bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of lipid‐based carrier systems and inclusion complexes of diethyldithiocarbamate–iron to trap nitric oxide in biological systems
Authors: Charlier Nicolas , Préat Véronique , Gallez Bernard
Published: December 2005

The success of spin trapping techniques in vivo hinges on whether spin traps with high trapping efficiency and biocompatibility can be developed. Currently, two iron chelates based on the dithiocarbamate structure (hydrophilic ferro‐di(N‐methyl‐D‐glucamine‐dithiocarbamate, or Fe(II)‐MGD, and lipophilic ferro‐di(diethyldithiocarbamate), or Fe(II)‐DETC), are used for spin trapping of nitric oxide (NO) in biologic systems. However, detection efficiency is hampered by a complex redox chemistry for Fe(II)‐MGD and by the insolubility of Fe(II)‐DETC in water. To circumvent these problems, two new spin trap formulations based on Fe(II)‐DETC were developed: a lipid‐based carrier system stabilized by lecithin and inclusion complexes in hydroxypropyl‐β‐cyclodextrin. The capability of these two systems to trap NO was determined and compared to the standard spin traps in vitro (in the presence of an NO donor) and in vivo (after induction of septic shock in mice). The sensitivity of the detection of NO was significantly increased (by a factor of 4) using the lipid‐based carrier systems or inclusion complexes compared to the standard spin trap agents. Magn Reson Med, 2006. © 2005 Wiley‐Liss, Inc.
In vivo magnetic resonance imaging of single cells in mouse brain with optical validation
Authors: Heyn Chris , Ronald John A. , Mackenzie Lisa T. , MacDonald Ian C. , Chambers Ann F. , Rutt Brian K. , Foster Paula J.
Published: December 2005

In the current work we demonstrate, for the first time, that single cells can be detected in mouse brain in vivo using magnetic resonance imaging (MRI). Cells were labeled with superparamagnetic iron oxide nanoparticles and injected into the circulation of mice. Individual cells trapped within the microcirculation of the brain could be visualized with high‐resolution MRI using optimized MR hardware and the fast imaging employing steady state acquisition (FIESTA) pulse sequence on a 1.5 T clinical MRI scanner. Single cells appear as discrete signal voids on MR images. Direct optical validation was provided by coregistering signal voids on MRI with single cells visualized using high‐resolution confocal microscopy. This work demonstrates the sensitivity of MRI for detecting single cells in small animals for a wide range of application from stem cell to cancer cell tracking. Magn Reson Med, 2006. © 2005 Wiley‐Liss, Inc.
Stiffness‐weighted magnetic resonance imaging
Authors: Glaser Kevin J. , Felmlee Joel P. , Manduca Armando , Kannan Mariappan Yogesh , Ehman Richard L.
Published: December 2005

An imaging method is introduced in which the signal in MR images is affected by the stiffness distribution in the object being imaged. Intravoxel phase dispersion (IVPD) that occurs during MR elastography (MRE) acquisitions decreases the signal in soft regions more than in stiff regions due to changes in shear wave amplitude and wavelength. The IVPD effect is enhanced by lowpass filtering the MR k‐space data with a circular Gaussian lowpass filter. A processing method is introduced to take the time series of MRE magnitude images with IVPD and produce a final stiffness‐weighted image (SWI) by calculating the minimum signal at each pixel from a small number of temporal samples. The SWI technique is demonstrated in phantom studies as well as in the case of a preserved postmortem breast tissue specimen with a stiff lesion created by focused ultrasound ablation to mimic a breast cancer. When free of significant sources of depth‐dependent wave attenuation, interference, and boundary effects, SWI is a simple, fast, qualitative technique that does not require the use of phase unwrapping or inversion algorithms for localizing stiff regions in an object. Magn Reson Med, 2006. © 2005 Wiley‐Liss, Inc.
Assessment of dynamic susceptibility contrast cerebral blood flow response to amphetamine challenge: A human pharmacological magnetic resonance imaging study at 1.5 and 4 T
Authors: Rose Stephen E. , Janke Andrew L. , Strudwick Mark W. , McMahon Katie L. , Chalk Jonathan B. , Snyder Peter , De zubicaray Greig I.
Published: December 2005

Pharmacological MRI (phMRI) techniques can be used to monitor the neurophysiological effects of central nervous system (CNS) active drugs. In this study, we investigated whether dynamic susceptibility contrast (DSC) perfusion imaging employing the use of superparamagnetic iron oxide nanoparticles (Resovist) could be used to measure hemodynamic response to d‐amphetamine challenge in human subjects at both 1.5 and 4 T. Significant changes in cerebral blood flow (CBF) were found in focal regions associated with the nigrostriatal circuit and mesolimbic and mesocortical dopaminergic pathways. More significant CBF responses were found at higher field strength, mainly within striatal structures. The results from this study indicate that DSC perfusion imaging using Resovist can be used to assess the efficacy of CNS‐active drugs and may play a role in the development of novel psychiatric therapies at the preclinical level. Magn Reson Med, 2006. © 2005 Wiley‐Liss, Inc.
Gradient and stimulated echo (GRASTE) imaging
Authors: Finsterbusch Jürgen , Frahm Jens , Koch Martin A.
Published: December 2005

