bluuebunny/crossref_metadata_2025 huggingface dataset:
A staggered approach to structural shape and topology optimization
Authors: Riehl Stefan , Steinmann Paul
Published: October 2015

This contribution is concerned with the design and evaluation of a staggered approach to computational shape and topology optimization. The main idea is to interrelate a classical boundary variation scheme based on the results from shape sensitivity analysis and an evolutionary‐type element removal procedure that relies on the topological sensitivity as a rejection criterion. The key ingredient in this perspective is to consider an advancing front algorithm that is gradually removing, from the evolving boundary of the domain, a number of finite elements based on the evaluation of the topological sensitivity.

This process is repeated until the minimum topological sensitivity is no longer encountered at the boundary but in the interior of the domain, such that a topological change is to be considered for the current design layout. However, we first aim to establish a more accurate approximation of the true optimal shape of the newly established (zig‐zag representation) of the design boundary. This is achieved by the evaluation of the shape sensitivity and the accompanying boundary variations obtained by a basic descent algorithm. Only then, we create a hole in the interior of the domain by removing all cells that are adjacent to the nodal point that exhibits the minimum topological sensitivity and resume the advancing front algorithm to alter the newly established design boundary. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Extended Hamiltonian Hessenberg Matrices arise in Projection based Model Order Reduction
Authors: Ferranti Micol , Mach Thomas , Vandebril Raf
Published: October 2015

We show that extended Hamiltonian Hessenberg matrices arise naturally in projection‐based model order reduction. Therefore we reduce a large dynamical system by projecting it on an extended Krylov subspace. The eigenvalues of the reduced order model can then be computed directly by applying the extended Hamiltonian QR algorithm. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A new Interpolatory Model Reduction Approach for Quadratic Bilinear Descriptor Systems
Authors: Ahmad Mian Ilyas , Benner Peter , Feng Lihong
Published: October 2015

We propose interpolation based projection techniques for model reduction of quadratic bilinear descriptor systems. The approach identifies projection matrices from the bilinear approximation of the original quadratic bilinear descriptor system and applies Petrov‐Galerkin projection to the original system to construct the required reduced quadratic bilinear descriptor system. Two different techniques of computing the projection matrices from the bilinear approximation are proposed. One is based on linear parametric model reduction and the other is the bilinear rational Krylov method. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Upwind Based Parameter Uniform Convergence Analysis for Two Parametric Parabolic Convection Diffusion Problems by Moving Mesh Methods
Authors: Das Pratibhamoy , Mehrmann Volker
Published: October 2015

A parabolic two parametric convection‐diffusion reaction problem is considered for the moving mesh error analysis. The continuous problem is discretized by the first order upwind scheme on a non uniform mesh. A curvature based error monitor function is proposed to generate the layer adapted mesh. It is proved that the numerical solution converges to the exact solution on the mesh obtained by the equidistribution of the proposed monitor function. The convergence is first order accurate. The present analysis generalizes the results obtained in earlier publications [8,9]. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multigrid preconditioning for time‐periodic Navier–Stokes problems
Authors: Hupp Daniel , Obrist Dominik , Arbenz Peter
Published: October 2015

We propose to solve time‐periodic Navier–Stokes problems by a discrete Fourier transform in time. Truncating the Fourier series yields a nonlinear system of equations for the unknown Fourier coefficients. Its solution by Picard iteration requires to solve a sequence of linear systems of equations. The focus of this work is on an efficient method to solve these linear systems. We employ GMRES, complemented by an optimal block triangular preconditioner. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Using Schur complement for realtime automotive applications
Authors: Loderer Thomas , Bertsch Christian , Heuveline Vincent
Published: October 2015

Realtime simulation of stiff physical models of mechatronic systems within electronic control unit software functions poses amongst others the challenge to solve linear systems of equations with minimal comutational effort. For this, one key approach is exploiting the model structure. In this paper, Schur complement based reformulations are examined for a tailored exploitation of the sparsity of a pipe model on the level of linear equations. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Error measurement and FEM benchmark for phase field modeling
Authors: Münch Ingo
Published: October 2015

