloids
are slowly driven away from their preferred cold region.
In this case the Soret coefficient decreases its value inducing
eventually a sign change.
In order to investigate the effect of different attraction
ranges in the thermodiffusion properties of concentrated
colloidal suspensions, two types of attractive potentials are
used, Lennard-Jones in Eq. (10) and sticky in Eq. (13). First,
we compare two different LJ potentials as displayed in the
inset of Fig. 6, the difference between these two potentials
is the steepness of the repulsion (which has shown not to be
of importance), and the range of the attractive interaction.
Although both potentials show a decrease of S T (φ c ) for larger
volume fractions, they show a strongly different behavior.
The long-ranged potential shows positive Soret coefficients
for a large range of φ c . Meanwhile, S T is always negative for
the shorter ranged potential. This behavior is consistent with
the picture that for shorter attractions the excluded volume
interaction becomes important at much smaller values of φ c ,
contributing to a considerably decrease of the S T values.
Figure 7 shows the importance of the attraction range
also with a set of sticky potentials in Eq. (13). The functional
dependence in the case of these potentials is, independently
of the precise potential parameters, monotonically decaying
with increasing colloidal volume fraction. In Fig. 7(a), results
with three attraction ranges are presented for ɛ = 2. These
data show a clear agreement with the results obtained with the
Lennard-Jones potential, this is that decreasing the interaction
range translates into smaller Soret coefficients. Figures 7(b)
and 7(c) show similar results for smaller interaction strengths,
ɛ = 1 and ɛ = 0.5. In this case, the Soret coefficient seems
to be dominated by the repulsive interactions, not showing a
significant distinction for varying interaction range.
D. Effect of the attraction strength
Figure 8 displays the data for the sticky potentials already
shown in Fig. 7, although sorted now in different plots for
fixed attraction range, in order to analyze this dependence. In
all cases investigated, it is observed that an increase of the
interaction strength increases the Soret coefficient. The colloids
accumulate more effectively on the cold areas, where
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194904-9 D. Lüsebrink and M. Ripoll J. Chem. Phys. 137, 194904 (2012)
ε = 2.0
ε = 1.0
r c =1.0365 r c =1.1
r c =1.2
1.0 1.1 r/ σ 1.2
r c = 1.2
r c = 1.1
ε=2.0 r/ σ
1.0 1.1
ε = 0.5
0.0 0.1 0.2 0.3
φ c
FIG. 7. Soret coefficients S T as a function of the volume fraction φ c at various
attraction ranges, squares r c = 1.2, up-triangles r c = 1.1, and bullets
r c = 1.0365. Arrows indicate increasing attraction ranges. The attraction
strength are (a) ɛ = 2.0, (b) ɛ = 1.0, and (c) ɛ = 0.5. The inset in (b) is
an example of employed sticky potentials in Eq. (13).
r c = 1.0365
0.0 0.1 0.2 0.3
φ c
FIG. 8. Soret coefficients S T as a function of the volume fraction φ c at various
attraction ranges, squares ɛ = 2.0, up-triangles ɛ = 1.0, and bullets
ɛ = 0.5. Arrows indicate increasing attraction strength. The attraction
strength are (a) r c = 1.2, (b) r c = 1.1, and (c) r c = 1.0365. The inset in
(b) is an example of employed sticky potentials in Eq. (13).
the kinetic energy is smaller. This effect will be enhanced for
colloids with stronger attraction strengths. This result is consistent
with the argument discussed.
The effect of increasing attraction could be compared
with the experimental data of Ning et al. 22 since the employed
octadecyl coated silica particles are characterized by having
different attractive colloid-colloid interactions as a function
of the average temperature. At low volume fractions, the
trend found in our simulations agrees with the experimental
trend discussed in Sec. III, namely, that increasing attraction,
increases the Soret coefficient. At larger volume fractions,
the experimental S T becomes more negative independent of
the attraction, which we observe as well and interpret as the
increasing importance of the repulsive interactions.
The definition of the Soret coefficient in stationary state
in Eq. (3) can be formulated in terms the densities of each
component as
( ∇ρc
ρ c
− ∇ρ s
ρ s
. (17)
The standard definition of the thermal expansion β T can be
related to the density gradient as
β T = 1 ( ) ∂V
=− 1 ( ) ∂ρ
=− 1 ( ) ∇ρ
. (18)
V ∂T P ρ ∂T P ρ ∇T P
Equation (17) considers the density gradients of the colloids
∇ρ c and of the solvent ∇ρ s in the presence of both components.
In a first approximation though, the contribution due to
the presence of the other component can be neglected, such
that each density gradient can be approximated by the equation
of state of each isolated component. In this way, the Soret
coefficient in Eq. (17) can be approximated by
S T ≃ β T,c − β T,s . (19)
Here β T,s is the thermal expansion coefficient of the solvent,
which for the MPC fluid is known to be β T,s = 1/T.
In the case of purely repulsive interactions, the thermal
expansion coefficient of the colloids β T, c , can be estimated
by considering the Carnahan-Starling expression for hard
spheres 78–80
β T,c = 1
k B T
1 − 2φ 3 c + φ4 c
1 + 4φ c + 4φ 2 c − 4φ3 c + φ4 c
, (20)
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194904-10 D. Lüsebrink and M. Ripoll J. Chem. Phys. 137, 194904 (2012)
0.0 0.1 0.2 0.3
φ c
FIG. 9. Soret coefficient S T as a function of the volume fraction φ c . Symbols
are simulation results with rLJ n = 6 as displayed in Fig. 5. Dashed line corresponds
to Eq. (19) with β T, c in Eq. (20). Solid line includes the additional
contribution S m T = 0.02.
where φ c is the average volume fraction of the colloids. This
approximation neglects the softness of the potentials used in
the simulations, which should not be a problem as discussed
in Sec. VB. The mass effect discussed in Sec. VAwill
provide an additional contribution to the two components in
Eq. (19). The value estimated in Table II as ST
m ≃ 0.02 does
not change the quality of the prediction shown in Fig. 9. The
comparison of Eq. (19) and the simulation results in Fig. 9
shows a very good agreement. In the limit of high volume
fractions discussed in Sec. VA2,Eq.(20) is no longer
valid. When the close packing volume fraction is reached, the
colloid density does not vary anymore with temperature and
β T,c = 0, which implies that S T ≃−1/T.
This analysis leads to the conclusion that the collective
contribution to the Soret coefficient in a colloidal suspension
is mainly determined by the equations of state of each of the