As a modification of single‐shot stimulated echo acquisition mode (STEAM) MRI, a gradient and stimulated echo (GRASTE) sequence is presented that acquires multiple gradient echoes in addition to each stimulated echo. While “contiguous” GRASTE exploits all stimulated echoes for the central part of k‐space and the gradient echoes for outer lines, “interleaved” GRASTE assigns all echoes of a particular readout interval to directly neighboring lines. Phase distortions may be corrected by the reference signals of a single readout interval without phase encoding. Experimental results obtained for the human brain demonstrate that contiguous GRASTE yields up to 30% better SNR per acquisition time than conventional single‐shot STEAM due to a better efficiency and maintains most of its robustness. Interleaved GRASTE can improve the SNR by a factor of 2 because of the possibility of using larger flip angles in the readout interval. However, its more pronounced sensitivity to off‐resonance effects requires short echo trains. Magn Reson Med, 2006. © 2005 Wiley‐Liss, Inc.
The class of synthesizing cascade structures expansion of vibrating mechanical systems represented by graphs
Authors: Buchacz Andrzej
Published: December 2005

In the paper the problem of synthesis has been solved and its base has been formalized as far as the vibration discrete mechanical systems of the cascade structures graphs is concerned. In connection with this the basic field, the ideas connected with the class of considered structures and used graphs has been given. The manner of getting the “new” structures as a result of synthesis of the characteristics by means the continued fraction expansion method has been presented in farther part of this paper. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling of Gearbox Vibration and Noise
Authors: Hajžman Michal , Zeman Vladimír
Published: December 2005

The paper presents the methodology intended to the vibration and noise analysis of gearboxes or generally of large rotating systems. These systems are considered including their interior rotating shaft system and housing joined together by rollingelement bearings and gear couplings. The new developed bearing model respects real number of rolling bodies and roller contact forces acting between the journals and the outer housing. The model of a complete gearbox is created using the modal synthesis method. Steady state dynamic response of the whole gearbox excited by gear kinematic transmission errors is investigated. A noise radiated by the housing is calculated on the basis of the acoustic power density evaluation. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Einflussgrößen von Reibkräften in Kontakten mit Elastomeren
Authors: Kröger Matthias
Published: December 2005

Um die Ursachen selbsterregter Schwingungen in dynamischen Systemen zu verstehen, müssen oft Kontakte mit Elastomeren als ein Reibpartner genauer untersucht werden. Hierbei kann eine Vielzahl von Einflussgrößen auf die Reibkraft beobachtet werden, z.B. Relativgeschwindigkeit, Normalkraft, Temperatur, Abrieb, Schmierung. Diese Arbeit zeigt dabei wesentliche, für Elastomerkontakte typische Effekte und deren Ursachen auf. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Linear and Nonlinear Finite Element Analysis of Active Composite Laminates
Authors: Marinković Dragan , Köppe Heinz , Gabbert Ulrich
Published: December 2005

The paper presents a finite element concept for analysis of thin‐walled active structures featuring fiber reinforced composite laminate as a passive structural material. The structure is rendered active by embedding piezoelectric material as a multifunctional material. A 9‐node degenerated shell element based on the first order shear deformation theory is developed as a modelling tool capable of predicting the general behavior of the structure for controlling purposes. The von‐Kármán type nonlinearities are considered. The solution strategy of the geometrical nonlinear analysis is based on the incremental approach using the updated Lagrangian formulation. Some numerical results are given to demonstrate the behavior of the element. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The interaction of surface topography and friction dynamics in brake systems described by a Cellular Automaton
Authors: Müller M. , Ostermeyer G. P.
Published: December 2005

The friction coefficient μ , which is the quotient of the friction force R and the normal force N is in principal not a stationary material parameter, but also dependent on for instance the relative velocity, the normal load, the temperature, the climate conditions, the location and the event itself. The dynamics in the boundary layer between a brake disc and a brake pad is closely linked with the surface topography dynamics. Growing and destroying processes of hard, thin patches, carrying the friction power, determine the time‐dependence of the friction coefficient. This interaction between friction and wear has already been simulated with a set of differential equations [2‐4], which give an idea about the equilibrium of flow in the contact zone and which are able to describe the fading effect, for example. Based on this assumption we discretised the boundary layer with a Cellular Automaton [5], which makes it possible to have a more detailed look at the processes in the contact area. This paper will show new conclusions concerning the interdependencies of the friction behaviour and the surface topography. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Analysis of a Simple Impact Drill Model using Set‐Oriented Numerical Methods
Authors: Neumann Nicolai , Sattel Thomas , Wallaschek Jörg
Published: December 2005