Solid‐state phase‐transformation often deals with coupled field variables like mechanical stress or electric potential on different scales compared to the size of phase transition. Further, highly nonlinear equations rule the phase parameter. Thus, required mesh density to approximate phase field variables is often higher than for coupled fields. Finite element techniques applying h‐ or p‐adaptivity can help to increase the efficiency of such simulations. Therefore, it is important to define a benchmark test to verify numerical approaches. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computation of state variables of one‐dimensional non‐stationary pipe flow at orifices on pipe ends
Authors: Niessner Herbert
Published: October 2015

Boundary conditions of orifices in conjunction with the graphical method of characteristics given in [1] are reformulated and made ready to be used with finite difference methods. Orifice flow to the apparent narrowest cross‐section is assumed conserving entropy and energy, thereafter not recovering pressure without exceeding sound speed. These conditions allow to eliminate state variables at the narrowest cross‐section. Additional equations stem from mass conservation and a balance of the Riemann variable over the outgoing cross‐characteristic and either further energy conservation or a balance of entropy over the outgoing particle path. They permit to determine the state at the boundary of the computational grid for usual finite difference methods. A single nonlinear equation has to be solved only in case of outflow. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Online Parameter Identification for Traffic Simulation via Lagrangian Sensing
Authors: Thonhofer Elvira , Jakubek Stefan
Published: October 2015

This paper deals with parameter identification for traffic models. We present a method to estimate model parameters based on Lagrangian measurement data that can be used for online traffic simulation. In the context of Lagrangian sensing the sensor placement is reduced to the optimum choice of measurement vehicles currently moving with the traffic flow. Identifiability is investigated using the Fisher Information Matrix (FIM). Simulation results are presented and validated via simulation based on a car‐following‐model. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An Adaptive Local (AL) Basis for Elliptic Problems with Complicated Discontinuous Coefficients
Authors: Weymuth Monika , Sauter Stefan
Published: October 2015

We develop a generalized finite element method for the discretization of elliptic partial differential equations in heterogeneous media. In [5] a semidiscrete method has been introduced to set up an adaptive local finite element basis (AL basis) on a coarse mesh with mesh size H which, typically, does not resolve the matrix of the media while the textbook finite element convergence rates are preserved. This method requires O(log(1/H)d+1) basis functions per mesh point where d denotes the spatial dimension of the computational domain. We present a fully discrete version of this method, where the AL basis is constructed by solving finite‐dimensional localized problems, and which preserves the optimal convergence rates. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiple shooting methods for parabolic optimal control problems with control constraints
Authors: Carraro Thomas , Geiger Michael
Published: October 2015

In the context of ordinary differential equations, shooting techniques are a state‐of‐the‐art solver component, whereas their application in the framework of partial differential equations (PDE) is still at an early stage. We present two multiple shooting approaches for optimal control problems (OCP) governed by parabolic PDE. Direct and indirect shooting for PDE optimal control stem from the same extended problem formulation. Our approach reveals that they are structurally similar but show major differences in their algorithmic realizations. In the presented numerical examples we cover a nonlinear parabolic optimal control problem with additional control constraints. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A priori error estimates for nonstationary optimal control problems with gradient state constraints
Authors: Ludovici Francesco , Neitzel Ira , Wollner Winnifried
Published: October 2015

We are concerned with the discretization of semilinear parabolic optimization problems subject to constraints on the first derivative of the solution of the PDE. Constructing sequences of feasible controls for the dG(0)‐cG(1) discretization of the problem and relying on a quadratric growth condtion, we show convergence orders as temporal and spatial mesh tends to zero. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiobjective Optimization of the Flow Around a Cylinder Using Model Order Reduction
Authors: Peitz Sebastian , Dellnitz Michael
Published: October 2015

