bluuebunny/crossref_metadata_2025 huggingface dataset:
Diversity and fluctuation of spine morphology in CA1 pyramidal neurons after transient global ischemia
Authors: Ruan Yi‐Wen , Lei Zhigang , Fan Yuan , Zou Bende , Xu Zao C.
Published: August 2008

Dendritic spines form postsynaptic components of excitatory synapses in CA1 pyramidal neurons and play a key role in excitatory signal transmission. Transient global ischemia is thought to induce excitotoxicity that triggers delayed neuronal death in the CA1 region. However, the mechanism underlying structural changes of excitatory synapses after ischemia is not completely understood. Here, we demonstrate how dendritic spines change in their density and structure at an acute stage after transient global ischemia. Intracellular staining in vivo showed that the total spine density in basal, proximal, and distal apical dendrites increased at 12 hr and 24 hr after ischemia, but returned to control levels at 48 hr after ischemia. Consistent increase of spine density mainly appeared in non‐late depolarizing postsynaptic potential neurons, although late depolarizing postsynaptic potential neurons also showed slight increases in spine density in these dendrites at the same intervals after ischemia. Golgi staining showed increased spine density occurred in less swollen dendrites but decreased spine density appeared in severely swollen dendrites at 12 and 24 hr after ischemia. In addition, the density and percentage of stubby spines reduced at 12 hr and 48 hr, whereas the density of thin spines increased at 12 hr after ischemia. The density and percentage of filopodia increased nearly fivefold at 24 hr after ischemia. Moreover, the density of mushroom spines doubled and its percentage increased by 150% at 48 hr after ischemia. These morphological changes of spines may be related to neuronal injury in CA1 pyramidal neurons after ischemia. © 2008 Wiley‐Liss, Inc.
Raman spectroscopic study of the mineral guilleminite Ba(UO2)3(SeO3)2(OH)4·3H2O
Authors: Frost Ray L. , Čejka Jiří , Dickfos Marilla J.
Published: August 2008

The Raman spectrum of the mineral guilleminite Ba[(UO2)3O2(SeO3)2](H2O)3 was studied and complemented by the infrared spectrum of this mineral. Both spectra were interpreted and compared with the spectra of marthozite, larisaite, haynesite and piretite, all of which should have the same phosphuranylite anion sheet topology. The presence of symmetrically distinct water molecules and hydrogen bonds was inferred from the spectra. This is in agreement with the crystal structural analysis of guilleminite. UO bond lengths in uranyl and OH···O hydrogen bond lengths were calculated from the Raman and/or infrared spectra of guilleminite. Copyright © 2008 John Wiley & Sons, Ltd.
Raman spectroscopic study of the selenite mineral mandarinoite Fe2Se3O9·6H2O
Authors: Frost Ray L. , Keeffe Eloise C.
Published: August 2008

Selenites and tellurites may be subdivided according to formula and structure. There are five groups, based upon the formulae (a) A(XO3), (b) A(XO3·) xH2O, (c) A2(XO3)3·xH2O, (d) A2(X2O5) and (e) A(X3O8). Of the selenites, molybdomenite is an example of type (a); chalcomenite, clinochalcomenite, cobaltomenite and ahlfeldite are minerals of type (b); mandarinoite Fe2Se3O9·6H2O is an example of type (c). Raman spectroscopy has been used to characterise the mineral mandarinoite. The intense, sharp band at 814 cm−1 is assigned to the symmetric stretching (Se3O9)6− units. Three Raman bands observed at 695, 723 and 744 cm−1 are attributed to the ν3 (Se3O9)6− anti‐symmetric stretching modes. Raman bands at 355, 398 and 474 cm−1 are assigned to the ν4 and ν2 bending modes. Raman bands are observed at 2796, 2926, 3046, 3189 and 3507 cm−1 and are assigned to OH stretching vibrations. The observation of multiple OH stretching vibrations suggests the non‐equivalence of water in the mandarinoite structure. The use of the Libowitzky empirical function provides hydrogen bond distances of 2.633(9) Å (2926 cm−1), 2.660(0) Å (3046 cm−1), 2.700(0) Å (3189 cm−1) and 2.905(3) Å (3507 cm−1). The sharp, intense band at 3507 cm−1 may be due to hydroxyl units. It is probable that some of the selenite units have been replaced by hydroxyl units. Copyright © 2008 John Wiley & Sons, Ltd.
Pressure‐induced phase transitions in L‐leucine crystal
Authors: Façanha Filho P. F. , Freire P. T. C. , Melo F. E. A. , Lemos V. , Mendes Filho J. , Pizani P. S. , Rossatto D. Z.
Published: August 2008

