bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Control of Power for Efficient Batch Mixing
Authors: Layton R. A. , Murray W. R. , Garbini J. L. 
Published: May 2005

AbstractIn the batch mixing of composite solid propellants, small variations in the mixing process can lead to unacceptable variability in the properties and performance of the propellant grain. A new closed‐loop mixing strategy is proposed to improve the robustness of the mixing process with respect to these small variations, and thereby to reduce the variability of the finished grain from batch to batch. The new mixing strategy is based on the hypothesis that repeatability of mixing results can be improved by doing the same amount of work on each batch and that mixing efficiency can be improved by continuously controlling power. Justification of the hypothesis is given. The effectiveness of the new mixing strategy is demonstrated through simulations, using a process model based on measurements and analysis of an existing process for the batch mixing of an ammonium nitrate composite solid propellant. Results indicate that the new strategy improves the repeatability of the mixing process by reducing mixing power fluctuations and by eliminating variations in work done on the mixture from batch to batch. The new mixing strategy is shown to be feasible. Because the new mixing strategy is successful with wide robustness margins for this specific difficult mixing process, the strategy should be effective in the batch mixing of a wide range of composite solid propellants.
QM/MM modeling the Ras–GAP catalyzed hydrolysis of guanosine triphosphate
Authors: Grigorenko Bella L. , Nemukhin Alexander V. , Topol Igor A. , Cachau Raul E. , Burt Stanley K. 
Published: May 2005

AbstractThe mechanism of the hydrolysis reaction of guanosine triphosphate (GTP) by the protein complex Ras–GAP (p21ras – p120GAP) has been modeled by the quantum mechanical—molecular mechanical (QM/MM) and ab initio quantum calculations. Initial geometry configurations have been prompted by atomic coordinates of a structural analog (PDBID:1WQ1). It is shown that the minimum energy reaction path is consistent with an assumption of two‐step chemical transformations. At the first stage, a unified motion of Arg789 of GAP, Gln61, Thr35 of Ras, and the lytic water molecule results in a substantial spatial separation of the γ‐phosphate group of GTP from the rest of the molecule (GDP). This phase of hydrolysis process proceeds through the low‐barrier transition state TS1. At the second stage, Gln61 abstracts and releases protons within the subsystem including Gln61, the lytic water molecule and the γ‐phosphate group of GTP through the corresponding transition state TS2. Direct quantum calculations show that, in this particular environment, the reaction GTP + H2O → GDP + H2PO can proceed with reasonable activation barriers of less than 15 kcal/mol at every stage. This conclusion leads to a better understanding of the anticatalytic effect of cancer‐causing mutations of Ras, which has been debated in recent years. Proteins 2005. © 2005 Wiley‐Liss, Inc.
Structure of the tetrameric form of human L‐Xylulose reductase: Probing the inhibitor‐binding site with molecular modeling and site‐directed mutagenesis
Authors: El‐Kabbani Ossama , Carbone Vincenzo , Darmanin Connie , Ishikura Syuhei , Hara Akira 
Published: May 2005

AbstractL‐Xylulose reductase (XR) is a member of the short‐chain dehydrogenase/reductase (SDR) superfamily. In this study we report the structure of the biological tetramer of human XR in complex with NADP+ and a competitive inhibitor solved at 2.3 Å resolution. A single subunit of human XR is formed by a centrally positioned, seven‐stranded, parallel β‐sheet surrounded on either side by two arrays of three α‐helices. Two helices located away from the main body of the protein form the variable substrate‐binding cleft, while the dinucleotide coenzyme‐binding motif is formed by a classical Rossmann fold. The tetrameric structure of XR, which is held together via salt bridges formed by the guanidino group of Arg203 from one monomer and the carboxylate group of the C‐terminal residue Cys244 from the neighboring monomer, explains the ability of human XR to prevent the cold inactivation seen in the rodent forms of the enzyme. The orientations of Arg203 and Cys244 are maintained by a network of hydrogen bonds and main‐chain interactions of Gln137, Glu238, Phe241, and Trp242. These interactions are similar to those defining the quaternary structure of the closely related carbonyl reductase from mouse lung. Molecular modeling and site‐directed mutagenesis identified the active site residues His146 and Trp191 as forming essential contacts with inhibitors of XR. These results could provide a structural basis in the design of potent and specific inhibitors for human XR. Proteins 2005. © 2005 Wiley‐Liss, Inc.
Conformational characteristics of the complete cequence of group A streptococcal M6 protein
Authors: Fischetti Vincent A. , Parry David A. D. , Trus Benes L. , Hollingshead Susan K. , Scott June R. , Manjula Belur N. 
Published: May 2005