In this article an efficient numerical method to solve multiobjective optimization problems for fluid flow governed by the Navier Stokes equations is presented. In order to decrease the computational effort, a reduced order model is introduced using Proper Orthogonal Decomposition and a corresponding Galerkin Projection. A global, derivative free multiobjective optimization algorithm is applied to compute the Pareto set (i.e. the set of optimal compromises) for the concurrent objectives minimization of flow field fluctuations and control cost. The method is illustrated for a 2D flow around a cylinder at Re = 100. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dual‐weighted residual adaptivity for phase‐field fracture propagation
Authors: Wick Thomas
Published: October 2015

In this study, we consider phase‐field‐based fracture propagation in solid mechanics. The phase‐field model is based on a thermodynamically‐consistent version proposed by Miehe, Welschinger, Hofacker. The main focus is on goal‐oriented functional evaluations using a partition‐of‐unity dual‐weighted residual estimator for accurate measurement of, for example, point values, stresses, or crack opening displacements. Our developments are substantiated with a numerical test. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Controlled invariance for DAEs
Authors: Berger Thomas
Published: October 2015

We study the concept of locally controlled invariant submanifolds for nonlinear descriptor systems. In contrast to classical approaches, we define controlled invariance as the property of solution trajectories to evolve in a given submanifold whenever they start in it. It is then shown that this concept is equivalent to the existence of a feedback which renders the closed‐loop vector field invariant in the descriptor sense. This result is motivated by a preliminary consideration of the linear case.

Local controlled invariance leads to the concept of output zeroing submanifolds. We show that the outcome of the differential‐algebraic version of the zero dynamics algorithm yields a locally maximal output zeroing submanifold. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A counter‐example concerning regularity properties for systems of conservation laws
Authors: Caravenna Laura , Spinolo Laura V.
Published: October 2015

We exhibit an explicit counter‐example which rules the possibility of extending to systems of conservation laws a regularity property of scalar conservation laws known as Schaeffer's Theorem. Loosely speaking, Schaeffer's Regularity Theorem asserts that, for a generic smooth initial datum, the solution of the Cauchy problem can develop at most finitely many discontinuities on compact sets. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coordination of guidance and stabilization tasks for bicycle rider modelling
Authors: Edelmann Johannes , Haudum Martin , Plöchl Manfred
Published: October 2015

Learning to ride a bicycle requires practice and endurance fundamental to interpret the dynamics of a bicycle to control it. Modelling a virtual bicycle rider as a controller considering basic human characteristics is a similar demanding task. One approach for a virtual bicycle rider model is presented here, capable to stabilize the bicycle and follow a given course. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Minimal data rates and entropy in digitally networked systems
Authors: Kawan Christoph
Published: October 2015

In digitally networked systems the assumption of classical control theory that information can be transmitted instantaneously, lossless and with arbitrary precision is violated. This raises the question about the smallest data rate above which a control task can be solved. For a single control loop and the problem to make a set Q of states invariant, the minimal data rate can be described by an entropy‐like quantity, the so‐called invariance entropy. Under some controllability and hyperbolicity assumptions, the invariance entropy can be expressed in terms of Lyapunov exponents. Furthermore, one can show that for making Q invariant with a data rate close to the smallest, no strategies more complicated than stabilization at periodic trajectories are necessary. For a network with n subsystems, which can all communicate with each other, there are different ways to formulate the question about the smallest data rate for the invariance problem, but also in this setting entropy‐like quantities yield important information. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonlinear Volume Flow Control of a Variable Displacement Vane Pump
Authors: Köster Marius , Fidlin Alexander
Published: October 2015

Variable displacement vane pumps are used for mid‐pressure applications in a variety of systems. Due to their potential for power loss reduction they are most prominently featured in automotive applications. They provide a hydraulic consumer with varying levels of volume flow, depending on the eccentricity of the cam ring of the pump. Eccentricity control is typically achieved by means of hydraulic actuation. In this contribution, a model of a hydraulic aggregate featuring a VDVP with a nonlinear control technique based on input‐output‐linearization for volume flow tracking requirements is presented. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Kalman‐Yakubovich‐Popov Inequality for Descriptor Systems
Authors: Reis Timo , Voigt Matthias
Published: October 2015

