bluuebunny/crossref_metadata_2025 huggingface dataset:
Complex regulation of CCR9 at multiple discrete stages of T cell development
Authors: Wurbel Marc‐André , Malissen Bernard , Campbell James J.
Published: December 2005

We have conducted a comprehensive assessment of CCR9 expression and function at the important milestone stages of murine thymocyte development. We reveal an unusually complex regulatory pattern, in which CCR9 influences T cell development at several widely dispersed stages. We find that CCR9 is not expressed within the thymus until the double‐negative (DN)3 stage, although it appears to contribute to T cell precursor development prior to residence in the thymus. CCR9 expression is influenced by pre‐T cell receptor signals, and is dramatically up‐regulated in a population that appears to be transitional between the DN4 and double‐positive stages. In the periphery, functional CCR9 is expressed by all naive CD8 T cells, but not by naive CD4 T cells. To our knowledge, this latter finding is the first difference observed in homing receptor expression between naive lymphocyte populations. This suggests that naive CD8 T cells might have access to lymphoid microenvironments from which naive CD4 T cells are excluded.
Electroanalytical Determination of Carbaryl in Natural Waters on Boron Doped Diamond Electrode
Authors: Codognoto Lucia , Tanimoto Sonia T. , Pedrosa Valber A. , Suffredini Hugo B. , Machado Sergio A. S. , Avaca Luis A.
Published: December 2005

The anodic voltammetric behavior of carbaryl on a boron‐doped diamond electrode in aqueous solution is reported. The results, obtained by square‐wave voltammetry at 0.1 mol L−1 Na2SO4 and pH 6.0, allow the development of a method to determine carbaryl, without any previous step of extraction, clean‐up, preconcentration or derivatization, in the range 2.5–30.0×10−6 mol L−1, with a detection limit of 8.2±0.2 μg L−1 in pure water. The analytical sensitivity of this electrochemical method diminished slightly, from 3.07 mA mmol−1 L to 2.90 mA mmol−1L, when the electrolyte was prepared with water samples collected from two polluted points in an urban creek. In these conditions, the recovery efficiencies obtained were around 104%. The effect of other pesticides (fenthion and 4‐nitrophenol) was evaluated and found to exert a negligible influence on carbaryl determination. The square‐wave voltammetric data obtained for carbaryl were typical of an irreversible electrode process with mass transport control. The combination of square‐wave voltammetry and diamond electrodes is an interesting and desirable alternative for analytical determinations.
Tris(2,2′‐bipyridyl)ruthenium(II) Electrogenerated Chemiluminescence Sensor Based on Sol–Gel‐Derived V2O5/Nafion Composite Films
Authors: Choi Han Nim , Lyu Young‐Ku , Lee Won‐Yong
Published: December 2005

Mesoporous V2O5/Nafion composite films have been used for the immobilization of tris(2,2′‐bipyridyl)ruthenium (II) (Ru(bpy)$\rm{ {_{3}^{2+}}}$) on an electrode surface to yield a solid‐state electrogenerated chemiluminescence (ECL) sensor. The electrochemical and ECL behavior of Ru(bpy)$\rm{ {_{3}^{2+}}}$ ion‐exchanged into the composite films has been characterized as a function of the amount of Nafion incorporated into the V2O5/Nafion composite. The composite film with 80% Nafion content has the largest pore diameter (4.19 nm) and yields the maximum ECL response for tripropylamine (TPA) because of the fast diffusion of analyte into the film with large pores. Due to the enlarged pore size and enhanced conductivity of the V2O5/Nafion composite, the present ECL sensor based on the composite films exhibited around 2 orders of magnitude higher ECL response and one order of magnitude lower detection limit for TPA (10 nM) compared to those obtained with the ECL sensors based on other types of sol–gel ceramic/Nafion composite films such as SiO2/Nafion and TiO2/Nafion.
Inducible and neuron‐specific gene expression in the adult mouse brain with the rtTA2S‐M2 system
Authors: Michalon Aubin , Koshibu Kyoko , Baumgärtel Karsten , Spirig Dominique Haingotiana , Mansuy Isabelle M.
Published: December 2005

To achieve inducible and reversible gene expression in the adult mouse brain, we exploited an improved version of the tetracycline‐controlled transactivator‐based system (rtTA2S‐M2, rtTA2 hereafter) and combined it with the forebrain‐specific CaMKIIα promoter. Several independent lines of transgenic mice carrying the CaMKIIα promoter‐rtTA2 gene were generated and examined for anatomical profile, doxycycline (dox)‐dependence, time course, and reversibility of gene expression using several lacZ reporter lines. In two independent rtTA2‐expressing lines, dox‐treatment in the diet induced lacZ reporter expression in neurons of several forebrain structures including cortex, striatum, hippocampus, amygdala, and olfactory bulb. Gene expression was dose‐dependent and was fully reversible. Further, a similar pattern of expression was obtained in three independent reporter lines, indicating the consistency of gene expression. Transgene expression could also be activated in the developing brain (P0) by dox‐treatment of gestating females. These new rtTA2‐expressing mice allowing inducible and reversible gene expression in the adult or developing forebrain represent useful models for future genetic studies of brain functions. genesis 43:205–212, 2005. © 2005 Wiley‐Liss, Inc.
Macrophage/microglia activation factor expression is restricted to lesion‐associated microglial cells after brain trauma
Authors: Lünemann Anna , Ullrich Oliver , Diestel Antje , Jöns Thomas , Ninnemann Olaf , Kovac Adam , Pohl Elena E. , Hass Ralf , Nitsch Robert , Hendrix Sven
Published: December 2005

