bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of air spring textile reinforcement by means of resolving the cord structure in FE analyses
Authors: Heinrich Nina , Donner Hendrik , Ihlemann Jörn
Published: March 2018

Textile reinforcement is, among many other applications, widely used in rubber bellows of air springs. The objective of this study is to compare the effect of two different cord set‐ups on local rubber matrix strains and stresses by means of FE analyses. For that purpose, a methodology for taking both the geometry of the cord and the filament structure of its yarns into account is employed. With this, a global FE model comprising a cyclic symmetric section of the bellows, and a submodel are analyzed. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Prevention of solidification cracking during pulsed laser beam welding
Authors: Bergmann Jean Pierre , Bielenin Martin , Herzog Roland A. , Hildebrand Jörg , Riedel Ilka , Schricker Klaus , Trunk Carsten , Worthmann Karl
Published: March 2018

We present a mathematical model to describe laser beam welding based on the heat equation. Since the material coefficients depend on the temperature, this leads to a quasi‐linear parabolic partial differential equation. It is our goal to prevent solidification cracking. We address this problem by means of optimal control. It is the intensity profile of the laser beam which acts as the control function. The main challenge is the formulation of a suitable objective function. In particular, high velocities of the solidification interface need to be properly penalized in order to deal with and avoid cracking phenomena. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Wave dispersion and propagation in a linear peridynamic solid
Authors: Butt Sahir N. , Meschke Günther
Published: March 2018

Peridynamics is a nonlocal continuum model which offers benefits over classical continuum models when there are discontinuities, such as cracks, present in the deformation field. However, the nonlocal characteristics of peridynamics leads to a dispersive dynamic response of the medium. In this study, we focus on the dispersion properties of a one‐dimensional state‐based linearized peridynamics model and investigate the effect of different peridynamic parameters on the dispersion relation. Furthermore, a physical interpretation of the peridynamic horizon is discussed and its relation to the experimental dispersion data is presented. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Laser shock peening process modelling and experimental validation of AA2198‐T3 and AA2198‐T8
Authors: Keller Sören , Kashaev Nikolai , Klusemann Benjamin
Published: March 2018

Laser shock peening (LSP) is a surface treatment which improves the fatigue life of metallic structures by laser‐induced compressive residual stresses. The purpose of this work is the prediction of the measured residual stresses after LSP in sheets consisting of AA2198. Therefore, a finite element model is set‐up. The Johnson‐Cook material model is used to model the strain rate depend material behaviour during plastic deformations. Stress averaging enables the comparison between measured and predicted residual stresses. Residual stress measurements are performed using the incremental hole drilling method. The initially unknown pressure pulse is identified for AA2198‐T3 and validated with AA2198‐T8. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Basic Ideas for the Quantification of Uncertainty Associated with the Material's Microstructure Morphology using Statistically Similar RVEs
Authors: Miska Niklas , Prüger Stefan , Balzani Daniel
Published: March 2018

A method to quantify macroscopic uncertainty caused by variation of the microstructure morphology is proposed by expanding the idea of SSRVEs to variations of microstructures within certain bounds of statistical descriptors. Subsequent homogenization of the RVEs leads to statistical information regarding the variation of macroscopic material properties for further uncertainty analysis. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Modeling of Textile Membranes with Nonlinear Anisotropic Material Behavior
Authors: Motevalli Mehran , Balzani Daniel , Uhlemann Jörg , Stranghöner Natalie
Published: March 2018

Coated fabric membranes have been widely used in construction of light‐weight structures. The material behavior of textile membranes is highly nonlinear and anisotropic which may not be sufficiently represented by commonly used linear elastic orthotropic models. This contribution presents a formulation of a suitable nonlinear anisotropic polyconvex energy function for textile membranes in the geometrically nonlinear framework. Representation of total in‐plane material behavior is the main goal of this paper, however, the induced thickness change is also considered in the continuum model. The material parameters of the energy function are adjusted by introducing and minimizing an objective function enforcing the model response to be as similar as possible to the experimental data. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Modelling of Thermo‐Viscoplasticity of Case‐Hardening Steels Over a Wide Temperature Range
Authors: Oppermann Philip , Denzer Ralf , Menzel Andreas
Published: March 2018

The aim of this work is the development of a thermodynamically consistent fully coupled thermo‐viscoplastic material model for metals. The model is based on a split of the free energy into a thermo‐elastic, a thermo‐plastic and a purely thermal part and covers nonlinear cold‐work hardening and thermal softening. Nonlinear temperature dependent effects are accounted for the elastic moduli, the plastic hardening moduli, the thermal expansion, the heat capacity and the heat conductivity. Furthermore, strain rate‐dependency of the current yield stress is realized using a temperature dependent nonlinear Perzyna‐type viscoplastic model based on an associative flow rule. The model and its parameters are fitted against experimental data for case hardening steel 16MnCr5 (1.7131). (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling and Simulation of the Thickness Dependence in Die Casting Structures
Authors: Martinez Page Maria Angeles , Ruf Matthias , Hartmann Stefan
Published: March 2018

