bluuebunny/crossref_metadata_2025_split huggingface dataset:
Aluminium‐27 NMR investigation of the influence of cation type on aluminosilicate solutions
Authors: Azizi Naser , Harris Robin K. , Samadi‐Maybodi Abdolraouf 
Published: August 2002

AbstractThe effects of tetraalkylammonium (TAA) and alkali metal cations on the equilibrium distribution of aluminosilicate oligomers in aqueous alkaline aluminosilicate solutions were investigated using 27Al NMR spectra and their evolution with time. The results indicate that there are no differences in the initial equilibria involving solutions containing both TAA and alkali metal cations on the one hand and those containing alkali metal cations only. However, re‐equilibration of the aluminosilicate species for TAA/Na aluminosilicates is slow (usually not detectable on the time‐scale of the experiments), whereas when purely alkali metal cations are used, the spectra alter over a period of ∼1 h, such that resolution is degraded substantially. In the latter case, it is suggested that the anions aggregate into larger systems, although the solutions are still clear. 29Si NMR evidence for slow equilibration of silicate and aluminosilicate solutions at higher concentrations is also discussed. Copyright © 2002 John Wiley & Sons, Ltd.
One‐dimensional TOCSY 1H NMR experiments on adducts of amino acid esters with cobalt(III) tetramethylchiroporphyrin. Prospects for the analysis of amino acid mixtures
Authors: Claeys‐Bruno Magalie , Bardet Michel , Marchon Jean‐Claude 
Published: August 2002

AbstractCobalt(III) tetramethylchiroporphyrin, CoCl(TMCP), is a useful chiral shift reagent for structure attribution, absolute configuration assignment and enantiomeric excess determination of amino acid methyl esters by 1H NMR spectroscopy. However, it has two axial sites available for amine coordination, a structural feature which generates n(n + 1)/2 diastereomeric species and n2 distinct spin systems from a mixture of n amino ester enantiomers, making the analysis of complex amino acid samples exceedingly difficult by classical 1‐D or 2‐D NMR methods when n > 3. The 1‐D TOCSY experiment is shown to be a powerful tool for the selective excitation and detection of every single component of a mixture of four amino acid methyl esters bound to CoCl(TMCP): those of(S)‐Leu, (S)‐Asp, (R)‐Asp and (S)‐Glu, for example. The potential utility of this methodology for the determination of amino acid enantiomers in carbonaceous meteorites or other extraterrestrial samples is suggested. Copyright © 2002 John Wiley & Sons, Ltd.
A [Pd (η3‐PhCHCHCHPh)(phosphino‐oxazoline)]+ complex with almost identical P‐ and N‐trans influences. 13C chemical shifts and allylic alkylation chemistry
Authors: Dotta Pascal , Anil Kumar P. G. , Pregosin Paul S. 
Published: August 2002

AbstractThe Pd‐catalysed enantioselective allylic alkylation of a 1,3‐diphenylallyl substrate using a bulky phosphinooxazoline auxiliary leads to a relatively small enantiomeric excess of 66%. The ca 30% loss, relative to related P,N‐auxiliaries, is rationalized by (a) the presence of additional isomers, (b) a dynamic equilibrium between two of these as shown by exchange spectroscopy and (c) the identification of one exchanging diastereomer in which there is almost no difference between the two terminal allyl 13C chemical shifts, i.e. these P‐ and N‐donors reveal an almost identical trans influence. Copyright © 2002 John Wiley & Sons, Ltd.
NMR study of E/Z isomerism in N‐alkoxybenzoimidic acid derivatives
Authors: Schraml Jan , Blechta Vratislav , Karban Jindřich , Mindl Jaromir 
Published: August 2002

AbstractWell defined E/Z isomers of N‐methoxy‐p‐nitrobenzimidoyl chloride, N‐methoxybenzimidoyl chloride, methyl N‐methylbenzohydroximate and ethyl N‐hydroxybenzimidate were prepared in order to provide model data for studies of benzhydroximic acid derivatives and related compounds. NMR parameters [1H, 13C and 15N chemical shifts and 1J(13C, 13C) coupling constants] were determined. The results show that stereochemically most significant are the values of 1J(13C, 13C) couplings between aromatic Cipso and CN carbons and that the relationship, |Jcis| > |Jtrans|, known for this coupling from oximes, is not affected by electronegative substituents at the CN carbon atom, but the values are. Copyright © 2002 John Wiley & Sons, Ltd.
Effect of pH on the rotational conformations of 1,3‐diamino‐2‐hydroxypropane
Authors: Cheng Jim M. , Heller Jessica P. , Petterson Krag A. , Roberts John D. 
Published: August 2002

