bluuebunny/crossref_metadata_2025_split huggingface dataset:
Primal–dual Newton interior point methods in shape and topology optimization
Authors: Hoppe R. H. W. , Petrova S. I. 
Published: May 2004

AbstractWe consider non‐linear minimization problems with both equality and inequality constraints on the state variables and design parameters as they typically arise in shape and topology optimization. In particular, the state variables are subject to a partial differential equation or systems of partial differential equations describing the operating behaviour of the device or system to be optimized. For the numerical solution of the appropriately discretized problems we emphasize the use of all‐in‐one approaches where the numerical solution of the discretized state equations is an integral part of the optimization routine. Such an approach is given by primal–dual Newton interior point methods which we present combined with a suitable steplength selection and a watchdog strategy for convergence monitoring. As applications, we deal with the topology optimization of electric drives for high power electromotors and with the shape optimization of biotemplated microcellular biomorphic ceramics based on homogenization modelling. Copyright © 2004 John Wiley & Sons, Ltd.
Interior‐point method for non‐linear non‐convex optimization
Authors: Lukšan Ladislav , Matonoha Ctirad , Vlček Jan 
Published: May 2004

AbstractIn this paper, we propose an algorithm for solving non‐linear non‐convex programming problems, which is based on the interior point approach. Main theoretical results concern direction determination and step‐length selection. We split inequality constraints into active and inactive to overcome problems with stability. Inactive constraints are eliminated directly while active constraints are used to define symmetric indefinite linear system. Inexact solution of this system is obtained iteratively using indefinitely preconditioned conjugate gradient method. Theorems confirming efficiency of several indefinite preconditioners are proved. Furthermore, new merit function is defined, which includes effect of possible regularization. This regularization can be used to overcome problems with near linear dependence of active constraints. The algorithm was implemented in the interactive system for universal functional optimization UFO. Results of extensive numerical experiments are reported. Copyright © 2004 John Wiley & Sons, Ltd.
Scalable FETI with optimal dual penalty for a variational inequality
Authors: Dostál Zdeněk , Horák David 
Published: May 2004

AbstractThe FETI method with the natural coarse grid is combined with the penalty method to develop an efficient solver for elliptic variational inequalities. A proof is given that a prescribed bound on the norm of feasibility of solution may be achieved with a value of the penalty parameter that does not depend on the discretization parameter and that an approximate solution with the prescribed bound on violation of the Karush–Kuhn–Tucker conditions may be found in a number of steps that does not depend on the discretization parameter. Results of numerical experiments with parallel solution of a model problem discretized by up to more than eight million of nodal variables are in agreement with the theory and demonstrate numerically both optimality of the penalty and scalability of the algorithm presented. Copyright © 2004 John Wiley & Sons, Ltd.
Fourier two‐level analysis for discontinuous Galerkin discretization with linear elements
Authors: Hemker P. W. , Hoffmann W. , van Raalte M. H. 
Published: May 2004

AbstractIn this paper we study the convergence of a multigrid method for the solution of a linear second‐order elliptic equation, discretized by discontinuous Galerkin (DG) methods, and we give a detailed analysis of the convergence for different block‐relaxation strategies. To complement an earlier paper where higher‐order methods were studied, here we restrict ourselves to methods using piecewise linear approximations. It is well known that these methods are unstable if no additional interior penalty is applied.As for the higher‐order methods, we find that point‐wise block‐relaxations give much better results than the classical cell‐wise relaxations. Both for the Baumann–Oden and for the symmetric DG method, with a sufficient interior penalty, the block‐relaxation methods studied (Jacobi, Gauss–Seidel and symmetric Gauss–Seidel) all make excellent smoothing procedures in a classical multigrid setting. Independent of the mesh size, simple MG cycles give convergence factors 0.2–0.4 per iteration sweep for the different discretizations studied. Copyright © 2004 John Wiley & Sons, Ltd.
A preconditioner for the equations of linear elasticity discretized by the PEERS element
Authors: Klawonn Axel , Starke Gerhard 
Published: May 2004

