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ENGLEWOOD, Colo. — Willis McGahee knew when he showed up at minicamp this week that he faced long odds of keeping his starting job since the Denver Broncos had used a high draft pick to select a running back for the second straight season.
Forty-eight hours after his arrival, that reality hit home for McGahee when the Broncos released the 31-year-old running back who led them in rushing last season despite missing the final two months with a right knee injury.
"It's never easy to part ways with a veteran player who made so many positive contributions to our team and community," Broncos Executive Vice President John Elway said in a statement Thursday. "I appreciate all of the competitiveness, toughness and leadership Willis brought to the Broncos. He was an integral part of our team's turnaround during the past two seasons, and I wish him the best as he continues his NFL career."
Even with second-rounder Montee Ball, who scored an NCAA record 83 touchdowns at Wisconsin, joining second-year speedster Ronnie Hillman in the Broncos' backfield, McGahee shunned the team's three weeks of voluntary workouts this spring.
Upon his return for the Broncos' mandatory minicamp Tuesday, McGahee said he skipped the OTAs for family reasons, insisted he would still be the starter come September and suggested that missing those 10 workouts didn't put him at a decided disadvantage by giving the youngsters a head start.
"I probably would have been behind the 8-ball either way," he said Tuesday. "Younger group. Just being real, right?"
Now he'll be looking to carry the ball for someone else.
The 11-year veteran who was set to make $2.5 million in 2013, should draw interest across the league. Although he's pushing 32, he doesn't have the wear and tear that would be expected of a running back who has been in the league a decade because he spent much of his career sharing snaps.
He played in Buffalo from 2003-06 and Baltimore from 2007-10 before joining the Broncos for an eventful two seasons in which he was an integral part of the Tim Tebow experiment and then the Peyton Manning comeback tour.
McGahee, who became one of the NFL's most dependable runners despite tearing all the ligaments in his left knee during his last game for the University of Miami, tore a ligament in his right knee in a game against San Diego last November and missed the rest of the year. Still, he led the team with 731 yards rushing.
He didn't need surgery, and although he still had a limp, he would have been eligible to return to the field for the AFC championship had the Broncos not lost to Baltimore in the playoffs.
McGahee said Tuesday that he's 100 percent and felt he had plenty of football left in him, especially with the way the rules severely limit padded practices now.
He also said he wasn't bothered by the Broncos selecting another running back high in the draft, suggesting, "I'm a different breed. I can block, I can run, I can get the tough yards. Everybody can't do that."
Gore inspired by critics
SANTA CLARA, Calif. — Frank Gore doesn't see turning 30 as a bad thing, even if it's the age when most NFL running backs start to decline.
If anything, the San Francisco 49ers' career rushing leader has embraced the milestone and sees it as another means of motivation.
Not that Gore has ever needed extra incentive.
Whether it was being bypassed in the 2005 draft when he was the sixth running back selected or the string of injuries he's endured and overcome since then, Gore has always felt the need to prove people wrong. Even his spot on a recently released list of the top 100 players in the NFL didn't sit well with the ninth-year veteran. Gore was 32nd.
The 49ers clearly know Gore's value and have limited his participation in the offseason workouts, including this week's three-day minicamp.
Fitzgerald learns new offense
TEMPE, Ariz. — In his record-breaking decade in the NFL, Larry Fitzgerald has grown comfortable in one position.
Now new Arizona Cardinals coach Bruce Arians has Fitzgerald on the move, learning to play all three wide receiver spots.
Fitzgerald says after having some success it's hard to shake his familiar role, but he's working to do just what Arians wants.
Arians says it's a simple concept. Moving his star receiver around will make it much harder for defenses to zero in on him with double coverage.
Fitzgerald and the rest of the Cardinals practiced for just a half-hour in their final day of minicamp on Thursday as Arians let them go early as a reward for all the offseason work they had done.
Ravens begin quest to repeat
OWINGS MILLS, Md. — Coach John Harbaugh was "very pleased" with Baltimore's minicamp and the Super Bowl champion won't unite as a team again until late July.
The Ravens finished their three-day mandatory offseason session on Thursday. Afterward, Harbaugh said, "I was very pleased with the effort, very pleased with what we accomplished. I think we're in a good place as a football team."
Baltimore lost nine significant contributors from last season's team, most notably Ray Lewis, Ed Reed, Anquan Boldin and Matt Birk. They've been replaced by a host of newcomers — including Elvis Dumervil, Chris Canty, Marcus Spears and Michael Huff.
For that reason, it seems as if the Ravens are starting over.
Tackle Bryant McKinnie says, "The chemistry kind of has to grow with all the new people and everything."
Bush returns to old role
ALLEN PARK, Mich. — Detroit Lions running back Reggie Bush says his role will be similar to the one he had in New Orleans and not much like his job description was with the Miami Dolphins.
The Lions plan to put Bush in the backfield and out wide at receiver, trying to take advantage of his speed. Detroit hope Bush becomes the big-play running back it hasn't had since concussions took Jahvid Best off the field.
Bush signed a $16 million, four-year contract with the Lions in March. Bush says he could've re-signed in Miami or played for Arizona, Seattle or Atlanta.
He has run for 4,162 yards and 29 touchdowns and caught 372 passes for 2,730 yards and 15 scores in two seasons in Miami and five years with the Saints.
Eagles and Barkley agree to deal
PHILADELPHIA — Quarterback Matt Barkley and the Philadelphia Eagles have agreed on a four-year contract.
Barkley was selected in the fourth round of the NFL draft after a standout career at Southern California. The move announced Thursday leaves only one draft pick unsigned.
Barkley rewrote the conference record book during a USC-record 47 starts over four seasons, becoming the Pac-12's leader in touchdown passes, yards passing, completions and total offense.
He's competing with Michael Vick and Nick Foles for the starting job.
BC-FBN—NFL Security, 2nd Ld-Writethru,480 NFL to limit bags brought into stadiums AP Photo NY176
FLORHAM PARK, N.J. (AP) — Bring yourself to the game. Leave the cooler and backpack at home.
The NFL is tightening stadium security starting this preseason, limiting the size and type of bags fans can bring to the game.
The restrictions are designed to enhance security while speeding up entry into stadiums.
With the exception of medically necessary items, only clear plastic, vinyl or PVC bags no larger than 12 inches by 6 inches by 12 inches will be allowed. One-gallon clear plastic freezer bags also will be OK, as will small clear plastic bags approximately the size of someone's hand, with or without a handle or strap.
One of those clear bags and a small clutch bag will be allowed per person.
Binoculars, cameras, and smartphones also will be permitted.
Banned items will include purses larger than a clutch bag; coolers; briefcases; backpacks; fanny packs; cinch bags; seat cushions; luggage; computer bags; and camera bags or any bag larger than the permissible size.
The league is encouraging fans not to bring any bags to games.
"Our fans deserve to be in a safe and secure environment," Jeffrey Miller, the NFL's chief security officer, said Thursday. "Public safety is our top priority. This will make the job of checking items much more efficient and effective. We will be able to deliver a better and quicker experience at the gates and also provide a safer environment. We appreciate our fans' cooperation."
An NFL committee on stadium security recommended these measures in May and the owners have approved them.
A secondary buffer area well outside the stadium will be established where security personnel will check for prohibited items or bags being carried toward the ballpark. Fans with prohibited bags will be turned away until they dispose of those bags. Stadium personnel are being encouraged to have approved bags on hand to give to fans, or to have a place outside the restricted areas to check items, so that fans can reclaim after games.
Recently, the NFL has done pat downs and bag checks and also used metal detectors to upgrade security. The new policy announced Thursday has worked well at colleges such as Penn State, Michigan and Michigan State, which do not permit any bags in their stadiums. Boston's TD Garden allows only clutch bags.
The NFL ramped up security at the draft in late April, its one major event since the Boston Marathon bombings. In a statement Thursday, the league said:
"We had been discussing a new approach to bag restrictions before the Boston Marathon incident. We have come up with a way to do it that will actually make access more convenient for fans than it has been. We think the fans will embrace and appreciate it."
Stadium workers and media will continue to enter NFL stadiums through designated gates where they will be subject to screening and bag inspections.


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This section contains 448 words
(approx. 2 pages at 300 words per page)
Cannibals and Missionaries Summary & Study Guide Description
Cannibals and Missionaries Summary & Study Guide includes comprehensive information and analysis to help you understand the book. This study guide contains the following sections:
This detailed literature summary also contains Techniques on Cannibals and Missionaries by Mary McCarthy.