AbstractThe effect of pH on the rotational conformations of 1,3‐diamino‐2‐hydroxypropane in aqueous solution was investigated by proton NMR. Both the observed chemical shifts and coupling constants were used to calculate experimental pKa values. The observed couplings were correlated with the expected couplings for the various possible staggered conformations to try to determine the pattern of conformations for the diamine and its conjugate acids. The best fits suggested a modest preference for the gauche–gauche conformation, especially at low pH, where the diprotonated hydroxydiamine predominates. In methanol, dimethyl sulfoxide and trichloromethane solutions, it was only possible to evaluate the conformational equilibria of the diamine. Slow proton exchange, which caused uncertainties in both chemical shifts and couplings for the monoprotonated and unprotonated diamine, nullified efforts to determine whether or not hydrogen bonding was important for these species in less polar solvents. Copyright © 2002 John Wiley & Sons, Ltd.
A unified approach to the implicit integration of standard, non‐standard and viscous plasticity models
Authors: de Borst René , Heeres Otto M. 
Published: August 2002

AbstractIt is shown how modern concepts to integrate the elasto‐plastic rate equations of standard plasticity via an implicit algorithm can be generalized to plasticity without an explicitly defined yield surface and to overstress‐type models of viscoplasticity, where the stress point can be located outside the loading surface. For completeness, a tangent operator is derived that is consistent with the update algorithm. Copyright © 2002 John Wiley & Sons, Ltd.
A 2‐D constitutive model for cyclic interface behaviour
Authors: Mortara Giuseppe , Boulon Marc , Ghionna Vito Nicola 
Published: August 2002

AbstractThe paper concerns a 2‐D constitutive model for interface behaviour between sand and solid inclusions under cyclic loading. The model is based on the experimental results obtained from laboratory direct shear interface tests conducted under both constant normal load (CNL) and constant normal stiffness (CNS) conditions. The model is formulated in terms of interface stresses and relative velocities and has been derived by extending an elastoplastic isotropic model previously formulated for monotonic loading to stress reversal paths. Such extension consists in adding to the isotropic hardening mechanism a kinematic rotational one defined by an inner conical surface rotating around the origin of the stress space. This allows one to store the memory of the previous stress and relative displacement history giving to the model the capability to analyse the interface behaviour under cyclic loading. After a brief description of the criteria governing the monotonic model, the paper describes in detail the features of the kinematic hardening. Finally, the predictions of the model are compared with the experimental results obtained from CNL and CNS interface tests. Copyright © 2002 John Wiley & Sons, Ltd.
Evaluation of a constitutive model for clays and sands: Part I – sand behaviour
Authors: Pestana Juan M. , Whittle Andrew J. , Salvati Lynn A. 
Published: August 2002

AbstractThis paper evaluates the performance of a generalized effective stress soil model for predicting the rate independent behaviour of freshly deposited sands, while a companion paper describes model capabilities for clays and silts. Most material parameters can be obtained from standard laboratory data, including hydrostatic or one‐dimensional compression, drained and undrained triaxial shear testing. A compilation of data on compression behaviour allows for estimation of compression parameters when this type of data is not available. Extensive comparisons of model predictions with measured data from undrained triaxial shear tests shows that the model gives excellent predictions of the transition from dilative to contractive shear response as the confining pressure and/or the initial formation void ratio increases. A parametric study of drained response shows that the model describes realistically the variation of peak friction angle and dilation rate as a function of confining pressure and density when compared with an empirical correlation valid for many sands. The proposed formulation predicts a unique critical state locus for both drained and undrained triaxial testing which is non‐linear over the entire range of stresses and is in excellent agreement with recent experimental data. Overall, the model provides excellent predictions of the stress–strain–strength relationships over a wide range of confining pressures and formation densities. Copyright © 2002 John Wiley & Sons, Ltd.
Application of 13C‐filtered 1H NMR to evaluate drug action on gluconeogenesis and glycogenolysis simultaneously in isolated rat hepatocytes
Authors: Hansen Svend Høime , McCormack James G. 
Published: August 2002