Set‐oriented numerical methods provide a relatively new way for obtaining global insight into a non‐linear or even non‐smooth dynamical system. The need for analysis of systems with dynamical behaviour of high complexity arose from investigations on a piezoelectric drilling device, in which vibrational energy is transmitted from an actuator to the drill stem via a free‐flying, impacting mass. Detailed understanding of the dynamics inside of this device is missing to the present day. Here, the use of a set‐oriented approach will be suggested and demonstrated on a basic model for the free‐flying mass. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Torsional Vibration Damping Through Frictional Torsion Damper with Structural Friction and Slide Taken into Consideration
Authors: Skup Zbigniew
Published: December 2005

The paper is concerned with a non‐linear discrete stationary mechanical system containing a frictional torsion damper. Proper effect of vibration damping in a two‐degree‐of freedom system can be reached by the right selection of geometrical parameters for given loads, as pre‐determined by a mathematical model. Structural friction was considered, as well as small relative sliding of damper's discs cooperating with a plunger. The system vibrates under harmonic excitation. The problem was considered on the assumption of uniform unit pressure distribution between the contacting surfaces of friction discs and the plunger. When the discs are sliding, the friction coefficient varies, depending on relative angular velocity. Friction characteristics were assumed on the basis of the author's own research and experimental testing by other authors. Properties of the material were assumed to be in accordance with classical theory of elasticity. The author analysed the influence of parameters of the dynamic system upon amplitude and frequency characteristics as well as on phase and frequency characteristics. The equation of motion was solved by means of the slowly‐varying‐parameters method and, in order to compare the results, by means of numerical simulation. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Reduction Methods for FE Analysis in Nonlinear Structural Dynamics
Authors: Spiess Holger , Wriggers Peter
Published: December 2005

The computation of the nonlinear motion of large structures with implicit time integration schemes is costly. In each time step a large system of linear equations needs to be solved several times. In finite element models often a fine discretization is necessary to represent the geometry and to yield accurate results for the stress field. But from experience it is known that only a small number of degrees of freedom is sufficient to account for the dominant parts of a dynamic motion. Similar to modal decomposition, methods were developed to reduce the number of degrees of freedoms in nonlinear problems. Even though it is not possible to decompose the motion into decoupled modes, a reduction of the number of degrees of freedom yields less computational effort in many cases. The choice of appropriate basis vectors is important. Often used are load‐dependent ‘Ritz’ vectors, which should be updated during the computation to yield sufficient accuracy. Dominant modes, computed by a proper orthogonal decomposition of a previous calculation can be used for repeated analyses of the same system with different loads. Significant time savings can be achieved with reduction methods. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On nonsmooth bifurcations in a simple friction oscillator
Authors: Teufel Andreas , Steindl Alois , Troger Hans
Published: December 2005

We consider a simple friction oscillator with one degree of freedom using a non‐smooth, three‐parameter fricion model accounting for both, a decreasing and increasing dynamic friction force depending on the relative velocity. An analysis of global non‐smooth bifurcations is performed numerically and parameter domains are computed for the existence of stick‐slip oscillations. Special emphasis is placed upon the occurrence of stick‐slip oscillations with negative relative velocity. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Control of Electrodynamic Tether Vibrations in Space
Authors: Viennet Emmanuel , Steindl Alois , Troger Hans
Published: December 2005

First, we simulate the behaviour of a satellite tethered with a continuous electrodynamic cable moving on a circular orbit. Second we extinguish for a simple discrete model small angle librations by controlling the current in the tether. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Note on a Longitudinal and Torsional Type of Ultrasonic Motor with two Stators
Authors: Yi Youping , Gausmann Rainer , Seemann Wolfgang , Zhong Jue
Published: December 2005

This paper deals with an ultrasonic motor, which consist of one rotor and two stators. The main parts of each stator are one longitudinal and one torsional piezoceramic actuator, which are used to generate the desired elliptical orbit on the stator surface. For the purpose of a high efficiency, the longitudinal and the torsional resonant frequency should ideally coincide with the operational frequency. To match the resonant frequencies, two adjustable rings are added to the stators. The influence of the mass and the position of the rings on the first longitudinal and the first torsional eigenfrequency and their mode shapes is investigated. The experimental results fit very well with the theoretical predictions and show that the adjusting rings can be used to match the eigenfrequencies of the two mode shapes. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Dynamics of Belt Drives
Authors: Zwiers U. , Braun M.
Published: December 2005

In modelling the dynamics of belt drives, one has to distinguish between taut and slack belts. While the former can be described by a linear model, the latter is inherently nonlinear and needs a more sophisticated analysis. The paper at hand presents an analytical approach to modelling slack belts in plane motion. To simplify the setting, the pulleys are assumed to have equal radii, such that only one quarter of the total system needs to be considered. The extension to a more general geometry is straightforward. The belt is assumed to have non‐zero bending stiffness. The slackness of the belt should be high enough to allow .exural vibrations even if the belt is inextensible. The static and the stationary solutions are formulated analytically in terms of elliptic functions. As a preliminary study, the special case of a travelling string is considered yielding a .rst insight into the complexity of belt dynamics. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Value‐Restricted Functions for Robust and Simultaneous Stability
Authors: Batra Prashant
Published: December 2005

