bluuebunny/crossref_metadata_2025_split huggingface dataset:
Use of intravenous pulsed cyclophosphamide in severe, generalized myasthenia gravis
Authors: Gustavo De Feo Lucas , Schottlender Juan , Martelli Néstor A. , Molfino Néstor A. 
Published: October 2002

AbstractTwenty‐three myasthenia gravis (MG) subjects, mean (SD) age 41.6 years (14), showing poor disease control or steroid‐related side effects, received treatment for 12 months with intravenous cyclophosphamide (CP; n = 12) or placebo (PL; n = 11) in a randomized, double‐blind trial. Pulses were given monthly at an initial dose of 500 mg/m2 of body surface, and titrated according to changes of peripheral muscle strength or side effects. Changes of muscle strength, steroid and pyridostigmine requirements, and development of ventilatory failure or swallowing impairment were evaluated at 0, 3, 6, and 12 months. No differences were observed between groups at baseline. Statistically significant reductions of methylprednisone doses were noted in both groups but were more pronounced in subjects receiving CP than PL at 6 months (P < 0.05) and at 12 months (P < 0.03). At 12 months, five subjects on CP had tapered off their steroids whereas no subject on PL achieved further reductions (P < 0.03). Four CP subjects were not receiving steroids 36 months after completing the study and three other CP subjects had stopped pyridostigmine. CP improved muscle strength at 3 and 6 months, and this reached statistical significance compared to PL at 12 months mainly in the bulbar and masticatory (P < 0.009) and extraocular muscles (P < 0.03). Ventilatory failure was noted in one subject on CP (due to bronchopneumonia) and two on PL (due to muscle weakness). No significant increases of CP‐related side effects were observed. Thus, this study suggests that intravenous pulses of CP allow reductions of systemic steroids usage without muscle strength deterioration or CP‐related side effects. © 2002 Wiley Periodicals, Inc. Muscle Nerve 26: 31–36, 2002
Micromechanics of saturated and unsaturated porous media
Authors: Chateau Xavier , Dormieux Luc 
Published: October 2002

AbstractThe homogenization method is used to determine the formulation of the behaviour of both saturated and unsaturated porous media. This approach makes it possible to assess the validity of the effective stress concept as a function of the properties of the porous media at the microscopic scale. Furthermore, the influence of the morphologies of the solid and fluid phases on the macroscopic behaviour is studied. The strain induced by drying is examined as a function of the morphological properties. Copyright © 2002 John Wiley & Sons, Ltd.
A self‐regulating TCP acknowledgment (ACK) pacing scheme
Authors: Aweya James , Ouellette Michel , Montuno Delfin Y. 
Published: October 2002

AbstractWe describe in this paper a new TCP ACK pacing scheme that dynamically tunes its behavior to account for variations or changes in the network load. The scheme does not require the knowledge of when TCP is in the slow‐start or congestion avoidance phase to determine the proper ACK pacing rate. Copyright © 2002 John Wiley & Sons, Ltd.
ECVBA traffic‐smoothing scheme for VBR media streams
Authors: Chao Han‐Chieh , Hung C. L. , Tsuei T. G. 
Published: October 2002

AbstractWe propose an effective and efficient traffic‐smoothing called the efficient changes and variability bandwidth allocation (ECVBA) scheme. This algorithm not only minimizes the peak rate of a stream but also increases the likelihood of successful VBR stream transmission. The main benefit is that it can immediately release bandwidth to other sites in the network. Copyright © 2002 John Wiley & Sons, Ltd.
A branch‐and‐price algorithm for switch‐box routing
Authors: Jørgensen David Grove , Meyling Morten 
Published: October 2002