Preview of Cannibals and Missionaries Summary:
Like The Group (1963), Cannibals and Missionaries is concerned with confusion about values and with the difficulty of generating manners and standards of conduct which live up to ideology. The milieu, urban terrorism, conflicting ideologies, and great gaps not only between haves and have-nots but between priorities and values, create a condition of instability and isolation which requires some form of balancing. A rational sense of the self and one's relationship to others and to "things" must temper the increasing irrationality of contemporary life, reflected in the novel as Jeroen, the terrorist leader — devoted to the leveling of "things" and the elevation of people — destroys his comrades and the paintings as well in an explosive suicide pact with Vermeer's Girl with which he has fallen in love.
A preoccupation with the terrorist threat to "civilized values" has been a benchmark of 1970s and...
This section contains 448 words
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subset: commoncrawl


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Tesco Joins AT&T Selling Euro Bonds as Borrowing Costs Decline
Tesco Plc (TSCO), the U.K.'s biggest grocer, and AT&T Inc. (T), the largest U.S. telephone company, are selling bonds in euros as borrowing costs approach the lowest in 4 1/2 months in Europe.
It's Tesco's first sale of notes in the currency since 2011, while AT&T joins a surge of U.S. companies selling the most debt in Europe in six months, according to data compiled by Bloomberg.
U.K. services growth unexpectedly accelerated in October to the fastest in 16 years, indicating continued strength in the economic recovery at the start of the fourth quarter. Borrowing costs may start to increase next year when the Federal Reserve reduces its stimulus program, which economists forecast will happen in March.
"Yields are still attractive on a historical level so companies are making the most of it," said Nick Burns, a credit strategist at Deutsche Bank AG in London. "Companies may also be aware that while consensus doesn't expect tapering before March, at some point it will come back on the radar and cause yields to rise. It could be the perfect combination of factors to issue debt now."
The average yield on investment-grade bonds is at 1.8 percent, near the lowest since June 17, Bloomberg bond index data show. The cost of insuring the debt against losses is holding near a 3 1/2-year low, with the Markit iTraxx Europe index little changed at 83 basis points at 11:30 a.m. in London.
Tesco Bonds
Tesco is marketing 500 million euros ($675 million) of seven-year notes to yield 68 basis points more than the mid-swap rate. The Cheshunt, England-based company is also selling 500 million euros of four-year notes with a spread of 45 basis points, according to a person familiar with the matter.
"Market conditions are supportive and this is an opportune time for us to refinance debt that is maturing early next year," Tom Hoskin, a spokesman for Tesco in Cheshunt, said by e-mail. The retailer has 600 million pounds ($963 million) of bonds coming due in February 2014, according to data compiled by Bloomberg.
AT&T is offering 1 billion euros of bonds due December 2021 to yield 95 basis points more than the swap rate. It's also marketing 1 billion euros of 12-year notes with a spread of 130 basis points, a person with knowledge of that transaction said.
The Dallas-based company will use the proceeds for general corporate purposes and to help fund a debt buyback, said the person. AT&T said in a statement today it is offering to buy back as much as $4 billion of bonds.
Sarah Lubman, an external spokeswoman for AT&T based in New York, didn't respond to an e-mail seeking comment sent outside office hours.
Also in the European market today, French carmaker Renault SA (RNO) is adding 250 million euros to 300 million euros to its 3.625 percent bonds due September 2018 while France's postal service, La Poste SA, is adding 250 million euros to its 2.75 percent bonds maturing in November 2024, according to people familiar with the deals.
-- Editors: Jennifer Joan Lee, Michael Shanahan
To contact the reporter on this story: Katie Linsell in Madrid at firstname.lastname@example.com
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Gordon Getty's 80th, 'A Prayer for My Daughter' premiere
Published 12:38 pm, Friday, January 17, 2014
The day before his 80th birthday party last month, we sat down with composer Gordon Getty, who expressed some hesitation about the San Francisco Symphony's recent world premiere of his new work, "A Prayer for My Daughter."
"Usually a big premiere you'd rather have at some smaller venue in another town," he joked. "So to have this one in center court, it's nervous making."
But no nerves were necessary for Getty at the Symphony's birthday tribute concert starring mezzo-soprano Frederica von Stade, soprano Lisa Delan and tenor Plácido Domingo earlier this month. Because while the music program read like a blockbuster, the stellar celebration felt more like a family musicale for a beloved, down-home friend.
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Organized by his daughter-in-law and son, Vanessa and Billy Getty, this fete featured a sold-out, preconcert supper soiree for 370 supporters who raised funds for the Symphony's free music education programs.
Inside Davies Hall (artfully reimagined by designer Stanlee Gatti), a riot of red-hot ribbons suspended from the ceiling greeted guests who supped at long tables set with roses and a masterful McCall Associates meal.
"I met Gordon 40 ago years at Tanglewood," recalled maestro Michael Tilson Thomas, "where I noticed this curly haired man waxing poetic about Mahler and life."
Things haven't changed much in Getty's world: He remains a dedicated music maker, economic theorist, vintner, generous philanthropist and a longtime Symphony board governor who is prone to exclaiming such enthusiasms as, "Jeepers creepers!" "Holy flying mackerel!" and "Dearheart!"
"Gordon never rests on his laurels; he's constantly tweaking his music," toasted Thomas. "It's remarkable to know someone who is 80 and still a total work in progress."
Among Gordon's fans: his wife, Ann Getty, and stepmother, Teddy Getty Gaston; Rep. Nancy Pelosi and her husband, Paul Pelosi; Charlotte Shultz; Mayor Ed Lee and his wife, Anita: SF Symphony President Sako Fisher and her husband, Bill Fisher; Joshua Robison; Maryon Davies Lewis; composer John Adams and his wife, photographer Deborah O'Grady; Attorney General Kamala Harris; Lt. Gov. Gavin Newsom with family including his dad, Bill Newsom, and sister and brother-in-law, Hilary and Geoff Callan; Ellen Magnin Newman; Ditsa and Alex Pines; Alice Waters; Yves Béhar and Sabrina Buell; Jo Schuman Silver; Alexis and Trevor Traina; Dede Wilsey; Salesforce.com founder-CEO Marc Benioff; Tatum and Alexander Getty; Denise Hale; and Joachim and Nancy Bechtle.
Inside Davies Hall, a full house delighted in the program that included works by Tallis, Strauss, Verdi, Beethoven and Getty, including the world premiere of "A Prayer for My Daughter."
As the spotlight beamed down on the composer's curly, salt-and-pepper mop, he rose from his seat, raising his hands like a prizefighter in salute, the crowd roaring in approval.
And his 80th tour is going global, too: In April, he travels to Munich to record with the Bavarian Radio Symphony Orchestra for his label, PentaTone. In June, the Welsh National Opera premieres his one-act opera, "Usher House," on a double bill with Debussy's work on the same theme, in Cardiff. And Getty continues to strive to get some of his economic theories on the map.
"I've been dumb lucky. Lucky that music is my vocation. Lucky that people, on the whole, have treated me well. Lucky in family and health," mused Getty, last month.
"I've never been less retired," he continued, with his signature basso laugh. "Though I still feel like a teenager."
Catherine Bigelow is The San Francisco Chronicle's society correspondent. E-mail: firstname.lastname@example.com


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research papers
Applications of leverage analysis in structure refinement
aSchool of Chemistry and Centre for Science at Extreme Conditions, The University of Edinburgh, King's Buildings, West Mains Road, Edinburgh EH9 3JJ, Scotland, bNovartis Institutes for BioMedical Research, 4002 Basel, Switzerland, cAgilent Technologies, Unit 10, Mead Road, Yarnton, Oxfordshire OX5 1QU, England, and dChemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, England
*Correspondence e-mail: firstname.lastname@example.com
Leverages measure the influence that observations (intensity data and restraints) have on the fit obtained in crystal structure refinement. Further analysis enables the influence that observations have on specific parameters to be measured. The results of leverage analyses are discussed in the context of the amino acid alanine and an incomplete high-pressure data set of the complex bis(salicylaldoximato)copper(II). Leverage analysis can reveal situations where weak data are influential and allows an assessment of the influence of restraints. Analysis of the high-pressure refinement of the copper complex shows that the influence of the highest-leverage intensity observations increases when completeness is reduced, but low leverages stay low. The influence of restraints, notably those applying the Hirshfeld rigid-bond criterion, also increases dramatically. In alanine the precision of the Flack parameter is determined by medium-resolution data with moderate intensities. The results of a leverage analysis can be incorporated into a weighting scheme designed to optimize the precision of a selected parameter. This was applied to absolute structure refinement of light-atom crystal structures. The standard uncertainty of the Flack parameter could be reduced to around 0.1 even for a hydrocarbon.
Keywords: leverage analysis; crystal structure refinement; restraints.
1. Introduction
Observations (reflection intensities and restraints) do not contribute equally to data fitting during crystal structure refinement. Some observations are extremely influential, while others have hardly any influence at all. The quantity that measures the influence that an observation has on the fit obtained in a refinement is called the leverage, and it can be calculated from the matrix that is used to describe the model in least squares. The leverage tells us how the value of a data point calculated by the model changes in response to a change in the observed value.