Different problems, like robust stability of interval plants, stability dependent of delay, and simultaneous stabilizability of three systems are treated via a single method. The value set properties for certain derived functions allow usage of computational analytic inequalities. This approach leads to necessary conditions for the parameters of the stability problems. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Feedforward Control Strategies for Hot Rolling in a Reversing Plate Mill
Authors: Kiefer Thomas , Heeg Roland , Kugi Andreas
Published: December 2005

This contribution is devoted to a new feedforward control concept for the thickness control in a hot rolling mill. The core of this concept is an accurate forward slip model for the calculation of the entry thickness profile. This forward slip is derived by means of the fundamental equations of hydrodynamics for a viscoplastic material in the roll gap. The proposed control strategy advantageously uses the additional information of the rolled plate in form of this entry thickness profile. Simulated and measured data demonstrate the feasibility of the forward slip model and the control concept. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental study of digital force control
Authors: Kisfalusi Krisztián , Stréli Tamás , Stépán Gábor
Published: December 2005

A one degree of freedom experimental rig was designed and manufactured to test the stability properties of digital force control and to compare the theoretical and measured stability charts. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Model Reduction for a Class of PDAE Systems
Authors: Reis Timo
Published: December 2005

We investigate a class of input‐output sytems which consist of partial differential equations whose boundary values fulfill some differential algebraic conditions. Abstractly, these systems can be written down as descriptor systems with an infinite dimensional state space. The aim is to find finite dimensional approximations of these systems and to give error estimates. This means, we approximate a system governed by partial differential algebraic equations (PDAE) by a differential algebraic one. As error measure, we take the ℋ∞‐norm. Applications are e.g. given by the model reduction of time delay systems. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computation of Lie Derivatives of Tensor Fields Required for Nonlinear Controller and Observer Design Employing Automatic Differentiation
Authors: Röbenack Klaus
Published: December 2005

Differential‐geometric concepts are widely used in nonlinear controller and observer design. The design algorithms often require certain types of Lie derivatives. In the past, these derivatives have been computed symbolically. The author suggests an alternative approach based on automatic differentiation. The computation of Lie derivatives of different tensor fields is discussed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computer Algebra Tests on Identifiability of Nonlinear Implicit Dynamical Systems
Authors: Zehetleitner Kurt , Schlacher Kurt
Published: December 2005

In this contribution criteria on identifiability of system parameters of nonlinear implicit dynamical systems, also denoted differential algebraic equation systems (DAEs), are presented. Two interesting questions can be posed in this context: We ask for identifiability along a given trajectory and the existence of a trajectory through a given point in the state space such that the parameters are identifiable along it. A computer algebra algorithm to test these properties is provided. As a special case systems in explicit form are considered and a mechanical example is shown as application. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Contact of Planar Flexible Multibody Systems Using a Linear Complementarity Formulation
Authors: Ebrahimi Saeed , Eberhard Peter
Published: December 2005

Descriptions leading to Linear Complementarity Problems (LCPs) are well established in the contact modeling of rigid multibody systems and have a very strong mathematical basis. These approaches yield exact solutions for contact problems consisting of contact (force/acceleration level) and impact (impulse/velocity level). By utilizing these methods, also frictional contact can be handled appropriately, see [1] and [2].

In this paper a formulation for extending these methods for consideration of planar deformable bodies is given. In the case of deformable bodies, a finite wave propagation speed is inherent and, thus, impact computations on impulse/velocity level which lead to jumps in velocity are no longer required. In this paper only the case of continual contact is taken into account. For this purpose, the complementarity relations are reformulated in such a way that contact modeling of constrained and non‐constrained planar deformable bodies is possible, too. In this formulation, deformable bodies are modeled based on the moving frame of reference approach with modal coordinates which is frequently used for the simulation of deformable multibody systems [3]. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ein Reduktionsalgorithmus für die Bewegungsgleichungen von Mehrkörpersystemen
Authors: Keppler Rainer , Barthels Pierre , Seemann Wolfgang
Published: December 2005

Auf der Basis des Roberson‐Wittenburg'schen Mehrkörperformalismus wurde ein Programm entwickelt, daß die Bewegungsgleichungen baumstrukturierter Mehrkörpersysteme in analytischer Form generiert. Es wird ein Algorithmus vorgestellt, der den Auswerteaufwand der Bewegungsgleichungen verringert. Grundidee ist dabei, Terme geringen Einflusses zu eliminieren. Die Effizienz des Algorithmus wird anhand räumlichern‐fach Pendel demonstriert. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modellierung einer adaptronischen Kompensationseinheit für Werkzeugmaschinen mit Parallelkinematiken
Authors: Rudolf Christian , Wauer Jörg
Published: December 2005

Bei Werkzeugmaschinen mit Parallelkinematiken mit zwei bzw. drei translatorischen Freiheitsgraden sind die rotatorischen Freiheitsgrade kinematisch gesperrt. Aufgrund von Fertigungs‐ und Montageungenauigkeiten kommt es zu Verspannungen in der Kinematikstruktur. Daraus resultieren Verlagerungen des Werkzeug‐ bzw. des Werkst ückhalters und die Fertigungsgenauigkeit der Maschine und damit die Werkstückqualität werden reduziert. Der translatorische Anteil dieser Maschinenfehler kann durch die genannte Kinematikklasse korrigiert werden, der rotatorische Anteil nur sehr begrenzt.

