bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective proper orthogonal decomposition model reduction for forming simulations
Authors: Radermacher Annika , Reese Stefanie , Hadoush Ashraf Moh'd Hasan
Published: November 2013

Robot‐based incremental sheet metal forming is a cost‐effective and flexible method for prototype and low batch size production. The simulation of such processes is very challenging and elaborate from the computational point of view. To reduce the computational effort model reduction techniques such as proper orthogonal decomposition (POD) can be applied. But the reduction of highly non‐linear models in solid mechanics for example forming simulation still leads to problems of efficiency and accuracy. Therefore, the aim of this paper is to present an alternative way to use POD for forming processes. The presented selective POD (SPOD) method is used to split the model into two domains depending on the degree of plastic strain. Only the domain with approximately linear elastic behavior will be reduced by using POD. Utilizing the SPOD method for the example of forming a horizontal flute reduces the computational time up to around 30 per cent. High accuracy with approximation errors smaller than one per mill is achieved. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An explicit update formula for implicit time integration within finite strain viscoelasticity
Authors: Shutov Alexey , Landgraf Ralf , Ihlemann Jörn
Published: November 2013

In this paper a model of finite strain viscoelasticity and its numerical integration is considered. The mechanical behaviour can be represented by the one‐dimensional rheological model of Maxwell fluid which consists of an elastic spring (Hooke body) and a viscous dashpot (Newton body) connected in series. The constitutive model is formulated within the framework of nonlinear continuum mechanics and is based on the decomposition of the deformation gradient into elastic and inelastic parts. The elastic part of the model is defined by a Neo‐Hookean hyperelastic relation between elastic strains and stresses. Furthermore, an incompressible flow rule for the description of viscous flow is assumed. The numerical integration of the inelastic flow rule is accomplished using the implicit integration scheme of Euler‐backward method. To this end, Shutov et al. (2013) recently proposed a new closed form solution for the corresponding time stepping algorithm. The algorithm retains all favourable characteristics of the Euler‐backward method. Moreover, no local iterative procedure is required which results in a highly efficient implicit time stepping scheme. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stress Integration of the Hoek‐Brown Material Model Using Incremental Plasticity Theory
Authors: Rakic Dragan , Zivkovic Miroslav , Milovanovic Vladimir
Published: November 2013

This paper presents the formulation of the stress integration procedure for the Hoek‐Brown (HB) material model with non‐associative yielding condition by using the incremental plasticity method. Main idea of this method is to reach the solution by calculating the plastic matrix according to the method of incremental plasticity (used for elastic constitutive matrix corrections), and with the use of the total strain increment. Computational procedure is implemented within the PAK program package. Results of this procedure were compared with the solutions obtained by other program that contains this material model. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mathematical modelling of finite strain magneto‐viscoelastic deformations
Authors: Saxena Prashant , Hossain Mokarram , Steinmann Paul
Published: November 2013

Large strain magneto‐viscoelastic deformations in the presence of a finite magnetic field are modelled in this paper. Internal dissipation mechanisms are proposed using a multiplicative decomposition of the deformation gradient and an additive decomposition of the magnetic induction. Using thermodynamically consistent constitutive and evolution laws, numerical results showing stress relaxation and magnetic field evolution are presented to illustrate the theory. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Complex‐Step Derivative Approximation Schemes for the Robust Calculation of Numerical Constitutive Tangent Moduli
Authors: Tanaka Masato , Fujikawa Masaki , Balzani Daniel , Schröder Jörg
Published: November 2013

Many material models lead to complicated formulations of the exact consistent tangent modulus tensor and therefore its derivation and implementation might be elaborate. In this case numerical approximations of the moduli can provide an alternative in particular for scientific development purposes. Here, a robust numerical approximation of the tangent modulus tensor that can be implemented within FE‐software is proposed using an innovative numerical derivative scheme. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Carbon‐dioxide storage and phase transitions: on the numerical modelling of injection and leakage
Authors: Häberle Kai , Ehlers Wolfgang
Published: November 2013

The injection of supercritical CO2 into deep saline aquifers is regarded as one possible alternative to lessen the impact of emitted CO2 on the greenhouse effect. During injection, a great variety of thermodynamical and mechanical changes of both the fluid phases and the porous solid matrix can be expected. The prediction of these processes is crucial to prevent from critical incidents during CO2 injection, such as leakage of CO2 or contamination of drinking water.

For simulation purpose, a macroscopic, fully coupled description of multi‐phasic flow inside a deformable porous medium based on the Theory of Porous Media (TPM) is generated. Appropriate constitutive relations are applied to account for changes in the fluid properties of both the saline water and CO2 during injection and leakage. Furthermore, an elasto‐plastic description of solid deformations of the porous matrix is included.

