bluuebunny/crossref_metadata_2025 huggingface dataset:
Towards modelling the curing process in particle‐filled electro‐active polymers
Authors: Hossain Mokarram , Steinmann Paul
Published: October 2015

A large actuation voltage is required to produce a desired mechanical deformation in dielectric elastomers. To reduce the amount of the actuation voltage, several mechanisms can be applied and the inclusion of high dielectric permittivity fillers in the matrix material in the uncured stage is one of them. Moreover, to obtain a maximum advantage from the high dielectric permittivity fillers, an electric field is applied during the curing process which helps the particles to align in a preferred direction. The stiffness gaining during curing is modelled by an appropriate constitutive relation where the temporal evolution of the material parameters is considered. In this paper we present a phenomenologically‐inspired large strain framework for simulating the curing process of polymers that can work under the use of an electro‐mechanically coupled load. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A global damping factor for a non‐invasive form finding algorithm
Authors: Landkammer Philipp , Steinmann Paul
Published: October 2015

Inverse form finding based on the finite element method (FEM) aims in determining the optimal material (undeformed) configuration when knowing the target spatial (deformed) configuration in a discretized setting. The strategy is to iteratively update the material coordinates and recompute the spatial configuration by a FEM simulation until the computed spatial nodal positions are close enough to a priori given spatial nodal positions. A form finding algorithm is utilized, which is purely based on geometrical considerations and can be coupled with arbitrary external FEM software via subroutines in a non‐invasive fashion. At large deformations degenerated elements can occur when updating the material coordinates. Evaluating the mesh quality of the updated material configuration and adjusting a global damping factor before recomputing the next spatial configuration helps to avoid mesh distortions. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
FE‐simulation of spatially graded gelation during adhesive's curing
Authors: Rudolph Martin , Landgraf Ralf , Ihlemann Jörn
Published: October 2015

In this contribution main aspects of material characterization and modelling of a curing adhesive are denoted. It is pointed out how to deal with the exothermic heat generation during curing, both, how to obtain it experimentally as well as how to account for it in the continuum mechanical an FE‐modelling framework. Furthermore, a strategy to simulate spatially graded gelation processes in ANSYS® is presented. An academic simulation example completes this work. By the help of this simulation tool a better understanding of a novel manufacturing process of smart semi‐finished light weight structures is ensured. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational Homogenization in Micro‐Magneto‐Elasticity
Authors: Sridhar Ashish , Keip Marc‐André , Miehe Christian
Published: October 2015

The overall macroscopic response of magneto‐mechanically coupled materials stems from complex magnetization evolution and corresponding domain wall motion occurring on a lower length scale. In order to account for such effects we propose a computational homogenization approach that incorporates a ferromagnetic phase‐field formulation into a macroscopic Boltzmann continuum. This scale‐bridging is obtained by rigorous definition of rate‐type and incremental variational principles. An extended version of the classical Hill‐Mandel macro‐homogeneity condition is obtained as a consequence. In order to satisfy the unity constraint of the magnetization on the micro‐scale, an efficient operator‐split method is proposed. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of Micro‐ and Macro‐Instability Phenomena in Computational Homogenization of Finite Electro‐Statics
Authors: Vallicotti Daniel , Miehe Christian
Published: October 2015

Dielectric materials such as electro‐active polymers (EAPs) belong to the class of functional materials which are used in advanced industrial environments as sensors or actuators and in other innovative fields of research. Driven by Coulomb‐type electrostatic forces EAPs are theoretically able to withstand deformations of several hundred percents. However, large actuation fields and different types of instabilities prohibit the ascend of these materials. One distinguishes between global structural instabilities such as buckling and wrinkling of EAP devices, and local material instabilities such as limit‐ and bifurcation‐points in the constitutive response. We outline variational‐based stability criteria in finite electro‐elastostatics and design algorithms for accompanying stability checks in typical finite element computations. These accompanying stability checks are embedded into a computational homogenization framework to predict the macroscopic overall response and onset of local material instability of particle filled composite materials. Application and validation of the suggested method is demonstrated by representative model problems. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling thermoplastic material behaviour of dual‐phase steels on a microscopic length scale
Authors: Zeller Sebastian , Löhnert Stefan , Wriggers Peter
Published: October 2015

On a microscopic length scale dual‐phase steels exhibit a polycrystalline microstructure consisting of ferrite and martensite. In this work a material model for the temperature dependent hardening behaviour of the ferritic phase is presented. As the dislocation structure determines the resistance to dislocation glide, dislocation densities are introduced as state variables to capture the dependence of the material behaviour on the loading history. Motivated by the elementary processes of multiplication by the Frank‐Read‐mechanism and annihilation by cross‐slip, evolution equations for the dislocation densities are introduced. Based on the interaction of dislocations on different slip systems and the Peierls‐stress, the resistance to dislocation motion with its temperature dependence is formulated to describe the hardening behaviour. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermodynamically consistent description of mass transfer in porous media by a singular surface
Authors: Häberle Kai , Ehlers Wolfgang
Published: October 2015

