bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic displacement parameters for Ni(ND3)4(NO2)2 from 9 K X-ray and 13 K time-of-flight neutron diffraction data
Authors: Iversen B. B. , Larsen F. K. , Figgis B. N. , Reynolds P. A. , Schultz A. J.
Published: July 2002

Structural parameters derived from 9 1) K X-ray diffraction data and 13 (1) K time-of-flight neutron diffraction data on perdeuterated tetraamminedinitronickel(II), Ni(ND3)4(NO2)2, are compared. It is shown that excellent agreement can be obtained for both positional and thermal parameters derived separately from the two experiments, provided that great care is taken in all steps of the process, including data collection, data reduction, and nuclear and electronic structure refinement. The mean difference in the thermal parameters, <|ΔUij
|>, is as low as 0.00034 Å2 and <(ΔUij/σ)2>1/2 = 1.92, showing that, even without any form of scaling between the parameters, the same values can be obtained. This, compared with other such studies, indicates that time-of-flight neutron diffraction data can give structural information of a quality comparable to monochromatic neutron diffraction. The excellent correspondence between the thermal parameters derived separately from X-ray and neutron diffraction data gives confidence in the deconvolution of the thermal motion from the X-ray diffraction data, which is necessary for any study of a static electron density distribution.
Importance of True Satellite Reflections in the Analysis of Modulated, Composite Crystal Structures. I. A New Refinement of [M
2Cu2O3]7+δ[CuO2]10, M = Bi0.06Sr0.46Ca0.48
Authors: Jensen A. F. , Larsen F. K. , Iversen B. B. , Petříček V. , Schultz T. , Gao Y.
Published: July 2002

A new structural model for the composite crystal bismuth strontium calcium cuprate [M
2Cu2O3]7+δ[CuO2]10 with M = Bi0.06Sr0.46Ca0.48 and δ = 0.03 has been determined. The structure is orthorhombic with a = 11.380 (2), b = 12.960 (4) Å and incommensurate along c. Sublattice 1 of composition (CuO2)4 has c
1 = 2.7522 (4) Å and sublattice 2 of composition (M
2Cu2O3)4 has c
2 = 3.9155 (5) Å; superspace group F222(001 + γ)001; modulation vector q
l = γc2* with γ = 0.7029 (2). The structural analysis has been based on 603 main reflections, 428 first-order and 64 second-order satellite reflections. The final residual is R = 0.0632 for all reflections, R = 0.0614 for main reflections, R = 0.0735 for first-order and R = 0.1084 for second-order satellite reflections; λ = 0.6565 Å, μ = 19.4 mm−l The satellite reflections have been collected with X-ray synchrotron radiation. In this context, special experimental problems are discussed. It is shown that the true satellite reflections, which are the satellite reflections that are not also main reflections for one of the sublattices, are necessary in the least-squares refinement in order to avoid large correlations between displacive modulation amplitudes and thermal vibration amplitudes and thus to obtain a reasonable coordination chemistry.
A Modulation Wave Approach to the Structural Characterization of Three New Cristobalite-Related Sodium Magnesiosilicates
Authors: Withers R. L. , Lobo C. , Thompson J. G. , Schmid S. , Stranger R.
Published: July 2002

The crystal structures of three new cristobalite-related sodium magnesiosilicates [Na2MgSiO4, M

r
= 162.37, orthorhombic, Pna21, a = 10.835 (5), b = 5.279 (12), c = 7.067 (8) Å, D

x
= 2.668 g cm−3, Z = 4, Cu Kα, λ = 1.5418 Å, μ = 75.96 cm−l, F(000) = 319.87; Na1.74Mg0.79Al0.15Si1.06O4, M

r
= 157.02, orthorhombic, Pbca, a = 10.487 (7), b = 14.351 (4), c = 5.243 (6) Å, D

x
= 2.643 g cm−3, Z = 8, Cu Kα, λ = 1.5418 Å, μ = 76.70 cm−l, F(000) = 619.04; Na1.8Mg0.9Si1.1O4, M

r
= 158.15, tetragonal, P41212, a = 5.330 (6), c = 7.086 (5) Å, D

x
= 2.609 g cm−3, Z = 2, Cu Kα, λ= 1.5418 Å, μ = 75.44 cm−l, F(000) = 155.94] are determined by Rietveld refinement from X-ray powder diffraction data. Plausible starting models were derived from a modulation wave approach based on the ideal C9 structure type and assuming regular SiO4 and MgO4 tetrahedra.
The piezoelectric tensor element d
33 of KTiOPO4 determined by single crystal X-ray diffraction
Authors: Graafsma H. , Heunen G. W. J. C. , Dahaoui S. , El Haouzi A. , Hansen N. K. , Marnier G.
Published: July 2002

The d
33 piezoelectric constant of KTiOPO4 (potassium titanium orthophosphate, KTP) has been determined for two different samples and at temperatures between 100 and 220 K, using high-resolution X-ray diffraction of a single-crystal in an electric field. The observed value of 15 (2) \times 10−12 m V−1 is between the two values of 10.4 and 25.8 \times 10−12 m V−1 found in the literature. The value of d
33 is shown to be constant over the temperature range 100–220 K and no anomaly was observed at the conductor–insulator transition at 150 K. The results obtained are believed to be sample-independent, since the same value was obtained for two different crystals, measured at different sources.
Crystal and Molecular Structure of Thiocarbonyl-ethoxo(tetraphenylporphyrinato)ruthenium(II), [Ru(TPP)(CS)(HOC2H5)]. A Case of Centrosymmetric–Noncentrosymmetric Ambiguity
Authors: Bartczak T. J. , Rachlewicz K. , Latos-Grażynski L.
Published: July 2002