After traumatic brain lesion, microglial cells are rapidly activated, migrate toward the sites of injury, and cause secondary damage that accounts for most of the loss of brain function. In the present study, we have characterized a new macrophage/microglia activation factor (MAF). Using the monocytic cell line U937, we were able to demonstrate that MAF is upregulated after TPA‐induced differentiation into macrophages. We have generated a specific antibody against MAF. In BV‐2 microglial cells, MAF is partially co‐localized with IB4, a classical microglial marker. In addition, we have analyzed the in vivo expression patterns of MAF after entorhinal cortex lesion. We were able to show a substantial upregulation of MAF on selected CD11b+ and IB4+ macrophages/microglial cells in the deafferented hippocampus and in the perilesional region, while no MAF expression was detectable on the contralateral side. Confocal microscopy revealed a lysosome‐like expression pattern in BV‐2 cells, as well as in ECL‐associated macrophages/microglial cells in vivo. Furthermore, we were able to demonstrate that U937 cells with downregulated MAF converted slower and to a significantly reduced extent to the macrophageal phenotype after TPA treatment. In addition, MAF downregulation in BV‐2 microglial cells substantially reduced the phagocytotic uptake of dextran beads. Our data indicate that MAF is expressed in selected macrophages/microglial cells around the lesion and in the degenerating hippocampus after ECL. Furthermore, MAF expression in monocytic cells seems to play a functional role in the differentiation to a phagocytosing phenotype and may be, at least partially, required for phagocytotic activity, specifically in lesioned tissue after brain trauma. © 2005 Wiley‐Liss, Inc.
A method for multitask fMRI data fusion applied to schizophrenia
Authors: Calhoun Vince D. , Adalı Tulay , Kiehl Kent A. , Astur Robert , Pekar James J. , Pearlson Godfrey D.
Published: December 2005

It is becoming common to collect data from multiple functional magnetic resonance imaging (fMRI) paradigms on a single individual. The data from these experiments are typically analyzed separately and sometimes directly subtracted from one another on a voxel‐by‐voxel basis. These comparative approaches, although useful, do not directly attempt to examine potential commonalities between tasks and between voxels. To remedy this we propose a method to extract maximally spatially independent maps for each task that are “coupled” together by a shared loading parameter. We first compute an activation map for each task and each individual as “features,” which are then used to perform joint independent component analysis (jICA) on the group data. We demonstrate our approach on a data set derived from healthy controls and schizophrenia patients, each of which carried out an auditory oddball task and a Sternberg working memory task. Our analysis approach revealed two interesting findings in the data that were missed with traditional analyses. First, consistent with our hypotheses, schizophrenia patients demonstrate “decreased” connectivity in a joint network including portions of regions implicated in two prevalent models of schizophrenia. A second finding is that for the voxels identified by the jICA analysis, the correlation between the two tasks was significantly higher in patients than in controls. This finding suggests that schizophrenia patients activate “more similarly” for both tasks than do controls. A possible synthesis of both findings is that patients are activating less, but also activating with a less‐unique set of regions for these very different tasks. Both of the findings described support the claim that examination of joint activation across multiple tasks can enable new questions to be posed about fMRI data. Our approach can also be applied to data using more than two tasks. It thus provides a way to integrate and probe brain networks using a variety of tasks and may increase our understanding of coordinated brain networks and the impact of pathology upon them. Hum Brain Mapp, 2005. © 2005 Wiley‐Liss, Inc.
Molecular mimicry: Sensitization of Lewis rats with Campylobacter jejuni lipopolysaccharides induces formation of antibody toward GD3 ganglioside
Authors: Usuki Seigo , Thompson Stuart A. , Rivner Michael H. , Taguchi Kyoji , Shibata Keiko , Ariga Toshio , Yu Robert K.
Published: December 2005

Recently we have reported cases of demyelinating inflammatory neuropathy showing elevated titers of anti‐GD3 antibodies, which occurs rarely in Guillain‐Barré syndrome. To examine the correlation between the anti‐GD3 antibody titer and Campylobacter jejuni infection, we sensitized female Lewis rats with lipopolysaccharides (LPSs) from serotype HS19 of C. jejuni and examined changes in nerve conduction velocity and nerve conduction block (P/D ratio). After 16 weeks of sensitization, animals revealed decreases of nerve conduction velocity and conduction block (P/D ratio) and high titer of anti‐GD3 antibodies. These anti‐GD3 antibodies also blocked transmission in neuromuscular junctions of spinal cord‐muscle cells cocultures. The GD3 epitope was verified to be located on the Schwann cell surface and nodes of Ranvier in rat sciatic nerve. To determine the target epitope for GD3 antibodies in causing nerve dysfunction, the LPS fraction containing the GD3 epitope was purified from the total LPS by using an anti‐GD3 monoclonal antibody‐immobilized affinity column. Subsequently, chemical analysis of the oligosaccharide portion was performed and confirmed the presence of a GD3‐like epitope as having the following tetrasaccharide structure: NeuAcα2‐8NeuAc2‐3Galβ1‐4Hep. Our data thus support the possibility of a contribution of GD3 mimicry as a potential pathogenic mechanism of peripheral nerve dysfunction. © 2005 Wiley‐Liss, Inc.
Analytical and semipreparative resolution of ranolazine enantiomers by liquid chromatography using polysaccharide chiral stationary phases
Authors: Luo Xingping , Zhai Zongde , Wu Xiaomei , Shi Yanping , Chen Liren , Li Yongmin
Published: December 2005

