bluuebunny/crossref_metadata_2025 huggingface dataset:
A phase transition in a 3D growth-disorder model; erratum
Authors: Welberry T. R. , Miller G. H.
Published: July 2002

The following corrections should be made in Welberry & Miller [Acta Cryst. (1978). A34, 120-123]. 1. Equation (2) on p. 121 should read: E(σ) = - \sum_{{\rm all_{sites}}} σi,j,k
[J(σ

i - 1, j, k + 1 + σ

i,j + 1, k - 1 + σ

i + 1 j - 1, k
) + K (σ

i - 1, j,k
+ σ

i,j - 1,k
+ σ

i,j,k - 1) + L(σ

i - 1, j,k

σ

i,j - 1, k

σ

i,j,k - 1)]. 2. The expression for J on p. 121 should be J = 1/8 In [a(1 - a)/b(1 - b)]. 3. In the second paragraph of the second column on p. 121 'J and - K' should be replaced by 'K and -J'. All information is given in the Abstract.
Pushing the boundaries of molecular replacement with maximum likelihood
Authors: Read Randy J.
Published: July 2002

The molecular-replacement method works well with good models and simple unit cells, but often fails with more difficult problems. Experience with likelihood in other areas of crystallography suggests that it would improve performance significantly. For molecular replacement, the form of the required likelihood function depends on whether there is ambiguity in the relative phases of the contributions from symmetry-related molecules (e.g. rotation versus translation searches). Likelihood functions used in structure refinement are appropriate only for translation (or six-dimensional) searches, where the correct translation will place all of the atoms in the model approximately correctly. A new likelihood function that allows for unknown relative phases is suitable for rotation searches. It is shown that correlations between sequence identity and coordinate error can be used to calibrate parameters for model quality in the likelihood functions. Multiple models of a molecule can be combined in a statistically valid way by setting up the joint probability distribution of the true and model structure factors as a multivariate complex normal distribution, from which the conditional distribution of the true structure factor given the models can be derived. Tests in a new molecular-replacement program, Beast, show that the likelihood-based targets are more sensitive and more accurate than previous targets. The new multiple-model likelihood function has a dramatic impact on success.
Crystallization of an intact GST-estrogen receptor hormone binding domain fusion protein
Authors: Lally John M. , Newman Richard H. , Knowles Philip P. , Islam Suhail , Coffer Arnold I. , Parker Malcolm , Freemont Paul S.
Published: July 2002

Crystals of an intact GST–estrogen receptor hormone binding domain fusion protein have been grown from solutions of MPD. The crystals grew as clusters of thin plates and needles of maximum dimensions 100 × 20 × 1 µm but were unsuitable for X-ray diffraction analysis. However, examination by electron microscopy shows an ordered lattice in which the protein molecules are clearly visible. Image analysis of electron micrographs of the protein crystals revealed electron stain-excluding density which showed a two-domain trimeric structure in projection, with each molecule of dimensions 12.0 × 5.0 nm diameter. The use of GST-fusion proteins in crystallization are discussed.
Crystals of Thermus thermophilus tRNAAsp Complexed with its Cognate Aspartyl-tRNA Synthetase Have a Solvent Content of 75%. Comparison with Other Aminoacylation Systems
Authors: Briand Christophe , Poterszman Arnaud , Mitschler André , Yusupov Marat , Thierry Jean-Claude , Moras Dino
Published: July 2002

Thermus thermophilus tRNAAsp, purified from a non-recombinant source, has been crystallized in a complex with its cognate dimeric (α2) aspartyl-tRNA synthetase. Crystals diffract to 2.9 Å resolution and belong to space group P63 with cell parameters a = b = 258, c = 90.9 Å. The crystals contain one aspartyl-tRNA synthetase dimer and two tRNA molecules in the asymmetric unit, corresponding to a Vm
of 4.85 Å3 Da−1 and 75% solvent content. When compared with those obtained for globular proteins these values are high, but fall within the range observed for other aminoacyl-tRNA synthetases, either free or complexed with their tRNAs. A comparative survey is presented here.
Production, crystallization and diffraction to atomic resolution of an antibody Fv specific for the blood-group A oligosaccharide antigen
Authors: Patenaude Sonia I. , MacKenzie C. Roger , Bilous Doris , To Rebecca J. , Ryan Stephen E. , Young N. Martin , Evans Stephen V.
Published: July 2002

The histoblood-group ABO carbohydrate antigens are well known as important factors in blood transfusions, but they can also act as receptors for infectious agents and have been implicated in susceptibility to certain carcinomas. A single-chain variable-domain antigen-binding fragment (scFv) gene based on the known sequence of an anti-blood-group-A monoclonal antibody (AC1001) has been synthesized and expressed in Escherichia coli. The purified scFv preparation existed primarily in the monomeric form but also contained large amounts of dimeric and higher oligomeric forms. The corresponding variable-domain antigen-binding fragment (Fv) was generated by cleaving the VL–VH linker with subtilisin, and its activity was demonstrated by surface plasmon resonance with an immobilized bovine serum albumin A–trisaccharide conjugate (KD
= 290 µM). AC1001 Fv crystals grown in the presence of N-acetylgalactosamine diffracted to 0.93 Å resolution. This is the first reported example of a crystal of an antibody antigen-binding fragment diffracting to atomic resolution.
Overexpression, purification, crystallization and preliminary X-ray diffraction analysis of the receiver domain of PhoB
Authors: Solà Maria , Gomis-Rüth F.-Xavier , Guasch Alicia , Serrano Luis , Coll Miquel
Published: July 2002

