bluuebunny/crossref_metadata_2025_split huggingface dataset:
Non‐linear initial boundary value problemsof hyperbolic–parabolic type. A general investigationof admissible couplings between systems of higher order. Part 1: linear theory
Authors: Ebenfeld Stefan 
Published: January 2005

AbstractIn this article (which is divided in three parts) we investigate the non‐linear initial boundary value problems (1.2) and (1.3). In both cases we consider coupled systems where each system is of higher order and of hyperbolic or parabolic type.Our goal is to characterize systematically all admissible couplings between systems of higher order and different type.By an admissible coupling we mean a condition that guarantees the existence, uniqueness and regularity of solutions to the respective initial boundary value problem.In part 1 at hand, we develop the underlying theory of linear hyperbolic and parabolic initial boundary value problems. Testing the PDEs with suitable functions we obtain a priori estimates for the respective solutions. In particular, we make use of the regularity theory for linear elliptic boundary value problems that was previously developed by the author. In part 2, we prove the local in time existence, uniqueness and regularity of solutions to the quasilinear initial boundary value problem (1.2) using the so‐called energy method. In the above sense, the regularity assumptions about the coefficients and right‐hand sides define the admissible couplings. In part 3, we extend the results of part 2 to the non‐linear initial boundary value problem (1.3). In particular, the assumptions about the respective parameters correspond to the previous regularity assumptions and hence define the admissible couplings now. Moreover, we exploit the assumptions about the respective parameters for the case of two coupled systems. Copyright © 2002 John Wiley & Sons, Ltd.
Phase‐field systems for multi‐dimensional Prandtl–Ishlinskii operators with non‐polyhedral characteristics
Authors: Sprekels Jürgen , Krejčí Pavel 
Published: January 2005

AbstractHysteresis operators have recently proved to be a powerful tool in modelling phase transition phenomena which are accompanied by the occurrence of hysteresis effects. In a series of papers, the present authors have proposed phase‐field models in which hysteresis non‐linearities occur at several places. A very important class of hysteresis operators studied in this connection is formed by the so‐called Prandtl–Ishlinskii operators. For these operators, the corresponding phase‐field systems are in the multi‐dimensional case only known to admit unique solutions if the characteristic convex sets defining the operators are polyhedrons. In this paper, we use approximation techniques to extend the known results to multi‐dimensional Prandtl–Ishlinskii operators having non‐polyhedral convex characteristicsets. Copyright © 2002 John Wiley & Sons, Ltd.
On the Stokes system and on the biharmonic equation in the half‐space: an approach via weighted Sobolev spaces
Authors: Boulmezaoud Tahar Z. 
Published: January 2005

AbstractIn this paper, we investigate the Stokes system and the biharmonic equation in a half‐space of ℝn. Our approach rests on the use of a family of weighted Sobolev spaces as a framework for describing the behaviour at infinity. A complete class of existence, uniqueness and regularity results for both the problems is proved. The proofs are mainly based on the principle of reflection. Copyright © 2002 John Wiley & Sons, Ltd.
Optimal control of singular systems via piecewise linear polynomial functions
Authors: Razzaghi Mohsen , Marzban Hamid‐Reza 
Published: January 2005

AbstractA method for finding the optimal control of linear singular systems with a quadratic cost functional using piecewise linear polynomial functions is discussed. The state variable, state rate, and the control vector are expanded in piecewise linear polynomial functions with unknown coefficients. The relation between the coefficients of the state rate with state variable is provided and the necessary condition of optimality is derived as a linear system of algebraic equations in terms of the unknown coefficients of the state and control vectors. A numerical example is included to demonstrate the validity and the applicability of the technique. Copyright © 2002 John Wiley & Sons, Ltd.
Legendre wavelets method for constrained optimal control problems
Authors: Razzaghi Mohsen , Yousefi Sohrabali 
Published: January 2005

AbstractA numerical method for solving non‐linear optimal control problems with inequality constraints is presented in this paper. The method is based upon Legendre wavelet approximations. The properties of Legendre wavelets are first presented. The operational matrix of integration and the Gauss method are then utilized to reduce the optimal control problem to the solution of algebraic equations. The inequality constraints are converted to a system of algebraic equalities; these equalities are then collocated at the Gauss nodes. Illustrative examples are included to demonstrate the validity and applicability of the technique. Copyright © 2002 John Wiley & Sons, Ltd.
An upper and lower solution approach for singular boundary value problems with sign changing non‐linearities
Authors: Agarwal Ravi P. , O'Regan Donal 
Published: January 2005