AbstractRouting in VLSI design concerns the wiring of a chip after the logical modules have been placed. A subproblem occurring in VLSI design is switch‐box routing. Switch‐box routing can be formulated as the problem of packing Steiner trees in a grid graph. The only previous exact solution method for switch‐box routing uses a branch‐and‐cut approach. The aim of this work was to solve the switch‐box routing problem to optimality by using a branch‐and‐price algorithm based on an IP model where variables represent Steiner trees and where the pricing problem becomes the problem of finding a Steiner tree in a graph. In the primal algorithm, the focal points are branching strategy, pricing strategy, perturbation of the linear program, and computation of lower bounds to terminate column generation early. The final implementation yielded optimal solutions in the knock‐knee model to seven classic switch‐box instances, of which three had not been solved to optimality prior to this work. © 2002 Wiley Periodicals, Inc.
Topology optimization in wavelet space
Authors: Poulsen Thomas A. 
Published: October 2002

AbstractWe investigate the use of wavelet methods for the design description in topology optimization. This is a new setting for topology optimization that does not take the material densities in the elements of the finite element model as the design space. This new approach has advantages and limitations which are discussed. It is shown how the control of wavelet coefficients can be used to prevent the formation of checkerboard patterns and to obtain some geometry control. Problems related to overlapping basis functions are analysed and solution methods are proposed. Examples of optimized designs using the described methods are given. Copyright © 2001 John Wiley & Sons, Ltd.
Variational principles for non‐conforming finite element methods
Authors: Chen Wanji 
Published: October 2002

AbstractVariational principles with relaxed inter‐element continuity requirement for non‐conforming element methods in linear and non‐linear analyses are developed. Based on the principles, any non‐conforming element displacement can be used directly to derive the explicit expressions of non‐conforming displacement function, which can ensure the passage of the patch test C for the requirement of convergence Copyright © 2001 John Wiley & Sons, Ltd.
On time integration of viscoplastic constitutive models suitable for creep
Authors: Schreyer H. L. 
Published: October 2002

AbstractCreep of critical components such as electrical solder connections may occur over long periods of time. Efficient numerical simulations of such problems generally require the use of quasi‐static formulations with conjugate‐gradient techniques for solving the large number of algebraic equations. Implicit in the approach is the need to solve the constitutive equation several times for large time steps and for loading directions that may have no resemblance to the actual solution. Therefore, an unconditionally stable and efficient algorithm for solving the constitutive equation is essential for the overall efficiency of the solution procedure. Unfortunately, constitutive equations suitable for simulating the materials of interest are notoriously difficult to solve numerically and most existing algorithms have a stability limit on the time step which may be several orders of magnitude smaller than the desired time step. Here an algorithm is proposed which is a combination of the use of a trapezoidal rule and an iterative Newton–Raphson method for solving implicitly the non‐linear equations. The key to the success of the proposed approach is to always use an initial guess based on the steady‐state solution to the constitutive equation. A representative viscoplastic constitutive equation is used as a model for illustrating the approach. The algorithm is developed and typical numerical results are provided to substantiate the claim that stability has been achieved. Copyright © 2001 John Wiley & Sons, Ltd.
Variable thermal singularity boundary elements in the study of neighbouring singularities
Authors: Mukhopadhyay N. K. 
Published: October 2002

AbstractTwo new boundary elements are presented for the simulation of variable order thermal singularities in two dimensions. The first can model the variable order temperature derivative and heat flux singularities at one end of the element. The second element can simulate the temperature derivative and heat flux singularities at both the ends of the element simultaneously. These elements are useful for studying the interaction of variable order thermal neighbouring singularities. They are employed here for the computation of stress intensity factors in the crack–crack interaction problems under thermal load. To improve the accuracy of such computations a modified crack closure integral based method is adapted. Examples of mode I and mode II centre crack, two collinear neighbouring cracks, kinked crack in a plate, and tee joint with a kinked edge crack under thermal or thermal and mechanical loading are studied to illustrate the usefulness of these elements in the study of neighbouring thermal singularities. Copyright © 2001 John Wiley & Sons, Ltd.
A hybrid boundary node method
Authors: Zhang Jianming , Yao Zhenhan , Li Hong 
Published: October 2002