Durch den Einsatz kraftgeregelter Piezoaktoren in den Streben sollen die rotatorischen Maschinenfehler im laufenden Betrieb korrigiert werden. Ein erster Schritt hierzu ist die Modellbildung einer beliebigen Strebe, in die ein Modell eines Piezoaktors integriert ist. Die Strebe wird am Kopfende geführt und soll am Fußende eine Kraft erfahren. Durch Analyse und Simulation können die Einflüsse verschiedener Maschinen‐ und Prozessparameter untersucht werden. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A time‐stepping method for non‐smooth mechanical systems
Authors: Studer Christian , Glocker Christoph
Published: December 2005

Time‐stepping algorithms allow a robust simulation of dynamical problems with many unilateral constraints and friction. It's idea is to calculate velocity updates instead of accelerations. As a consequence, contact behaviour and impact can be treated by the same equations. The unilateral constraints are modelled by set‐valued force laws. The resulting inequalities can be solved by writing inclusions as non‐linear equations. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Modelling of Prestressed Medium Thickness Uniperiodic Plates
Authors: Baron Eugeniusz
Published: December 2005

The aim of this contribution is to propose and apply a new averaged 2D ‐model for the analysis of vibration and stability problems of prestressed uniperiodic, elastic, medium thickness plates. Contrary to the known homogenized model [3], the proposed model describes the effect of the period length on the overall plate behaviour. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On a von Kármán System for Anisotropic Viscoelastic Plates
Authors: Bock Igor
Published: December 2005

We deal with a nonlinear system of equations describing the in‐plane displacements and the deflection of the anisotropic viscoelastic plate made of a long memory material acting under the perpendicular load. We derive the full von Kármán system for the in‐plane displacements and the deflection of the middle surface of the plate. The system contains the nonlinear integropartial differential operators applied to the in‐plain strain tensor and to the tensor product of the displacement gradients. If the right‐hand side of the system fulfils some estimate then the existence of a weak solution can be derived using the Rothe's method. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Flexural Properties of Fiber‐Reinforced Composites
Authors: Haasemann Georg , Ulbricht Volker
Published: December 2005

To describe the macroscopic mechanical behavior of composite materials with biaxial weft‐knitted fabric reinforcement, a difference between the flexural and tensile stiffness must be taken into account. Due to the periodic structure of the composite, the material behavior can be investigated on a unit cell. A homogenization technique based on the Hill‐Mandel energy balance is used to replace a heterogenous Boltzmann medium by a homogenous COSSERAT continuum. To simulate the material behavior, this homogenization method is applied to the Binary Model. Tensile, shear and bending tests were performed to verify the simulation results. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transient dynamic response of sandwich shells with transversely compressible core
Authors: Hohe Jörg , Librescu Liviu
Published: December 2005

The present study provides an investigation of the effect of the transverse core compressibility on the dynamic buckling response of sandwich structures. The study utilizes a previous v. Kármán type higher‐order model for shallow sandwich shells. An analytical solution is obtained by means of an extended Galerkin procedure in conjunction with an explicit fourth order Runge‐Kutta algorithm to solve the transient problem. In an example analysis, it is observed that the transverse core compressibility can have strong effects even on the global response of sandwich structures. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
FE Treatment of InhomogeneitiesWithin the Intervertebral Disc
Authors: Karajan N. , Ehlers W. , Markert B. , Acartürk A. , Wieners C.
Published: December 2005

One natural category of porous materials is represented by the intervertebral disc (IVD) as a charged, hydrated, biological soft tissue. The challenge of describing the IVD lies in its complex microstructure consisting of mostly ionized water and collagen fibers embedded in an extracellular meshwork of charged protein compounds. As a naturally grown material, its inner structure and thus, the associated physical properties are inhomogeneously distributed over the 3‐d domain of the IVD.

The substantial increase of people suffering from low back pain also causes a higher research interest regarding numerical simulation techniques, aiding the design of new implants. The Finite Element Method (FEM) in combination with an elaborated model has the potential to be the best choice.

