bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure and Non-linear Optical Properties of β -Barium Borate
Authors: Xue D. F. , Zhang S. Y.
Published: July 2002

The non-linear optical (NLO) properties of crystalline β-BaB2O4 (β-barium borate, BBO) have been investigated from the chemical bond viewpoint. The contributions of each type of chemical bond to the total NLO coefficient have been quantitatively determined. The calculations indicate that the true space group of BBO is R3 rather than R3c.
Structures of Fluoroarsenates KAsF6n
(OH)
n
, n = 0, 1, 2: Application of the Heavy-Atom Method for Modulated Structures
Authors: Peterková J. , Dusek M. , Petrícek V. , Loub J.
Published: July 2002

Structures of KAsF6−n
(OH)
n
, n = 0, 1, 2, have been determined from single-crystal X-ray diffraction data. Potassium hexafluoroarsenate, KAsF6, has a standard structure, potassium hydroxopentafluoroarsenate, KAsF5(OH), has a superstructure, and potassium dihydroxotetrafluoroarsenate, KAsF4(OH)2, has an incommensurate modulated structure. The superstructure has been solved both in the supercell by standard methods and in the basic cell as a commensurate modulated structure, giving the same results in both cases. The heavy-atom method for modulated structures has been developed and applied to identify a good starting point for the refinement of strongly modulated KAsF4(OH)2. Moreover, the influence of hydrogen bonding on a regular disturbance of simple translation symmetry of the structure is discussed.
Neutron structures of ammonium tetrafluoroberyllate
Authors: Srivastava R. C. , Klooster W. T. , Koetzle T. F.
Published: July 2002

It is thought that hydrogen bonding is responsible for the ferroelectricity in ammonium tetrafluoroberyllate, (NH_{4})_{2}BeF_{4}. In the past X-ray data have been collected, but these did not permit accurate determination of the H-atom positions. In order to obtain more accurate information the neutron structures have now been determined for the paraelectric and ferroelectric phases. Going from the paraelectric to the ferroelectric phase, both the BeF_4^{2-} and the NH_4^+ ions rotate and shift from the mirror planes of the paraelectric phase. This results in removal of the mirror-plane symmetry and formation of a superlattice with the a axis doubled. Along the polar c axis, the NH_4^+ ions move towards the BeF_4^{2-} ions within chains of molecules and the chains move slightly relative to one another. The rotations and translations give rise to stronger hydrogen-bonding interactions.
The oversampling phasing method
Authors: Miao J. , Kirz J. , Sayre D.
Published: July 2002

Sampling the diffraction pattern of a finite specimen more finely than the Nyquist frequency (the inverse of the size of the diffracting specimen) corresponds to surrounding the electron density of the specimen with a no-density region. When the no-density region is bigger than the electron-density region, sufficient information is recorded so that the phase information can be retrieved from the oversampled diffraction pattern, at least in principle. By employing an iterative algorithm, the phase information from the oversampled diffraction pattern of a micrometre-sized test specimen has been successfully retrieved. This method is believed to be able to open a door for high-resolution three-dimensional structure determination of complex and non-crystalline biological specimens, i.e. whole cells and sub-micrometre molecular clusters and micrometre-sized protein crystals. With the possible appearance in the future of X-ray free-electron lasers, it may become possible to image single molecules by recording diffraction patterns before radiation damage manifests itself.
Molecular replacement by evolutionary search
Authors: Kissinger Charles R. , Gehlhaar Daniel K. , Smith Bradley A. , Bouzida Djamal
Published: July 2002

Stochastic search algorithms can be used to perform rapid six-dimensional molecular-replacement searches. A molecular-replacement procedure has been developed that uses an evolutionary algorithm to simultaneously optimize the orientation and position of a search model in a unit cell. Here, the performance of this algorithm and its dependence on search model quality and choice of target function are examined. Although the evolutionary search procedure is capable of finding solutions with search models that represent only a small fraction of the total scattering matter of the target molecule, the efficiency of the search procedure is highly dependent on the quality of the search model. Polyalanine models frequently provide better search efficiency than all-atom models, even in cases where the side-chain positions are known with high accuracy. Although the success of the search procedure is not highly dependent on the statistic used as the target function, the correlation coefficient between observed and calculated structure-factor amplitudes generally results in better search efficiency than does the R factor. An alternative stochastic search procedure, simulated annealing, provides similar overall performance to evolutionary search. Methods of extending the evolutionary search algorithm to include internal optimization, selection and construction of the search model are now beginning to be investigated.
The Protein Data Bank
Authors: Berman Helen M. , Battistuz Tammy , Bhat T. N. , Bluhm Wolfgang F. , Bourne Philip E. , Burkhardt Kyle , Feng Zukang , Gilliland Gary L. , Iype Lisa , Jain Shri , Fagan Phoebe , Marvin Jessica , Padilla David , Ravichandran Veerasamy , Schneider Bohdan , Thanki Narmada , Weissig Helge , Westbrook John D. , Zardecki Christine
Published: July 2002

The Protein Data Bank [PDB; Berman, Westbrook et al. (2000), Nucleic Acids Res.
28, 235–242; http://www.pdb.org/] is the single worldwide archive of primary structural data of biological macromolecules. Many secondary sources of information are derived from PDB data. It is the starting point for studies in structural bioinformatics. This article describes the goals of the PDB, the systems in place for data deposition and access, how to obtain further information and plans for the future development of the resource. The reader should come away with an understanding of the scope of the PDB and what is provided by the resource.
Structure Determination of Nudaurelia capensis ω Virus
Authors: Munshi Sanjeev , Liljas Lars , Johnson John E.
Published: July 2002