PhoB is the response regulator of the E. coli two-component signal transduction system for phosphate regulation. It is a transcription factor that activates more than 30 genes of the pho regulon. Crystals of the receiver domain of PhoB were obtained by applying the hanging-drop vapour-diffusion method. X-ray diffraction data have been collected using synchrotron radiation to 1.88 Å resolution. The crystals belong to the orthorhombic space group P212121 with unit-cell constants a = 34.11, b = 60.42, c = 119.97 Å. The Matthews parameter suggests that PhoB crystallizes with two molecules per asymmetric unit, suggesting that activating dimerization occurs in the crystal.
New Tools and Resources for Analysing Protein Structures and Their Interactions
Authors: Luscombe Nicholas M. , Laskowski Roman A. , Westhead David R. , Milburn Duncan , Jones Susan , Karmirantzou Maria , Thornton Janet M.
Published: July 2002

The determination of protein structures has furthered our understanding of how various proteins perform their functions. With the large number of structures currently available in the PDB, it is necessary to be able to easily study these proteins in detail. Here new software tools are presented which aim to facilitate this analysis; these include the PDBsum WWW site which provides a summary description of all PDB entries, the programs TOPS and NUCPLOT to plot schematic diagrams representing protein topology and DNA-binding interactions, SAS a WWW-based sequence-analysis tool incorporating structural data, and WWW servers for the analysis of protein–protein interfaces and analyses of over 300 haem-binding proteins.
Directional Preferences of Intermolecular Contacts to Hydrophobic Groups
Authors: Cole Jason C. , Taylor Robin , Verdonk Marcel L.
Published: July 2002

Analysis of data from the IsoStar library shows that many hydrophobic groups exhibit strikingly strong directional preferences in their intermolecular interactions. Specific directional interactions may occur because of the large quadrupole moments of many aromatic ring systems, the residual electropositive charge on most carbon-bound H atoms and the effects of polarization on soft hetero-ring atoms such as sulfur. In consequence, the binding of a hydrophobic group to a hydrophobic protein cavity is not simply a matter of matching complementary shapes. Directional preferences of nonbonded contacts to hydrophobic groups may need to be taken into account in parameterizing the next generation of protein–ligand docking programs.
Real-space molecular-dynamics structure refinement
Authors: Chen Zhi , Blanc Eric , Chapman Michael S.
Published: July 2002

Real-space targets and molecular-dynamics search protocols have been combined to improve the convergence of macromolecular atomic refinement. This was accomplished by providing a local real-space target function for the molecular-dynamics program X-PLOR. With poor isomorphous replacement experimental phases, molecular dynamics does not improve real-space refinement. However, with high-quality anomalous diffraction phases convergence is improved at the start of refinement, and torsion-angle real-space molecular dynamics performs better than other available least-squares or maximum-likelihood methods in real or reciprocal space. It is shown that the improvements result from an optimization method that can escape local minima and from a reduction of overfitting through the implicit use of phases and through use of a local refinement in which errors in remote parts of the structure cannot be mutually compensating.
Crystallization and preliminary X-ray crystallographic analysis of the Pseudomonas aeruginosa cyclohexadienyl dehydratase
Authors: Kongsaeree Palangpon , Liang Jun , Jensen Roy A. , Clardy Jon
Published: July 2002

The title protein has been crystallized in a new crystal form. The crystals belong to the cubic space group P4132 (or P4332) with unit-cell dimensions a = b = c = 126.1 Å at 100 K and typically diffract beyond 1.6 Å at the Cornell High Energy Synchotron Source (CHESS) A1 beamline.
The incorporation of a non-natural amino acid (aza-tryptophan) may help to crystallize a protein and to solve its crystal structure. Application to bacteriophage λ lysozyme.
Authors: Evrard Christine , Fastrez Jacques , Declercq Jean-Paul
Published: July 2002

Until now, wild-type bacteriophage λ lysozyme had been impossible to crystallize. This difficulty could be overcome by the replacement of the four tryptophan residues by aza-tryptophans. Analysis of the intermolecular and intramolecular contacts in this modification allows understanding of the differences in behaviour between the native and modified molecules. Furthermore, this mutation was very useful for the creation of new heavy-atom binding sites and for the solution of the non-crystallographic symmetry, which is extremely important for phase improvement. This procedure seems to be generally applicable, at least in the search for new possibilities for heavy-atom binding sites.
How many water molecules can be detected by protein crystallography?
Authors: Carugo Oliviero , Bordo Domenico
Published: July 2002

The number of water molecules which are expected to be experimentally located by protein crystallography was determined by multiple regression analysis on a test set of 873 known protein crystal structures determined at room temperature and on another set of 33 structures determined at low temperature. The dependence of the number of water molecules included in the protein models as a function of a number of significant regressors, such as resolution, fraction of crystal volume occupied by the solvent, number of residues in the asymmetric unit, fraction of apolar protein surface or secondary structure, has been studied. The number of water molecules included in crystallographic models depends primarily on the resolution at which the structure has been solved, while the temperature of the data collection has only marginal influence. On average, at 2.0 Å resolution one water molecule per residue is included in the model, while at 1.0 Å resolution about 1.6–1.7 are crystallographically located. At 2.0 Å resolution the well known rule-of-thumb of `one water per protein residue' is confirmed, though the number of water molecules experimentally observed is strongly dependent on resolution. The results presented are useful in assessing the quality of a protein crystal structure, in selecting structural results to be compared and in evaluating the expected improvement on the solvent structure when increasing the crystallographic resolution.
Structures of thrombin retro-inhibited with SEL2711 and SEL2770 as they relate to factor Xa binding
Authors: Mochalkin Igor , Tulinsky A.
Published: July 2002