Raman spectra of a crystal of L‐leucine, an essential amino acid, were obtained for pressures between 0 and 6 GPa. The results show anomalies at three pressure values, one between 0 and 0.46 GPa, another between 0.8 and 1.46 GPa, and a third at P ∼ 3.6 GPa. The first two anomalies are characterized by the disappearance of lattice modes (which can indicate occurrence of phase transitions), the appearance of several internal modes, or the splitting of modes of high wavenumbers. The changes of internal modes are related to CH and CH3 unit motions as well as hydrogen bonds, as can be inferred from the behavior of bands associated with CO2− moieties. The third anomaly is a discrete change of the slopes of the wavenumber versus pressure plots for most modes observed. Further, decompression to ambient pressure generates the original Raman spectrum, showing that the pressure‐induced anomalies undergone by L‐leucine crystals are reversible. Copyright © 2008 John Wiley & Sons, Ltd.
Differentiation and quantification of xylene isomers by combining headspace solid‐phase microextraction/gas chromatography and self‐ion molecule reaction in an ion trap tandem mass spectrometry
Authors: Yang Chih‐Hao , Khan Nadeem Ahmad , Wu Hui‐Fen
Published: August 2008

A headspace solid‐phase microextraction (HS‐SPME) method using polydimethylsiloxane (PDMS)‐coated fiber coupling with GC/self‐ion molecule reaction (SIMR)/MS/MS (GC/SIMR/MS/MS) has been developed for the differentiation of o‐, m‐, and p‐xylene isomers. The optimization parameters of this method are: extraction time 20 min, stirring rate 1200 rpm, sampling temperature 28°C, and salt concentration 5%. The LODs were found to be in the range of 3–9 ng/mL under the SIM mode of GC/MS. The RSDs were below 1% (n = 5). The linear dynamic range of the calibration curve was from 0.05 to 10.0 μg/mL with correlation coefficient (r2) > 0.9089. The advantages of this technique are sensitive, selective, ease of operation, simple device, solvent free, and extremely little sample consumption. This technique is the first example using SIMR combined MS/MS applied in the GC/MS and it can be applied to other volatile compounds for future application.
Robust open tubular layer ofS‐ketoprofen imprinted polymer for chiral LC separation
Authors: Zaidi Shabi Abbas , Cheong Won Jo
Published: August 2008

This study is about the preparation of an open tubular capillary column of molecularly imprinted polymer (MIP) and its application to chiral separation by μLC. A non‐covalentin‐situmolecular imprinting polymerization protocol was used to synthesize theS‐ketoprofen MIP. A special procedure was employed to secure formation of an open tubular and rigid MIP layer in a silica capillary of 100 μm id. The capillary was filled with the reaction mixture, sealed, and placed in a water bath at 50°C for 3 h. Then it was flushed with a 0.5 MPa nitrogen flow for 5 min, and was again placed in the water bath for 2 h to complete MIP formation. Methacrylic acid (MAA) has been known to be an inefficient functional monomer in preparation of MIP of an acid molecule. However, MAA was used with ethylene glycol dimethacrylate in preparation of theS‐ketoprofen MIP in this study. The open tubular structure and the μLC mode of separation enabled free optimization without any restriction, thus a very good resolution (R= 4.7) of ketoprofen enantiomers was achieved when a mobile phase composed of 30% acetonitrile and 70% acetate buffer at pH 4.5 was used with 5 mbar inlet pressure. This may be partially attributed to the open tubular structure of our MIP, enabling low column back‐pressure and free optimization of eluent composition, as well as to the small capillary dimensions. Our MIP capillary column also showed some versatility in chiral separation, thus a good chiral separation was observed for naproxen, ibuprofen, and fenoprofen enantiomers.
Resonance Rayleigh scattering for detection of proteins in HPLC
Authors: Lu Xin , Luo Zhihui , Liu Chengwei , Zhao Shulin
Published: August 2008

An HPLC–resonance Rayleigh scattering (RRS) (HPLC–RRS) detection system is described for separation and detection of proteins. This system is based on the modification of a commercial HPLC instrument involving the addition of a pump and a T‐shaped interface, and a common fluorescence detector was used for detection. The detection principle is based on the change of RRS intensity of the ion‐association complex formed from biebrich scarlet (BS) and protein. The RRS signal was detected at λex = λem = 376 nm. The utility of the presented method was demonstrated by the separation and determination of four proteins involving cytochrome (Cyt‐c), lysozyme (Lys), HSA, and γ‐globulin (γ‐Glo). An LOD of 0.2–1.0 μg/mL was reached and a linear range was found between peak area and concentration in the range of 0.20–3.0 μg/mL for Cyt‐c, 0.25–2.5 μg/mL for Lys, 1.5–10 μg/mL for HSA, and 2.0–15 μg/mL for γ‐Glo, with linear regression coefficients all above 0.99. The method presented has been applied to determine HSA and γ‐Glo in human serum samples synchronously.
On‐Line multitasking analytical proteomics: How to separate, reduce, alkylate and digest whole proteins in an on‐Line multidimensional chromatography system coupled to MS
Authors: Tran Bao Quoc , Loftheim Håvard , Reubsaet Leon , Lundanes Elsa , Greibrokk Tyge
Published: August 2008