The structure of Nudaurelia capensis ω virus (NωV), a single-stranded RNA virus, was determined to 2.8 Å resolution. Triclinic crystals (a = 413.6, b = 410.2, c = 419.7 Å, α = 59.13, β = 58.9, γ = 64.0°) diffracted X-rays beyond 2.7 Å resolution. The unit cell contained one icosahedral virus particle, providing 60-fold non-crystallographic symmetry (n.c.s.) and structural redundancy. The particle orientation in the unit cell was determined by self-rotation function analyses. Initial phases to 18 Å resolution were derived from a hollow spherical model of 192 Å outer radius and 139 Å inner radius, filled with uniform electron density. Radii of the model were determined by maximizing the correlation of the model-based calculated data with the low-resolution X-ray diffraction and solution-scattering data. Phases were refined by 60-fold non-crystallographic electron-density averaging and extended in small steps to a resolution of 5 Å. The phases obtained represented a mixture of four different phase sets, each consistent with the icosahedral symmetry constraints. The resulting electron density was not interpretable. A difference Fourier map computed with the native and an isomorphous heavy-atom derivative data sets and phases refined by real-space averaging was interpretable only if data within the 10 Å resolution shell were used. Maps calculated with data significantly higher than 10 Å resolution failed to display a constellation of heavy-atom sites consistent with the T = 4 icosahedral symmetry. Attempts to extend the phases beyond 10 Å resolution, starting with either phases based on a model or single isomorphous replacement, were unsuccessful. Successful phase extension was achieved by computing the phases for the higher resolution reflections from a partial atomic model (poly gly) built into the averaged 10 Å electron-density map. Phases from this model served as the starting point for n.c.s. phase refinement and extension to slightly higher resolution. The atomic model was improved at each extension interval and these phases were used for the subsequent phase calculation and extension. The entire polypeptide backbone corresponding to the NωV structure was built into the map at 4 Å. The same procedure for phase refinement was used to extend the phases to 2.8 Å in small increments of resolution. The overall molecular averaging R factor and correlation coefficient at 2.8 Å resolution were 18.4% and 0.87, respectively.
Crystallization and preliminary X-ray diffraction studies of piratoxin II, a phospholipase A2 isolated from the venom of Bothrops pirajai
Authors: Lee W.-H. , Gonçalez M. C. , Ramalheira R. M. F. , Kuser P. R. , Toyama M. H. , Oliveira B. , Giglio J. R. , Marangoni S. , Polikarpov I.
Published: July 2002

The phospholipases A2 (PLA2, E.C. 3.1.1.4, phosphatide sn2 acylhydrolases) are the major components of the venom of several snakes. They are responsible for several important pharmacological effects observed in ophidian incidents. PLA2 piratoxin II from Bothrops pirajai has been crystallized by the vapour-diffusion technique. X-ray diffraction data have been collected to 2.04 Å resolution (90.2% complete, R
merge = 0.070). The space group is P21 and the cell parameters are a = 46.19, b = 60.36, c = 58.74 Å and β = 96.05°. The structure has been solved by molecular replacement using the crystallographic structure of PLA2 from Bothrops asper (PDB code 1CLP) as a search model.
Stabilization of the i-motif by intramolecular adenine–adenine–thymine base triple in the structure of d(ACCCT)
Authors: Weil Jonathan , Min Tongpil , Yang Cheng , Wang Shuren , Sutherland Cory , Sinha Nanda , Kang ChulHee
Published: July 2002

The crystal structure of d(ACCCT), solved by molecular replacement, shows a four-stranded i-motif conformation, where two parallel duplexes intercalate with one another in opposite orientations. Each duplex is stabilized by hemi-protonated C–C+ base pairing between parallel strands, and a string of water molecules bridge the cytosine N4 atoms to phosphate O atoms. This structure of d(ACCCT) shows examples of reversed Hoogsteen and Watson–Crick base pairing in both intermolecular and intramolecular manners to stabilize the tetraplex. Noticeably, the four-stranded complex is further stabilized at one end by a three-base hydrogen-bonding network, in which two adenines and a thymine form four hydrogen bonds via a reverse Hoogsteen and an asymmetric adenine–adenine base pairing. The structure of d(ACCCT) shows a similar local structure to that found in the d(TAA) part of the crystal structure of d(TAACCC) and provides further structural evidence that these base arrangements are essential for stabilizing these novel DNA super-secondary structures.
Atomic resolution structure of biotin-free Tyr43Phe streptavidin: what is in the binding site?
Authors: Freitag Stefanie , Le Trong Isolde , Klumb Lisa A. , Stayton Patrick S. , Stenkamp Ronald E.
Published: July 2002

The streptavidin–biotin system is an example of a high-affinity protein–ligand pair (Ka
≃ 1013 mol−1). The thermodynamic and structural properties have been extensively studied as a model system for protein–ligand interactions. Here, the X-ray crystal structure of a streptavidin mutant of a residue hydrogen bonding to biotin [Tyr43Phe (Y43F)] is reported at atomic resolution (1.14 Å). The biotin-free structure was refined with anisotropic displacement parameters (using the SHELXL97 program package). The high-resolution data also allowed interpretation of side-chain and residue disorder in 41 residues where alternate conformations were refined. The Y43F mutation is unambiguously observed in difference maps, although only a single O atom per monomer is altered. The atomic resolution enabled the identification of 2-methyl-2,4-pentanediol (MPD) molecules in the biotin-binding pocket for the first time. Electron density for MPD was observed in all four subunit binding sites of the tetrameric protein. This was not possible with data at lower resolution (1.8–2.3 Å) for wild-type streptavidin or mutants in the same crystal form using MPD in the crystallization. The impact of MPD binding on these studies is discussed.
Purification, crystallization and preliminary X-ray analysis of Drosophila melanogaster ferrochelatase
Authors: Wang Kai-Fen , Wu Chia-Kuei , Sellers Vera M. , Rose John P. , Wang Bi-Cheng , Dailey Harry A.
Published: July 2002

