bluuebunny/crossref_metadata_2025 huggingface dataset:
Dependence of the Raman spectra of drug substances upon laser excitation wavelength
Authors: Thorley Fiona C. , Baldwin Kurt J. , Lee David C. , Batchelder David N.
Published: January 2006

The laser excitation wavelength is an important parameter in obtaining definitive Raman spectra from pharmaceutical drug substances. This paper investigates the effect of changing wavelength on the Raman spectra of four different drug substances: paracetamol, paroxetine and ranitidine (polymorphic forms I and II). Excitation wavelengths in the range 244 nm to 785 nm have been used. The fluorescence intensities in the Raman spectra were found to be negligible at the two extreme laser wavelengths but tended to interfere in the visible range. Resonance Raman enhancement was observed with 244 nm excitation but there was evidence for sample degradation. Furthermore, the site selective nature of the resonance enhancement reduced the differences between the Raman spectra of the two ranitidine polymorphs. Copyright © 2006 John Wiley & Sons, Ltd.
Vibrational and EPR spectroscopic investigation of heavy‐metal‐oxide glasses and vitroceramics containing manganese
Authors: Simon S. , Baia L. , Radu A.
Published: January 2006

Heavy‐metal‐oxide (HMO) glasses and vitroceramics of [3Bi2O3·2PbO] and 20MnO·80[3Bi2O3·2PbO] compositions were investigated by Raman, infrared (IR) and electron paramagnetic resonance (EPR) spectroscopies. Changes in the local structure of the heavy‐metal host glass induced by manganese addition, and those determined by partial crystallisation of samples are seen.

Raman and IR spectroscopies have been employed in order to obtain information on the role of Bi2O3 and PbO in the local structure of the investigated samples and on the effect of MnO on the bismuth and lead environments. EPR results have evidenced the influence of the vitreous 3Bi2O3·2PbO network on Mn2+ ions' environment and the changes in structural relaxation and magnetic interactions caused by sample crystallisation. Copyright © 2006 John Wiley & Sons, Ltd.
Critical Conditions and Limiting Conditions in Liquid Chromatography of Synthetic Polymers
Authors: Berek Dušan
Published: January 2006

Distinctions between liquid chromatography of synthetic polymers under critical conditions (LC CC) and liquid chromatography under limiting conditions (LC LC) are elucidated. Surface adsorption retention mechanism of macromolecules is employed in the chromatographic systems composed of 10 and 30 nm pore diameter bare silica gels, poly (methyl methacrylate)s of different molar masses, and mixed eluents acetonitrile/dichloromethane of different compositions, and at different temperatures. Increased robustness of the LC LC methods compared to LC CC is confirmed: the LC LC elution behavior is much less sensitive to eluent composition changes compared to LC CC. Still, the LC CC system under study is, surprisingly robust in terms of temperature variations. LC LC methods produce narrow, focused polymer peaks while a peak broadening is observed in LC CC. The results demonstrate importance of sample solvent applied in the isocratic coupled polymer HPLC methods.
Cover Picture: Macromol. Symp. 231/2005
Authors: Helbert William , Nyvall‐Collen Pi , Michel Gurvan , Czjzek Mirjam
Published: January 2006

Cover: The figure shows the ribbon and surface representation of the structural model of a beta‐agarase from Z. galactanivorans (coloured in blue) in interaction with an agarose double helix (stick representation, the colour code is yellow for carbon atoms and red for oxygen atoms). The crystal structure of this beta‐agarase in complex with agaro‐octaoses reveals two parallel agarose binding sites, one located in the catalytic groove and a second on the molecular surface. Further details can be found in the article by W. Helbert, P. Nyvall‐Collen, G. Michel, M. Czjzek on page 11.
Painless legs moving toes in a patient with Wilson's disease
Authors: Papapetropoulos Spiridon , Singer Carlos
Published: January 2006

We describe and present a video of a 20‐year‐old woman with Wilson's disease (WD) who developed the painless variant of painful legs and moving toes (PLMT) syndrome. The symptoms appeared during a subsequent minor exacerbation of her extrapyramidal symptomatology, only to gradually disappear 3 to 4 months later. We suggest that, in our case, a structural central nervous system lesion caused by WD may have been associated with the development of PLMT. © 2006 Movement Disorder Society
In vivo detection of single cells by MRI
Authors: Shapiro Erik M. , Sharer Kathryn , Skrtic Stanko , Koretsky Alan P.
Published: January 2006