An on‐Line multidimensional system has been developed, consisting of pH gradient strong anion exchange chromatography of native proteins in the first dimension with subsequent trapping and on‐column reduction/alkylation on C4 trap columns and RP separation of the alkylated proteins in the second dimension followed by on‐column tryptic digestion and electrospray MS detection. The system was evaluated using model proteins and a human urine sample. Compared to the commonly used in‐solution alkylation method, the developed on‐column method provides an equivalent efficiency. The recovery from the C4 trap columns of the alkylated proteins relative to the native state was from 94 to 102%. On‐column tryptic digestion was satisfactory for many, but not for all proteins. The whole analytical procedure was performed on‐Line with packed capillary columns for a total time of 320 min for the first ion exchange fraction, with additional 60 min for each subsequent fraction.
Supercritical fluid extraction for identification and determination of volatile metabolites from Angelica dahurica by GC‐MS
Authors: Chen Qinhua , Li Peng , He Jing , Zhang Zhuo , Liu Jia
Published: August 2008

The volatile components of Angelica dahurica were obtained by supercritical fluid extraction (SFE) method. These oils obtained were analyzed by GC‐MS (identification and determination of metabolites). The compounds were identified according to their retention indices and mass spectra (electron impact (EI), 70 eV). The effects of different parameters, such as pressure, temperature, flow rate of CO2, and the amount of modifier, on the SFE of A. dahurica oil were investigated. A total of 50 compounds of SFE extracts were identified. Phellopterin (PO), isoimperatorin (IO), imperatorin (IM), alloimperatorin (AM), byakangelicin, isooxypeucedanin, and pimpinellin were the major coumarin compounds identified in A. dahurica SFE extracts. The quantitations of PO, IO, IM, and AM were then accomplished. The calibration curves showed good linearity (R2 >0.99) in the concentration ranges tested. The recoveries were higher than 85%, with RSDs less than 10%. The GC‐MS method was successfully validated and applied to the quantitation of A. dahurica.
Retracted:Comments on ‘Upper bound solution to elasticity problems: A unique property of the linearly conforming point interpolation method (LC‐PIM)’ by G. R. Liu and G. Y. Zhang, International Journal for Numerical Methods in Engineering, DOI: 10.1002/nme.2204
Authors: Liu G. R. , Zhang Guiyong
Published: August 2008

The following article from International Journal for Numerical Methods in Engineering, Comments on ‘Upper bound solution to elasticity problems: A unique property of the linearly conforming point interpolation method (LC‐PIM)’ by G. R. Liu and G. Y. Zhang, published online on 15 August 2008 in Wiley InterScience (www.interscience.wiley.com), has been retracted by agreement between the authors, the journal Editor‐in‐Chief, Ted Belytschko and John Wiley & Sons, Ltd. The retraction has been agreed due to the article being published out of sequence with a related article and with insufficient citation details.
A time‐parallel implicit method for accelerating the solution of non‐linear structural dynamics problems
Authors: Cortial Julien , Farhat Charbel
Published: August 2008

The parallel implicit time‐integration algorithm (PITA) is among a very limited number of time‐integrators that have been successfully applied to the time‐parallel solution of linear second‐order hyperbolic problems such as those encountered in structural dynamics. Time‐parallelism can be of paramount importance to fast computations, for example, when space‐parallelism is unfeasible as in problems with a relatively small number of degrees of freedom in general, and reduced‐order model applications in particular, or when reaching the fastest possible CPU time is desired and requires the exploitation of both space‐ and time‐parallelisms. This paper extends the previously developed PITA to the non‐linear case. It also demonstrates its application to the reduction of the time‐to‐solution on a Linux cluster of sample non‐linear structural dynamics problems. Copyright © 2008 John Wiley & Sons, Ltd.
Upper and lower bounds in limit analysis: Adaptive meshing strategies and discontinuous loading
Authors: Muñoz J. J. , Bonet J. , Huerta A. , Peraire J.
Published: August 2008

Upper and lower bounds of the collapse load factor are here obtained as the optimum values of two discrete constrained optimization problems. The membership constraints for Von Mises and Mohr–Coulomb plasticity criteria are written as a set of quadratic constraints, which permits one to solve the optimization problem using specific algorithms for Second‐Order Conic Program (SOCP). From the stress field at the lower bound and the velocities at the upper bound, we construct a novel error estimate based on elemental and edge contributions to the bound gap. These contributions are employed in an adaptive remeshing strategy that is able to reproduce fan‐type mesh patterns around points with discontinuous surface loading. The solution of this type of problems is analysed in detail, and from this study some additional meshing strategies are also described. We particularise the resulting formulation and strategies to two‐dimensional problems in plane strain and we demonstrate the effectiveness of the method with a set of numerical examples extracted from the literature. Copyright © 2008 John Wiley & Sons, Ltd.
A local multigrid X‐FEM strategy for 3‐D crack propagation
Authors: Rannou J. , Gravouil A. , Baïetto‐Dubourg M. C.
Published: August 2008