Ferrochelatase (protoheme ferrolyase, E.C. 4.99.1.1), the terminal enzyme in the heme biosynthetic pathway, catalyzes the insertion of ferrous iron into protoporphyrin IX to form protoheme. In eukaryotes, the protein is associated with the inner surface of the inner mitochondrial membrane, and in higher animals the enzyme contains a [2Fe–2S] cluster. This cluster is highly sensitive to NO and is coordinated by four Cys residues whose spacing in the primary sequence is unique. Ferrochelatase from Drosophila melanogaster has been expressed in Escherichia coli with an amino-terminal six-histidine tag and purified to homogeneity. The protein has been crystallized with the [2Fe–2S] cluster intact. The crystals belong to space group I422, with unit-cell dimensions a = b = 158.1, c = 171.2 Å and two molecules in the asymmetric unit, and diffract to 3.0 Å resolution.
Crystallization and preliminary X-ray analysis of the formiminotransferase domain from the bifunctional enzyme formiminotransferase–cyclodeaminase
Authors: Kohls Darcy , Croteau Nathalie , Mejia Narciso , MacKenzie Robert E. , Vrielink Alice
Published: July 2002

Formiminotransferase–cyclodeaminase (E.C. 2.1.2.5–E.C. 4.3.1.4) is a bifunctional enzyme involved in the histidine-degradation pathway which exhibits specificity for polyglutamylated folate substrates. The first function of the enzyme transfers the formimino group of formiminoglutamate to the N
5 position of tetrahydrofolate, while the second function catalyses the cyclodeamination of the formimino group, yielding N
5,10-methenyl-tetrahydrofolate, with efficient channeling of the intermediate between these activities. Initial studies have shown that the enzyme consists of eight identical subunits of 62 kDa each, arranged as a circular tetramer of dimers. It is this formation which results in two different dimeric interfaces, which are necessary for the two different activities. The identical subunits have been shown to consist of two domains, each of which can be obtained as dimers. The formiminotransferase domain has been crystallized in the presence of the substrate analogue folinic acid. The crystals belong to space group P212121, with unit-cell dimensions a = 64.4, b = 103.7, c = 122.3 Å. Both a native data set and a mercurial derivative data set have been collected to 2.8 Å resolution.
Taking MAD to the extreme: ultrafast protein structure determination
Authors: Walsh Martin A. , Dementieva Irene , Evans Gwyndaf , Sanishvili Ruslan , Joachimiak Andrzej
Published: July 2002

Multiwavelength anomalous diffraction data were measured in 23 min from a 16 kDa selenomethionyl-substituted protein, producing experimental phases to 2.25 Å resolution. The data were collected on a mosaic 3 × 3 charge-coupled device using undulator radiation from the Structural Biology Center 19ID beamline at the Argonne National Laboratory's Advanced Photon Source. The phases were independently obtained semiautomatically by two crystallographic program suites, CCP4 and CNS. The quality and speed of this data acquisition exemplify the opportunities at third-generation synchrotron sources for high-throughput protein crystal structure determination.
Crystallization and preliminary X-ray characterization of VanA from Enterococcus faecium BM4147: towards the molecular basis of bacterial resistance to the glycopeptide antibiotic vancomycin
Authors: Huyton Trevor , Roper David I.
Published: July 2002

A recombinant form of Enterococcus facieum BM4147 D-alanine-D-lactate ligase (VanA) has been prepared and crystallized. VanA was found to crystallize only in the presence of a phosphinate inhibitor analogue of D-alanine-D-alanine. The crystals grow in 40–45% ammonium sulfate, 0.1 M 3-(N-morpholino)-propanesulfonic acid pH 6.0 and reach dimensions of 0.4 × 0.2 × 0.1 mm. The crystals diffract to at least 2.5 Å and are in the centred orthorhombic space group C2221, with unit-cell dimensions a = 123.2, b = 225.4, c = 72.4 Å.
The geometry of metal–ligand interactions relevant to proteins
Authors: Harding Marjorie M.
Published: July 2002

Geometrical data which could be of relevance in the structure determination, structure refinement, assessment or understanding of metalloproteins have been extracted from the Cambridge Structural Database (CSD). The CSD contains crystallographic data from `small-molecule' structures determined by X-ray or neutron diffraction to an accuracy much better than that of most current protein structure determinations. The structures selected have a crystallographic R factor ≤ 0.065 and contain Ca, Mg, Mn, Fe, Cu or Zn interacting with ligands which are analogues of the amino-acid side chains commonly found in proteins; they include carboxylate groups, alcohols, phenolates, thiolates, imidazole groups and also water molecules. For each pair, the mean metal–donor-atom distance, the sample standard deviation and the range of observed values are tabulated, using ∼4500 observations in all. Where practicable, subsets with different coordination numbers and/or oxidation states are given. Also included are inter-bond angles at the ligand donor atom, the orientation of carboxylate and imidazole groups with respect to the metal–donor-atom bond and some other aspects of ligand geometry. Thus, for example, target distances and their standard deviations could be easily looked up for the validation of a metalloprotein structure or for use in restrained refinement with low-resolution data.
Crystal engineering: a case study using the 24 kDa fragment of the DNA gyrase B subunit from Escherichia coli
Authors: D'Arcy Allan , Stihle Martine , Kostrewa Dirk , Dale Glenn
Published: July 2002