AbstractWe obtain via Schauder's fixed point theorem new results for singular second‐order boundary value problems where our non‐linear term f(t,y,z) is allowed to change sign. In particular, our problem may be singular at y=0, t=0 and/or t=1. Copyright © 2002 John Wiley & Sons, Ltd.
On a non‐uniqueness in fragmentation models
Authors: Banasiak J. 
Published: January 2005

AbstractEquations of fragmentation describing e.g. the polymer degradation, despite their apparent simplicity, have numerous non‐typical features. One of them is the existence of multiple solutions. In this paper, applying classical results of Hille and Phillips, we explain their occurrence and prove that nevertheless the uniqueness holds for a large class of physically reasonable solutions. Copyright © 2002 John Wiley & Sons, Ltd.
Modern proton‐detected 1D 1H–15N NMR experiments. Application to the measurement of 1H,15N coupling constants at natural abundance
Authors: Parella Teodor , Belloc Jordi 
Published: January 2005

AbstractNon‐selective and selective versions of several proton‐detected 1D NMR experiments to be applied to 15N are proposed. Clean, artifact‐free 1D spectra are easily obtained by the effective coherence selection by pulsed‐field gradients and the attainable sensitivity is maximized using modern pulse schemes. Despite the low sensitivity inherent to 15N NMR spectroscopy, the successful application of these experiments is demonstrated for resonance assignments and accurate measurement of both one‐bond and long‐range proton–nitrogen coupling constants on a model tripeptide at natural abundance. Copyright © 2001 John Wiley & Sons, Ltd.
A rare occurrence of a β‐turn in an amyloid βA4 peptide
Authors: Tauro Savita , Coutinho Evans , Srivastava Sudha 
Published: January 2005

AbstractThe fragment β(25–35) of the amyloid β‐peptide, like its parent βA4, has shown neurotrophic and late neurotoxic activities in cultured cells. The 3D structure of this important peptide was examined by 1H and 13C 2D‐NMR and MD simulations in DMSO‐d6 and water. The NMR parameters of chemical shift, 3J(N,Hα) coupling constants, temperature coefficients of NH chemical shifts and the pattern of intra and inter‐residue NOEs were used to deduce the structures. In DMSO‐d6, the peptide was found to take up a type I β‐turn around the C‐terminal residues Ile8–Gly9–Leu10–Met11, whereas in water at pH 5.5, it adopts a random coil conformation. This is only the second report of a β‐turn in the β‐amyloid class of peptides. The solution structures generated using restrained molecular dynamics were refined by MARDIGRAS to an R factor of 0.33 in the case of DMSO‐d6 and to 0.56 for water. Copyright © 2002 John Wiley & Sons, Ltd.
Computational mechanics of the steel–concrete interface
Authors: Ben Romdhane M. R. , Ulm F.‐J. 
Published: January 2005

AbstractConcrete cracking in reinforced concrete structures is governed by two mechanisms: the activation of bond forces at the steel–concrete interface and the bridge effects of the reinforcement crossing a macro‐crack. The computational modelling of these two mechanisms, acting at different scales, is the main objective of this paper. The starting point is the analysis of the micro‐mechanisms, leading to an appropriate choice of (measurable) state variables describing the energy state in the surface systems: on the one side the relative displacement between the steel and the concrete, modelling the bond activation; on the other hand, the crack opening governing the bridge effects. These displacement jumps are implemented in the constitutive model using thermodynamics of surfaces of discontinuity.On the computational side, the constitutive model is implemented in a discrete crack approach. A truss element with slip degrees of freedom is developed. This degree of freedom represents the relative displacement due to bond activation. In turn, the bridge effect is numerically taken into account by modifying the post‐cracking behaviour of the contact elements representing discrete concrete cracks crossed by a rebar. First simulation results obtained with this model show a good agreement in crack pattern and steel stress distribution with micro‐mechanical results and experimental results. Copyright © 2001 John Wiley & Sons, Ltd.
A visco‐plastic constitutive model for granular soils modified according to non‐local and gradient approaches
Authors: di Prisco C. , Imposimato S. , Aifantis E. C. 
Published: January 2005