[Ru(TPP)(CS)(EtOH)] crystallizes in the triclinic system. Crystal data: C47H34N4ORuS, M

r
= 803.91, a = 10.607 (3), b = 11.308 (5), c = 17.699 (2) Å, \alpha = 77.53 (2), \beta = 73.17 (1), \gamma = 69.85 (3)°, V = 1891.6 (10) Å3, P\overline 1 (C^{1}_{i}, no. 2), Z = 2, F(000) = 824, D

x
= 1.410, D

m
= 1.39 Mg m−3 (by flotation in aqueous KI), \mu(Mo K\alpha) = 0.512 mm−1, R = 0.094, wR = 0.098, S = 2.28 for 4610 independent reflections with F

o
> 5\sigma(F

o
). A second data set was collected using Cu K\alpha radiation. The structure was refined by standard least-squares and difference-Fourier methods in space groups P1 and P\overline 1 using both the Mo K\alpha and Cu K\alpha data sets. Both data sets favor space group P\overline 1, the Mo data giving a slightly better result than the Cu data. The two independent Ru atoms lie on the inversion centers ½,0,0 and ½,½,½ of space group P\overline 1. Consequently, the two independent molecules have crystallographically imposed \overline 1 symmetry, the CS and EtOH axial groups are disordered and the RuN4 portions of the molecules are planar. The deviations from planarity of the porphyrinato core are very small. The Ru—C—S groups are essentially linear with an average Ru—C—S bond angle of 174 (1)°. The mean Ru—C(CS) and Ru—O (Et) bond lengths are 1.92 (4) and 2.15 (3) Å, respectively.
Experimental Electron-Density Study of 4-Cyanoimidazolium-5-olate at 120 K
Authors: Bianchi R. , Gervasio G. , Viscardi G.
Published: July 2002

This paper presents an analysis of the electron density in 4-cyanoimidazolium-5-olate, determined by the rigid pseudoatom model from accurate X-ray data measured at 120 K. A comparison of the electrostatic potential between experiment and theory is given for the isolated molecule. The results confirm the typical mesoionic electron distribution of the title compound and the presence of three hydrogen bonds in the crystal structure. The atomic charges and molecular dipole moment derived from the ab initio Hartree–Fock method are close to those obtained from the multipole model, which includes the kappa radial parameters. Electrostatic energies are also calculated for hydrogen bonding and molecular stacking interactions.
β-K2SO4-Type Isomorphs: Prediction of Structures and Refinement of Rb2CrO4
Authors: Aleksovska S. , Nyburg S. C. , Pejov Lj. , Petrusevski V. M.
Published: July 2002

The crystal structures of members within a group of isostructural compounds may be successfully predicted. This is demonstrated for the β-K2SO4 group isomorphs with the general formula M
2
XO4, which were chosen as a family of very closely related compounds nearly all with accurately refined crystal structures. The unit-cell parameters and the fractional atomic coordinates are shown to exhibit systematic variations with both cation and anion size, as well as the Mulliken charge on the O atom in the tetrahedral anion. This allows the prediction of the crystal structures of members in the series, with only the chemical composition of the compound being known. The agreement is good, except for an early structure determination of Rb2CrO4. The now refined structure gives excellent agreement with that predicted.
Structure of Ammonium Hydrogen Succinate at 80 and 20 K
Authors: Kashino S. , Taka J. , Yoshida T. , Kubozono Y. , Ishida H. , Maeda H.
Published: July 2002

The crystal structure of ammonium hydrogen succinate has been determined at 80 and 20 K in order to clarify the structural change at the second-order phase transition at 170 K. The geometries of all the hydrogen bonds in the structure were analyzed by combining new geometric data with data obtained previously at 297, 190 and 150 K. The O...O distances of two O—H...O hydrogen bonds involving the hydrogen succinate ions increase as the temperature decreases below T

c
and the N...O distance of a weak bifurcated hydrogen bond involving the ammonium ion decreases below T

c
. It is noted that the phase transition occurs so that the bifurcated hydrogen bond is retained below T

c
. There was no evidence of a descent in space group from P1¯ to P1 below T

c
and the formation of a superstructure below T

c
was not detected.
Renormalization of the phase transition in lead phosphate, Pb3(PO4)2, by high pressure: lattice parameters and spontaneous strain
Authors: Angel R. J. , Bismayer U.
Published: July 2002

The unit-cell parameters of lead phosphate, Pb3(PO4)2, have been measured by single-crystal X-ray diffraction in a diamond–anvil cell under hydrostatic conditions to a maximum pressure of 6 GPa. The compound undergoes an improper ferroelastic phase transition at 1.81 ± 0.01 GPa at 298 ± 1 K from a low-pressure monoclinic phase (space group C2/c) to a high-pressure trigonal phase. The space group of the high-pressure phase is R3¯m or R3m and the phase boundary is the same as that crossed at ca 450 K at room pressure. The evolution of the spontaneous strain components arising from the phase transition is linear with pressure, indicating an effective critical exponent for the phase transition of β = 0.50 ± 0.03. Thus, the application of pressure strongly renormalizes the effective critical exponent of the order parameter from the value of 0.236 found in high-temperature experiments.
X-ray study of deformation density and spontaneous polarization in ferroelectric NaNO2
Authors: Gohda T. , Ichikawa M. , Gustafsson T. , Olovsson I.
Published: July 2002

