bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Simulation of Highly Viscoelastic Polymer Melts using VF and DEVSS Methods
Authors: Al‐Baldawi Ammar , Wünsch Olaf
Published: December 2011

Viscoelastic polymer melts are usually modeled with a macro approch. This is done using an anisotropic mobility tensor to generalize the Maxwell model. In recent works the use of micro approches is increasing, e.g. the so‐called POM‐POM model. In this work a frame independent flow type property is introduced in order to help visualizing the elongation and shear regions in a 3D flow. Which in turn helps to choose the right material model, since the model parameters are adjusted with 1D shear flows and the elongation properties are mostly neglected. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coupling of the Reynolds Fluid‐Film Equation with the 2D Navier‐Stokes Equations
Authors: Esmaeili L. , Schweizer B.
Published: December 2011

The pressure field in thin fluid films can quite precisely be calculated by Reynolds fluid‐film equation. In some problems, it may be useful to couple thin fluid‐films with general 2D or 3D fluid flows. In the current work, we analyze the fluid flow, pressure and temperature field in a hydrodynamic journal bearing with a rectangular oil groove. Pressure and temperature in the fluid gap are calculated by means of the Reynolds equation and the 2D energy equation. Cavitation effects are taken into account by incorporating a 2‐phase cavitation approach. In order to calculate the velocity and pressure field in the oil groove, the 2D Navier‐Stokes equations are used; the temperature distribution in the oil groove is computed by means of the 2D energy equation. Appropriate coupling conditions for velocity, pressure and temperature are formulated in order to couple the flow in the fluid gap with the flow in the oil groove. Thermal expansion of journal shaft and bearing housing are also taken into account, since the bearing clearance changes with increasing temperature. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonlinear effects due to cavitation in self‐lubricated bearings
Authors: Neacşu Ioana Adina , Scheichl Bernhard , Kluwick Alfred
Published: December 2011

Self‐lubricating bearings are journal bearings having a porous network which acts as a reservoir of fluid. Impregnation is done once, and is enough to sustain life‐time lubrication. Our concern in this type of application is with the phenomena of fluid film cavitation under th.e assumption of purely hydrodynamic lubrication. In this sense we solve a modified Reynolds equation numerically, including a refinement of the pressure‐density relation, and iteratively couple the result in terms of pressure with Darcy's law for flows through porous media. The resulting method resorts to a simulated‐annealing strategy, which properly accounts for the nonlinearity due to the presence of cavitation and the density variations inside the cavitation region, together with the continuous phase change from the the fully liquid regime. Most importantly, it is found both analytically and numerically that recondensation is associated with the occurrence of density jumps. The numerical results provide an accurate description of the pressure and density distributions. Also, statements concerning existence and essential properties of the solutions can be made for both the sintered and a massive bearing (uncoupled case). The most interesting limiting case studied thoroughly is the one for which the eccentricity ε is quite high (ε → 1−), corresponding to highly loaded bearings, which captures the bounds of applicability of the present approach. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Boundary element method based algorithm for simulation of fluid flow in 3D
Authors: Ravnik Jure , Škerget Leopold
Published: December 2011

A boundary element method based numerical scheme that solves the velocity‐vorticity formulation of Navier‐Stokes equation is presented. The developed method is validated and used to simulate laminar viscous flow coupled with heat transfer in 3D. Benchmark test cases were use to determine the validity of the method. Flow around a hotstrip is presented as a test case. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Mixed Convection Flow past a Horizontal Plate in a Channel: Wake ‐ Potential Flow Interaction
Authors: Steinrück Herbert
Published: December 2011

The mixed convection flow past a horizontal plate in a horizontal channel in a distinguished limit of large Reynolds and Grashof numbers is considered. An interaction problem between the wake and the potential flow is formulated and analyzed. It turns out that stationary solutions exist only if a suitable defined interaction parameter is below a critical value. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Sensitivity Studies of Large Eddy Simulations of Combustion Systems with an Unstructured Implicit Solver
Authors: Aschmoneit Kai , Kuenne Guido , Janicka Johannes
Published: December 2011

Isothermal as well as reacting turbulent flows are investigated by means of LES with the implicit, unstructured code PRECISE‐UNS. Primarily, the swirl burner configuration TECFLAM is simulated isothermal. Calculations with different time step sizes are taken out to examine the influence of the Courant number on the LES solution. In addition, the impact of the spatial resolution is investigated. Next, the jet diffusion flame configuration Sandia Flame D is calculated with the Flamelet Generated Manifold (FGM) approach. Mean profiles of the velocity components, mixture fraction and temperature as well as their variances are compared to experimental data. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamical structure of the turbulent boundary layer on rough surface
Authors: Uruba Václav , Jonáš Pavel , Hladík Ondřej
Published: December 2011

The experiments on structure of turbulent boundary layer on the plane rough wall without pressure gradient are presented. Sand roughness of the wall is considered. Measurements are carried out using Time‐Resolved PIV technique in planes parallel and perpendicular to the wall. The results on rough wall are compared with the base case of boundary layer on smooth wall. Hairpin vortices have been detected. Topology and typical size of those structures substantially differ in the cases in question. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulations of acoustic emissions due to offshore‐pile installation
Authors: Henke Sascha , Milatz Marius , Grabe Jürgen
Published: December 2011

The use of renewable energy is growing due to economic reasons and a spreading sense of ecology. One possible source for renewable energy is wind energy. It is predicted that the number of offshore wind parks will be increasing within the next ten years. The foundation piles of offshore wind power plants are normally installed by impact driving. This leads to an emission of acoustic noise which possibly influences or even damages the sense of hearing of marine mammals like seals and whales.

