bluuebunny/crossref_metadata_2025_split huggingface dataset:
Construction of shape functions for theh‐ andp‐versions of the FEM using tensorial product
Authors: Bittencourt M. L. , Vazquez M. G. , Vazquez T. G. 
Published: December 2006

AbstractThis paper presents an uniform and unified approach to constructh‐ andp‐shape functions for quadrilaterals, triangles, hexahedral and tetrahedral based on the tensorial product of one‐dimensional Lagrange and Jacobi polynomials. The approach uses indices to denote the one‐dimensional polynomials in each tensorization direction. The appropriate manipulation of the indices allows to obtain hierarchical or non‐hierarchical and inter‐elementC0continuous or non‐continuous bases. For the one‐dimensional elements, quadrilaterals, triangles and hexahedral, the optimal weights of the Jacobi polynomials are determined, the sparsity profiles of the local mass and stiffness matrices plotted and the condition numbers calculated. A brief discussion of the use of sum factorization and computational implementation is considered. Copyright © 2006 John Wiley & Sons, Ltd.
Closed‐form minimax time‐delay filters for underdamped systems
Authors: Singh Tarunraj , Muenchhof Marco 
Published: December 2006

AbstractThis paper derives closed‐form solutions for the parameters of a time‐delay filter designed to be robust to uncertainties in frequencies to be cancelled. It is shown that the slope of the magnitude plot of the two time‐delay filter is zero at the nominal frequency indicating that it is a local maximum. This information is used for deriving the solution of the parameters of the time‐delay filter in closed form. Three time‐delay filters are also designed which force a zero of the filter to be located at the nominal frequency of the system. Uniform and non‐uniform distributions of the penalty over the uncertain regions are permitted in this formulation. The applicability of the proposed technique for the control of multi‐mode systems is also illustrated. Copyright © 2006 John Wiley & Sons, Ltd.
Approximate solutions to convex optimization problems under stochastic uncertainty
Authors: Dabbene Fabrizio , Calafiore Giuseppe 
Published: December 2006

AbstractIn this paper, we survey two standard philosophies for finding minimizing solutions of convex objective functions affected by uncertainty. In a first approach, the solution should minimize the expected value of the objective w.r.t. uncertainty (average approach), while in a second one it should minimize the worst‐case objective (worst‐case, or min‐max approach). Both approaches are however numerically hard to solve exactly, for general dependence of the cost function on the uncertain data. Here, a brief account is given on two techniques based on uncertainty randomization that permit to solve efficiently some suitable probabilistic relaxation of the indicated problems, with full generality with respect to the way in which the uncertainty enters the problem data. A specific application to uncertain least‐squares problems is examined. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Mountain Pass and its Applications
Authors: Horák Jiří , Lord Gabriel J. , Peletier Mark A. 
Published: December 2006

AbstractThe mountain pass theorem is an important tool in the calculus of variations and in finding solutions to nonlinear PDEs in general. The mountain pass structure can be exploited numerically, as well. We explain the main ideas on an example of buckling of a cylindrical shell. First, we prove existence of an MP‐solution for almost all values of a given load parameter. Then, we find a numerical approximation of such a solution. Finally, we compare the results of a numerical continuation in the load parameter with results of physical experiments and make a few comments about further numerical investigations of the problem. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cell membranes, Lipid Bilayers, and the Elastica Functional
Authors: Röger Matthias , Peletier Mark A. 
Published: December 2006

AbstractWe study an energy functional that arises in a simplified two‐dimensional model for lipid bilayer membranes. We demonstrate that this functional, defined on a class of spatial mass densities, favours concentrations on ‘thin structures’. Stretching, fracture and bending of such structures all carry an energy penalty. In this sense we show that the models captures essential features of lipid bilayers, namely partial localisation and a solid‐like behaviour.Our findings are made precise in a Gamma‐convergence result. We prove that a rescaled version of the energy functional converges in the ‘zero thickness limit’ to a functional that is defined on a class of planar curves. Finiteness of the limit value enforces both optimal thickness and non‐fracture; if these conditions are met, then the value of this functional is given by the classical Elastica (bending) energy. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Constraint Preserving, Inexact Solution of Implicit Discretizations of Landau–Lifshitz–Gilbert Equations and Consequences for Convergence
Authors: Bartels Sören 
Published: December 2006