AbstractAn already available non‐associated elastic–viscoplastic constitutive model with anisotropic strain hardening is modified in order to describe both the constitutive parameter dependency on relative density and the spatio‐temporal evolution of strain localization. To achieve this latter goal, two distinct but similar approaches are introduced: one inspired by the gradient theory and one by the non‐local theory. A one‐dimensional case concerning a simple shear test for a non‐homogeneous infinitely long dense sand specimen is numerically discussed and a finite difference scheme is employed for this purpose. The results obtained by following the two different approaches are critically analysed and compared. Copyright © 2001 John Wiley & Sons, Ltd.
Explicit solutions for the instantaneous undrained contraction of hollow cylinders and spheres in porous elastoplastic medium
Authors: Giraud A. , Homand F. , Labiouse V. 
Published: January 2005

AbstractIn this article we present closed‐form solutions for the undrained variations in stress, pore pressure, deformation and displacement inside hollow cylinders and hollow spheres subjected to uniform mechanical pressure instantaneously applied to their external and internal boundary surfaces. The material is assumed to be a saturated porous medium obeying a Mohr–Coulomb model failure criterion, exhibiting dilatant plastic deformation according to a non‐associated flow rule which accounts for isotropically strain hardening or softening. The instantaneous response of a porous medium submitted to an instantaneous loading is undrained, i.e. without any fluid mass exchange. The short‐term equilibrium problem to be solved is now formally identical to a problem of elastoplasticity where the constitutive equations involve the undrained elastic moduli and particular equivalent plastic parameters. The response of the model is presented (i) for extension and compression undrained triaxial tests, and (ii) for unloading problems of hollow cylinders and spheres through the use of appropriately developed closed‐form solutions. Numerical results are presented for a plastic clay stone with strain hardening and an argilite with strain softening. The effects of plastic dilation, of the strain softening law and also of geometry of the cavity on the behaviour of the porous medium have been underlined. Analytical solutions provide valuable benchmarks enabling various numerical methods in undrained conditions with a finite boundary to be verified. Copyright © 2002 John Wiley & Sons, Ltd.
Integration and calibration of a plasticity model for granular materials
Authors: Jacobsson L. , Runesson K. 
Published: January 2005

AbstractA new macroscopic constitutive model for non‐cohesive granular materials, with the focus on coarse‐sized materials (railway ballast), is presented. The model is based on the concepts of rate‐independent isotropic plasticity. The Backward Euler rule is used for integrating the pertinent evolution equations. The resulting incremental relations are solved in the strain space that is extended with the internal (hardening) variables. The model is calibrated using data from Conventional Triaxial Compression (CTC) tests, carried out at the University of Colorado at Boulder. A function evaluation method is used for the optimization, whereby a ‘multi‐vector’ strategy for choosing the appropriate start vector is proposed. Copyright © 2002 John Wiley & Sons, Ltd.
Image‐based modelling and analysis of microstructures for two‐scale problems in geomechanics
Authors: Terada Kenjiro , Kyoya Takashi , Kazama Motoki , Lee Kiho , Oyang Lizhu 
Published: January 2005

AbstractThis paper focuses on the geometry modelling and numerical analysis of microstructures of geomaterials employing the concept of image‐based engineering. The novel modelling and analysis techniques with digital images are incorporated with the mathematical homogenization method to study the interaction between individual phases, each of whose shape and spatial distribution are irregular. Owing to the distinctive features of these computational techniques, the evaluation of homogenized properties for geomaterials provides the reliable information about the micro‐ or macroscopic mechanical behaviours for engineering practice. It is, naturally, inevitable that engineers' demands on safety and efficient design place emphasis on quantitative estimates for these values. Thus, calibration accompanied with actual measurements comes within the scope of this study so that these properties would be realistic and practical from the engineering viewpoints. Copyright © 2002 John Wiley & Sons, Ltd.
Fundamental solutions for a fluid‐saturated, transversely isotropic, poroelastic solid
Authors: Taguchi I. , Kurashige M. 
Published: January 2005