AbstractA new variational formulation for boundary node method (BNM) using a hybrid displacement functional is presented here. The formulation is expressed in terms of domain and boundary variables, and the domain variables are interpolated by classical fundamental solution; while the boundary variables are interpolated by moving least squares (MLS). The main idea is to retain the dimensionality advantages of the BNM, and get a truly meshless method, which does not require a ‘boundary element mesh’, either for the purpose of interpolation of the solution variables, or for the integration of the ‘energy’. All integrals can be easily evaluated over regular shaped domains (in general, semi‐sphere in the 3‐D problem) and their boundaries.Numerical examples presented in this paper for the solution of Laplace's equation in 2‐D show that high rates of convergence with mesh refinement are achievable, and the computational results for unknown variables are most accurate. No further integrations are required to compute the unknown variables inside the domain as in the conventional BEM and BNM. Copyright © 2001 John Wiley & Sons, Ltd.
Convergence analysis of a hierarchical enrichment of Dirichlet boundary conditions in a mesh‐free method
Authors: Han Weimin , Wagner Gregory J. , Liu Wing Kam 
Published: October 2002

AbstractImplementation of Dirichlet boundary conditions in mesh‐free methods is problematic. In Wagner and Liu (International Journal for Numerical Methods in Engineering 2001; 50:507), a hierarchical enrichment technique is introduced that allows a simple implementation of the Dirichlet boundary conditions. In this paper, we provide some error analysis for the hierarchical enrichment mesh‐free technique. We derive optimal order error estimates for the hierarchical enrichment mesh‐free interpolants. For one‐dimensional elliptic boundary value problems, we can directly apply the interpolation error estimates to obtain error estimates for the mesh‐free solutions. For higher‐dimensional problems, derivation of error estimates for the mesh‐free solutions depends on the availability of an inverse inequality. Numerical examples in 1D and 2D are included showing the convergence behaviour of mesh‐free interpolants and mesh‐free solutions when the hierarchical enrichment mesh‐free technique is employed. Copyright © 2001 John Wiley & Sons, Ltd.
Speeding up the solution of thermal EHL problems
Authors: Ford Judith M. , Chen Ke 
Published: October 2002

AbstractThis paper considers the fast solution of large, dense linear systems arising from thermal EHL problems.We present an efficient preconditioner for these, based on a novel combination of wavelet compression with the Schur complement. Numerical results illustrate the effectiveness of this approach. Copyright © 2002 John Wiley & Sons, Ltd.
A comparative study of axisymmetric finite elements for the vibration of thin cylindrical shells conveying fluid
Authors: Zhang YongLiang , Reese Jason M. , Gorman Daniel G. 
Published: October 2002

AbstractA comparative study of the relative performance of several different axisymmetric finite elements, when applied to the dynamic problem of thin cylindrical shells conveying fluid, is presented. The methods used are based on (1) the Sanders' theory of thin shells and the potential flow theory, and (2) the theory of elasticity and the Euler equations. The elements studied are: linear, paralinear, parabolic and cubilinear. Extensive comparison with experiment is carried out for the free vibration of cylindrical shells in the absence of, and containing, quiescent and flowing fluid. The analysis of the relative competence of these elements is presented for shell length‐to‐radius ratios 1.95≤L/R≤32, shell radius‐to‐thickness ratios 10≤R/h≤375 and boundary conditions: clamped–clamped, clamped–free and simply supported. We show that natural frequencies of thin cylindrical shells in the absence of, and containing, quiescent and flowing fluid can be assessed accurately when using two‐ and eight‐noded elements, and the latter are also applicable to the dynamic problem of thick cylindrical shells. Copyright © 2002 John Wiley & Sons, Ltd.
An adaptive finite element framework for fatigue crack propagation
Authors: Givoli Dan , Zusman Ron 
Published: October 2002