Novel HPLC methods were developed for the analytical and semipreparative resolution of new antianginal drug ranolazine enantiomers. Good baseline enantioseparation was achieved using cellulose tris (3,5‐dimethylphenylcarbamate) (CDMPC) chiral stationary phases (CSPs) under both normal‐phase and polar organic modes. The validation of the analytical methods including linearity, LODs, recovery, and precision, and the semipreparative resolution of ranolazine racemate were carried out using methanol as mobile phase without any basic and acidic additives under polar organic mode, using CDMPC CSPs. At analytical scale, the elution times of both enantiomers were less than 7.5 min at 20°C and 1.0 mL/min, with the separation factor (α) 1.88 and the resolution factor (Rs) 2.95. At semipreparative scale, about 14.3 mg/h enantiomers could be isolated and elution times of both enantiomers were less than 13 min at 2.0 mL/min. To increase the throughput, the technique of overlapping injections was used. The first eluted enantiomer was isolated with a purity of 99.6% enantiomer excess (e.e.) and >99.0% yield. The second enantiomer was isolated with a purity of 98.8% e.e. and >99.0% yield. In addition, optical rotation and circular dichroism spectroscopy of both ranolazine enantiomers isolated were also investigated.
Identification of objects in an acoustic wave guide inversion II: Robin–Dirichlet conditions
Authors: Lee Doo‐Sung , Gilbert R. P.
Published: December 2005

In this paper we investigate the unknown body problem in a wave guide where one boundary has a pressure release condition and the other an impedance condition. The method used in the paper for solving the unknown body inverse problem is the intersection canonical body approximation (ICBA). The ICBA is based on the Rayleigh conjecture, which states that every point on an illuminated body radiates sound from that point as if the point lies on its tangent sphere. The ICBA method requires that an analytical solution be known exterior to a canonical body in the wave guide. We use the sphere of arbitrary centre and radius in the wave guide as our canonical body. We are lead then to analytically computing the exterior solution for a sphere between two parallel plates. We use the ICBA to construct solutions at points ranging over the suspected surface of the unknown object to reconstruct the unknown object using a least‐squares matching of computed, acoustic field against the measured, scattered field. Copyright © 2005 John Wiley & Sons, Ltd.
On a hierarchy of models for electrical conduction in biological tissues
Authors: Amar M. , Andreucci D. , Bisegna P. , Gianni R.
Published: December 2005

In this paper we derive a hierarchy of models for electrical conduction in a biological tissue, which is represented by a periodic array of period ε of conducting phases surrounded by dielectric shells of thickness εη included in a conductive matrix. Such a hierarchy will be obtained from the Maxwell equations by means of a concentration process η → 0, followed by a homogenization limit with respect to ε. These models are then compared with regard to their physical meaning and mathematical issues. Copyright © 2005 John Wiley & Sons, Ltd.
Temporal diffusion spectroscopy: Theory and implementation in restricted systems using oscillating gradients
Authors: Parsons Edward C. , Does Mark D. , Gore John C.
Published: December 2005

The theory of temporal diffusion spectra is reviewed. In contrast to q‐space spectroscopy, which measures the displacement spectrum of spins in a spatial domain, the spectral density of the velocity correlation function (VCF) in the temporal domain is considered. It is demonstrated that casting diffusion in this domain may facilitate measurements of microscopic geometry and the decomposition of the diffusion signal into components due to disperse flow and restricted diffusion. An oscillating gradient (OG) method of diffusion spectroscopy was developed and implemented. Microscopic pore sizes, surface‐to‐volume ratios (S/Vs), and diffusion path tortuosities were extracted from model systems using this method. Cases are discussed in which this type of experiment may allow the characterization of pore geometry when spatial domain experiments fail. OGs may be combined with imaging sequences to map complex patterns of diffusion and flow. Moreover, scalar apparent diffusion coefficient (ADC) measurements in complex biological systems may be subtly dependent on specific pulse sequence parameters. Thus, scalar ADC measurements using gradient pulses with different frequency spectra may give different results. Conversely, the frequency dependence of motion‐sensitizing gradient pulses may be exploited to deduce the origin of ADC changes. Magn Reson Med, 2006. © 2005 Wiley‐Liss, Inc.
Dephased MRI
Authors: Bakker Chris J.G. , Seppenwoolde Jan‐Henry , Vincken Koen L.
Published: December 2005