Several die casting materials show different mechanical responses for specimens with different thicknesses. This can be observed in the variation of parameters, such as the Young's modulus, the tensile strength or hardness of the material in specimens with different thicknesses. In order to model this effect, we have experimentally investigated a specimen of a zinc die casting alloy. We concentrate in the modeling of the porosity distribution and its influence on the mechanical response using Mori‐Tanaka proposal for incorporating porosity. The applicability of the model is shown with a simulation example. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermomechanical Simulation of Friction Stir Welding of Aluminum Using an Adaptive Element‐Free Galerkin Method
Authors: Talebi Hossein , Frönd Martin , dos Santos Jorge F. , Klusemann Benjamin
Published: March 2018

The coupled themomechanical modeling of the friction stir welding (FSW) process is a challenging process when typical finite element methods are used. In this study we use a the Element Free Galerkin (EFG) method to model the material flow during the FSW process. We use a two‐way adaptive method (rh‐adaptive) during the coupled thermomechanical process to overcome potential numerical problems arising from the extensive mesh distortion and material deformation. We test the simulation strategy to simulate FSW of aluminum. The results show that the new simulation strategy can handle extreme plastic deformation of the metal efficiently. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Surface Wetting with Droplets: A Phase Field Approach
Authors: Diewald Felix , Kuhn Charlotte , Heier Michaela , Horsch Martin , Langenbach Kai , Hasse Hans , Müller Ralf
Published: March 2018

In order to be able to predict the static solution of three dimensional wetting scenarios, a free energy functional that is dependent on a continuous order parameter is formulated. This free energy functional can be linked to molecular dynamics (MD) simulations by input parameters. Static equilibrium configurations can be computed by minimizing the overall free energy using an evolution equation of Allen‐Cahn type. Details of the presented model are followed by illustrative examples that demonstrate the pertinency of the approach. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High‐Order Numerical Methods for Electromagnetic Induction
Authors: Gleim Tobias , Kuhl Detlef
Published: March 2018

The present paper establishes an axisymmetric benchmark model of a conducting loop, which implies an electromagnetic induction. Therein, the fully coupled MAXWELL equations are demonstrated in a monolithic solution strategy. This dynamic problem is solved with a high order finite element discretization using GALERKIN's method in space as well as in time. Furthermore, high order RUNGE‐KUTTA time integration methods are analyzed. Studies regarding an h error estimation and the order of convergence are examined. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
FEM‐analysis of a multiferroic nanocomposite – comparison of experiment and numerical simulation
Authors: Lemke Veronica , Labusch Matthias , Schröder Jörg , Wende Heiko
Published: March 2018

The combination of electric and magnetic materials opens new possibilities in the field of sensor technologies and data storage [1]. These magneto‐electric (ME) materials have the property to change a physical ferroic quantity into another, i.e. a magnetic field can change the electric polarization and vice versa. The combination of multiple ferroic characteristics within materials is called multiferroic. Since magneto‐electric single‐phase materials are rare in nature and typically operate only at very low temperature, they are not favorable in technical applications. However, ME composites, consisting of ferroelectric and ferromagnetic phases, produce a strain‐induced magneto‐electric product property at room temperature [2]. In these composites, two different effects can be differentiated, the direct and the converse ME effect. The first one describes a polarization which is magnetically caused. In detail, a magnetic field is applied which produces a deformation of the magneto‐active phase which is transferred to the electro‐active phase and as a consequence this phase exhibits a polarization. Therefore, one can discover a strain‐induced polarization. The second effect to observe is a magnetization caused by an electric field. In our contribution, we focus on a (1‐3) composite, where cobalt ferrite nanopillars are embedded in a barium titanate matrix, see the experiments described in [3]. In the numerical simulations we compare the changes of the strain‐induced inplane polarizations of the ferroelectric matrix with experimental measurements. Furthermore, we analyze the magneto‐electric coupling coefficient. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A kinetic energy preserving DG scheme applied to mechanical FSI
Authors: Ortleb Sigrun
Published: March 2018

In the context of mechanical fluid‐structure interaction (FSI) comprising moving or deforming structures, fluid discretizations need to cope with time‐dependent fluid domains and resulting grid deformations in addition to the general challenges regarding e.g. boundary layers and turbulent phenomena. Recent approaches in the simulation of compressible turbulent flow are based on so‐called split forms of conservation laws to guarantee the preservation of secondary physical quantities such as kinetic energy. For the simulation of turbulent flows, this often leads to a better representation of the kinetic energy spectrum. Initially, kinetic energy preserving(KEP) DG schemes have been constructed on Gauss‐Legendre‐Lobatto(GLL) nodes containing the interval end points, however, KEP DG schemes based on the classical Gauss‐Legendre(GL) nodes are potentially more accurate and may be also more efficient than its GLL variant for certain applications. In this work, the KEP‐DG schemes both on GL and GLL nodes are applied to the classical moving piston test case via an ALE formulation on moving fluid grids showing a more accurate frequency representation of the structure displacement in case of GLL nodes. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magneto‐electro‐active polymers: material properties and structural effects
Authors: Rambausek Matthias , Keip Marc‐André
Published: March 2018

