bluuebunny/crossref_metadata_2025_split huggingface dataset:
Free‐surface and admittivity estimation in electrical impedance tomography
Authors: Tossavainen O.‐P. , Kolehmainen V. , Vauhkonen M. 
Published: January 2006

AbstractIn electrical impedance tomography (EIT) currents are applied through an array of electrodes attached on the surface of the object and the resulting voltages are measured using the same electrodes. Based on these voltage measurements an estimate for the internal admittivity distribution is computed. The reconstruction is usually made in a fixed pixel grid. However, if it is known that the object consists of a few separate subregions of different materials with constant admittivity values one can employ shape estimation methods. In this study, we propose a novel shape estimation method for the recovery of a free‐surface which is an open interface between two regions of unknown admittivities. The motivation for the method stems from the industrial process tomography applications of EIT. We are especially interested in the estimation of free‐surface between air and conductive liquid in industrial process pipelines, and in addition, in the estimation of free‐surface between oil and water. The proposed method is tested with computer simulations. From the simulations a promising performance of the approach can be seen. Copyright © 2005 John Wiley & Sons, Ltd.
Evolutionary topology optimization using design space adjustment based on fixed grid
Authors: Jang In Gwun , Kwak Byung Man 
Published: January 2006

AbstractDesign space optimization for topology based on fixed grid is proposed and its superiority to conventional topology optimization is shown. In the conventional topology optimization, the design domain is fixed. It is, however, desirable to make the design domain evolve into a better one during optimization process by increasing or decreasing the number of design pixels or variables, which we call design space optimization. A breakthrough in obtaining sensitivities when design space expands has been made recently with necessary mathematical background, but due to coupling effect and others, sensitivity results have not been satisfactory. Three innovative implementations are developed in this paper. Firstly, the proper characteristics of artificial material are defined. The second one is to decouple neighbouring elements for exact design space sensitivities. The previous design space optimization has been tedious because only one layer can be added. So, the third innovation is a new expansion strategy with multi‐layers based on design space sensitivities. As a result, the proposed evolutionary method can get an optimum much faster than ever before especially for large‐scale problems. It is also conjectured that this gives higher probability of getting the global optimum, as confirmed by numerical examples. Copyright © 2005 John Wiley & Sons, Ltd.
Eigensolution reanalysis of modified structures using epsilon‐algorithm
Authors: Chen Su Huan , Wu Xiao Ming , Yang Zhi Jun 
Published: January 2006

AbstractBased on the Neumann series expansion and epsilon‐algorithm, a new eigensolution reanalysis method is developed. In the solution process, the basis vectors can be obtained using the matrix perturbation or the Neumann series expansion to construct the vector sequence, and then using the epsilon algorithm table to obtain the approximate eigenvectors. The approximate eigenvalues are computed from the Rayleigh quotients. The solution steps are straightforward and it is easy to implement with the general finite element analysis system. Two numerical examples, a 40‐storey frame and a chassis structure, are given to demonstrate the application of the present method. By comparing with the exact solutions and the Kirsch method solutions, it is shown that the excellent results are obtained for very large changes in the design, and that the accuracy of the epsilon‐algorithm is higher than that of the Kirsch method and the computation time is less than that of the Kirsch method. Copyright © 2005 John Wiley & Sons, Ltd.
Galerkin boundary integral analysis for the axisymmetric Laplace equation
Authors: Gray L. J. , Garzon Maria , Mantič Vladislav , Graciani Enrique 
Published: January 2006

AbstractThe boundary integral equation for the axisymmetric Laplace equation is solved by employing modified Galerkin weight functions. The alternative weights smooth out the singularity of the Green's function at the symmetry axis, and restore symmetry to the formulation. As a consequence, special treatment of the axis equations is avoided, and a symmetric‐Galerkin formulation would be possible. For the singular integration, the integrals containing a logarithmic singularity are converted to a non‐singular form and evaluated partially analytically and partially numerically. The modified weight functions, together with a boundary limit definition, also result in a simple algorithm for the post‐processing of the surface gradient. Published in 2005 by John Wiley & Sons, Ltd.
A front remeshing technique for a Lagrangian description of moving interfaces in two‐fluid flows
Authors: Cruchaga Marcela , Celentano Diego , Breitkopf Piotr , Villon Pierre , Rassineux Alain 
Published: January 2006