AbstractThe effects of two inhibitors of hepatic glucose production, AICAR (5‐aminoimidazole‐4‐carboxamide riboside) and metformin, whose precise mechanisms of action are a matter of some controversy, have been investigated in isolated rat hepatocytes by application of a novel NMR‐based method whereby effects on metabolic flow from the two glucose‐producing pathways, glycogenolysis and gluconeogenesis, and also lactate production, can be studied simultaneously. Hepatocytes were pre‐incubated for 24 h with 15 mM 1‐13C‐glucose to load the cells with labeled glycogen, which under subsequent glycogenolytic conditions would yield predominantly 1‐13C glucose and 3‐13C‐lactate, followed (after washing) by incubation in media with 2‐13C‐glycerol, which under subsequent gluconeogenic conditions would yield 2,5‐13C‐glucose, or if metabolized to lactate, 2‐13C‐lactate. Glucose production was then stimulated by glucagon for 3 h in the absence or presence of the inhibitors and then incubation media were analyzed by 13C‐HSQC (heteronuclear single quantum coherence)‐filtered 1H NMR spectra. The results show that metformin only inhibits glucose production by inhibition of gluconeogenesis, but also that it increases lactate production from both glycogenolysis and from glycerol, whereas, and contrary to expectations, AICAR inhibits glucose production by inhibiting both gluconeogenesis and glycogenolysis, and also increases lactate production from glycerol. The data show that application of this methodology can be used to answer important questions about drug action on hepatic metabolism that are not readily accessible by alternative means. Copyright © 2002 John Wiley & Sons, Ltd.
Differentiation of hydatid cyst from cysticercus cyst by proton MR spectroscopy
Authors: Garg Monika , Chawla Sanjeev , Prasad Kashi N. , Roy Raja , Sikora Sadiq S. , Kumar Rajesh , Husain Mazhar , Khetrapal C. L. , Gupta Rakesh K. 
Published: August 2002

AbstractThe metabolite patterns obtained by ex vivo proton MR spectroscopy of fluid from different locations of hydatid cysts of sheep and humans (n = 16) and cysticercus cysts of swine and humans (n = 25) were compared with an objective of differentiating the two parasites on the basis of their metabolite pattern. The spectra from hydatid fluid differed from cysticercus cyst by the absence of creatine in the former. When the hydatid cyst was fertile, malate and/or fumarate was also observed, which was absent in cysticercus cyst. The most likely explanation for the presence of creatine only in the cysticercus fluid is its active diffusion from the surrounding host tissue along with a contribution from the musculature present in the bladder wall of the cyst. Copyright © 2002 John Wiley & Sons, Ltd.
In vivo brain 31P‐MRS: measuring the phospholipid resonances at 4 Tesla from small voxels
Authors: Jensen J. Eric , Drost Dick J. , Menon Ravi S. , Williamson Peter C. 
Published: August 2002

AbstractAn optimized phosphorous (31P) three‐dimensional chemical‐shift imaging (3D‐CSI) protocol was developed at 4 T to study the phospholipid metabolism from discrete regions in the human brain without the need for 1H‐decoupling or nuclear Overhauser enhancement (NOE). In this study, a spherically bound, weighted average, random point omission 3D‐CSI technique was developed and tested, based on methods proposed in the literature. The technique yields a significant (p < 0.001, two‐tailed, 5% confidence level) increase in signal‐to‐noise (SNR) efficiency over conventional 3D‐CSI (phantom 32%), without an increase in voxel bleedthrough. An automated time‐domain fitting procedure utilizing prior spectral knowledge quantified the individual brain phospholipid metabolites from 15 cm3 effective (8.0 cm3 nominal) volumes from the left/right‐parieto‐occipital cortex and left/right thalamus in 10 normal volunteers. Individual constituents from the phosphomonoester (PME) region; phosphoethanolamine (PEth), phosphocholine (PCh) and the phosphodiester (PDE) region; glycerophosphoethanolamine (GPEth), glycerophosphocholine (GPCh) and membrane phospholipids (MP) were separately quantified to assess the precision of our method at 4 T against previous 1H‐decoupled 31P‐MRS brain studies at lower fields and much larger voxels. Derived concentrations (mM/l tissue) for PEth, PCh, GPEth, GPCh and MP in the left‐parieto‐occipital cortex were 0.81 ± 0.21, 0.46 ± 0.14, 0.74 ± 0.30, 1.15 ± 0.43 and 1.54 ± 0.95 mM, respectively, and 0.94 ± 0.16, 0.46 ± 0.17, 0.83 ± 0.22, 1.14 ± 0.40 and 1.26 ± 0.78 mM for the right parieto‐occipital cortex. Derived concentrations (mM/l tissue) for PEth, PCh, GPEth, GPCh and MP in the left‐thalamus were 0.69 ± 0.18, 0.42 ± 0.16, 0.63 ± 0.20, 1.05 ± 0.42 and 0.93 ± 0.56 mM, respectively, and 0.68 ± 0.24, 0.34 ± 0.18, 0.60 ± 0.23, 1.09 ± 0.36 and 0.74 ± 0.48 mM for the right‐thalamus. This is the first study to our knowledge that has been able to quantify each of these individual phospholipid metabolites from such small voxels in the brain within a clinically reasonable scan time and without 1H‐decoupling or NOE. Copyright © 2002 John Wiley & Sons, Ltd.
Changes in phosphate metabolism in thymoma cells suggest mechanisms for resistance to dexamethasone‐induced apoptosis. A 31P NMR spectroscopic study of cell extracts
Authors: Lutz N. W. , Tome M. E. , Aiken N. R. , Briehl M. M. 
Published: August 2002