In this contribution the propagation of acoustic waves in air and water due to pile driving is investigated using the finite element method (FEM) with an explicit time integration scheme. In the analyses a mass representing the pile hammer falls on an elastically modeled offshore monopile. The surrounding media is varied between air and water in order to investigate the acoustic emissions due to the pile driving process with respect to the medium. The numerical results are compared to measurements which can be found in literature to verify the numerical models. Furthermore, as a practical example the numerical model can be used in order to simulate noise reduction techniques such as the bubble curtain. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Impact and Damage Localisation of Carbon‐Fibre‐Reinforced Plastic Plates
Authors: Ungethuem Andy , Lammering Rolf
Published: December 2011

Due to increasing usage of light weight structures and carbon‐fibre‐reinforced plastics well‐known procedures for the examination of components inefficient in terms of efforts or costs. Therefore, the development of a complementary system is suggested which allows for detecting damaging events and damages in a structure. A new wave migration model enables to determine the location of an impact for non‐isotropic plates. The method is based on the wave propagation after an impact. Piezo‐electric sensors capture the strain caused by the propagating wave. The evaluation and processing of the signals of at least four sensors allow for the calculation of the impact location from the runtime of the signals. In the case of non‐isotropic material the shape of the wave front has to be known for the structure under investigation, for example experimentally due to measurement and monitoring of the wave propagation by a Laservibrometer or analytically by calculating the propagation speed of bending waves. On the same basis damage localisation in anisotropic carbon‐fibre‐reinforced plastic plates is possible. Considerations to signal analysis using wavelet transformation are presented and both models are validated experimentally. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Virtual test facilities for building acoustic predictions using FEM
Authors: Wulkau Meike , Langer Sabine
Published: December 2011

The most important characteristic in building acoustics is the transmission loss which describes the insulation performance of a separating component. This quantity is defined by the ratio of inclined sound power to transmitted power. The transmission loss is usually measured in costly experimental set‐ups of either real size facilities or down scaled test models. In order to reduce the effort and to gain further insight into the complex behavior of wave propagation in coupled structure‐fluid systems, virtual test facilities using numerical methods (FEM) are established. An appropriate determination of the reverberation time is essential for obtaining good quality simulations. The results of the simulated transmission loss are presented and compared with common analytical prediction methods based on the transfer matrix method. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Formation of crystalline bubble structure in wet metal foams
Authors: Heitkam Sascha , Fröhlich Jochen
Published: December 2011

Small monodispersed bubbles form regular patterns when they agglomerate. Many experimental investigations revealed a preference of f.c.c. packing against h.c.p. packing in these structures, that could not yet be explained. In the present work this feature is reproduced numerically and analyzed. It is shown that drainage from layers above causes the preference. By investigating the transient crystal growth and packing rearrangement a mechanism is found that reduces the stability of h.c.p. packing and explains the phenomenom. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Singularities on the boundaries of magnetorotational instabilities and scaling laws
Authors: Kirillov Oleg , Stefani Frank
Published: December 2011

In the theory of magnetorotational instability and its modern extensions such as the helical MRI, non‐trivial scaling laws between the critical parameters are observed. In case of the standard MRI it is well known that the Reynolds and Hartmann numbers are scaled as Re ∼ Ha2 while for the helical MRI Re ∼ Ha3. What is less known is that the thresholds of SMRI and HMRI plotted as surfaces in the space of parameters, possess singularities that determine the scaling laws. Moreover, the two paradoxes of SMRI and HMRI in the limits of infinite and zero magnetic Prandtl number (Pm), respectively, sharply correspond to the singularities on the instability thresholds. In either case, it is the local Plücker conoid structure that explains the non‐uniqueness of the critical Rossby number, and its crucial dependence on the Lundquist number. For HMRI, we have found an extension of the former Liu limit Roc ≃ −0.828 (valid for Lu = 0) to a somewhat higher value Ro ≃ −0.802 at Lu = 0.618 which is, however, still below the Kepler value. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Generation of the vortex train using plasma barrier discharge actuator
Authors: Procházka Pavel , Uruba Václav
Published: December 2011

The plasma actuator is used to generate periodical train of vortices moving along the surface. For generation the high‐frequency high‐voltage AC is used forming more‐or‐less steady wall‐jet‐like flow by the dielectric barrier discharge or corona discharge. Low‐frequency modulation of the supply voltage is applied to generate vortices. Parameters of the vortex train are studied as function of the generator setting using TR‐PIV technique. The generated flow patterns are to be applied for control of a boundary layer. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Korn's inequality for incompatible tensor fields
Authors: Neff Patrizio , Pauly Dirk , Witsch Karl‐Josef
Published: December 2011