AbstractM protein is considered a virulence determinant on the streptococcal cell wall by virtue of its ability to allow the organism to resist attack by human neutrophils. The complete DNA sequence of the M6 gene from streptococcal strain D471 has allowed, for the first time, the study of the structural characteristics of the amino acid sequence of an entire M protein molecule. Predictive secondary structural analysis revealed that the majority of this fibrillar molecule exhibits strong alpha‐helical potential and that, except for the ends, nonpolar residues in the central region of the molecule exhibit the 7‐residue periodicity typical for coiled‐coil proteins. Differences in this heptad pattern of nonpolar residues allow this central rod region to be divided into three subdomains which correlate essentially with the repeat regions A, B, and C/D in the M6 protein sequence. Alignment of the N‐terminal half of the M6 sequence with PepM5, the N‐terminal half of the M5 protein, revealed that 42% of the amino acids were identical. The majority of the identities were “core” nonpolar residues of the heptad periodicity which are necessary for the maintenance of the coiled coil. Thus, conservation of structure in a sequence‐variable region of these molecules may be biologically significant. Results suggest that serologically different M proteins may be built according to a basic scheme: an extended central coiled‐coil rod domain (which may vary in size among strains) flanked by functional end domains.
Localization of hydrogen‐bonds within modules in barnase
Authors: Noguti Tosiyuki , Sakakibara Hirofumi , Gō Mitiko 
Published: May 2005

AbstractProteins in eukaryotes are composed of structural units, each encoded by discrete exons. The protein module is one such structural unit; it has been defined as the least extended or the most compact contiguous segment in a globular domain. To elucidate roles of modules in protein evolution and folding, we examined roles of hydrogen bonds and hydrophobic cores, as related to the stability of these modules. For this purpose we studied barnase, a bacterial Rnase from Bacillus amylolique‐faciens. Barnase is decomposed into at least six modules, M1–M6; the module boundaries are identified at amino acid residues 24, 52, 73, 88, and 98. Hydrogen bonds are localized mainly within each of the modules, with only a few between them, thereby indicating that their locations are designed to primarily stabilize each individual module. To obtain support for this notion, an analysis was made of hypothetical modules defined as segments starting at a center of one module and ending at the center of the following one. We found that the hydrogen bonds did not localize in each hypothetical module and that many formed between the hypothetical modules. The native conformations of modules of barnase may be specified predominantly by interactions within the modules. © 1993 Wiley‐Liss, Inc.
An analysis of the conformational paths of citrate synthase
Authors: El‐Kettani Mohammed Anass Ech‐Cherif , Zakrzewska Krystyna , Durup Jean , Lavery Richard 
Published: May 2005

AbstractPrevious simulation studies have provided reaction pathways leading from the closed to the open form of citrate synthase. We now undertake a detailed analysis of these pathways using a variety of different tools including backbone dihedral angles, P‐Curves helicoidal parameters, inter‐helix geometrical parameters, and accessibility calculations. The results point to a relatively small number of residues, mostly in loop regions, which are responsible for the majority of the conformational changes observed. An important role is attributed to transient changes in the backbone which facilitate movement along the reaction coordinate. Comparisons between the two pathways show that they share many common features despite the different algorithms used to generate them. © 1993 Wiley‐Liss, Inc.
Steric and conformational features of the aconitase mechanism
Authors: Lauble Hanspeter , Stout Charles David 
Published: May 2005