isolated components. In a further analysis, it will be interesting
to investigate how the inclusion of the single particle effects
may or not modify this conclusion. A significant effect
could indicate that the interaction of each colloid with the surrounding
solvent varies due to the presence of the neighbouring
Two additional aspects of the comparison of our simulations
with existing investigations are important to be emphasized.
On the one hand, the theoretical work of Dhont
20, 21
considers an incompressible fluid, and although the experimental
system 22 is not perfectly incompressible, it will definitely
have a different equation of state than the ideal gas
behavior of the MPC fluid. The qualitative agreement of the
results validates the model, although this limitation should be
taken into account.
A second aspect to be considered is that in the experimental
work, 22 different temperatures are related with different
colloid-colloid interactions. Meanwhile, the theoretical
approach in Eq. (6) is performed for hard-sphere colloids,
assuming that the single and collective contributions for the
thermal diffusion coefficient are independent of each other,
as discussed in Sec. II. This means that the dependence of
the Soret coefficient on volume fraction at low concentration
in Eq. (6) only relies on the different single particle contributions.
Our simulations clearly take different colloid-colloid
interactions into account with a unique single particle contribution.
The trend displayed is in principle similar to the one
in experiments, although the experimental dependence in the
low volume fraction regime should be carefully taken into account
given the large experimental errors in the considered
relative quantities. The agreement in the trend of our simulations
and of the experiments arising from the different colloidcolloid
interactions would support that the single and collective
contributions are independent for the Soret coefficient but
not for the self-diffusion coefficient. This conclusion should
be though verified in the case of a more accurate model, where
the single particle contribution to the thermodiffusion coefficient
is more explicitly taken into account.
In this paper, a simulation study of the thermodiffusion
properties of concentrated colloidal suspensions is presented.
Our model considers the presence of colloids with explicit
solvent particles and disregards the specific interactions of the
colloids surface with the surrounding solvent. These interactions
are responsible for the single particle effects which are
the main contribution to the Soret coefficient. This simulation
model, therefore, allows us to separately investigate the effect
of the much less understood contribution of collective interactions
to the Soret coefficient.
The experimental data of Ning et al. 22 are first discussed
and reanalyzed by subtracting the single particle contribution.
This enables us to perform the comparison of our simulation
data with experiments. Our simulation study considers different
colloid-colloid interactions. These are purely repulsive,
or repulsive combined with attraction. For the repulsive
potentials, we consider several softness at short distances,
while with the attraction we study the effect of the range and
strength of the attraction with two different potential shapes.
The main trends found in our study can be summarized as
follows. Repulsive interactions among colloids disfavor an inhomogeneous
distribution of the colloids with the temperature
gradient. In our simulation model, this translates into negative
values of the Soret coefficient of increasing magnitude with
increasing concentration. In contrast, attractive interactions
favor an inhomogeneous distribution of the colloids with the
temperature gradient, which translates into a more effective
accumulation of the colloids in the cold areas and, therefore,
higher values of the Soret coefficient. In this way, increasing
the concentration, always increases the importance of the
repulsive interaction, such that the S T values decrease. On the
other hand, increasing the range or strength of the attraction
leads to larger values of S T , while changing details in the
interaction like potential shape or repulsion steepness is
relatively unimportant. These trends nicely explain all our
simulation results qualitatively. Experimental results also
follow this behavior, namely, that S T increases with increasing
attraction at low volume fractions and S T decreases with increasing
concentration at high volume fraction. Furthermore,
a reasonable quantitative agreement between simulation and
experimental results is found, as discussed in Sec. IV E.
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194904-11 D. Lüsebrink and M. Ripoll J. Chem. Phys. 137, 194904 (2012)
A theoretical estimation of S T for colloidal suspensions
with repulsive colloid-colloid interactions is obtained by
assuming that colloids and fluid distribute along the temperature
gradient following their individual equations of
state, this is disregarding the mutual interactions. Although
complementary studies are still desirable, the good agreement
between this estimation and our simulation result indicates
that the collective contribution to the Soret coefficient in
concentrated colloidal suspensions can be determined from
the equilibrium properties of each of the system components.
Additional experimental results and further simulations of
concentrated colloidal systems taking into account more
explicit colloid-solvent interactions will bring valuable information.
These results could support the approach made in
our simulation model about the independence of the single
particle and collective contributions to the Soret coefficient.
This would be on the one hand an important concept in the
fundamental understanding of the thermodiffusion effect. On
the other hand, it could help in the development of practical
applications of thermodiffusion in concentrated systems,
such as thermal flow field fractionation.
The authors want to thank helpful discussions with Simone
Wiegand, Gerrit A. Vliegenthart, Mingcheng Yang, and
Gerhard Gompper. We also want to acknowledge S. Wiegand
for making directly available to us experimental data in
Ref. 22 and to G. A. Vliegenthart for proofreading the paper.
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Soft Matter 6, 4556 (2010).
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Downloaded 16 May 2013 to 126.96.36.199. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://jcp.aip.org/about/rights_and_permissions