We prove a Korn‐type inequality for bounded Lipschitz domains in $\Omega {\rm ~in~}{\rm I\!R}^3$ and non‐symmetric square integrable tensor fields $P : \Omega \to {\rm I\!R}^{3\times 3}$ having square integrable rotation ${\rm Curl~}P : \Omega \to {\rm I\!R}^{3\times 3}$. For skew‐symmetric P or compatible $P =\nabla\;v$ our estimate reduces to non‐standard variants of Poincaré's or Korn's first inequality, respectively, for which our new estimate can be viewed as a common generalized version. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Global existence result for rate‐independent processes in viscous solids with heat transfer
Authors: Paoli Laetitia , Petrov Adrien
Published: December 2011

This note deals with three‐dimensional models for rate‐independent processes describing materials undergoing phase transformations with heat transfer. The problem is formulated within the framework of generalized standard solids by the coupling of the momentum equilibrium equation and the flow rule with the heat transfer equation. The existence of a global solution for this thermodynamically consistent problem is obtained by using a fixed‐point argument combined with global energy estimates. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Class of Evolutionary Problems with an Application to Acoustic Waves with Impedance Type Boundary Conditions.
Authors: Picard Rainer
Published: December 2011

A well‐posedness result for a time‐shift invariant class of evolutionary operator equations is considered and exemplified by an application to an impedance type initial boundary value problem for the system of linear acoustics. The problem class allows for memory effects in the domain as well as on the domain boundary. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Topology and Geometry Optimization of Branched Sheet Metal Products
Authors: Göllner Thea , Günther Ute , Hess Wolfgang , Martin Alexander , Ulbrich Stefan
Published: December 2011

In order to optimize branched sheet metal profiles consisting of several chambers, decisions concerning topology and geometry have to be made. This leads to a problem entailing discrete and nonlinear features. We describe an integrated approach combining both aspects. The underlying idea is to use a branch‐and‐bound algorithm. In each node of the branch‐and‐bound tree, a nonlinear optimization problem has to be solved. We describe how the branch‐and‐bound tree is constructed, i.e., how the topology decision can be classified in a meaningful way. Moreover, we explain how to approach the nonlinear optimization problem arising in the nodes of the tree. We conclude by presenting a numerical example. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimum Experimental Design for Nonlinear Process Models
Authors: Körkel Stefan
Published: December 2011

In order to validate nonlinear dynamic process models, parameters have to be estimated from experimental data. The method of nonlinear optimum experimental design can improve the statistical reliability of parameter estimates drastically. This article discusses the problem formulation, numerical solution approaches and application strategies for nonlinear experimental design optimization problems. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
State‐constrained optimization for identification of small inclusions
Authors: Kovtunenko Victor A.
Published: December 2011

The inverse problem of identification of small geometric objects (defects, inclusions) of unknown topological properties is under the investigation. This problem is treated within the state‐constrained optimization framework. Using topological sensitivity analysis and methods of singular perturbations, a proper approximation by the asymptotic model is justified rigorously. The underlying parametric optimization problem is solved semi‐analytically by a variational calculus. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Towards optimal Runge‐Kutta smoothers for multigrid methods for unsteady flow problems
Authors: Birken Philipp
Published: December 2011

We consider Runge‐Kutta smoothers in a dual time stepping multigrid method for unsteady flow problems. These smoothers are easily parallelizable and Jacobian‐free, making them very attractive for 3D calculations. Existing methods have been designed for steady flows, leading to slow convergence for unsteady problems. Here we determine the free parameters of the smoother to provide optimal damping for high frequency components for the unsteady linear advection equation. This is compared with an RK smoother designed for steady state problems, as commonly used in CFD codes. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Rational multistep methods via modified φj‐functions
Authors: Auzinger Winfried , Łapińska Magdalena
Published: December 2011

A class of rational multistep methods, in particular of Adams‐Padé type, is designed via rational modification of the φj‐functions inherent in exponential integrators. Convergence properties and implementation issues are discussed. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Simulation of the Boltzmann Equation: Deterministic vs. Monte Carlo Schemes
Authors: Babovsky Hans
Published: December 2011

Kinetic Lattice Group Models [1] provide a valuable tool for the numerical simulation of the Boltzmann equation. Here we introduce a Monte Carlo version of these. With this we have the unique opportunity to compare deterministic versions with Monte Carlo versions of the same model. We introduce the system and discuss some results. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Convergence and quasi‐optimality of adaptive FEM with inhomogeneous Dirichlet data
Authors: Feischl Michael , Page Marcus , Praetorius Dirk
Published: December 2011