The use of high‐relaxivity, intracellular contrast agents has enabled MRI monitoring of cell migration through and homing to various tissues, such as brain, spinal cord, heart, and muscle. Here it is shown that MRI can detect single cells in vivo, homing to tissue, following cell labeling and transplantation. Primary mouse hepatocytes were double‐labeled with green fluorescent 1.63‐μm iron oxide particles and red fluorescent endosomal labeling dye, and injected into the spleens of recipient mice. This is a common hepatocyte transplantation paradigm in rodents whereby hepatocytes migrate from the spleen to the liver as single cells. One month later the animals underwent in vivo MRI and punctuated, dark contrast regions were detected scattered through the livers. MRI of perfused, fixed samples and labeled hepatocyte phantoms in combination with histological evaluation confirmed the presence of dispersed single hepatocytes grafted into the livers. Appropriate controls were used to determine whether the observed contrast could have been due to dead cells or free particles, and the results confirmed that the contrast was due to disperse, single cells. Detecting single cells in vivo opens the door to a number of experiments, such as monitoring rare cellular events, assessing the kinetics of stem cell homing, and achieving early detection of metastases. Magn Reson Med, 2006. Published 2006 Wiley‐Liss, Inc.
Influence of SENSE on image properties in high‐resolution single‐shot echo‐planar DTI
Authors: Jaermann T. , Pruessmann K.P. , Valavanis A. , Kollias S. , Boesiger P.
Published: January 2006

Limited spatial resolution is a key obstacle to the study of brain white matter structure with diffusion tensor imaging (DTI). In its frequent implementation with single‐excitation spin‐echo echo‐planar sequences, DTI's ability to resolve small structures is strongly restricted by T2 and T decay, B0 inhomogeneity, and limited signal‐to‐noise ratio (SNR). In this work the influence of sensitivity encoding (SENSE) on diffusion‐weighted (DW) image properties is investigated. Computer simulations showed that the PSF becomes narrower with increasing SENSE reduction factors, R, enhancing the intrinsic resolution. After a brief theoretical discussion, we describe the estimation of SNR on a pixel‐by‐pixel basis as a function of R. The mean image SNR behavior is manifold: SENSE is capable of increasing SNR efficiency by reducing the echo time (TE). Each SNR(R) curve reveals a maximum that depends on the amount of partial Fourier encoding used. The overall best SNR efficiency for an eight‐element head coil array and a b‐factor of 1000 s/mm2 is achieved at R = 2.1 and partial Fourier encoding of 60%. In vivo tensor maps of volunteers and a patient, with an in‐plane resolution of 0.78 × 0.78 mm2, are also presented to demonstrate the practical implementation of the parallel approach. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
2D axial moving table acquisitions with dynamic slice adaptation
Authors: Ludwig Ute , Sommer Gregor , Zaitsev Maxim , Ghanem Nadir , Hennig Jürgen , Fautz Hans‐Peter
Published: January 2006

A method for axial multi‐slice imaging during continuous table motion has been developed and implemented on a clinical scanner. Multiple axial slice packages are acquired consecutively and combined to cover an extended longitudinal FOV. To account for the table motion during the acquisition, the RF pulse frequencies are continuously updated according to the actual table velocity and slice position. Different strategies for the spatial‐temporal acquisition sequence with extended FOV are proposed. They cover different regimes of scan requirements regarding table velocity, used scan range, and slice resolution. The method is easy to implement and compatible with most kinds of sequences. The robustness of the proposed approach has been tested in phantom studies and healthy volunteers using T1‐, T2‐, and STIR‐weighted multi‐slice techniques that are based on gradient and turbo spin echo sequences and compared to a stationary approach usually used in clinical routine. The method provides artifact free gradient echo based images during continuous table motion, while for turbo spin echo sequences limitations in choosing table translations occur due to gradient non‐linearity effects. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Model‐free arterial spin labeling quantification approach for perfusion MRI
Authors: Petersen Esben Thade , Lim Tchoyoson , Golay Xavier
Published: January 2006

In this work a model‐free arterial spin labeling (ASL) quantification approach for measuring cerebral blood flow (CBF) and arterial blood volume (aBV) is proposed. The method is based on the acquisition of a train of multiple images following the labeling scheme. Perfusion is obtained using deconvolution in a manner similar to that of dynamic susceptibility contrast (DSC) MRI. Local arterial input functions (AIFs) can be estimated by subtracting two perfusion‐weighted images acquired with and without crusher gradients, respectively. Furthermore, by knowing the duration of the bolus of tagged arterial blood, one can estimate the aBV on a voxel‐by‐voxel basis. The maximum of the residue function obtained from the deconvolution of the tissue curve by the AIF is a measure of CBF after scaling by the locally estimated aBV. This method provides averaged gray matter (GM) perfusion values of 38 ± 2 ml/min/100 g and aBV of 0.93% ± 0.06%. The average CBF value is 10% smaller than that obtained on the same data set using the standard general kinetic model (42 ± 2 ml/min/100 g). Monte Carlo simulations were performed to compare this new methodology with parametric fitting by the conventional model. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Balanced alternating steady‐state elastography
Authors: Bieri O. , Maderwald S. , Ladd M.E. , Scheffler K.
Published: January 2006