The deformation electron density of ferroelectric sodium nitrite has been determined from X-ray diffraction data at 30 K, using Hirshfeld deformation functions. Owing to the strong correlation between odd terms of the deformation coefficients, constraints were imposed in the refinement. The net charges for Na, N and O atoms were estimated to be 0.27, 0.20 and −0.24 e, respectively. The calculated spontaneous polarization using these net charges and atomic dipole terms, 7.8 µC cm−2, is much closer to the recently measured value, 12 µC cm−2, as compared with the value calculated from the formal point charges (74 µC cm−2).
Evaluation of paracrystalline distortions from line broadening
Authors: Vogel W. , Hosemann R.
Published: July 2002

If the units building up a three-dimensional lattice have different sizes and/or shapes and are randomly distributed the long-range order of the point lattice is destroyed. The integral widths δb of the Debye–Scherrer lines increase quadratically with sin θ for a given set of netplanes. Studying the slopes for the reflexions h00, hh0 and hhh one obtains quantitative information on the paracrystalline distortions in the lattice. In the present paper these slopes are calculated for p.c., b.c.c. and f.c.c. lattices and identical coordination statistics with cylindrical symmetry and two fluctuation parameters α,β. The slopes can be conveniently normalized to the fluctuation Δxa
of a lattice cell. In a logarithmic Δxa

versus
β
2/(α
2 + β
2) plot of all these types of paracrystalline lattices, observed Δxa
values of manganese-rich spinels are fitted as well as possible. A body centred paracrystalline lattice is observed with α/β = 0.7 ± 0.1. This example may illustrate how to analyse reasonably paracrystalline lattices.
Solution solution: using NMR models for molecular replacement
Authors: Chen Yu Wai
Published: July 2002

NMR structures can serve as a good source of search models in crystal structure determination by molecular replacement. However, owing to the inherent problems of NMR models, this procedure is not always straightforward. Here, an updated overview is presented with particular emphasis on the preparation of NMR search models and the latest trends in methodology. An experimental protocol developed recently is described and results on its use in solving a new structure as well as its test against a difficult published case are presented.
Crystallization and preliminary X-ray analysis of the 12S form of phosphofructokinase from Saccharomyces cerevisiae
Authors: Obmolova Galina , Kopperschläger Gerhard , Heinisch Jürgen , Rypniewski Wojciech R.
Published: July 2002

The tetrameric 12S form of yeast phosphofructokinase, obtained by limited proteolytic cleavage of the native enzyme, was crystallized under a variety of conditions. The crystals have been characterized in the X-ray beam and are suitable for crystallographic studies.
Crystallization and preliminary X-ray studies of hORF6, a novel human antioxidant enzyme
Authors: Choi Hee-Jeong , Kang Sang Won , Yang Chul-Hak , Rhee Sue Goo , Ryu Seong-Eon
Published: July 2002

HORF6 is a member of the novel antioxidant enzyme family found in humans. A recombinant form of hORF6 expressed and purified from E. coli has been crystallized by the hanging-drop method using various PEG's as precipitating agents. HORF6 crystallizes in two different monoclinic space groups, P21 and C2. The P21 crystals have unit-cell dimensions of a = 47.85, b = 75.17, c = 63.30 Å and β = 110.21° and contain two monomers per asymmetric unit, while the C2 crystals have unit-cell dimensions of a = 165.27, b = 95.44, c = 166.44 Å and β = 128.97° and contain more than six monomers per asymmetric unit. The P21 crystals with the smaller unit cell diffract X-rays better and behave well for the X-ray analysis. A native data set from a single crystal of the P21 space group gas been collected to 2.0 Å resolution.
Expression, purification, crystallization and crystallographic characterization of the human MHC class I related protein MICA
Authors: Bauer S. , Willie S. T. , Spies T. , Strong R. K.
Published: July 2002

Crystals of the human MHC-encoded molecule MICA, a homologue of MHC class I proteins, have been grown in hanging-drop vapor-diffusion trials using ammonium sulfate as a precipitating agent with recombinant protein expressed in a baculovirus-based system. Cryo-preserved crystals of MICA belong to the cubic space group F4132 with lattice constants a = b = c = 260.7 Å and diffract to a resolution limit of 3.0 Å when cryo-preserved. These crystals do not diffract when handled conventionally.
Crystallization and preliminary X-ray crystallographic analysis of the unusual ferritin from Listeria innocua
Authors: Ilari Andrea , Savino Carmelinda , Stefanini Simonetta , Chiancone Emilia , Tsernoglou Demetrius
Published: July 2002

Single crystals of ferritin extracted from Listeria innocua have been obtained by the vapour-diffusion method using PEG 1000 as precipitant. The crystals are orthorhombic, space group P212121, with unit-cell dimensions a = 87.7, b = 137.5, c = 173.1 Å. The crystals diffract to 2.9 Å resolution on a rotating-anode X-ray source and to 2.35 Å resolution on a synchrotron X-ray source. The asymmetric unit contains one molecule formed by 12 subunits, corresponding to a packing density of 2.41 Å3 Da−1
Rapid automated molecular replacement by evolutionary search
Authors: Kissinger Charles R. , Gehlhaar Daniel K. , Fogel David B.
Published: July 2002

A new procedure for molecular replacement is presented in which an efficient six-dimensional search is carried out using an evolutionary optimization algorithm. In this procedure, a population of initially random molecular-replacement solutions is iteratively optimized with respect to the correlation coefficient between observed and calculated structure factors. The sensitivity and reliability of the method is enhanced by uniform sampling of the rotational-search space and the use of continuously variable rotational and translational parameters. The process is several orders of magnitude faster than a systematic six-dimensional search, and comparisons show that it can identify solutions using significantly less accurate or less complete search models than is possible with two existing molecular-replacement methods. A program incorporating the method, EPMR, allows the rapid and highly automated solution of molecular-replacement problems involving single or multiple molecules in the asymmetric unit. EPMR has been used to solve a number of difficult molecular-replacement problems.
Further additions to MolScript version 1.4, including reading and contouring of electron-density maps
Authors: Esnouf Robert M.
Published: July 2002