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Sustainability. It's in our nature.
????"Dear count, you must let me look after your daughters! Though I am not staying here long this time- nor are you- I will try to amuse them. I have already heard much of you in Petersburg and wanted to get to know you," said she to Natasha with her stereotyped and lovely smile. "I had heard about you from my page, Drubetskoy. Have you heard he is getting married? And also from my husband's friend Bolkonski, Prince Andrew Bolkonski," she went on with special emphasis, implying that she knew of his relation to Natasha. To get better acquainted she asked that one of the young ladies should come into her box for the rest of the performance, and Natasha moved over to it.,Therefore it doth much add to a man\'s reputation, and is (as Queen Isabella said) like perpetual letters commendatory, to have good forms. To attain them, it almost sufficeth, not to despise them: for so shall a man observe them in others: and let him trust himself with the rest. For if he labour too much to express them, he shall lose their grace; which is to be natural and unaffected. ,????Jean Valjean blew out the light and placed himself in this angle.,???? Let us turn back,--that is one of the story-teller's rights,-- and put ourselves once more in the year 1815, and even a little earlier than the epoch when the action narrated in the first part of this book took place....????This meant two stockings, which by a secret process known only to herself Anna Makarovna used to knit at the same time on the same needles, and which, when they were ready, she always triumphantly drew, one out of the other, in the children's presence. ,????"I don't like those fashionable churches," she said, evidently priding herself on her independence of thought. "God is the same every where. We have an excellent priest, he conducts the service decently and with dignity, and the deacon is the same. What holiness is there in giving concerts in the choir? I don't like it, it's just self-indulgence!",????Evidently Natasha needed to tell that painful yet joyful tale.;