AbstractCrystal structures of mitochondrial aconitase with α‐methylisocitrate and with sulfate bound have been solved and refined at 2.0 Å resolution with R factors of 18.2 and 16.8%, respectively. The steric factors and conformational effects observed in both new structures support the proposed mechanism for the overall reaction catalyzed by aconitase. The alternate substrate α;methylisocitrate is derived from α;methyl‐cis‐aconitate during crystallization and is observed to bind in the active site in a manner very similar to that observed for isocitrate. The methyl group is accommodated by favorable contact with Ile‐425. However, the other potential hydration product of α;methyl‐cis‐aconitate,α;methylcitrate, cannot be accommodated in the active site due to steric conflict of the methyl group with Asp‐165. The results are consistent with the requirement that cis‐aconitate must bind in two ways, in the citrate mode and in the isocitrate mode. Crystals of aconitase with sulfate bound are isomorphous to those with isocitrate bound. However, the structure displays significant conformational changes, providing a model for the substrate‐free state of enzyme. Three water molecules bind in place of the Cα; and Cβ‐hydroxyl and carboxyl groups of isocitrate, while sulfate binds in place of the Cγ;carboxyl Group. Side chains of Ser‐642 and Arg‐447 in the active site rotate to pair with other side chains in the absence of substrate. The new conformation of Arg‐447 triggers a concerted set of shifts which transmits conformational change to the surface of the protein, 30 Å from the active site. In the absence of substrate, a chain segment containing the [4Fe‐4S] ligand Cys‐358 also shifts, resulting in the net translation and reorientation of the Fe‐S cluster. © 1995 Wiley‐Liss, Inc.
Purification and crystallization of a schistosomal glutathione S‐Transferase
Authors: McTigue Michele A. , Bernstein Susan L. , Williams DeWight R. , Tainer John A. 
Published: May 2005

AbstractThe 26‐kDa glutathione S‐transferase from Schistosoma japonica (Sj26), a potential antischistosomal vaccine antigen, has been crystallized in an unligated form. Sj26 was recombinantly produced in E. coli without using a glutathione affinity column to facilitate preparation of unligated enzyme. The recombinant protein contains all 218 residues of Sj261,2 and an additional 13 residues linked to the C‐terminus. Crystals of recombinant Sj26 were obtained by the vapor diffusion method using ammonium sulfate as the precipitant at pH 5.6. The crystals belong to the hexagonal space group P6322 with unit cell dimensions a = b = 125.2 Å and c = 72.0 Å and contain one Sj26 monomer per asymmetric unit. A complete native diffraction data set has been obtained to 2.4 Å resolution. © 1995 Wiley‐Liss, Inc.
Cation distribution and magnetic properties of nickel–chromium ferrites NiCrxFe2–xO4 (0 ≤ x ≤ 1.4)
Authors: Rais A. , Gismelseed A. M. , Al‐Omari I. A. 
Published: May 2005

AbstractNickel–chromium ferrites NiCrxFe2–xO4 (0 ≤ x ≤ 1.4) were studied using X‐ray diffraction, magnetization measurements and Mössbauer spectroscopy. X‐ray diffraction patterns show that all samples have cubic spinel structure. The temperature dependent magnetic measurements revealed that a magnetic compensation point appears at chromium concentration x = 0.9, 1.2 and 1.4. Moreover, it was observed that the Curie temperature TC decreases and approaches the compensation temperature TK as Cr3+ substitution for Fe3+ increases. The magnetization data at all concentrations are discussed in the light of Néel's molecular field model taking into account the cation distributions obtained using the analysis of Mössbauer spectra. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Location of epoxy rings in a long chain acetogenin by fast‐atom bombardment and linked scan (B/E) mass spectrometry of lithium‐cationized molecules
Authors: Laprévote Olivier , Girard Christian , Das Bhupesh C. , Laugel Thierry , Roblot François , Leboeuf Michel , Cavé André 
Published: May 2005

AbstractFast‐atom bombardment desorption combined with mass spectrometry (using linked scans at constantB/E) of a lithium‐cationized long‐chain acetogenin was used to determine the position of two epoxy rings in thhe alkyl chain. Analysis of metastable and collision‐induced dissociations gave structurally useful information which could not be obtained by other spectroscopic methods such as nuclear magnetic resonance. A direct effect of lithium of thhe observed decomposition pathways was demonstrated.
Accuracy and precision of gas chromatography/combustion isotope ratio mass spectrometry for stable carbon isotope ratio measurements
Authors: Wong William W. , Hachey David L. , Zhang Shide , Clarke Lucinda L. 
Published: May 2005