In this work gradient dephasing is treated as a mechanism for manipulating contrast in otherwise conventional MR images. The paper provides a theoretical and experimental framework for this approach. It starts from the observation that dephasing gradients invoke a shift in k‐space. From this it is inferred that the effects of in‐plane and through‐plane dephasing can be systematically explored in the context of any given imaging experiment by sampling k‐space more widely and densely than dictated by the field of view (FOV) and the spatial resolution of the desired images. The oversampled k‐space allows an ensemble of lower‐resolution dephased images to be reconstructed in which the degree and direction of dephasing are determined by the off‐center position of the reconstruction window. The efficacy of this approach is demonstrated for standard gradient‐echo acquisitions in a phantom. The results indicate the potential of the proposed methodology for evaluating 3D image data and optimizing gradient dephasing in applications that rely on the exploitation of partial volume and susceptibility effects (e.g., tracking interventional devices and tracing magnetically labeled substances). Magn Reson Med, 2006. © 2005 Wiley‐Liss, Inc.
Beyond the g‐factor limit in sensitivity encoding using joint histogram entropy
Authors: Larkman David J. , Batchelor Philip G. , Atkinson David , Rueckert Daniel , Hajnal Jo V.
Published: December 2005

The maximum practical speed‐up that can be achieved using parallel imaging methods is widely accepted to be limited by g‐factor noise. An approximate expression for the g‐factor noise as a function of the principal eigenvector of the inverse sensitivity matrix is derived. This formulation allows g‐factor enhanced noise to be reduced by a constrained optimization procedure with joint image histogram entropy between a reference image and a SENSE image as an image quality metric. The reference image does not need to have identical resolution or contrast. The reference image may also be used for coil calibration. The limits of the method are explored using simulated and real array coil data with high g‐factor using a variety of contrast and resolution combinations. The method preserves image structure, contrast, and lesions even when these were not observable in the reference data. In all cases g‐factor was dramatically reduced. Magn Reson Med, 2006. © 2005 Wiley‐Liss, Inc.
Diffusion tensor spectroscopy (DTS) of human brain
Authors: Ellegood Jacob , Hanstock Chris C. , Beaulieu Christian
Published: December 2005

The diffusion tensor of N‐acetyl aspartate (NAA), creatine and phosphocreatine (tCr), and choline (Cho) was measured at 3T using a diffusion weighted STEAM 1H‐MRS sequence in the healthy human brain in 6 distinct regions (4 white matter and 2 cortical gray matter). The Trace/3 apparent diffusion coefficient (ADC) of each metabolite was significantly greater in white matter than gray matter. The Trace/3 ADC values of tCr and Cho were found to be significantly greater than NAA in white matter, whereas all 3 metabolites had similar Trace/3 ADC in cortical gray matter. Fractional anisotropy (FA) values for all 3 metabolites were consistent with water FA values in the 4 white matter regions; however, metabolite FA values were found to be higher than expected in the cortical gray matter. The principal diffusion direction derived for NAA was in good agreement with expected anatomic tract directions in the white matter. Magn Reson Med, 2006. © 2005 Wiley‐Liss, Inc.
Crane Dynamics with Modulated Hoisting
Authors: Bockstedte Andreas , Kreuzer Edwin
Published: December 2005

For many types of cranes commonly used in technical applications, the reduction of payload pendulations is an important design issue. Especially for cranes with variable cable length, oscillations are boosted by the hoisting of the payload due to nonlinear effects. Most of the techniques for active damping are based on a control input that displaces the support of the hoisting mechanism perpendicularly to the direction of the pendulum. However, controlled motion of the carrying structure might not be suitable or even impossible for some applications.

The possibility to influence and reduce pendulations by means of feedback controlled variations of the cable length is hardly used in crane technology. A control strategy based on the phenomenon of autoparametric resonances in nonlinear dynamical systems is presented that manipulates the desired hoisting velocity by superposition of a suitably modulated motion in order to reduce amplifications of the pendulations, in particular in absence of other effective control inputs. Experimental results for a simple pendulum setup are presented. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dissipation induced instabilities in continuous non‐conservative systems
Authors: Kirillov Oleg N. , Seyranian Alexander P.
Published: December 2005

In this contribution we analyze the stabilizing and destabilizing effect of small damping for rather general class of continuous non‐conservative systems, described by the non‐self‐adjoint boundary eigenvalue problems. Explicit asymptotic expressions obtained for the stability domain allow us to predict when a given combination of the damping parameters leads to increase or to decrease in the critical non‐conservative load. The results obtained explain why different types of internal and external damping so surprisingly influence on the stability of non‐conservative systems. As a mechanical example the stability of a viscoelastic rod with small internal and external damping, loaded by tangential follower force, is studied in detail. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Damping of Vibrations in a SystemWith Two Beams by Structural Friction
Authors: Kosior Andrzej
Published: December 2005

This paper presents the results of tests on free and forced harmonic vibrations in a system with two beams with structural friction taken into account. The beams are clamped together with uniform unitary pressure. The hysteresis loop describing the frictional‐elastic properties of the system has a form of a parallelogram. The autor created a mathematical model of the vibrating system with two beams. During free vibrations of the system, its damping characteristics were tested by a digital simulation method. The vibration damping decrement as a function of amplitude displacement was determined. When vibrations were harmonically forced, the amplitude ‐ frequency characteristics of the system were determined numerically. The system was used as a nonlinear vibration damper in a linear system with a harmonic force. The equations of motion of the nonlinear two‐degree of freedom system were solved by means of a digital simulation method. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Results from Bifurcation Analysis in Ship Dynamics
Authors: Kreuzer Edwin , Markiewicz Marian , Pick Marc‐André
Published: December 2005