subset: commoncrawl


text: This year marks the 50th anniversary of the Hospice movement.\r\n\r\nThe first modern hospice, St Christopher's, was founded by nurse Cicely Saunders who established the discipline of palliative care. She introduced the idea that dying people need dignity, compassion and respect.\r\n\r\nThe 50th anniversary provides a talking point for\u00a0hospices to encourage conversations about their work and shine a light on the impact they have on the community.\r\n\r\nIn 1967 Saunders\u00a0set up St Christopher's in London, one of the 200 hospice care centres across the UK.\r\n\r\nShe\u00a0had a single minded vision to revolutionise the way people with terminal illnesses or life limiting conditions were treated. She wanted to find a more dignified way to provide end of life care.\r\n\r\nSt Christopher's celebrated the\u00a050th anniversary at a New Year's Day Parade in central London, representing the Boroughs of Bromley and Lambeth and raising \u00a311,000 for the charity.\r\n\r\nSaunders left behind a blueprint for hospices in\u00a0the UK, many of which are self-funded. The 2017 anniversary will be an awareness raising opportunity for hospices across the country.\r\n\r\nFind\u00a0out more about Remember A Charity's hospice charity members.


text:
Turning Tables fellows will be serving drinks at 'Thirteenth Night is for King Cake', a celebration of Crescent City tradition in the style of musical chairs presented by Cantine. Enjoy nearly 30 different interpretations of the traditional king cake, music, drinks, and more!
A group of talented bakers helps us collect donations for Congreso de Jornaleros (Congress of Day Laborers) who are doing substantial work in town supporting the rights and lives of immigrants and asylum seekers in N.O.
Nearly 30 different interpretations of the traditional king cake will be available for raffle and silent auction. Raffle winners will strut their stuff to pick their preferential pastries in a game of musical chairs, deejayed by vinyl spinning extraordinaire Ann Glaviano of Heatwave! dance party. All money collected at this event will be donated directly to Congreso de Jornaleros. We have much more in store (like a guided children's activity, an interactive installation adorned by Milagros Collective, punches, and on-site screen printing by Team Acid) and will keep the details trickling in.
Copyright 2019
Liberty's Kitchen