AbstractThe numerical analysis of two‐fluid flows involves the treatment of a discontinuity that appears at the separating interface. Classical Lagrangian schemes applied to update the front position between two immiscible incompressible fluids have been long recognized to provide a sharp representation of the interface. However, the main drawback of these approaches is the progressive distortion in the distribution of the markers used to identify the material front. To avoid this problem, an interface remeshing algorithm based on the diffuse approximation of the interface curvature is proposed in this work. In addition, the remeshed front is enforced to preserve the global volume. These new aspects are incorporated in an existing fluid dynamics formulation for the analysis of two‐fluid flows problems. The resulting formulation is called in this work as the moving Lagrangian interface remeshing technique (MLIRT). Copyright © 2005 John Wiley & Sons, Ltd.
Truncation error in mesh‐free particle methods
Authors: Quinlan N. J. , Basa M. , Lastiwka M. 
Published: January 2006

AbstractA truncation error analysis has been developed for the approximation of spatial derivatives in smoothed particle hydrodynamics (SPH) and related first‐order consistent methods such as the first‐order form of the reproducing kernel particle method. Error is shown to depend on both the smoothing length h and the ratio of particle spacing to smoothing length, Δx/h. For uniformly spaced particles in one dimension, analysis shows that as h is reduced while maintaining constant Δx/h, error decays as h2 until a limiting discretization error is reached, which is independent of h. If Δx/h is reduced while maintaining constant h (i.e. if the number of neighbours per particle is increased), error decreases at a rate which depends on the kernel function's smoothness. When particles are distributed non‐uniformly, error can grow as h is reduced with constant Δx/h. First‐order consistent methods are shown to remove this divergent behaviour. Numerical experiments confirm the theoretical analysis for one dimension, and indicate that the main results are also true in three dimensions. This investigation highlights the complexity of error behaviour in SPH, and shows that the roles of both h and Δx/h must be considered when choosing particle distributions and smoothing lengths. Copyright © 2005 John Wiley & Sons, Ltd.
The discontinuous enrichment method for elastic wave propagation in the medium‐frequency regime
Authors: Zhang Lin , Tezaur Radek , Farhat Charbel 
Published: January 2006

AbstractThe discontinuous enrichment method (DEM) is specified and developed for the solution of two‐dimensional elastic wave propagation problems in the frequency domain. The classical finite element polynomial approximation of the displacement field is enriched by the superposition of discontinuous pressure and shear wave functions. The continuity of the solution across the element interfaces is weakly enforced by suitable Lagrange multipliers. Higher‐order rectangular DEM elements are constructed and benchmarked against the standard higher‐order polynomial Galerkin elements for two‐dimensional problems in the medium frequency regime. In general, it is found that for such applications, DEM can achieve the same accuracy as the p finite element method using a similar computational complexity but with about 10 times fewer degrees of freedom. This highlights the potential of this hybrid method for problems where the scale of vibrations is very small compared to the characteristic dimension of the physical medium. Copyright © 2006 John Wiley & Sons, Ltd.
A mathematical homogenization perspective of virial stress
Authors: Chen Wen , Fish Jacob 
Published: January 2006

AbstractA continuum stress measure is derived from molecular dynamics equations using a generalized mathematical homogenization (GMH) theory. GMH consists of solving a coupled fine‐scale (atomistic unit cell) problem and a coarse‐scale (continuum) problem. The fine‐scale problem derived can be interpreted as a molecular statics (at 0 K) problem, where the coarse‐scale problem derived is a constitutive law‐free continuum equation, which calculates the Cauchy stress directly from atomistics. The continuum stress derived is compared to various versions of the virial stress formula. Copyright © 2005 John Wiley & Sons, Ltd.
Performance of fully coupled algebraic multilevel domain decomposition preconditioners for incompressible flow and transport
Authors: Lin Paul T. , Sala Marzio , Shadid John N. , Tuminaro Ray S. 
Published: January 2006