We consider an adaptive mesh‐refining algorithm for a lowest‐order finite element method (AFEM). Contrary to prior works, where the Poisson equation with homogeneous Dirichlet data is analyzed, our focus is on the case of inhomogeneous Dirichlet data g ≠ 0. As is usually done in practice, we use nodal interpolation to discretize g. Besides convergence of AFEM, which is proven by means of an appropriate contraction quantity, we also discuss quasi‐optimality of the proposed algorithm. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulation of transversely isotropic material using adaptive FEM
Authors: Meyer Arnd , Weise Michael
Published: December 2011

Lightweight construction plays an important role in the global task to save energy. A common approach to reduce the weight of structures is the use of composite materials like fibre reinforced polymers (FRP). FRP can be characterised by transversely isotropic material behaviour, a special case of anisotropy. In our arcticle we present the necessary efforts to include such material behaviour into an existing adaptive FEM code. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dual weighted residual method for optimal control of hyperbolic equations of second order
Authors: Kröner Axel
Published: December 2011

In this paper the dual weighted residual method for optimal control problems of hyperbolic equations of second order is considered. The state equation is written as a first order system in time and a posteriori error estimates separating the influences of time, space, and control discretization are derived to obtain a better accurancy of the discrete solution. A numerical example for optimal control of a nonlinear wave equation is presented. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
State Estimation and Fault Detection of an Aircraft Using Nonlinear Filters
Authors: Christmann Julia , Kappenberger Carsten , Marheineke Nicole
Published: December 2011

An aircraft is a complex technical system, which has to satisfy high safety standards. The whole system of an aircraft has to be monitored because more and more actions happen automatically. Therefore unpredictable errors should be detected as fast as possible. In this work two different nonlinear filters namely the Extended Kalman Filter (EKF) and the Particle Filter (PF) are studied for the application of fault detection with simultaneous estimations of states. Results show that EKF leads to better approximation for nearly linear problems, while PF yields a more accurate approximation for worst case scenarios. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Uncertainty relations for sets of self adjoint operators
Authors: Held Stefan
Published: December 2011

Uncertainty relations quantify the joint localisation in time respectively space domain and Fourier domain. For that reason they are an important tool in the design of wavelets. Uncertainty relations in higher dimension are most often realized as the tensor product of one dimensional uncertainty relations, whence these uncertainty relations are not invariant under rotations. The property of invariance with respect to rotation is however very desirable for image processing. We will give a new uncertainty relation for sets of self‐adjoint operators that yields the desired invariance in many examples. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transformations, Implementations, and Pitfalls
Authors: Sauer Tomas
Published: December 2011

Transformations are ubiquitous in practically every field of signal processing and the choice of the right transformation can be crucial for extracting the information from the data. In computational practice, however, the fact that one tries to implement an infinite transformation defined on a continuum for finite discrete data can lead to unwanted and often also unexpected effects. Using the example of the continuous wavelet transform, this note points to some of these effects and gives explanation why this happens and how it can be avoided. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A fast Kriging‐based strategy for the optimization of electrical device
Authors: Chaigne Benoît , Trinitis Carsten
Published: December 2011

The primary goal of a shape optimization problem is to find the best design w.r.t. a given criterion. A however non less important goal is to achieve this task within a reasonable time. In realistic situations, a reliable but slow method might not always provide its best capacity if the computational resources are worked out before convergence. The expensive simulation‐based optimization of a physical system is one of these situations. In order to tackle this issue, we consider a fast but low‐fidelity model given by a Kriging method. We propose a simple adaptive scheme in order to enhance the reliability of the optimization procedure and thus avoid a premature convergence. Numerical experiments are conducted for the electrostatic design of a realistic device. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Massively Parallel Particle Simulations on Graphics Processing Units with CUDA
Authors: Fischer Katrin , Ostermeyer Georg‐Peter
Published: December 2011

Particle methods are a powerful tool to model dynamic systems. Thereby, the system is discretized by a large number of particles, which are interacting via local, predefined particle‐particle interaction laws. The resulting computational effort includes neighborhood search, computation of interaction forces and state update via time integration. Particle methods are used in a lot of different fields of applications like computer science, physics and engineering sciences.

As the analyzed systems' number of particles constantly grow, performance enhancement has become an important part of present algorithm development. Besides the well‐established approach of algorithm parallelization on multi‐core CPUs or CPU clusters, modern graphics processing units (GPUs) present a different and trend‐setting possibility for massive parallelization even on desktop computers. Among the top four supercomputers of the world, three are already using NVIDIA GPUs.

In late 2006, NVIDIA introduced the first GPUs optimized for general purpose calculations. This was followed by the introduction of a new computing architecture differing from the standard graphics user‐interface like OpenGL. This architecture is called Compute Unified Device Architecture (CUDA). It enables the user to program the GPU using standard C commands with few additional runtime functions. The differences in architecture between CPU and GPU result in a completely different algorithm implementation.