The model is tested based on a benchmark problem. Therein, the leakage of CO2 through an abandoned well after injection is investigated. The fully coupled approach between fluid flow and solid deformation allows additional results to be gained from the simulation. Quantification of the leakage rate through the abandoned well and localisation of phase‐change events are addressed to calibrate the presented model. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Finite Deformation Microsphere Model for Magneto‐Visco‐Elastic Response in Magnetorheological Elastomers
Authors: Ethiraj Gautam , Zäh Dominic , Miehe Christian
Published: November 2013

In this work we present a novel approach to the modeling of magnetorheological elastomers (MREs) for finite deformations. Keeping in mind the composite nature at the microscale, we employ the microsphere model as an effective tool to capture the constitutive response of the material. The microsphere model has been successfully applied to the modelling of rubber‐like materials. Here, we extend this approach by taking into account the effect of the magnetic dipole‐dipole interactions on the orientation of the polymer chains. Thus, the presented microsphere model is directly motivated by considering the underlying phenomena at the microscale level. Finally the material model is embedded in a finite element framework and the results of a boundary value problems is presented. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Equations of Motion of Robotic System With Piezo‐Modified Viscoelastic and Magnetorheological Elements of Fractional Order
Authors: Cajić Milan , Lazarević Mihailo
Published: November 2013

In this communication, the Rodriguez method is proposed for modeling dynamics of the robotic system, where Lagrange's equations of second kind of rigid bodies system in covariant form are used. Discrete hybrid elements with so called piezo‐modified Kelvin‐Voight (PKV) and magnetorheological (MRD) type of viscoelastic models with fractional order derivatives are introduced in to the system of motion equations by means of generalized forces. The results obtained are illustrated by numerical examples. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Finite element simulation for material accumulation and welding processes including a free melt surface
Authors: Jahn Mischa , Luttmann Andreas , Schmidt Alfred
Published: November 2013

A modeling and simulation approach for problems with solid‐liquid‐solid phase transitions and a free surface, feasible for material accumulation processes based on laser‐based free form heading and welding processes for joining different metallic materials is presented. Both named processes are modeled within the framework of continuum mechanics by coupling the Stefan problem with the Navier‐Stokes equations including a free capillary surface. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An analytical solution for the mechanically coupled diffusion problem in thin‐film electrodes
Authors: Stein Peter , Zhao Ying , Xu Baixiang
Published: November 2013

This paper presents a quasi‐static solution for the mechanically coupled diffusion problem in a Lithium‐ion battery thin film electrode during charge. The concentration field and the stresses are calculated under the assumption of a constant flux. The influence of the electrode's stiffness, its thickness, and of the current density on the results are discussed. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A monolithic finite element discretization for coupled Darcy‐Stokes flow
Authors: Braack Malte , Nafa Kamel
Published: November 2013

We consider a Stokes system and a Darcy system in a porous media, mutually coupled together by the the well‐known Beaver‐Joseph‐Saffman interface conditions. Standard approaches use different finite elements in the two parts in order to account for the different stability properties of the two equation systems. In contrast to this, we use standard equal‐order finite elements in both parts. Stability is obtained by adding local projection terms (LPS) to the Galerkin formulation. We formulate the scheme and give an a priori estimate. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polycrystal vs. Classical Continuum Models for Structures
Authors: Prygorniev Oleksandr , Naumenko Konstantin , Altenbach Holm
Published: November 2013

In this work a comparison of polycrystal and classical continuum models illustrated by examples of full structures is investigated. The general idea is to represent the averaged distribution of displacement, stress and strain fields for statistically randomized realizations of discrete structures. A technique for averaging fields in the FEM program ABAQUS is proposed and implemented. To improve the computation efficiency mesh dependence was investigated. Results of simulation are given for a rectangular plate and for the Kirsch's problem for both examples elastic as well as inelastic material behavior. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The hp‐d version of the finite cell method with local enrichment for multiscale problems
Authors: Joulaian Meysam , Düster Alexander
Published: November 2013

The finite cell method is extended to enable the computation of solids consisting of heterogeneous materials. The approach is based on a domain decomposition utilizing the hp‐d method. Our results reveal that the proposed method improves the accuracy of the finite cell method significantly. It also paves the way for combining the finite cell method with other approaches like partition of unity based methods which can be of interest in many cases, such as dealing with composites and numerical homogenization. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A crystal plasticity framework based on the Continuum Dislocation Dynamics theory: relaxation of an idealized micropillar
Authors: Monavari Mehran , Schmitt Severin , Sandfeld Stefan
Published: November 2013