AbstractBlock diagonal preconditioners for the mixed finite element formulation of planar linear elasticity using the PEERS element by Arnold et al. (Jpn. J. Ind. Appl. Math. 1984; 1:347–367) are studied. This mixed finite element approach treats the stress tensor, the displacement field and the anti‐symmetric part of the strain tensor as independent variables. The resulting linear system of equations is symmetric but indefinite due to its saddle‐point structure. The validity of an inf–sup condition with respect to the H (div,Ω)2 × L2(Ω)2 × L2(Ω) norm suggests an optimal block diagonal preconditioner for the MINRES iterative method. Equivalent preconditioning of the blocks associated with stresses, displacements and anti‐symmetric part leads to convergence rates of the block diagonal preconditioner uniformly bounded with respect to the refinement level and the Lamé parameter λ which determines the compressibility of the material. While the L2(Ω) blocks can simply be preconditioned by its diagonal parts, a multilevel technique is employed for the H(div,Ω) block. The smoothing iteration for this technique is based on the discrete Helmholtz decomposition of the underlying finite element space similar to the approach by Hiptmair (Electron. Trans. Numer. Anal. 1997; 6:133–152). Numerical tests for a benchmark problem of planar linear elasticity illustrate the efficiency of this preconditioner, in particular, its level independence and uniform convergence in the incompressible limit. Copyright © 2004 John Wiley & Sons, Ltd.
Eigenvalue analysis of the SIMPLE preconditioning for incompressible flow
Authors: Li C. , Vuik C. 
Published: May 2004

AbstractIn this paper, an eigenvalue analysis of the SIMPLE preconditioning for incompressible flow is presented. Some formulations have been set up to characterize the spectrum of the preconditioned matrix. This leads to a generalized eigenvalue problem. The generalized eigenvalue problem is investigated. Some eigenvalue bounds and the estimation for the spectral condition number in the symmetric case are given. Numerical tests are reported to illustrate the theoretical discussions. Copyright © 2004 John Wiley & Sons, Ltd.
Truncated Newton type solver with application to grid untangling problem
Authors: Garanzha V. , Kaporin I. , Konshin I. 
Published: May 2004

AbstractA practical stopping criterion for inner conjugate gradient iterations in the truncated Newton type unconstrained optimization method is proposed. Numerical results are given for a family of large‐scale geometrical optimization problems. The comparison with the standard residual norm stopping rule demonstrates an essential gain in efficiency. Copyright © 2004 John Wiley & Sons, Ltd.
Generalizations to discrete and analytical Crouzeix–Velte decompositions
Authors: Stoyan G. , Strauber G. , Baran Á. 
Published: May 2004

AbstractIn this paper, the Crouzeix–Velte decomposition is generalized with respect to boundary conditions and boundary value problems, moreover, in the discrete case, the gap between the first‐order staggered grid approximation and the high‐order Scott–Vogelius elements (which was the only finite element family until now for which such a decomposition was known) is filled by proving that the (second‐order) Fortin–Soulie elements also admit such a decomposition—which is of advantage when iteratively solving the corresponding boundary value problems (Stokes, linear elasticity) and for long‐term calculations. Copyright © 2004 John Wiley & Sons, Ltd.
On the computation of the multivariate structured total least squares estimator
Authors: Markovsky Ivan , Huffel Sabine Van , Kukush Alexander 
Published: May 2004

AbstractA multivariate structured total least squares problem is considered, in which the extended data matrix is partitioned into blocks and each of the blocks is Toeplitz/Hankel structured, unstructured, or noise free. Two types of numerical solution methods for this problem are proposed: (i) standard local optimization methods in combination with efficient evaluation of the cost function and its first derivative, and (ii) an iterative procedure proposed originally for the element‐wise weighted total least squares problem. The computational efficiency of the proposed methods is compared with this of alternative methods. Copyright © 2004 John Wiley & Sons, Ltd.
Structured weighted low rank approximation
Authors: Schuermans M. , Lemmerling P. , Van Huffel S. 
Published: May 2004

AbstractThis paper extends the weighted low rank approximation (WLRA) approach towards linearly structured matrices. In the case of Hankel matrices an equivalent unconstrained optimization problem is derived and an algorithm for solving it is proposed. The correctness of the latter algorithm is verified on a benchmark problem. Finally the statistical accuracy and numerical efficiency of the proposed algorithm is compared with that of STLNB, a previously proposed algorithm for solving Hankel WLRA problems. Copyright © 2004 John Wiley & Sons, Ltd.
Variational principles in grid generation and geometric modelling: theoretical justifications and open problems
Authors: Garanzha V. A. 
Published: May 2004