AbstractWe evaluated the precision, accuracy and linearity of three commercial gas chromatography/combustion isotope ratio mass spectrometry (GC/C‐IRMS) instruments in regard to stable carbon isotope ratio measurements of fatty acids with 13C enrichment levels ranging from natural abundance to 924‰, in comparison to measurements by conventional gas isotope ratio mass spectrometry (GIRMS). Memory effect was also evaluated with a fatty acid mixture containing methyl myristate and methyl stearate at natural abundance levels of 13C but methyl palmitate at 13C enrichment levels of 460 or 924‰. At natural abundance, the δ13C values of fatty acids measured by the GC/C‐IRMS instruments were reproducible to within 0.34‰ (range: 0.11‰ to 0.32‰) and accurate to −0.38±0.40‰ (mean difference ± standard deviation; range: −0.03±0.25‰ to −0.84±0.39‰). At enrichment levels of 13C (23 to 924‰), the δ13C values were reproducible to within 1.48‰ (range 0.20‰ to 1.00‰) and accurate to −1.11±3.16‰ (range: −1.02±3.23‰ to +4.56±13.42‰). Stable carbon isotope ratio measurements by all three GC/C‐IRMS instruments were found to be linear from −30 to 924‰ (r2 > 0.9999; p ⩽ 0.004) in comparison to those measured by GIRMS. Significant memory effect was found in only one system. Based on our data, the GC/C‐IRMS instruments can provide linear, precise and accurate stable carbon isotope ratio measurements and require only pico‐and nanogram quantities of samples.
Effects of chemical state on quantitative AES of metal–sulfur compounds
Authors: Griffis D. P. , Linton R. W. 
Published: May 2005

AbstractA quantitative approach to AES is illustrated for various metal–sulfur compounds involving: (a) intensity measurements via integral areas of background subtracted N(E) spectra (including sample probe potential biasing to improve background subtraction); (b) low primary electron dose, pulse‐count spectrum acquisition to minimize primary electron beam damage and charging artifacts; (c) corrections to spectral intensity for variations in electron backscattering and inelastic Auger electron mean free path for each metal–sulfur compound matrix; (d) XPS quantitative analysis to correct for differences in surface vs. bulk stoichiometries. Although the above approach results in improved analytical precisions, a residual difference of greater than a factor of 2 remains in the Auger elemental sensitivity factor for sulfur (LMM) in corresponding metal sulfate vs. sulfide compounds. This suggests a chemical state dependent Auger electron yield (core level ionization cross section times the Auger transition probability). Accurate AES quantification, therefore, may require chemical state specific sensitivity factors, particularly for valence shell transitions.
Inelastic electron tunnelling spectroscopy of silane coupling agents
Authors: Brewis D. M. , Comyn J. , Oxley D. P. , Pritchard R. G. , Reynolds S. , Werrett C. R. , Kinloch A. J. 
Published: May 2005

AbstractInelastic electron tunnelling (IET) spectra are reported and assigned for some trialkoxysilanes adsorbed on aluminium oxide. Spectra of the triethoxysilanes have many common features, and there is some evidence that these compounds are attached to the oxide surface by their ethoxy groups. There are differences in the trimethoxysilane spectra which may be due to a reaction at the oxide surface during junction preparation. In particular, IET spectra of 3‐glycidoxypropyltrimethoxysilane show that the epoxide group reacts to produce magnified image groups.
Characterization of contamination layers by emission angle dependent XPS with a double‐pass CMA
Authors: Hofmann S. , Sanz J. M. 
Published: May 2005

AbstractThe use of non destructive depth profiling by emission angle dependent XPS analysis is demonstrated for a thin contamination layer consisting of carbon, hydrogen and hydride‐bonded oxygen on top of an anodic oxide of Nb2O5 on Nb. Using a double‐pass CMA with an angle resolved aperture and measured intensity ratios of O 1s (hydroxide)/O 1s (oxide) and O 1s (hydroxide‐/C 1s) as a function of the emission angle, the thickness (d = 3.3 nm) and composition are determined.
XPS: Energy calibration of electron spectrometers. 1—An absolute, traceable energy calibration and the provision of atomic reference line energies
Authors: Anthony M. T. , Seah M. P. 
Published: May 2005

AbstractAtomic standards of binding energies are presented for the calibration of X‐ray photoelectron spectrometers. The binding energies are measured using a VG Scientific ESCA 3 Mk II for which the photoelectron peak positions can be established with a measurement precision standard deviation of 5 meV. The absolute calibration of the voltage scale is established with an accuracy of 11 ppm over the binding energy range 0–1250 eV, using a measurement chain traceable to the NPL primary voltage standards. The zero of energy is set to ±11 meV on the differential of the Ni Fermi edge using Mg Kα12 radiation and absolute binding energies, for the Cu 2p3/2, Cu L3MM, Cu 3p, Ag 3d5/2, Ag M4NN and Au 4f7/2 peaks, are established with errors of 0.01 to 0.02 eV. An analysis is made of literature calibrations to assess their zero setting and voltage scaling errors. Preliminary tests have been made to show that the calibrations may be reproduced on instruments outside NPL using a simple work procedure.
Status report on the ASTM E‐42 Committee on surface analysis
Authors: Nelson G. C. 
Published: May 2005