Phase transition processes are important and ubiquitous physical phenomena. These processes are not limited to systems like batch reactors, but can also appear inside porous solids such as in the sequestration of CO2 or in the food industry. In these processes, mainly first‐order transitions between the liquid and the gaseous phases of a certain fluid occur and are characterised by a jump in density and the coexistence of both phases during phase change. This jump is numerically handled by introducing a singular surface, which allows for a thermodynamically consistent description of the mass transfer during phase transition. The mass transfer is driven by the change in internal energy and couples the two mass balance relations of the two fluid phases.

The formulation of a model for a multiphasic porous aggregate in a non‐isothermal environment, while accounting for the thermodynamics of the fluids and the phase transition, requires a potent theory for its description. Here, the Theory of Porous Media (TPM) provides a well‐founded, continuum‐mechanical basis to model deformable, fluid‐saturated porous media. In this particular case, a three‐phasic model is proposed, consisting of the thermoelastic solid phase, which is percolated by the compressible gaseous and liquid fluid phases. The representation of the interface between the fluid phases by a singular surface results in additional terms in the balance relations. The evaluation of these terms leads to a consistent formulation of the mass transfer, which basically compares the energy added to the system with the latent heat of the phase transition. This mass‐transfer term is furthermore dependent on the interfacial area, a factor defined by porosity and saturation.

Finally, the proposed model for phase transition inside a porous medium is based on the mixture momentum balance, the volume balances of the fluid phases and the energy balance. Consequently, the four primary variables are the solid deformation, the effective pore pressures of the two fluid phases and the temperature. The numerical simulation of condensation or evaporation of CO2 in a porous solid rock, which can be either caused by changes in temperature or in pressure, allows for the demonstration of possible application areas for the presented model. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hydraulic fracturing based on the Theory of Porous Media
Authors: Luo Chenyi , Ehlers Wolfgang
Published: October 2015

Hydraulic fracturing is a widely‐used technology in the field of energy exploitation. The relevant study is intricate owing to the crack‐inducing instability and the coupling between different constituents in stratum. The proposed model is based on the phase‐field theory and extended to the Theory of Porous Media. The former removes crack discontinuity by substituting sharp crack with smeared one and the later provides clear and distinct description of multi‐phasic material in macroscopic scale. A new variable, the order parameter ϕ is imported to characterise material as unbroken porous media and the crack zone, the evolution of which is governed by potential energy of solid. With the change of ϕ, the stiffness of solid is decreasing while the fluid transport is transferring from Darcy‐type to Navier‐Stokes‐type. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A continuum mechanical, bi‐phasic, two‐scale model for thermal driven phase transition during solidification
Authors: Moj Lukas , Ricken Tim , Steinbach Ingo
Published: October 2015

This articel focuses on a bi‐scale numerical description for solidification process simulation. The macro‐scale implies two phases which are the solid and liquid metallic alloy physical states described using the theory of porous media (TPM) enhanced by strong thermal coupling and finite elastic‐plastic‐creep temperature dependent material behaviour. Furthermore, a linear viscous melt as well as a laminar melt flow are adopted. The thermal driven physics of solidification is covered by a microscopic phase‐field model. Therefore, a Ginzburg‐Landau type free energy function is employed. After discussing the main model details, a real Bridgman oven numerical pre‐model will demonstrate the principal performance. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Efficient Simulation of the Heat Flux Input in Moving Contacts
Authors: Partzsch Marian , Beitelschmidt Michael
Published: October 2015

In thermal simulations moving parts can be included by discretely adjusting their position within the steps of a transient analysis, whereby frictional heating is considered as a pre‐determined, time‐depended NEUMANN‐BC within the contact zone. Now when using a coarse time discretization, the rarely conducted update of the actual loaded friction is the reason for one proportion of the occurring lack in result quality. In this paper we present an idea to counter this systematic error source by some low‐effort editing of the applied load data. The proposed method is based on the conservation of the provided frictional energy between the continuous and discrete motion and considers the actually used time discretization. Its performance is shown for a simplified case at the end of this paper. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase field simulation on mechanically induced 180 degree switching in nanomagnets
Authors: Yi Min , Xu Bai‐Xiang
Published: October 2015

The mechanically induced 180° switching of the magnetization in cylindrical nanomagnets is demonstrated through the switching dynamics simulation by a constraint‐free phase field model which is fully magneto‐mechanical coupled. By using the overrun behavior of the magnetization during the mechanically induced precessional switching, a deterministic 180° switching can be achieved. It is found that the residual torque resulting from the azimuthal‐angle dependence of the magneto‐elastic coupling and the overrun and precessional dynamics are responsible for the switching mechanism. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fluid‐Porous‐Media Interaction: A Decoupled Solution Algorithm via Localised Lagrange Multipliers
Authors: Zinatbakhsh Seyedmohammad , Koch David , Ehlers Wolfgang
Published: October 2015