AbstractTreatment of the mouse thymoma‐derived WEHI7.2 cell line with dexamethasone, a synthetic glucocorticoid, causes the cells to undergo apoptosis. Previous studies have shown that WEHI7.2 cell variants with an increased antioxidant defense exhibit increased resistance to dexamethasone‐induced apoptosis, suggesting that oxidative stress may play a role in glucocorticoid‐induced apoptosis. In this work we compared metabolic profiles of WEHI7.2 parental cells with those of WEHI7.2 variants with an increased antioxidant defense or overexpressing bcl‐2, to determine whether bolstering the antioxidant defense results in altered metabolic parameters that could translate into increased resistance to dexamethasone‐induced apoptosis. WEHI7.2 parental cells and cells overexpressing catalase, thioredoxin or bcl‐2, or selected for resistance to 200 µM H2O2 were cultured in low‐glucose DMEM medium supplemented with 10% calf serum, and extracted using chloroform–methanol–water (1:1:1). Metabolites contained in the aqueous and organic phases of the extracts were processed separately and subjected to high‐resolution 31P NMR spectroscopy. In most of the steroid‐resistant variants, ATP levels and energetic status were decreased compared with the steroid‐sensitive parental cell line, while the concentrations of hexose and triose phosphates were increased. Furthermore, the ratio of choline‐containing phospholipids to ethanolamine‐containing phospholipids was generally reduced in steroid‐resistant cells. Phosphatidylethanolamine and its derivatives contain a higher amount of polyunsaturated fatty acids (PUFA) than the choline‐containing analogs, and PUFA are readily oxidized by reactive oxygen species. Therefore, an increased initial amount of phosphatidylethanolamine may increase the ‘buffering capacity’ of this antioxidant and may thus contribute to the steroid resistance of WEHI7.2 variants. Copyright © 2002 John Wiley & Sons, Ltd.
Study of delay patterns of weighted voice traffic of end‐to‐end users on the VoIP network
Authors: Han Jeong‐Soo , Ahn Seong‐Jin , Chung Jin‐Wook 
Published: August 2002

AbstractIn this paper we study delay patterns of weighted voice traffic of end‐to‐end users on the Voice over Internet Protocol (VoIP) network. We compare the delay performance of voice traffic which varies with queue management techniques such as First‐In First‐Out (FIFO) and Weighted Fair Queuing (WFQ) and voice codec algorithms such as G.723 and G.729 and select an optimal algorithm. Copyright © 2002 John Wiley & Sons, Ltd.
Reducing signaling traffic in wireless ATM networks through handoff scheme improvement
Authors: Hać Anna , Zhang Yongcan 
Published: August 2002

AbstractWe propose a new handoff call management scheme which reduces signaling traffic in wireless ATM networks and improves the efficiency of the virtual channel. Chaining followed by a make‐break algorithm is a suitable handoff scheme for various situations. In the chaining part of the scheme, a chain routing algorithm is studied and compared with the hop‐limiting scheme. When the algorithm is implemented in our scheme, it improves the performance of the existing scheme in call drop rates so as to reduce the signaling traffic in wireless ATM networks. Copyright © 2002 John Wiley & Sons, Ltd.
Network management abroad
Authors: Hendriks J. C. W. , Spruit M. E. M. , Looijen M. 
Published: August 2002

AbstractThis paper presents a number of interim results of a survey that, on the basis of a case study, establishes links between conditions in various countries and steering the management of an international network. It shows that the impact of factors in other countries on the network can largely be controlled from within an organization. Copyright © 2002 John Wiley & Sons, Ltd.
Traffic behavior analysis and modeling of sub‐networks
Authors: Chen Yen‐Wen 
Published: August 2002