So, a performance evaluation of different types of particle systems implemented on a GPU using CUDA and on a standard CPU is presented. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Block Preconditioners in the Parallel Toolbox
Authors: Aurel Neic , Haase Gundolf
Published: December 2011

We present a parallel solver for second order scalar PDE called The Parallel Toolbox. We investigate certain performance issues which arise when high performance compute nodes with a relatively slow network interconnect are used. These performance issues motivate the introduction of block methods which reduce network usage and thus increase parallel performance. First benchmarks computed on a GPU cluster evaluate the success of this attempt. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the historical development of human walking dynamics
Authors: Schiehlen Werner
Published: December 2011

Human walking is an interdisciplinary research topic. It started in the Ancient World with early observations and questions in philosophy, it was treated in the Middle Ages with experiments and data collection by physiologists, and in the 20th century models were designed, equations of motion were generated and simulations by multibody dynamics approaches were performed. More recently parameter optimization was used to overcome the problem of muscle overactuation and inverse dynamics methods were introduced. In the first part of the paper the early developments and mechanism models are described while in the second part parameter optimization is applied to gait disorder simulations as an example of recent research results. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Jacobi‐Davidson method for two real parameter nonlinear eigenvalue problems arising from delay differential equations
Authors: Meerbergen Karl , Schröder Christian , Voss Heinrich
Published: December 2011

The critical delays of a delay‐differential equation can be computed by solving a nonlinear two‐parameter eigenvalue problem. For large scale problems, we propose new correction equations for a Jacobi‐Davidson type method, that also forces real valued critical delays. We present two different equations: one complex valued equation using a direct linear system solver, and one Jacobi‐Davidson style correction equation which is suitable for an iterative linear system solver. A numerical example of a large scale problem arising from PDEs shows the effectiveness of the method. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Calculation of probability density functions for nonlinear vibration systems
Authors: Martens Wolfram , von Wagner Utz
Published: December 2011

Technical systems are subjected to a variety of excitations that cannot generally be described in deterministic ways. Random excitations such as road roughness, wind gusts or loads on marine structures are commonly described by stochastic differential equations (SDEs). Given a set of SDEs, the main task is in finding probability density functions (PDFs), which yield statistical information about the system states. Monte‐Carlo simulations represent a general way of generating PDFs, however, reliable integration methods can be time‐consuming for complex systems. An alternative way of finding PDFs lies in the analysis of the Fokker‐Planck equation, a partial differential equation of the PDF. Linear problems under Gaussian excitation can be solved analytically, which is the case only for a small class of nonlinear problems. As a result, there are a number of methods of approximating PDFs for general problems. Most of these are restricted to comparably low dimensions, such as d=4 ("curse of dimensionality"), limiting the relevance to technical applications. This paper presents solutions to problems of dimensions up to d=10, applying a Galerkin‐method that expands approximate solutions into orthogonal polynomials. Problems include polynomial nonlinearities in damping and restoring terms, such as classical Duffing‐elements, as well as other types of nonlinearities, demonstrated on a typical problem in vehicle dynamics. All results are compared with results from Monte‐Carlo simulations or exact solutions, where available. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A three‐field, bi‐domain based approach to the strongly coupled electromechanics of the heart
Authors: Dal Hüsnü , Göktepe Serdar , Kaliske Michael , Kuhl Ellen
Published: December 2011

We propose a novel, unconditionally stable and fully coupled finite element method for the bidomain based approach to cardiac electromechanics. To this end, the transmembrane potential, the extracellular potential, and the displacement field are treated as independent variables such that the already coupled electrophysiology problem in the bidomain setting is further extended to the electromechanical coupling. In this multifield problem, the intrinsic coupling arises from both excitation‐induced contraction of cardiac cells and the deformation‐induced generation of intra‐cellular currents. The respective bidomain reaction‐diffusion and the momentum balance equations are recast into the corresponding weak forms through a conventional isoparametric Galerkin approach. The resultant set of non‐linear residual equations is consistently linearized. The monolithic scheme is employed to avoid stability issues that may arise due to the strong coupling between excitation and deformation. The performance of the put forward framework is further assessed through three‐dimensional representative electromechanical initial‐boundary value problems. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Relaxed loading conditions for higher order homogenisation approaches
Authors: Jänicke Ralf , Uribe David , Ruiz Oscar E. , Steeb Holger
Published: December 2011

The present paper deals with the formulation of minimal loading conditions for the application of numerical homogenisation techniques, namely the FE2 methodology. Based on the set of volume averaging rules connecting the heterogeneous micro and the homogeneous macro scale, the minimal constraints on the deformation of a micro volume are derived for a classical Cauchy continuum as well as for a micromorphic continuum theory. For both cases, numerical studies are included highlighting the main aspects of the proposed procedure within the context of small deformations. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Copper oxide thin films by chemical vapor deposition: Synthesis, characterization and electrical properties
Authors: Eisermann Sebastian , Kronenberger Achim , Laufer Andreas , Bieber Johannes , Haas Gunther , Lautenschläger Stefan , Homm Gerd , Klar Peter J. , Meyer Bruno K.
Published: December 2011