This contribution presents a constrained minimization formulation of incompressible finite‐strain magneto‐electro‐elasticity. We employ this formulation in multiscale (FE2) simulations where we analyze the effective magneto‐electric coupling properties of soft‐matter based magneto‐electric composites. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Heat Conduction in a Phase Field Model for Martensitic Transformation
Authors: Schmidt Simon , Müller Ralf
Published: March 2018

We study the martensitic transformation with a phase field model, where we consider the Bain transformation path in a small strain setting. For the order parameter, interpolating between an austenitic parent phase and martensitic phases, we use a Ginzburg‐Landau evolution equation, assuming a constant mobility. In [1], a temperature dependent separation potential is introduced. We use this potential to extend the model in [2], by considering a transient temperature field, where the temperature is introduced as an additional degree of freedom. This leads to a coupling of both the evolution equation of the order parameter and the mechanical field equations (in terms of thermal expansion) with the heat equation. The model is implemented in FEAP as a 4‐node element with bi‐linear shape functions. Numerical examples are given to illustrate the influence of the temperature on the evolution of the martensitic phase. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Consistent macroscopic tangent computation for FFT‐based computational homogenization at finite strains
Authors: Göküzüm Felix S. , Keip Marc‐André
Published: March 2018

The present work addresses the efficient computation of effective properties of periodic microstructures by the use of Fast Fourier Transforms. While effective quantities in terms of stresses and deformations can be computed from surface integrals along the boundary of an RVE, the computation of the associated moduli is not straight‐forward. The contribution of the present paper is thus the derivation and implementation of an algorithmically consistent macroscopic tangent operator that comprises the effective properties of the RVE. In contrast to finite‐difference based approaches, an exact solution for the macroscopic tangent is derived by means of the classical Lippmann‐Schwinger equation. The problem then reduces to the solution of a system of linear equations even for nonlinear material behaviour. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of discrete stress distribution for dry powder compaction using Discrete Element Method and weighted Voronoi tesselation
Authors: Rasche Stefan , Tahir Arshad , Könke Carsten
Published: March 2018

Powder compaction of granular material plays a substantial role in the manufacturing process of ceramics industry and powder metallurgy industry. The compaction behaviour is ruled by granular flow and densification of deformable particles. Discrete element method (DEM) allows to investigate the powder compaction process numerically on the microscale by modeling the forces on the particle level and simulating the particle motion. Three‐dimensional data about particle size distribution and spatial structure of the particle packing can be extracted from micro‐computed tomography (µCT). An average stress tensor can be computed from DEM results, evaluating the contact forces and the distances from the particle center to the contact point with respect to an average cell volume. A weighted Voronoi tesselation of the polydisperse particle assembly is proposed for mapping a cell volume to each individual particle. With this approach all structural information of the particle system can be transferred from a discrete particle model to a heterogeneous volume model of micro‐structure. Discrete stress distributions for uniaxial powder compaction are presented. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A hierarchical multiscale finite element approach for modelling the heat affected zone of welded joints
Authors: Wudtke Idna , Silani Mohammad , Kraus Matthias
Published: March 2018

In the present work a hierarchical multiscale approach, based on finite element method, is applied in order to characterize the heat affected zone (HAZ) of a welded joint with parent material S460M. The metallurgical constituents of particular regions of the HAZ was determined experimentally and, regarding the multiscale approach, a first‐order computational homogenization method was implemented. In this context, effective stress‐strain‐relations in particular spots of the HAZ are determined applying prescribed displacement boundary conditions. The obtained relations were considered in subsequent finite element calculations of butt‐welded joints under tensile loading, allowing a comparison of the numerical strain states to experimental results. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Measurements of partially lubricated contacts on different scales
Authors: Müller Michael , Ostermeyer Georg‐Peter
Published: March 2018

This paper focuses on experimental investigations for lubricated contacts with partially filled gaps. The measurements are performed on two different scales. A pin‐on‐disc test bench represents the microscopic scale whereas a novel test bench with asperities in the range of centimeters corresponds to a rather macroscopic scale. The results are compared and conclusions towards the tribological properties are drawn. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Euler‐Lagrange Simulations of Turbulent Two‐phase Flows with an Advanced Deterministic Bubble Coalescence Model
Authors: Hoppe Felix , Breuer Michael
Published: March 2018

The present paper is concerned with an advanced version of the deterministic coalescence model [1] and its application to turbulent bubble‐laden flows. The major drawback of this film drainage model – its incapability to handle large numbers of coalescence processes – is avoided by an a‐priori determination of a parametric relation for the transition time between the main drainage mechanisms. The comparison with experimental results yields a good overall agreement, while the application to a downward pipe flow demonstrates the ability of the model to efficiently handle large numbers of coalescence processes. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The lift on a small sphere in a linear shear flow near the interface of two immiscible fluids
Authors: Scheichl Stefan
Published: March 2018