To assure safe ship operations on one hand side and to reduce operational restrictions to a minimum a proper knowledge of the ship's behavior in waves is necessary. One approach to achieve this is to generate an exact mathematical model of a ship and the fluid–structure–interaction in order to determine dangerous and safe operational conditions by analyzing the behavior with present numerical methods from nonlinear dynamics theory. Comparison between numerical simulations and experimental results as well as two sets of save and dangerous conditions for a given model of a real ship are shown. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Applications of Artificial Neural Networks for Periodic Structures Analysis
Authors: Krzyżyński Tomasz , Brochocki Andrzej
Published: December 2005

The paper presents the nondeterministic, based on artificial neural network application approach analysis of periodic structures. We can distinguish several examples where the problem may be observed: conventional and magnetic railways, high building constructions that consist of repeatable blocks, ship and aeroplane bodies, space‐shuttle periodic designs, long‐beam antenna structures or mistuned blade disks with friction damping elements. The scope of research is to examine possibilities of use the neural networks for mistuning parameters definition and also to denominate its possible causes. The results obtained via neural network simulator training process are compared with the calculations based on mathematical model. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Suppression of Induced Vibrations using Dynamic Shape Control with Distributed Piezoelectric Actuation
Authors: Nader M. , v. Garssen H.‐G. , Irschik H.
Published: December 2005

In the present contribution, the complete suppression of elastic vibrations of structures by means of an additional piezoelectric eigenstrain distribution is considered. A vibrating cantilever is used as a descriptive example. First, according to the theory of dynamic shape control, a continuous distribution for the actuation is derived. Then, positions for discrete piezoelectric patches are suggested. The introduced theoretical strategy is validated by .nite element computations and an appropriate laboratory experiment. Based on frequency response measurements, a feedback controller is designed in the frequency domain. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fourier‐Analyse versus Wavelet‐Analyse
Authors: Schlagner S. , Strehlau U.
Published: December 2005

Sollen aus Zeitsignalen y (t ) spezifische Informationen gewonnen werden, so kann dies mit Hilfe geeigneter Analysen, also Transformationen geschehen. Die wohl bekannteste Transformation ist die Fourier‐Transformation, welche ein Signal spektral, d.h. in seinen Frequenzinhalten darstellt. Da diese Transformation das zu transformierende Signal als Gesamtobjekt betrachtet, beinhaltet sie nur globale Frequenzinformationen. Oft ist jedoch eine zeitliche Einordnung spektraler Eigenschaften instationärer Signale, z. B. bei der Lokalisierung von Stößen von Interesse. Dies kann die Fourier‐Transformation nicht leisten. An dieser Stelle bietet die Short‐Time‐Fourier‐Transformation bedingt eine Möglichkeit der zeitlichen Zuordnung spektraler Eigenschaften, indem sie das Signal in Zeitbereiche unterteilt.

Eine bessere Möglichkeit zur Untersuchung instationärer Signale stellt die Wavelet‐Transformation dar. Sie kann Signalstrukturen zeitlich besser erfassen und bietet somit dieMöglichkeit, sowohl den Frequenzinhalt als auch die Frequenzdynamik zu untersuchen. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Vibrations of Pipes with Internal Flow and Rigid Body Degrees of Freedom
Authors: Stangl Michael , Irschik Hans
Published: December 2005

In the present paper the nonlinear dynamics of elastic pipes conveying fluid at arbitrary flow rates are investigated. The nonlinear equations of motion are derived using a unified form of the Lagrange Equations for non‐material volumes formulated by Irschik and Holl [1], see also Chapter 3 of [2]. In a first step cantilevered pipes are considered using elastic degrees of freedom combined with a Ritz‐Galerkin Ansatz of arbitrary order for modelling the deformations of the pipes. The Lagrange Equations for non‐material volumes include a nonzero surface integral of the kinetic energy due to the moving outlet surface at the end of the pipe. The linear equations of motion obtained from this model are then analytically investigated utilizing the corresponding Eigenvalue problem. The results are visualized in an Argand representation of the corresponding Eigenvalues of the system matrix and compared to existing results obtained by using different formulations, such as the Hamilton Principle for Open‐Systems, formulated by Benjamin [4], as demonstrated by Païdoussis [5], see also chapter 3.5 of [6]. In a next step an elastic pipe with a rigid body degree of freedom combined with a Ritz‐Galerkin Ansatz is modelled with one supported and one free end. The derivation of the equations of motion is performed by using a floating‐frame of reference formulation which leads to a system of nonlinear second order differential equations describing the motion of the pipe. Finally, the stability of the solutions of the equations of motion for varying flow rate is studied numerically. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability and stabilisation of acausal discrete linear repetitive processes
Authors: Galkowski Krzysztof , Kummert Anton , Cichy Blazej , Rogers Eric
Published: December 2005