The aim of the present paper is to discuss how information on leverages can be used during structure analysis and interpretation. We will show that leverages provide valuable information on factors such as the importance of weak data in modelling and the efficacy of restraints; we will further show that they can be used to address one of the most pressing issues in chemical crystallography, the precise determination of absolute structure for organic compounds that contain no element heavier than oxygen.
An understanding of the kind of information that leverages convey can be obtained by consideration of a simple one-parameter straight-line fit to y = mx. The data in Fig. 1 were constructed to give a best fit line of y = 0.0x, and illustrate different ways in which points can contribute to the fit. The figure in parentheses next to each of the points in Fig. 1 is the leverage of that point. Point A, at x = −5, has a leverage of 0.11, i.e. if the observed value of A changed from y = 4 to y = 5 the model would alter such that the calculated value of y at point A would change from zero to 0.11. Leverages can thus be interpreted as the effect that an observation has on its own calculated value (see below). This idea is illustrated further by the points at x = 0. The fit to y = mx requires the solution to intercept the y axis at y = 0, and the calculated values of y at points B and C will always be zero no matter what the measured value of y is. Both points therefore have zero leverage, and no matter how large their deviation from the model, these points exert no influence on the fit and therefore on their own calculated values. The most extreme points (D and E), at x = 10, have the highest leverages (0.44) and therefore the most influence on the model. Point D has zero error and a large leverage, while E has a large error and large leverage. D and E have exactly the same leverage values, despite having different deviations from the model, because the leverage is derived from the model and not the observed values (more detail is given below). Note also that the sum of the five leverages for points A–E is equal to 1, the number of parameters being fitted.
The calculation of leverages in crystallographic least squares has been discussed by Prince and co-workers (Prince, 2004; Prince & Nicholson, 1985; Prince & Spiegelman, 2004a,b); a discussion of the topic is also available in standard statistics texts such as Rawlings et al. (1998). The mathematics is given in full detail in the articles and book by Prince and co-workers, and only a summary is given here. The analysis is based on the projection matrix P, which relates the observed (y) and calculated () values of the observations: Py = . It is derived as follows: a set of linear equations relates a set of undetermined parameters x to a set of observations y, so that y = Ax, where A is the design matrix. The parameters , which minimize the squared residual between the observations, y, and their calculated values, , are found by solving the normal equations , where W is a weight matrix. Pre-multiplying both sides by the inverse of ATWA gives the solution . Pre-multiplying both sides of this equation by A gives : . Note that the calculation of P is based on the design and weight matrices; the observations are not used.
It is computationally convenient to define a matrix P′ which is related to P by pre-multiplying both sides of y = Ax by U, the upper-right Cholesky factor of the weight matrix, W, to give P′y′ = ′, where y′ = Uy. For a diagonal weight matrix, P′ has the same diagonal as P, but it is now symmetric and may be constructed using only a single matrix Z = UA: P′ = Z(ZTZ)−1ZT. P and P′ are square matrices of dimensions Nobs × Nobs, where Nobs is the number of observations used in the refinement.
In other branches of statistics P is sometimes referred to as the hat matrix because it relates y to . The relationship Py = enables each calculated ŷi to be written as a linear combination of the observations contained in y. This means that an element along the leading diagonal of P (Pii) measures the contribution that an observation yi makes to its own calculated value, something that was illustrated in the simple straight-line-fit example above. The values of Pii are the leverages. They have a maximum value of 1 and a minimum value of 0, and they measure how much influence an observation has on its calculated value. A value of 1.0 means that the observation entirely determines its own calculated value but has no influence on any other observation. The average leverage for a refinement is equal to Nparameters/Nobservations.
Prince extended his analysis by considering which observations are most important for determining the precision of a particular parameter. The analysis enables us to state the amount by which re-measurement of the ith data point will reduce the variance of the estimate of the jth parameter. The dot product of the ith row of Z and the jth column of the inverse normal matrix, (ZTZ)−1, yields the value of a quantity designated tij. The value of tij2/(1 + ) measures the influence of the ith observation on the variance of the jth parameter; we shall refer to this quantity as Tij2. It should be noted that the product of Z and the inverse normal matrix is related by a matrix transpose to the matrix that is used to solve the normal equations for x. The significance of this matrix is that it reveals the magnitude and sense of the contribution that each observed value makes to each model parameter; this feature is discussed in more detail in §3.4.
A high value of Tij2 implies that the ith observation is very important for determination of the jth parameter. Information of this type was used by David et al. (1993) to analyse the influence of different regions of the neutron powder diffraction pattern of C60 on parameters used to track disorder that develops as temperature is increased. The procedure was also used by Hazen & Finger (1989) to optimize the precision of the oxygen positional parameters in pyrope by collecting reflections that were most sensitive to these parameters. The most recent work on leverage analysis has been published by Merli et al. (2001, 2000, 2002), who have applied it to refinements of mineral structures. Their approach has been applied particularly to understanding the role of different classes of data in determining occupancies on mixed metal sites in minerals. The same group has used leverages and other statistical tools such as Cook's distances to identify outliers in refinement, applying this information to improve the robustness of crystallographic least squares (Merli, 2005; Merli & Sciascia, 2011; Merli et al., 2010).
2. Experimental
2.1. Calculation of leverages and T2 values
One factor that has hindered wider application of leverage analysis is that the matrices required for the necessary calculations are not available as output from commonly used refinement packages. The program CRYSTALS (Betteridge et al., 2003) has been modified to output the matrix Z, and the normal matrix and its inverse. (In CRYSTALS, the command sequence
outputs files containing the matrix Z and the normal matrix and its inverse, which are used as input to a program called HATTIE.)
HATTIE has been written to calculate and output leverages and T and T2 values for observations to a file suitable for input into a spreadsheet program. Also written to the file are the Miller indices, Yo, σ(Yo), Yc, sinθ/λ and Yo/σ(Yo) for each reflection, where Y may represent |F| or |F|2, and the subscripts o and c refer to observed and calculated quantities. The calculations apply both to intensity data and to any restraints applied during refinement. The code makes use of several subroutines available in the CrysFML Fortran library (Rodríguez-Carvajal & Platas, 2009). Leverages, which have a maximum value of 1.0, are multiplied by 100, and T values, which are numerically very small, are scaled so that |Tmax| = 100.
Leverage analysis was carried out using both simulated and experimental data on two crystal structures: the amino acid L-alanine and the metal complex bis(salicylaldoximato)copper(II) [which is abbreviated to Cu(sal)2]. All leverage analyses were performed at refinement minima.
2.2. L-Alanine
L-Alanine is the simplest chiral amino acid (see Fig. S1a in the supplementary material1). It is zwitterionic in the solid state with formula +H3NCH(Me)CO2−. The crystal structure is orthorhombic, forming in space group P212121. Experimental intensity data were collected at 100 K on an Agilent Technologies SuperNova diffractometer using a Cu Kα microsource. Data were collected to a resolution of 0.84 Å with an average redundancy of 14.9. A multiscan correction for systematic errors was applied, and data were merged (in point group 222) in SORTAV (Blessing, 1997). The structure of alanine was refined in CRYSTALS against |F|2 using all data. Weights equal to 1/σ2(|F|2) were applied, with a robust-resistant modifier (Prince & Nicholson, 1983) which zero weighted 14 out of 740 reflections as outliers; all such outliers were omitted from further analysis. All non-H atoms were refined with anisotropic displacement parameters. H-atom positions and isotropic displacement parameters were subject to typical bond distance and angle restraints, with Uiso(H) restrained to 1.2 or 1.5 times Uequiv of the parent C or N atom. The program defaults were used for standard deviations applied to the restraints: 0.02 Å, 2° and 0.002 Å2 for the distances, angles and displacement parameters, respectively. The extinction coefficient refined to 4.92 (11) and the Flack (1983) parameter refined to 0.00 (13). The final conventional R factor (unweighted, calculated on |Fo| using data with |Fo| > 4σ(|Fo|) was 1.59%. The goodness of fit was 2.715, but the normal probability plot was linear, with an intercept of 0.04 and a correlation coefficient of 0.996.
A simulated data set was calculated using XPREP (Sheldrick, 2001) to a resolution of 0.4 Å. Uncertainties were estimated according to σ(|F|2) = 0.02|F|2 + 〈|F|2〉/1000. Gaussian random errors were added to the simulated intensities [subroutine GASDEV from Press et al. (1992)].