AbstractThe fundamental solutions were obtained for step‐like point forces acting in three orthogonal directions and an instantaneous fluid point source in a fluid‐saturated, porous, infinite solid of transversely isotropic elasticity and permeability. After expressing the governing equations in the form of matrix in the Laplace space, we employed Kupradze's method together with the triple Fourier transforms. This method reduces the simultaneous partial differential equations with respect to three displacement components and a pore fluid pressure to a differential equation in terms of only one potential scalar function, which can be operationally solved in the transformed space. After the Laplace inversion of the potential, the residue theorem was applied to its Fourier inverse transform with respect to one of the transformation variables. The Fourier transforms with respect to two other variables were rewritten into the Hankel transforms. Copyright © 2002 John Wiley & Sons, Ltd.
Source signature and elastic waves in a half‐space under a sustainable line‐concentrated impulsive normal force
Authors: Ziv Moche 
Published: January 2005

AbstractFirst, the response of an ideal elastic half‐space to a line‐concentrated impulsive normal load applied to its surface is obtained by a computational method based on the theory of characteristics in conjunction with kinematical relations derived across surfaces of strong discontinuities. Then, the geometry is determined of the obtained waves and the source signature—the latter is the imprint of the spatiotemporal configuration of the excitation source in the resultant response. Behind the dilatational precursor wave, there exists a pencil of three plane waves extending from the vertex at the impingement point of the precursor wave on the stress‐free surface of the half‐space to three points located on the other two boundaries of the solution domain. These four wave‐arresting points (end points) of the three plane waves constitute the source signature. One wave is an inhibitor front in the behaviour of the normal stress components and the particle velocity, while in the behaviour of the shear stress component, it is a surface‐axis wave. The second is a surface wave in the behaviour of the horizontal components of the dependent variables, while the third is an inhibitor wave in the behaviour of the shear stress component. An inhibitor wave is so named, since beyond it, the material motion is dying or becomes uniform. A surface‐axis wave is so named, since upon its arrival, like a surface wave, the dependent variable in question features an extreme value, but unlike a surface wave, it exists in the entire depth of the solution domain. It is evident from this work that Saint‐Venant's principle for wave propagation problems cannot be formulated; therefore, the above results are a consequence of the particular model proposed here for the line‐concentrated normal load. Copyright © 2002 John Wiley & Sons, Ltd.
Failure criteria of anisotropically damaged materials based on the critical plane concept
Authors: Mróz Zenon , Maciejewski Jan 
Published: January 2005

AbstractThe damage state of a cracked material is assumed to be specified by crack density distribution on physical planes. The critical plane approach is used with account for damaged and intact area fractions on the plane. The maximum of failure function is specified for all potential failure planes and the critical plane orientation is determined. The resulting failure condition is applied to study strength evolution for triaxially compressed specimens with varying orientation of principal stress and damage tensor axes. Both Coulomb and non‐linear failure conditions of Mohr type are applied to specify the representative critical plane. A general stress state is considered and the failure condition is specified for different relative orientations of orthotropy and principal stress axes. Copyright © 2002 John Wiley & Sons, Ltd.
Modelling of hygro‐thermal behaviour and damage of concrete at temperature above the critical point of water
Authors: Gawin D. , Pesavento F. , Schrefler B. A. 
Published: January 2005

AbstractIn this paper, a model for the analysis of the behaviour of concrete at temperature largely exceeding critical point of water, is presented. In this temperature range liquid phase, i.e. capillary phase, and gas phase cannot be distinguished and only the latter exists. Consequently, capillary pressure has no more physical meaning above this point and liquid water is present only as physically adsorbed water. In this work, we give a different physical interpretation to the capillary pressure and use it still for the description of the hygrometric state of concrete in the zone, where temperature exceeds the critical point of water. Considerable thermal dilatation of the liquid water and the real behaviour of water vapour close to critical temperature are taken into account. Moreover, a special switching procedure in order to avoid the Stefan‐like problem, which subsequently arises, is described and employed in the calculations. Finally, several numerical examples demonstrating the robustness of the adopted solution have been shown. Copyright © 2002 John Wiley & Sons, Ltd.
In vivo and in vitro NMR spectroscopy reveal a putative novel inborn error involving polyol metabolism
Authors: Moolenaar Sytske H. , Knaap Marjo S. van der , Engelke Udo F. H. , Pouwels Petra J. W. , Janssen‐Zijlstra Fokje S. M. , Verhoeven Nanda M. , Jakobs Cornelis , Wevers Ron A. 
Published: January 2005

