bluuebunny/crossref_metadata_2025_split huggingface dataset:
Constructing compact Markov processes for correlated workload modeling
Authors: Heindl Armin , Telek Miklós 
Published: December 2008

AbstractUnnecessarily large submodels aggravate the state‐space explosion problem for large Markov models. The orders of these submodels may multiplicatively flow into the size of the overall model quickly leading to intractable state spaces. To mitigate this effect, compact and correlated Markov processes, in particular Markovian arrival processes (MAPs) of low order, have been developed, which can be used for workload modeling.Different ways how to construct MAPs from information on marginal moments and the correlation structure are addressed with pointers to the relevant literature. A canonical form for MAPs of second‐order is presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Scalar shift strategy for accelerating forward iterations on Sm –1
Authors: Shen Hao , Hüper Knut 
Published: December 2008

AbstractA result on how to accelerate simple forward iteration algorithms on the unit sphere, in the framework of a scalar shift strategy, to achieve local quadratic convergence is developed in this note. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A multiple‐scales solution of the undular hydraulic jump problem
Authors: Jurisits Richard , Schneider Wilhelm , Bae Yee Seok 
Published: December 2008

AbstractA non‐linear third‐order ODE governing the free surface of an undular hydraulic jump is solved by means of a multiple‐scales analysis. The resulting solutions are compared with direct numerical solutions of the ODE, and good agreement is found. Furthermore, new flow features, which are not evident in the numerical solutions, are revealed by the multiple‐scales solutions. The results of the analysis are also compared with numerical solutions of the full equations of motion and with experimental data, and satisfactory agreement is obtained. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hypertumors in cancer can be caused by tumor phosphorus demand
Authors: Nagy John D. 
Published: December 2008

AbstractIn cancer, tumoral and peritumoral environmental conditions are controlled mostly by the unusual metabolism of malignant cells. For example, tumors typically demand much more phosphorus (P) than normal tissue does, primarily because tumor cells upregulate ribosome biogenesis. Here I use mathematical models to show that this unusual demand for P can lead to a hypertumor, which is a region of highly aggressive cells growing parasitically on the original tumor that can kill all or part of it. Previous work has suggested that hypertumors may develop when a tumor is invaded by an aggressive cell type that fails to secrete angiogenesis factors. In this talk I introduce an entirely different mechanism of hypertumor development. In this case, the aggressive strain upregulates phosphate transporters, leading to increased growth potential, which allows tumor cells to outpace growing blood vessels. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Life, a modern and unified C++ implementation of finite‐element and spectral‐element methods in 1D, 2D and 3D
Authors: Prud'homme Christophe 
Published: December 2008

AbstractWe present a brief overview of Life, a unified framework for finite element and spectral element methods in 1D, 2D and 3D inC++. First, we describe some basic principles, then we focus on the two cornerstones of the library, the polynomial library and FEEL++, aC++ embedded language designed for partial differential equations. The applications range is potentially quite large; at the moment Life is essentially used for the development of new numerical methods and the exhaustive comparisons between standard ones e.g. high order methods, stabilisation methods. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Patch dynamics: macroscopic simulation of multiscale systems
Authors: Samaey Giovanni , Kevrekidis Ioannis G. , Roose Dirk 
Published: December 2008

AbstractWe describe a numerical algorithm to perform time integration of a partial differential equation (PDE) which is not available in closed from; instead we are given a more microscopic description of the system behaviour. The proposed methods mimic a macroscopic finite difference (FD) or finite volume (FV) scheme for the unavailable PDE; they extract a macroscopic time derivative (for FD schemes) or flux (for FV schemes) from appropriately initialized, but otherwise unconstrained simulations with the given microscopic model. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On large‐scale diagonalization techniques for the Anderson model of localization
Authors: Schenk Olaf , Bollhöfer Matthias , Römer Rudolf A. 
Published: December 2008

AbstractWe propose efficient preconditioning algorithms for an eigenvalue problem arising in quantum physics, namely the computation of a few interior eigenvalues and their associated eigenvectors for large‐scale sparse real and symmetric indefinite matrices of the Anderson model of localization. Our preconditioning approaches for the shift‐and‐invert symmetric indefinite linear system are based on maximum weighted matchings and algebraic multi‐level incomplete LDLT factorizations. These techniques can be seen as a complement to the alternative idea of using more complete pivoting techniques for the highly ill‐conditioned symmetric indefinite Anderson matrices. Our numerical examples reveal that recent algebraic multi‐level preconditioning solvers can accelerate the computation of a large‐scale eigenvalue problem corresponding to the Anderson model of localization by several orders of magnitude. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Covariance analyis for active vehicle suspensions
Authors: Schiehlen Werner , Fehr Jörg , Jung Kim Yun 
Published: December 2008