A multiscale method for 3‐D crack propagation simulation in large structures is proposed. The method is based on the extended finite element method (X‐FEM). The asymptotic behavior of the crack front is accurately modeled using enriched elements and no remeshing is required during crack propagation. However, the different scales involved in fracture mechanics problems can differ by several orders of magnitude and industrial meshes are usually not designed to account for small cracks. Enrichments are therefore useless if the crack is too small compared with the element size. To overcome this drawback, a project combining different numerical techniques was started. The first step was the implementation of a global multigrid algorithm within the X‐FEM framework and was presented in a previous paper (Eur. J. Comput. Mech. 2007; 16:161–182). This work emphasized the high efficiency in cpu time but highlighted that mesh refinement is required on localized areas only (cracks, inclusions, steep gradient zones). This paper aims at linking the different scales by using a local multigrid approach. The coupling of this technique with the X‐FEM is described and computational aspects dealing with intergrid operators, optimal multiscale enrichment strategy and level sets are pointed out. Examples illustrating the accuracy and efficiency of the method are given. Copyright © 2008 John Wiley & Sons, Ltd.
Transient heat conduction in a medium with multiple spherical cavities
Authors: Gordeliy Elizaveta , Crouch Steven L. , Mogilevskaya Sofia G.
Published: August 2008

This paper considers a transient heat conduction problem for an infinite medium with multiple non‐overlapping spherical cavities. Suddenly applied, steady Dirichlet‐, Neumann‐ or Robin‐type boundary conditions are assumed. The approach is based on the use of the general solution to the problem of a single cavity and superposition. Application of the Laplace transform and the so‐called addition theorem results in a semi‐analytical transformed solution for the case of multiple cavities. The solution in the time domain is obtained by performing a numerical inversion of the Laplace transform. A large‐time asymptotic series for the temperature is obtained. The limiting case of infinitely large time results in the solution for the corresponding steady‐state problem. Several numerical examples that demonstrate the accuracy and the efficiency of the method are presented. Copyright © 2008 John Wiley & Sons, Ltd.
An efficient numerical method for solid–liquid transitions in optical rewritable recording
Authors: Brusche J. H. , Segal A. , Vuik C.
Published: August 2008

Melting and solidification processes are encountered in a variety of industrial applications. Examples include the steel industry, food processing and the recording of data in optical data storage. The phase transition, induced by a heat source, can be described by a two‐phase Stefan formulation. To solve such highly non‐linear moving boundary problems within industrially relevant domains, we propose an extension to 3D space of the temperature‐based method described by Fachinotti et al. (Int. J. Numer. Meth. Engng 1999; 44(12):1863–1884). By the use of discontinuous spatial integration accurate solutions can be efficiently obtained for isothermal problems that are driven by the boundary conditions. However, the temperature approach can fail for isothermal problems that are driven by an (external) source. This is remedied by introducing an artificial mushy region around the melting temperature. The developed method has been applied to 3D optical rewritable recording simulations. Copyright © 2008 John Wiley & Sons, Ltd.
Lattice Boltzmann simulation of dispersion in two‐dimensional tidal flows
Authors: Banda Mapundi K. , Seaïd Mohammed , Thömmes Guido
Published: August 2008

A lattice Boltzmann method (LBM) is applied to problems of dispersion in two‐dimensional water flows. The water flow is modelled by shallow water equations. A two‐distribution lattice Boltzmann equation algorithm is presented to solve the pollutant transport problem within the framework of shallow water flow. One distribution models the shallow water flow. The other distribution models the pollutant transport. Flow characteristics and concentration profiles of dispersive species are obtained at various flow regimes. For fast water flow, the concentration profiles are highly affected by the flow advection and become completely different from those at slow water flow. Numerical results are presented for pollutant transport in bounded and open channel flows. The proposed LBM is also used to simulate a pollution event in the Strait of Gibraltar. The obtained results indicate that the present method is useful for the investigation of transport phenomena by shallow water flows in complex geometries and practical flow problems. Copyright © 2008 John Wiley & Sons, Ltd.
A palaeopathological investigation of the third intercondylar tubercle of Parsons
Authors: Mays S. , Cooper L.
Published: August 2008

The third intercondylar tubercle of Parsons (TITP) is a bony protuberance which is sometimes present on the tibial plateau. It corresponds to the insertion of the anterior fibres of the anterior cruciate ligament (ACL). Reasons why TITP is present in some knees and not others are at present unclear. TITP is studied in knee joints from 68 adult individuals from a medieval cemetery. Associations are investigated with age, sex, knee osteoarthritis, clinical and subclinical DISH, and skeletal signs of trauma, with the aim of evaluating existing ideas on the causation of TITP. Only trauma showed an association with the presence of TITP. The results offer support for the aetiology of trauma to the ACL in the formation of TITP. Copyright © 2008 John Wiley & Sons, Ltd.
Numerical methods for the chemical master equation and applications to stochastic models or receptor oligomerisation
Authors: MacNamara Shev , Burrage Kevin , Sidje Roger B.
Published: August 2008

The chemical master equation is an important model for studying chemical kinetics, especially in the context of systems biology where noise is known to play an important role and so a discrete and stochastic framework is required. However due to the high dimensional nature of the equations it has often been felt to be too difficult to tackle numerically, although recently much progress has been made. Here some novel numerical methods are presented and applied to stochastic models of receptor oligomerisation, which have previously been studied only by simulation. This gives a novel perspective on these models and suggests some insights into the phenomena of the role they play in buffering cell signals. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fracture mechanical behaviour of visco‐elastic materials
Authors: Näser Bastian , Kaliske Michael , Dal Hüsnü
Published: August 2008