MolScript is one of the most popular programs for the generation of publication-quality figures and the recent re-working of the program should ensure its continued popularity. However, some functionality of particular interest to crystallographers is not part of the standard program. A modified MolScript version 1.4 has been described previously, with more flexible colouring schemes among its new features. This report describes further enhancements to MolScript version 1.4, including facilities for drawing rods for helices and ribbons for oligonucleotides and allowing several formats of electron-density maps to be read and contoured using either lines or smoothed triangulated surfaces.
Influence of packing interactions on the average conformation of B-DNA in crystalline structures
Authors: Tereshko V. , Subirana J. A.
Published: July 2002

The molecular interactions in crystals of oligonucleotides in the B form have been analysed and in particular the end-to-end interactions. Phosphate–phosphate interactions in dodecamers are also reviewed. A strong influence of packing constraints on the average conformation of the double helix is found. There is a strong relationship between the space group, the end-to-end interactions and the average conformation of DNA. Dodecamers must have a B-form average conformation with 10 ± 0.1 base pairs per turn in order to crystallize in the P212121 and related space groups usually found. Decamers show a wider range of conformational variation, with 9.7–10.6 base pairs per turn, depending on the terminal sequence and the space group. The influence of the space group in decamers is quite striking and remains unexplained. Only small variations are allowed in each case. Thus, crystal packing is strongly related to the average DNA conformation in the crystals and deviations from the average are rather limited. The constraints imposed by the crystal lattice explain why the average twist of the DNA in solution (10.6 base pairs per turn) is seldom found in oligonucleotides crystallized in the B form.
Specific lipid–protein interactions in a novel honeycomb lattice structure of bacteriorhodopsin
Authors: Sato Hidenori , Takeda Kazuki , Tani Koji , Hino Tomoya , Okada Tetsuji , Nakasako Masayoshi , Kamiya Nobuo , Kouyama Tsutomu
Published: July 2002

In the purple membrane of Halobacterium salinarium, bacteriorhodopsin trimers are arranged in a hexagonal lattice. When purple membrane sheets are incubated at high temperature with neutral detergent, membrane vesicularization takes place, yielding inside-out vesicles with a diameter of 50 nm. The vesicular structure becomes unstable at low temperature, where successive fusion of the vesicles yields a crystal which is composed of stacked planar membranes. X-ray crystallographic analysis reveals that the bacteriorhodopsin trimers are arranged in a honeycomb lattice in each membrane layer and that neighbouring membranes orient in opposite directions. The native structure of the trimeric unit is preserved in the honeycomb lattice, irrespective of alterations in the in-plane orientation of the trimer. One phospholipid tightly bound to a crevice between monomers in the trimeric unit is suggested to act as a glue in the formation of the trimer.
Structure of the histidine-containing phosphotransfer (HPt) domain of the anaerobic sensor protein ArcB complexed with the chemotaxis response regulator CheY
Authors: Kato Masato , Shimizu Toshiyuki , Mizuno Takeshi , Hakoshima Toshio
Published: July 2002

The three-dimensional structure of the HPt domain of ArcB complexed with CheY has been determined using the molecular-replacement method. The structure was refined to a crystallographic R factor of 18.3% at 2.68 Å resolution. The final model included 1899 protein atoms (117 residues from the HPt domain and 128 residues from CheY), one sulfate ion and 44 solvent molecules. In the crystal, CheY molecules stacked along the a axis of the cell with no interactions between neighbouring rows and the HPt domain bridged the CheY molecules. The phosphodonor residue His715 was fully exposed to the solvent region, even though the HPt domain was in contact with four molecules of CheY. CheY showed significant conformational change. This indicates that the HPt domain has a rigid structure when complexed with CheY.
Crystallization and preliminary X-ray diffraction studies of D-glyceraldehyde-3-phosphate dehydrogenase from the hyperthermophilic archaeon Methanothermus fervidus
Authors: Charron C. , Talfournier F. , Isupov M. N. , Branlant G. , Littlechild J. A. , Vitoux B. , Aubry A.
Published: July 2002

The homotetrameric holo-D-glyceraldehyde-3-phosphate dehydrogenase from the hyperthermophilic archaeon Methanothermus fervidus has been crystallized in the presence of NADP+ using the hanging-drop vapour-diffusion method. Crystals grew from a solution containing 2-methyl-2,4-pentanediol and magnesium acetate. A native data set has been collected to 2.1 Å using synchrotron radiation and cryocooling. Diffraction data have been processed in the orthorhombic system (space group P21212) with unit-cell dimensions a = 136.7, b = 153.3, c = 74.9 Å and one tetramer per asymmetric unit.
Crystallization, characterization and measurement of MAD data on crystals of dengue virus NS3 serine protease complexed with mung-bean Bowman–Birk inhibitor
Authors: Krishna Murthy H. M. , Judge K. , DeLucas L. , Clum S. , Padmanabhan R.
Published: July 2002