2.3. Bis(salicylaldoximato)copper(II) [(Cu(sal)2]
The complex consists of two salicylaldoximate ligands bound to Cu in a square planar arrangement (Fig. S1b ). The data used for the present calculations were collected as part of a wider investigation into the effects of high pressure on complexes of salicylaldoximate ligands; the full results of this study (Byrne et al., 2011) will be reported later. The crystal structure is monoclinic, forming in P21/c with the Cu atoms located on inversion centres. Data were collected with synchrotron radiation on beamline I19 at Diamond Light Source with λ = 0.4959 Å at a pressure of 0.55 GPa; the crystal was held in a modified Merrill–Bassett diamond anvil cell with a half-opening angle of 40° (Moggach et al., 2008; Merrill & Bassett, 1974). The average redundancy was 6.1. The diffractometer on I19 consists of a Crystal Logic four-circle κ-goniometer with a Rigaku Saturn CCD detector. The data collection images were converted to Bruker .sfrm format using the program ECLIPSE (Parsons, 2004) and processed using SAINT (Version 7; Bruker–Nonius, 2006). Shading of the detector by the pressure cell was taken into account using integration masks, also generated by ECLIPSE. A multiscan correction was applied using SADABS (Sheldrick, 2008b), and data were merged with SORTAV. The completeness of the final data set was 51.2% to a resolution of 0.85 Å.
The crystal structure was refined in CRYSTALS as described above for L-alanine. A robust-resistant modifier was applied to the 1/σ2(|F|2) weighting scheme, leading to zero weighting of 40 out of 567 reflections, mostly having diffracted beams very close to the opening angle limits of the cell. High-pressure data sets are usually incomplete and it is common practice to apply restraints to help stabilize refinements. The bond distances and angles of the salicylaldoximate ligand were restrained to the values determined from a complete data set measured at ambient pressure. Rigid-bond and rigid-body similarity restraints were applied to the anisotropic displacement parameters of the C, N and O atoms. The H atoms attached to sp2 carbon atoms were restrained to be coplanar with the ligand. The standard deviations applied to the restraints were 0.01 Å, 1°, 0.01 Å, and 0.005 and 0.04 Å2 for the distances, angles, planarity, and rigid-bond and rigid-body restraints. Restraints were applied to H atoms as described above for L-alanine (also using the same standard deviations as for L-alanine). The final conventional R factor was 2.87%. The goodness of fit was 1.080, and the normal probability plot had an intercept of −0.07 and a correlation coefficient of 0.999.
For the purposes of comparison a complete data set was collected under ambient conditions using a Bruker APEXII diffractometer and Mo Kα radiation. Integration was carried out using SAINT and an absorption correction applied using SADABS. The structure was refined using the same procedure outlined above for the high-pressure data set.
2.4. Test data for absolute structure refinements
§3.6 describes a method where leverage analysis is used to improve the precision of the Flack parameter in some absolute structure refinements. Seventeen data sets were used to test the method.
Data sets were collected using Cu Kα radiation at 100 K using a Bruker Microstar fine-focus rotating-anode generator with a SMART 6000 CCD detector, a Bruker D8 microsource, also equipped with a SMART 6000 detector, or an Agilent Technologies SuperNova, also incorporating a microsource generator. For data collections with the Bruker instruments a typical data collection comprised 16 ω scans at varying φ angles (four scans at 2θ = 46° and 12 scans at 2θ = 94°), yielding complete data up to 0.84 Å. The redundancy for orthorhombic crystals is around 11; for monoclinic crystals it is almost 6. The exposure times for the high- and low-resolution scans differed by a factor of 3–4 to ensure sufficient signal-to-noise ratios in the high-resolution shells. Data were processed with SAINT and corrected for absorption and systematic errors using SADABS. For the data collections using the Agilent system a strategy was calculated to a defined redundancy. Processing, including integration and a multiscan absorption correction, was accomplished with CrysAlis Pro (Oxford Diffraction, 2010).
Data were merged using the program SORTAV using unit weights and robust-resistant down-weighting of outliers. The standard deviations output by SORTAV are estimates of the standard uncertainty of the population rather than of the sample-estimated mean. This quantity should converge to an approximately constant value as redundancy increases. Its use in merging data has been justified by Blessing (1997).
Structures were refined against |F|2 in CRYSTALS using all data. All non-H atoms were refined with anisotropic displacement parameters. H-atom positions and isotropic displacement parameters were refined subject to restraints. Flack and extinction parameters were also refined. The weights were equal to 1/σ2(|F|2) multiplied by a robust-resistant modifier as described by Prince & Nicholson (1983). Reflections given zero weight in this procedure were omitted. Goodness-of-fits, S, were in the region of 2, and the weights were rescaled using a facility available in CRYSTALS to give S ≃ 1. These weights were output along with other files needed for leverage analysis and used for the modified weight calculations described in §3.6.
3. Results and discussion
Figs. 2–4 illustrate the results of the leverage analyses described below. The value of |Fo| (scaled to |Fo,max| = 100) is used to represent intensity even though refinements were carried out on |F|2; this is to be consistent with existing literature and also aids comparisons and provides clearer dispersion of points for low-intensity data. Leverages were normalized by dividing them by Nparameters/Nobservations, that is by the mean leverage value. Observations take the form of intensity data and any restraints applied during refinement.
3.1. Leverages in alanine
Figs. 2(a)–2(c) show plots of leverage against |Fo|, |Fo|/σ(|Fo|) and sinθ/λ for the |F|2 refinement of aniline against all data with 1/σ2 weights. From Fig. 2(a) it can be seen that the most influential data are those with moderately weak intensities, the leverage falling off towards very low or very high intensity; a similar effect is apparent when leverages are plotted against |Fo|/σ(|Fo|) (Fig. 2b). Fig. 2(c) reveals the importance of the high-resolution data, with leverages showing an increasing trend with sinθ/λ.
Although weak data do not appear to be especially influential in alanine the same is not necessarily true of all structures. Weak data may be very important in pseudosymmetric structures, for example in distinguishing between centrosymmetric and noncentrosymmetric models (Dunitz, 1995; Kassner et al., 1993; Marsh, 1981). The organic compound 4-cyano-4′-[(4R)-4,5-epoxypentyloxy]biphenyl, which has one asymmetric carbon centre, crystallizes in P21 with two molecules in the asymmetric unit (Clegg et al., 1998). With the exception of the asymmetric carbon atom these two molecules are related by a pseudo-inversion centre so that the space group is almost P21/n. The leverages, calculated using the intensity data available as supplementary material to the article by Clegg and co-workers, are plotted against |Fo|/σ(|Fo|) in Fig. 3; this should be compared with Fig. 2(b), which shows the same data for alanine. There are more high-leverage points amongst the weak data in the former, attesting to the importance of weak data in this structure.
3.2. Leverage analysis of restraints in alanine
Restraints are incorporated into refinement in the least-squares design matrix, and the calculations described above yield leverage values for restraints as well as intensity data. Restraints were applied in the alanine refinement, and the column of points at the far left of the plots in Figs. 2(a)–2(c) corresponds to their leverages; they are clearest in Fig. 2(c). The normalized leverages are generally above average (i.e. greater than 1), showing that the restraints have an important influence on the refinement.
The highest leverage values correspond to restraints applied to the isotropic displacement parameters of the H atoms, assigning target values equal to some multiple (1.2 or 1.5) of the equivalent isotropic displacement parameter of their parent atoms. These points have normalized leverages of above 4 and absolute leverage values in the region of 0.5. This means that, though the restraints are important, the values of the H-atom displacement parameters are significantly influenced by the intensity data. Had the absolute leverages been closer to 1 this would have implied that the displacement parameters were simply fitting the restraint applied with little or no influence from the intensity data. The next block of points at the far left of Fig. 2(c), with normalized leverages of between 1 and 2, corresponds to restraints applied to N—H and C—H distances, while the lowest points with normalized leverages of less than 1 correspond to the H—N—H and H—C—H angle restraints.
Leverage analysis is useful in the interpretation of the results of a restrained refinement because it shows which restraints are significantly influencing the fit and to what extent they define the final value of a parameter. A leverage value close to 0 implies that the data point in question has little influence. A restraint with a very low leverage might as well be deleted, or, if it is thought to be important, it should have its uncertainty decreased, though not beyond a realistic estimate of the spread of values that the restrained parameter might adopt. Conversely, if a restraint has an absolute leverage near 1.0 this indicates a forced fit: the refinement has converged on whatever value was typed into the restraint list of the refinement program.
3.3. The effects of incomplete data: leverage analysis of Cu(sal)2
The data set for Cu(sal)2 was collected at high pressure, and the completeness is low as a result of shading of reciprocal space by the pressure cell. The plots shown in Figs. 4(a)–4(c) show leverage versus |Fo|, |Fo|/σ(|Fo|) and sinθ/λ plots for the refinement of Cu(sal)2. Here the trends are seen to be different from those described above for alanine, with a larger spread of leverage values. There is a broad distribution of points spreading from low to moderately high values of |Fo| in Fig. 4(a), and the sharp peak in the |Fo| versus leverage plot present in Fig. 2(a) is absent. The standard deviations of the normalized leverage values are 0.75 for alanine and 1.07 for Cu(sal)2.