Fluid‐porous‐media interaction (FPMI) refers to a surface interaction among several non‐overlapping subsystems, composed of either a bulk fluid or a porous medium. This could be the interaction of blood with a blood vessel wall, a body of water with an earth‐dam structure, or acoustic waves with acoustic panels used in soundproofing, etc. These are highly coupled phenomena inheriting different coupling mechanisms which take place within the interacting subdomains as well as across common boundaries. Consequently, the mathematical models of such phenomena also consist of sets of coupled differential equations, which are commonly solved numerically, following a monolithic or a decoupled approach. Here, the focus is on the latter.

The design of an algorithm for the decoupled solution of the fluid‐porous‐media‐interaction problem can be advantageous in several ways. First and foremost, the process of decoupling breaks down the problem into several subproblems, which can be solved efficiently employing specialised fluid and porous‐media solvers. Furthermore, solution of several decoupled subproblems instead of one highly coupled problem may be more economical in terms of computational costs. This is especially the case if the scheme permits parallel treatment of the produced subproblems.

Here, the applicability of using the method of localised Lagrange multipliers for a partitioned solution of the problem of FPMI in the 2‐dimensional space is demonstrated. In this regard, the concept of modified Eulerian description for studying the motion of fluid bodies within moving boundaries is introduced. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A two‐scale homogenisation approach for fluid saturated porous media based on TPM and FE2‐Method
Authors: Bartel Florian , Ricken Tim , Schröder Jörg , Bluhm Joachim
Published: October 2015

Thinking about the description of biomaterials, e.g. human tissue, plants or sponges, we always have to take into account a global design composed of various substructures with different characteristics on a lower level. Examples of such substructures are pores which can be saturated with fluids or gases, fibres with different orientations or cells which can be influenced by chemical reactions. For the theoretical description of the behaviour, enhanced continuum mechanical models give promising approaches. Up to now, due to the high complexity, it has not been possible to simulate a biological system with only one design model. Hence, it is necessary to think about techniques which simplify the model but still consider the essential characteristics. This contribution will present a two‐scale homogenisation approach for fluid saturated porous media with a reduced two‐phase material model, which covers the behaviour of large poro‐elastic deformation. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational characterization of magneto‐electric composites: the role of ferroelectric pre‐polarization
Authors: Labusch Matthias , Schröder Jörg , Keip Marc‐André , Lupascu Doru C.
Published: October 2015

The interaction between electric and magnetic fields enables smart devices which can find applications in sensor technology and data storage. Materials showing magneto‐electric (ME) coupling combine different ferroic characteristics. In the present contribution we focus on composites, which combine ferroelectric and ferromagnetic phases due to strain couplings, such that they generate a strain‐induced ME coupling. We derive a two‐scale homogenization approach for the determination of effective properties in consideration of microscopic morphologies. Furthermore, we demonstrate the strong influence of ferroelectric polarization states on the ME‐coefficient by modeling the switching of remanent polarizations on the microscale. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Block Conjugate Gradient Iteration for Fourier‐Galerkin Homogenization of Periodic Media
Authors: Mishra Nachiketa , Vondřejc Jaroslav , Zeman Jan
Published: October 2015

The Fourier‐Galerkin method is considered here for the solution of the unit cell problem that describes the homogenized properties of periodic materials in the scalar elliptic setting. The method is based on a Galerkin approximation with trigonometric polynomials and leads to linear systems suitable for iterative solvers. In [1], Zeman et al show the effectiveness of Conjugate gradients (CG) which is compared here with its block version (BCG). We show that the latter version outperforms the CG especially for anisotropic materials with non‐symmetric distribution of material properties. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coupling atomistic and continuum models with nodes having translational and rotational degrees of freedom
Authors: Niederhöfer Florian , Wackerfuß Jens
Published: October 2015

This paper deals with the coupling of atomistic simulations and nodes having translational and rotational degrees of freedom (dof). Especially the (non‐)occurrence of boundary effects is a main issue of the following remarks. The presented approach is formulated within the finite element method and can be the groundwork for multiscale simulations, when coupled with continuum models. In particular, atomistic models can be coupled with continuum ones having translational and rotational dofs like beams and shells. After the introduction of the main ideas of the approach, it is applied to an atomistic chain. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability analysis of the flow past miniature vortex generators in a Blasius boundary layer
Authors: Siconolfi Lorenzo , Camarri Simone , Fransson Jens H. M.
Published: October 2015