Cu2O thin films were grown on sapphire (0001) and MgO (100) substrates by chemical vapor deposition. The crystalline, vibrational and electrical properties of the layers and the amount of incorporated background impurities have been examined. X‐ray diffraction measurements revealed, that the polycrystalline films grew in (111) and (100) orientation on sapphire and in (100) orientation on MgO. Raman measurements indicated the presence of CuO inclusions in the films. The electrical properties are dominated by an acceptor level located 150 meV above the valence band. This level may originate from unintentionally incorporated silicon impurities.
Metal–semiconductor transition in SmxMn1−xS solid solutions
Authors: Aplesnin Sergey , Romanova Oxana , Har'kov Anton , Balaev Dmitrii , Gorev Michail , Vorotinov Alexander , Sokolov Vladimir , Pichugin Andrey
Published: December 2011

The electrical resistivity of the SmxMn1−xS (0.15 ≤ x ≤ 0.25) solid solutions in the temperature range of 80–300 K was measured. Minimum and maximum in the temperature dependence of the resistivity were found, respectively, at T = 220 K for x = 0.15 and at T = 100 K for x = 0.2 compounds. This behavior is explained from the result of the mobility‐edge movement, the disorder being due to elastic deformation and spin density fluctuations with short‐range order. Metal–semiconductor phase transition versus concentration at xc = 0.25 is observed. Resistivity is described by scattering electrons with acoustic phonon mode and with localized manganese spin. From the thermal expansion coefficient the compression of the lattice below the Néel temperature for Sm0.2Mn0.8S is found.
Influence of polymer dielectric surface energy on thin‐film transistor performance of solution‐processed triethylsilylethynyl anthradithiophene (TES‐ADT)
Authors: Chen Liang‐Hsiang , Lin Pang , Kim Choongik , Chen Ming‐Chou , Huang Peng‐Yi , Ho Jia‐Chong , Lee Cheng‐Chung
Published: December 2011

This study investigates the correlation between surface energy of polymer dielectrics and the film morphology, microstructure, and thin‐film transistor performance of solution‐processed 5,11‐bis(triethylsilylethynyl) anthradithiophene (TES‐ADT) films. The low surface energy polyimide (PI) dielectric induced large grains with strong X‐ray reflections for spin‐cast TES‐ADT films in comparison to high surface en‐ ergy poly(4‐vinyl phenol) (PVP) dielectric. Furthermore, thin‐film transistors based on spin‐cast TES‐ADT films on PI dielectric exhibited enhanced electrical performance, small hysteresis, and high stability under bias stress with carrier mobility as high as 0.43 cm2/Vs and a current on/off ratio of 107. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Antifibrotic Effects of Triptolide on Hepatic Stellate Cells and Dimethylnitrosamine‐intoxicated Rats
Authors: Chong Lee‐Won , Hsu Yi‐Chao , Chiu Yung‐Tsung , Yang Kuo‐Ching , Huang Yi‐Tsau
Published: December 2011

Triptolide (C38H42O6N2, TP, a diterpene triepoxide derived from Tripterygium wilfordii Hook F.), is a potent immunosuppresive and antiinflammatory agent. The present study investigated whether TP exerted antihepatofibrotic effects in vitro and in vivo. A cell line of rat hepatic stellate cells (HSC‐T6) was stimulated with tumor necrosis factor‐α (TNF‐α) or transforming growth factor (TGF)‐β1. The inhibitory effects of TP on the nuclear factor‐κB (NFκB) signaling cascade and fibrosis markers, including α‐smooth muscle actin (α‐SMA) and collagen, were assessed. An in vivo therapeutic study was conducted in dimethylnitrosamine (DMN)‐treated rats. The rats were randomly assigned to one of three groups: control rats, DMN rats receiving vehicle only and DMN rats receiving TP (20 μg/kg). Treatment was given by gavage twice daily for 3 weeks starting 1 week after the start of DMN administration. TP (5–100 nm) concentration‐dependently inhibited the NFκB transcriptional activity induced by TNF‐α, lipopolysaccharide and phorbol 12‐myristate 13‐acetate in HSC‐T6 cells. In addition, TP also suppressed TNF‐α and TGF‐β1‐induced collagen deposition and α‐SMA secretion in HSC‐T6 cells. In vivo, TP treatment significantly reduced hepatic fibrosis scores, collagen contents, IL‐6 and TNF‐α levels, and the number of α‐SMA and NFκB‐positive cells in DMN rats. The results showed that TP exerted antifibrotic effects in both HSC‐T6 cells and DMN rats. Copyright © 2011 John Wiley & Sons, Ltd.
Using gas chromatography/isotope ratio mass spectrometry to determine the fractionation factor for H2 production by hydrogenases
Authors: Yang Hui , Gandhi Hasand , Shi Liang , Kreuzer Helen W. , Ostrom Nathaniel E. , Hegg Eric L.
Published: December 2011