A number of the restraints have normalized leverages of >5 and absolute leverage values of 0.8 or more; these occur at the top of the column of points at the left of Figs. 4(a)–4(c). Some of these correspond to restraints applied to H-atom displacement parameters and to planarity restraints involving H atoms. The C—H and N—H distance restraints have absolute values of 0.5–0.7, substantially higher than in alanine. The high leverage values for restraints involving H-atom parameters are quite reasonable for a heavy-atom compound.
Also found amongst the highest leverage values are rigid-bond restraints applied to the anisotropic displacement parameters (ADPs) of atoms forming the ligand; these are known as `DELU' restraints to SHELX (Sheldrick, 2008a) users, and apply the Hirshfeld rigid-bond criterion as a restraint. The smallest leverages, with values close to 0, relate to rigid-body (`SIMU') restraints, which restrain the Uij values of neighbouring atoms to be equal. Refinement of ADPs against incomplete high-pressure data sets usually leads to elongation along the direction where data are missing, and it is therefore not unexpected that restraints applied to ADPs should have high leverage values. However, the rigid-bond restraints are much more influential than the rigid-body restraints. Although rigid-bond restraints are usually applied with higher weight than rigid-body restraints, the complete lack of any leverage for the latter was surprising, and the analysis shows that in view of the acceptable ADPs obtained in the refinement (Fig. S1b ) the rigid-body restraints might as well be deleted.
A possible procedure for assessing the effect of completeness on leverages might be to compare leverages from a refinement using the high-pressure data set just discussed with another using a complete data set collected at ambient pressure. The problem with this procedure is that the experimental values of σ(|Fo|2) would differ between the two data sets and so any comparison would be complicated by the effect of different refinement weights. Instead a complete data set was collected under ambient conditions and a partial data set generated from this by taking only those data which had been measured in the high-pressure data set. The weights [= 1/σ2(|Fo|2)] for equivalent reflections in refinements using the complete and partial data sets are then the same. The same set of restraints (see Experimental) was applied in both refinements.
A plot of leverage values for equivalent reflections in the two refinements is shown in Fig. 4(d), in which intensity data are shown as dots and restraints as plus signs. The average leverage (Nparameters/Nobservations) must be larger in the incomplete data set, and essentially all points in the graph are to the right of the line y = x. There is a tendency for intensity data that are already influential when the data are complete to become more influential when the data are incomplete. Low-leverage reflections tend to stay low. Lack of completeness also has a significant effect on some of the restraint leverages. There is a horizontal spread of plus signs in Fig. 4(d) near the x axis, corresponding to a marked increase in the influence of rigid-bond restraints applied to the anisotropic displacement parameters of the ligand. The highest restraint leverages, which apply to H-atom isotropic displacement parameters, are the same for both data sets.
3.4. Interpretation of T2 and T values
While leverages measure the overall influence that a data point has on a refinement, it may be of more interest to ask which data points influence a specific parameter. This information is contained in the T2 values that can be generated in a leverage analysis. A high T2 value indicates an influential observation.
David and co-workers (David et al., 1993; David, 2004) have recommended analysis of signed T values [= tij/(1 + )1/2] as they show whether a data point makes a parameter more positive or more negative. These authors illustrated this idea using displacement parameter T values in a Rietveld refinement. Short-d-spacing data all had negative T values because a relative increase in the intensities of these data would make the displacement parameter smaller. Conversely, long-d-spacing data all had positive T values. Fig. 2(d) shows the variation of T values for the extinction parameter in alanine. The numerically largest values of T occur for the strong data, as expected, and they are all negative: increasing the intensities of strong data will reduce the value of the extinction parameter.
Rather than analysing the influence of data on a single parameter it may be of more interest, or simply less time consuming, to study groups of parameters. If only one parameter is being refined the leverage and T2 values for the parameter in question amount to the same thing; this implies that one method for analysing a group of parameters is to study leverages from a refinement in which only those parameters are allowed to vary. This technique was used by Merli and co-workers in their work on minerals (e.g. Merli et al., 2000). An alternative approach, which avoids the need to carry out multiple refinements, is to sum the T2 values for groups of parameters. Fig. 2(e), which shows sums of T2 values for the fractional coordinates in a refinement of alanine against simulated data, displays a marked drop-off in values above sinθ/λ = 0.6 Å−1. This result can be contrasted with that described in Merli et al.'s (2000) leverage analysis of the silicate mineral pyrope. Here, high-resolution data were found to be important in determining the precision of oxygen positional parameters. This result was reflected in the importance of high-resolution data that had been noted anecdotally in Merli's laboratory in systematic work with garnets (Merli et al., 2000).
In alanine, data above sinθ/λ = 0.6 Å−1 are most influential for the ADPs (Fig. 2f).
3.5. T2 analysis of the Flack parameter in alanine
The Flack parameter is refined for noncentrosymmetric crystal structures in order to establish the absolute structure (Flack, 1983). The most important practical application of absolute structure refinement is in the determination of the absolute configuration of chiral compounds. The ability to distinguish one absolute structure from its inverted analogue depends on the resonant (or anomalous) scattering effects having sufficient magnitude to lead to measurably different intensities for Friedel pairs, something that depends on the elements present in the crystal and the wavelength of the X-rays used to collect intensity data.
Before any conclusions regarding absolute structure can be made the standard uncertainty of the Flack parameter should be less than 0.1, even if a material is known to be enantiopure (Flack & Bernardinelli, 2000). However, resonant scattering effects for elements such as C, N and O are small for commonly available X-ray energies, making it difficult to determine the Flack parameter with sufficient precision to establish absolute structure for organic compounds such as alanine. The likely success of an absolute structure determination can be gauged using the Friedif parameter (Flack & Bernardinelli, 2008; Flack & Shmueli, 2007). If Friedif has a value of about 80, absolute structure determination should present little problem. The value of Friedif for alanine is only 33.9. Accordingly, the value of the Flack parameter obtained from the refinement of alanine was 0.00 (13). The data set was of excellent quality, yet the precision of the Flack parameter is (just) too large to enable a definitive statement to be made regarding the absolute structure (Flack & Bernardinelli, 2000).
Fig. 5 shows the results of a T2 analysis for the Flack parameter in alanine. T2 values for reflections that form Bijvoet pairs are strongly correlated, as expected (Fig. 5a). Values of |T| are also closely correlated with
the calculated Bijvoet difference divided by its uncertainty as derived from those of the experimental observations (Fig. 5b). The most influential reflections are those with weak-to-moderate intensities, 10–15% of |F|max (Fig. 5c). It is also notable that there are only a few (about 15) data that strongly affect the precision of the Flack parameter: most data have rather little effect.
Fig. 5(d) shows the distribution of T2 values as a function of sinθ/λ. The most influential data lie at sinθ/λ ≃ 0.4–0.5 Å−1, but the trend seems to drop off towards higher resolution. Similar features are seen for the other light-atom structures. Nonresonant X-ray scattering factors decrease with sinθ/λ, whereas the resonant corrections (f′ and f′′) are constant, and so the relative contribution of resonant scattering effects increases with resolution. Influential observations are expected to lie amongst the high-resolution data.
The increasing contribution of the resonant scattering factors at high resolution has led to the suggestion that collecting very high resolution data should enable precise absolute structure determination even for light-atom structures. However, in order to obtain such data it is necessary to use short-wavelength radiation for which resonant scattering effects are very small. Data for alanine were simulated to a resolution of 0.4 Å using scattering factors for Mo Kα radiation. The structure of alanine was refined (along with the Flack parameter) against this data set. The T2 versus |Fo| plots for the experimental data (Fig. 5c) and the simulated data (Fig. 5e) show the same trend for moderate values of |Fo| being the most influential, though the distribution in Fig. 5(e) is sharper. Fig. 5(f) shows the values of T2 for the Flack parameter in this refinement plotted as a function of sinθ/λ. While there is a general increase in the T2 values with sinθ/λ, the distribution is peaked in the middle of the resolution range, indicating that very high resolution data do not dominate the precision of the Flack parameter.
The reasons for expecting high-resolution data to be influential in determining the precision of the Flack parameter were outlined above, and it is perhaps surprising that there is a fall-off in T2 values at the highest resolution in Figs. 5(d) and 5(f). However, Fig. 5(b) shows that an important factor in determining the influence that a particular Bijvoet pair has on the Flack parameter is how high the intensity difference is relative to its measurement standard uncertainty. It seems that the influence of reflections on the Flack parameter is the result of a balance between the increased contribution of the resonant scattering factors and the overall reduction in the signal-to-noise ratio of the intensities, which both occur as sinθ/λ increases. At high resolution data will be weak and the Bijvoet ratios small relative to the measurement uncertainties, leading to a reduced influence on the Flack parameter. The fall-off can also be associated with the trends shown in Figs. 2(e) and 2(f), which show, respectively, the sums of T2 values for the positional parameters and the non-H ADPs. The low-angle data most strongly influence the positional parameters, while the highest T2 values for the ADPs are seen for the high-angle data. The largest Flack parameter T2 values are seen between these two regions. The leverage of very high resolution data is `spent' on defining the displacement parameters rather than the Flack parameter.