In order to ef.ciently simulate the physiological behaviour of the IVD on the macroscale, the electro‐chemomechanical couplings between the constituents as well as the viscoelastic and anisotropic properties of the extracellular matrix must be considered. Moreover, the fiber vectors, which represent the aligned collagen in a continuum mechanical sense, as well as the location dependent material parameters must be inhomogeneously distributed over the discretized IVD. These requirements are implemented in the framework of the Theory of Porous Media (TPM), which consistently allows for the description of multiphasic continua with internal interactions. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Direct central impact of different elastic bodies of rotation
Authors: Marchenko Tetiana
Published: December 2005

A direct central collision of two bodies of revolution is studied. A nonstationary mixed boundary‐value problem with an unknown moving boundary is formulated. Its solution is represented by a series in term of Bessel functions. An infinite system of Volterra equations of the second kind for the unknown expansion coefficients is derived by satisfying the boundary conditions. The basic characteristics of the collision process are determined depending on the physic‐mechanical properties of the bodies. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Objective stress rates in repeated elastic deformation cycles
Authors: Meyers Albert , Bruhns Otto , Xiao Heng
Published: December 2005

The Eulerian elastoplastic description of initially isotropic materials essentially depends on the accurate formulation of the elastic deformation. This is often represented by Truesdell's hypoelastic equation, which involves an objective stress rate. Many objective stress rates have been presented in the past. With Bernstein's integrability conditions it has been shown that only a particular rate, namely the logarithmic stress rate, makes the hypoelastic relation exactly integrable.

Here, we propose a simple, one‐parameter closed deformation cycle to demonstrate the error which will considerably accumulate over several cycles, whenever a non‐appropriate stress rate is in use. For this, several objective stress rates are compared in this cycle and the residual stresses at the end of the cycles are examined. By such a simple procedure the mathematical results of non‐integrability are evidenced by example. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability of nonlinear viscoelastic systems under stochastic excitation
Authors: Potapov Vadim
Published: December 2005

The dynamic behaviour of viscoelastic system with due account of finite deflections but under condition of small strains is described by the system of nonlinear integro‐differential equations. On an example of a thin plate subjected to loads, which are assumed as random wide‐band stationary noises and applied in the plate plane, the stability of nonlinear systems is considered. The stability in a case of finite deflections of the plate is considered as stability with respect to statistical moments of perturbations and almost sure stability. For the solution of the problem, a numerical method is offered, which is based on the statistical simulation of input stochastic stationary processes, which are assumed in the form of Gaussian ”colored” noises, and on the numerical solution of integro‐differential or differential equations. The conclusion about the stability of the considered system is made on the basis of Lyapunov exponents. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A finite strain viscoplasticitymodel for cold compaction processes ofmetal powders
Authors: Bier Wolfgang , Hartmann Stefan
Published: December 2005

The production of metal parts by powder metallurgical methods is of increasing interest due to energy and material efficiency of the processes. However, there is still a lack of reliable numerical methods and constitutive models to describe the compaction process from the loose powder to the green (un‐sintered) compact via die‐compaction or cold isostatic pressing. A new phenomenological constitutive model within the framework of viscoplasticity with internal variables is developed. A central part of the model is a unique and smooth single surface yield function. The applied evolution equations together with the assumed associated flow rule and the convexity of the yield function guarantee thermodynamic consistency of the model. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spherical indentation into a fcc single crystal – the squaring of the circle?
Authors: Eidel Bernhard , Gruttmann Friedrich
Published: December 2005

Spherical microindentation into the (100) surface of a fcc single crystal results in a remaining indent shape which looks rather like a square than like a circle. This contribution aims to elucidate this curious phenomenon observed in a recently performed experiment within SFB 298 at TU Darmstadt. The applied methodology is threefold: (i) On the modelling side, a phenomenological orthotropic finite‐strain plasticity model is proposed and applied within finite‐element simulations. (ii) On the experimental side, the topography of the indentation crater is reconstructed by means of scanning‐electron microscopy along with image‐processing. (iii) Experimental observations are explained by plastic slip mechanisms. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling and Simulation of Polyoxymethylene
Authors: Hartmann Stefan
Published: December 2005

This essay is aimed at a brief representation of a constitutive model for a plastic called polyoxymethylene. This kind of plastic shows phenomena like tension‐compression asymmetry, non‐linear rate‐dependence as well as a pronounced relaxation behaviour. The tension‐compression asymmetry is modelled by the elastic part of the equilibrium stress state whereas the hysteretic part is described by an Armstrong&Frederick‐type evolution equation. A particular viscosity function is used for describing the evolution of the viscous strains occuring in the overstress part. The model is able to represent most of the aforementioned phenomena in tension, compression and torsion experiments. In the second part of the article, the implementation of the constitutive model into the .nite element program ANSYS is described followed by a test calculation treating a nut of a bolt. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An observation on the physical essence of elastoplastic deformations
Authors: Xiao Heng , Bruhns Otto , Meyers Albert
Published: December 2005

On account of the basic physical feature of elastoplastic deformations, namely, the occurrence of internal self‐equilibrated stress field upon removal of external loadings, a process of destressing an elastoplastic body with non‐uniform stress field would inevitably lead to loss of the line element concept in the resultant incompatible unstressed configuration. This would mean the loss of the kinematic ground or prerequisite for defining kinematic quantities in usual material continua. Then, an additional variable labelled as “elastic” or “plastic” via destressing could not be endowed with the necessary kinematic and physical content characterising a deformation quantity and, accordingly, might actually be a formal variable in mathematical sense. Thus follows an observation that the elastoplastic deformation would be an inherently inseparable physical entity. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation von Kohlenstoffnanoröhren mit Stone‐Wales Defekten
Authors: Ernst Gerald , Nasdala Lutz , Rothert Heinrich
Published: December 2005