Site-directed mutagenesis was used to determine the efficacy of changing surface residues to improve crystal quality. Nine mutants of the 24 kDa fragment of the Escherichia coli DNA gyrase B subunit were produced, changing residues on the protein's surface. The mutations changed either the charge or the polarity of the wild-type amino acid. It was found that single amino-acid changes on the surface could have a dramatic effect on the crystallization properties of the protein and generally resulted in an improvement in the number of crystal-screen hits as well as an improvement in crystal quality. It is concluded that crystal engineering is a valuable tool for protein crystallography.
Evaluation of macromolecular electron-density map quality using the correlation of local r.m.s. density
Authors: Terwilliger Thomas C. , Berendzen Joel
Published: July 2002

It has recently been shown that the standard deviation of local r.m.s. electron density is a good indicator of the presence of distinct regions of solvent and protein in macromolecular electron-density maps [Terwilliger & Berendzen (1999). Acta Cryst. D55, 501–505]. Here, it is demonstrated that a complementary measure, the correlation of local r.m.s. density in adjacent regions on the unit cell, is also a good measure of the presence of distinct solvent and protein regions. The correlation of local r.m.s. density is essentially a measure of how contiguous the solvent (and protein) regions are in the electron-density map. This statistic can be calculated in real space or in reciprocal space and has potential uses in evaluation of heavy-atom solutions in the MIR and MAD methods as well as for evaluation of trial phase sets in ab initio phasing procedures.
Lactate dehydrogenase from the hyperthermophilic archaeon Methanococcus jannaschii: overexpression, crystallization and preliminary X-ray analysis
Authors: Lee Byung Il , Chang Changsoo , Cho Seung-Je , Han Gye Won , Yu Yeon Gyu , Eom Soo Hyun , Suh Se Won
Published: July 2002

L(+)-Lactate dehydrogenase (LDH) is a key enzyme in anaerobic metabolism which converts pyruvate to lactate. LDH from the hyperthermophilic archaebacterium Methanococcus jannaschii has been overexpressed in Escherichia coli and crystallized in two crystal forms at 297 K using 2-methyl-2,4-pentanediol as precipitant. Type I crystals grew rapidly and diffracted to at least 2.8 Å Bragg spacing upon exposure to Cu Kα X-rays. X-ray diffraction data to 2.9 Å have been collected from a native crystal. The type I crystal is tetragonal, belonging to the space group P42212, with unit-cell parameters a = b = 99.74, c = 170.00 Å. The asymmetric unit contains two LDH subunits, with a corresponding crystal volume per protein mass (V

m
) of 3.05 Å3 Da−1 and a solvent content of 59.7%. Type II crystals, which grew more slowly, diffracted to at least 1.8 Å Bragg spacing upon exposure to Cu Kα X-rays. X-ray diffraction data to 1.9 Å have been collected from a native crystal. The type II crystal is orthorhombic, belonging to the space group P21212, with unit-cell parameters a = 47.65, b = 125.10, c = 58.08 Å. The asymmetric unit contains a single LDH subunit, with a corresponding crystal volume per protein mass (V

m
) of 2.50 Å3 Da−1 and a solvent content of 50.8%. Therefore, the type II crystal is more suitable for high-resolution structure determination than the type I crystal.
Anomalous X-ray scattering for determining the partial structural functions of binary liquids
Authors: Saito Masatoshi , Waseda Yoshio
Published: July 2002

The availability of intense white X-rays from synchrotron radiation sources has greatly improved both acquisition and quality of anomalous X-ray scattering (AXS) measurements. A demonstration is given of the usefulness of the AXS method for determining three partial structural functions of liquid matter by some selected examples of molten salts such as CuBr and RbBr.
Atomic surrounding of Co implanted in AlN at high energy
Authors: Traverse A. , Delobbe A. , Zanghi D. , Rentería M. , Gailhanou M.
Published: July 2002

AlN bulk ceramic has been implanted with energetic Co ions. In order to accurately characterise the atomic surrounding of the implanted ions, X-ray absorption measurements were carried out at 80 K in the fluorescence mode at the Co K edge in the as-implanted and annealed states. Simulation of the EXAFS oscillations allowed us to identify a first stage where Co is inserted in the AlN matrix followed by a second stage where Co precipitates form.
XAFS in a single macrophage cell
Authors: Kitamura Norio , Ektessabi A. M.
Published: July 2002

In this paper, a novel approach using XAFS will be introduced for the study of the problem of cytotoxicity to metal ions. A micro beam from a SR source was used to measure the time-dependent distributions and chemical states of elements in mouse microphages that were cultured in metallic solutions of different concentration. It is revealed that the concentrations and distributions of calcium, zinc and potassium in a single cell are closely related to the uptake of the metal. Using XAFS analysis, it is shown that metal elements absorbed by the cell interact with the cell and that the chemical state of the metal is changed.
Theory of photon interference X-ray absorption fine structure
Authors: Nishino Yoshinori , Materlik Gerhard
Published: July 2002