AbstractIn this paper the covariance analysis will be extended to active suspension systems with skyhook dampers. The covariance matrix of the entire vehicle system follows from an algebraic equation, the so‐called Ljapunov matrix equation, and no integrations are required. An essential prerequisite of the covariance analysis is a white noise input process. This can always be provided by modelling the random vehicle excitation by means of a shape filter. Performance criteria are presented and appropriate design parameters are found by optimization. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Reduced kinematic model of the human spine
Authors: Simonidis Christian , Scharmacher Manuel , Seemann Wolfgang 
Published: December 2008

AbstractAccording to the difficulty of marker based motion reconstruction of human torso movements a reduced kinematic formulation of the human spine is introduced, which describes the movement of the first thoracic vertebra in relation to the pelvis. The formulation is for implementation in a multibody model of the human body. As a result the formulation offers convenience in marker based motion capture and motion reconstruction via an optimization based kinematic approach and provides human‐like motion characteristics of torso motion. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Basic convergence results for conforming adaptive finite elements
Authors: Morin Pedro , Siebert Kunibert G. , Veeser Andreas 
Published: December 2008

AbstractWe report on a result establishing plain convergence for conforming adaptive finite elements under relatively general assumptions on problem class and adaptive algorithm. Moreover, we indicate some applications and give a sketch of the proof. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the influence of crosswind on the overturning stability of railway vehicles
Authors: Wetzel Christian , Yalamas Claire , Proppe Carsten 
Published: December 2008

AbstractIn recent years modern railway vehicle design shows a trend to faster, lighter and more energy efficient railway systems. These developments unfortunately alter the crosswind stability in a negative manner and so the risk of overturning of railway vehicles during operation in strong winds becomes a critical issue. The risk of overturning is quantified by the probability that a railway vehicle capsizes. To improve the crosswind stability it is very important to know the influence of the design and excitation variables on the wheel unloading of the railway car. Sensitivity coefficients of the design and excitation variables with respect to the probability of failure are calculated and the most influential variables are accentuated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
DNS of MHD turbulence in liquid metals based on the least dissipative modes
Authors: Dymkou Vitali , Pothérat Alban 
Published: December 2008

AbstractWe investigate numerically the incompressible Navier‐Stokes equations under an externally imposed magnetic field. The results obtained for the simplified geometry of a three dimensional periodic box and show a lower computational complexity and stronger relationship between the physical reality and its numerical representation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
MR image reconstruction from undersampled data by using the iterative refinement procedure
Authors: He Lin , Chang Ti‐Chiun , Osher Stanley , Fang Tong , Speier Peter 
Published: December 2008

AbstractMagnetic resonance imaging (MRI) reconstruction from sparsely sampled data has been a difficult problem in medical imaging field. We approach this problem by formulating a cost functional that includes a constraint term that is imposed by the raw measurement data in k‐space and the L1 norm of a sparse representation of the reconstructed image. The sparse representation is usually realized by total variational regularization and/or wavelet transform. We have applied the Bregman iteration to minimize this functional to recover finer scales in our recent work. Here we propose nonlinear inverse scale space methods in addition to the iterative refinement procedure. Numerical results from the two methods are presented and it shows that the nonlinear inverse scale space method is a more efficient algorithm than the iterated refinement method. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The numerical analysis of the trapezoidal thread rolling process
Authors: Kukielka Krzysztof , Kukielka Leon 
Published: December 2008

AbstractThe thread rolling is difficult technological process. Improve quality and contemporary reduce manufacture cost of the trapezoidal thread requires acquaintances of physical phenomena observed in the contact zone between rolls and deform work‐pieces. Therefore, in this paper the physical and mathematical models of deformations (displacements and strains) and stress in the cold process of trapezoidal thread rolling, were developed. The process is considered as a geometrical and physical non‐linear, initial as well as boundary value problem. The phenomena on a typical incremental step were described using a step‐by‐step incremental procedure, with an updated Lagrangian formulation. The state of strains was described by Green‐Lagrange's tensor, while the state of stress by the second symmetrical Pioli‐Kirchhoff's tensor. The object was treated as an elastic (in the reversible zone) and visco‐plastic body (in non‐reversible zone) with mixed hardening. The variational equation of motion in three dimensions for this case was proposed. Then, the finite elements methods (FEM) and dynamic explicit method (DEM) were used to obtain the solution. The application developed for in the ANSYS programme, which provides a complex time analysis for displacement, strains and stresses occurring in the object. The recommendations concern modeling the trapezoidal thread rolling process, where reduce degrees of freedom in numerical model is very important and provide convergence calculated results for maximum stress and strain values in the thread surface layer, were elaborated. The influence a various process conditions on the states deformation and stress for examples calculations, were presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Negative specific heat in a quasi‐2D vortex system
Authors: Andersen Timothy D. , Lim Chjan C. 
Published: December 2008