Most thrombin active-site inhibitors form a short antiparallel β-strand with residues Ser214–Gly216. However, the Selectide Corp. inhibitors SEL2711 and SEL2770 bind to thrombin in a retro fashion, making a parallel β-strand with Ser214–Gly216 similar to other retro-binding inhibitors. The crystallographic structures of thrombin–hirugen complexed with SEL2711 and SEL2770, which are isostructural with the binary thrombin–hirugen complex, have been determined and refined in the 9.0–2.1 Å resolution range to final R values of 16.5 and 16.7%, respectively. The structures of the SEL2711 and SEL2770 complexes contain 131 and 104 water molecules, respectively, both of which correspond to occupancies of greater than 0.5. The L-4-amidinophenylalanyl residues of SEL2711 and SEL2770 are fixed at the S1 specificity site, utilizing favorable ionic and hydrogen-bonding interactions between the N atoms of the amidino group and the side-chain O atoms of Asp189. The Glu192 residue of thrombin adopts an extended conformation, which allows the L-cyclohexylglycyl residue in the P2 retro-binding position of the inhibitors to occupy a similar site to the P3 aspartate in thrombin platelet-receptor peptides bound to thrombin. The N-terminal acetyl group of both inhibitors is located in the S2 subsite, while the L-3-pyridyl-(3-methyl)-alanyl of SEL2711 and the L-(N,N-dimethyl)lysine of SEL2770 occupy the S3 D-Phe subsite of D-PheProArg chloromethyl ketone (PPACK) in the thrombin–PPACK complex. The two C-terminal residues of SEL2711 (leucine and proline) point into the solvent and have no electron density in the thrombin complex. Those of SEL2770 are also positioned into the solvent, but surprisingly produce weak electron density with high B values (〈B〉 = 50 Å2). Since the Selectide inhibitors are about 104 times more specific for factor Xa, modeling retro-binding to the latter suggests that the selectivity can be a consequence of interactions of the inhibitors in the S3–S4 binding subsites of factor Xa.
Crystallization and improvement of crystal quality for X-ray diffraction of maltooligosyl trehalose synthase by reductive methylation of lysine residues
Authors: Kobayashi Masanori , Kubota Michio , Matsuura Yoshiki
Published: July 2002

Maltooligosyl trehalose synthase, one of the two enzymes in the coupled trehalose biosynthesis system in Sulfolobus acidocaldarius, has been purified and crystallized. The chemical modification of this enzyme by reductive methylation of lysine residues significantly improved the crystal quality for X-ray diffraction experiments. The crystals of the modified enzyme belong to orthorhombic space group P212121, with unit-cell parameters a = 56.70, b = 140.1, c = 205.2 Å measured at cryo-temperature, and are found to contain two enzyme molecules per asymmetric unit.
Complementing crystallography: the role of cryo-electron microscopy in structural biology
Authors: Grimes Jonathan M. , Fuller Stephen D. , Stuart David I.
Published: July 2002

Dramatic improvements in experimental methods and computational techniques have revolutionized three-dimensional image reconstruction from electron micrographs (EM) of vitrified samples. Recent results include the first determination of a protein fold (for the core protein of the hepatitis B virus) by non-crystalline imaging techniques. These developments have generated interest within the crystallographic community and have led to a re-evaluation of the technique, particularly amongst those working in the field of virus structure or struggling with the phasing of large macromolecular assemblies. A simple discussion of the techniques of EM image reconstruction and its advantages and problems in terms familiar to crystallographers will hopefully allow an appreciation of the essential complementarity of the two techniques and the practical potentials for phasing applications.
Crystallization and preliminary X-ray diffraction analysis of malic enzyme from pigeon liver
Authors: Tsai Li-Chu , Kuo Chen-Chin , Chou Wei-Yuan , Chang Gu-Gang , Yuan Hanna S.
Published: July 2002

Recombinant pigeon-liver malic enzyme was expressed in Escherichia coli and purified to homogeneity. Two different crystal forms were grown by the hanging-drop vapour-diffusion method. Both types of crystals belong to the tetragonal space group P4222, with unit-cell dimensions a = b = 163.8, c = 174.3 Å for the octahedral crystals and a = b = 124.5, c = 179.2 Å for the rod-like crystals. X-ray diffraction data were collected at 100 K using a synchrotron-radiation X-ray source. The Matthews parameter suggests that there are four and two molecules per asymmetric unit for the larger and the smaller tetragonal unit cells, respectively.
Crystallization and preliminary X-ray analysis of the catalytic core of the alkylhydroperoxide reductase component AhpF from Escherichia coli
Authors: Bieger Boris , Essen Lars-Oliver
Published: July 2002