Analytical expressions have been derived which predict, to lowest order, the inertial lift and the lateral migration velocity of a rigid sphere translating and rotating in a linear shear flow field near the flat interface of two immiscible fluids. This asymptotic analysis is primarily based on the assumption that the two Reynolds numbers defined by the gap width between the interface and the sphere, the shear rate and the translational slip velocity with which the spherical particle moves parallel to the interface are small. Furthermore, the radius of the sphere is assumed to be small compared to the gap width. To leading order in this creeping flow regime, the linear Stokes equations are obtained and a symmetry argument can be used to show that the Stokes solution does not predict any lift force. The transverse force experienced by the sphere and its migration velocity are due to the small but finite inertial terms in the Navier‐Stokes equations, which can be studied by perturbation techniques. By applying a Green's function approach and matched asymptotic methods, which also incorporate the effects of the outer Oseen‐like flow regime, the three components comprising the lift velocity have been calculated in closed form: the one induced by the shear rate only, the purely slip induced one and the one due to the interaction of the slip velocity with the shear flow field. The thus obtained expressions for the case of two immiscible fluids with arbitrary density and viscosity ratios extend the results that already exist in the literature for other flow configurations, such as an unbounded shear flow field [1] or a wall‐bounded one, where the wall lies either within the leading order Stokes region [2] or in the outer Oseen region [3]. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Tikhonov Functionals Incorporating Tolerances
Authors: Gralla Phil , Piotrowska‐Kurczewski Iwona , Maaß Peter
Published: March 2018

Tikhonov functionals are a well known method for solving inverse problems. They consist of a discrepancy and a penalty term. The first term evaluates the deviation of simulated data from measured data. We alternate this term by incorporating tolerances, which neglects small deviations from the data within a prescribed tolerance. This approach adapts ideas from support vector regression, which utilizes such a tolerance for identity operators and semi discrete problems. Furthermore, the application for inverse problems is motivated by applications where such tolerances naturally occur, e.g. application with multiple measurements. In this case instead of one measurement a confidence interval for the measurement can be used.

In this work we provide an overview on the necessary analysis and alternation of Tikhonov functionals incorporating tolerances. In addition, an example of applications are shown and discussed. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Some basic boundary value problems for plane theory of elasticity of porous Cosserat media with triple‐porosity
Authors: Gulua Bakur , Janjgava Roman
Published: March 2018

The static equilibrium of porous elastic materials with triple‐porosity is considered in the case of an elastic Cosserat medium. A two‐dimensional system of equations of plane deformation is written in the complex form and its general solution is represented by means of three analytic functions of a complex variable and three solutions of Helmholtz equations. The constructed general solution enables one to solve analytically a sufficiently wide class of plane boundary value problems of the elastic equilibrium of porous Cosserat media with triple‐porosity. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transient Modeling and Simulation of Gas Pipe Networks with Characteristic Diagram Models for Compressors
Authors: Huck Christoph , Tischendorf Caren
Published: March 2018

One challenge for the simulation and optimization of real gas pipe networks is the treatment of compressors. Their behavior is usually described by characteristic diagrams reflecting the connection of the volumetric flow and the enthalpy change or shaft torque. Such models are commonly used for an optimal control of compressors and compressor stations [4,7] using stationary models for the gas flow through the pipes. For transient simulations of gas networks, simplified compressor models have been studied in [1–3]. Here, we present a transient simulation of gas pipe networks with characteristic diagram models of compressors using a stable network formulation as (partial) differential‐algebraic system. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On approximation of finite‐energy sequences of Müller's functional with non‐standard 2‐well potential
Authors: Raguž Andrija
Published: March 2018

We present the basic results and conjectures regarding possibility of approximating finite‐energy sequences of Müller's functional (which was for the first time, and in its simplest form, studied in paper S. Müller: Singular perturbations as a selection criterion for periodic minimizing sequences, Calc. Var. Partial Differential Equations 1(2), 169–204 (1993)) by 1‐Lipschitz and 1‐periodic finite‐energy sequences. Our results extend known results in the case of simplest pinning term concerning the actual minimizers as small parameter epsilon tends to zero, whereby standard assumption on growth of 2‐well potential at infinity (which immediately yields equi‐coercivity) is replaced by non‐standard one. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fuzinsumo ‐ Fuzzy investigation with surrogate models
Authors: Oberleiter Thomas , Willner Kai
Published: March 2018

In this contribution, we investigate the accuracy of surrogate models for fuzzy systems. Within a virtual tolerance analysis, unknown uncertainties are considered by fuzzy numbers. These fuzzy numbers consist of higher‐dimensional intervals, where each interval is assigned a membership value. To reproduce fuzzy numbers correctly, a large number of system evaluations is needed. Instead of evaluating numerically expensive full systems, we employ surrogate models with radial basis functions. In order to find sufficiently accurate surrogate models with as few as possible sampling points, we investigate the influence of the sampling points on the respective fuzzy number intervals. As an example, we investigate the tilting of an X‐ray aperture, which shows different accuracy for different sampling strategies. The reference results for the nonlinear multi‐body system are calculated by a Matlab optimizer and are compared to the results of the surrogate models. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Greedy Subspace Method for Computing the ℒ∞‐Norm
Authors: Aliyev Nicat , Benner Peter , Mengi Emre , Schwerdtner Paul , Voigt Matthias
Published: March 2018