AbstractIn vivo NMR spectroscopy was performed on the brain of a patient with a leukoencephalopathy, revealing unknown resonances between 3.5 and 4.0 ppm. In addition, urine and CSF of the patient were measured using high‐resolution NMR spectroscopy. Also in these in vitro spectra, unknown resonances were observed in the 3.5–4.0 ppm region. Homonuclear 1H two‐dimensional J‐resolved spectroscopy (JRES) and 1H–1H correlation spectroscopy (COSY) were performed on the patient's urine for more accurate assignment of resonances. The NMR spectroscopic studies showed that the unknown resonances could be assigned to arabinitol and ribitol. This was confirmed using gas chromatography. The arabinitol was identified as D‐arabinitol. The patient is likely to suffer from an as yet unknown inborn error of metabolism affecting D‐arabinitol and ribitol metabolism. The primary molecular defect has not been found yet. Urine spectra of patients suffering from diabetes mellitus or galactosemia were recorded for comparison. Resonances outside the 3.2–4.0 ppm region, which are the most easy to recognize in body fluid spectra, allow easy recognition of various sugars and polyols. The paper shows that NMR spectroscopy in body fluids may help identifying unknown resonances observed in in vivo NMR spectra. Copyright © 2001 John Wiley & Sons, Ltd.

Abbreviations used:

Cho

choline‐containing compounds

COSY

1H–1H correlation spectroscopy

Cr

creatine

CSF

cerebrospinal fluid

GC

gas chromatography

Glx

glutamine and glutamate

JRES

homonuclear 1H two‐dimensional J‐resolved spectroscopy

Myo‐Ins

myo‐inositol

NAA

N‐acetylaspartate

Scyllo‐Ins

scyllo‐inositol

STEAM

stimulated echo acquisition mode

PRESS

point resolved spectroscopy.
In vivo single‐voxel proton MR spectroscopy in brain lesions with ring‐like enhancement
Authors: Kimura Teruo , Sako Kazuhiro , Gotoh Takumi , Tanaka Kunio , Tanaka Tatsuya 
Published: January 2005

AbstractIt is often difficult to make a correct diagnosis of ring‐like enhanced lesions on Gd‐enhanced MR brain images. To differentiate these lesions using proton MR spectroscopy (1H‐MRS), we retrospectively evaluated the correlation between the 1H‐MR spectra and histopathological findings. We evaluated proton MR spectra obtained from the lesions in 45 patients, including metastasis (n = 19), glioblastoma (n = 10), radiation necrosis (n = 7), brain abscess (n = 5), and cerebral infarction (n = 4). The rate of misdiagnosis was found to be lowest at the threshold level of 2.48 for the (choline containing compounds)/(creatine and phosphocreatine) ratio (Cho/Cr) obtained from the whole lesions, which include the enhanced rim and the non‐enhanced inner region. That is, the positively predictive values of a Cho/Cr greater than 2.48 for diagnosing metastasis or glioblastoma was 88.9 and 60.0%, respectively, and the positively predictive value of a Cho/Cr less than 2.48 for diagnosing radiation necrosis or cerebral infarction was 71.4 and 100%, respectively. For further differentiating between metastasis and glioblastoma, information about the presence and absence of an N‐acetyl‐aspartate (NAA) peak and lipid‐ or lactate‐dominant peak was found to be useful. In 73.7% of metastasis cases a lipid‐dominant peak was observed in the whole lesion without an NAA peak in the inner region, whereas the same pattern was observed in only 10% of the glioblastoma cases.
Correlation with the histopathological findings showed that a high Cho signal is suggestive of neoplasm. Lipid signal in the non‐enhanced central region was correlated to necrosis. Lactate signals were often observed in glioblastoma, abscess and sometimes metastasis, presumably reflecting the anaerobic glycolysis by the living cells in the ring‐like enhanced rim. Single‐voxel proton MR spectroscopy may serve as a potential tool to provide useful information of differentiation of ring‐like enhanced lesions that cannot be diagnosed correctly using enhanced MR images alone. Copyright © 2001 John Wiley & Sons, Ltd.