Alkylhydroperoxide reductases (AhpR, E.C. 1.6.4.x) are essential for the oxygen tolerance of aerobic organisms, converting otherwise toxic hydroperoxides of lipids or nucleic acids to their corresponding alcohols. The AhpF component (521 amino-acid residues, 56.2 kDa) belongs to the family of pyridine nucleotide–disulfide oxidoreductases and channels electrons from NAD(P)H via a series of disulfides towards the AhpC component, which finally reduces the hydroperoxide substrates. Crystals of the proteolytically truncated AhpF component (residues Asn208–Ala521) of the alkyl hydroperoxide reductase from Escherichia coli were grown under oxidizing conditions. The crystals belong to space group P3221, with unit-cell parameters a = 60.4, c = 171.8 Å. X-ray diffraction data were collected to 1.9 Å resolution using synchrotron radiation. A molecular-replacement solution was found using the structure of thioredoxin reductase from Arabidopsis thaliana as a search model.
Fluorescence EXAFS for the in situ study on the state of promotors in catalysis
Authors: Grunwaldt Jan-Dierk , Kappen Peter , Hammershøi Birgitte S. , Tröger Larc , Clausen Bjerne S.
Published: July 2002

The fluorescence EXAFS (FLEXAFS) technique has been combined with an in situ cell and on-line gas analysis. For this purpose a seven-element silicon drift detector has been used, which has high count rate capabilities and can be operated at room temperature. The potential of this technique is shown by the study of the state of copper promoter atoms in Fe-Cr based high temperature shift (HTS) catalysts. The FLEXAFS measurements revealed that Cu (0.17–1.5 wt%) is present in the metallic state under working conditions of the catalysts but easily re-oxidizes upon air exposure. The reduction behaviour of copper depends strongly on the copper concentration and the pre-treatment, i.e. if the catalysts have been calcined or used in the HTS reaction. For used catalysts, a Cu(I) phase was detected as intermediate during reduction. Its stability was especially high at low copper concentration.
Development of multipurpose laboratory XIEES spectrometer and its application to surface XAFS analysis of Al2O3 films
Authors: Lee Jae Cheol , Song Se Ahn , Yuryev Yury , Terada Yasuko , Nakai Izumi , Lim Chang Bin
Published: July 2002

A new laboratory spectrometer for X-ray Induced Electron Emission Spectroscopy (XIEES) has been developed. This spectrometer is suitable for measurements of X-ray Absorption Fine Structure (XAFS) spectrum in surface sensitive fluorescence and electron emission detection modes as well as in standard transmission mode. It is the advantage of this spectrometer that a wide range of X-ray energy scanning between 0.48 and 41 keV is available. At the Cu K-edge, an energy resolution of about 2 eV has been achieved. The spectrometer has been used to analyze the Al2O3 (40 Å and 500 Å)/Si(100) with total electron yield measurement.
XAFS studies on the local structures of Ti-HMS mesoporous molecular sieves and their photocatalytic properties
Authors: Zhang Jinlong , Matsuoka Masaya , Yamashita Hiromi , Anpo Masakazu
Published: July 2002

Various Ti-containing HMS mesoporous molecular sieves having high surface areas and pore volumes have been prepared at ambient temperature. The Ti-HMS samples exhibited a well-defined XRD pattern of typical hexagonal lattice. UV-vis and XAFS spectra for the calcined forms of Ti-HMS indicated that the Ti ions are tetrahedrally coordinated in the framework of HMS for the samples of Ti-HMS(1) and Ti-HMS(2), while at least a fraction of Ti-oxides in Ti-HMS(10) is in octahedral coordination. UV irradiation of the Ti-HMS catalysts in the presence of NO was found to lead to the decomposition of NO to form N2, O2, and N2O at 273 K with different yields and product distributions. The photocatalytic performance of Ti-oxides appears to be completely modified by their incorporation structure and reaction environment. High efficiency and selectivity for the formation of N2 and O2 in the photocatalytic decomposition of NO was achieved with the Ti-HMS(1) having highly dispersed isolated tetrahedral titanium oxide species, while the reactivity decreased with an increase in the Ti content.
Time-dependent XAS studies of trapped enzyme-substrate complexes of alcohol dehydrogenase from Thermoanaerobacter brockii
Authors: Kleifeld Oded , Frenkel Anatoly , Sagi Irit
Published: July 2002

The understanding of structure-function relationships in proteins has been significantly advanced with the advent of the biotechnological revolution. A goal yet to be realized for many metalloenzyme systems is to characterize the dynamic changes in structure that bridge the static endpoints provided by crystallography. We present here a series of edge and EXAFS spectra of the metalloenzyme alcohol dehydrogenase from Thermoanaerobacter brockii (TbADH) complexed with its substrate. The enzyme-substrate complexes were trapped by fast freezing at various times, following their enzyme activity. Our edge and EXAFS analyses both reveal the time-dependent changes in the structure of the active site of TbADH.
Carboplatin and oxaliplatin decomposition in chloride medium, monitored by XAS
Authors: Curis Emmanuel , Provost Karine , Bouvet Diane , Nicolis Ioannis , Crauste-Manciet Sylvie , Brossard Denis , Bénazeth Simone
Published: July 2002

The stability of carboplatin and oxaliplatin aqueous solutions has been studied under different chloride ions concentration and pH conditions. For both compounds, we demonstrate the chloration of the platinum first coordination shell.
An X-ray absorption spectroscopy study of the pressure and temperature dependence of ZnBr2 aqueous supercritical solutions
Authors: Calzavara Y. , Simonet V. , Hazemann J. L. , Argoud R. , Geaymond O. , Raoux D.
Published: July 2002