AbstractA new finite element (FE) framework for fatigue crack propagation (FCP) analysis is proposed. This framework combines the simplicity of standard industrial FCP analysis with the generality and accuracy of a full FE analysis and can be implemented on a small computer by combining standard existing computational tools. In this way it constitutes an attractive alternative to existing approaches. The framework is based on linear elastic fracture mechanics and on FE mesh adaptation. Some novel features are introduced in several of its steps in order to make it efficient and at the same time reasonably accurate. Various computational aspects of the scheme are discussed. A few two‐dimensional numerical examples involving FCP in thin sheets under plane‐stress conditions are presented to demonstrate the performance of the framework. Some of the numerical results are compared to those of laboratory experiments. Copyright © 2002 John Wiley & Sons, Ltd.
Physics‐based preconditioner for iterative algorithms in multi‐scatterer and multi‐boundary method of moments formulations
Authors: Hagen Jürgen v. , Wiesbeck Werner 
Published: October 2002

AbstractAn efficient method to solve electromagnetic scattering problems involving several metallic scatterers or bodies composed of dielectric and metallic regions is proposed. So far, the method of moments has successfully been applied to large arrays of identical scatterers when it was combined with preconditioned iterative algorithms to solve for the linear system of equations. Here, the method is generalized to geometries that are composed of several metallic elements of different shapes and sizes, and also to scatterers that are composed of metallic and dielectric regions. The method uses in its core an iterative algorithm, preferably the transpose‐free quasi‐minimum residual (TFQMR) algorithm, and a block diagonal Jacobi preconditioner. For best performance, the blocks for the preconditioner are chosen according to individual scatterers or groups of scatterers for the array case, and according to the electric and magnetic current basis functions for dielectric/metallic scatterers. The iterative procedure converges quickly for an optimally chosen preconditioner, and is robust even for a non‐optimal preconditioner. Reported run times are compared to run times of an efficiently programmed LU factorization, and are shown to be significantly lower. Copyright © 2002 John Wiley & Sons, Ltd.
Non‐local dispersive model for wave propagation in heterogeneous media: multi‐dimensional case
Authors: Fish Jacob , Chen Wen , Nagai Gakuji 
Published: October 2002

AbstractThree non‐dispersive models in multi‐dimensions have been developed. The first model consists of a leading‐order homogenized equation of motion subjected to the secularity constraints imposing uniform validity of asymptotic expansions. The second, non‐local model, contains a fourth‐order spatial derivative and thus requires C1 continuous finite element formulation. The third model, which is limited to the constant mass density and a macroscopically orthotropic heterogeneous medium, requires C0 continuity only and its finite element formulation is almost identical to the classical local approach with the exception of the mass matrix. The modified mass matrix consists of the classical mass matrix (lumped or consistent) perturbed with a stiffness matrix whose constitutive matrix depends on the unit cell solution. Numerical results are presented to validate the present formulations. Copyright © 2002 John Wiley & Sons, Ltd.
A micro‐mechanical damage model based on gradient plasticity: algorithms and applications
Authors: Chen Jian , Yuan Huang 
Published: October 2002

AbstractAs soon as material failure dominates a deformation process, the material increasingly displays strain softening and the finite element computation is significantly affected by the element size. Without remedying this effect in the constitutive model one cannot hope for a reliable prediction of the ductile material failure process. In the present paper, a micro‐mechanical damage model coupled to gradient‐dependent plasticity theory is presented and its finite element algorithm is discussed. By incorporating the Laplacian of plastic strain into the damage constitutive relationship, the known mesh‐dependence is overcome and computational results are uniquely correlated with the given material parameters. The implicit C1 shape function is used and can be transformed to arbitrary quadrilateral elements. The introduced intrinsic material length parameter is able to predict size effects in material failure. Copyright © 2002 John Wiley & Sons, Ltd.
Behaviour of isoparametric quadrilateral family of Lagrangian fluid finite elements
Authors: Gopalakrishnan S. 
Published: October 2002