We consider the computation of the ℒ∞‐norm for a general class of ℒ∞‐functions and focus on the case where the function is represented in terms of large‐scale matrix‐valued factors. We propose a subspace projection method to obtain reduced approximations of this function by interpolation techniques. The ℒ∞‐norms are computed for the resulting reduced functions, then the subspaces are refined by means of the optimizer of the ℒ∞‐norm of the reduced function. In this way we obtain much better performance compared to existing methods. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability of a family of flux‐correction methods as a remedy against overshoot in unsteady flow computation
Authors: Niessner Herbert
Published: March 2018

Still Lax‐Wendroff schemes are occasionally used calculating one‐dimensional flow. Supplementary flux‐correction allows to reduce or even prevent unphysical overshoot occuring with discontinuous initial conditions. There is a whole family of variants [4] based on damping or smoothing with different stability limits, which will be considered here in more detail. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Zeno phenomenon in hybrid dynamical systems
Authors: Dashkovskiy Sergey , Feketa Petro
Published: March 2018

A way to prolong Zeno solutions to hybrid dynamical system beyond Zeno time is proposed. Additionally, we provide a new definition of asymptotic stability that is equipped with sufficient conditions for its verification. It allows to investigate long‐term behavior of the prolonged solutions to hybrid dynamical systems. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimization of ship manoeuvring within the project GALILEOnautic
Authors: Roy Sylvain , Wernsing Heinrich , Büskens Christof
Published: March 2018

The goal of the project GALILEOnautic is to develop a system for autonomous navigation and optimal manoeuvring of cooperative ships within safety‐critical areas. In this context, many challenges arise in the field of optimization and optimal control. The research presented here addresses one of them, namely, the calculation of optimal trajectories and controls for a group of cooperative ships navigating within the limits of a harbour. The adopted approach is to embed all aspects of the problem into a single optimal control problem, whose objective is to minimize the time to destination of each ship as well as their overall energy consumption. Path constraints are applied to maintain the ships at a safe distance from each other and from the infrastructure of the harbour. A two‐ship scenario is implemented, for which optimal trajectories and controls are successfully computed. The numerical computation of this problem is performed using the software library WORHP, the official ESA NLP solver, and moreover the software TransWORHP, which transcribes optimal control problems into optimization problems. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Sparse phase retrieval of structured signals by Prony's method
Authors: Beinert Robert , Plonka Gerlind
Published: March 2018

The phase retrieval problem consists in the recovery of a complex‐valued signal from the magnitudes of its Fourier transform. Restricting ourselves to the case of sparse structured signals f, which can be represented as a linear combination of N arbitrary translations of a given generator function, we show that almost all f can be recovered from 𝒪 (N2) intensity measurements |ℱ[f](ω)| up to trivial ambiguities. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A theoretical guarantee for data completion via geometric separation
Authors: King Emily J. , Murphy James M.
Published: March 2018

Scientific and commercial data is often incomplete. Recovery of the missing information is an important pre‐processing step in data analysis. Real‐world data can in many cases be represented as a superposition of two or more different types of structures. For example, images may often be decomposed into texture and cartoon‐like components. When incomplete data comes from a distribution well‐represented as a mixture of different structures, a sparsity‐based method combining concepts from data completion and data separation can successfully recover the missing data. This short note presents a theoretical guarantee for success of the combined separation and completion approach which generalizes proofs from the distinct problems. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Application of the AAK theory and Prony‐like Methods for sparse approximation of exponential sums
Authors: Pototskaia Vlada , Plonka Gerlind
Published: March 2018

We derive a new method for optimal ℓ2‐approximation of discrete signals on ℓ2(ℕ0) whose entries can be represented as an exponential sum of finite length. Our approach employs Prony's method in a first step to recover the exponential sum that is determined by the signal. In the second step we use the theory of Adamjan, Arov and Krein (AAK) to derive an algorithm for computing a shorter exponential sum that approximates the original signal in the ℓ2‐norm well. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
GPU Accelerated Gauss‐Jordan Elimination on the OpenPOWER platform – A case study
Authors: Köhler Martin , Saak Jens
Published: March 2018

The solution of linear systems is still one of the basic building blocks in scientific computing. Therefore, it needs to be adapted to each new hardware platform in order to exploit the new features of the platform in an optimal way. During the last decade many of these building blocks were accelerated by the usage of GPUs and similar accelerator devices. In our contribution we will focus on the solution of linear systems with many right hand sides, where a fast solution not only requires an optimized LU decomposition, but also needs an efficient forward and backward substitution phase. Since the triangular shape of the factors leads to a rather sequential resolution step, this is a difficult task for parallelization and optimization. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Crack Detection in Experimental Data by Means of a Spiking Response Model
Authors: Leichsenring Ferenc , Graf Wolfgang , Kaliske Michael
Published: March 2018