X-ray absorption spectroscopy (XAS) experiments have been performed on 1.0 and 1.6 M ZnBr2 aqueous solutions under ambient to supercritical conditions. Both the X-ray absorption near-edge structure (XANES) and the extended X-ray absorption fine structure (EXAFS) show striking evolutions, which indicate major structural changes, with a strong reduction in hydration and the increasing formation of ZnBr pairs. A quantitative analysis of the evolution of the Zn environment is presented that supports the existence of a transition from an octahedral to a tetrahedral environment.
Investigation of undercooled liquid metals using XAFS, temperature scans and diffraction
Authors: Filipponi Adriano , Di Cicco Andrea , De Panfilis Simone , Trapananti Angela , Itiè Jean-Paul , Borowski Michael , Ansell Stuart
Published: July 2002

Novel techniques and the experimental station for experiments on condensed matter under extreme conditions that have been developed at the BM29 beamline of the European Synchrotron Radiation Facility (ESRF) are described. The experimental setup includes facilities to collect high-quality extended X-ray absorption fine structure (EXAFS) spectra, to perform controlled temperature scans while monitoring the sample absorption for the direct detection of phase transitions, and to collect high-resolution energy-scanning X-ray diffraction (ESXD) data, with recent enhancements through the installation of a two-channel collimator detector system. Facilities for X-ray absorption temperature scans, introduced five years ago, are now exploited for a wide variety of purposes. A method for the measurement of the nucleation rate in undercooled liquids has been proposed recently. All these advances in the experimental setup and techniques, combined with a simple but rigorous X-ray absorption fine structure (XAFS) data analysis scheme for disordered matter, have contributed to make feasible challenging experiments on undercooled liquid matter that were not even conceivable only a few years ago. An example of the application of these methods to undercooled liquid indium (In) is presented.
The role of XAFS in the in situ and ex situ elucidation of active sites in designed solid catalysts
Authors: Thomas John Meurig , Sankar Gopinathan
Published: July 2002

New mesoporous and microporous catalysts based on silica, aluminophosphates, or aluminophosphates containing one or other of the heteroatoms Ti, Co, Mn, Fe and Cr, are ideally suited for study by X-ray absorption fine structure (XAFS). The information derived from X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) elucidates the nature of the catalytically active site, generally (but not invariably) under in situ conditions. This, in turn, provides new insights into the mechanism of the catalysis and suggests methods of improving the performance of the original catalyst. In this way, significant advances have recently been made in designing catalysts for the selective oxidation of alkanes, for the epoxidation of alkenes and for the dehydration of alcohols to yield olefins. Combined with density functional theory (DFT) computations, XAFS studies have also yielded fresh insights into the architecture of nanoparticle catalysts, such as Ru12Cu4C2 supported on mesoporous silica.
Zinc incorporation in human dental calculus
Authors: Barrea Raúl A. , Pérez Carlos A. , Ramos Aline Y.
Published: July 2002

We present here the first study of the local environment of zinc ions in biological calcium phosphates. It was suggested from in vitro studies that zinc inhibits the formation of hydroxyapatite and promotes the formation of more soluble phases, like tricalcium phosphate. Several mechanisms of zinc - calcium phosphate interaction were proposed, yielding either to the adsorption or to the incorporation of zinc ions into the phosphate structure. The results obtained here show that, under in vivo conditions, the zinc atoms are fully incorporated into the crystalline structure of the calcium phosphates.
Local structure of Ge nanocrystals embedded in SiO2 studied by X-ray absorption fine structure
Authors: Kolobov A. V. , Oyanagi H. , Maeda Y. , Tanaka K.
Published: July 2002

Local structure of Ge nanocrystals embedded in SiO2 has been studied by X-ray absorption fine structure on the Ge K-edge. The XANES and EXAFS results indicate that Ge atoms in samples with the Ge concentration x=25-40 mol. % are coordinated with oxygen atoms, while they exist as amorphous Ge clusters in samples with x=60 mol. %. Upon annealing, completely relaxed crystalline Ge phase is formed for samples with x=60 mol. %, in contrast to the x=25-40 mol. % sample, which show little or no indication of Ge cluster formation. A possible mechanism of Ge nanocluster formation is discussed.
Polarization-dependent XANES study of Bi2Sr2Ca1-x
Pr
x
Cu2O8-δ insulating single crystal
Authors: Garg K. B. , Dalela S. , Dalela B. , Venkatesh S. , Lee J. F. , Choy J.-H. , Chaturvedi D. , Singhal R. K. , Garcia-Ruiz J.
Published: July 2002

Pr doping has been extensively studied in cuprate superconductors to understand the mechanism of quenching of superconductivity in cuprate perovskites. Experience has revealed that it acts differently in different cuprate perovskites. We have made high resolution polarization XANES measurements on a Pr-doped single crystal within the ab-plane on the Cu K and Pr LIII absorption edges to ascertain the valence state of Pr cation and thereby try learning how it is quenching superconductivity in the present case. Our results show that besides the Pr quenching holes the possibility of its localizing some holes through hybridization with O 2p and Cu 3d cannot be ruled out.
Energy-Resolving X-ray Fluorescence Detection Using Synthetic Multilayers
Authors: Zhang K. , Rosenbaum G. , Bunker G.
Published: July 2002