Kraftfelder sind eine bewährte Methode für die Berechnung atomarer Strukturen wie Kohlenstoffnanoröhren. Die Bedeutung des Auftretens von Defekten für die mechanischen Eigenschaften der Kohlenstoffnanoröhren kann mit einem auf Kraftfeldern basierenden finiten Element nachgewiesen werden. Bei einer Belastung der Kohlenstoffnanoröhren kommt es in Abhängigkeit von der Last entweder zu Material‐ oder Stabilitätsversagen. Ein interessantes Ergebnis ist, dass bei Torsion Verzweigungsprobleme durch Defekte in Durchschlagsprobleme überführt werden. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling of Mass Changes in Anisotropic Materials
Authors: Himpel Grieta , Kuhl Ellen , Menzel Andreas , Steinmann Paul
Published: December 2005

For the modelling of biomaterials with changing mass one can distinguish between a coupling of mass changes and deformations at the constitutive level, see e.g. [3], and a coupling at the kinematic level, see e.g. [4]. The constitutive coupling is typically realised by weighting the free energy function with the relative density. Such an ansatz enables the simulation of density changes and is generally used to model hard tissues. The kinematic coupling is characterised by a multiplicative split of the deformation gradient into an elastic part and a growth part. Such an ansatz enables the simulation of mass changes as changes in density and volume and is appropriate to model soft tissues. In this contribution the agreements and disagreements of both approaches should be presented by means of a transversely isotropic material and studied by numerical examples. For a more detailed description of the discussed topic, the reader is also referred to [2]. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A constitutive model for thermoplastic materials subjected to high strain rates
Authors: Kolling S. , Haufe A.
Published: December 2005

Reliable prediction of the behaviour of structures made from polymers is a topic under considerable investigation in engineering practice. Especially, if the structure is subjected to dynamic loading, constitutive models considering the mechanical behaviour properly are not available in commercial finite element codes yet. A constitutive model is derived including important phenomena like necking, strain rate dependency, unloading behaviour and damage. In particular, different yield surfaces in compression and tension and strain rate dependent failure, the latter with damage induced erosion, is taken into account. With the present formulation, standard verification tests can be simulated successfully. Also, an elastic damage model can be used to approximate the unloading behaviour of thermoplastics adequately. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiscale Modeling of the Interphase Interactions in the Mechanics of Materials
Authors: Lurie Sergey , Volkov‐Bogorodsky Dmitrij , Tuchkova Natalia
Published: December 2005

The consistent and correct model of media taking into account scale effects (cohesion and adhesive interactions) is constructed as a special case of the Cosserat's pseudocontinuum model. The variant of the interphase layer theory is elaborated, which includes the following moments: formal mathematical statement, physical constitutive equations, numerical estimations of an interphase layer influence on the stress state and energy density distribution in a composite. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the physically motivated choice of internal variables describing martensitic phase transformations
Authors: Oberste‐Brandenburg Claus
Published: December 2005

Phenomenological models which describe phase transformation in solids often employ a single scalar variable, the mass (or volume) fraction of one of the phases involved. However, the orientation of the applied stress has a major influence on the microstructure developing during the phase transition and thus the overall mechanical behavior. Therefore, additional internal variables of higher order have to be introduced in order to capture this aspect.

The choice of these internal variables is often based on purely phenomenological considerations. In contrast to this, based on local observations at the phase boundary, a thermodynamically dual pair of second order tensors is introduced here.

Constitutive relations for shape menory alloys in the pseudoelastic and pseudoplastic range are proposed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase Transformation and Singularity Theory
Authors: Simon Werner
Published: December 2005

Phase transformation plays an important role in thermodynamics and materials science. Based on the theory of singularities, a new method to construct phase diagrams is presented. Analysing singularities on base of root sequences, see Tamaschke [16], will help to develop singularity graphs, where workings by H. Whitney, R. Thom, and V. I. Arnold provide fundamentals. The generated singularity graphs build the starting point for singularity phase diagrams. A powerful characteristic of such singularity graphs is that higher‐dimensional surfaces can be transformed to a two‐dimensional diagram. The attained singularity diagram can be used in materials science for analytical models of temperature‐concentrated diagrams. As tools from algebra and analysis build a sound basis for singularity diagrams, it is possible to evolve computer software generating these phase diagrams. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Continua with affine microstructure: Theoretical aspects and applications
Authors: Steeb Holger , Diebels Stefan
Published: December 2005