In engineering tasks, multiple types of neural networks, such as e.g. feed‐forward neural networks (FNN) or radial basis function neural networks (RBFN) are common solution methods for a wide scope of applications [1, 2]. Beside the different kinds of artificial neural networks, spiking neural networks (SNN) represent a continuous development in information processing within the computational units of a net. In the contribution, the Spiking Response Model (SRM) [3], a derivative of the Hodgkin‐Huxley model, is utilized, whereas the specific properties of this neuron type are used in order to facilitate the evaluation of uniaxial tension test data sets of carbon reinforced concrete specimens. The evaluation procedure of the experimental data targets the identification of major crack appearance based on the load cell data. For reasons of comparison and standardization, numerous uniaxial experiments are performed within the collaborative research project Carbon Concrete Composite C3. Crack detection is considered as showcase for further development of evaluation methods based on SNNs with focal point to engineering experiments. Essential for the evaluation is the transition of the experimental data (load cell data) to the temporal domain of the neuron. Therefore, rate coding [4] is applied resulting in a pre‐synaptic spike train. The actual detection of cracks in the pre‐synaptic spike train is carried out by an evaluation neuron. The heuristic approach is validated by multiple examples and presents a sufficient accuracy as well as it retains the temporal information regarding the crack occurrence. A feed‐forward network structure containing additional evaluation neurons in combination with extra experimental data (e.g. strain gauge data, load cell data) enables extended information extraction such as determining crack location with respect to the attached strain gauges. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An estimate on the non‐real spectrum of a singular indefinite Sturm‐Liouville operator
Authors: Behrndt Jussi , Gsell Bernhard , Schmitz Philipp , Trunk Carsten
Published: March 2018

It will be shown with the help of the Birman‐Schwinger principle that the non‐real spectrum of the singular indefinite Sturm‐Liouville operator sgn(·)(−d2/dx2 + q) with a real potential q ∈ L1 ∩ L2 is contained in a circle around the origin with radius

. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Band‐dominated operators on metric measure spaces
Authors: Seifert Christian
Published: March 2018

We generalise the notion of band‐dominated operators originally introduced for the space ℓp(ℤn) to the setup of metric measure spaces and show various algebraic properties of this space of operators. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Synergistic effects of thermoplastic and nanoclay on the performance properties and morphology of epoxy resin
Authors: Bakar Mohamed , Białkowska Anita , Kuřitka Ivo , Hanuliková Barbora , Masař Milan
Published: March 2018

The present work investigates the properties and morphology of nanobent/poly(methyl methacrylate) (PMMA)/epoxy resin hybrid nanocomposites which were successfully prepared by solvent and ultrasonication methods. Nanobent ZS1 were added in amount of 1, 2, 3, and 4 wt% and 5, 10, and 15 wt% for PMMA. The fracture toughness (impact strength and critical stress intensity factor) and flexural properties were evaluated for epoxy composites. Obtained results showed improvement of the epoxy resin mechanical properties due to the addition of PMMA and nanobent. Composites containing 5 wt% of polymeric modifier or 1 wt% nanobent exhibited maximally improved properties. In the case of hybrid composites, synergistic effect was obtained with flexural strain at break and flexural energy to break of hybrid nanocomposite based on 1 wt% nanobent and 5 wt% PMMA. However, epoxy nanocomposites based on 2 wt% nanobent and 5 wt% PMMA showed synergism with IS and brittle fracture energy toward the composites with one modifier. Fourier transform infrared (FTIR) spectra analysis confirmed interactions between incorporated modifiers and reactive groups of the epoxy matrix. Moreover, scanning electron microscope (SEM) micrographs of hybrid epoxy nanocomposites exhibited a morphology with large plastic yielding associated with significant roughness of the fracture surface with embedment of nanobent in the polymer system. This study clearly demonstrates that the improvement of mechanical properties of the epoxy resin could be attributed to the synergistic toughening effect of PMMA and nanobent without deterioration of thermal stability. POLYM. COMPOS., 39:E2540–E2551, 2018. © 2018 Society of Plastics Engineers
Mechanical properties of gamma‐irradiated EPDM/Waste newsprint microfibers composites treated using acrylic styrene emulsion as a coupling agent
Authors: Ali Magdy A. M. , El‐Nemr Khaled F. , Hassan Medhat M. , Abd‐Elhady Wafaa S.
Published: March 2018