The motion and interaction of dislocation lines are the physical basis of the plastic deformation of metals. Although ‘discrete dislocation dynamic’ (DDD) simulations are able to predict the kinematics of dislocation microstructure (i.e. the motion of dislocations in a given velocity field) and therefore the plastic behavior of crystals in small length scales, the computational cost makes DDD less feasible for systems larger than a few micro meters. To overcome this problem, the Continuum Dislocation Dynamics (CDD) theory was developed. CDD describes the kinematics of dislocation microstructure based on statistical averages of internal properties of dislocation systems. In this paper we present a crystal plasticity framework based on the CDD theory. It consists of two separate parts: a classical 3D elastic boundary value problem and the evolution of dislocation microstructure within slip planes according to the CDD constitutional equations. We demonstrate the evolution of dislocation density in a micropillar with a single slip plane. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical experiments for the appropriate representative volume element size selection on thin texturized metals under mechanical loads
Authors: Montalvo‐Urquizo Jonathan , Ungermann Mischa
Published: November 2013

In this work, we analyze a strategy for the selection of the adequate RVE size for elastic problems on thin sheets with strong texture. The selection strategy includes the construction of the geometric descriptor as periodic tesselation of the sheets and the stochastic assignment of stiffness matrices for the different material grains inside the RVE. The procedure is illustrated with an example on DC01 steel sheets with thickness 50 µm. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Designing Statistically Similar RVEs for 3D Dual Phase Steel Microstructures
Authors: Scheunemann Lisa , Balzani Daniel , Brands Dominik , Schröder Jörg
Published: November 2013

This contribution presents a method for the construction of three‐dimensional Statistically Similar Representative Volume Elements (SSRVEs) for dual phase steels (DP steels). From such kind of advanced high strength steels, enhanced material properties are observed, which originate in the interaction of the individual constituents of the material on the microscale. Our aim is to directly incorporate the microstructure in the material modeling, which can be accomplished by applying i. e. the FE2 method. A RVE representing the real material is used in the microscopic boundary value problem, which is solved at each macroscopic integration point. Since such RVEs usually exhibit a high complexity due to the underlying real microstructure, high computational costs are a drawback of the approach. We replace this RVE with a SSRVE, which has a lower complexity but which is still able to represent the mechanical behavior of the RVE and thus of the real microstructure. Virtual experiments show the performance of the method. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Variational Approach to Dynamic Recrystallization Using Probability Distributions
Authors: Nguyen Hai Van , Hackl Klaus , Renner Jörg
Published: November 2013

We investigate a model of dynamic recrystallization in polycrystalline materials. A probability distribution function is introduced to characterize the state of individual grains by grain size and dislocation density. Specifying free energy and dissipation within the polycrystalline aggregate we are able to derive an evolution equation for the probability density function via a thermodynamic extremum principle. Once the distribution function is known macroscopic quantities like average strain and stress can be calculated. For distribution functions which are constant in time, describing a state of dynamic equilibrium, we obtain a partial differential equation in parameter space which we solve using a marching algorithm. Numerical results are presented and their physical interpretation is given. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A model for fluid flow in non‐fully filled tribological interfaces – Part 2: Simulations
Authors: Müller Michael , Bubser Florian , Ostermeyer G.‐P.
Published: November 2013

The paper presents simulation results of an algorithm for non‐fully filled gaps, as it was introduced in part one of this work. The model considers the roughness of two solid surfaces moving relative to each other in reference to its effect on the fluid displacement. Due to the lack of fluid in the gap, the area where a hydrodynamic pressure can build up is rather small. However approaching asperities can build up local pressure. The non‐linear effect of the filling ratio on the pressure build‐up and the fluid flow is shown using a simplified topography of two ellipsoidal asperities. Depending on the filling ratio the fluid is squished out of the decreasing gap volume between the two asperities. So the amount of solid to solid contact is reduced by the fluid flow. The paper also discusses the behaviour of a multi asperity contact by means of two Gaussian height distributed surfaces sliding over each other. It is discussed how the starved regime influences the local pressure distribution and the gap geometry. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of the Free‐Surface Flow in Partially Filled Extruders
Authors: Lübke Martin , Wünsch Olaf
Published: November 2013

In this work we present the free‐surface flow of high viscous Newtonian liquids in a simplified extruder model, namely the flat‐plate model. Due to high density and viscosity ratios, a free‐surface approach based on the volume of fluid method is used. The material distribution for different degree of fillings and the resulting power consumption is investigated. In addition, the obtained power characteristic is compared against analytical consideration and numerical simulation of a fully filled case. The investigation shows that the power characteristic of a partially filled extruder can be estimated by a fully filled computation. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A numerical investigation on the dynamic stall of a vertical axis wind turbine
Authors: Frunzulica Florin , Dumitrescu Horia , Dumitrache Alexandru
Published: November 2013

In the last years, for home user, the wind turbine with vertical axis (VAWT) began to be more attractive due benefits in exploitation. In terms of aerodynamics, when the wind speed approaches the speed of operation (low value of tip speed ratio ‐TSR) the blade airfoil exceeds the critical angle of incidence for static conditions. Angle of incidence varies quickly across blade and the blade works in dynamic stall condition. The goal of the present work is to investigate the two‐dimensional dynamic stall phenomenon around the NACA 0012 airfoil at relatively low Reynolds. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Utilizing CFD‐Simulations to Assess Flow‐Induced Vibrations of Slender Beams in Cross‐Flow
Authors: Strecha Johannes , Steinrück Herbert
Published: November 2013