Repetitive processes are a distinct class of two‐dimensional systems (i.e. information propagation in two independent directions occurs) of both systems theoretic and applications interest. In this paper we introduce a new model for these processes in order to represent dynamics which arise in some applications areas and which are not included in those currently available. Then we proceed to de.ne quadratic stability for this case, obtain conditions for its existence, and also use feedback control to solve a stabilization problem. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal Control of Iterative Solution Methods for Linear Systems of Equations
Authors: Helmke Uwe , Jordan Jens
Published: December 2005

Iterative solution methods for linear systems of equations can be regarded as discrete‐time control systems, for which a stabilizing feedback control has to be found. Well known algorithms such as GMRES(m) may exhibit unstable dynamics or sensitive dependence on initial conditions, thus preventing the algorithm to converge to the desired solution. Based on linear system feedback design techniques a new algorithm is proposed that does not suffer under such shortcomings. Global convergence to the desired solution is shown for any initial state. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of Vertebrae Motion with Computer Simulation Using Elementary Contact Pairs
Authors: Liem K. , Dhanu Singh M. , Kecskeméthy A.
Published: December 2005

To simulate the motion of two adjacent vertebrae a computer model is created. Described in the paper is the mathematical modelling of a vertebrae pair using multibody methods and impact analysis techniques with elementary contact geometry for the facet joints. The ligaments and the intervertebral disc are modeled as a parallel connection of a spring and a damper. The results are compared with existing approaches and experimental data. In order to enhance the results, piecewise linear functions instead of a constant spring stiffness for the model of the intervertebral disc are used. The simulation allows the motion in three‐dimensional space (three translations and three rotations, see figure 1). The investigations are focused on the vertebrae pair C5‐C6 but can be easily extended to other vertebrae. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On artificial geometry errors in the adaptive analysis of eigenvalues and eigenmodes of curved shell structures using the finite element method
Authors: Ewert Eduard , Schweizerhof Karl
Published: December 2005

The standard procedure to compute design loads for shell structures as also proposed in design rules is based on the computation of the limit load taking into account the modification of the so‐called stability loads due to geometrical imperfections. The imperfections are mostly chosen affine to the buckling patterns, which are solutions of the eigenvalue‐problem for the geometrically perfect structure. Thus, the eigenvalue‐problems for stability points have to be solved very accurately. In the present contribution an adaptive h ‐refinement procedure is taken for the solution using low order shell elements. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A general polyconvex strain‐energy function for fiber‐reinforced materials
Authors: Markert Bernd , Ehlers Wolfgang , Karajan Nils
Published: December 2005

The continuum mechanical modeling and numerical simulation of fiber‐reinforced materials, such as carbon‐fiber‐reinforced plastics or collagenous biological tissues, are of great interest in the field of material science. In this regard, various strainenergy functions have been proposed to capture the inherent anisotropy of these types of materials ranging from simple exponential functions applied in biomechanics [5] to more sophisticated formulations based on the theory of invariants [8]. The goal of this contribution is to present an alternative ansatz, which basically adopts the general idea of the wellestablished isotropic hyperelasticity law of Ogden [7]. In particular, a polynomial strain‐energy function formulated in the fiber stretch is proposed, which allows the description of the general nonlinear elastic response of various kinds of fiber materials, such as collagen, nylon or sisal, in a very concise form. Moreover, the formulation still meets the requirements of a stress‐free reference state and material stability, whereas the number of material parameters is kept to a minimum. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Imperfection Sensitivity and Limit Loads of Spherical Shells under Radial Pressure
Authors: Pontow Jens , Dinkler Dieter
Published: December 2005

The evaluation of the imperfection sensitivity of shell structures and the estimation of their limit loads are widely discussed phenomena. The perturbation energy concept according to Dinkler et al. [1], [2] enables to assess the imperfection sensitivity of shell structures by means of an energy value, the perturbation energy. A buckling criterion may be developed from the comparison between the perturbation energy and experimental data. This paper focuses on the imperfection sensitivity and limit loads of spherical shells of revolution under radial pressure. The investigations include the influence of the meridional angle and different types of boundary conditions. By comparing the numerical results with the German design rule DIN 18800, critical values for the perturbation energy are derived to predict the limit loads. These critical values for the perturbation energy allow to judge whether the German design rule DIN18800 predicts the limit loads of spherical shells under external pressure with varying meridional angles and different boundary conditions with the same reliability in respect of the perturbation energy. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability of linear and nonlinear elastic columns under action of a parametric force in form of a random stationary process
Authors: Treckmann Malte , Potapov Vadim D.
Published: December 2005

Forces on structures, which are often simplified assumed as static loads, are frequently exhibited as random processes. Statements about the stability of similar structures can be determined i.e. by help of numeric procedures, which are based on methods using the Lyapunov‐exponent. Furthermore, the stability of systems made from nonlinear material is considered. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Abaqus‐Implementierung eines Dehnungsraum‐Stoffgesetzesnach Besdo
Authors: Besdo D. , Ihlemann J. , Kirbach J.
Published: December 2005