A conventional balanced steady‐state free precession (b‐SSFP) sequence scheme was modified such that the dynamic equilibrium becomes very sensitive to small cyclic displacements, generating two distinct and alternating steady states. This novel technique is proposed for the visualization of propagating transverse acoustic shear waves, as used in MR elastography (MRE) to determine the mechanical properties of materials or in vivo soft tissue. Experiments with tissue‐like agarose gel phantoms and simulations demonstrate that the novel sequence offers an increase in phase sensitivity by about one order in magnitude compared to standard motion‐encoding methods. In addition, the new method benefits from the very short acquisition times achieved by b‐SSFP protocols. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Quantification of prostate MRSI data by model‐based time domain fitting and frequency domain analysis
Authors: Pels Pieter , Ozturk‐Isik Esin , Swanson Mark G. , Vanhamme Leentje , Kurhanewicz John , Nelson Sarah J. , Huffel Sabine Van
Published: January 2006

This paper compares two spectral processing methods for obtaining quantitative measures from in vivo prostate spectra, evaluates their effectiveness, and discusses the necessary modifications for accurate results. A frequency domain analysis (FDA) method based on peak integration was compared with a time domain fitting (TDF) method, a model‐based nonlinear least squares fitting algorithm. The accuracy of both methods at estimating the choline + creatine + polyamines to citrate ratio (CCP:C) was tested using Monte Carlo simulations, empirical phantom MRSI data and in vivo MRSI data. The paper discusses the different approaches employed to achieve the quantification of the overlapping choline, creatine and polyamine resonances. Monte Carlo simulations showed induced biases on the estimated CCP:C ratios. Both methods were successful in identifying tumor tissue, provided that the CCP:C ratio was greater than a given (normal) threshold. Both methods predicted the same voxel condition in 94% of the in vivo voxels (68 out of 72). Both TDF and FDA methods had the ability to identify malignant voxels in an artifact‐free case study using the estimated CCP:C ratio. Comparing the ratios estimated by the TDF and the FDA, the methods predicted the same spectrum type in 17 out of 18 voxels of the in vivo case study (94.4%). Copyright © 2006 John Wiley & Sons, Ltd.
Shape optimization of flow guides in three‐dimensional extrusion processes by an approximation scheme based on state variable linearization
Authors: Lee S. R. , Yang D. Y.
Published: January 2006

A new scheme of shape optimization is applied to the design of a flow guide in flat‐die extrusion processes. In general, tremendous time is inevitably required for the optimization of large‐scale three‐dimensional extrusion processes. This is because the finite element analysis requires large computation time owing to the complexity of the die geometry and flow behaviour. The proposed scheme effectively reduces the computation time for the optimization process by approximating the objective function. This is achieved by introducing a transformed equation of the state variables. The scheme is then applied to the practical extrusion processes to produce ‘l’, ‘H’ and ‘L’ sections. The objective of the optimization is to make a balanced flow of the material in the exit region. Control points of a Bezier curve describing the outline of the flow guide are regarded as the design variables. Through application to large‐scale problems, the effectiveness and usefulness of the proposed scheme is demonstrated. Copyright © 2005 John Wiley & Sons, Ltd.
Derivation of 3D masonry properties using numerical homogenization technique
Authors: Wu Chengqing , Hao Hong
Published: January 2006