In this paper, we consider the Kalman‐Yakubovich‐Popov lemma for descriptor systems. We study the arising linear matrix inequality in more detail. In particular, we give details about stabilizing solutions which play an important role for linear‐quadratic control problems. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Reachable Sets of Quasilinear Hyperbolic Control Systems with Applications to Separation Processes
Authors: Zuyev Alexander
Published: October 2015

This paper is devoted to the analysis of reachable sets for quasilinear distributed parameter systems by using smooth finite dimensional controls. The class of systems under consideration includes models of a moving bed chromatographic process. We propose sufficient conditions on the states of such quasilinear systems to be approximately reachable with a family of controls corresponding to their finite dimensional approximations. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multivariate generalized sampling type series: estimates of pointwise convergence
Authors: Bardaro Carlo , Mantellini Ilaria
Published: October 2015

In this short note we consider suitable linear combinations of Bochner‐Riesz type multivariate sampling series, which greatly improve the order of pointwise approximation. In particular we state some asymptotic formulae of Voronovskaja type which are of interest in image reconstruction. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ambiguities in one‐dimensional phase retrieval of structured functions
Authors: Beinert Robert , Plonka Gerlind
Published: October 2015

Phase retrieval means that we wish to recover a complex‐valued signal (discrete or continuous) from the magnitudes of its Fourier transform. Here we restrict ourselves to the recovery of structured functions, e.g. linear spline functions with equidistant knots. First, a complete characterization of the occurring ambiguities is presented. Moreover, we investigate additionally given moduli of the signal itself regarding their ability to reduce the set of ambiguities. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multivariate sampling Kantorovich operators: from the theory to the Digital Image Processing algorithm
Authors: Costarelli Danilo , Vinti Gianluca
Published: October 2015

In this note we consider the theory of sampling Kantorovich operators, and we show how it is possible to deduce an algorithm for Digital Image Processing starting from the general theory. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Application of learning algorithms for colour recognition on underwater images
Authors: Hoth Julian , Kowalczyk Wojciech
Published: October 2015

Objects look very different in the underwater environment compared to their appearance in sunlight. High quality images with correct colouring simplify the detection of underwater objects. Hence, image processing is required to obtain images of high quality and correct colouring. Current algorithms focus on the colour reconstruction of scenery at diving depth where a significant part of sunlight is still present and different colours can still be distinguished. At greater depth the filtering is much stronger such that this is not possible. In this study it is investigated whether machine learning can be used to transform image data obtained in a controlled laboratory setup. The images are fed through learning machines with or without pre‐filters. It is shown that k‐nearest neighbour and support vector machines are most suitable for the given task and yield excellent results. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Prony's Method for Multivariate Signals
Authors: Peter Thomas , Plonka Gerlind , Schaback Robert
Published: October 2015

The problem of recovering translates and corresponding amplitudes of sparse sums of Gaussians out of sampling values as well as reconstructing sparse sums of exponentials are nonlinear inverse problems that can be solved for example by Prony's method. Here, we want to demonstrate a new extension to multivariate input data. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Digital image processing algorithms for diagnosis in arterial diseases
Authors: Costarelli Danilo , Seracini Marco , Vinti Gianluca
Published: October 2015

Computed Tomography images (C.T.) are currently part of the routine procedure in medical diagnostic techniques and can be used for the evaluation of occlusion rate of arterial vessels in presence of many diseases. The correct individuation of the morphology of these arterial anomalies allows specialists to diagnose the risk rate for the health of patients and to decide for surgical stent implants. Multivariate sampling Kantorovich operators are suitable for studying not necessarily continuos signals/images as the ones involved in the medical field. Convergent results for such a family of discrete operators translate into reconstruction and even enhancement of a given signal/image increasing the sampling rate. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A unifying approach for the study of linear sampling type operators in function spaces
Authors: Vinti Gianluca , Zampogni Luca
Published: October 2015

Sampling series play a crucial role in Signal and Image Processing. In this note, we illustrate a general method to construct Sampling series and to determine their convergence in Orlicz spaces. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Parallel simulation of large scale multibody systems
Authors: Klöppel Michael , Naumann Andreas , Waurich Volker , Walther Marcus , Wensch Jörg
Published: October 2015

Virtual prototyping plays an ever increasing role in the engineering disciplines. Nowadays, engineers can rely on powerful tools like object oriented modeling languages, e.g., Modelica. Models written in this language can be simulated by open source software as well as commercial tools. The advantage of this approach is that the engineers can concentrate themselves on modeling, whereas the numerical intricacies of the simulation are handled by the software. On the other hand the simulations are usually slower than implementations which are parallelized and optimized manually. This can lead to computation times which are infeasible in practice, e.g., when a real time simulation is necessary for a hardware‐in‐the‐loop simulation.