Flow‐induced vibrations of a slender U‐beam in cross‐flow are assessed, using the proprietary CFD‐solver ANSYS‐CFX. The U‐beam has two degrees of freedom: heaving motion and rotation. The flow‐ and motion‐governing equations are solved together, using an iterative coupling method. We find, that using this iterative coupling does not ensure a valid long‐time behaviour of the solution. The results of free vibration simulations would allow investigation of the excitation mechanisms. But for determining possibility of large amplitude vibrations, methods relying on forced motion are deemed more promising. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Discrete Adjoint based Sensitivity Analysis for Optimal Active Flow Control of High‐Lift Configurations
Authors: Nemili Anil , Özkaya Emre , Gauger Nicolas
Published: November 2013

Blowing and suction type of active flow control techniques can be used to delay the flow separation on the flap and to enhance the aerodynamic performance of high‐lift configurations. Effective separation control and maximum enhancement in the mean lift coefficient are achieved by finding the optimal actuation parameters. The optimal set of actuation parameters can be obtained by combining the gradient based algorithms with discrete adjoints. In the present work, an unsteady discrete adjoint incompressible RANS solver is developed for the optimal active separation control. The adjoint solver is applied to the test case of active flow control on the flap of a 2D high‐lift configuration. Sensitivity gradients are presented to demonstrate the accuracy of unsteady adjoint RANS solver. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Convergence of a finite difference method for the time‐fractional diffusion equation with concentrated capacity
Authors: Delić Aleksandra
Published: November 2013

We investigate the convergence of difference scheme for the time‐fractional differential equation with fractional derivative of an order $\alpha\in(0,1)$ with the coefficient at the time derivative containing Dirac delta distribution. Convergence order of $O(\tau^{2-\alpha}+h^2)$ is proved. A numerical example demonstrates the theoretical results. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Tensile‐bending coupling in the limitting 1D beam equations resulting from the frictional contact
Authors: Bare Zoufine , Orlik Julia
Published: November 2013

The asymptotic dimension reduction for beam contact problems without friction leads to decoupled ODE systems in the longitudinal variable, see [4]. This decoupling is due to the fact that friction is not taken into account. In this work we extend [2] by an alternative scaling of the tensile force in the 3D formulation that permits us to reduce the dimension of a contact problem with friction in tensile direction, too. The tension and the bending component in the direction of the contact normal are coupled due to the friction. The coupling of the displacement components is illustrated by a numerical example. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Approximation rate and invertibility for some singular integral operators
Authors: Vasilyev Alexander , Vasilyev Vladimir
Published: November 2013

We consider discrete analogues of multi‐dimensional singular integrals and integral operators in a half‐space in square integrable and Hölder spaces with weight, and invertibility of discrete operators, and give the approximation rate for discrete operators. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Galerkin Approach for Solving Matrix Equations with Hierarchical Matrices
Authors: Boysen Dirk , Börm Steffen
Published: November 2013

We consider a new approach for computing solutions of certain matrix equations, for example AXA = C, AX + XB = C or AX = I. This approach is based on a variational formulation in the matrix space, employing the Frobenius inner product. Using the space of ℋ2‐matrices as trial space leads to a sparse linear system that can be solved by iterative methods to compute an approximate solution of the underlying matrix equation. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Acceleration of Kaczmarz Projection Algorithm
Authors: Pomparău Ioana
Published: November 2013

In the paper [1], a direct version of the classical Kaczmarz algorithm was proposed, which gives us in only one iteration a solution of an arbitrary consistent system of linear equations. Unfortunately, as any direct method applied to large sparse matrices, this algorithm is based on some modifications of the system matrix sparsity structure such that a big fill‐in appears. In order to overcome this difficulty, in the present paper we propose a modified version of this direct Kaczmarz algorithm in which the transformations applied to the system matrix try to conserve the initial sparsity structure. This transformations are done via clustering using Jaccard and Hamming distances. The modified Kaczmarz algorithm is no more a direct method, but we obtain an acceleration of convergence with respect to the classical Kaczmarz algorithm. Numerical experiments which ilustrate the efficiency of our algorithm are also presented. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
LQR control for a Diesel engine's air system
Authors: Kemper Anna , Wöbbekind Mitja , Büskens Christof , Schollmeyer Michael
Published: November 2013

Due to more and more restrictive emission standards, the air system of Diesel engines has evolved into a complex system with several coupled actuating and controlled variables. In this paper, a linear‐quadratic regulator (LQR) is used as a model‐based, multivariable, optimal control of the air system. This technique is validated by results of an on‐board test. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiobjective Optimization including Safety of Operation Applied to a Linear Drive System
Authors: Meyer Tobias , Hölscher Christian , Menke Michael , Sextro Walter , Zimmer Detmar
Published: November 2013

In this contribution, we introduce a multiobjective optimization used to calculate safe optimal working points for a mechatronic system by including stochastic safety‐critical signals in an objective function.