AbstractThe paper is devoted to analysis of variational principles for construction of mappings with prescribed properties in grid generation and geometric modelling. An attempt is made to formulate general requirements which should be satisfied by the variational principle. Theoretical justification is considered along with review of unsolved problems and fundamental mathematical difficulties. Copyright © 2004 John Wiley & Sons, Ltd.
Generalized polynomial chaos and random oscillators
Authors: Lucor D. , Su C.‐H. , Karniadakis G. E. 
Published: May 2004

AbstractWe present a new approach to obtain solutions for general random oscillators using a broad class of polynomial chaos expansions, which are more efficient than the classical Wiener–Hermite expansions. The approach is general but here we present results for linear oscillators only with random forcing or random coefficients. In this context, we are able to obtain relatively sharp error estimates in the representation of the stochastic input as well as the solution. We have also performed computational comparisons with Monte Carlo simulations which show that the new approach can be orders of magnitude faster, especially for compact distributions. Copyright © 2004 John Wiley & Sons, Ltd.
Anisotropic mesh adaption by metric‐driven optimization
Authors: Bottasso Carlo L. 
Published: May 2004

AbstractWe describe a Gauss–Seidel algorithm for optimizing a three‐dimensional unstructured grid so as to conform to a given metric. The objective function for the optimization process is based on the maximum value of an elemental residual measuring the distance of any simplex in the grid to the local target metric. We analyse different possible choices for the objective function, and we highlight their relative merits and deficiencies. Alternative strategies for conducting the optimization are compared and contrasted in terms of resulting grid quality and computational costs. Numerical simulations are used for demonstrating the features of the proposed methodology, and for studying some of its characteristics. Copyright © 2004 John Wiley & Sons, Ltd.
Adaptive embedded unstructured grid methods
Authors: Löhner Rainald , Baum Joseph D. , Mestreau Eric , Sharov Dmitri , Charman Charles , Pelessone Daniele 
Published: May 2004

AbstractA simple embedded domain method for node‐based unstructured grid solvers is presented. The key modification of the original, edge‐based solver is to remove all geometry‐parameters (essentially the normals) belonging to edges cut by embedded surface faces. Several techniques to improve the treatment of boundary points close to the immersed surfaces are explored. Alternatively, higher‐order boundary conditions are achieved by duplicating crossed edges and their endpoints. Adaptive mesh refinement based on proximity to or the curvature of the embedded CSD surfaces is used to enhance the accuracy of the solution. User‐defined or automatic deactivation for the regions inside immersed solid bodies is employed to avoid unnecessary work. Several examples are included that show the viability of this approach for inviscid and viscous, compressible and incompressible, steady and unsteady flows, as well as coupled fluid–structure problems. Copyright © 2004 John Wiley & Sons, Ltd.
Prediction of stress–strain relation using cone indentation: effect of friction
Authors: DiCarlo Anthony , Yang Henry T. Y. , Chandrasekar Srinivasan 
Published: May 2004

AbstractAtkins and Tabor's approach (J. Mech. Phys. Solids 1965; 13: 149) for predicting uniaxial stress–strain relation of metals from cone indentation tests has been studied using numerical (finite element) simulation of cone indentation. Two indentation parameters, namely representative strain and constraint factor, which are central to the prediction approach, have been estimated using the simulation for cone indenters of different apical angles. The effect of specimen–indenter interface friction on these parameters has been characterized. It is shown that uncertainty in our knowledge of this friction condition has an important bearing on the prediction of the stress–strain curve. However, a good estimate of the stress–strain curve can be obtained by making reasonable assumptions about the nature of the friction at the specimen–indenter interface. The simulation results are found to agree well with those reported in the experimental study of Atkins and Tabor, when a coefficient of friction value typical for the specimen–indenter interface is used. Copyright © 2004 John Wiley & Sons, Ltd.
Geometry independence for a meshing engine for 2D manifolds
Authors: Simpson R. B. 
Published: May 2004