In the present contribution we discuss an axiomatic stucture of extended continua with affine microstructure in the sense of Eringen [2]. Postulating and evaluating the observer‐invariance of the balance of energy we obtain the governing balance equations of generalized continua which are closed by a specific set of kinematical assumptions and constitutive equations. Furthermore, we discuss two specific models characterized by an additional scalar (volumetrical) order parameter. Interestingly, the resulting effects lead to completely different interpretations of the results with respect to the coupling effects. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quantitative proteome analysis of CD95 (Fas/Apo‐1)‐induced apoptosis by stable isotope labeling with amino acids in cell culture, 2‐DE and MALDI‐MS
Authors: Thiede Bernd , Kretschmer Annikki , Rudel Thomas
Published: December 2005

Proteome analysis of Jurkat T cells induced to undergo apoptosis by CD95 (Fas/Apo‐1) treatment was performed to identify modified proteins. We used stable isotope labeling with amino acids in cell culture (SILAC) using leucine to identify proteins of apoptotic and control Jurkat T cells by 2‐DE and MALDI‐MS. Out of 224 spots analyzed, we quantified 213 spots with 3.5 leucine‐containing peptide pairs on average; 28 proteins with a relative abundance of higher than 1.5 were found. Five new modified proteins including calcyclin binding protein, cytosolic acyl coenzyme A thioester hydrolase, heterogeneous ribonucleoprotein M, replication factor C 37‐kDa subunit, and tropomyosin 4 chain were identified as being modified in response to apoptosis. In comparison to differential proteome analysis via silver‐stained 2‐D gels and PMF of total Jurkat T cell lysates, 15 additional apoptosis‐modified proteins were identified though 8 proteins were not found. The described approach using SILAC instead of silver staining for relative quantification was simpler to perform regarding the number of required 2‐D gels, that cumbersome gel comparisons were avoided, and more apoptosis‐modified proteins were identified, but with a higher demand on data interpretation of the mass spectra obtained.
Proteomic analysis of malignant lymphocyte membrane microparticles using double ionization coverage optimization
Authors: Miguet Laurent , Pacaud Karine , Felden Claire , Hugel Bénédicte , Martinez M. Carmen , Freyssinet Jean‐Marie , Herbrecht Raoul , Potier Noelle , van Dorsselaer Alain , Mauvieux Laurent
Published: December 2005

Shed membrane microparticles (MPs) are microvesicles generated from the plasma membrane when cells are submitted to stress conditions. Although MPs reflect the cell state (at least in vitro), little is known on their protein composition. We describe the first set of experiments aiming to characterize the MP proteome. Two ways of triggering MP formation from a T‐lymphocytic cell line were analyzed using a 1‐D gel approach coupled with LC‐MS/MS and the results were compared with those obtained from a classic membrane preparation. In total, 390 proteins were identified in MPs, among which 34% were localized to the plasma membrane. The MPs revealed a broad representation of plasma membrane proteins including 17 hematopoietic clusters of differentiation. This approach was successfully applied to one human chronic B‐cell lymphoid malignancy. In all, 413 proteins were identified, including 117 membrane proteins, many of them being pathology associated. The sequence coverage in identified proteins was improved combining both nano‐LC‐MS/MS and MALDI‐MS data. The suppression effect, observed on very complex peptide mixtures, was remediated by chromatographic fractionation. MPs may represent a new tool for studying plasma membrane proteins, displaying the advantages of reproducibility, minimal organelle contamination, and being potentially applicable to most cell types.
Pedigree analysis of an elite rice hybrid using proteomic approach
Authors: Xie Zhensheng , Wang Jingqiang , Cao Mengliang , Zhao Caifeng , Zhao Kang , Shao Jianmin , Lei Tingting , Xu Ningzhi , Liu Siqi
Published: December 2005

The definition of dominance or epistasis is generally on the basis of a descriptive characterization for these crops in the field, such as yield per hectare and the weight of grain. Since these trait examinations lack molecular information, how to precisely predict the phenotypic changes in filial generation is still a problem in heterosis studies. For rice, the genetic information caused by hybridization can be archived through analyzing of proteomes of rice seeds. Differential analysis of proteomes was introduced for the rice seeds of three cultivars, 9311, PA64S and LYP9, an elite rice hybrid from cross between 9311 and PA64S. In the three rice endosperms, the expression profiles of proteins were similar with the stained spots of 47 ± 1, 46 ± 0.6 and 44 ± 0.6, for 9311, PA64S and LYP9, respectively; however, the number of proteins expressed in the rice embryos was significantly increased with the stained spots of 395.3 ± 12.9, 350 ± 9.2, and 389.3 ± 16.4, for 9311, PA64S and LYP9, respectively. Importantly, the image comparisons and protein identifications have revealed in significantly different embryo protein spots among the three rice cultivars. By carefully analyzing these different 2‐DE spots, many of them from the three embryos were shown to display a mirrored relationships between parents and the first filial generation. Furthermore, all of stained spots in LYP9 embryo were found on the 2‐DEs from its parents, indicating that there was a genetic linkage. These results suggest that proteomic approach is able to serve pedigree analysis and functional prediction for new rice breeds.