It is shown in the literature that Tollmien−Schlichting waves can be damped and transition delayed by a proper modulation of the streamwise velocity in a boundary layer (BL), which can be obtained using miniature vortex generators (MVGs). Experiments show that the amplitude of TS waves is not always monotonically damped past the MVGs. In this study, direct numerical simulations and local stability analysis have been performed in order to provide an interpretation of the experiments and to characterize further the stabilization mechanism induced by this type of control. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of wake effects of windfarms using an Actuator Disk implementation
Authors: Hornung Cordula , Viellieber Mathias , Class Andreas
Published: October 2015

Wind turbines extract energy from the approaching flow field resulting in reduced wind speeds, increased turbulence and a wake downstream of the wind turbine. Wakes extending up to 20 km downstream of a windfarm are reported [1]. In [2] a multi‐scale numerical method is proposed that addresses length scales of the boundary layer, windfarm and meso‐scale. As a step towards full realization of the multi scale approach the implementation of an Actuator Disk (AD) model into OpenFOAM including a proper atmospheric boundary layer (ABL) is presented. For a meso‐scale area of open sea, the standard ABL conditions of OpenFOAM can not be used. The pre implemented ABL boundary condition for OpenFOAM is restricted to roughness lengths greater than 0.001 m. The boundary condition are modified in order to achieve adequate homogeneous flow properties throughout the considered domain enabling almost constant velocity profiles. A new AD class is implemented in OpenFOAM to establish an arbitrary number and location of windturbines. The class uses the standard k‐ϵ turbulence model. The wake effect of windfarms composed of windturbines with different heights and different lateral spacing is investigated. Specifically the windfarm Trianel Borkum in the North Sea of Germany is simulated. Within this work wakes extending up to 20 km in length could be observed, suggesting to study the ABL‐windfarm interaction in more detail. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Local and instantaneous turbulence modification induced by small spherical bubbles
Authors: Santarelli Claudio , Roussel Jean , Fröhlich Jochen
Published: October 2015

The paper provides insight into the local and instantaneous turbulence modification induced by small spherical bubbles in an upward directed turbulent channel flow. This is accomplished by analyzing each term of the transport equation of the local and instantaneous kinetic energy for bubbly flows and dedicated flow visualizations are provided to address the mechanisms involved in the turbulence modification. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Towards higher‐order XFEM for interfacial flows
Authors: Fries Thomas‐Peter
Published: October 2015

The simulation of immiscible two‐phase flows is a challenging task, in particular with higher‐order accuracy. We use an interface capturing approach combined with the extended finite element method (XFEM) to represent inner‐element jumps and kinks across the interface. The position of the interface is defined by the curved zero‐level set of a higher‐order scalar function. Here, we focus on the higher‐order accurate integration on the two sides of the interface (i.e., the zero‐level set). (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical investigation of a liquid displacing a gas in thin porous layers
Authors: Neumann Tim , Boettcher Konrad , Ehrhard Peter
Published: October 2015

This article deals with a liquid displacing a gas in a thin heterogeneous porous material, which occurs e.g. during the filling process of a lithium‐ion battery with an electrolyte. The investigation is based upon the local volume‐averaged Navier‐Stokes equations, using a Volume‐of‐Fluid method to treat the interface. For the flow the wall effect and capillary forces have to be considered. Capillary rise experiments are used to determine the permeability. Since the layers are thin and the characteristic size of the particles is comparatively large, friction with the electrode is taken into account with respect to the mobility of the contact line. The implemented models are validated against analytical results, showing a good agreement. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Interaction of a finite‐size particle with the moving lid of a cavity
Authors: Romanò Francesco , Kuhlmann Hendrik C.
Published: October 2015

The motion of a solid particle in a lid‐driven cavity is investigated. If the tangential velocity of the lid is large the streamlines are dense near the moving lid and the finite size of a particle can have a profound effect on its trajectory. To assess this effect different particle‐motion models are examined: inertial point particles (Maxey–Riley equation) one‐way coupled to the flow and finite‐size particles the flow around which is fully resolved (two‐way coupling). We compare the corresponding trajectories with those obtained using the particle–surface interaction model originally introduced by Hofmann and Kuhlmann [Phys. Fluids 23, 0721106 (2011)]. The finite‐size effect on the particle's trajectory is quantified and discussed. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Plasticity as the Γ‐limit of a Nonlinear Dislocation Energy with Mixed Growth
Authors: Ginster Janusz
Published: October 2015

We consider a model for straight parallel edge dislocations with a nonlinear elastic energy with mixed growth. By means of Γ‐convergence we show that the suitably rescaled energy converges to a strain‐gradient plasticity model. As a tool we proof a generalized rigidity estimate which bounds the distance of a field with non‐vanishing curl to a specific rotation by the distance to all rotations. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Phase‐field Model of Dislocations on Parallel Slip Planes
Authors: Gladbach Peter
Published: October 2015