AbstractThe ‘meshing engine’ of the title is a software component that generates unstructured triangular meshes of two‐dimensional triangles for a variety of contexts. The mesh generation is based on the well‐known technique of iterative Delaunay refinement, for which the Euclidean metric is intrinsic. The meshing engine is to be connected to applications specific host programs which can use a geometry that is different from the intrinsic geometry of the mesh, i.e. locally, the Euclidean plane. An application may require a surface mesh for embedding in a three‐dimensional geometry, or it might use a Riemannian metric to specify a required anisotropy in the mesh, or both.We focus on how the meshing engine can be designed to be independent of the embedding geometry of a host program but conveniently linked to it. A crucial tool for these goals is the use of an appropriate local co‐ordinate system for the triangles as seen by the meshing engine. We refer to it as the longest edge co‐ordinate system. Our reference to ‘linking’ the meshing engine and host system is both general and technical in the sense that the example meshes provided in the paper have all been generated by the same object code of a prototype of such a meshing engine linked to host programs defining different embedding geometries. Copyright © 2004 John Wiley & Sons, Ltd.
Free vibrations of solid and hollow wedge beams with rectangular or circular cross‐sections and carrying any number of point masses
Authors: Wu Jong‐Shyong , Chiang Lieh‐Kwang 
Published: May 2004

AbstractSince the literature relating to the natural frequencies and mode shapes of the double‐tapered wedge beams carrying multiple point masses is rare, the object of this paper is to present some information in this aspect. First of all, the closed‐form solutions in terms of the Bessel functions for the natural frequencies and normal mode shapes of the ‘bare’ wedge beams (without carrying any point masses) were determined. Next, the partial differential equation of motion for the ‘loading’ wedge beams (carrying any number of point masses) were transformed into the matrix equation by using the expansion theorem and the foregoing natural frequencies and normal mode shapes of the ‘bare’ wedge beam. Finally, the eigenvalue equation associated with the last matrix equation was solved to give the natural frequencies and the mode shapes of the ‘loading’ wedge beams. The formulation of this paper is available for the solid and hollow wedge beams with square, rectangular or circular cross sections. In other words, the taper ratio for the width and that for the depth may be equal or unequal. All the numerical results were compared with the existing literature or the conventional finite element method results and good agreement was achieved. Copyright © 2004 John Wiley & Sons, Ltd.
Expression of Fhit, cell adhesion molecules and matrix metalloproteinases in atypical adenomatous hyperplasia and pulmonary adenocarcinoma
Authors: Kerr Keith M , MacKenzie Suzi J , Ramasami Sharmini , Murray Graeme I , Fyfe Nicky , Chapman Andrea D , Nicolson Marianne C , King George 
Published: May 2004

AbstractInvasive parenchymal‐type lung adenocarcinoma develops from atypical adenomatous hyperplasia (AAH), through an intermediate in situ stage of bronchioloalveolar carcinoma (BAC). We examined the expression of the putative tumour suppressor gene product Fhit, cell adhesion molecules CD44v6, E‐cadherin and β‐catenin, and matrix metalloproteinase 2 and its inhibitor, TIMP‐2, in a range of AAH lesions, BACs and invasive adenocarcinomas, to determine the changes in molecular expression associated with this form of neoplastic progression. Sections of formalin‐fixed wax‐embedded archival tissue were stained by standard Immunohistochemical techniques and scored semi‐quantitatively, resulting in a grading of negative/low‐ or high‐level staining. Fhit protein was retained at high levels in over 90% of AAH and 83% of BAC, but was found in only 6% of stromally invasive tumours (p < 0.0001). CD44v6 staining was high‐level in 64% of AAH but fell to 26% in stromally invasive tumour (p = 0.007). E‐cadherin and β‐catenin showed the opposite, with more high‐level staining as adenocarcinoma developed (p < 0.001). High‐level MMP‐2 and TIMP‐2 expression was relatively infrequent in AAH (32% and 40% respectively), rose in BAC (89% each) but fell in stromally invasive tumour (31% and 17% respectively) (p < 0.01). Unlike in central bronchial carcinogenesis, loss of Fhit expression is a relatively late event in this putative progression of lung adenocarcinogenesis, and has potential as a surrogate marker of invasion, which could be of value in screening patients for lung cancer. Loss of CD44v6 expression follows the convention of falling adhesion molecule expression as malignancy develops. Increased expression of E‐cadherin and β‐catenin may reflect increased cell–cell contact as tissue architecture changes in the transition from AAH to adenocarcinoma. Loss of MMP‐2 and TIMP‐2 in stromally invasive tumour may reflect a particular role for MMP‐2 at the BAC stage, with later down‐regulation of this particular enzyme. Copyright © 2004 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Vascular endothelial growth factor (VEGF)‐A and platelet‐derived growth factor (PDGF) play a central role in the pathogenesis of digital clubbing
Authors: Atkinson Stephen , Fox Stephen B 
Published: May 2004