AbstractThe Landau‐Lifshitz‐Gilbert equation describes dynamics of ferromagnetism. Nonlinearity of the equation and a non‐convex side constraint make it difficult to design reliable approximation schemes. In this paper, we discuss the numerical solution of nonlinear systems of equations resulting from implicit, unconditionally convergent discretizations of the problem. Numerical experiments indicate that finite‐time blow‐up of weak solutions can occur and thereby underline the necessity of the design of reliable discretization schemes that approximate weak solutions. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coupling 3D and 1D fluid‐structure interaction models for blood flow simulations
Authors: Formaggia L. , Moura A. , Nobile F. 
Published: December 2006

AbstractThree‐dimensional (3D) simulations of blood flow in medium to large vessels are now a common practice. These models consist of the 3D Navier‐Stokes equations for incompressible Newtonian fluids coupled with a model for the vessel wall structure. However, it is still computationally unaffordable to simulate very large sections, let alone the whole, of the human circulatory system with fully 3D fluid‐structure interaction models. Thus truncated 3D regions have to be considered.Reduced models, one‐dimensional (1D) or zero‐dimensional (0D), can be used to approximate the remaining parts of the cardiovascular system at a low computational cost. These models have a lower level of accuracy, since they describe the evolution of averaged quantities, nevertheless they provide useful information which can be fed to the more complex model. More precisely, the 1D models describe the wave propagation nature of blood flow and coupled with the 3D models can act also as absorbing boundary conditions.We consider in this work the coupling of a 3D fluid‐structure interaction model with a 1D hyperbolic model. We study the stability of the coupling and present some numerical results. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Remarks on Duality in Graph Spaces of First‐Order Linear Operators
Authors: Jensen Max 
Published: December 2006

AbstractGraph spaces provide a setting alternative to Sobolev spaces and BV spaces, which is suitable for the analysis of first‐order linear boundary value problems such as Friedrichs systems. Besides investigations of the well‐posedness of the continuous problem there is also an increasing interest in the error analysis of finite element methods within a graph space framework. In this text we elucidate various methods for an explicit representation of dual spaces of graph spaces. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Wavelet‐based Adaptive Grids for the Simulation of Multirate Partial Differential‐Algebraic Equations
Authors: Bartel Andreas , Knorr Stephanie 
Published: December 2006

AbstractWe present an adaptive method to solve biperiodic problems in chip design with widely separated time scales and steep gradients due to digital‐like signal structures. Motivated from the example of the switched capacitor filter, we explain the multidimensional signal model and the transformation of network equations to the hyperbolic multirate differential‐algebraic system. Then adapted hat‐wavelets are introduced to detect the steep gradients. In this way, an adaptive grid is defined for the efficient application of a finite difference method to solve the limit cycle problem. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Quadratic Eigenproblem in the Analysis of a Time Delay System
Authors: Jarlebring Elias 
Published: December 2006

AbstractIn this work we solve a quadratic eigenvalue problem occurring in a method to compute the set of delays of a linear time delay system (TDS) such that the system has an imaginary eigenvalue. The computationally dominating part of the method is to find all eigenvalues z of modulus one of the quadratic eigenvalue problem
equation image
where φ 1, …, φ m –1 ∈ ℝ are free parameters and u a vectorization of a Hermitian rank one matrix.Because of its origin in the vectorization of a Lyapunov type matrix equation, the quadratic eigenvalue problem is, even for moderate size problems, of very large size. We show one way to treat this problem by exploiting the Lyapunov type structure of the quadratic eigenvalue problem when constructing an iterative solver. More precisely, we show that the shift‐invert operation for the companion form of the quadratic eigenvalue problem can be efficiently computed by solving a Sylvester equation. The usefulness of this exploitation is demonstrated with an example. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structured Condition Numbers of Multiple Eigenvalues
Authors: José Peláez María , Moro Julio 
Published: December 2006

AbstractWe analyze the influence of matrix structure on the condition number of multiple, possibly defective eigenvalues. We show that the structured and unstructured Hölder condition numbers coincide for multiple eigenvalues of matrices belonging to certain classes of structured matrices, which can be characterized as either Jordan or Lie Algebras. We do this by explicitly finding a specific perturbation matrix, analogous to the classical Wilkinson perturbation, which attains the maximal variation within the class of structured matrices. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micromechanics‐Supported Conversion of Computer Tomographic (CT) Images into Anisotropic and Inhomogeneous Finite Element Models of Organs: the Case of a Human Mandible
Authors: Hellmich Christian , Kober Cornelia 
Published: December 2006