text:
Israeli airline El Al blasted for asking female passengers to move after ultra-Orthodox men refused to sit next to them
The flight from New York to Tel Aviv was delayed for more than an hour as new seats were found for the pair
AN ISRAELI airline has been blasted for moving two female passengers after ultra-Orthodox Jewish men refused to sit next to them.
The El Al flight was delayed for more than an hour as new seats were found for the pair.
But when crew on the New York to Tel Aviv flight tried to reason with the men, they refused to speak to them - because they too were female.
A man who claims he was a passenger, Khen Rotem, took to Facebook to report the events as they unfolded.
In one post, reported by the Times of Israel, he wrote: "All the men in the crew, except for the captain, are now only dealing with this instead of preparing for take-off and serving the passengers."
He added that eventually an elderly American and young Israeli switched seats allowing the plane to take-off.
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STING ON THE TRAILJogger left in agony after huge swarm of bees attacks her while she is out running
Khen described one of the men as "particularly devout" and explained how he got on the plane with his eyes closed and kept them shut for the duration of the flight.
In a statement given to Times of Israel, El Al apologised for the "inconvenience" to passengers.
It said: "Any discrimination against passengers is absolutely forbidden.
"El Al flight attendants do all they can in order to provide service to a wide variety of passengers with different and diverse requests and try to assist to the best of their ability."
This week's disturbance follows a similar incident last year when a case of discrimination was filed against the airline by a woman who had also been shifted from her designated seat for the same reason.
In that instance, Israel's Supreme Court ruled that asking a passenger to move seat based on gender is a form of discrimination.
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text:
Unlike 2012, when the Iranian police force cracked down on illegal foreign exchange dealers in Tehran and other big cities, the police have this time no plan to intervene in the market unless top authorities order them to do so, Police Chief Brigadier General Esmail Ahmadi-Moghaddam said on Monday.
In 2012, the rial lost about 70 percent of its value due to macroeconomic mismanagement and intensification of economic sanctions imposed by the West on Iran over its nuclear energy program.
In recent months, the rial has lost further ground versus major foreign currencies. The general said senior banking officials already seek police assistance to restrain illegal dealings that add to exchange rate volatility.
The issue of illegal foreign exchange trade has long been troubling the domestic forex market. Taking a casual stroll through Tehran's Ferdowsi area, when foreign exchange dealers have authorized offices, one is sure to run into many individual dealers who regularly do business on every street corner. Although the independent dealers have commonly been blamed for disrupting the market, thus far, governments haven't been successful in ridding the market of illegal trade.
Speaking on the sidelines of the first conference of police detectives, the police chief clarified that the Headquarters for Fighting Economic Corruption, set up in late 2013 by President Hassan Rouhani, has the matter under control and any measures that the police force take are assigned by the headquarters, ISNA reported.
The police commander noted that correcting illegal foreign exchange trade is a "highly sensitive matter."
When foreign exchange rates sky rocketed in 2012, the previous government called on the police force to take extreme strict measures against the unauthorized dealers, he explained.
Nonetheless, in light of the fact that the government itself was short on foreign exchange, the crackdown proved counterproductive and further raised foreign exchange rate volatility.
Past experience has it that crackdowns and radical measures are not the correct way to deal with economic problems, he said, adding that for now, the matter is being logically assessed at a steady pace and solutions have been put forth.


text:
Maintain your momentum at Portland Marriott City Center. Our modern hotel near the Pearl District has the sophisticated comforts and social opportunities you need to recharge. Relax in our stylish rooms with plush Marriott bedding, free Wi-Fi, accessible features, and Concierge Lounge access in select accommodations. Stop by DEN, our onsite Portland restaurant, to enjoy local food, wine, and art. Explore restaurants near our hotel, including Il Solito, Jake's Grill, Imperial by Chef Vitaly Paley, and Portland City Grill. Get moving at our hotel gym, open 24/7. During your stay, enjoy easy access to top Portland destinations, including International Rose Test Garden, Powell's City of Books, Oregon Convention Center, and Portland State University campus. Our convenient downtown location also makes our flexible event venues a smart choice for your upcoming meeting, wedding, or special occasion in Portland. Mix business and pleasure at Portland Marriott City Center.Show More
Enjoy easy access to shopping, dining, and entertainment in downtown Portland with the MAX Light Rail station less than a mile from our hotel.
Host your upcoming business meeting, wedding, or special occasion in our Portland venues, featuring over 3,300 sq. ft. of versatile event space.
Savor local food and wine at DEN, our onsite restaurant and bar. Open daily, DEN offers a relaxing, sophisticated space to dine and connect.


text:
Thomas Bulfinch, as one reviewer put it, "created ananthology of mythology." This audiobook contains the first fourteen chapters ofThe Age of Fable, the first of three volumes, comprising Bulfinch's completework.
The Age of Fablerecounts stories of Greek gods, demigods, and best-known characters inmythology. In our times, many references are made to these stories andcharacters in the arts, especially in the fine arts, theater, and literature. ChaptersincludeIntroductionPrometheus… (more)
|Total Loans
|Concurent Loans
|Maximum lending period
|1 loans
|59 days
Publisher: Alcazar AudioWorks (February 20, 2014)
Duration: 30:20 hours
File size: 626 MB
Language: English