The potential of synthetic multilayers for energy-resolving the X-ray fluorescence in X-ray absorption fine structure (XAFS) experiments is discussed. Two detection systems, one using curved multilayers and the other using graded multilayers to select X-ray fluorescence photons, have been designed to cover a wide energy range with a usefully large solid angle. Such a detector will be more advantageous than the barrel-like crystal-array detector because of the unique properties of synthetic multilayers, such as larger horizontal acceptance angles and bandwidth. In addition, the detector should be much simpler to construct and readily accommodates energy changes, especially the detector using graded multilayers. Comparison of the multilayer array detector with conventional detectors, such as ionization chambers and conventional 13-element Ge detectors, shows that the proposed system will be superior, particularly with the increased photon fluxes available from insertion devices and with decreased sample concentration, since this detection system eliminates the `bad' photons before they enter any X-ray detector. Consequently, the X-ray detector proper for this system does not suffer from the incident-count-rate bottleneck common to current X-ray fluorescence detectors with energy resolution by signal processing. Thus, this new fluorescence detection system will provide tremendous opportunities for XAFS measurements on dilute systems, such as biological systems, at third-generation synchrotron sources.
Angular Resolution of Parallel Foils on a Synchrotron Powder Diffractometer
Authors: Roberts M. A. , Tang C. C.
Published: July 2002

In an attempt to improve the resolution in flat-plate diffraction geometry, a new set of parallel foils, 100 µm spacing, 365 mm long with an aperture of 20 × 20 mm2, has been commissioned. The study was carried out using the two-circle diffractometer of station 2.3 at the SRS. In order to properly quantify the improvements, a detailed and comparative study of the instrumental resolution using the new and existing foils, of 200 µm spacing, is reported. A number of cubic materials, BaF2, Si and CeO2, that are known to show well defined Bragg peaks over the full 2θ angular range available, were investigated.
2,2′-Iminobis(ethylammonium) phthalate
Authors: Edwards Selvin H. , Kahwa Ishenkumba A. , Mague Joel T.
Published: July 2002

The phthalate salt of diprotonated diethylenetriamine, C4H15N3+·C8H4O4−, was obtained during ongoing studies of the hydrolytic chemistry of phthalimides for the synthesis of efficient sensitizers for EuIIIand TbIIIphotoluminescence.
5-tert-Butyl-3-methyl-1H-pyrazole at 240 K
Authors: Foces-Foces Concepción , Trofimenko Swiatoslaw
Published: July 2002

The title compound, C8H14N2, exists in the solid state as a tetramer with hydrogen bonding around the \overline 4 axis.
(2R,3S,4S,5R)-4-Hydroxy-3-iodo-5-methyltetrahydro-2-furylmethyl benzoate
Authors: Bew Sean P. , Light Mark E. , Hursthouse Michael B. , Knight David W. , Middleton Robert J.
Published: July 2002

The crystal structure determination of the title compound, C13H15IO4, has allowed the relative stereochemistry between the tetrasubstituted C atoms on the tetrahydrofuran moiety to be confirmed. The title compound is a precursor of the ionophoric antibiotic Aplasmomycin. The compound is involved in both intra- and intermolecular hydrogen bonding, the latter link the molecules into chains running along thebaxis.
Supramolecular adduct of tetrachlorogallate with cucurbituril: (H7O3)4[GaCl4]2Cl2·C36H36N24O12·2H2O
Authors: Virovets Alexander V. , Samsonenko Denis G. , Sokolov Maxim N. , Fedin Vladimir P.
Published: July 2002

During the investigation of the Ga3+–HCl–cucurbituril system, we prepared crystals of the title compound, tetrakis(hydroxonium) bis(tetrachlorogallate) dichloride cucurbituril decahydrate, by slow evaporation of an aqueous hydrochloric solution containing Ga3+and cucurbituril at room temperature in air. The compound appeared to be isostructural with the cucurbituril tetrachloroferrate(III) adduct. The structure contains H7O3+cations, [GaCl4]−anions, cucurbituril and water molecules. The centres of the cucurbituril molecules are arranged as body-centered packing and [GaCl4]−anions are situated in space between them. There is a complicated network of hydrogen bonds in the structure.
Network technology and language learning
Authors: Hill Brian , Slater Paul
Published: July 2002

Since the 1950s early adopters of a succession of new technologies have been working to see how these could be exploited in the language learning field. However, this pioneering work has had relatively little impact on the teaching and learning of languages. Is this pattern going to be repeated with the introduction of network technologies into language education? Raises some key themes which need attention if this cycle is to be broken. The central questions are: Why should language teachers be trying to integrate the use of network technologies into their curricula? If they should, how can this be achieved? To support this discussion recent experimental work in the area is described and considered. Concludes by stressing the need for skilful management of technological innovation in the education sector, and the importance of applying sound pedagogical principles.
Viscoplastic Anand model for solder alloys and its application
Authors: Cheng Z.N. , Wang G.Z. , Chen L. , Wilde J. , Becker K.
Published: July 2002

A viscoplastic constitutive model, the Anand model, in which plasticity and creep are unified and described by the same set of flow and evolutionary relations, was applied to represent the inelastic deformation behavior for solder alloys. After conducting creep tests and constant strain rate tests, the material parameters for the Anand model of the Pb‐rich content solder 92.5Pb5Sn2.5Ag were determined from the experimental data using a nonlinear fitting method. The material parameters for 60Sn40Pb, 62Sn36Pb2Ag and 96.5Sn3.5Ag solders were fitted from the conventional model in the literature where plasticity and creep are artificially separated. Model simulations and verifications reveal that there is good agreement between the model predictions and experimental data. Some discussion on this unified model is also presented. This viscoplastic constitutive model for solder alloys possesses some advantages over the separated model. The achieved Anand model has been applied in finite element simulation of stress/strain responses in solder joints for chip component, thin quad flat pack and flip‐chip assembly. The simulation results are in good agreement with the results in the literature. It is concluded that the Anand model could be recommended as a useful material model for solder alloys and can be used in the finite element simulation of solder joint reliability in electronic packaging and surface mount technology.
Internet consumer catalog shopping: findings from an exploratory study and directions for future research
Authors: Jones Joseph M. , Vijayasarathy Leo R.
Published: July 2002