AbstractCommittee E‐42 on Surface Analysis was formed by the American Society for Testing and Materials in 1976 from its predecessor, Subcommittee E‐02.02, to advance the quality of standard practices, standard materials, and reference data in the area of surface analysis. These objectives are accomplished through sponsoring symposia and workshops at the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy in the spring and the National Symposium of the American Vacuum Society in the autumn of each year as well as through the development of recommended practices, standard materials, round robin comparisons, and publications. Subcommittees which are currently active are Editorial, Terminology, Standard Reference Materials, Ion Beam Sputtering, Energetic Ion Analysis, Auger, ESCA, ISS, and SIMS. This report summarizes their progress to the end of 1983.
The role of electron spectroscopy in the evolution of long‐range industrial R&D illustrated by AES studies in adhesion, catalysis and corrosion
Authors: van Ooij W. J. , Visser T. H. , Biemond M. E. F. 
Published: May 2005

AbstractThe improvement in spatial resolution of scanning Auger spectroscopy in recent years has increased its applicability to industrial problems markedly, as is illustrated by several case studies in adhesion, corrosion and related areas. It is shown that the analytical capabilities of AES are enhanced if complemented by simultaneous energy‐dispersive x‐ray analysis. Suggestions for further development of AES instruments for use in industrial R&D are given.
The adsorption of diethyldithiophosphate on cuprous sulphide
Authors: Mielczarski J. , Minni E. 
Published: May 2005

AbstractThe adsorption of diethyldithiophosphate (DTP) from its aqueous solutions has been studied on cuprous sulphide (chalcocite) surfaces by measuring the characteristic changes in the positions and relative integrated intensities of C 1s, P 2p, S 2p, O 1s and Cu 2p3/2 XPS lines and by observing the changes in the in situ internal reflection IR (infrared) spectra at various stages of adsorption. A multistage model is suggested for DTP adsorption on a freshly formed chalcocite surface. During adsorption components preadsorbed on the surface are removed. The DTP ions are initially distributed on the surface without any special orientation but later form islands. The degree of orientation increases with coverage and later, a well oriented close packed monolayer is found. When the adsorption continues beyond this stage the additionally deposited molecules form a randomly oriented layer on the close packed oriented monomolecular layer.
Quantitative XPS: The calibration of spectrometer intensity—energy response functions. 1—The establishment of reference procedures and instrument behaviour
Authors: Seah M. P. , Anthony M. T. 
Published: May 2005

AbstractThe ASTM E‐42 committee round robin on XPS measurements found, in a simple survey, that the intensity‐energy response of electron spectrometers was unacceptably unreliable. In this paper new, high accuracy, reference procedures are developed to define the relative intensity‐energy response function of spectrometers, for the constant ΔE and ΔE/E modes, for analysts to calibrate their own instruments. Two procedures are developed, one involving the measurement of peak areas, for Cu, Ag and Au, carefully specified to reduce the effects of measurement noise, and the second, for use on well‐designed spectrometers, through the measurement of the spectrum background. The measurements on Cu, Ag and Au reference foils show that intensity ratios are reproducible to within 2% standard deviation and, from preliminary tests, that the ratio of the response functions of a VG Scientific ESCALAB I and the NPL ESCA 3 Mk II is proportional to E0.094, except for the low pass energy of 20 eV in the ESCALAB I where the proportionality changes to E−0.156. Similarly the ratio of the functions for a Perkin‐Elmer PHI 550 and the VG Scientific ESCA 3 Mk II is proportional to E−0.244 over the normal XPS measurement range to an accuracy of 2%.
X‐Ray photoelectron spectroscopic studies of the surface of sputter ion plated films
Authors: Robinson Kevin S. , Sherwood Peter M. A. 
Published: May 2005

AbstractX‐ray photoelectron spectroscopic analysis of a reactively sputter ion plated titanium nitride film showed the surface to be oxidised to TiO2, with a sub‐layer of oxynitride. Argon ion etching gave a depth profile of the film, but it preferentially sputtered titanium nitride, and caused mixing of TiO2 and TiN phases to form titanium oxynitrides. Titanium oxynitride was also produced by nitrogen ion implantation into titanium metal with a surface layer of titanium dioxide.