AbstractThis paper presents the formulation of both the consistent and inconsistent four‐, eight‐ and nine‐noded isoparametric quadrilateral fluid finite elements that are based on Lagrangian frame of reference. The mesh locking phenomenon due to simultaneous enforcement of twin constraints, namely the incompressibility and irrotationality constraints, is studied in detail. The study shows that the characteristic of the locked fluid elements is that it always generates numerous spurious acoustic (volume change) modes upon the enforcement of rotational constraints. That is, the rotational constraints change the character of certain volume change modes. The study further reinforces the necessity of rotational constraints in not only identifying the spurious pressure modes, but also in reducing the computational effort for determining the eigenvalues and eigenvectors. It is found that all fully integrated inconsistent models exhibit locking behaviour. However, the inconsistent eight‐ and nine‐noded elements, integrated with full integration of volumetric stiffness and one point integration of the rotational stiffness matrices, gives excellent performance, although they do not pass the inf–sup test. The four‐ and nine‐noded consistent models are found to give locking free performance while their eight‐noded counterpart exhibited locking behaviour. The study shows that only consistent nine‐noded element models pass the inf–sup test. The utility of these elements in the coupled fluid–structure interaction problem is also demonstrated. Copyright © 2002 John Wiley & Sons, Ltd.
Topology optimization of periodic microstructures with a penalization of highly localized buckling modes
Authors: Neves Miguel M. , Sigmund Ole , Bendsøe Martin P. 
Published: October 2002

AbstractThe problem of determining highly localized buckling modes in perfectly periodic cellular microstructures of infinite extent is addressed. A double scale asymptotic technique is applied to the linearized stability problem for a periodic structure built from linearly elastic microstructures. The obtained stability condition for the microscale level is then used to establish a comparative analysis between different material distributions in the base cell subjected to the same strain field at the macroscale level. The idea is illustrated by some two‐dimensional finite element examples and used to design materials with optimal elastic properties that are less prone to localized instability in the form of local buckling modes at the scale of the microstructure. Copyright © 2002 John Wiley & Sons, Ltd.
A fictitious domain decomposition method for the solution of partially axisymmetric acoustic scattering problems. Part I: Dirichlet boundary conditions
Authors: Farhat Charbel , Hetmaniuk Ulrich 
Published: October 2002

AbstractWe present a fictitious domain decomposition method for the fast solution of high‐frequency acoustic scattering problems characterized by a partially axisymmetric sound‐soft scatterer. We apply this method to the solution of various mockup submarine problems, and highlight its computational advantages and intrinsic parallelism. Copyright © 2002 John Wiley & Sons, Ltd.
Numerical integration of the stiff dynamics of geometrically exact shells: an energy‐dissipative momentum‐conserving scheme
Authors: Romero I. , Armero F. 
Published: October 2002

AbstractThis paper presents a new family of time‐stepping algorithms for the integration of the dynamics of non‐linear shells. We consider the geometrically exact shell theory involving an inextensible director field (the so‐called five‐parameter shell model). The main characteristic of this model is the presence of the group of finite rotations in the configuration manifold describing the deformation of the solid. In this context, we develop time‐stepping algorithms whose discrete solutions exhibit the same conservation laws of linear and angular momenta as the underlying physical system, and allow the introduction of a controllable non‐negative energy dissipation to handle the high numerical stiffness characteristic of these problems. A series of algorithmic parameters for the different components of the deformation of the shell (i.e. membrane, bending and transverse shear) fully control this numerical dissipation, recovering existing energy‐momentum schemes as a particular choice of these algorithmic parameters. We present rigorous proofs of the numerical properties of the resulting algorithms in the full non‐linear range. Furthermore, it is argued that the numerical dissipation is introduced in the high‐frequency range by considering the proposed algorithm in the context of a linear problem. The finite element implementation of the resulting methods is described in detail as well as considered in the final arguments proving the aforementioned conservation/dissipation properties. We present several representative numerical simulations illustrating the performance of the newly proposed methods. The robustness gained over existing methods in these stiff problems is confirmed in particular. Copyright © 2002 John Wiley & Sons, Ltd.