Our application example consists of a linear drive for a rail‐bound vehicle and an actuation unit. The linear drive's secondary part is fixed; the primary part is vehicle‐mounted and can be adjusted vertically to account for deviations of the height of the secondary part. A small air gap between both parts improves efficiency, but increases the risk of a collision between the two parts.

Using height data of the secondary part, a trajectory for the vertical adjustment of the primary part is calculated. However, unexpected deviations necessitate a readjustment of the air gap. The probability of such unexpected height deviations can be calculated from the readjustment data. The system is equipped with sensors to measure the air gap. Assuming that the sensor noise is normally distributed, noise characteristics are determined. Using this information and the probability distribution of unexpected height deviations, the probability of a collision is determined.T

he sensor noise and the probability of a collision between both parts of the linear drive are included in the dynamical model of the system. Using multiobjective optimization, pareto‐optimal working points for the controller of the air gap are obtained. By selecting an appropriate working point, safe operation can be ensured. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Averaging for switched DAEs
Authors: Iannelli Luigi , Pedicini Carmen , Trenn Stephan , Vasca Francesco
Published: November 2013

Switched differential‐algebraic equations (switched DAEs) $E_{\sigma(t)}\dot{x}(t) = A_{\sigma(t)}x(t)$ are suitable for modeling many practical systems, e.g. electrical circuits. When the switching is periodic and of high frequency, the question arises whether the solutions of switched DAEs can be approximated by an average non‐switching system. It is well known that for a quite general class of switched ordinary differential equations (ODEs) this is the case. For switched DAEs, due the presence of the so‐called consistency projectors, it is possible that the limit of trajectories for faster and faster switching does not exist. Under certain assumptions on the consistency projectors a result concerning the averaging for switched DAEs is presented. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Sensitivity analysis of linear dynamical systems in uncertainty quantification
Authors: Pulch Roland , ter Maten E. Jan W. , Augustin Florian
Published: November 2013

We consider linear dynamical systems including random parameters for uncertainty quantification. A sensitivity analysis of the stochastic model is applied to the input‐output behaviour of the systems. Thus the parameters that contribute most to the variance are detected. Both intrusive and non‐intrusive methods based on the polynomial chaos yield the required sensitivity coefficients. We use this approach to analyse a test example from electrical engineering. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Performance aspects of a mixed s‐v LSFEM for the incompressible Navier‐Stokes equations with improved mass conservation
Authors: Schwarz Alexander , Schröder Jörg , Serdas Serdar , Turek Stefan , Ouazzi Abderrahim , Nickaeen Masoud
Published: November 2013

In the present contribution we propose an improved mixed least‐squares finite element method (LSFEM) and compare it with standard LSFEMs with respect to performance aspects. In detail, we consider an approach for Newtonian fluid flow, which is described by the incompressible Navier‐Stokes equations. The basis for the associated symmetric minimization problem is a reduced stress‐velocity (s‐v) two‐field approach, see e.g. CAI ET AL. [1] and SCHWARZ & SCHRÖDER [2]. The main idea for the proposed formulation is to add an additional equation, which yields an overconstrained first‐order system. This approach does not introduce additional unknowns, so the advantage of two variables (stresses and velocities) remains. Finally, we present a numerical example in order to show the capability of the proposed formulation. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An improved criterion for absence of eigenvalues of one‐dimensional Schrödinger operators
Authors: Seifert Christian , Vogt Hendrik
Published: November 2013

We study one‐dimensional Schrödinger operators with complex measures as potentials and present an improved criterion for absence of eigenvalues which involves a weak local periodicity condition. As an application we consider quasiperiodic measures as potentials. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Class of Fractional Evolutionary Equations
Authors: Picard Rainer
Published: November 2013

A well‐posedness result for a time‐shift invariant class of evolutionary operator equations involving material laws with fractional time‐derivatives is considered and exemplified by an application to a fractional Kelvin‐Voigt type model. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Two‐scale computational homogenization of magneto‐electric composites
Authors: Keip Marc‐André , Labusch Matthias , Schröder Jörg
Published: November 2013

This contribution presents a two‐scale computational homogenization framework for the micro‐macro simulation of magneto‐electro‐mechanically coupled materials. Energetically consistent micro‐macro transition conditions will be derived from a generalized form of the classical Hill‐Mandel condition. A focus of the work is on the computation of effective magneto‐electric moduli which are derived on the basis of an algorithmically consistent linearization of the macroscopic field equations. The method will be applied to the homogenization of magneto‐electric composites which are composed of piezomagnetic and piezoelectric phases. The effective magneto‐electric moduli of two‐phase composites will be computed. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Privatizing health care in times of new public management: Investigating the role of psychological empowerment using cluster analysis
Authors: Hansen Niklas , Baraldi Stephan , Berntson Erik , Andersson Håkan
Published: November 2013