AbstractWe here present a strategy for reliable prediction of elastic properties from X‐ray attenuation coefficients visualized in Computer Tomographic images, as basis for Finite Element models. By example, we show the distribution of the axial normal stress throughout a human mandible, due to a bite on the leftmost premolar. Remarkably, this distribution is not heavily altered if we replace the inhomogeneous material distribution by one discerning merely cortical and trabecular bone, but it is strongly affected by the consideration of material anisotropy. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Homogenization approach to the multi‐compartment model of perfusion
Authors: Rohan Eduard 
Published: December 2006

AbstractThe paper deals with modelling of the coupled diffusion‐deformation processes in biological tissues with potential applications in describing the blood perfusion, or fluid filtration phenomena in general. The micromodel to be homogenized is based on the Biot type model for the incompressible medium. Due to the strong heterogeneity in the permeability coefficients associated with three compartments of the representative microstructural cell (RMC), the homogenization of the model leads to the double diffusion phenomena. The resulting homogenized equations, involving the stress‐equilibrium equation and other two equations governing the mass redistribution, describe the parallel diffusion in two high‐conducting compartments (arterial and venous sectors) separated by the low conducting matrix which represents the perfused tissue. To obtain the homogenized model, the method of two scale convergence is applied. The homogenized coefficients are defined in terms of the characteristic response of the RMC. It is possible to identify the instantaneous and fading memory viscoelastic coefficients; other effective parameters, controlling the fluid redistribution between the compartments, are involved also in time convolutions. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Prediction of diffusion length in multicrystalline silicon solar cells from trapping images on starting material
Authors: Schubert Martin C. , Warta Wilhelm 
Published: December 2006

AbstractAreas with high crystal defect density are known to have a strong impact on the performance of silicon solar cells. Trapping has been reported to be correlated with crystal defects. We compare spatially resolved measurements of the trapping effect on unprocessed wafers with diffusion length measurements on solar cells. An excellent correlation is found between these two measurements. This allows a prediction of diffusion length for the processed solar cell directly from the trap image, for a given cell process and comparable material. This technique has thus a great potential for inline process control of starting material in solar cell production. Copyright © 2006 John Wiley & Sons, Ltd.
Synthesis and properties of novel poly(arylene ether)s and poly(arylene thioether)s based on a pyridazine biphenol or a phthalazine biphenol
Authors: Xu J. , Meng Y. Z. , Wang S. J. , Hay A. S. 
Published: December 2006

AbstractNovel sulfur‐containing biphenol monomers were prepared in high yields by the reaction of 4‐mercaptophenol with chloropyridazine or chlorophthalazine compounds. High‐molecular‐weight poly(arylene ether)s were synthesized by a nucleophilic substitution reaction between these sulfur‐containing monomers and activated difluoro aromatic compounds. The inherent viscosities of these polymers ranged from 0.34 to 0.93 dL/g. The poly(pyridazine)s exhibited glass‐transition temperatures greater than 165 °C. The poly(phthalazine)s showed higher glass‐transition temperatures than the poly(pyridazine)s. A polymer synthesized from a bisphthalazinebiphenol and bis(4‐fluorophenyl)sulfone had the highest glass‐transition temperature (240 °C). The thermal stabilities of the poly(pyridazine)s and poly(phthalazine)s showed similar patterns of decomposition, with no significant weight loss below 390 °C. The poly(phthalazine)s were soluble in chlorinated solvents such as chloroform, and the poly(pyridazine)s were soluble in dipolar aprotic solvents such as N,N′‐dimethylacetamide. The soluble poly(pyridazine)s and poly(phthalazine)s could be cast into flexible films from solution. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 262–268, 2007
Luminescent copolyethers containing isolated 1,4‐distyrylbenzene derivatives backbone and 7‐oxy‐4‐methylcoumarin side group: Synthesis and characterization
Authors: Tsai Cheng‐Jang , Yeh Kun‐Ming , Chen Yun 
Published: December 2006