text:
An abandoned property in Flushing has been both an eyesore and a headache for neighbors for over a decade, according to residents.
The dilapidated residence located at 35-20 167th St. has posed quality-of-life concerns for nearby residents — especially next-door neighbors Joe and Joanne Vitulli, who have lived in Flushing for over 40 years and have been dealing with problems stemming from the residence for over a decade.
"[The house] should be either condemned or knocked down," Joanne Vitulli said. "God forbid it goes on fire."
Vitulli said the abandoned residence houses a number of animals, including raccoons, opossums and rats, and that she and her husband frequently find the animals on the back and front yards of their property.
"My daughter-in-law walks in the morning to go to work, she takes the train," Joanne Vitulli said. "She said she actually has to go in the street because of the raccoons and the possums that run out of there."
"It breeds that kind of environment, and that's what we're complaining about," neighbor Sylvia Moreau said.
Joe Vitulli added that the home's basement is full of water, which poses structural concerns all well as attracts mosquitoes, and that the widows on the property have been boarded up for about three years now.
Residents also raised concerns about people they've seen on the property late at night, including teenagers who go into the backyard to smoke or sleep.
"It looks abandoned. Doesn't it look abandoned to you? So that brings teenagers here," Sylvia Moreau said. "We have kids on this block; we just want to make sure it stays safe."
"The cops were here because there were three boys coming out of the kitchen, I guess it is. And I said, 'What are you guys doing?'" Joanne said, who said the teens responded with a sleeping gesture.
Neighbors also expressed concerns about the overgrown vegetation surrounding the home, as well as a large tree on edge of the property which is not maintained and slants out toward the street.
"Don't park your car here; it's gonna fall," said Joanne Vitulli.
Neighbors said they have filed numerous complaints with NYC 311 and the Department of Buildings (DOB) and have seen city employees on the property, but have seen no real change.
Joanne Vitulli said she and her husband last saw the homeowner — who neighbors know only as Robert — on the property a couple of weeks ago, but that he hasn't lived in the residence for years.
"He just passes by," Joe Vitulli said. "He doesn't even go in."
"We've been trying to do something for years," Joanne Vitulli said. "They say: we're gonna take care of this, we're gonna take care of this.' Ten years they've been taking care of it."
"The Department most recently received a complaint that the building was open and unguarded to the public on June 27, 2016," a DOB spokesperson said. "A DOB inspector determined that the building was properly sealed and was not open to the public. No violation was issued. On Dec. 17, 2015, DOB inspectors issued a violation when it was determined that a garage door was missing, rendering the building open and unguarded. The department will continue to provided additional enforcement actions as necessary."
QNS was unable to get in contact with the homeowner.


text:
More Louisiana families are home-schooling
Alexandria Town Talk
Aug 4, 12:00 AM
More Louisiana families are home-schooling
According to figures from the state department of education, there are as many as 26,000 students being instructed at home. Another 4,000-plus online charter school students are being educated virtually at home rather than in a traditional classroom.
Tags: school choice


text:
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Yes the diminuitive table top is done in black and white...I am known for my love of black 'n white....I just think black gives a touch like nothing else...thanks for visiting my site..
Welcome Judy! Happy to see new people still coming into the site...... It's great here, as you will find, once you start moving about the site. The photos are awesome and the people are too! Everyone here is very friendly, helpful, kind and just plain great to chat with. We are always finding something new and different with one another...........
Have a wonderful holiday!
Carol from upstate NY....
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Real estate and urban design blog network Curbed compiled a map of 12 locations used for the filming of "8 mile", the movie that made the world familiar with Detroit urban hip-hop scene and its cityscape.
Adding some local knowledge to the research done by Movie-Locations.com they come up with a guide to Detroit of 1995 that is partly imagined, partly lost and partly immortalised in Eminem's music.
From an incredible parking lot in a derelict theatre where Rabbit's crew battled to an unfortunate cow's head, you can find it all here >>>