This study investigated the effect of gamma radiation and acrylic styrene emulsion as a coupling agent on mechanical properties of the ethylene propylene diene monomer (EPDM)/newsprint microfibers composite. The recycled newsprint paper was subjected to chemical pulping and the resulted micro fibers treated by using a different ratio of acrylic styrene emulsion (5, 10, and 15 wt% to the microfibers) before mixing with EPDM rubber matrix. The effect of the treated microfibers concentration, namely, 5 up to 50 phr (part per hundred part of rubber) and the effect of different doses of gamma radiation on the mechanical properties of the EPDM/newsprint microfibers composites was investigated. The newsprint microfibers structure and EPDM/treated microfibers composite were investigated using X‐ray diffraction and FTIR analysis. The results indicated that bonding had occurred between the treated microfibers and EPDM polymer matrix. EPDM/untreated newsprint microfibers composites have achieved higher mechanical properties than EPDM matrix up to 10 phr microfibers concentration and up to 60 kGy. Meanwhile, treatment of the newsprint microfibers by using acrylic styrene emulsion leads to improve mechanical properties of EPDM/treated microfibers composites higher than that of the EPDM/untreated fibers composites. Newsprint microfibers treated using 10% acrylic styrene and gamma irradiated at 60 kGy, was found to maintain a higher tensile strength, modulus of 100% strain and toughness. POLYM. COMPOS., 40:1209–1227, 2019. © 2018 Society of Plastics Engineers
Extended Venous Thromboembolism Prophylaxis in Medically Ill Patients
Authors: Cave Brandon , Hough Augustus , Dobesh Paul P.
Published: March 2018

Prophylaxis for venous thromboembolism (VTE) in hospitalized acutely ill medical patients is a well‐established practice. Despite the increased use of inpatient prophylaxis, the duration of hospitalization is typically shorter than the duration of VTE prophylaxis provided in clinical trials. In addition, VTE events after hospitalization are not unusual, with most events occurring within 30 days of hospital discharge. Therefore, the 30‐day time period postdischarge has been identified as a stage in which patients are still at high risk of developing VTE. Attempts to provide extended prophylaxis with enoxaparin, rivaroxaban, or apixaban in patients with acute medical illness have been met with mixed results. Although some of these agents have reduced the incidence of VTE with extended prophylaxis, all of these agents have also demonstrated a significant increase in major bleeding that seems to offset any potential benefit. A recent trial of a new direct factor Xa inhibitor, betrixaban, demonstrated a reduction in VTE events with extended prophylaxis without significantly increasing the risk of major bleeding. Understanding appropriate patient selection, dosing, and outcomes associated with betrixaban will be important to potentially reducing the continued risk of VTE in patients with acute medical illness.
Molecular design of antimicrobial peptides based on hemagglutinin fusion domain to combat antibiotic resistance in bacterial infection
Authors: Ye Hui
Published: March 2018

Antimicrobial peptides are derived from the viral fusion domain of influenza virus hemagglutinin based on rational analysis of the intermolecular interaction between peptides and bacterial outer membrane. It is revealed that the isolated viral fusion domain is a negatively charged peptide HAfp1‐23 that cannot effectively interact with the anionic membrane. Conversion of the native HAfp1‐23 to a positively charged peptide HAfp1‐23_KK by E11K/D19K mutation can promote the peptide‐membrane interaction substantially; this confers to the peptide a moderate antibacterial potency against antibiotic‐resistant bacterial strains. Cyclization of the linear peptide HAfp1‐23_KK results in a cyclic peptide cHAfp1‐23_KK, which can largely minimize entropy penalty upon the peptide‐membrane binding by pre‐stabilizing peptide hairpin configuration in solvent, where the linear peptide would incur in a considerable conformational change/folding from intrinsic disorder (in water) to the structured hairpin conformation (in lipid). As might be expected, the cyclization considerably improves peptide antibacterial activity with minimum inhibitory concentration of 67 and 34 μg/mL against multidrug‐resistant Pseudomonas aeruginosa and methicillin‐resistant Staphylococcus aureus, respectively.
Control of Crystal Structure of Ga2O3 on Sapphire Substrate by Introduction of α‐(AlxGa1−x)2O3 Buffer Layer
Authors: Jinno Riena , Uchida Takayuki , Kaneko Kentaro , Fujita Shizuo
Published: March 2018

An annealed α‐(Al0.4Ga0.6)2O3 buffer layer is introduced to achieve either α‐Ga2O3 or ϵ‐Ga2O3 growth on sapphire substrates, depending on the growth temperature, using the mist chemical vapor deposition method. Transmission electron microscopy reveals that the epitaxial relationship between ϵ‐Ga2O3 and the α‐(Al0.4Ga0.6)2O3 buffer layer is ϵ‐Ga2O3 [100] || α‐(Al0.4Ga0.6)2O3 [110], and the two hexagonal lattices are consequently rotated in the ab plane by 30° with respect to each other. The lattice mismatch between the buffer layer and ϵ‐Ga2O3 is 1.2%, while that between the buffer layer and α‐Ga2O3 is 2.2%. When the growth temperature is below 600 °C, ϵ‐Ga2O3, which had the smaller lattice mismatch, is produced. On the other hand, higher temperature leads to a longer diffusion length, and atoms reach the step edges. Therefore α‐Ga2O3, which has the same structure as the buffer layer, is grown along the step edges above 600 °C. As a result, ϵ‐Ga2O3 and α‐Ga2O3 grow below and above 600 °C, respectively.
A Highly Efficient Self‐Biased Nickel‐Zinc Ferrite/Metglas/PZT Magnetoelectric Gyrator
Authors: Leung Chung Ming , Sreenivasulu G. , Zhuang Xin , Tang Xiao , Gao Min , Xu Junran , Li Jiefang , Zhang Jitao , Srinivasan G. , Viehland D.
Published: March 2018