Crystallization and preliminary characterization of the essential dengue virus NS3 serine protease complexed with a Bowman–Birk-type inhibitor from mung beans are reported. As the structure proved resistant to solution by molecular replacement and multiple isomorphous replacement methods, multi-wavelength anomalous diffraction data at the L
III edge of a holmium derivative have been measured. Promising Bijvoet and dispersive signals which are largely consistent with expected values have been extracted from the data. The structure, when determined, will provide a structural basis for the design, synthesis and evaluation of inhibitors of the protease for chemotherapy of dengue infections.
Crystallographic analysis of potent and selective factor Xa inhibitors complexed to bovine trypsin
Authors: Whitlow Marc , Arnaiz Damain O. , Buckman Brad O. , Davey David D. , Griedel Brain , Guilford William J. , Koovakkat Sunil K. , Liang Amy , Mohan Raju , Phillips Gary B. , Seto Marian , Shaw Kenneth J. , Xu Wei , Zhao Zuchun , Light David R. , Morrissey Michael M.
Published: July 2002

Factor Xa is a serine protease which activates thrombin (factor IIa) and plays a key regulatory role in the blood-coagulation cascade. Factor Xa is, therefore, an important target for the design of anti-thrombotics. Both factor Xa and thrombin share sequence and structural homology with trypsin. As part of a factor Xa inhibitor-design program, a number of factor Xa inhibitors were crystallographically studied complexed to bovine trypsin. The structures of one diaryl benzimidazole, one diaryl carbazole and three diaryloxypyridines are described. All five compounds bind to trypsin in an extended conformation, with an amidinoaryl group in the S1 pocket and a second basic/hydrophobic moiety bound in the S4 pocket. These binding modes all bear a resemblance to the reported binding mode of DX-9065a in bovine trypsin and human factor Xa.
Crystallization, preliminary X-ray diffraction analysis and Patterson search of oxyhaemoglobin I from the wolf (Chrysocyon brachiurus)
Authors: Smarra A. L. S. , Fadel V. , Dellamano M. , Olivieri J. R. , de Azevedo W. F. , Bonilla-Rodriguez G. O.
Published: July 2002

Oxyhaemoglobin I isolated from the Brazilian wolf Chrysocyon brachiurus has been crystallized and X-ray diffraction data has been collected to 2.06 Å resolution using a synchrotron-radiation source. Crystals were determined to belong to the space group P212121 and preliminary structural analysis revealed the presence of one tetramer in the asymmetric unit. The structure was determined using standard molecular-replacement techniques and is currently being refined using maximum-likelihood protocols. This is the first haemoglobin isolated from a member of the Canidae family to be crystallized and it will provide further insights in the comparative biochemistry of vertebrate haemoglobins.
Co K-edge XAS study on a new cobalt-doped-SiO2 pillared clay
Authors: Choy Jin-Ho , Jung Hyun , Yoon Joo-Byoung
Published: July 2002

New Co-doped-SiO2-sol pillared montmorillonite has been synthesized by interlayer hydrolysis and condensation of tetraethylorthosilicate (TEOS) in the presence of Co2+ ion using an organic template. The Co K-edge XANES and EXAFS analyses for the CoO-SiO2-PILC (before and after calcination) and for the references such as CoO and Co(OH)2 were performed in order to obtain electronic and local structural information of cobalt species, which may act as a catalytic active site for the selective reduction of NOx, hydrodesulfurization, and Fischer-Tropsch reaction. According to the XANES spectra, the divalent cobalt ion is stabilized in an octahedral symmetry. The EXAFS result shows a significant change in local symmetry around cobalt ion upon calcination. The EXAFS fitting result before calcination shows that the cobalt species is in the form of hydroxide, with a small number of (Co-Co) pairs compared to the bulk Co(OH)2. After calcining at 550°C, the first nearest neighbours were fitted to six oxygen atoms with two different distances, and the second and the third neighbours were fitted to two Si and one Co atoms. It is, therefore, reasonable to suggest a structure model, where the cobalt species on the SiO2 sol exists as a nano cluster of Co(OH)2 before calcination but transforms to a nanosized cobalt oxide covalently bound to the surface of SiO2 pillar after calcination.
EXAFS spectra above Pb and Pt K edges observed at low temperature
Authors: Nishihata Y. , Mizuki J. , Emura S. , Uruga T.
Published: July 2002

X-ray absorption spectra near K edges of Pb (88.0keV) and Pt (78.4keV) for the foils were measured in transmission mode at SPring-8. We succeeded for the first time in observing the EXAFS oscillation of the Pb foil at 12K, although it was failed at room temperature in a previous experiment. The amplitude of the EXAFS oscillation of the Pt foil at 12K considerably increased in comparison with that at room temperature, indicating that the amplitude is very sensitive to the Debye-Waller factor at high-k values.
Pt L-edge XANES as a probe of Pt clusters
Authors: Ankudinov A L. , Rehr J. J. , Low J. J. , Bare S. R.
Published: July 2002

The sensitivity of Pt L-edge XANES to local geometric and electronic structure in various Pt
n
clusters is investigated using the ab initio self-consistent FEFF8 code. Calculations based on FEFF8 are found to be in good agreement with experiment. For pure Pt clusters the XANES can distinguish between 2- and 3-dimensional clusters. Self-consistency is important in determining the variation of XANES with cluster size. The effect of a support is also studied. In Pt-Cl
x
clusters the presence of a Cl-Pt bond leads to a `hybridization peak', i.e., a peak in the Cl d-density of states (d-DOS) mixed with Pt d-states. For Pt-H clusters hydrogen addition is well correlated with the growth of a broad shoulder on the white line. This change is attributed largely to AXAFS, i.e. to a corresponding change in the atomic background absorption.
XAFS study on Mn-Ni/Al2O3 catalyst for carbon dioxide reforming of methane
Authors: Choi Sun Hee , Seok Seung-Ho , Lee Jae Sung
Published: July 2002