Hydrogenases catalyze the reversible formation of H2, and they are key enzymes in the biological cycling of H2. H isotopes have the potential to be a very useful tool in quantifying hydrogen ion trafficking in biological H2 production processes, but there are several obstacles that have thus far limited the application of this tool. Here, we describe a new method that overcomes some of these barriers and is specifically designed to measure isotopic fractionation during enzyme‐catalyzed H2 evolution. A key feature of this technique is that purified hydrogenases are employed, allowing precise control over the reaction conditions and therefore a high level of precision. In addition, a custom‐designed high‐throughput gas chromatograph/isotope ratio mass spectrometer is employed to measure the isotope ratio of the H2. Using our new approach, we determined that the fractionation factor for H2 production by the [NiFe]‐hydrogenase from Desulfovibrio fructosovorans is 0.273 ± 0.006. This result indicates that, as expected, protons are highly favored over deuterium ions during H2 evolution. Potential applications of this newly developed method are discussed. Copyright © 2011 John Wiley & Sons, Ltd.
Distributed OSGi built over message‐oriented middleware
Authors: Psiuk Marek , Żmuda Daniel , Zieliński Krzysztof
Published: December 2011

This paper describes key aspects of remote service invocation in federations of OSGi containers. It refers to the OSGi Remote Service Admin specification and describes its efficient implementation over message‐oriented middleware. Scalability problems of several different approaches to implementation are identified, and a solution in a form of innovative Remote Service Admin model extension is proposed. The extension, named On‐demand Remote Service Admin, is analyzed and validated in the context of a motivating scenario. Validation includes performance and scalability evaluation, which confirms that all assumed requirements have been satisfied by the constructed prototype. Finally, the presented research is compared with related works. Copyright © 2011 John Wiley & Sons, Ltd.
Wireless local area network cards identification based on transient fingerprinting
Authors: Zhao Caidan , Chi Ting‐Yun , Huang Lianfen , Yao Yan , Kuo Sy-Yen
Published: December 2011

This paper proposes a time–frequency‐based fingerprinting identification approach by extracting the transient characterizations regarding highly integrated wireless local area network (WLAN) cards. The transient energy envelope is derived from the slice of spectrogram in the time–frequency domain. Then this transient response is fitted to a polynomial under least square criteria, and the polynomial coefficients are regarded as the feature vector. A data acquisition system has been set up to capture IEEE 802.11b Wi‐Fi (wireless fidelity) signals. The results exhibit an approving distinctiveness of up to 94% to classify different manufactories of WLAN cards and of 78.4% for the WLAN cards of the same manufactory. Copyright © 2011 John Wiley & Sons, Ltd.
Production of the Finnish Wind Atlas
Authors: Tammelin Bengt , Vihma Timo , Atlaskin Evgeny , Badger Jake , Fortelius Carl , Gregow Hilppa , Horttanainen Matti , Hyvönen Reijo , Kilpinen Juha , Latikka Jenni , Ljungberg Karoliina , Mortensen Niels Gylling , Niemelä Sami , Ruosteenoja Kimmo , Salonen Kirsti , Suomi Irene , Venäläinen Ari
Published: December 2011

The Finnish Wind Atlas was prepared applying the mesoscale model AROME with 2.5 km horizontal resolution and the diagnostic downscaling method Wind Atlas Analysis and Application Programme (WAsP) with 250 m resolution. The latter was applied for areas most favourable for wind power production: a 30 km wide coastal/offshore zone, highlands, large lakes and large fields. The methodology included several novel aspects: (i) a climatologically representative period of real 48 months during 1989–2007 was simulated with the mesoscale model; (ii) in addition, the windiest and calmest months were simulated; (iii) the results were calculated separately for each month and for sectors 30° wide; (iv) the WAsP calculations were based on the mesoscale model outputs; (v) in addition to point measurements, also radar wind data were applied for the validation of the mesoscale model results; (vi) the parameterization method for gust factor was extended to be applicable at higher altitudes; and (vii) the dissemination of the Wind Atlas was based on new technical solutions. The AROME results were calculated for the heights of 50, 75, 100, 125, 150, 200, 300 and 400 m, and the WAsP results for the heights of 50, 75, 100, 125 and 150 m. In addition to the wind speed, the results included the values of the Weibull distribution parameters, the gust factor, wind power content and the potential power production, which was calculated for three turbine sizes. The Wind Atlas data are available for each grid point and can be downloaded free of charge from dynamic maps at www.windatlas.fi. Copyright © 2011 John Wiley & Sons, Ltd.
Verification of computational simulations of the NREL 5 MW rotor with a focus on inboard flow separation
Authors: Chow Raymond , van Dam C. P.
Published: December 2011

The aerodynamic characteristics of the NREL 5 MW rotor have been examined using a Reynolds‐averaged Navier–Stokes method, OVERFLOW2. A comprehensive off‐body grid independence study has been performed. A strong dependence on the size of the near‐body wake grid has been found. Rapid diffusion of the wake appears to generate an overprediction of power and thrust. A large, continuous near‐wake grid at a minimum of two rotor diameters downstream of the rotor appears to be necessary for accurate predictions of near‐body forces. The NREL 5 MW rotor demonstrates significant inboard flow separation up to 30% of span. This separation appears to be highly three dimensional, with a significant amount of radial flow increasing the size of the separated region outboard. A simple, continuous full‐chord fence was applied at the maximum chord location of the blade, within the region of separation. This non‐optimized device reduced the boundary‐layer cross‐flow and resulting separation. The fence increased energy capture by nearly 1% at a wind speed of 8 m s−1 and slightly increased blade loading over the length of the span. Copyright © 2011 John Wiley & Sons, Ltd.
The Production of Conjugated α‐Linolenic, γ‐Linolenic and Stearidonic Acids by Strains of Bifidobacteria and Propionibacteria
Authors: Hennessy Alan A. , Barrett Eoin , Paul Ross R. , Fitzgerald Gerald F. , Devery Rosaleen , Stanton Catherine
Published: December 2011