The material force approach is an efficient, elegant and accepted means to compute the J‐integral as a fracture mechanical parameter for elastic and inelastic materials. With the formulation of a multiplicative split of the deformation gradient at hand, rate‐dependent (visco‐elastic) materials based on the Bergström‐Boyce‐Model can be investigated. For these investigations, the so‐call material body forces have to be computed to separate the driving force acting on the inelastic zone around the crack tip from the driving force acting on the crack tip itself, representing the crack driving force or the J‐integral, respectively. For that purpose, the complete balance for the material motion problem for rate‐dependent, inelastic materials has to be known and the balance has to be fulfilled at every nodal point in a finite element discretization.

In this contribution, the so‐called dwell effect should serve as an example for the application of the material force method for inelastic materials. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experiments in non‐smooth mechanics with a passive‐actuated robotic arm
Authors: Welge‐Luessen Tobias
Published: August 2008

This paper describes various experiments for the parameter identification of a two‐link passive‐actuated robot manipulator. The proposed experiments can be used to determine the flexible properties of the physical structure, especially of both arms and of the shafts within the joints connecting them. In addition experiments for the major joint elements, namely the motor and the electromagnetically powered brake are being presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the stabilization of tetrahedral finite elements using volume and area bubble functions
Authors: Caylak Ismail , Mahnken Rolf
Published: August 2008

In order to overcome the oscillatory effects of the bi‐linear Galerkin formulation for tetrahedral elements the mixed method of incompatible modes and the mixed method of enhanced strains are reformulated, thus giving both the interpretation of a mixed finite element method with stabilization terms. For nonlinear problems these are nonlinearly dependent on the current deformation state, and therefore are replaced by linearly dependent stabilization terms. The approach becomes most attractive for the numerical implementation, since the use of quantities related to the previous Newton iteration step, typically arising for mixed enhanced elements, is completely avoided. The stabilization matrices for the mixed method of incompatible modes and the mixed method of enhanced strains are obtained with volume and area bubble functions. Cook's membrane problem illustrates successfully the stabilization effect for bi‐linear tetrahedral elements. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Smolyak algorithms based on digital (t, α, d)‐sequences for multivariate integration
Authors: Dick Josef , Leobacher Gunther , Pillichshammer Friedrich
Published: August 2008

We use so‐called (t, α, d)‐sequences and Smolyak's algorithm to construct d × l ‐dimensional integration rules with optimal convergence rates in a suitable function space. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A three‐phase FE‐model for the simulation of partially saturated soils
Authors: Nagel Felix , Meschke Günther
Published: August 2008

While for many numerical simulations in geotechnics use of a two‐phase model is sufficient, separate consideration of all three phases is mandatory for numerical simulations of partially saturated soils subjected to compressed air. This is a common technique frequently applied for temporary ground support in tunnelling. For the numerical simulation of tunnelling using compressed air, a multiphase model for soft soils is developed, in which the individual constituents of the soil – the soil skeleton, the fluid and the gaseous phase – and their interactions are considered. The three phase model is formulated within the framework of the Theory of Porous Media (TPM), based upon balance equations and constitutive relations for the soil constituents and their mixture. Water is modelled as an incompressible and air as a compressible phase. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Representation of the interface conditions of the acoustic transmission problem at a curved contact of heterogeneous media in terms of transmission and reflection operators
Authors: Ayzenberg Milana , Aizenberg Arkady , Pajchel Jan
Published: August 2008

We schematically derive rigorous transmission and reflection operators at a curved interface between heterogeneous acoustic media. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Language technologies for semantic markup in mathematics
Authors: Caprotti Olga
Published: August 2008

The Web Advanced Learning Technologies project showed how, by applying state of the art language technologies to semantic markup of mathematics, it is possible to automatically produce renderings of mathematical content in a variety of languages. The intended application area of this work is that of computer assisted assessment and testing in mathematics where standardized entry examinations for perspective students could be used independently of country and language. A similar multilingual approach can be developed for any situation in which it is possible to identify a specific mathematical jargon. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase field simulations on the interaction of ferroelectric domains with point defects
Authors: Schrade D. , Xu B.X. , Müller R. , Gross D.
Published: August 2008

One of the suspected micro‐mechanical mechanisms causing electric fatigue in ferroelectric materials is the hindering and blocking of domain wall movement. These blocking or pinning phenomena are thought to be due to point defects which interact with domain walls and applied external loads. A phase field model employing the spontaneous polarization as an order parameter is used to simulate the inhomogeneous material behavior. The coupled field equations are solved using the Finite Element Method. The influence of a stationary point defect on a domain wall is shown in a numerical simulation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A boundary‐value problem for an infinite elastic strip with a semi‐infinite crack
Authors: Itou Hiromichi , Tani Atusi
Published: August 2008