Das Lagrange‐formulierte Materialgesetz im Dehnungsraum nach Besdo [1] berücksichtigt Effekte der isotropen Verfestigung und Formen der Anisotropie (plastisch induzierte und kinematische Verfestigung) unter Berücksichtigung des plastic spin . Oftmals ist es bereits bei der Formulierung eines Materialgesetzes (elastisches Potential, Fließregel, Fließbedingung) notwendig, sich den Konventionen des anvisierten FE‐Programmsystems anzupassen, weil der Übergang zwischen der Eulerschen und der Lagrangeschen Betrachtungsweise unter Beibehalt identischer tensorieller Aussagen nicht gelingt. Mit Hilfe des Übertragungsoperators nach Ihlemann [2] ist ein freier Umgang in der Betrachtungsweise möglich. Am Beispiel der Materialtangente nach Besdo [4] wird nun das Konzept des Übertragungsoperators auf 4‐stufige Tensoren erweitert und dessen Anwendung zur Aufbereitung einer Abaqus‐konformen Steifigkeitsmatrix demonstriert. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Formulation of Finite Viscoplasticity for Glassy Polymers in the Logarithmic Strain Space
Authors: Göktepe Serdar , Méndez Joel , Miehe Christian
Published: December 2005

This contribution extends the recently proposed kinematical approach by Miehe et al. [4] to a constitutive formulation for elasto–visco–plastic behavior of amorphous glassy polymers below their glass transition temperature. In contrast to the existing kinematical approaches in the literature, the latter is constructed in the logarithmic strain space yielding a formulation analogous to the geometrically linear theory of plasticity in the six–dimensional space. Its analogy to a geometrically linear theory makes this formalism very attractive, especially with regard to its algorithmic implementation. Conceptually, elasto–visco–plastic model with an intrinsic non–linear kinematic hardening is considered in the logarithmic strain space. The evolution law of the plastic strains is adopted from Argon's [1] double–kink theory. The proposed formulation is validated by means of experimental data obtained from both homogeneous and non–homogeneous experiments. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling and simulation of chip formation in high speed cutting
Authors: Hortig Christian , Svendsen Bob
Published: December 2005

The purpose of this short work is the thermomechanical modeling of shear band and chip formation during high‐speed cutting. Shear bands develop in areas of maximal mechanical dissipation in which temperature‐dependent softening dominates strainand strain‐rate‐dependent hardening. In the simulations, the well‐known problem of the mesh‐dependence of the shear‐band development is addressed, involving both mesh size and mesh orientation. An example simulation is presented. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Solution‐precipitation creep – micromechanical modelling and numerical results
Authors: Ilić Sandra , Hackl Klaus
Published: December 2005

Our aim is to present a continuum mechanical model for solution‐precipitation creep as well as to compare the numerical results based on that model with experimental observations. The formulation of the problem is based on the minimization of a Lagrangian consisting of elastic power and dissipation. Elastic energy is chosen to be in a standard form but dissipation is strongly adapted to the solution‐precipitation process by introducing two new quantities: the velocity of material transport within the crystallite‐interfaces and the normal velocity of precipitation or solution respectively. The model enables one to give an analytical solution for the case of a single crystal and numerical solution based on a finite element method for more complex, polycrystalline materials. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling and simulation of induced anisotropy and directional hardening effects due to an evolving microstructure in metals
Authors: Wang J. , Levkovitch V. , Reusch F. , Svendsen B.
Published: December 2005

The purpose of the current work is the formulation, numerical implementation and application of a material model for anisotropic hardening in metals taking the interplay between the the direction of inelastic deformation, the orientation of dislocation structures, and the current deformation/loading direction into account. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A finite element modeling of piezoelectric materials with a superimposed stress
Authors: Arockiarajan A. , Delibas B. , Menzel A. , Seemann W.
Published: December 2005

Based on the mechanism of domain switching, a three dimensional nonlinear finite element model for piezoelectric materials subjected to electromechancial loading is developed in this contribution. The finally considered model problem deals with differently oriented grains whereby uni‐axial, quasi‐static cyclic loading is applied. It is assumed that a crystal orientation switches if the reduction in free energy of the grain exceeds a critical energy barrier. The nonlinearity in the small electromechanical loading range is addresses via a polynomial probability function for domain switching. Hysteresis behavior is discussed taking the influence of a superimposed compression state into account. It is observed that the hysteresis loop flattens under the axial compression but elongates under the transverse compression. Irrespective of how the compression is applied, the remnant polarization and as well as the coercive electric field decrease. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of Anisotropic Damage in Arterial Walls
Authors: Balzani Daniel , Schröder Jörg , Gross Dietmar
Published: December 2005

In a certain range of overexpansion arterial walls are characterized by an orthotropic elastic material behavior. Due to different stabilities of the helically arranged fibers, i.e. breakage of collagen crosslinks between the fibers, damage effects are observed in experiments. Because of the fibrous composition it is assumed that damage mainly occurs in the fiber direction. The proposed damage model is extended to arterial wall applications by introducing a referential damage state. The damage approach is applied to a polyconvex model for the hyperelastic behavior of arteries in order to obtain a materially stable model, which guarantees the existence of solutions of the underlying boundary value problem. The performance of the proposed model is presented in a numerical example, where the overexpansion of an atherosclerotic artery is simulated. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computer simulations for the mechanical analysis of skeletal muscles
Authors: Böl Markus , Reese Stefanie
Published: December 2005