AbstractNegative specific heat is a dramatic phenomenon where processes decrease in temperature when adding energy. It has been observed in gravo‐thermal collapse of globular clusters. We now report finding this phenomenon in bundles of nearly parallel, periodic, single‐sign generalized vortex filaments in the electron magnetohydrodynamic (EMH) model for the unbounded plane under strong magnetic confinement. We derive the specific heat using a steepest descent method and a mean field property. Our derivations show that as temperature increases, the overall size of the system increases exponentially and the energy drops. The implication of negative specific heat is a runaway reaction, resulting in a collapsing inner core surrounded by an expanding halo of filaments. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Semi‐analytical modelling of cracks with interacting faces in isotropic materials under harmonic load
Authors: Menshykov Oleksandr V. , Mykhailova Iryna I. , Guz Igor A. 
Published: December 2008

AbstractThe present work is devoted to the investigation of the contact interaction of the faces of cracks located in the homogeneous, isotropic, linearly elastic 3‐D medium under a harmonic loading. The Signorini contact constraints are imposed and the friction is governed by the Coulomb law. The problem is solved by the method of the boundary integral equations with the use of the iterative procedure. The dependence of the stress intensity factors on the friction coefficient and parameters of the incident wave parameters (frequency, angle of incidence, etc.) is studied. Numerical results are compared with those obtained without allowance for the contact interaction. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal singular control for quasi‐linear systems with small parameters
Authors: Popescu Mihai 
Published: December 2008

AbstractThe present study deals with the general case of the quasi‐linear command systems with a small parameter. We shall determine an approximate solution of the problem of optimum which minimizes the class of the quadratic functionals in a non‐specified final time. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability of viscoelastic systems under stochastic excitation
Authors: Potapov Vadim 
Published: December 2008

AbstractAn effective method for the investigation of the stability for viscoelastic systems under a parametric stochastic excitation is proposed. The parametric force is assumed in the form of a Gaussian stationary colored noise. The method is based on the simulation of random processes, the numerical solution of differential equations, describing the perturbed motion of the considered system, and the calculation of top Liapunov exponents. The considered method makes it possible to estimate the almost sure stability and the stability with respect to statistical moments of the different order. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multirate models for simulating a colpitts oscillator
Authors: Pulch Roland 
Published: December 2008

AbstractA model based on multirate partial differential algebraic equations yields an efficient numerical simulation of electric circuits in radio frequency applications. Considering frequency modulation, free parameters of the model are determined appropriately by a minimisation strategy. We apply the multirate approach to simulate a modified version of a Colpitts oscillator, which exhibits frequency modulation at widely separated time scales. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Interval techniques for enclosures of regions of reachability and controllability and for guaranteed state and parameter estimation of dynamical systems
Authors: Rauh Andreas , Kletting Marco , Hofer Eberhard P. 
Published: December 2008

AbstractInterval techniques are a powerful means for calculation of enclosures of the regions of reachability and controllability of dynamical systems with uncertainties during analysis and design of controllers. In this contribution, both discrete‐time and continuous‐time dynamical systems are considered. Using suitable algorithms, guaranteed state enclosures can be determined for systems with uncertain parameters, uncertain initial conditions, nonlinearities, and time‐varying characteristics.Although both uncertain system parameters and bounded control variables are assumed to be represented by interval boxes in the following, they have to be distinguished in reachability and controllability analysis. Typically, robustness specifications for controllers of dynamical systems are given in terms of bounds on the system's time response which must not be violated for any possible operating condition. Hence, reachability as well as controllability of states have to be proven for all possible parameter values but for at least one admissible control sequence.Robust control strategies for nonlinear systems usually rely on knowledge of all current states. However, the complete state vector is not always directly accessible for measurement. In this case, observers are applicable to reconstruct non‐measurable state variables. Furthermore, they can reduce the uncertainties of the measured quantities by model‐based recursive computation of estimates and fusion of information gathered by different measurement devices. If guaranteed bounds of all uncertain parameters of a dynamical system (including the sensor characteristics) and conservative bounds of all disturbances can be specified, the presented interval observer provides guaranteed enclosures of all reachable states. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coupled CFD analysis of hot gas and coolant flow in effusion‐cooled combustion chambers
Authors: Riccius Jörg , Gernoth Andreas , Greuel Dirk 
Published: December 2008