AbstractFour new copolyethers (P1–P4) consisting of two isolated emitting chromophores [2,5‐dihexyloxy‐1,4‐distyrylbenzene (HODSB) and 2,5‐dihexyloxy‐1,4‐di(4‐methylenestyryl)benzene (HOMDSB) for P1 and P2, 2,5‐dihexyl‐1,4‐distyrylbenzene (HDSB) and HOMDSB for P3 and P4] in the backbone, in which P2 and P4 further contain electron‐transporting chromophores [7‐oxy‐4‐methylcoumarin (OMC)] in the side chain, were successfully prepared by the Heck coupling reaction. The photoluminescence spectra and quantum yields of the copolymers depended mainly on compositions of the isolated fluorophores. Their highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels were estimated from their cyclic voltammograms. Electrochemical investigations proved that the oxidation started at hole‐transporting DSB segments, whereas reduction began at electron‐transporting OMC groups in P2 and P4. The electron affinity of P2 and P4 was enhanced by introducing electron‐transporting OMC chromophores. Double‐layer light‐emitting diodes (ITO/PEDOT:PSS/polymer/Al) of P1 and P2 revealed green electroluminescence, and those of P3 and P4 emitted blue light. Moreover, incorporation of OMC side groups effectively reduced turn‐on electric field and enhanced luminance efficiency of the EL devices due to increased electron affinity. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 211–221, 2007
Phase separation and polymer crystallization in a poly(4‐methyl‐1‐pentene)–dioctylsebacate–dimethylphthalate system via thermally induced phase separation
Authors: Tao Haijun , Zhang Jun , Wang Xiaolin , Gao Jiali 
Published: December 2006

AbstractThe effects of the polymer concentration and quenching temperature on the phase separation, the membrane morphology and polymer crystallization behavior in a poly(4‐methyl‐1‐pentene) (TPX)‐dioctylsebacate (DOS)‐dimethylphthalate (DMP) system via thermally induced phase separation were studied with a pseudobinary phase diagram, with the weight ratio of DOS:DMP = 1:1. SEM was used to observe the membrane morphology and structure, whereas the TPX crystallization behavior was studied with DSC and WAXD. Liquid‐liquid phase separation occurred, although quenching under the crystallization temperature. As the quenching temperature decreased, the pore size decreased, with better connected pore structure formed. The membranes quenched at 333 and 363 K showed good cellular structures, with an average pore size of about 2.3μm, whereas the pores of the membranes quenched at 393 and 423 K were not well formed, with some lamellar crystals on the inner side. The diluent assisted the mobility of the polymer chain, which improved the polymer crystallization. Dual‐melting‐peak behavior occurred for all the samples studied here. As the quenching temperature increased, the first peak of the melting trace moved to a higher temperature, whereas the second one stayed almost the same. The flexibility of the TPX main chain was restricted by the side groups, which allowed liquid‐liquid phase separation to occur first when quenched below the equilibrium crystallization temperature. This allowed primary and secondary crystallization, which was responsible for the dual‐melting‐peak behavior. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 153–161, 2007
Antiinflammatory activity of ethanol extracts of Hypericum perforatum L., H. barbatum Jacq., H. hirsutum L., H. richeri Vill. and H. androsaemum L. in rats
Authors: Šavikin Katarina , Dobrić Silva , Tadić Vanja , Zdunić Gordana 
Published: December 2006

AbstractEthanol extracts of the aerial parts of six Hypericum species, H. barbatum, H. androsaemum, H. richerii, H. hirsutum, H. perforatum and H. perforatum cultivated on mountain Tara were tested for antiinflammatory activity in comparison with indomethacin (IND) using the carrageenan‐induced rat paw edema test. It was found that all examined extracts produced antiinflammatory activity, particularly those from H. hirsutum, and both wild and cultivated H. perforatum. A dose‐dependent antiinflammatory effect was especially pronounced in extracts showing some lower antiinflammatory activity. There was no correlation between the amount of hypericin in the extracts and their antiinflammatory activity. Copyright © 2006 John Wiley & Sons, Ltd.
NKCC1 activity modulates formation of functional inhibitory synapses in cultured neocortical neurons
Authors: Nakanishi Keiko , Yamada Junko , Takayama Chitoshi , Oohira Atsuhiko , Fukuda Atsuo 
Published: December 2006