A high efficiency self‐biased magnetoelectric (ME) gyrator operating under zero magnetic bias field (HBias = 0) was developed. It consists of a three‐phase nickel‐zinc ferrite/Metglas/piezoelectric longitudinal–transverse (L‐T) ME laminate and a solenoid. Laminates with different length–width (L/W) ratios, together with various thickness (number of Metglas foils) ratios between ferrite and Metglas layers, were studied. A maximum power conversion efficiency (η) of 72% was found at the fundamental electromechanical resonance for a high L/W ratio of 18.7. The high zero‐bias η could be attributed to a higher mechanical quality factor (Qm) and the low demagnetization effect (Nz) of nickel‐zinc ferrite laminates of higher L/W. Eliminating the external magnetic bias will facilitate miniaturization of ME gyrators for use in portable electronics and medical applications.
Conservative finite‐volume schemes for the quasi‐geostrophic equation on coastal‐conforming unstructured primal–dual meshes
Authors: Chen Qingshan , Ju Lili
Published: March 2018

In this article we propose finite‐volume schemes for solving the inviscid and viscous quasi‐geostrophic equations on coastal‐conforming unstructured primal–dual meshes. Several approaches for enforcing the boundary conditions are also explored along with these schemes. The pure transport parts in these schemes are shown to conserve the potential vorticity along fluid paths in an averaged sense, and conserve the potential enstrophy up to the time truncation errors. Numerical tests based on the centroidal Voronoi–Delaunay meshes are performed to confirm these properties, and to distinguish the dynamical behaviours of these schemes. Finally some potential applications of these schemes in different situations are discussed.
Theory and practice of phase‐aware ensemble forecasting
Authors: Schulte Justin , Georgas Nickitas
Published: March 2018

Skilfully forecasting the intensity of flood events with advanced lead times is necessary for the issuing of flood warnings that subsequently provide adequate time for evacuations and infrastructural preparations. The ensemble mean is often used for deterministic guidance, but it is numerically demonstrated that the presence of large timing differences among ensemble members generates ensemble skewness that renders the ensemble mean an underestimate of the magnitude of an event. We show that one can associate to an ensemble forecast a complementary phase‐aware ensemble forecast whose corresponding statistics are unaffected by timing differences among ensemble members. Corresponding to a phase‐aware ensemble forecast is a phase‐aware mean that remedies the magnitude underestimation problem of the ensemble mean. Uncertainty around the phase‐aware mean is captured by phase‐aware spread, which quantifies the spread of the magnitude of an event. We show that the uncertainty envelope associated with the phase‐aware spread better preserves the structure of the individual ensemble member trajectories. The new methods were applied to storm surge reforecasts for Hurricanes Irene and Sandy at 13 stations located around the New York City metropolitan area. Consistent with theory, the phase‐aware mean was found to be a better representation of storm surge magnitude than the ensemble mean. The phase‐aware uncertainty envelopes around the phase‐aware means were also found to depict the uncertainty of event magnitudes better than traditional uncertainty envelopes. The storm surge applications suggest that such methods should be incorporated into ensemble forecasting frameworks in which timing uncertainty is present, and thus a Matlab toolbox implementing the new methodology has been developed.
The CD11a and Endothelial Protein C Receptor Marker Combination Simplifies and Improves the Purification of Mouse Hematopoietic Stem Cells
Authors: Karimzadeh Alborz , Scarfone Vanessa M. , Varady Erika , Chao Connie , Grathwohl Karin , Fathman John W. , Fruman David A. , Serwold Thomas , Inlay Matthew A.
Published: March 2018

Hematopoietic stem cells (HSCs) are the self-renewing multipotent progenitors to all blood cell types. Identification and isolation of HSCs for study has depended on the expression of combinations of surface markers on HSCs that reliably distinguish them from other cell types. However, the increasing number of markers required to isolate HSCs has made it tedious, expensive, and difficult for newcomers, suggesting the need for a simpler panel of HSC markers. We previously showed that phenotypic HSCs could be separated based on expression of CD11a and that only the CD11a negative fraction contained true HSCs. Here, we show that CD11a and another HSC marker, endothelial protein C receptor (EPCR), can be used to effectively identify and purify HSCs. We introduce a new two-color HSC sorting method that can highly enrich for HSCs with efficiencies comparable to the gold standard combination of CD150 and CD48. Our results demonstrate that adding CD11a and EPCR to the HSC biologist's toolkit improves the purity of and simplifies isolation of HSCs.