AbstractThis study investigates algebraic multilevel domain decomposition preconditioners of the Schwarz type for solving linear systems associated with Newton–Krylov methods. The key component of the preconditioner is a coarse approximation based on algebraic multigrid ideas to approximate the global behaviour of the linear system. The algebraic multilevel preconditioner is based on an aggressive coarsening graph partitioning of the non‐zero block structure of the Jacobian matrix. The scalability of the preconditioner is presented as well as comparisons with a two‐level Schwarz preconditioner using a geometric coarse grid operator. These comparisons are obtained on large‐scale distributed‐memory parallel machines for systems arising from incompressible flow and transport using a stabilized finite element formulation. The results demonstrate the influence of the smoothers and coarse level solvers for a set of 3D example problems. For preconditioners with more than one level, careful attention needs to be given to the balance of robustness and convergence rate for the smoothers and the cost of applying these methods. For properly chosen parameters, the two‐ and three‐level preconditioners are demonstrated to be scalable to 1024 processors. Copyright © 2006 John Wiley & Sons, Ltd.
A three‐dimensional finite element method with arbitrary polyhedral elements
Authors: Rashid M. M. , Selimotic M. 
Published: January 2006

AbstractThe ‘variable‐element‐topology finite element method’ (VETFEM) is a finite‐element‐like Galerkin approximation method in which the elements may take arbitrary polyhedral form. A complete development of the VETFEM is given here for both two and three dimensions. A kinematic enhancement of the displacement‐based formulation is also given, which effectively treats the case of near‐incompressibility. Convergence of the method is discussed and then illustrated by way of a 2D problem in elastostatics. Also, the VETFEM's performance is compared to that of the conventional FEM with eight‐node hex elements in a 3D finite‐deformation elastic–plastic problem. The main attraction of the new method is its freedom from the strict rules of construction of conventional finite element meshes, making automatic mesh generation on complex domains a significantly simpler matter. Copyright © 2006 John Wiley & Sons, Ltd.
A generalized space–time mathematical homogenization theory for bridging atomistic and continuum scales
Authors: Chen Wen , Fish Jacob 
Published: January 2006

AbstractA generalized space–time mathematical homogenization theory, which constructs an equivalent continuum description directly from molecular dynamics (MD) equations, is developed. The noteworthy theoretical findings of this work are: (i) the coarse‐scale continuum equations (PDEs) obtained from the homogenization of MD equations are identical to those obtained from the classical homogenization of the fine‐scale continuum, (ii) the lower order effective continuum properties (such as the fourth‐order elasticity tensor) have similar characteristics to those resulting from the homogenization of fine‐scale continuum, (iii) the higher order effective properties, such as polarization and dispersion tensors, substantially differ from those of continuum due to the discreteness effect. (Both the heterogeneous continuum and discrete media possess the size effect, but only atomistic medium has the discreteness effect.) Some demonstrative numerical examples are presented to verify the formulation. Copyright © 2005 John Wiley & Sons, Ltd.
An optimal weighted upwinding covolume method on non‐standard grids for convection–diffusion problems in 2D
Authors: Liang Dong , Zhao Weidong 
Published: January 2006

AbstractIn this paper we develop an optimal weighted upwinding covolume method on non‐standard covolume grids for convection–diffusion problems in two dimensions. The novel feature of our method is that we construct the non‐standard covolume grid in which the nodes of covolumes vary in the interior of different volumes of primary grid depending on the local weighted factors and further on the local Peclet's numbers. A simple method of finding the local optimal weighted factors is also derived from a non‐linear function of local Peclet's numbers. The developed method leads to a totally new scheme for convection–diffusion problems, which overcomes numerical oscillation, avoids numerical dispersion, and has high‐order accuracy. Some theoretical analyses are given and numerical experiments are presented to illustrate the performance of the method. Copyright © 2006 John Wiley & Sons, Ltd.
Nonconforming finite element methods with subgrid viscosity applied to advection‐diffusion‐reaction equations
Authors: El Alaoui Linda , Ern Alexandre 
Published: January 2006