As an effective catalyst for carbon dioxide reforming of methane, manganese-promoted Ni/Al2O3 catalyst was studied with XAFS. The catalysts after the reduction above 1073 K contained the metallic nickel, and several phases of manganese were shown by XANES and EXAFS. Results of EXAFS curve fitting indicated that the surface of large metallic nickel particles was partly covered with patches of MnO and metallic Mn. Radial structure function (RSF) of Mn K-edge showed the peaks due to Mn-Ni scattering without Mn-Mn scattering, indicating that the metallic manganese was attached to nickel in a highly dispersed state. Separate manganese phase was also formed without interaction with nickel.
Adsorptive properties of metal oxide dispersed carbon materials and characterization of metal oxide fine particles by XAFS
Authors: Hattori Yoshiyuki , Kaneko Katsumi
Published: July 2002

Surface modification of activated carbon fiber (ACF) with metal oxide increases the adsorptivity of the ACF for supercritical gas such as NO and CH4. In this study, pitch-based activated carbon fibers (P20) were modified with nickel oxide particles. The adsorptive properties and micropore structures of NiO dispersed P20 (NiO-P20) were investigated by nitrogen adsorption isotherms at 77 K. The isotherm was of type I, suggesting that the NiO-P20 has microporosity. The micropore volume and surface area for NiO-dispersed P20 were smaller than that of P20 by about 15%. The Ni K-edge X-ray absorption fine structure of NiO-P20 has been investigated in order to characterize the species dispersed on P20. The local structure of the NiO particles on the P20 showed some different features compared with the local structure of powdered NiO.
Local structure evolution of Fe
x
Ni77–x
Cu1Nb2P14B6 soft magnetic materials by mechanical alloying
Authors: Yin Shilong , Wei Shiqiang , Bian Qing , Li Zhongrui
Published: July 2002

Mechanically alloyed FexNi77-xCu1Nb2P14B6 soft magnetic materials have been prepared with different atomic compositions. The alloy structures are investigated by X-ray absorption fine structure (XAFS). The results show that mechanical alloying (MA) can drive the FexNi77-xCu1Nb2P14B6 powder mixture to produce amorphous alloy while the atomic concentration of Fe element is about and over 40%. On the contrary, the MA FexNi77-xCu1Nb2P14B6 is a solid solution with a fcc-like structure in the region of lower Fe atomic concentration (<22%), preserving a medium-range order around Ni and Fe atoms. Moreover, we have found that the local structure geometry of Fe atom is similar to that of Ni atom for all the MA FexNi77-xCu1Nb2P14B6 samples. It indicates that the local structures of Fe and Ni atoms in a FexNi77-xCu1Nb2P14B6 sample only depend on the x value of element Ni after ball milling.
Experimental and theoretical XANES study of the effects of Fe–Mg solid solution in the enstatite–ferrosilite series
Authors: Wu Ziyu , Paris Eleonora , Giuli Gabriele , Mottana Annibale , Seifert Friedrich
Published: July 2002

Synthetic orthopyroxenes in the join enstatite - ferrosilite (Mg2Si2O6-Fe2Si2O6) have been studied by XANES with the aim to interpret the variations found in the spectra and evaluate the effects of the Mg-Fe substitution in the orthopyroxene (OPX) structure. The experimental Fe- and Mg-K edge XANES spectra show variations of the peaks intensity as a function of the chemical composition of the samples along the EN-FS join. In the region of the Fe edge, the intensity ratio between peak A and B (IB/IA) varies linearly (R=0.99) with the Mg/Fe substitution. Multiple scattering calculation have been performed both at the Fe and Mg K-edge, to study the geometrical modifications of the M1 and M2 octahedral sites induced by the Mg-Fe substitutions. The spectra, obtained locating Fe (or Mg) in both M1 and M2 and weighing the contributions using the occupancy data for the M1 and M2 sites determined by XRD, allow to discriminate the effects to the total spectrum due to Fe (Mg) located in each sites separately.
Geometric local structure at the Mn site in charge-ordered mixed valence manganites
Authors: Sánchez M. C. , García J. , Subías G. , Blasco J. , Proietti M. G.
Published: July 2002

An extensive study of Mn K-edge absorption spectroscopy has been carried out in La1-xCaxMnO3 and Tb1-xCaxMnO3 (x=0, 0.33, 0.5, 0.67, 1) series as a function of temperature. The EXAFS analysis for the charge ordering compounds (x ≥ 0.5) shows the presence of a static distortion of the MnO6 octahedron in the whole temperature range. However, this local distortion is lower than the distortion found for Jahn-Teller compounds. Magnetoresistive compounds (x=0.33) show a regular octahedron in the low temperature metallic phase. Instead, no changes are found for the first coordination shell (Mn-O) across the charge ordering transition while Mn-Mn distribution shows minor variations with the temperature. The structural analysis of the second coordination shell suggests that the Mn-O-Mn angle is the most relevant parameter to describe the electric and magnetic behaviour of these compounds.
Bis[hexaaquacerium(III)] tetraaquacopper(II) tetrasquarate dihydrate
Authors: Ng Seik Weng , Hu Sheng-Zhi , Razak Ibrahim Abdul , Fun Hoong-Kun
Published: July 2002

The cerium ion in the title compound, [Ce(OH2)6]2[Cu(OH2)4](C4O4)4·2H2O, is nine-coordinate in a monocapped square-prismatic geometry. The squarate (3,4-dihydroxy-3-cyclobutene-1,2-dionate) group links the cerium and copper ions into a three-dimensional network structure.
What defence companies have done to be more commercially successful
Authors: Georgiades Diane , Kleiner Brian H.
Published: July 2002