The theory of photon interference X-ray absorption fine structure (πXAFS) is described. Due to coherent X-ray scattering from atoms, a spatial variation of the X-ray intensity is produced inside the sample. The intensity at the X-ray absorbing atom changes according to the incident energy. Thus πXAFS in extended absorption spectra is produced. It extends in a wide energy range over absorption edges. For powders the πXAFS formula has equivalent form as the EXAFS formula, and the Fourier transform provides distances of neighboring atoms from the absorbing atom. Due to a long mean free path of the photon, πXAFS for powders contains sharp structures. They are explained as a crystal grain orientation averaging of the X-ray standing wave effect.
EXAFS and molecular dynamics studies of ionic solutions
Authors: D'Angelo Paola , Pavel Nicolae Viorel
Published: July 2002

This paper focuses on recent advances in the X-ray absorption spectroscopy (XAS) analysis of ionic solutions. The asymmetry of radial distribution functions g(r) associated with the solvent molecules surrounding the ions has to be taken into account to perform a reliable structural analysis. Molecular dynamics (MD) simulations provide reliable g(r)'s which can be used as starting models in the XAS data analysis. The combined MD-XAS investigation reduces meaningfully the indetermination of the structural parameters, especially for coordination numbers and Debye–Waller factors. Double-electron excitation channels can be present in the XAS spectra of ionic solutions and they have to be accounted for in the background extraction. The ability of the XAS technique to probe three-body correlation functions in ionic solutions with the aid of MD g(r_1,r_2,\theta) has been shown. The analysis of the low-k region of the spectra allows the detection of a weak but significant hydrogen structural signal. The XAS technique is especially well suited to determine the detailed shape of the nearest-neighbor peak in the atom–atom pair correlation functions of disordered systems. The information that they contain about the short-range atom–atom pairwise interactions can be very helpful for specifying and properly modifying model potentials used in MD simulations.
Characterization of relaxed photo-excited magnetized states in prussian-blue analogous magnets
Authors: Yokoyama Toshihiko , Okamoto Kaoru , Matsumura Daiju , Ohta Toshiaki , Ohkoshi Shin-ichi , Hashimoto Kazuhito
Published: July 2002

Local structure of a photo- or x-ray-induced ferrimagnet Cs0.8Co1.3 [W(CN)8](3-cyanopyridine)1.9(2.1H2O was investigated by means of Co K- and W L-edge XAFS spectroscopy. The Co K-edge XANES spectra provide quantitative information on the ratio of Co(II) and Co(III) by virtue of the factor analysis. It was found that the Co(II) ratios are 81.9% at 300 K and 32.7% at 150 K. When the sample was irradiated by x rays at 30 K, a phase transformation occurred in a similar manner to the visible-light irradiation and a relaxed excited state that exhibits ferrimagnetism was formed. The relaxed excited state gives the Co(II) ratio of 67.0%. The W LIII-edge EXAFS spectra determine the W-C, W-N and W-Co distances. The results of the distances were obtained as R(W-C)=2.16 Å, R(W-N)=3.31 Å, R(W-CoII)=5.37 Å and R(W-CoIII)=5.19 Å, irrespective of the three phases. The local structure of the relaxed excited state was found to be identical with that of the high-temperature (300 K) phase. The phase transformation is concluded to be caused by the charge transfer and the spin flipping from the -WIV(S=0)-CN-CoIII (S=0)- configuration to -WV(S=1/2)-CN-CoII (S=3/2)-.
Electronic states in Cu2MnX (X = Al, In and Sn) Heusler alloy studied by XMCD and multiple scattering calculations
Authors: Uemura Shigeaki , Maruyama Hiroshi , Kawamura Naomi , Yamazaki Hitoshi , Nagamatsu Shin-ichi , Fujikawa Takashi
Published: July 2002

X-ray magnetic circular dichroism (XMCD) has been measured at Mn and Cu K-edge in Cu2MnX (X = Al, In, and Sn) Heusler alloy. The Mn K-edge spectrum shows a dispersion-type profile and the Cu K-edge resembles the Mn spectrum, which suggests that polarization of the p unoccupied bands originates commonly in Mn 3d states. To reproduce the observed spectrum by full multiple scattering calculations, Madelung potential has been taken into account. Charge redistribution is an important factor for the electronic structure in Cu2MnX Heusler alloy.
Piezo-QEXAFS: advances in time-resolved X-ray absorption spectroscopy
Authors: Richwin Matthias , Zaeper Ralf , Lützenkirchen-Hecht Dirk , Frahm Ronald
Published: July 2002

The Piezo-QEXAFS technique is a novel tool for time-resolved X-ray absorption spectroscopy in the hard X-ray range. Monochromator components consisting of specialized tilt stages to perform fast energy scans, lightweight crystal holders, bending mechanics, and control electronics are being installed and commissioned. It is planned to perform fast EXAFS scans with time resolution in the millisecond range. With Piezo-QEXAFS all typical X-ray absorption experiments will be possible as it retains the standard linear geometry. The achieved time resolution opens interesting insights into the dynamics of phase transitions and chemical reactions.
XAFS studies of gold and silver–gold nanoparticles in aqueous solutions
Authors: Shibata Tomohiro , Tostmann Holger , Bunker Bruce , Henglein Arnim , Meisel Dan , Cheong Seongkyun , Boyanov Maxim
Published: July 2002

The X-ray absorption fine structure (XAFS) of colloidal Au and Au/Ag nanoparticles (3.5 nm and 20 nm mean diameter) in an aqueous solution has been investigated. Size dependent alloying was observed upon deposition of Ag on Au core. Ag forms distinct layers around the 20 nm Au nanoparticles. In contrast, random mixing is found for Ag deposited on 3.5 nm Au particles.
Oxygen K-edge X-ray absorption near edge structures (XANES) of sublimated films of amino acids
Authors: Tanaka Masahito , Nakagawa Kazumichi , Koketsu Toshiyuki , Agui Akane , Yokoya Akinari
Published: July 2002