We establish a line‐tension energy for dislocation networks concentrated in finitely many parallel slip planes as the limit of a Peierls‐Nabarro energy. Dislocations in different planes interact depending on their distance. At intermediate distances a two‐scale dislocation microstructure is optimal. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multi‐criteria optimisation of the vibro‐isolation properties
Authors: Krzyznski Tomasz , Maciejewski Igor
Published: October 2015

The paper deals with a methodology of shaping the vibro‐isolation properties of suspensions applied in automotive systems. The developed optimisation procedure allows to find the Pareto‐optimal system configuration for the conflicted vibro‐isolating criteria. The correctness of proposed methodology is evaluated using the semi active and active systems with optimal controller settings. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Backward error of polynomial eigenvalue problems solved by linearization
Authors: Lawrence Piers , Van Barel Marc , Van Dooren Paul
Published: October 2015

It is commonplace in many application domains to utilize polynomial eigenvalue problems to model the behaviour of physical systems. Many techniques exist to compute solutions of these polynomial eigenvalue problems. One of the most frequently used techniques is linearization, in which the polynomial eigenvalue problem is turned into an equivalent linear eigenvalue problem with the same eigenvalues, and with easily recoverable eigenvectors. The eigenvalues and eigenvectors of the linearization are usually computed using a backward stable solver such as the QZ algorithm. Such backward stable algorithms ensure that the computed eigenvalues and eigenvectors of the linearization are exactly those of a nearby linear pencil, where the perturbations are bounded in terms of the machine precision and the norms of the matrices defining the linearization. Although we have solved a nearby linear eigenvalue problem, we are not certain that our computed solution is in fact the exact solution of a nearby polynomial eigenvalue problem. Here, we perform a backward error analysis for the solution of a specific linearization for polynomials expressed in the monomial basis. We use a suitable one‐sided factorization of the linearization that allows us to map generic perturbations of the linearization onto structured perturbations of the polynomial coefficients. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Parallel Bidiagonal SVD via the Method of Multiple Relatively Robust Representations
Authors: Winkelmann Jan , Bientinesi Paolo
Published: October 2015

A bidiagonal SVD solver based on the Method of Multiple Relatively Robust Representations (MR3) promises to be an improvement over the current state of the art by providing lower asymptotic runtime and the ability to calculate a subset of singular triplets at reduced cost. Currently, no MR3 based SVD solver is readily available. Using results by Willems and Lang [2], we provide an initial implementation of such a solver and compare it to LAPACK's Divide and Conquer solver. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal control for lithium‐ion batteries
Authors: Vossen Georg , Struck Alexander , Roos Dirk
Published: October 2015

Modelling, simulation and optimal control for a lithium‐ion battery cell is discussed. The model involves ionic concentrations, currents and potentials in the electrodes and the separator together with the battery temperature as state variables. The resulting system is a nonlinear PDAE system with 10 partial, 1 ordinary differential and 4 algebraic equations involving the Butler‐Volmer kinetics for describing the interaction of ionic currents and potentials. Time‐optimal charging of the battery subject to age‐preventing leads to a state‐constrained optimal control problem which is solved in two ways. A first‐discretize‐then‐optimize approach leads to a high‐dimensional nonlinear optimization problem which is solved by an efficient solver. As an alternative, a feedback control law along an active arc of the state constraint of order 1 is derived to formulate and solve the corresponding so‐called induced optimization problem. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Functional a posteriori estimates for elliptic optimal control problems
Authors: Wolfmayr Monika
Published: October 2015

In this note, new results on functional type a posteriori estimates for elliptic optimal control problems with control constraints are presented. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Automated generation of a dynamic feedforward control law using local model networks with disturbance inputs
Authors: Euler‐Rolle Nikolaus , Hametner Christoph , Jakubek Stefan
Published: October 2015

An effective approach is presented, which automatically generates a dynamic feedforward control law for nonlinear dynamic systems represented by a discrete‐time local model network (LMN) as one class of data‐driven models. In this context, feedback linearization is applied to the generic model structure of LMN and the resulting input transformation is used as model inverse. Thus, by representing a nonlinear dynamic system by an LMN and applying the proposed feedforward control law generation, a dynamic feedforward control for such a nonlinear system can be found automatically with the knowledge of measured input/output data only. In addition, several disturbance inputs are considered in the feedforward control law without restrictions on their relative degree. However, only multiple input LMN where no internal dynamics are involved, i.e. the LMN has full relative degree with respect to the control signal input, are considered in this manuscript. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Control design of the vibration reduction systems
Authors: Maciejewski Igor , Krzyzynski Tomasz
Published: October 2015

The paper deals with an original control algorithm for semi‐active and active suspension that are often used in automotive systems. The developed procedure assists in finding the structure of control system, which consists of the primary controller and calculates the desired active force. Then the desired force has to be approximately achieved by the semi‐active or active element with calculated input signal using the inverse model. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Controllability characterization of switched DAEs
Authors: Küsters Ferdinand , Trenn Stephan
Published: October 2015