As a result of the end of the cold war, the US Government’s defence spending has decreased significantly since 1989. Consequently, many aerospace companies in the defence industry have begun the transition to commercial products. Reviews the commercial success strategies of Lockheed Martin, Hughes Electronics and Rockwell. Commercial success strategies discussed include: mergers, derived products, partnerships, consolidation, fresh blood in management, subsidiaries and acquisitions. Examines the negative side‐effects ‐ which include downsizing and less investment in technology research ‐ of the commercial transition.
Advances in rotorcraft
Authors: Ford Terry
Published: July 2002

Reviews recent advances in rotorcraft technology as presented at a recent Royal Aeronautical Society conference on innovation in rotorcraft technology and the 1997 Paris Air Show. Reports research initiatives to improve key rotorcraft technologies in the areas of obstacle detection, vibration and noise reduction and smart structures. Also mentions advances in overcoming rotorcraft speed limitations through use of tiltrotor and tiltwing aircraft.
Actel FPGAs for Hi‐Rel and space applications
Authors: Speers Ted , Biddle Andy
Published: July 2002

Describes Actel’s programmable technology. Early adopters of this technology, in both Europe and North America in experimental and telecommunication space programmes used these field programmable gate arrays (FPGAs) very successfully. Owing to the success of these early adopters, Actel transferred its technology to a radiation hardened wafer fab and now offers a rad hard version of its commercial product, serving the needs of the traditional government end use space market and long lifetime missions. Since the introduction of the rad hard FPGAs the industry has undergone major shifts in attitudes. While there is still a significant demand for radiation hardened devices, lower cost alternatives with a lower level of radiation tolerance are expected to exist in the majority of space programmes.
High definition plasma ‐ an alternative to laser technology
Authors: Kirkpatrick Ian
Published: July 2002

Lasers are currently the technological flavour of the month. The dazzling versatility of light at work tends to blind the onlooker both in its deficiencies and the availability of credible alternatives. This paper compares laser cutting and plasma cutting technologies. It concludes that careful appraisal of manufacturing requirements would probably reveal that equally satisfactory productivity was possible, and higher acceptable dimensional accuracy and edge finish, by opting for high definition plasma profiling. In doing so a lot of money would be saved.
A new method for predicting rotor wake geometries and downwash velocity field
Authors: Cao Yihua
Published: July 2002

A new method for predicting rotor wake in low speed and hovering flight is described to investigate the motion of the helical tip vortex. Beginning with the generalized wake model, a semi‐empirical correction for the vortex core effect on rotor wake is made and free wake calculation is carried out. As an example of its engineering application, the calculated downwash velocity field along the rocket launch line is presented and simply analysed. In terms of theory, the method developed here may provide of a referable basis for further study the formation mode of the tip vortex and vortex core interior structure.
The influence of some condensation products on corrosion inhibition of mild steel in acidic solutions
Authors: Quraishi M.A. , Jamal Danish
Published: July 2002

Selected condensation products of aromatic aldehydes and thiosemicarbazide have been synthesized and evaluated as corrosion inhibitors of mild steel in 1N hydrochloric acid and 1N sulphuric acid by weight loss and potentiodynamic polarization methods. The values of activation energy and free energy of adsorption have also been determined to understand the mechanism of inhibition. The potentiodynamic polarization studies carried out at room temperature revealed that all the compounds are of mixed type inhibitors in both the acids. The adsorption of all the condensation products on the mild steel surface from both the acids has been found to obey Temkin’s adsorption isotherm. The inhibition efficiency of these compounds has been found to vary with the nature and concentration of the compounds, temperature, immersion time and nature of the acids.
Electrodeposition and dissolution of Fe‐Ni alloy films on platinum
Authors: Aravinda C.L. , Ramesh L. , Mayanna S.M. , Muralidharan V.S.
Published: July 2002

Cyclic voltametric studies were carried out on mixtures of nickel sulphate, ferrous ammonium sulphate containing ethylene diamine tetra acetic acid, triammonium citrate, boric acid, Sodium chloride in the pH range of 8.5‐10.5 on platinum. The deposition of iron was found to involve the formation of FeOH+ and the second electron transfer is slow. The formation of iron nickel alloy film is anomalous. The charge transfer rates of FeOH+ and NiOH+ determine the deposition. Stripping voltametric curves revealed the dissolution of iron from an intermediate phase rich of iron in the iron‐nickel films.
Synergistic effect of 2‐chloroethyl phosphonic acid and Zn2+
Authors: Rajendran S. , Apparao B.V. , Palaniswamy N.
Published: July 2002

2‐chloroethyl phosphonic acid (2‐Cl EPA) and Zn2+ show a synergistic effect in controlling corrosion of carbon steel in a neutral aqueous environment containing 60 ppm Cl‐. The protective film consists of Fe2+–2–Cl EPA complex and Zn(OH)2; it is found to be uv‐luminescent.
Residual ductility management and life‐predication
Authors: Mukherjee D.
Published: July 2002

The surface science and engineering discipline has emerged recently and become more high‐profile. Functional performance of the surface is given top priority, although some of the bulk parameters play a very important role in the performance of the surface. Residual ductility is one such parameter, which directly controls the probability of surface embrittlement during the service stage of any engineering product, thereby controlling the embrittlement‐induced galvanic corrosion. Residual ductility also indirectly controls the metal dissolution in a corrosive environment by improving the adhesion of the corrosion product films to the surface. Discusses the role of residual ductility, in the control of environmentally induced deterioration of the metallic surfaces, highlighting the parameters which may eventually interfere with its level on the surface. Improvement of ductility also improves the attachment of the nearest neighbour elements of the matrix, resulting in the improvement of the surface stability. On the contrary, a brittle surface undergoes higher reactive interaction with the environment. Also discusses the possibility of using the residual ductility parameter for obtaining the rate values of an imaginary defect for subsequent extrapolation of the approximate residual life values of some carbon‐steel materials.
Metallic finishing by diffusion coating
Authors: Mukherjee D.
Published: July 2002