Although privatization within health care is usually justified using arguments based on efficiency and productivity, the empirical investigations underpinning such arguments are few and ambiguous in their results. Presenting a new theoretical and analytical approach to this research field, we argue that psychological empowerment, reflecting individuals' intrinsic change motivation state, is a crucial prerequisite for the transformation of a nonprofit health care organization to a for‐profit one. The general aims of this study were to explore empowerment cognitions during a privatization, to relate these to a selection of key work‐related outcome variables, and to identify the effects of privatization in terms of individual level changes in empowerment after privatization. A sample of health care workers (n = 210) provided survey longitudinal data that were analyzed using cluster analysis. Eight clusters were identified at both pre‐ and postprivatization with each cluster mirroring specific empowerment patterns: Empowered, In Control, Quasi‐Empowered, Competent/Normed, Reference, Underused, Misfit, and Powerless. The clusters discriminated on positive work attitudes, mental health complaints, and turnover intentions. The analysis also revealed the complexity of privatization in that a homogenization as well as a differentiation tendency was observed, thereby implicating both socio‐structural equality and inequality effects. The results highlighted the relevance of allocating importance to health care workers' psychological empowerment during the privatization process, and of viewing such organizational transformations not as simple shifts in the state of affairs, but as nonlinear processes involving dynamic changes in individual perceptions over time.
Risk of acute myocardial infarction, stroke, or death in patients initiating olmesartan or other angiotensin receptor blockers — a cohort study using the Clinical Practice Research Datalink
Authors: Zhou Esther H. , Gelperin Kate , Levenson Mark S. , Rose Martin , Hsueh Ya‐Hui , Graham David J.
Published: November 2013

Purpose

Results of two randomized trials (ROADMAP and ORIENT) suggest that high‐dose (40 mg/day) olmesartan (Olm) is associated with increased cardiovascular mortality compared to placebo in diabetic patients. We evaluated the risks of acute myocardial infarction (AMI) and death in patients initiating Olm compared with an active comparator group, other angiotensin receptor blockers (ARBs), with a focus on high‐dose and diabetic subgroups.

Methods

We conducted a cohort study with patients who initiated Olm or another ARB between 2003 and 2011, using the UK Clinical Practice Research Datalink GOLD. We included patients who had no prior ARB or angiotensin converting enzyme inhibitor exposure during the preceding 6 months. Hazard ratios (HRs) were estimated using Cox regression models with both multivariable adjustment and propensity score matching.

Results

There were 3964 Olm and 54 653 other‐ARB initiators, respectively. Adjusted HRs comparing Olm and other‐ARBs were 1.04 (95% CI: 0.75–1.42) for AMI and 1.16 (0.95–1.42) for death, using multivariable adjustment. Comparing patients initiated with a high‐dose Olm and a high‐dose other‐ARB, HRs were 3.09 (0.94–10.13) for AMI and 2.03 (0.74–5.61) for death, using multivariable adjustment; and 4.38 (0.97–19.66) and 1.99 (0.63–6.32) for AMI and death, using propensity score matching.

Conclusions

Overall, no differences in risk were observed in the main cohort analyses comparing Olm initiators with patients initiating therapy with other ARBs; however, HRs were marginally increased for all study endpoints which compared high‐dose subgroups, suggesting potential increased risk may be associated with high‐dose Olm. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.
Self‐assembly of nanorod/nanoparticle mixtures in polymer brushes
Authors: Zhang Dong , Jin Yankang , Cheng Jun , Jiang Yangwei , He Linli , Zhang Linxi
Published: November 2013

The aggregation behavior and phase separation of nanorod (NR)/nanoparticle (NP) nanoinclusions immersed in semiflexible polymer brushes (PBs) are investigated by using molecular dynamics simulations. A variety of phases are formed by varying the size ratio q = σr/σp, where σr and σp are the diameters of NR and NPs, respectively, and the attractive interactions εM between NR/NP nanoinclusions and PBs. Ordered structures of NRs surrounded by large NPs are observed for the small size ratio q, and a dispersed mixture phase appears for the moderate size ratio q at weak attractive interaction. Meanwhile, the crystallization of NRs occurs at strong attractive interaction for the large size ratio q and a main face‐centered cubic (fcc) structure combined with a small amount of hexagonal‐closed packed (hcp) structure is observed. This investigation can provide some insights into the self‐assembly of complex nanoinclusions and promise a new approach for controlling the self‐assemble behavior of NPs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 299–309
Magnetic field‐induced morphology‐dependent resonances of a coupled composite metglas slab with a polymeric optical resonator
Authors: Ioppolo Tindaro , Rubino Edoardo
Published: November 2013