We study controllability of switched differential algebraic equations (switched DAEs) with fixed switching signal. Based on a behavioral definition of controllability we are able to establish a controllability characterization that takes into account possible jumps and impulses induced by the switches. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A robust estimation method for camera calibration with known rotation
Authors: Egozi Amir , Maass Peter , Sagiv Chen
Published: October 2015

Imagine that hundreds of video streams, taken by mobile phones during a rock concert, are uploaded to a server. One attractive application of such prominent dataset is to allow a user to create his own video with a deliberately chosen but virtual camera trajectory. This is the challenge addressed by the Scenenet project, programme FET‐Open SME (GA 309169). One of the most basic tasks related to creating such a video, is the spatial registration of the individual video stream prior to combining them into a new virtual video. At its core, this requires to estimate the pairwise relative geometry of images taken by different cameras. This is known as the relative pose problem [1], and is fundamental to many computer vision algorithms. In practice, efficiency and robustness is of highest relevance for big data applications as the ones address in the EU‐FET_SME project Scenenet. In this paper, we present an improved algorithm that exploits additional data from inertial sensors, such as accelerometer, magnetometer or gyroscopes, which by now are available in most mobile phones. We demonstrate that in this case the pose estimation problem reduces to a 3‐dimensional least‐squares optimization problem, which can be readily implemented into a 3‐points RANSAC scheme. Experimental results on synthetic and real data demonstrate the accuracy and efficiency of our algorithm. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonnegative Matrix Factorization based on the Geometry of Positive Numbers
Authors: Jeuris Ben , Iannazzo Bruno , Pompili Filippo
Published: October 2015

We consider the problem of nonnegative matrix factorization where the typical objective function is altered based on geometrical arguments. A noneuclidean geometry on positive real numbers is used to describe the nonnegative entries of a nonnegative matrix, influencing the factorization model. We design an optimization procedure from a differential geometric point of view for the newly proposed model. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
EWE: Toward electro‐mechanical cardiac simulations with MOOSE
Authors: Ruprecht Daniel , Winkel Mathias , Krause Rolf
Published: October 2015

We present the software framework EWE, which is designed for coupled electromechanical simulations in computational cardiology. EWE is build on the multi‐physics framework MOOSE. Numerical simulations of coupled problems on an idealized geometry for a left ventricle are shown. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Does Boris‐SDC conserve phase space volume?
Authors: Winkel Mathias , Speck Robert , Ruprecht Daniel
Published: October 2015

In this paper we investigate the conservation of phase space volume of the Boris‐SDC algorithm. This method provides a generic way to extend the standard, second‐order accurate Lorentz force integrator commonly used for charged particles in an electric and magnetic field to a high‐order method using spectral deferred corrections. For a single particle in a Penning trap and different frequencies of the electric and magnetic fields, we assess the conservation properties of the method by computing the update matrix of one step of Boris‐SDC as well as its determinant. We compare the results to the convergence regions and relate them to energy conservation properties of the method. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Sensitivities Calculation for Unsteady Flow Problems
Authors: Stoia‐Djeska Marius , Frunzulica Florin
Published: October 2015

In this work we present an efficient approach for the calculation of the sensitivities in the case of unsteady problems like the compressible high‐speed flows. The sensitivities are of a known response with respect to the initial conditions. If the number of parameters is large, the adjoint method is preferred since the cost of computing the sensitivities is independent of the number of design parameters. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Constancy of spectra of equivariant (non‐selfadjoint) operators over minimal dynamical systems
Authors: Seifert Christian
Published: October 2015

We show that for a large class of equivariant continuous, possibly non‐selfadjoint, operators over minimal dynamical systems the spectrum as a set is in fact independent of the random parameter. Furthermore, the spectrum agrees with the essential spectrum. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Domenico Fontana and the entrance of mechanics in architecture
Authors: Masiani R. , Tocci C.
Published: October 2015

The analysis of archival documents related to the static restoration of the abacus of Marcus Aurelius Column and the reading of the description of the operations performed to move the Vatican Obelisk allow illustrating the mastery that Domenico Fontana exhibits about the statics of elementary machines – deriving from the knowledge of the technical literature of the second half of the sixteenth century – and his ability to exploit it as a support in the phase of structural invention. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nineteenth century molecular models with a glance at modern discrete—continuum theories
Authors: Trovalusci Patrizia
Published: October 2015

The origins of multiscale modelling, lying in the classical molecular models of Nineteenth century originally formulated to provide explanations per causas of elasticity, are investigated with the aim of drawing suggestions for the modelling of new complex materials. Conceptual guidelines for deriving scale dependent continuum formulations, here continuum models with additional degrees of freedom (multifield continua), are defined starting from non‐classical corpuscular descriptions and the historical and epistemological settings of the current modelling proposals are highlighted. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On numerical schemes for phase‐field models for electrowetting with electrolyte solutions
Authors: Metzger Stefan
Published: October 2015

We present an energy‐stable, decoupled discrete scheme for a recent model (see [1]) supposed to describe electrokinetic phenomena in two‐phase flow with general mass densities. This model couples momentum and Cahn–Hilliard type phase‐field equations with Nernst–Planck equations for ion density evolution and an elliptic transmission problem for the electrostatic potential.