AbstractA nonconforming (Crouzeix–Raviart) finite element method with subgrid viscosity is analyzed to approximate advection‐diffusion‐reaction equations. The error estimates are quasi‐optimal in the sense that keeping the Péclet number fixed, the estimates are suboptimal of order
${1\over 2}$
in the mesh size for the L2‐norm and optimal for the advective derivative on quasi‐uniform meshes. The method is also reformulated as a finite volume box scheme providing a reconstruction formula for the diffusive flux with local conservation properties. Numerical results are presented to illustrate the error analysis. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2006
Fetal and neonatal histiocytoses
Authors: Isaacs Hart 
Published: January 2006

AbstractPurposeThe histiocytoses are a group of disorders of the monophagocytic system having a variety of clinical and pathological findings. They occur less often during the perinatal period than later in life. Their biologic behavior, response to therapy, and histologic types are not the same.MethodsThe study consisted of 221 fetuses and neonates collected from the literature and from personal files.ResultsLangerhans' cell histiocytosis (LCH), the hemophagocytic lymphohistiocytoses (HLH), and juvenile xanthogranuloma (JXG), in order of rank, were the main histiocytoses occurring in the perinatal period. HLH accounted for the highest mortality (74%) followed by disseminated LCH (52%) and JXG (11%). All neonates with LCH and JXG limited to the skin and/or subcutaneous tissue survived with or without treatment.ConclusionsThis study suggests that there is an increased incidence of spontaneous regression of certain histiocytic lesions in neonates as compared to older individuals. Cutaneous forms JXG and LCH had the highest incidence of regression followed by infection associated HLH. Pediatr Blood Cancer. © 2006 Wiley‐Liss, Inc.
Chain microstructure of homogeneous ethylene‐1‐alkene copolymers and characteristics of single site catalysts using a direct 13C NMR peak method I. Theory and models
Authors: Karssenberg F. G. , Mathot V. B. F. , Zwartkruis T. J. G. 
Published: January 2006

AbstractTo describe the detailed microstructure of homogeneous ethylene‐1‐alkene copolymer chains and to study the characteristics of single site catalysts, Markov statistics are used to fit peak intensities of all relevant 13C NMR signals of series of copolymers. In the case of the occurrence of inverted comonomer units, a first‐order Markov terpolymer is applied, otherwise a second‐order Markov copolymer model. Chain propagation probabilities are obtained via modeling of the entire NMR spectrum. This procedure results in an accurate reproduction of the chain microstructure, including ethylene, 1‐alkene, and methylene sequence length distributions. If the experimental (co)monomer feeds are known, the reactivity ratios and the theoretical (co)monomer feeds are also found providing information about the copolymerization kinetics and the characteristics of the catalyst. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 722–737, 2006
Chain microstructure of homogeneous ethylene‐1‐alkene copolymers and characteristics of single site catalysts using a direct 13C NMR peak method. Part II. Application to ethylene–propylene copolymers showing inversion
Authors: Karssenberg F. G. , Mathot V. B. F. 
Published: January 2006

AbstractAll relevant 13C NMR signals of a series of 19 homogeneous ethylene–propylene copolymers were used to fit the first‐order Markov reactivity ratios of the catalyst and the theoretical feeds. The copolymers cover a broad range of comonomer incorporations, from 17.0 to 56.5%, and show both primary (1,2) and secondary (2,1) insertions. As expected, two solutions are found, the normal solution showing a better fit and reliability > 99.5%. The reactivity ratios, r12 = 20.0, r13 = 162.0, r21 = 0.015, r23 = 1.3, and r31 = 0.060, provide direct information about the vanadium‐based catalyst, the kinetics, and the chain microstructure. The values also explain the comonomer content‐dependent inversion and even predict a 100% secondary insertion PP homopolymer. With these results, the direct peak method shows that the use of all relevant 13C NMR peaks improves the accuracy of first‐order Markov modeling. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 738–746, 2006
Folding with downhill behavior and low cooperativity of proteins
Authors: Zuo Guanghong , Wang Jun , Wang Wei 
Published: January 2006