Internet shopping has received considerable attention in the popular press as the future of in‐home shopping. Although actual sales figures attributed to this direct mode of shopping are relatively modest in comparison to predictions, there are too many potential benefits to consumers and retailers alike to ignore Internet shopping as a fad. The authors present findings from an exploratory, empirical investigation of perceptions of Internet catalog shopping and more traditional print catalog shopping. The study extends previous research on strategy developments for direct modes of shopping and examines two factors (personality and important other people) that might influence perceptions. Preliminary results suggest that there are significant differences in individuals’ perceptions of Internet catalog shopping and print catalog shopping, and perceptions differ by individual differences in personality (levels of need‐for‐cognition) and influence of important other people. Finally, the authors present research propositions that deserve further attention.
The Risks and Returns of Brady Bonds in a Portfolio Framework
Authors: Dahiya Sandeep
Published: July 2002

This paper examines the risks and returns of Brady bonds for the period 1990–1995 in a Modern Portfolio Theory framework. We find: (1) that the realized returns of Brady bonds are lower than the realized returns of other asset classes such as US stocks or US bonds; and (2) Brady bonds exhibit higher volatility compared to the other asset classes. These findings are largely explained by the influence of Mexico's devaluation of the Peso in December 1994. In addition, Mexico's devaluation is found to have had a strong (adverse) contagion effect on the returns on Brady bonds of other countries. The paper also finds that Brady bonds exhibit low correlations with US stocks and bonds markets. Thus, we find that there are potentially positive diversification gains from including Brady bonds in a domestic (US investor's) portfolio.
Velocity Statistics of Plane Self-Preserving Buoyant Turbulent Adiabatic Wall Plumes
Authors: Sangras R. , Dai Z. , Faeth G. M.
Published: July 2002

Measurements of the velocity properties of plane buoyant turbulent adiabatic wall plumes (adiabatic wall plumes) are described, emphasizing conditions far from the source where self-preserving behavior is approximated. The experiments involved helium/air mixtures rising along a smooth, plane, and vertical wall. Mean and fluctuating streamwise and cross-stream velocities were measured using laser velocimetry. Self-preserving behavior was observed 92–156 source widths from the source, yielding smaller normalized plume widths and larger near-wall mean velocities than observations within the flow development region nearer to the source. Unlike earlier observations of concentration fluctuation intensities, which are unusually large due to effects of streamwise buoyant instabilities, velocity fluctuation intensities were comparable to values observed in nonbuoyant turbulent wall jets. The entrainment properties of the present flows approximated self-preserving behavior in spite of continued development of the wall boundary layer. Measurements of temporal power spectra and temporal and spatial integral scales of velocity fluctuations are also reported. [S0022-1481(00)00504-1]
Static and Fatigue Strength of a Fixation Device Transducer for Measuring Anterior Cruciate Ligament Graft Tension
Authors: Zacharias Isaac , Hull M. L. , Howell Stephen M.
Published: July 2002

To determine which exercises do not overload the graft-fixation complex during intensive rehabilitation from reconstructive surgery of the anterior cruciate ligament (ACL), it would be useful to measure ACL graft loads during rehabilitative activities in vivo in humans. A previous paper by Ventura et al. (1998) reported on the design of an implantable transducer integrated into a femoral fixation device and demonstrated that the transducer could be calibrated to measure graft loads to better than 10 percent full-scale error in cadaveric knees. By measuring both the static and fatigue strengths of the transducer, the purpose of the present study was to determine whether the transducer could be safely implanted in humans without risk of structural failure. Eight devices were loaded to failure statically. Additionally, seven devices were tested using the up-and-down method to estimate the median fatigue strength at a life of 225,000 cycles. The average ultimate strength was 1856±74 N and the median fatigue strength was 441 N at a life of 225,000 cycles. The maximum graft load during normal daily activities is estimated to be 500 N and the 225,000 cycle life corresponds to that of the average healthy individual during a 12-week period. Considering that patients who have had an ACL reconstruction are less ambulatory than normal immediately following surgery and that biologic incorporation of the graft should be well developed by 12 weeks thus decreasing the load transmitted to the fixation device, the FDT can be safely implanted in humans without undue risk of structural failure. [S0148-0731(00)00606-3]
A Nested Finite Element Methodology (NFEM) for Stress Analysis of Electronic Products—Part II: Durability Analysis of Flip Chip and Chip Scale Interconnects
Authors: Darbha Krishna , Dasgupta Abhijit
Published: July 2002

The nested finite element methodology (NFEM) presented in Part I of this series, is used in this paper to analyze the viscoplastic stress-state in a flip-chip-on-board (FCOB) and a chip scale package subjected to temperature cycling loads. The results are validated with conventional finite element method (CFEM). An energy-partitioning (EP) damage model is used to predict cycles to failure, based on the energy densities obtained from NFEM and CFEM, and results are compared with experiments.
Planar Circle-Point Equations for Finitely Separated and Double-Point Positions
Authors: Jun Kim Hyoung , Sodhi Raj S.
Published: July 2002