The transport velocities in our scheme are based on the old velocity field updated via a discrete time integration of the force densities. This allows to split the equations into three blocks which can be treated sequentially: The phase‐field equation, the equations for ion transport and electrostatic potential, and the Navier–Stokes type equations. By establishing a discrete counterpart of the continuous energy estimate, we are able to prove the stability of the scheme. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Current controversies in prenatal diagnosis 1: should NIPT routinely include microdeletions/microduplications?
Authors: Rose Nancy C. , Benn Peter , Milunsky Aubrey
Published: October 2015

What's already known about this topic?

Technology is available to add microdeletion testing to cell free DNA screening.

What does this study adds?

This report summarizes an oral debate presented at the 19th International Conference on Prenatal Diagnosis and Therapy in Washington, DC, USA, on 14 July 2015.

Through the debate, the benefits, limitations, and challenges of potential wide‐scale implementation of microdeletion testing with prenatal samples was reviewed and discussed.
Psychometric properties of the Fear of Cancer Recurrence Inventory: an item response theory approach
Authors: Costa Daniel S. J. , Dieng Mbathio , Cust Anne E. , Butow Phyllis N. , Kasparian Nadine A.
Published: October 2015

Objective

Classical psychometric methods have been used to demonstrate the validity and reliability of the 42‐item Fear of Cancer Recurrence Inventory (FCRI). Our aim was to expand on this evidence with information on the discriminative value of the individual items when administered to people with a personal history of melanoma, using an item response theory (IRT) approach.

Methods

We used a two‐parameter IRT model to examine all items of the FCRI, primarily regarding whether people with a personal history of melanoma use the response scale as expected (as indicated by item characteristic curves), and whether the items can discriminate between those low and high on the constructs assessed by the instrument.

Results

The sample was comprised of 286 adults with a personal history of melanoma (58% male, mean age: 59.1 years). The established factor structure of the FCRI was generally confirmed. IRT highlighted several items with problematic item characteristic curves, including most items in the Reassurance and Coping Strategies domains. Several other items exhibited poor discrimination.

Conclusions

Based on this IRT analysis, we outline suggestions for refinement of the FCRI and potential development of a short‐form, that could reduce respondent burden. Generalisability of these findings beyond melanoma warrants further examination. Copyright © 2015 John Wiley & Sons, Ltd.
PECVD Synthesis of Flexible Optical Coatings for Renewable Energy Applications
Authors: Fuerst Thomas F. , Reese Matthew O. , Wolden Colin A.
Published: October 2015

The design, fabrication, and evaluation of flexible, multilayer optical coatings deposited by plasma‐enhanced chemical vapor deposition at low temperature are demonstrated using hybrid nanolaminates consisting of TiO2 and silicone (SiOxCyHz) as the high and low refractive index materials, respectively. A broadband anti‐reflection coating was designed and deposited onto a variety of substrates including flexible polyethylene terephthalate (PET) and CdTe solar cells which was shown to increase absolute transmission by an average of 3% over 410–850 nm wavelengths and results in a commensurate increase in short circuit current density. An infrared reflector was designed and applied to PET which was found to provide 70% reflectance in the near‐IR while maintaining >80% transmittance for visible light. The optical performance of these flexible coatings on PET remained unchanged after automated bend testing, and were shown to be robust with respect to humidity and thermal shock tests.
Analysis of free modeling predictions by RBO aleph in CASP11
Authors: Mabrouk Mahmoud , Werner Tim , Schneider Michael , Putz Ines , Brock Oliver
Published: October 2015

The CASP experiment is a biannual benchmark for assessing protein structure prediction methods. In CASP11, RBO Aleph ranked as one of the top‐performing automated servers in the free modeling category. This category consists of targets for which structural templates are not easily retrievable. We analyze the performance of RBO Aleph and show that its success in CASP was a result of its ab initio structure prediction protocol. A detailed analysis of this protocol demonstrates that two components unique to our method greatly contributed to prediction quality: residue–residue contact prediction by EPC‐map and contact‐guided conformational space search by model‐based search (MBS). Interestingly, our analysis also points to a possible fundamental problem in evaluating the performance of protein structure prediction methods: Improvements in components of the method do not necessarily lead to improvements of the entire method. This points to the fact that these components interact in ways that are poorly understood. This problem, if indeed true, represents a significant obstacle to community‐wide progress. Proteins 2016; 84(Suppl 1):87–104. © 2015 Wiley Periodicals, Inc.
Toward decrypting the allosteric mechanism of the ryanodine receptor based on coarse‐grained structural and dynamic modeling
Authors: Zheng Wenjun
Published: October 2015