AbstractIn this paper, the characteristics of sub‐network traffic is analyzed from the correlation point of view. It is easy to see that the traffic histogram of a sub‐network has a 24‐hour seasonal variation due to daily usage behavior. The auto correlation factor (ACF) and partial auto correlation factor (PACF) tests are applied first to examine the correlation of the traffic among consecutive hours and the correlation with a specific hour. The seasonal auto‐regressive integrated moving average (ARIMA) model is applied to characterize the above properties of the network traffic. Modeling performance is evaluated by examining the coincidence of the histogram and the moving average of traffic volume between the actual traffic collected from the network and the traffic generated by the proposed model. The experimental results illustrate that the proposed model can effectively capture traffic behaviors of the sub‐network and can then be used as a suitable traffic model for analysis of Internet performance. Copyright © 2002 John Wiley & Sons, Ltd.
Relaxation iterative algorithms for solving cathodic protection systems with non‐linear polarization curves
Authors: Sun W. 
Published: August 2002

AbstractThis paper discusses the calculation of potential distribution of impressed cathodic protection (CP) models with non‐linear polarization curves. We propose a relaxation iterative algorithm for the non‐linear problem and prove both theoretically and numerically that this iterative sequence is convergent for any physical polarization curves. This feature is of significant importance in developing a computer code for the design of CP systems. Copyright © 2002 John Wiley & Sons, Ltd.
Semi‐discretization method for delayed systems
Authors: Insperger Tamás , Stépán Gábor 
Published: August 2002

AbstractThe paper presents an efficient numerical method for the stability analysis of linear delayed systems. The method is based on a special kind of discretization technique with respect to the past effect only. The resulting approximate system is delayed and also time periodic, but still, it can be transformed analytically into a high‐dimensional linear discrete system. The method is applied to determine the stability charts of the Mathieu equation with continuous time delay. Copyright © 2002 John Wiley & Sons, Ltd.
Evaluation of three unstructured multigrid methods on 3D finite element problems in solid mechanics
Authors: Adams Mark 
Published: August 2002

AbstractMultigrid has been a popular solver method for finite element and finite difference problems with regular grids for over 20 years. The application of multigrid to unstructured grid problems, in which it is often difficult or impossible for the application to provide coarse grids, is not as well understood. In particular, methods that are designed to require only data that are easily available in most finite element applications (i.e. fine grid data), constructing the grid transfer operators and coarse grid operators internally, are of practical interest. We investigate three unstructured multigrid methods that show promise for challenging problems in 3D elasticity: (1) non‐nested geometric multigrid, (2) smoothed aggregation, and (3) plain aggregation algebraic multigrid. This paper evaluates the effectiveness of these three methods on several unstructured grid problems in 3D elasticity with up to 76 million degrees of freedom. Published in 2002 by John Wiley & Sons, Ltd.
Material state remapping in computational solid mechanics
Authors: Rashid M. M. 
Published: August 2002

AbstractA computational procedure for remapping material state information from one finite element mesh to another is described. The procedure is useful in connection with evolving meshes for inelastic problems, as for example occur in the context of fracture simulation and adaptive mesh refinement. The proposed method is based on weak enforcement of equality between corresponding fields on the two meshes, where piecewise‐constant fields on both meshes are generalized from the quadrature‐point values. The essential algorithmic problem is that of calculating the volume partition of an arbitrary convex region with respect to a covering set of disjoint convex regions. Instead of geometrically resolving the associated intersections, the problem is herein approximated by a constrained optimization problem, which may be readily and efficiently solved computationally. This formulation is a main contribution of the paper. Computational examples are given that illustrate the effectiveness of the proposed procedure. Copyright © 2002 John Wiley & Sons, Ltd.
Mesh data structure selection for mesh generation and FEA applications
Authors: Garimella Rao V. 
Published: August 2002

AbstractThe data structure representing a mesh and the operators to create and query such a database play a crucial role in the performance of mesh generation and FE analysis applications. The design of such a database must balance the conflicting requirements of compactness and computational efficiency. In this article, 10 different mesh representations are reviewed for linear tetrahedral and hexahedral meshes. A methodology for calculating the storage and computational costs of mesh representations is presented and the 10 data structures are analysed. Also, a system for ranking different data structures based on their computational and storage costs is devised and the various mesh representations are ranked according to this measure. Copyright © 2002 John Wiley & Sons, Ltd.