In this paper we consider a boundary value problem for an infinite elastic strip with a semi‐infinite crack. The mass forces are supposed to be zero; on the crack the free traction boundary conditions are posed. The usage of the plane elastic single and double layer potentials reduces the problem to a system of singular integral equations. It is shown that this system is uniquely solvable in the appropriate Hölder spaces by the Fredholm alternative. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical analysis and adaptive computation for solutions of elliptic problems with randomly perturbed coefficients
Authors: Målqvist Axel , Estep Donald , Tavener Simon
Published: August 2008

We develop a reliable efficient method for computing solutions to the Poisson equation a with randomly perturbed coefficient. We assume the perturbation to be piecewise constant and use a non‐overlapping domain decomposition algorithm, where the domains coincides with regions where the perturbation is constant, to solve the equations. On each sub‐domain we use an truncated Neumann series to approximate the inverse of the local stiffness matrix. By doing so we can solve for all samples simultaneously in a very efficient way. We derive a posteriori error estimates and construct an adaptive algorithm to tune the method parameters automatically. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling Ziegler‐Natta polymerization in high‐pressure reactors
Authors: Fasano A. , Mancini A.
Published: August 2008

We present a study of some mechanical aspects of the polymerization processes named after the names of the Nobel laureates (1963) Karl W. Ziegler and Giulio Natta.

Using the ideas of [1] as a starting point, we formulate a mathematical model encompassing the mechanical behavior of the polymer while it grows around the nanometric catalytic particles. As a basis we use the theory of [5]. The full model is exposed in [3]. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A comparison of static optimization criteria for resolving the 3D muscle redundancy problem during human gait
Authors: Ou Ye , Kecskeméthy Andrés
Published: August 2008

In this paper, different approaches of static optimization for predicting muscle forces during human walking are investigated. In order to better reflect the true mechanics of the human body, a three‐dimensional musculoskeletal model of a single leg is developed. The joint moments generated by muscles during walking are computed from inverse dynamics. The muscle force is estimated by different optimization criteria, each satisfying the moment constraints at all joints and the lower and upper muscle force constraints. Several polynomial and non‐polynomial criteria frequently used in literature are studied. Then the results obtained from these calculations are compared with each other. This paper provides an overview of the effects of different optimization criteria on the 3D muscle force distribution problem during human walking. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling and simulation of population balances in particulate systems
Authors: Qamar Shamsul
Published: August 2008

This article focuses on the modeling and simulation of population balance equations (PBEs) for simultaneous growth, nucleation and aggregation processes. Two numerical method are proposed for this purpose. The first method combines the method of characteristics (MOC) for growth process with a finite volume scheme (FVS) for aggregation process. The second method uses a high resolution finite volume scheme to solve the resulting PBEs. The numerical results show that both methods give accurate results. However, the first method is more efficient and accurate as compared to the second method. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Assessment of high‐order discretization schemes for the DNS of compressible swirling mixing layers
Authors: Müller S.B. , Kleiser L.
Published: August 2008

We report on results of highly accurate Direct Numerical Simulations (DNS) solving the Navier‐Stokes equations in cylindrical coordinates. The DNS code computes a compressible swirling mixing layer at Mach number Ma = 0.8. We present two simulations differing in the spatial discretization schemes for the convective terms. On the same grid, comparisons of flow simulations using different discretization schemes for otherwise identical conditions can be performed quantitatively and improve the understanding of the effects of numerical errors and in particular numerical dissipation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effective matrix formalism for singularity analysis of differential equations and new intergrable system in nonlinear elasticity
Authors: Novozhilova L.S. , Urazhdin S.V.
Published: August 2008

We introduce a simple matrix formalism for Taylor series and generalized Laurent series that can be used for implementing the Taylor method for nonlinear ODEs and singularity analysis of differential equations. Advantages of this approach over conventional techniques are shown on model examples. Surprisingly, the same formalism can be used for proving C‐integrability of a 3D model in nonlinear elasticity. An alternative proof is obtained by using similarity between the model in nonlinear elasticity and the classic Pohlmeier‐Lund‐Regge model from high energy physics. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Interior point methods specialized to optimal pump operation costs of water distribution networks
Authors: Lima Aline , Oliveira Aurelio
Published: August 2008

In the water distribution problem the loss is important and the objective function must consider it combined with pump costs. The problem becomes complex because the loss in each branch is as a nonlinear function of water outflow. The objective of this work consists in solving the water distribution problem using interior point methods and to exploit the particular structure of the problem and the specific matrix sparse pattern of the of the resulting linear systems. The interior point methods show to be robust, achieving fast convergence in all instances tested. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bridging scales: An attempt to incorporate cellular responses within a three‐dimensional FEM model of active muscle contraction
Authors: Röhrle O. , Davidson J.B. , Kim J.H.K. , Pullan A.J.
Published: August 2008