The structure of a skeletal muscle can be seen as a complex hierarchical organisation in which thousands of muscle fibers are arranged within a connective tissue network. Inside of the single muscle fibre many force‐producing cells, known as sarcomeres, are connected and take care of the contraction of the whole muscle. The material behaviour of muscles is nonlinear. Due to the fact that muscles can have large deformations in space, geometrical non‐linearities must additionally be taken into account. For the simulation of such a behaviour the finite element method is used in the present approach. The material behaviour of the muscle is split into a so‐called active and a passive part. To describe the passive part special unit cells consisting of one tetrahedral element and six truss elements have been derived. Additionally to these unit cells other truss elements are attached representing bundles of muscle fibers and therefore the active part of the material behaviour. The contractile behaviour of the muscle is mainly in.uenced by the stretch of the muscle fibres, the shortening velocity and the activation status of the muscle. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Anisotropic elasto‐plastic damage formulation for finite strains using a damage structural tensor and the effective stress concept
Authors: Kintzel Olaf , Meschke Günther
Published: December 2005

Using the strain equivalence principle and the effective stress concept an anisotropic finite strain damage model is proposed as a direct extension of the classical isotropic LEMAITRE damage model to the anisotropic finite strain case. The damage tensor is included as a structural tensor in the complementary energy potential. This approach allows to consider a wide range of anisotropic damage phenomena on the level of continuum mechanics. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A composite model for municipal solid waste
Authors: Krase Volker , Dinkler Dieter
Published: December 2005

The mechanical behaviour of municipal solid waste is very complex due to the internal structure and differs considerably from ordinary materials. The fundamental idea of the presented mechanical constitutive model is the split of the material into two solid phases, justified by experimental observations, where fibrous particles signi.cantly influence the composite behaviour. Constitutive laws are independently introduced for each phase. A .nite deformation theory is applied, whereas the concept of elastoplasticity allows reproducing the highly non‐linear stress‐strain relations. A creep law describes time‐depending deformation under compression loads. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micromechanical Approach of Martensitic Transformation Problem in Steels
Authors: Zhang Wenge , Hunkel Martin , Zoch Hans‐Werner
Published: December 2005

To determine the mechanical behavior of material involving the martensitic phase transformation (for example, steels like 100Cr6), a representative volume element (RVE) model including phase transformation criterion is desireable at micromechanical approach. A framework combining the Eshelby's inclusion theory as well as continuum mechanics with phase‐transformation (PT) critical condition at RVE model is presented briefly. And application of this model to estimate the critical aspect ratio of martensitic plate or lath inside homogeneneous stress field is also included, where the RVE can be under uniaxial tension/compression or pure shear loading case. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Identification and characterization of a “biomarker of toxicity” from the proteome of the paralytic shellfish toxin‐producing dinoflagellate Alexandrium tamarense (Dinophyceae)
Authors: Chan Leo Lai , Sit Wai‐Hung , Lam Paul Kwan‐Sing , Hsieh Dennis Paul Hsientang , Hodgkiss Ivor John , Wan Jennifer Man‐Fan , Ho Alvin Yam‐Tat , Choi Nicola Man‐Chi , Wang Da‐Zhi , Dudgeon David
Published: December 2005

The objective of this study was to identify and characterize a “biomarker of toxicity” from the proteome of Alexandrium tamarense, a paralytic shellfish toxin (PST)‐producing dinoflagellate. A combination of 2‐DE and MS approaches was employed to identify proteins of interest in the vegetative cells of several strains of A. tamarense with different toxin compositions and from different geographical locations. The electrophoretic analysis of the total water‐soluble proteins from these toxic strains by 2‐DE showed that several abundant proteins, namely AT‐T1, AT‐T2 and AT‐T3, differing slightly in apparent Mr and pIs, were consistently present in all toxic strains of A. tamarense. Further analysis by MALDI‐TOF MS and N‐terminal amino acid sequencing revealed that they are isoforms of the same protein. Even more intriguing is that these proteins in A. tamarense have similar amino acid sequences and are closely related to a “biomarker of toxicity” previously reported in A. minutum. Unambiguous and highly species‐specific identification was later achieved by comparing the PMFs of proteins in these two species. An initial attempt to characterize these proteins by generation of murine polyclonal antibodies against the AT‐T1 protein was successful. Western blot analysis using the murine AT‐T1‐polycolonal antibodies identified all the toxic strains of A. tamarense and A. minutum, but not the nontoxic strain of A. tamarense. These results indicate that these protein characteristics for toxic strains are species‐specific and that they are stable properties of the tested algae which are clearly distinguishable irrespective of geographical location and toxin composition. To our knowledge, this is the first study to demonstrate the use of polyclonal antibodies against marker proteins purified from 2‐DE gels to distinguish different strains and species of the PST‐producing dinoflagellate Alexandrium. It provides the basis for the production of monoclonal antibody probes against the “biomarkers of toxicity” for those dinoflagellates whose genome is incompletely characterized. Potentially, immunoassays could be developed to detect the presence of toxic algae in routine monitoring programs as well as to predict bloom development and movement.