3.6. Use of T values in a weighting scheme
There is a long-standing interest in finding ways to improve the precision of the Flack parameter in light-atom structures. In the past, when four-circle instruments with point detectors were in use, a selected set of data with the highest Bijvoet ratios could be measured to a desired precision and statistical tests performed on the intensities to assess absolute structure (Le Page et al., 1990). More recently, a post-refinement statistical procedure has been described by Hooft et al. (2010, 2008), while a method that can be used during refinement, based on combining Bijvoet intensity measurements and applying them as restraints, has been described by Parsons et al. (2010). It has also been shown that precision may be improved by the use of aspherical scattering factors (Dittrich et al., 2006).
A method explored by Bernardinelli & Flack (1985) showed that precision can also be improved by modifying the refinement weights, up-weighting reflections calculated to be sensitive to the value of the Flack parameter. By this procedure the standard uncertainty of the Flack parameter could be reduced to an arbitrarily small value, but at the cost of causing the value of the parameter itself to deviate from its true value.
Information on the sensitivity of parameters to specific data is, of course, available from a leverage analysis in the form of the T and T2 values, and the potential for improving the precision of the Flack parameter by incorporating these into the refinement weights was explored.
After some experimentation the following procedure for reweighting was used. The value of τ = 0.5{max[a|T(h)|b, c] + max[a|T(−h)|b, c]} was evaluated for each reflection with a = 0.1, b = 1.0 and c = 1.0. The overall mean τ, 〈τ〉, was also determined. The reflection weights (w) were then modified (w′) according to , where S is the goodness of fit obtained in the refinement with the original weights w. Larger values of a and b correspond to stronger up-weighting of sensitive data, though the placing of T values on a relative scale with Tmax = 100 also implies a greater up-weighting in cases where resonant effects are weak.
For the alanine data set a Flack parameter of 0.00 (13) was obtained using F2 refinement with weights equal to 1/σ2(|Fo|2) multiplied by a robust modifier as described by Prince & Nicholson (1983). The value of the Flack parameter obtained on reweighting with a = 0.1, b = 1.0 and c = 1.0 was −0.02 (5). Reweighting using the parameters a = 0.5, b = 1.0 and c = 0.5 yielded x = −0.02 (7).
Reweighting modestly increased the value of the unweighted R factor based on |F| and all data by 0.2%. A normal probability plot based on w1/2(|Fo|2 − |Fc|2) had a gradient and correlation coefficient near unity and an intercept near 0; analyses of variance based on resolution or intensity were flat.
Hooft et al. (2010, 2008) have emphasized the value of normal probability plots (Abrahams & Keve, 1971) based on weighted Bijvoet differences in absolute structure refinement, and these proved to be a much more sensitive procedure for validating the weighting scheme. While the central region of the plot showed the expected behaviour, there was deviation from linearity at the extremes (Fig. 6a), suggesting that some data had been over-weighted. Over-weighting could be corrected using a second program, REWEIGHT, which fits a straight line to the central region of the normal probability plot and uses the equation of this line to define a factor to down-weight the deviating data points (Fig. 6b). The normal probability plot based on w1/2(|Fo|2 − |Fc|2) was still linear after this procedure (Fig. 6c). The value of the Flack parameter was −0.02 (6).
The procedure described above was tested on a number of other absolute structure refinements, and the results are listed in Table 1. All data sets were collected with high redundancy using Cu Kα radiation at 100 K. All are `difficult cases' for absolute structure refinement, all except one having Friedif parameters of 34 or less. One conclusion to be drawn from Table 1 is that robust-resistant 1/σ2 weights can be very effective for absolute structure refinements. However, precision was improved by application of the T-scaled weighting scheme, which yielded Flack parameters in most cases with standard uncertainties of around 0.1 or less. In the majority of cases the Flack parameter itself moved closer to zero, with a value within one standard deviation of zero. In all cases the normal probability plots based on w1/2(|Fo|2 − |Fc|2) or Bijvoet differences were linear, while analyses of variance based on intensity, resolution and parity group were flat.
A particularly encouraging result was obtained for entry 17 in Table 1. These data refer to cholestane, a hydrocarbon with a Friedif parameter of only 9. Refinement of the Flack parameter using unmodified weights yielded a value of 0.36 (45), clearly an uninterpretable result. Reweighting yielded a Flack parameter of 0.10 (14); increasing the influence of sensitive data still further using a = 0.2 (and b = c = 1.0 as before) yielded a value of 0.10 (11).
One disadvantage of the reweighting procedure is that it can amplify noise in the data, and Bijvoet normal probability plots were useful for detecting outliers. Outliers can cause the Flack parameter to deviate from its true value: in example 15, deletion of just two outliers changed x from 0.35 (12) to 0.02 (14). In cases such as this one we recommend, in preference to selective deletion of data, that the whole experiment be repeated.
The down-weighting procedure based on linearization of the weighted Bijvoet difference normal probability plot to some extent reduces the sensitivity of the results to the values of the parameters a, b and c defined above. We note in passing that in all cases the weighted Bijvoet difference normal probability plots had gradients much less than unity, spanning the range 0.28–0.75. Hooft et al. (2010) have also noted this feature, pointing out that it implies that the values of the Bijvoet difference uncertainties used to calculate the plots are overestimated. The variances of Bijvoet differences are calculated as , but this neglects a further covariance term equal to −2cov[|Fo(h)|2, |Fo(−h)|2]. The small numerical values of the probability plot gradients suggests that the errors in |Fo(h)|2 and |Fo(−h)|2 are positively correlated. The correlation between errors suggests that it may be appropriate to include off-diagonal weights in absolute structure refinements. However, we are grateful to Professor Howard Flack for pointing out that the `AD refinement' method of Flack et al. (2011) is equivalent to inclusion of these off-diagonal weighting terms, and when tested, this did not lead to substantial changes in either the Flack parameter or its standard deviation
The procedure described here alters the relative weights of observations in such a way as to improve the precision of a selected parameter. In an absolute structure determination the aim of the experiment is to obtain a precise value of the Flack parameter; our weighting scheme effectively refocuses the information present in the data in line with the aim of the experiment. The precision of other parameters may be decreased in a similar way. As an illustrative example, data sensitive to the x, y and z fractional coordinates of one of the ammonium H atoms in alanine were up-weighted (using a = b = c = 1.0). Prior to reweighting the coordinates were 0.4601 (16), 0.4089 (13) and 0.6476 (7); after reweighting they were 0.4608 (10), 0.4090 (8) and 0.6475 (5). The N—H bond distance changed from 0.907 (9) to 0.912 (6) Å.
In principle the precision of other parameters should decrease as a result of reweighting. The effect is small in our absolute structure tests because the number of data being up-weighted is also quite small (there are only a few really sensitive data). For the structures in Table 1 the maximum change in position was 0.004 Å and the maximum change in Uij was 0.002 Å2, these values being similar to the standard uncertainties in C—C bond distances and Uij values in the structures concerned. In another test (using the data set collected for alanine) data sensitive to the scale factor were up-weighted using parameters a = b = c = 1.0. The scale factor changed from 4.91 (11) to 4.93 (6). The precision of the extinction parameter also improved [20 (4) to 23.0 (9)], reflecting the fact that strong low-resolution data are important for both parameters. The precision of the displacement parameters, which are most sensitive to high-resolution data (see above), decreased slightly, with the average standard uncertainty changing from 0.0028 to 0.0031 Å2.
4. Conclusions
Leverage analysis can be based either on the values of the leverages themselves, which give information on overall data fitting, or on T values, which enable the influence of observations with respect to specific parameters or groups of parameters to be investigated. Use of leverage analysis in crystallography is still quite rare, and the aim of this paper was to describe how it might prove useful in routine structure analysis.
Application of leverage analysis to outlier detection has been described previously by Merli (2005). Merli and co-workers have also shown that it can be used to rationalize the sensitivities of different mineral structures to the quality of high-resolution data, and to inform or justify refinement strategies of mixed site occupancies (Merli et al., 2000). The role of different classes of data in a refinement has been described by David et al. (1993). The identification of refinements where weak data are important was described here.
A further application of the technique is in determining the effectiveness of restraints: a restraint with almost zero leverage might as well be removed or up-weighted. Equally, leverages are useful in deciding whether a parameter is determined solely by the restraints that have been applied or whether the intensity data retain some influence.