A mathematical model of the cellular responses of skeletal muscles has been integrated within a three‐dimensional biomechanical Finite Element (FEM) model. The FEM model is based on a tri‐cubic Hermite Finite Element discretisation of the governing equations of finite elasticity theory and a transversely isotropic constitutive law. To incorporate the cellular information, homogenised values of key physiological parameters, e.g. the pre‐ and post‐power stroke concentration of crossbridge attachments, are computed at the Gauss points of the FEMintegration scheme. These values are then used to modify the stress tensor in such a way that it resembles the contractile response. The advantages of such an improved three‐dimensional FEM model are far reaching. These models can be used, for example, to investigate and study local muscle contraction, muscle recruitment patterns, force generation, or fatigue response of skeletal muscles. As an illustrative example, one twitch of the tibialis anterior, in which 25% of the muscle fibres are excited by a nerve stimulus, is simulated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal control of a large PDAE molten carbonate fuel cell model
Authors: Rund Armin , Sternberg Kati , Pesch Hans Josef , Chudej Kurt
Published: August 2008

Molten carbonate fuel cells are well suited for stationary power production and heat supply. In order to enhance service life time, hot spots, resp. high temperature gradients inside the fuel cell have to be avoided. In conflict with that, there is the desire to achieve faster load changes while temperature gradients stay small. For the first time, optimal fast load changes have been computed numerically. The dimensionless model is based on the description of physical and chemical phenomena. The numerical procedure is based on a method of lines approach via spatial discretization and the solution of the resulting very large scale optimal control problem s.t. a differential‐algebraic equation system by a nonlinear programming approach. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Subset selection for parameter estimation in an HIV model
Authors: Fink Martin , Attarian Adam , Tran Hien
Published: August 2008

This paper discusses methodologies for subset selection for nonlinear least squares parameter estimation. In particular, we will present approaches for partitioning the parameter space into well‐conditioned and ill‐conditioned subsets. The algorithms are applied to a simplified mathematical model of the physiologic response of the human immunodeficiency virus (HIV) in humans. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Physics‐based preconditioners for solving PDEs on highly heterogeneous media
Authors: Aksoylu Burak , Klie Hector
Published: August 2008

Eigenvalues of smallest magnitude become a major bottleneck for iterative solvers especially when the underlying physical properties have severe contrasts. These contrasts are commonly found in many applications such as composite materials, geological rock properties, and thermal and electrical conductivity. The main objective of this work is to construct a method as algebraic as possible that could efficiently exploit the connectivity of highly heterogeneous media in the solution of diffusion operators. We propose an algebraic way of separating binary‐like systems according to a given threshold into high‐ and low‐conductivity regimes of coefficient size O (m) and O (1), respectively where m ≫ 1. The condition number of the linear system depends both on the mesh size and the coefficient size m. For our purposes, we address only the m dependence since the condition number of the linear system is mainly governed by the high‐conductivity subblock. Thus, the proposed strategy is inspired by capturing the relevant physics governing the problem. Based on the algebraic construction, a two‐stage preconditioning strategy is developed as follows: (1) a first stage that comprises approximation to the components of the solution associated to small eigenvalues and, (2) a second stage that deals with the remaining solution components with a deflation strategy (if ever needed). The deflation strategies are based on computing near invariant subspaces corresponding to smallest eigenvalues and deflating them by the use of recycled the Krylov subspaces. More detail on the proposed preconditioners can be found in [1]. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High order boundary integral methods forMaxwell's equations using Microlocal Discretization and Fast Multipole Methods
Authors: Darrigrand E. , Gatard L. , Mer‐Nkonga K.
Published: August 2008

An efficient method to solve time harmonic Maxwell's equations in exterior domain for high frequencies is obtained by using the integral formulation of Després combined with a coupling method (MLFMD) based on the Microlocal Discretization method (MD) and the Multi‐Level Fast Multipole Method (MLFMM) [1]. In this paper, we consider curved finite elements of higher order in the MLFMD method. Moreover, we improve the MLFMD method by sparsifying the translation matrix of the MLFMM, which involves privileged directions in that application. This improvement leads to a significant reduction of the algorithm complexity. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
FEM‐BEM coupling for elasto‐plastic analysis: automatic adaptive generation of the FEM and BEM zones of discretization
Authors: Elleithy W.
Published: August 2008

In this paper, we present the concept and implementation issues of an adaptive FEM‐BEM coupling method for two – dimensional elasto‐plastic analysis. Considerable attention is devoted to the generation and progressive adaption of the FEM and BEM discretizations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational micro‐macro transitions at large strains for curvilinear physical directions
Authors: Grytz Rafael , Meschke Günther
Published: August 2008