AbstractThe downhill folding observed experimentally for a small protein BBL is studied using off‐lattice Gō‐like model. Our simulations show that the downhill folding has low cooperativity and is barrierless, which is consistent with the experimental findings. As an example of comparison in detail, the two‐state folding behavior of proteins, for example, protein CI2, is also simulated. By observing the formation of contacts between the residues for these two proteins, it is found that the physical origin of the downhill folding is due to the deficiency of nonlocal contacts which determine the folding cooperatively. From a statistics on contacts of the native structures of 17 well‐studied proteins and the calculation of their cooperativity factors κ2 based on folding simulations, a strong correlation between the number of nonlocal contacts per residue NN and the factors κ2 is obtained. Protein BBL with a value of NN = 0.73 has the lowest cooperativity factor κ2 = 0.34 among all 17 proteins. A crossover around N ∼ 0.9 could be defined to separate the two‐state folders and the downhill folder roughly. A protein would behave downhill folding when its NN = N. For proteins with their NN values are about (or slightly larger than) N, the folding behaves with low cooperativity and the barriers are small, showing a weak two‐state behavior or a downhill‐like behavior. Furthermore, simulations on mutants of a two‐state folder show that a mutant becomes a downhill folder when its NN is reduced to a value smaller than N. These could enable us to identify the downhill folding or the cooperative two‐state folding behavior solely from the native structures of proteins. Proteins 2006. © 2006 Wiley‐Liss, Inc.
Substrate‐free structure of a monomeric NADP isocitrate dehydrogenase: An open conformation phylogenetic relationship of isocitrate dehydrogenase
Authors: Imabayashi Fumie , Aich Sanjukta , Prasad Lata , Delbaere Louis T. J. 
Published: January 2006

AbstractBoth monomeric and dimeric NADP+‐dependent isocitrate dehydrogenase (IDH) belong to the metal‐dependent β‐decarboxylating dehydrogenase family and catalyze the oxidative decarboxylation from 2R,3S‐isocitrate to yield 2‐oxoglutarate, CO2, and NADPH. It is important to solve the structures of IDHs from various species to correlate with its function and evolutionary significance. So far, only two crystal structures of substrate/cofactor‐bound (isocitrate/NADP) NADP+‐dependent monomeric IDH from Azotobacter vinelandii (AvIDH) have been solved. Herein, we report for the first time the substrate/cofactor‐free structure of a monomeric NADP+‐dependent IDH from Corynebacterium glutamicum (CgIDH) in the presence of Mg2+. The 1.75 Å structure of CgIDH‐Mg2+ showed a distinct open conformation in contrast to the closed conformation of AvIDH‐isocitrate/NADP+ complexes. Fluorescence studies on CgIDH in the presence of isocitrate/or NADP+ suggest the presence of low energy barrier conformers. In CgIDH, the amino acid residues corresponding to the Escherichia coli IDH phosphorylation‐loop are α‐helical compared with the more flexible random‐coil region in the E. coli protein where IDH activation is controlled by phosphorylation. This more structured region supports the idea that activation of CgIDH is not controlled by phosphorylation. Monomeric NADP+‐specific IDHs have been identified from about 50 different bacterial species, such as proteobacteria, actinobacteria, and planctomycetes, whereas, dimeric NADP+‐dependent IDHs are diversified in both prokaryotes and eukaryotes. We have constructed a phylogenetic tree based on amino acid sequences of all bacterial monomeric NADP+‐dependent IDHs and also another one with specifically chosen species which either contains both monomeric and dimeric NADP+‐dependent IDHs or have monomeric NADP+‐dependent, as well as NAD+‐dependent IDHs. This is done to examine evolutionary relationships. Proteins 2006. © 2006 Wiley‐Liss, Inc.