AbstractIntracellular Cl− concentration ([Cl−]i) in immature neurons is higher than that expected for a passive distribution, therefore the equilibrium potential for chloride is more positive than the resting membrane potential, and the resulting GABA renders immature neurons depolarization. The higher [Cl−]i in immature neurons is thought to be attributed to the uptake of Cl− mediated by NKCC1 (Na+, K+‐2Cl− cotransporter). Thus, a dysfunction of this transporter could affect synaptic development through a GABAA receptor‐mediated pathway. To test this possibility, we examined the effects of a Cl−‐uptake inhibitor on the development of synaptic activities of rat neocortical neurons in culture. Chronic treatment with bumetanide at 10 μM during the culture diminished the amplitude of synaptically‐driven rhythmic depolarizing potentials (RDPs) in neurons and also decreased the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) but not of spontaneous excitatory postsynaptic currents (sEPSCs). Chronic treatment with bumetanide decreased vesicular GABA transporter (VGAT)‐immunopositive particles without affecting paired‐pulse ratio of evoked IPSCs (eIPSCs), indicating decrease in the number of functional GABAergic synapses. Acute treatment with bumetanide (10 μM) decreased neuronal [Cl−]i, the amplitude of RDPs, and neuronal excitability, while bumetanide had no effect on RDPs and neuronal excitability in the presence of bicuculline. These results suggest that the uptake of Cl− by NKCC1 affects the development of inhibitory synapses by promoting a depolarizing GABA‐mediated response. Synapse 61:138–149, 2007. © 2006 Wiley‐Liss, Inc.
Acute sublethal global hypoxia induces transient increase of GAP‐43 immunoreactivity in the striatum of neonatal rats
Authors: Valdez Susana R. , Patterson Sean I. , Ezquer Marcelo E. , Torrecilla Mariana , Lama M. Cristina , Seltzer Alicia M. 
Published: December 2006

AbstractWe assessed immunoreactivity (IR) in the cerebral cortex (CC), hippocampus (Hipp), and striatum (ST) of a growth‐associated protein, GAP‐43, and of proteins of the synaptic vesicle fusion complex: VAMP‐2, Syntaxin‐1, and SNAP‐25 (SNARE proteins) throughout postnatal development of rats after submitting the animals to acute global postnatal hypoxia (6.5% O2, 70 min) at postnatal day 4 (PND4). In the CC only the IR of the SNARE protein SNAP‐25 increased significantly with age. The hypoxic animals showed the same pattern of IR for SNAP‐25, although with lower levels at PND11, and also a significant increase of VAMP‐2. SNAP‐25 (control): PND11 P < 0.001 vs. PND18, 25, and 40, SNAP‐25 (hypoxic): P < 0.001 vs. PND18, 25, and 40; VAMP‐2 (hypoxic): P < 0.05 PND11 vs. PND18, and P < 0.01 vs. PND25 and PND40; one‐way ANOVA and Bonferroni post‐test. In the Hipp, SNAP‐25 and syntaxin‐1 increased significantly with age, reaching a plateau at PND25 through PND40 in control animals (one‐way ANOVA: syntaxin‐1: P = 0.043; Bonferroni: NS; SNAP‐25: P = 0.013; Bonferroni: P < 0.01 PND11 vs. PND40). Hypoxic rats showed higher levels of significance in the one‐way ANOVA than controls (syntaxin‐1: P = 0.009; Bonferroni: P < 0.05 PND11 vs. PND25 and P < 0.001 PND11 vs. PND40). In the ST, GAP‐43 differed significantly among hypoxic and control animals and the two‐way ANOVA revealed significant differences with age (F = 3.23; P = 0.037) and treatment (F = 4.84; P = 0.036). VAMP‐2 expression also reached statistical significance when comparing control and treated animals (F = 6.25, P = 0.018) without changes regarding to age. Elevated plus maze test performed at PND40 indicated a lower level of anxiety in the hypoxic animals. At adulthood (12 weeks) learning, memory and locomotor abilities were identical in both groups of animals. With these results, we demonstrate that proteins of the presynaptic structures of the ST are sensitive to acute disruption of homeostatic conditions, such as a temporary decrease of the O2 concentration. Modifications in the activity of these proteins could contribute to the long term altered responses to stress due to acute hypoxic insult in the neonatal period. Synapse 61:124–137, 2007. © 2006 Wiley‐Liss, Inc.