Biological tissues such as those involved in the eye, heart, veins or arteries are heterogeneous on one or another spatial scale and can undergo very large elastic strains. Frequently, these tissues are characterized by shell‐like structures at the macroscopic scale and the physical material directions follow curvilinear paths. We consider a homogenized macro‐continuum formulated in curvilinear convective coordinates with locally attached representative micro‐structures. Micro‐structures attached to different macroscopic points are assumed to be rotated counterparts according to the curvilinear path of the physical material directions at the macro‐scale. The solution of such multi‐scale problems according to the computational homogenization scheme [1, 2, 3] would need a different RVE at each macroscopic point. The goal of this paper is to use the same initial RVE at each macroscopic point by generalizing the computational homogenization scheme to a formulation considering different physical spaces at the micro‐ and macro‐scale. The deformation and the reference frame of the micro‐structure are assumed to be coupled with the local deformation and the local reference frame at the corresponding point of the macrocontinuum. For a consistent formulation of micro‐macro transitions physical reference directions are defined on both scales, where the macroscopic one follows a curvilinear path. To formulate the generalized micro‐macro transitions in absolute tensor notation the operations scale‐up and scale‐down are introduced. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical implementation of seismic wavefield operators via path integrals
Authors: Lamoureux Michael P. , Margrave Gary F.
Published: August 2008

The seismic imaging problem centers around mathematical and numerical techniques to create an accurate image of the earth's subsurface, using recorded data from geophones that capture reflected seismic waves. Using a path integral approach, a wavefield extrapolater can be expressed as a limit of depth‐sliced path steps through a variable velocity medium. An image is created from the correlation between upward and downward going waves. We report on the mathematical issues that arise in implementing numerical algorithms based on the path integral approach, in particular convergence, stability, and accuracy. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A few typical delamination patterns of compressed thin films
Authors: Pham V.D. , Gruttmann F.
Published: August 2008

In this paper we consider compressed flat thin films on rigid substrates. Residual compressive stresses arising e.g. from temperature loading are the driving quantities of the irreversible delamination process. A Reissner–Mindlin shell formulation is used as a model for the thin film, since small geometrical imperfections are considered to initiate buckling. For the interface we postulate the existence of a cohesive free energy as a function of the opening displacement vector and internal variables. The irreversible delamination process is described using a cohesive law of exponential type, where the parameters depend on the combination of the modes I, II and III. In order to analyse the delamination process exactly we use the energy criterion of the steady‐state growth. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Implementing Taylor models arithmetic with floating‐point arithmetic
Authors: Revol Nathalie
Published: August 2008

The implementation of Taylor models arithmetic may use floating‐point arithmetic to benefit from the speed of the floatingpoint implementation. The issue is then to take into account the roundoff errors. Here, we assume that the floating‐point arithmetic is compliant with the IEEE‐754 standard. We show how to get tight bounds of the roundoff errors, and more generally how to get high accuracy for the coefficients as well as for the bounds on the roundoff errors
A new level‐set technique for the crack‐detection problem
Authors: Alvarez Diego , Dorn Oliver , Moscoso Miguel
Published: August 2008

We present a new technique for recovering key characteristics of defects such as snake‐like cracks from boundary electrical measurements. We propose a shape‐based reconstruction algorithm adapting the level set techniques to the situation of modelling very thin shapes. Two level set functions are employed: the first one models the location and form of the crack, and the second one models its length and connectivity. Two Hamilton‐Jacobi type equations are derived to describe the evolution laws for these two level set functions in order to minimize the least squares data misfit. Numerical experiments in 2D show the efficiency of this method for reconstructing disconnected cracks in the presence of measurement noise. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The 3D asymptote generalization of MetaPost Bézier interpolation
Authors: Bowman John C.
Published: August 2008

The descriptive vector graphics language Asymptote provides for the typesetting of mathematical figures a capability analogous to what TEX provides for typesetting equations. Labels are typeset with TEX, for professional quality and overall document consistency, and the simplex linear programming method is used to solve overall size constraint issues between fixed‐sized and scalable objects. Asymptote's three‐dimensional generalization of the spline interpolation algorithms of Hobby (Discrete and Computational Geometry 1, 1986) is shape invariant under three‐dimensional affine transformations and reduces in the planar case to Hobby's prescription. By using recursive refinement to add additional Bézier control points, one can then efficiently approximate a perspective‐invariant nonuniform rational B‐spline. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Boundary optimal flow control with state constraints
Authors: de los Reyes Juan Carlos , Yousept Irwin
Published: August 2008

The numerical solution of the Dirichlet boundary optimal control problem of the Navier‐Stokes equations in presence of pointwise state constraints is investigated. A Moreau‐Yosida regularization of the problem is proposed to obtain regular multipliers. Optimality conditions are derived and the convergence of the regularized solutions towards the original one is presented. The paper ends with a numerical experiment. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mathematical modeling of stable quasi‐static crack extension by extended Griffith energy balance theory
Authors: Ohtsuka Kohji
Published: August 2008

A mathematical modeling of the stopping of crack extension is proposed by modification and extension of Griffith's energy balance theory. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal singular control for systems involving parameters
Authors: Popescu Mihai
Published: August 2008

What we shall take into consideration is represented by the problems of singular optimal control when the index of performance, the differential constraints and the final conditions contain parameters. What is determined is the trajectory of the neighboring extremal for the initial point perturbed at the constraints of the perturbed final manifold. The present study evaluates the variation of the command on the extremal. This one allows obtaining the second variation in the singular case. The sufficient conditions of minimum are a result of imposing the non‐negativity of the second variation. The application made analysis the optimality of the singular control for a system in the class of affine differential systems. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)