Conjugated fatty acids are regularly found in nature and have a history of biogenic activity in animals and humans. A number of these conjugated fatty acids are microbially produced and have been associated with potent anti‐carcinogenic, anti‐adipogenic, anti‐atherosclerotic and anti‐diabetogenic activities. Therefore, the identification of novel conjugated fatty acids is highly desirable. In this study, strains of bifidobacteria and propionibacteria previously shown by us and others to display linoleic acid isomerase activity were assessed for their ability to conjugate a range of other unsaturated fatty acids during fermentation. Only four, linoleic, α‐linolenic, γ‐linolenic and stearidonic acids, were converted to their respective conjugated isomers, conjugated linoleic acid (CLA), conjugated α‐linolenic acid (CLNA), conjugated γ‐linolenic acid (CGLA) and conjugated stearidonic acid (CSA), each of which contained a conjugated double bond at the 9,11 position. Of the strains assayed, Bifidobacterium breve DPC6330 proved the most effective conjugated fatty acid producer, bio‐converting 70% of the linoleic acid to CLA, 90% of the α‐linolenic acid to CLNA, 17% of the γ‐linolenic acid to CGLA, and 28% of the stearidonic acid to CSA at a substrate concentration of 0.3 mg mL−1. In conclusion, strains of bifidobacteria and propionibacteria can bio‐convert linoleic, α‐linolenic, γ‐linolenic and stearidonic acids to their conjugated isomers via the activity of the enzyme linoleic acid isomerase. These conjugated fatty acids may offer the combined health promoting properties of conjugated fatty acids such as CLA and CLNA, along with those of the unsaturated fatty acids from which they are formed.
Aberrations in Plasma Phospholipid Fatty Acids in Lung Cancer Patients
Authors: Murphy Rachel A. , Bureyko Taylor F. , Mourtzakis Marina , Chu Quincy S. , Clandinin M. Thomas , Reiman Tony , Mazurak Vera C.
Published: December 2011

Abnormalities in lipid metabolism have been frequently observed in cancer and are associated with a poor prognosis. However, a detailed, longitudinal characterization of fatty acid status is lacking. This study aimed to assess plasma phospholipid fatty acids before chemotherapy, immediately after and 1 month following chemotherapy in a group of 50 patients newly diagnosed with lung cancer and explore factors which may contribute to aberrations in fatty acids. Their mean ± SD characteristics: age 64 ± 8.5 years, 75% advanced stage disease, body mass index 27.0 ± 5.4 kg/m2, 6 month weight loss −4.6 ± 6.1%. Compared to patients with early stage disease, patients with advanced disease had abnormal fatty acid profiles including significantly lower (P < 0.05) amounts of total phospholipid fatty acids, saturated, and polyunsaturated fatty acids (linoleic, arachidonic, eicosapentaenoic and docosahexaenoic). Longitudinal analysis revealed that patients with advanced disease who completed chemotherapy had stable fatty acid levels and continued to maintain levels 1 month following completion of chemotherapy. Comparatively, patients who did not complete chemotherapy due to toxicity or disease progression had progressive loss of total phospholipid fatty acids, stearic, linoleic and n‐6 fatty acids and a trend towards lower docosahexaenoic, arachidonic, palmitic, n‐3 and saturated fatty acids. These results suggest that loss of fatty acids is prevalent, progressive and potentially influenced by advanced disease and chemotherapy treatment.
Ethnic identity and gender as moderators of the association between discrimination and academic adjustment among Mexican‐origin adolescents
Authors: Umaña‐Taylor Adriana J. , Wong Jessie J. , Gonzales Nancy A. , Dumka Larry E.
Published: December 2011

Existing work has identified perceived discrimination as a risk factor that may contribute to the relatively poorer academic outcomes exhibited by Mexican‐origin adolescents in the U.S. The current study examined the longitudinal associations among perceived discrimination and three indices of adolescent adjustment in the school setting (i.e., grade point average, teacher reports of externalizing, adolescents’ deviant peer associations) among 178 Mexican‐origin adolescents (53% female). Ethnic identity affirmation was examined as a protective factor expected to reduce the negative effects of discrimination on adolescents’ adjustment, and gender was examined as a potential moderator of the associations of interest. Findings indicated that the deleterious effects of discrimination on adolescents’ adjustment in school were particularly salient for Mexican‐origin male adolescents. Importantly, ethnic identity affirmation emerged as a protective factor for Mexican‐origin male adolescents by buffering the negative effects of discrimination on their externalizing behaviors in school.