These ideas were illustrated using restrained refinements of alanine and Cu(sal)2. In alanine the restraints were applied to H-atom positional and displacement parameters. Restraints placed on C—H and N—H bond distances were found to be more important than restraints placed on the angles involving H atoms. The leverages of the distance restraints were nevertheless only a little higher than average, and the intensity data were still important. The contrary was true in the Cu(sal)2 refinement. In this case the H-atom parameters were effectively determined by the restraints that had been applied. Of the restraints applied to the C-, N- and O-atom ADPs the rigid-bond restraints were very influential, but the rigid-body restraints had hardly any effect at all.
Another application was illustrated in T2 analysis applied to the Flack parameter in alanine. It has been suggested that a strategy for precise absolute structure determination for light-atom crystal structures is to collect very high resolution data with Mo Kα radiation. However, leverage analysis shows that the influence on the Flack parameter peaks at around sinθ/λ = 0.6 Å−1 and begins to decline at higher resolution. It was suggested that this trend is related to the observability of statistically significant Bijvoet intensity differences amongst weak high-resolution data.
The final application of leverages described here was in using T values as refinement weight modifiers to increase the precision of a parameter of interest. The parameter chosen was the Flack parameter in light-atom absolute structure refinements. The results obtained using T weighting are promising: not only are values of the Flack parameter more precise, they are also more accurate than values obtained in conventionally weighted refinements, clustering more closely around zero.
The method could, in principle, be applied to any parameter without the need to develop a physical model for identifying the most sensitive data, though we have not investigated this in detail, and careful testing would be required. In this work, it proved very important to examine refinement statistics critically, particularly so when resonant scattering effects are weak as the results are determined by up-weighting of a small number of data. Nevertheless, it does seem that given data of sufficient quality and high redundancy, reweighting based on leverage analysis might be employed to improve the precision of light-atom absolute structure determinations.
5. Programs
Windows executables for the programs HATTIE and REWEIGHT can be downloaded from the web site http://www.crystal.chem.ed.ac.uk/resource/ . The programs are intended to be used in conjunction with CRYSTALS, which is available from http://www.xtl.ox.ac.uk/category/crystals.html .
Supporting information
Figure S1. Molecular structures of alanine and bis(salicylaldoximato)copper(II). DOI: 10.1107/S0021889812015191/he5536sup1.pdf
We are grateful to Dr Martin Lutz (University of Utrecht) and Professor Howard Flack (University of Geneva) for their comments on the manuscript. We also thank Professor William David (ISIS and University of Oxford) for insightful comments made following a presentation of the results described in this paper, and an anonymous referee who read the manuscript with great care and diligence. We also thank Diamond Light Source for access to beamline I19 (proposal No. MT1200) and EPSRC (grant No. EP/G015333/1) for funding that contributed to the results on Cu(sal)2 presented here.
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© International Union of Crystallography. Prior permission is not required to reproduce short quotations, tables and figures from this article, provided the original authors and source are cited. For more information, click here.


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The Pharmacy Guild of Australia and Amneal Pharmaceuticals commissioned McCrindle to write up and design the Healthy Futures 2017 Report.
This report reveals the insights into consumers understanding of pharmaceuticals and pharmacy health services.
The findings were gathered from a national survey of 1,001 Australians aged 18+ and the results were delivered at the annual 2017 APP conference by Mark McCrindle.
From developing the survey through to conducting the analysis and communicating the insights, this piece is a great example of a thought leadership report that delves into Australians attitudes and sentiments towards pharmaceutical services.
If we can assist with any research, event speaking or infographic design please feel free to get in touch:
e: email@example.com
We have a passion for research that tells a story, that can be presented visually, that brings about change and improves organisations. And we hope these resources help you know the times.


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With our conference, osc11, fast approaching the excitement is building all over the project.
Its quite some work to get to create a reasonable schedule for a conference. For osc we want to have a program with talks that interest all our visitors. And as visitors have a wide rage of skill levels we also want to balance the depth of the talks. Another thing we wanted to create are "gravitation centers" for our key topics within the program. Oh and we also seek out for new contributors with our conference. And all that needs to be sorted between rooms with different sizes, within the tracks you think are useful, with breaks, time to change rooms and so on and son on. Quite some parameters to take into account. That said, we are very happy that we can announce the schedule for the openSUSE Conference 2011 today!
rest here [2]


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Uryű Ishida
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Having undergone formal training and possessing prior experience in combat, Uryű is one of the strongest protagonists in the series, with his victories roughly paralleling Ichigo's throughout the story. As a Quincy, Uryű's main weapon is a bow, but he is also able to use many Quincy techniques and items to augment his abilities, including some high-level techniques such as rans¨tengai, which are rare enough that even Mayuri Kurotsuchi, who had studied 2661 Quincy, had never seen them in person. Uryű's trademark finishing move involves shooting spiritual arrows at his opponents through their soul chain and soul sleep, depriving them of their powers and allowing him to win a bloodless victory.
Aside from his Quincy powers, Uryű is well-trained in both mind and body, having substantial athletic abilities and a genius intellect. He also possesses some knowledge of Spanish, as he understands the Spanish terms used by the arrancar.
When first introduced, Uryű uses a bow named Lone Sparrow (»ˇČ¸, K¨jaku?), which has a basic (albeit exaggerated) form and a luminescent, translucent blue quality to its appearance. Being made of free-flowing spirit particles, its size can be affected the amount of spirit particles and spiritual pressure available to it, as seen in his interaction with Ichigo during his first encounter with a Menos Grande. With this bow, Uryű is able to kill most hollows in a single strike.
As preparation for his travel to Soul Society, Uryű later masters the sanrei glove, greatly increasing his abilities via a form of resistance training. In this state, Uryű's bow is solid and covered in an intricate pattern. It is attached to his glove by a series of thin struts. This new bow allows Uryű to fire several shots simultaneously. By removing the glove, Uryű attains the Quincy Final Form. The Quincy Final Form gives him a vast increase in power, enough to defeat a captain-class shinigami with ease. All the extra energy collects on his right shoulder, much like how a quiver is worn, and resembles an angel's wing. As a result of removing the glove, however, the Quincy Final Form uses too much power for Uryű's body to handle, causing his body to block his Quincy powers completely after it wears off.
In the anime's Bount arc, Uryű recovers his powers for a short period through an ancient Quincy artifact which mimics the natural powers of a Quincy. The artifact produces an appropriate Quincy uniform on demand and creates a new metal crossbow mounted on Uryű's wrist. The artifact is unstable, however, firing arrows in odd arcs and with inconsistent power levels when first used. Additionally, it is fragile, eventually breaking after repeated use. Uryű eventually is able to use the artifact at its full efficiency, though it is soon destroyed.
After Uryű regains his powers with the aid of his father, he uses a new Quincy cross, this one resembling a pentangle, and a variant of his original bow called Lone Sparrow on a Silver Cliff (ăyŽX»ˇČ¸, Ginrei K¨jaku?). Unlike his original bow, this bow is shaped like a spiderweb and can fire up to 1,200 shots at once. Uryű also steals a set of Seele Schneiders (»ę¤ňÇФęÁѤŻ¤â¤ÎŁ¨ĄĽ©`ĄěĄ·ĄĺĄĘĄ¤ĄŔ©`, Z¨Ąre Shunaid¨ˇ?, German and Japanese for "soul cutter"), special arrows which can be used as swords. Seele Schneiders can also be used in a reiatsu-based pentacle with the target at the center. Upon receiving Uryű's spiritual energy, it explodes
As a child, Uryű mostly interacted and trained with his grandfather, Souken Ishida. His father, Ryűken Ishida, was less than enthusiastic about being a Quincy, claiming that it wasn't a profitable occupation. They don't appear to be on very good terms as a result, given Uryű's casual use of his father's given name, which is considered very rude in Japanese society. Souken understands Ryűken's reasoning, since being a Quincy is more about justice than material rewards and Ryűken has a family to support. S¨ken told Uryű that he would someday understand his father's motives, but thus far this isn't the case.
At a fairly young age, Uryű's grandfather was killed by hollows right in front of him.[7] This is one of the reasons he hates Soul Reapers, who, despite keeping the old man under near-constant survellance, didn't come to rescue Souken in time.[7] He long believed that the Soul Reapers were merely taking advantage of circumstances to be rid of him. It was later revealed that the current captain of the 12th Division, Mayuri Kurotsuchi, was behind the delay so that Souken's soul could be collected for study.