The ryanodine receptors (RyRs) are a family of calcium (Ca) channels that regulate Ca release by undergoing a closed‐to‐open gating transition in response to action potential or Ca binding. The allosteric mechanism of RyRs gating, which is activated/regulated by ligand/protein binding >200 Å away from the channel gate, remains elusive for the lack of high‐resolution structures. Recent solution of the closed‐form structures of the RyR1 isoform by cryo‐electron microscopy has paved the way for detailed structure‐driven studies of RyRs functions. Toward elucidating the allosteric mechanism of RyRs gating, we performed coarse‐grained modeling based on the newly solved closed‐form structures of RyR1. Our normal mode analysis captured a key mode of collective motions dominating the observed structural variations in RyR1, which features large outward and downward movements of the peripheral domains with the channel remaining closed, and involves hotspot residues that overlap well with key functional sites and disease mutations. In particular, we found a key interaction between a peripheral domain and the Ca‐binding EF hand domain, which may allow for direct coupling of Ca binding to the collective motions as captured by the above mode. This key mode was robustly reproduced by the normal mode analysis of the other two closed‐form structures of RyR1 solved independently. To elucidate the closed‐to‐open conformational changes in RyR1 with amino‐acid level of details, we flexibly fitted the closed‐form structures of RyR1 into a 10‐Å cryo‐electron microscopy map of the open state. We observed extensive structural changes involving the peripheral domains and the central domains, resulting in the channel pore opening. In sum, our findings have offered unprecedented structural and dynamic insights to the allosteric mechanism of RyR1 via modulation of the key collective motions involved in RyR1 gating. The predicted hotspot residues and open‐form conformation of RyR1 will guide future mutational and functional studies. Proteins 2015; 83:2307–2318. © 2015 Wiley Periodicals, Inc.
Formation of plasmonic nanoparticle arrays –rules and recipes for an ordered growth
Authors: Fleischer Karsten , Ualibek Oral , Verre Ruggero , Shvets Igor V.
Published: October 2015

We review a self‐assembled growth method for plasmonic nanoparticle arrays, based on glancing angle deposition. We produced ordered Ag, Au, and Cu nanoparticle arrays over large areas on different stepped oxide templates. Precise control over the final geometry can be difficult and we provide recipes to obtain macroscopically ordered structures. We discuss the influence of the adsorbate diffusion length and facet termination on the shape and size distributions of metallic nanoparticle arrays and show that an increased ad‐atom mobility leads to more regular arrays of spherical nanoparticles. We also show how in‐situ Reflectance Anisotropy Spectroscopy (RAS) can be used to extract indirect information on the nucleation and ripening the nanoparticles, as well as measure the plasmonic resonance.

Schematics of the RAS setup used to in‐situ monitor the growth of plasmonic nanoparticle arrays on stepped oxide templates.
Modeling of the Mechanical Response During Reversal Shear Loading: Application to Steels
Authors: Wen Wei , Borodachenkova Marina , Barlat Frédéric , Liao Juan , Grácio José Joaquim
Published: October 2015

A hardening model that considers the dislocation reversal‐related mechanisms is applied to predict the mechanical behavior of low carbon (LC) and twinning‐induced plasticity (TWIP) steels under forward–reverse shear test with various pre‐strain levels. The predicted results are presented in terms of stress–strain response and texture evolution. It is shown that the proposed model, embedded in the visco‐plastic self‐consistent (VPSC) framework, well captures the changes in the reloading yield stress and the hardening evolution due to the strain path reversal. The contributions of the different mechanisms are also discussed.
Bisimido Molybdenum Complexes of the Extremely Bulky Pr* Framework
Authors: Hering Florian , Varga Péter , Würtemberger Max , Radius Udo
Published: October 2015

Synthesis and characterization of molybdenum bisimido complexes featuring the extremely bulky Pr* framework [Pr* = 2,6‐bis(diphenylmethyl)‐4‐methylphenyl] are reported. The octahedral halide complex [Mo(NPr*)2Cl2(THF)2] (1) is readily available from ammonium dimolybdate and the amine Pr*NH2, and features two THF molecules in the coordination sphere of molybdenum. The chloride ligands in 1 may be exchanged with methyl or benzyl groups using Grignard reagents. The resulting complexes [Mo(NPr*)2Me2] (2) and [Mo(NPr*)2Bz2] (3) are monomeric and, in contrast to 1, do not coordinate further neutral two‐electron donor ligands in neither the solid state nor in solution.