Lots of research work has been conducted on homogenization technique, which derives global homogenized properties of masonry from the behaviour of the constitutive materials (brick and mortar). Such a technique mainly focused on two‐dimensional media in the previous studies with the out‐of‐plane properties of masonry material neglected. In this paper, homogenization technique and damage mechanics theory are used to model a three‐dimensional masonry basic cell to numerically derive the equivalent elastic properties, strength envelope, and failure characteristics of masonry material. The basic cell is modelled with distinctive consideration of non‐linear material properties of mortar and brick. Various displacement boundaries are applied on the basic cell surfaces in the numerical simulation. The detailed material properties of mortar and brick are modelled in a finite element program in the numerical analysis. The stress–strain relations of masonry material under various conditions are obtained from the simulation. The homogenized elastic properties and failure characteristics of masonry material are derived from the simulation results. The homogenized 3D model is then utilized to analyse the response of a masonry panel to airblast loads. The same panel is also analysed with distinctive material modelling. The efficiency and accuracy of the homogenized model are demonstrated. The homogenized material properties and failure model can be used to model large‐scale masonry structure response. Copyright © 2006 John Wiley & Sons, Ltd.
Algorithms by design with illustrations to solid and structural mechanics/dynamics
Authors: Zhou X. , Tamma K. K.
Published: January 2006

A novel procedure, concepts, and new ideas to tailor and design time operators under the notion of algorithms by design is formulated in this exposition with emphasis on applications to the broad area of computational mechanics, but with focus on solid and structural mechanics/dynamics as an illustration. The algorithms by design concepts capitalize upon: (i) the recently developed unified theory underlying computational algorithms (Int. J. Numer. Meth. Engng 2004; 59:597–668), and (ii) newly established design spaces and algorithmic measures for evaluating the quality of computational algorithms (Int. J. Numer. Meth. Engng 2005; 64:1841–1870). As a step in the forward direction, in this exposition we embark upon some challenging tasks with the objective to advance, tailor, and foster the design of computational algorithms for time‐dependent problems with desired and/or improved algorithmic attributes in the sense of accuracy, stability and other characteristics including algorithmic complexity in a well educated manner. The design process for computational algorithms is explained in the sense of the algorithms by design concepts via selected numerical illustrations of practical scenarios encountered in solid and structural mechanics/dynamics applications. Copyright © 2006 John Wiley & Sons, Ltd.
Discrete crack modelling of ductile fracture driven by non‐local softening plasticity
Authors: Mediavilla J. , Peerlings R. H. J. , Geers M. G. D.
Published: January 2006

A combined approach towards ductile damage and fracture is presented, in the sense that a continuous material degradation is coupled with a discrete crack description for large deformations. Material degradation is modelled by a gradient enhanced damage‐hyperelastoplasticity model. It is assumed that failure occurs solely due to plastic straining, which is particularly relevant for shear dominated problems, where the effect of the hydrostatic stress in triggering failure is less important. The gradient enhancement eliminates pathological localization effects which would normally result from the damage influence. Discrete cracks appear in the final stage of local material failure, when the damage has become critical. The rate and the direction of crack propagation depend on the evolution of the damage field variable, which in turn depends on the type of loading. In a large strain finite element framework, remeshing allows to incorporate the changing crack geometry and prevents severe element distortion. Attention is focused on the robustness of the computations, where the transfer of variables, which is needed after each remeshing, plays a crucial role. Numerical examples are shown and comparisons are made with published experimental results. Copyright © 2005 John Wiley & Sons, Ltd.
Free‐surface and admittivity estimation in electrical impedance tomography
Authors: Tossavainen O.‐P. , Kolehmainen V. , Vauhkonen M.
Published: January 2006

In 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

Design 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

Based 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

The 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

The 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

A 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

The 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

A 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

This 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

The ‘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

A 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

In 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

A 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

Purpose

The 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.

Methods

The study consisted of 221 fetuses and neonates collected from the literature and from personal files.

Results

Langerhans' 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.

Conclusions

This 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

To 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

All 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

The 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

Both 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.
Enhancement of natural disease resistance in potatoes by chemicals
Authors: Andreu Adriana B , Guevara María G , Wolski Erika A , Daleo Gustavo R , Caldiz Daniel O
Published: January 2006

The mechanism involved in systemic acquired resistance (SAR) can be non‐specifically induced in susceptible plants. In response to pathogens, plants' natural defence mechanisms include the production of lignin and phytoalexins and the induction of plant enzymes. The aim of this research was to study the induction of SAR mediated by the chemical activator DL‐3‐aminobutyric acid (BABA) and the fungicide fosetyl‐aluminium in potato cultivars with different levels of resistance against Phytophthora infestans (Mont) de Bary. To study the chemical induction of the resistance, the foliage of several potato cultivars was sprayed with BABA, fosetyl‐aluminium or water (as a control treatment). After 3 days the foliage was inoculated with P. infestans. Seven days after inoculation, development of disease symptoms in the foliage was assessed. In postharvest tuber samples, evidence for enhancement of the defence response was evaluated by measuring the protein content of several hydrolytic enzymes as well as the phenol and phytoalexin content. The highest level of protection against late blight was observed when the chemicals were applied at early stages of crop development. An increase in resistance to late blight was also detected in tubers after harvest. There was also an increase in the protein level of β‐1,3‐glucanase and aspartic protease as well as in the phenol and phytoalexin content of potato tuber discs obtained from postharvest tubers of treated plants. Thus the protective effect seemed to persist throughout the whole crop cycle. This treatment may offer the possibility of controlling both foliage and tuber blight and could have a major impact in reducing over‐winter survival of P. infestans in tubers. Copyright © 2006 Society of Chemical Industry
Effect of Bacillus thuringiensis subsp. israelensis and neonicotinoid insecticides on the fungus gnat Bradysia sp nr. coprophila (Lintner) (Diptera: Sciaridae)
Authors: Cloyd Raymond A , Dickinson Amy
Published: January 2006