In this article, the effect of an external magnetic field on the morphology‐dependent resonances (MDRs) of a polymeric dielectric microsphere is investigated. The microsphere is mechanically coupled to a composite polymeric Metglas slab. When an external magnetic field is applied to the slab, it elongates leading to a change in the morphology of the microsphere. This in turn leads to a shift in the excited optical resonances. Experiments are carried out to investigate the effect of an external static and harmonic magnetic field on the MDRs shift. The results show that this configuration can be used as an optical magnetic field sensor or as an optical tuning element. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 272–275
Telomere length as a risk factor for hereditary prostate cancer
Authors: Hurwitz Lauren M. , Heaphy Christopher M. , Joshu Corinne E. , Isaacs William B. , Konishi Yuko , De Marzo Angelo M. , Isaacs Sally D. , Wiley Kathy E. , Platz Elizabeth A. , Meeker Alan K.
Published: November 2013

BACKGROUND

Telomeres are repetitive nucleotide sequences that stabilize the ends of chromosomes. Critically short telomeres are thought to contribute to cancer development by increasing chromosomal instability. We hypothesized that shorter leukocyte telomere length, a surrogate for inherited prostate cell telomere length, would be associated with increased risk of prostate cancer in hereditary prostate cancer (HPC) families.

METHODS

One hundred twelve affected and 63 unaffected men from 28 families were drawn from the Johns Hopkins HPC family database. Relative mean telomere length was measured in isolated peripheral leukocyte DNA by quantitative PCR. Conditional logistic regression was used to estimate the association between quartile of age‐adjusted telomere length and prostate cancer.

RESULTS

Men in the shortest quartile of telomere length did not have increased odds of prostate cancer compared to men in the other three quartiles (OR = 0.84, 95% CI: 0.32–2.20, P = 0.73). However, when the analysis was restricted to affected men with blood drawn before or within a year of diagnosis (N = 39) and all unaffected men, shorter telomere length was moderately associated with increased odds of prostate cancer (OR = 3.55, 95% CI: 0.82–15.43, P = 0.09).

CONCLUSIONS

Though we found no association overall, shorter leukocyte telomere length may be associated with increased odds of prostate cancer when measured in pre‐diagnostic samples. Further prospective research is warranted exploring the utility of telomere length as a prostate cancer biomarker. Prostate 74:359–364, 2014. © 2013 Wiley Periodicals, Inc.
Evaluation of acid‐labile S‐protecting groups to prevent Cys racemization in Fmoc solid‐phase peptide synthesis
Authors: Hibino Hajime , Miki Yasuyoshi , Nishiuchi Yuji
Published: November 2013

Phosphonium and uronium salt‐based reagents enable efficient and effective coupling reactions and are indispensable in peptide chemistry, especially in machine‐assisted SPPS. However, after the activating and coupling steps with these reagents in the presence of tertiary amines, Fmoc derivatives of Cys are known to be considerably racemized during their incorporation. To avoid this side reaction, a coupling method mediated by phosphonium/uronium reagents with a weaker base, such as 2,4,6‐trimethylpyridine, than the ordinarily used DIEA or that by carbodiimide has been recommended. However, these methods are appreciably inferior to the standard protocol applied for SPPS, that is, a 1 min preactivation procedure of coupling with phosphonium or uronium reagents/DIEA in DMF, in terms of coupling efficiency, and also the former method cannot reduce racemization of Cys(Trt) to an acceptable level (<1.0%) even when the preactivation procedure is omitted. Here, the 4,4′‐dimethoxydiphenylmethyl and 4‐methoxybenzyloxymethyl groups were demonstrated to be acid‐labile S‐protecting groups that can suppress racemization of Cys to an acceptable level (<1.0%) when the respective Fmoc derivatives are incorporated via the standard SPPS protocol of phosphonium or uronium reagents with the aid of DIEA in DMF. Furthermore, these protecting groups significantly reduced the rate of racemization compared to the Trt group even in the case of microwave‐assisted SPPS performed at a high temperature. © 2013 The Authors. European Peptide Society published by John Wiley & Sons, Ltd.
Influence of DC bias fields on the linear/nonlinear magnetoelectric effect and the sensitivity in laminate composites
Authors: Liu Yuting , Jiao Jie , Li Lingying , Ma Jiashuai , Ren Bo , Chen Jianwei , Di Wenning , Zhao Xiangyong , Luo Haosu , Shi Ling
Published: November 2013