After Ichigo Kurosaki gains the Soul Reaper powers of Rukia Kuchiki, Uryű confronts him in an attempt to prove that Quincy are superior. Using some special bait, Uryű attracts a swarm of hollows to Karakura Town so that he and Ichigo can compete to see who can kill the most hollows in a day. This bait, however, attracts too many hollows, including a menos grande, and Uryű and Ichigo are forced to band together. They drive the menos off, but its brief time in Karakura Town attracts the attention of Soul Society. Two Soul Reapers are dispatched to capture Rukia. Uryű confronts the two in an attempt to stop them, but is easily defeated by the much stronger Soul Reapers. After they return to Soul Society with Rukia, Uryű realizes that he is not as strong as he thought he was. Wanting to go and save Rukia, Uryű trains to better equip himself for the next time he needs to battle a Soul Reaper. To this effect, he masters the sanrei glove, and joins the rescue team going to Soul Society. Their group is split up soon after their arrival, and Uryű ends up partnered with Orihime Inoue. Though the pair manage to avoid detection for some time, they are eventually found by 12th Division captain Mayuri Kurotsuchi, who quickly takes an interest in Orihime's abilities. Uryű sends her away to remove her from harm, and battles Mayuri in order to buy time. As their battle progresses, Uryű proves to be no match for the captain. Nevertheless, Mayuri comments on Uryű's impressive Quincy abilities, noting that the thousands of Quincy he has studied over the years fail to measure up to Uryű. When Mayuri shows Uryű a picture of the remains of his most recent test subject, Uryű's grandfather, Uryű decides to defeat Mayuri at all costs. He removes his sanrei glove, greatly increasing his Quincy powers and allowing him to beat Mayuri. However, Mayuri is able to escape and Uryű, robbed of his Quincy powers by the long-term side effects of removing the glove, is easily captured by Kaname T¨sen. He is soon reunited with other members of his rescue team that have also been imprisoned, and they are freed by Kenpachi Zaraki. Upon reuniting with Ichigo and saving Rukia, the rescue team returns to the human world. With his Quincy powers gone, Uryű is of little use during the initial stages of the Bount invasion. He accompanies Ichigo and the others from battle to battle, but is unable to make any major contributions. Needing access to his former abilities in order to help his friends, Uryű strikes a deal with Mayuri; if Uryű lets the Bount into Soul Society, Mayuri will briefly restore his Quincy powers. Uryű complies, giving the Bount access to the Soul Society, and receives a Quincy artifact for his troubles. Though inexperienced with it, Uryű is able to use the artifact to kill Yoshi. He later assists Ran'Tao in her battle with Jin Kariya, though the Quincy artifact is destroyed during the fight. Once Kariya and the remaining Bount are defeated, Uryű returns home. Back in Karakura Town, Uryű is attacked by two incomplete arrancar. He attempts to use some Quincy equipment to defeat the two, but is ultimately unsuccessful. It is not until the arrival of his father, Ryűken Ishida, that the arrancar are vanquished. Disappointed by Uryű's weakness, Ryűken offers to restore his Quincy powers on the condition that Uryű never associate with Soul Reapers again. Uryű agrees and trains with his father whilst arrancar continue to attack Karakura Town. After the third arrancar invasion ends Uryű regains his powers, ending his training. After learning that Orihime has been captured by the arrancar, Uryű joins Ichigo and the remainder of a rescue team organized to save her. Because the group believes that Soul Society has abandoned Orihime, Ichigo is technically not acting as a Soul Reaper, giving Uryű a loophole with which to accompany them. After they arrive in Hueco Mundo and their group splits up, Uryű is joined by Pesche Guatiche. Though Pesche continues to annoy Uryű, he proves invaluable in defeating Cirucci Thunderwitch. As they continue on their way they meet Renji Abarai as he is about to be killed by the eighth Espada, Szayel Aporro Granz. Uryű intervenes and is briefly able to drive Szayel off, but Szayel soon returns and forces Uryű, Renji, Pesche and Dondochakka into a corner. Just as their last hope of winning fades, Mayuri arrives and rescues them. He even heals the two of them using regenerative serum, despite vocal protests from Uryű.
First Appearance:
Bleach (2004) vol. 04
View a chronological listing of this character's appearances
Issue Appearances:
Bleach (2004)
3-in-1 Edition TPB vol. 02
3-in-1 Edition TPB vol. 03
3-in-1 Edition TPB vol. 07
3-in-1 Edition TPB vol. 08
vol. 04
- 'Quincy Archer Hates You'
vol. 05
- 'Right Arm of the Giant'
vol. 06
- 'The Death Trilogy Overture'
vol. 07
- 'The Broken Coda'
vol. 08
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vol. 09
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vol. 10
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vol. 14
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vol. 15
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vol. 17
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vol. 19
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vol. 21
- 'Be My Family Or Not'
vol. 22
- 'Conquistadores'
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vol. 26
- 'The Mascaron Drive'
vol. 27
- 'Goodbye Halcyon Days'
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Donald Trump was thundering about a minority group, linking its members to murderers and what he predicted would be an epic crime wave in America. His opponents raged in response—some slamming him as a racist—but Trump dismissed them as blind, ignorant of the real world. No, this is not a scene from a recent rally in…
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Ironic modern day renaissance man and professional dicknoser James Franco recently painted a mural in Williamsburg (because of course he did) depicting himself and all his co-stars in his new apocolyptic buddy comedy, "This Is The End" (opens today, possibly excellent).
But Franco apparently didn't run any of the likenesses by his co-stars, as Jonah Hill — who seems a bit temperamental — is a little bummed out about being depicted as a morphine addict from Picasso's blue period, as he explained to Conan last night after telling stories of being owned in a dark theater and making the mistake of asking Ice Cube who the greatest rapper of all-time is. Mural stuff starts around the 3:30 mark.
I think we can all agree Franco totally redeemed himself with Craig Robinson's t-shirt. As for Jonah, just the perfect opportunity for me to create my first ever entry to one of my favorite memes.


text:
What a absolute delight it has been teaching a great bunch of ladies at the True Blue Craft Fair the last couple of days. Over 30 individual classes taught and loved everyone's final finished projects!!! As promised below are the photo's of the finished projects if you want to continue to add and create with your own. If you have any questions please leave a comment and I will answer them in the next blog post!
Set of 5 Christmas Cards
Playing with chipboard and oxide pigment paints and stencils - love these - hope you all did too!!!! I have included an extra too just for inspiration - they were simply painted with the oxides and then coated with Tim Holtz's Rock Candy Crackle paint.
Toot Toot Steampunk Mini Album
Like I said in the classes mini albums are fun - the worst bit is covering each page with paper before you can sit back and play!! Lucky you had all the papers precut so here is the album with each page as you open up the album.
OK and now for those other little hints and bits and pieces I promised I would post and before I forget with my glass of wine!!!
If you have trouble getting an item from your local store (please ask them to order it in from Twiddleybitz first!) try Scrap Sanity - Tiff is a TBZ expert and will send anywhere!
Glues I use are and always have been Helmar's range of wonderful stickiness!! For ribbons use the Helmar 450 so to hide the wet glue marks on ribbons and it is the best for sticking metal etc.. Other great ones by Helmar is the blobby Liquid Scrap Dots (remember this needs a while to dry!) and the Premium Craft Glue (PVA glue) and you can get these by going here or Spotlight carry a good range too!
Projects you asked about
Miss Charlotte.
And the frame of Jess that someone will do x 3!!!!
Graphic 45 Communique papers!
Um... was there anything else???? been a busy couple of days! Link to Tim Holtz is in my sidebar..... If you have any questions at all please leave a comment and I can get back to you either in the next post or two or via email if you leave a contact detail!!
I do hope you had fun playing - remember to try anything and nothing is a mistake!!! Just enjoy creating :)
Saturday, August 4, 2012
Twiddleybitz True Blue 2012 classes
Posted by Melanie at 6:22 PM
2 comments:
- scissors said...
Hello Melanie,
It's true that we always use chipboard and oxide pigment paints, stencils in the season of Christmas but these new ideas gave us a surprise. We loved it really. Thanks for sharing here.
- December 30, 2012 at 10:38 PM
- Ray Ardiono said...
using blog as a diary.....
good idea....
if you don't mind please check this out:
- January 2, 2014 at 12:42 AM
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From Blacklistednews:
The massive expansion of insurance coverage under the health law and rapid growth in specialty drug spending fueled the uptick in medical costs, officials said. Annual spending growth was 3.7%, on average, during the last five years.
The country spent $9,523 per person on healthcare in 2014, including Medicare, Medicaid and private health insurance. That's far higher than what other developed countries pay, and healthcare spending now accounts for 17.5% of the U.S. economy.
Experts aren't predicting a return to double-digit increases in medical spending. But the latest trend underscores how difficult it will be for policymakers, employers and insurers to control healthcare costs going forward.


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"I am 27 years old and i didn't get my period for 7 - 8 months now. I went to see a infertility doctor and she prescribed to me Provera which i have to take for 10 days. It is unusual not to get monthly periods. I hope that i get my perio..."
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