Oxygen K-edge X-ray absorption near edge structures (XANES) spectra of amino acids (glycine, L-α-alanine, β-alanine, L-serine, L-asparic acid and L-tyrosine) were measured. Several peaks of XANES spectra were successfully assigned on the basis of DV-Xα calculation.
Magnetisation reorientation in ultra-thin Fe films on Cu(100) upon deposition of Co
Authors: Hunter Dunn Jonathan , Arvanitis Dimitri , Carr Roger , Mårtensson Nils
Published: July 2002

Ultra thin films of Fe deposited on the (100) surface of a Cu single crystal exhibit a net perpendicular magnetic anisotropy. The addition of very low coverages of Co results in the easy magnetic direction reorienting into the film plane. This behavior is in contrast to the addition of similar amounts of Fe, whereupon the ferromagnetic response vanishes. This result is discussed in terms of the anisotropy energies derived from the spectroscopic data.
X-ray magnetic circular dichroism in FeZrB amorphous alloys: the influence of the tensile stress
Authors: Orue I. , Fdez-Gubieda M. L. , Gorria P. , Pizzini S. , Fontaine A.
Published: July 2002

We present X-ray magnetic circular dichroism experiments (XMCD) on the Fe K edge of FeZrB metallic glasses performed under tensile stress. In these compounds the application of tensile stresses produces a large increase of the Curie Temperature. The XMCD signal presents the features expected for a weak ferromagnet but a gradual enhancement of the ferromagnetism is observed as boron and zirconium concentrations increase. The main effect of the tensile stress is to increase the density of states at the Fermi level as deduced from the increment of the amplitude of the XMCD signal with the stress.
X-ray absorption studies of carbon-related materials
Authors: Pong W. F. , Yueh C. L. , Chang Y. D. , Tsai M.-H. , Chang Y. K. , Chen Y. Y. , Lee J. F. , Wei S. L. , Wen C. Y. , Chen L. C. , Chen K. H. , Lin I. N. , Cheng H. F.
Published: July 2002

X-ray absorption near-edge structure (XANES) measurements have been performed on nitrogen-doped diamond films with three different dopant concentrations and iron-layer-stabilized carbon nanotube (CNT) structures with various diameters at the C K-absorption edge using the sample drain current mode. The C K-edge XANES spectra of these N-doped diamond films resemble that of the undoped diamond regardless of the dopant concentration, which suggest that the overall bonding configuration of the C atom is unaltered. N dopants are found to reduce the intensities of both the sp
2- and sp
3-bond-derived resonance features in the XANES spectra. On the other hand, the C K-edge XANES spectra of CNTs indicate that the intensities of the π* and σ* bands and the interlayer-state features vary with the diameter of the CNT. This phenomenon may be caused by the Fe-layer-catalysed bending of the graphite sheet and the interaction between C and Fe atoms.
X-ray induced reduction of rare earth ion doped in Na2O-Al2O3-B2O3 glasses
Authors: Shimizugawa Yutaka , Umesaki Norimasa , Hanada Katsumi , Sakai Ichiro , Qiu Jianrong
Published: July 2002

5Na2O-10Al2O3-85B2O3 glasses doped with 0.05 mol% Sm2O3 or 0.05 mol% Eu2O3 turn to orange after irradiation by focussed femtosecond pulsed laser or x-ray irradiation. To know the mechanism of photo-induced coloring, the glasses were studied by Sm or Eu LIII XANES before and after x-ray or UV irradiation. XANES in both edges showed that a part of trivalent ion converted to divalent ion upon the irradiation of x-ray. These facts reveal that photoreduction of rare earth ion is the mechanism of photo-induced coloring. However no photoreduction upon UV irradiation occurred in both glasses.
XANES study of charge ordering on the spin-Peierls phase transition of α′-NaV2O5
Authors: Shobu Takahisa , Noda Yukio , Ninomiya Emi , Sawa Hiroshi , Nagamatsu Shin-ichi , Fujikawa Takashi , Ueda Yutaka , Isobe Masahiko , Ikeda Naoshi , Uruga Tomoya
Published: July 2002

α′-NaV2O5 transforms at T

C
= 34 K, and the origin of the phase transition seems to be caused by the charge order and spin-Peierls mechanism. However the experiments which reveal the existence of charge order are very little. We measured XANES of V atoms which relates to the valence of V. It was found that the valences of V atoms in NaV2O5 were V4.5+ in the high temperature phase by comparing pre-edge and XANES of NaV2O5 with that of LiV$_2O5, CaV2O5 and V2O5. The analysis of EXAFS also shows the environment of the V4.5+ state.
Quick X-ray absorption spectroscopy for determining metal speciation in environmental samples
Authors: Gaillard Jean-Francois , Webb Samuel M. , Quintana John P. G.
Published: July 2002

We present a method for determining the chemical speciation of metals in environmental particles based on Quick-X-ray Absorption Spectroscopy. The approach can be applied to either the extended or the near edge fine structure, and consists in the decomposition of the XAS spectrum of an unknown sample on a reference set of standards' spectra using quadratic linear programming. The analysis accounts for the statistical experimental errors generated during the acquisition of X-ray absorption data, and leads to error estimates on the various fractions determined via a Monte Carlo procedure. An application example is presented for the speciation of inorganic Zn in a contaminated sediment sample.
Simultaneous measurement of XANES in halide-intercalated BSCCO(2212) using electron and fluorescence yield to compare their performance
Authors: Saxena S. G. , Dalela B. , Dalela S. , Chaturvedi D , Singhal R. K. , Parikh P. , Jain D. C. , Garg K. B.
Published: July 2002