Metallic finishing of materials, unlike non‐metallic finishing, comprises various popular surface modification processes, e.g. electroplating, conversion coating, anodizing, metal spraying, hot dip coating and also diffusion coatings. Diffusion coatings on metallic substrates are well known for their better abrasion resistance and adhesion to the substrate. Resistance to corrosion may also be incorporated on these surfaces by the addition of appropriate dopant elements like Cr, Ni and Al. However, these diffusion alloy‐layers are more sought after for functional properties than their aesthetic look. It appears that the concept of functional metal finishing is gaining ground for its longer service‐life and better performance. Discusses some of these aspects of diffusion alloy coatings on mild steel substrate and analyses their comparative merits and demerits. In this connection, three distinctly different types of barrier layers, namely, hard diffusion alloy layer, e.g. chromiding, Ni‐Cr diffusion coatings and soft‐diffusion layer, e.g. Pb‐Cd, Zn‐Sn barriers and those in between, e.g. hot dip zinc‐alloy coated barrier layers, have been highlighted for their corrosion resistance properties.
Lower concentration ultrafine particulates improve the surface properties of metals and alloys
Authors: Mukherjee D.
Published: July 2002

This paper discusses the lower concentration reinforcement of cathodic ultrafine ceramic particulates, on metal matrices like Zn, Al and alloy‐matrices like Cu Zn, Cu Mn, Al Zn and Ni‐P‐B alloy‐electrodeposits, etc. It is assumed that these ultrafine ceramic particulates in lower concentration‐range are effective in covering the anodic grain‐boundary networks and other anodic‐defect sites, such that there is an effective reduction of surface anodic‐current. It is shown that at a critical threshold particulate concentration, the surface dissolution is minimum, followed by a drastic increase above that concentration. Such increase in dissolution is attributed to the random dispersion of the particulates on the grain‐proper, as these cannot be accommodated within the anodic grain‐boundary channels, micro‐voids and other defect sites. As such they form stress‐raiser points and enhance surface dissolution. This paper also discusses the correlation of the grain boundary structures, particulate trapping capacity of the matrix and the galvanic stress factors due to random distribution of particulates.
Recent developments in aluminium diffusion
Authors: Kempster Adrian
Published: July 2002

Summarises various methods for diffusing aluminium into ferrous and non‐ferrous materials. Recent developments at Diffusion Alloys Ltd are discussed.
Comparison of different pretreatment‐primer systems on hot‐dip galvanized and Galfan coated steel
Authors: Puomi P. , Fagerholm H.M. , Rosenholm J.B. , Sipilä R.
Published: July 2002

The performance of different pretreatment‐primer systems for hot‐dip galvanized (HDG) and Galfan coated steel has been studied. The materials were pretreated with three pretreatment processes; an alkaline oxide pretreatment with either a chromate or a zirconium based post‐rinse, and a zinc phosphating pretreatment. After the pretreatment, the panels were coated with four commercially available primers. The chemically treated substrates were characterized by using ESCA and GD‐OES, and the cured paint films by using FTIR. Paint adhesion of primed panels was determined with a combined cross‐cut and impact test and also with the NMP test. Formability of the panels was tested by T‐bend test and corrosion resistance with a cyclic prohesion test. According to the prohesion test results, primed Galfan coated panels have better edge corrosion resistance than primed HDG panels. Test results also show that the effect of pre‐treatment is not as significant for the corrosion resistance as the effect of primer. However, in the case of zinc phosphated samples, excellent synergistics between the pretreatment and two of the primers was detected.
Study of the pigment type effect on the corrosion behaviour of epoxy painted steel/sea water systems
Authors: Santágata D.M. , Seré P.R. , Hornus Sack S. , Elsner I. , Mendivil G. , Di Sarli A.R.
Published: July 2002

The effect of different kind of pigments on the corrosion resistance properties of an epoxy paint has been investigated using electrochemical impedance spectroscopy and open circuit potential measurements. Painted naval steel samples were studied during the exposure to artificial sea water. The epoxy paint coatings were prepared employing red lead, zinc, red iron oxide or titanium dioxide as pigment with 0.8 of PVC/CPVC ratio. From the EIS and corrosion potential data analyis was found that the anticorrosive protection given by an anticorrosive (pigmented with red lead) and a top coat (pigmented with red iron oxide) epoxy painting scheme was both more lasting and more effective. This was attributed to the fact that both the effective adhesion provided by the chemical bonding between the steel surface and the epoxy paint groups and the constant high barrier effect afforded by this type of top coat were a perfect complement for the high corrosion inhibitive capacity of the red lead pigment.
Space allocation in UK grocery retailing
Authors: Davies Barry J. , Ward Philippa
Published: July 2002

Space allocation is usually explained through the use of optimization models. This study examines the perceptions of experienced managers in major UK grocery retailers relating to effective space utilization. From the literature, initial telephone survey and interviews, 48 variables relating to the same issue were identified. These then formed the basis of a questionnaire, which was postally administered to managers within the space planning function in six of the UK’s largest grocery retailers. Thirty completed questionnaires were returned. Principal components analysis was used to explore interrelationships among the variables. Of the 48 variables 18 were identified as most important. The 18 variables accounted for over 80 per cent of the total variance. These variables were associated with six underlying components. These six components (and the associated variable scores) were then examined using structural equation modelling. An SEM model was developed with a combined goodness of fit index of 0.85. The developed model is very different from the relations posited in existing space planning systems.