The soil bacterium Bacillus thuringiensis Berliner subsp. israelensis (Bti), the neonicotinoid insecticides dinotefuran, imidacloprid, thiamethoxam and clothianidin and the insect growth regulator pyriproxyfen were evaluated to determine their efficacy against the larval stages of the fungus gnat Bradysia sp nr. coprophila (Lintner) in the laboratory. Treatments were applied as a drench to the growing medium in polypropylene deli containers. The Bti treatments had no effect on either instar tested, whereas all the other compounds negatively affected both the second and third instars. This study demonstrates that the soil bacterium B. thuringiensis var. israelensis may not be active on these larval stages, whereas the neonicotinoid insecticides and the insect growth regulator pyriproxyfen are effective on these stages. The fact that Bti is not effective on the second and third instars of the fungus gnat means that greenhouse producers using this insecticide must make applications before fungus gnat populations build up and before overlapping generations develop. Copyright © 2006 Society of Chemical Industry
Prediction of intergranular strains using a modified self‐consistent elastoplastic approach
Authors: Gloaguen David , Berchi Tarek , Girard Emmanuel , Guillén Ronald
Published: January 2006

A novel approach is adopted to describe the plasticity evolution and determine the active deformation systems with an elastoplastic self‐consistent approach. A modified formulation of the crystal behaviour is proposed. This model is tested by simulating the development of intergranular strains during uniaxial tension of MONEL‐400 as well as commercial purity aluminium. Neutron diffraction measurements of the elastic strains are used as a reference. The results show the relevance of the model for fcc polycrystals. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Anisotropic superparamagnetic states of an isolated ferromagnetic nanoparticle with uniaxial single‐ion anisotropy
Authors: Kokorina E. E. , Medvedev M. V.
Published: January 2006

A molecular field approximation which takes into account both the thermal Brownian rotation of the total magnetic moment of a ferromagnetic nanoparticle and thermal deviations of atomic magnetic moments from the direction of the total magnetic moment has been elaborated. It has been shown by the example of an uniaxial single‐ion anisotropy of the second order that the different types of anisotropic superparamagnetic states can arise in such a nanoparticle depending on relationship between the anisotropy parameter (D > 0 or D < 0) and the intraparticle ferromagnetic exchange one (I > 0). In particular, for the case of a relatively weak anisotropy the ellipsoidal superparamagnetic state, as it is called, appears when the vector of the total magnetic moments moves during its Brownian rotation over the surface of prolated (at D > 0 – the easy‐axis anisotropy) or oblated (at D < 0 – the easy‐plane anisotropy) ellipsoid of rotation. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Co2MnSi as full Heusler alloy ferromagnetic electrode in magnetic tunneling junctions
Authors: Reiss G. , Hütten A. , Kämmerer S. , Schmalhorst J.
Published: January 2006

The discoveries of antiferromagnetic coupling in Fe/Cr multilayers by Grünberg, the Giant MagnetoResistance by Fert and Grünberg and a large tunneling magnetoresistance at room temperature by Moodera have triggered enormous research on magnetic thin films and magnetoelectronic devices. Large opportunities are especially opened by the spin dependent tunneling resistance, where a strong dependence of the tunneling current on an external magnetic field can be found. In order to obtain large magnetoresistance effects, materials with strongly spin polarized electron gas around the Fermi level have to be found. New materials with potentially 100% spin polarization will be discussed using the example of the full Heusler compound Co2MnSi. First, experimental aspects of the integration of this alloy in magnetic tunneling junctions will be addressed. With these junctions, we obtain up to 100% TMR at low temperature. The current status of this research will then be summarized with special regard to the complex diffusion mechanisms occurring in these devices and to the properties of the interfaces between the Heusler material and the insulator. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)