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Sanitation shifts to three-day schedule next week due to holiday
City of Ark City offices closed Nov. 28-29 for Thanksgiving; will reopen Dec. 2
ARKANSAS CITY, Kan. (Nov. 19, 2019) — The City of Arkansas City will shift to a three-day sanitation schedule next week due to the closure of all City offices Nov. 28-29 for Thanksgiving.
The Cowley County Landfill and the F Street Limb Disposal and Compost Site also will be closed Nov. 28 in observance of Thanksgiving.
All of Monday's route and part of Tuesday's route will be collected Nov. 25.
The part of Tuesday's route to be collected Monday is from Madison Avenue south to the Mill Canal, from Summit Street east to E Street and southeast through Sleeth Addition, and from Summit Street east to C Street between Birch Avenue and the C Street Canal.
(Please see accompanying map for full detail of pickup areas.)
The remainder of Tuesday's route, all of Wednesday's route and part of Thursday's route will be collected Nov. 26. The part of Thursday's route to be collected Tuesday is from Birch Avenue north to Kansas Avenue and from Sixth Street west to 15th Street.
The remainder of Thursday's route and Friday's entire route will be collected Nov. 27.
All refuse should be placed at normal pickup locations by 6 a.m. on the scheduled day of pickup.
There will be no return pickups. No recycling will be collected Nov. 30. Saturday recycling has been permanently discontinued and residents will have to use one of the three recycling trailers.


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74 days
Template for Manuscripts
Important Dates
Oct. 23-25, 2020
Full Paper Due:
Aug. 31, 2020
Abstract Due:
Aug. 31, 2020
Audience Registration Due:
Oct. 23, 2020
The 8th World Congress on Engineering and Technology (CET 2020) to be held on October 23-25, 2020 in Xi'an China, is composed of 5 Symposiums on the frontier topics in the engineering and technological subjects. It dedicates to facilitating the global development of engineering and technology and exploring ways in which the latest research results can be shared.
Int'l Conference on Industrial and Mechanical Engineering (CIME 2020)
Int'l Conference on Aerospace Engineering (ICAE 2020)
Int'l Conference on Applied and Engineering Mathematics (AEM 2020)
Int'l Conference on Traffic and Transportation Engineering (CTTE 2020)
Int'l Conference on Architecture and Civil Engineering(CACE 2020)
Xi'an, is the capital of Shaanxi province, located in central-northwest China, records the great changes of the country just like a living history book. Called Chang'an (meaning the eternal city) in ancient times, it is one of the birthplaces of the ancient Chinese civilization in the Yellow River Basin area. As the eastern terminal of the Silk Road and the site of the famous Terracotta Warriors of the Qin Dynasty, the city has won a reputation all over the world. More than 3,000 years of history including over 1,100 years as the capital city of ancient dynasties, have endowed the city with an amazing historical heritage. Visitors marvel at the numerous historical sites and cultural relics in and around the city.
If you need the PDF flyer of the conference, please click here to download it.


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The Comparison on the Side Feed Mode of Micro-strip Patch
Dang Wen, Liu Xinliang
Corresponding Author
Dang Wen
Available Online April 2018.
- https://doi.org/10.2991/icsnce-18.2018.21How to use a DOI?
- Keywords
- HFSS Simulation; Micro-strip Patch; Side-feed; Slot; Matching
- Abstract
- The feeding of the micro-strip patch is flexible and complex, especially side feeding. In this paper, a single micro-strip patch antenna with a center frequency of 2.45GHZ is taken as an example to explore the performance of the slotted feed and non-slotted feed and verified in HFSS15.0. Combined with HFSS15.0 software simulation and theoretical calculation, the corresponding conclusions can be obtained. The theoretical value and simulation results will show that: the required 1/4 converter sizes of the non-slotted side feed and slotted side feed are different. By contrasting with sizes of two feeding modes, electrical size of the slotted feed is smaller. It can be known that all performances of the slotted feed are more superior.
- Open Access
- This is an open access article distributed under the CC BY-NC license.
Cite this article
TY - CONF AU - Dang Wen AU - Liu Xinliang PY - 2018/04 DA - 2018/04 TI - The Comparison on the Side Feed Mode of Micro-strip Patch BT - 2018 Second International Conference of Sensor Network and Computer Engineering (ICSNCE 2018) PB - Atlantis Press SP - 101 EP - 104 SN - 2352-538X UR - https://doi.org/10.2991/icsnce-18.2018.21 DO - https://doi.org/10.2991/icsnce-18.2018.21 ID - Wen2018/04 ER -