The rigid body motion is studied for a combination of finitely and infinitesimally separated positions in planar kinematics. A general new method is developed for determining the locations of points in a rigid body moving through finitely and infinitesimally separated positions. These points would satisfy the constraints of the crank links for planar mechanisms. A new form of the circle-point curve equations is derived for the double-point position problem and also for the finitely separated position problem in planar kinematics.
Implementation of a Compressor Face Boundary Condition Based on Small Disturbances
Authors: Slater John W. , Paynter Gerald C.
Published: July 2002

A compressor-face boundary condition that models the unsteady interactions of acoustic and convective velocity disturbances with a compressor has been implemented into a three-dimensional computational fluid dynamics code. Locally one-dimensional characteristics along with a small-disturbance model are used to compute the acoustic response as a function of the local stagger angle and the strength and direction of the disturbance. Simulations of the inviscid flow in a straight duct, a duct coupled to a compressor, and a supersonic inlet demonstrate the behavior of the boundary condition in relation to existing boundary conditions. Comparisons with experimental data show a large improvement in accuracy over existing boundary conditions in the ability to predict the reflected disturbance from the interaction of an acoustic disturbance with a compressor.
Viscoelastic Functionally Graded Materials Subjected to Antiplane Shear Fracture
Authors: Paulino G. H. , Jin Z.-H.
Published: July 2002

In this paper, a crack in a strip of a viscoelastic functionally graded material is studied under antiplane shear conditions. The shear relaxation function of the material is assumed as μ=μ0 expβy/hft, where h is a length scale and f(t) is a nondimensional function of time t having either the form ft=μ∞/μ0+1−μ∞/μ0exp−t/t0 for a linear standard solid, or ft=t0/tq for a power-law material model. We also consider the shear relaxation function μ=μ0 expβy/h[t0 expδy/h/t]q in which the relaxation time depends on the Cartesian coordinate y exponentially. Thus this latter model represents a power-law material with position-dependent relaxation time. In the above expressions, the parameters β, μ0,μ∞,t0; δ, q are material constants. An elastic crack problem is first solved and the correspondence principle (revisited) is used to obtain stress intensity factors for the viscoelastic functionally graded material. Formulas for stress intensity factors and crack displacement profiles are derived. Results for these quantities are discussed considering various material models and loading conditions.
Hydration of Partially Sulfated Lime Particles From Fluidized Bed Combustors
Authors: Couturier M. F. , Volmerange Y. , Steward F.
Published: July 2002

The reaction between water and partially sulfated lime particles was studied under isothermal conditions using a microcalorimeter. Experiments were performed with spent sorbent particles from two industrial circulating fluidized bed combustors and with lime particles sulfated in the laboratory using a thermogravimetric analyzer. The rate of hydration of the partially sulfated lime particles was found to be independent of particle size, to increase with increasing temperature, and to decrease with increasing level of sulfation of the particles. A first-order kinetic model is shown to correlate well the effect of time and temperature on the extent of hydration of spent sorbent particles from fluidized bed combustors. The apparent activation energy of the hydration reaction is 45 kJ/mol.
Application of Macrolamination Technology to Lean, Premixed Combustion
Authors: Mansour A. , Benjamin M. , Straub D. L. , Richards G. A.
Published: July 2002

Macrolamination, a novel manufacturing technique, is used to develop a dual-fuel premixer. A spatially distributed injection strategy is used to enhance fuel placement, distribution, and mixing inside the premixer. Parametric studies are conducted with different configurations of the premixer to determine the effects of residence time and nozzle configuration on pollutant emissions and flame stability. Diesel fuel (DF-2) and natural gas are used as fuels. Tests are conducted at a pressure of 400 kPa (5 atmospheres), and an inlet air temperature of 533 K. The pollutant emissions and RMS pressure levels are presented for a relatively wide range of nozzle velocities (50–80 m/s) and equivalence ratios (0.54–0.75). These results indicate very good pollutant emissions for a prototype design. These results also indicate that the time-lag model, previously associated with combustion oscillations for gaseous-fuel applications, also applies to liquid-fuel operation.
Linear Thermoelastic Higher-Order Theory for Periodic Multiphase Materials
Authors: Aboudi J. , Pindera M.-J. , Arnold S. M.
Published: July 2002

A new micromechanics model is presented which is capable of accurately estimating both the effective elastic constants of a periodic multiphase composite and the local stress and strain fields in the individual phases. The model is presently limited to materials characterized by constituent phases that are continuous in one direction, but arbitrarily distributed within the repeating unit cell which characterizes the material’s periodic microstructure. The model’s analytical framework is based on the homogenization technique for periodic media, but the method of solution for the local displacement and stress fields borrows concepts previously employed by the authors in constructing the higher-order theory for functionally graded materials, in contrast with the standard finite element solution method typically used in conjunction with the homogenization technique. The present approach produces a closed-form macroscopic constitutive equation for a periodic multiphase material valid for both uniaxial and multiaxial loading which, in turn, can be incorporated into a structural analysis computer code. The model’s predictive accuracy is demonstrated by comparison with reported results of detailed finite element analyses of periodic composites as well as with the classical elasticity solution for an inclusion in an infinite matrix.