Total Yield with an escape depth of ~100-200 Å is known to be rather surface sensitive. Fluorescence Yield, on the other hand, with an escape depth of ~1000-2000Å is relatively less prone to surface effects but necessitates some corrections to obtain the true signal. Both have their plus and minus points and, if used with care, yield reliable data. In the present experiment both the techniques have been simultaneously employed for measuring orientation dependent O K and the Cu L3 edges from an uncleaved surface of I(2)BSCCO(2212) single crystal to compare the performance of the two modes of detection. Despite glaring differences in intensities the results from the two appear to show reasonable agreement in respect of relative intensities of the spectral features.
Measurements of photon interference X-ray absorption fine structure (πXAFS)
Authors: Tröger Larc , Kappen Peter , Nishino Yoshinori , Haack Nils , Materlik Gerhard
Published: July 2002

Experimental data are presented which demonstrate the existence of a fine structure in extended X-ray absorption spectra due to interference effects in the initial photon state (πXAFS). Interference occurs between the incident electromagnetic wave and its coherently scattered waves from neighboring atoms. Using fine platinum and tungsten powders as well as polycrystalline platinum foil, πXAFS was measured in high-precision absorption experiments at beamline X1 at HASYLAB/DESY over a wide energy range. πXAFS is observed below and above absorption-edge positions in both transmission and total-electron-yield detection. Based on experimental data it is shown that πXAFS is sensitive to geometric atomic structure. Fourier-transformed πXAFS data carry information, comparable with that of EXAFS, about the short-range-order structure of the sample. Sharp structures occur in πXAFS when a Bragg backscattering condition of the incident X-rays is fulfilled. They allow precise measurement of long-range-order structural information. Measured data are compared with simulations based on πXAFS theory. Although πXAFS structures are similarly observed in two detection techniques, the importance of scattering off the sample for the measurements needs to be investigated further. Disentangling πXAFS, multielectron photoexcitations and atomic XAFS in high-precision measurements close to absorption edges poses a challenge for future studies.
Scanning X-ray spectrometer for high-resolution Compton profile measurements at ESRF
Authors: Suortti P. , Buslaps T. , Fajardo P. , Honkimäki V. , Kretzschmer M. , Lienert U. , McCarthy J. E. , Renier M. , Shukla A. , Tschentscher Th. , Meinander T.
Published: July 2002

A scanning-type crystal spectrometer for high-resolution Compton profile measurements has been constructed at the High Energy Inelastic Scattering Beamline (ID15B) of the ESRF. Radiation from a seven-period asymmetrical permanent-magnet wiggler or from a superconducting wavelength shifter is focused horizontally onto the sample by a bent-crystal monochromator. Typical energies are 30, 50 and 60 keV, the flux on the sample is 1012 photons s−1, and the relative energy bandwidth is 3 × 10−4. The spectrometer operates in the Rowland circle geometry, where the sample is fixed and the cylindrically bent analyser crystal and the detector move on the focusing circle by synchronized translations and rotations. The main detector is a large-diameter NaI scintillation counter, the incident beam is monitored by an Si diode, and scattering from the sample is detected using a Ge detector. The recorded spectrum is corrected for the energy-dependent response of the spectrometer, background and multiple scattering, and converted to the momentum scale. The resolution of the spectrometer is calculated from the geometrical factors and the reflectivity curve of the analyser crystal, and the result is checked against the widths of the elastically scattered line and fluorescent lines. So far, 0.1 a.u. resolution in electron momentum has been achieved. The typical average count rate over the Compton profile is about 1000 counts s−1 from a weakly absorbing sample.
2-Amino-4,6-bis(phenylthio)pyrimidine
Authors: Lynch Daniel E. , McClenaghan Ian
Published: July 2002

The structure of the title compound, C16H13N3S2, (I), consists of molecules that associateviaN—H...N and N—H...S interactions to form a linear one-dimensional hydrogen-bonded chain. The dihedral angles between the two phenyl rings and the pyrimidine ring are 74.94 (7) and 75.47 (7)°.
Bis(N-cyclohexyl-N-ethyldithiocarbamato-S,S′)lead(II)
Authors: Baba Ibrahim , Farina Yang , Othman A. Hamid , Razak Ibrahim Abdul , Fun Hoong-Kun , Ng Seik Weng
Published: July 2002

The Pb atom in the title compound, [Pb(C9H16NS2)2], is chelated in an anisobidentate manner by the dithiocarbamate group [Pb—S = 2.710 (2)/2.883(2) Å and 2.700 (2)/2.841(2) Å]. The four-coordinate geometry is raised to six through the involvement of the double-bonded S atoms of adjacent dithiocarbamato groups; the Pb...S interactions [Pb...S = 3.457 (2) and 3.508 (2) Å] result in a chain structure for the compound.
2-(2-Chlorophenylamino)-4-methylsulfanyl-1,3,5-triazine
Authors: Chen Wei-Qiang , Weng Lin-Hong , Jin Gui-Yu
Published: July 2002

The crystal structure of the title compound, C10H9ClN4S, is reported. There is π-conjugation between triazine and the bridging N4 atom, where N atoms aresp2hybridized. The plane of the triazine ring forms a dihedral angle of 54.35 (4)° with the phenyl plane. There exists an intermolecular N—H...N hydrogen bond to form a dimer with an N...N separation of 2.991 (2) Å.
Bis(μ-N-ethyl-N-isopropyldithiocarbamato-S:S′)bis[(N-ethyl-N-isopropyldithiocarbamato-S,S′)zinc(II)]
Authors: Baba Ibrahim , Farina Yang , Othman A. Hamid , Razak Ibrahim Abdul , Fun Hoong-Kun , Ng Seik Weng
Published: July 2002