The nonlinear and linear properties in Metglas/piezofiber magnetoelectric composites under DC bias fields (Hbias) have been investigated via a frequency‐conversion technique. It was found that the major noise near the carrier frequency (fC) is caused by the driven source. Both linear ME coefficient and noise floor near fC (bandwidth of noise measurement is 10 Hz) were dependent on Hbias, while the nonlinear ME coefficient was independent. A high magnetic‐field sensitivity of 40 pT was obtained after optimizing Hbias. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cannabidiol Promotes Amyloid Precursor Protein Ubiquitination and Reduction of Beta Amyloid Expression in SHSY5YAPP+ Cells Through PPARγ Involvement
Authors: Scuderi Caterina , Steardo Luca , Esposito Giuseppe
Published: November 2013

The amyloidogenic cascade is regarded as a key factor at the basis of Alzheimer's disease (AD) pathogenesis. The aberrant cleavage of amyloid precursor protein (APP) induces an increased production and a subsequent aggregation of beta amyloid (Aβ) peptide in limbic and association cortices. As a result, altered neuronal homeostasis and oxidative injury provoke tangle formation with consequent neuronal loss. Cannabidiol (CBD), a Cannabis derivative devoid of psychotropic effects, has attracted much attention because it may beneficially interfere with several Aβ‐triggered neurodegenerative pathways, even though the mechanism responsible for such actions remains unknown. In the present research, the role of CBD was investigated as a possible modulating compound of APP processing in SHSY5YAPP+ neurons. In addition, the putative involvement of peroxisome proliferator‐activated receptor‐γ (PPARγ) was explored as a candidate molecular site responsible for CBD actions. Results indicated the CBD capability to induce the ubiquitination of APP protein which led to a substantial decrease in APP full length protein levels in SHSY5YAPP+ with the consequent decrease in Aβ production. Moreover, CBD promoted an increased survival of SHSY5YAPP+ neurons, by reducing their long‐term apoptotic rate. Obtained results also showed that all, here observed, CBD effects were dependent on the selective activation of PPARγ. Copyright © 2013 John Wiley & Sons, Ltd.
The distribution and variability of low‐level cloud in the North Atlantic trades
Authors: Nuijens L. , Serikov I. , Hirsch L. , Lonitz K. , Stevens B.
Published: November 2013

In the North Atlantic trades, variations in the distribution of low‐level cloud are rich. Using two years of observations from a remote‐sensing site located on the east coast of Barbados, the vertical distribution of cloud and its contribution to low‐level cloud amount are explored. The vertical distribution of first‐detected cloud‐base heights is marked by a strong peak near the lifting condensation level (LCL) from passive optically thin shallow cumuli. Cloud with a base near this level dominates the total cloud cover with a contribution of about two‐thirds. The other one‐third comes from cloud with its cloud base further aloft at heights > 1 km, such as cumulus edges or stratiform cloud below the trade inversion. Cloud found aloft, regardless of where its base is located, contains more variance, in particular near the inversion and on time‐scales longer than a day. In turn, cloud near the LCL is surprisingly invariant on longer time‐scales, although consistent with existing theories. Because this component does not systematically vary, changes in cloud cover in response to changes in meteorology or climate may be limited to changes in its contribution from cloud aloft.
Reduction of the small gain condition for large‐scale interconnections
Authors: Dashkovskiy S. , Kosmykov M.
Published: November 2013

The small gain condition is sufficient for input‐to‐state stability (ISS) of interconnected systems. However, verification of the small gain condition requires large amount of computations in the case of a large size of the system. To facilitate this procedure, we aggregate the subsystems and the gains between the subsystems that belong to certain interconnection patterns (motifs) by using three heuristic rules. These rules are based on three motifs: sequentially connected nodes, nodes connected in parallel, and almost disconnected subgraphs. Aggregation of these motifs keeps the structure of the mutual influences between the subsystems in the network. Furthermore, fulfillment of the reduced small gain condition implies ISS of the large network. Thus, such reduction allows to decrease the number of computations needed to verify the small gain condition. Finally, an ISS‐Lyapunov function for the large network can be constructed using the reduced small gain condition. Applications of these rules is illustrated on an example. Copyright © 2013 John Wiley & Sons, Ltd.
Teachers’ barriers to introducing system dynamics in K‐12 STEM curriculum
Authors: Skaza Heather , Crippen Kent J. , Carroll Kristoffer R.
Published: November 2013

Systems thinking tools and system dynamics simulations can provide a valuable means for helping students think their way around complex environmental problems. Using the results of a Web‐based survey and face‐to‐face focus group this study was designed to advance our understanding of teacher adoption of systems thinking and system dynamics modeling by documenting the perspective of a large group in an urban context tasked with a curriculum that included system dynamics simulations. Teachers identified the barriers to implementing simulation activities as both computer access and their own understanding. A test of teachers’ understanding of systems principles reveals inconsistencies in the way they interpret models, based on their previous understanding of the system. Strategies for addressing these issues include professional development that targets teacher self‐efficacy, understanding of systems and system models, as well as the provision of materials for model‐building and simulation use. Copyright © 2013 System Dynamics Society