AbstractDigital clubbing is associated with many unrelated serious diseases but its pathogenesis remains a clinical enigma. It has been hypothesized that platelet clusters impacting in the distal vasculature mediate the morphological changes of clubbing. Since the multifunctional cytokines vascular endothelial growth factor (VEGF) and platelet‐derived growth factor (PDGF) are released on platelet aggregation and are hypoxically regulated, the present study has examined their role in clubbing using immunohistochemistry. Basic fibroblast growth factor (bFGF), transforming growth factor‐beta 1 (TGF‐β1), microvessel density, carbonic anhydrase IX (CAIX), hypoxia inducible factor (HIF)‐1α, and HIF‐2α were also measured. There was a significant increase in VEGF (p = 0.01), pKDR (p = 0.03), PDGF (p = 0.017), and HIF‐1α and HIF‐2α (p = 0.004 and p = 0.004, respectively) expression together with a significant increase in microvessel density (p = 0.03) in the stroma in clubbed digits compared with controls. There was no difference in CAIX (p = 0.25), TGF‐β1 (p = 0.66) or bFGF (p = 0.18) between affected and control groups. These findings suggest that VEGF and PDGF are released after platelet impaction and that their expression is hypoxically enhanced in the stroma after capillary occlusion. VEGF may synergize with PDGF in inducing the stromal and vascular changes present in digital clubbing. Copyright © 2004 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Apparent activation energy of degradation of poly[acrylonitrile‐co‐(N‐vinylpyrrolidone)]
Authors: Chen Hou , Wang Cheng‐guo , Cai Hua‐su , Cui Chuan‐sheng 
Published: May 2004

AbstractDifferential scanning calorimetry results of the degradation of poly[acrylonitrile‐co‐(N‐vinylpyrrolidone)] in air are presented. The apparent activation energy of degradation was calculated using Kissinger's method. The effect of copolymerization conditions on the apparent activation energy was studied. Increasing the dimethylformamide concentration in the solvent mixture led to a rapid increase in the degradation apparent activation energy. The apparent activation energy decreased rapidly with increase in the comononer N‐vinylpyrrolidone concentration, and this change becomes less prominent as the weight ratio of N‐vinylpyrrolidone/acrylonitrile rises above 5/95. The apparent activation energy also increases with increasing copolymerization temperature. Copyright © 2004 Society of Chemical Industry
Ozonation of unstretched natural rubber film from Hevea brasiliensis studied by ozone consumption and 13C NMR
Authors: Rodrigues FHA , Santos EF , Feitosa JPA , Ricardo NMPS , Heatley F 
Published: May 2004

AbstractUnstretched films of natural rubber (NR) from Hevea brasiliensis were exposed to ozone flow of 15 ml min−1 from 4 to 300 min. The efficiency of reaction was determined by ozone consumption of NR films. Plots of reacted ozone mass versus film thickness show that the ozone penetration and the ozone reaction progressed into deeper layers (170 µm) than described in the literature (∼0.5 µm). The previous proposed model based on viscometry measurements was corroborated by ozone consumption results. The effect of thickness on the O3/NR stoichiometric ratio indicated that the diffusion process that controls the ozonation in unstretched film does not consist of the boundary progression behind which all reactive sites have been saturated. Ozonation in unstretched rubber film, while being less efficient than ozonolysis in solution, does have a reaction efficiency of the same order of magnitude. NMR spectroscopy was used to characterise the products formed by ozonation. Copyright © 2004 Society of Chemical Industry