AbstractThree different coupled CFD analyses of the hot gas and the coolant flow in effusion‐cooled combustion chambers are shown. The common feature of these CFD analyses are the following principles:• solution of the Navier Stokes equations• multi species analysis including hot gas (steam) and coolant (hydrogen)• compressible flow• ideal gas• distributed resistance according to Forchheimer in the combustion chamber wallThe differences between these models are given in the following table:imageThe detailed analysis of the combustion itself is avoided by defining the injector plate of the combustion chamber (left boundaries of the colour plots in figure 2) as an inlet of the by‐product of the combustion (steam). (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coupled time‐domain analysis with boundary and finite elements
Authors: Rüberg Thomas , Schanz Martin 
Published: December 2008

AbstractA methodology for the combination of boundary and finite element discretizations for the numerical analysis of time‐dependent problems is presented. The interface conditions arising from the partitioning of the problem are incorporated in a weak form by means of Lagrange multiplier fields and, therefore, allow for nonconform interface discretizations. The resulting system matrices have the same saddle point structure as in the FETI method. Possible applications of the proposed method are the dynamic analysis of soil‐structure interaction and similar wave propagation phenomena in unbounded media. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A nonlinear finite element framework for flexible multibody dynamics
Authors: Sänger Nicolas , Betsch Peter 
Published: December 2008

AbstractWe present a uniform treatment of rigid body dynamics and nonlinear structural dynamics. The advocated approach is based on a rotationless formulation of rigid bodies, nonlinear beams and shells. In this connection, the specific kinematic assumptions are taken into account by the explicit incorporation of holonomic constraints. This approach facilitates the straightforward extension to flexible multibody dynamics by including additional constraints due to the interconnection of rigid and flexible bodies. We further address the design of energy‐momentum schemes for the stable numerical integration of the underlying finite‐dimensional Hamiltonian systems.To demonstrate the superior numerical performance of the proposed methodology, the numerical examples deals with a multibody system containing both rigid and flexible bodies undergoing large deformations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cyclic martensitic phase transformation of monocrystals at finite strains
Authors: Sagar Gautam , Stein Erwin 
Published: December 2008

AbstractBased on Bain's principle, a C1‐continuous thermo‐mechanical micro‐macro constitutive model for martensitic phase transformation (PT) of monocrystals at finite strains and hyperelastic free energy function is used. It is represented by a unified non‐convex Lagrangian variational functional. The convexification problem is solved here by generalizing the explicit form of the lower Reuss bound for small strains given in [1] to finite strains. Abaqus is used for implementation of 3D finite elements in space, via UMAT‐interface which requires Jaumann rate of Kirchhoff stress tensor. Deterministic validation of the model is presented by comparing verified numerical results with experimental data for Cu82Al14Ni4[6] for quasiplastic PT. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Time variant Hamiltonian control systems – a covariant approach
Authors: Schöberl Markus 
Published: December 2008

AbstractIn this contribution we present an intrinsic description of time variant Hamiltonian control systems. This formulation is based on the splitting of the state bundle and the use of appropriate covariant derivatives, which guarantees that the structure of the equations is invariant with respect to time variant coordinate transformations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Least‐squares mixed finite elements with applications to anisotropic elasticity and viscoplasticity
Authors: Schwarz Alexander , Schröder Jörg 
Published: December 2008

AbstractThe objective of this work is to discuss a least‐squares finite element method with applications to physically nonlinear and anisotropic constitutive equations at small strains. The L2‐norm minimization of the residuals of the given first order system of differential equations leads to a functional, which is a two field formulation in the displacements and the stresses, see e.g. Cai & Starke [1]. These functionals provide the foundation for the formulations of the related least‐squares mixed finite elements. A main focus of the presentation lies on the extension of plane elasticity to anisotropic or nonlinear material behavior. In this context transversely isotropic elasticity and viscoplasticity is considered. Finally a numerical example is presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the homogenization of the Buckley‐Leverett equation including trapping effects at the micro scale
Authors: Schweizer Ben , Pop Iuliu Sorin 
Published: December 2008

AbstractWe consider a simplified, one dimensional model for two‐phase (oil/water) flow in a porous medium. The medium consist of alternating homogeneous blocks separated by interfaces, where trapping effects may occur. Two effective models are derived in [2] and [7]. In this paper we show that the two models are equivalent. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)