In the centrosymmetric title compound, [Zn2(C6H12NS2)4], one dithiocarbamate group chelates the Zn atom, whereas the other is bonded to two Zn atoms.
4-Methoxy-3-nitropyridinium chloride
Authors: Lynch Daniel E. , McClenaghan Ian
Published: July 2002

The structure of the title compound, C6H7N2O3+·Cl−, (I), comprises the hydrochloride salt of an essentially flat molecule with a single N—H...Cl association. Two additional C—H...Cl close contacts are also observed.
Principles of price and pricing policy for the information marketplace
Authors: Rowley Jennifer
Published: July 2002

Considers a number of aspects of pricing, including the classical relationship between price and supply and demand, pricing objectives, factors affecting pricing decisions and aspects of pricing policy and pricing methods. Explores the relevance of these concepts in the information marketplace. The central role that price plays in regulating a marketplace makes an understanding of pricing essential.
Does strategic planning create value? The stock market’s belief
Authors: Desai Ashay B.
Published: July 2002

This article addresses a key issue: is strategic planning rewarded by the stock market? Using event‐study methodology, this article examined the market values of companies during the time period that they revealed information about their strategic planning focus, function or orientation. The results indicate that the stock market favors the long range‐planning horizon adopted by companies.
Adulteration of foods – past and present
Authors: Sumar S. , Ismail H.
Published: July 2002

The adulteration of food has progressed from being a simple means
of fraud to a highly sophisticated and lucrative business. The problem
is further compounded by the lack of clear international definitions for
enforcement purposes. Reviews some examples of food adulteration and
methods of analysis used to determine authenticity. Adulteration of food
has ramifications within society and cannot be ignored since
interference with foodstuffs may potentially lead to the production of
food which is harmful to health.
Grease‐lubrication of roller bearings in railway waggons. Part 2: laboratory tests and selection of proper test methods
Authors: Lundberg Jan , Berg Sven
Published: July 2002

New, undestroyed greases of the same brands as those used in a field test, described in Part 1, were examined using conventional methods, such as the SKF V2F test, the roll stability test (ASTM D‐1831), the Grease Worker (ASTM D‐217), the torque test (ASTM 1478‐91), bleeding measurements ( IP 121), yield stress measurements, the 4‐ball test (ASTM D 2266‐86), base oil viscosity measurements, thickener content and the cone penetration test (ASTM D217‐88). The greases have also been tested with several new test methods developed at the University. A specification for relevant testing methods was drawn up and the connections between the tested parameters were investigated. It was found that the mechanical stability could be predicted with a combination of ASTM D‐1831 and the limiting shear stress coefficient γ. This coefficient is capable of predicting wear. It was found that the bearing temperature could be predicted by using the base oil viscosity.
Reconnecting education, development and training through learning: a holographic perspective
Authors: Antonacopoulou Elena P.
Published: July 2002

At the levels of both the national economy and organisations, learning is linked to competitiveness and it is frequently promoted as an all‐encompassing solution to the multiplicity of issues that organisations (and societies) face. This view, however, does not fully address how learning takes place and what the relationship may be between learning, education, training and development, which are frequently treated as isolated processes. Provides a re‐conceptualisation of these relationships by proposing a holographic perspective that can support their interaction while drawing closer the connections between individual, organisational and governmental practices. The main implications of the holographic perspective and its practical ramifications, particularly for the SME sector, are discussed at the end of the paper.
Relationships between productivity, efficiency, utilization, and quality
Authors: Al‐Darrab Ibrahim A.
Published: July 2002

This paper reviews the literature relating to concepts and definitions of productivity, utilization, and efficiency. From an analysis of these concepts and definitions, the author derives two unifying formulae, the first relating these factors to one another and the second adding in a quality factor. System improvement strategies are then discussed based on these two equations.
Industrial relations under new ownership – The case of provincial newspapers in Britain
Authors: Gall Gregor
Published: July 2002

This paper examines changes in industrial relations in a large number of provincial newspapers (existing and acquired) following expansion through acquisition by previously medium‐sized newspaper groups. It considers whether acquisition leads to forces for change or continuity, diversity or uniformity, resulting in differing industrial relations outcomes. It concludes that while there are severe difficulties in evaluating the consequences of acquisition on industrial relations, the degree of change is much less than might be expected.
Business Process Re‐engineering and Human Resource Management
Authors: Willmott Hugh
Published: July 2002

Reviews the business process re‐engineering (BPR) vision of radical
business process change, focusing on the use of information technology
to facilitate a shift away from linear/sequential work organization
towards parallel processing and multidisciplinary teamworking.
Highlights BPR′s cursory treatment of the human dimension of its
programme for radical organizational change and raises the question of
how human resource management specialists are to respond to its
trivialization of the complexities and dilemmas associated with the
re‐engineering of work processes.
Re‐engineering organizations: a critical appraisal
Authors: Grey Christopher , Mitev Nathalie
Published: July 2002

Addresses the latest vogue in managerial theory – business process re‐engineering (BPR). Locates BPR within other recent challenges to traditional modes of organizing work, and subjects it to some critical scrutiny in order to provide some markers for further work. Examines BPR in terms of the assumptions which it claims not to have, and in terms of the contradictions entailed by its use of concepts of commitment, empowerment and technology. Overall, aims to provide HRM professionals and academics with some of the arguments that may be deployed to challenge the excessive enthusiasm of some BPR advocates.