In this contribution we are concerned with speeding up such automated simulations by parallelization (on desktop hardware as well as HPC systems). We examine the parallelism across the system approaches. Additionally, the influence of the problem formulation on the simulation time is discussed. The implemented methods are demonstrated on engineering examples. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Qualitative Analysis and the Critical Hypersurfaces of Elliptic and Hyperbolic PDEs
Authors: Nastase Adriana
Published: October 2015

Many boundary value problems of PDEs of the applied mathematics lead to the solving of equivalent elliptic and hyperbolic quadratic algebraic equations (QAEs) with variable coefficients. The qualitative analysis of elliptic and hyperbolic QAEs is started here by the determination of their behaviors by systematical variation of their free and linear terms, from −∞ to +∞ and by their visualization. It comes out that, for these variations of their coefficients, the elliptic and hyperbolic QAEs have critical hypersurfaces, which are obtained by cancellation of their great determinant as in [1], [2]. The critical hypersurface can be considered as a limit of existence of real solutions of an elliptic QAE. The hyperbolic QAE degenerates jumps and breaks along its critical hypersurface, which is also its asymptote. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of coupled machine components on long time scales
Authors: Klöppel Michael , Naumann Andreas , Wensch Jörg
Published: October 2015

The accuracy requirements in recent mass production processes demand new compensation techniques and structures of tool machines. To achieve these requirements, one has to know the thermo‐elastic behavior and interaction of the coupled components during the design phase.

We discretize the machine components using finite elements. The heat exchange of the components couples the temperature fields, which leads to additional constraints on parallel FEM. The discretization in space leads to a system of coupled ODEs, which are of stiff parabolic type with fast time‐varying source terms. We concentrate on numerical methods to solve those equations on large timescales and reduce the timestep restriction to the fast coupling. This includes averaging techniques, as well as parallel in time methods. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adaptive space‐time finite element methods for dynamic linear thermoelasticity
Authors: Rademacher Andreas
Published: October 2015

This article focuses on goal oriented error control for dynamic linear thermoelastic problems. To this end, we present a space‐time formulation of this problem class. The corresponding space‐time Galerkin discretization is the basis for the derivation of the error estimator using the dual weighted residual (DWR) method. A numerical example substantiates the accuracy and efficiency of the presented approach. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Enriching the Finite Element Method with meshfree techniques in structural mechanics
Authors: Zanette Andrea , Ferronato Massimiliano , Janna Carlo
Published: October 2015

The automatic generation of meshes for the Finite Element method can be an expensive computational burden, especially in structural problems with localized stress peaks. The use of meshless methods can address such an issue, as these techniques do not require the existence of an underlying connection among the nodes selected in a general domain. However, a thoroughly meshfree technique can be computationally quite expensive. Usually, the most expensive tasks rely on identifying the nodal contacts and computing the Galerkin integrals. In this thesis we advance a novel hybrid technique that blends Finite Elements with the Meshless Local Petrov‐Galerkin method with the aim at exploiting the most attractive properties of each procedure. The idea relies on the use of the Finite Element Method to compute a background solution that is locally improved by enriching the approximating space with the basis functions associated to a few meshless nodes, thus taking advantage of the flexibility ensured by the use of particles disconnected from an underlying grid. Adding the meshless particles only where needed avoids the cost of mesh refining, or even of re‐meshing, without the prohibitive burden of a thoroughly meshfree approach. In particular, two enriching methods are introduced and discussed, with applications in structural mechanics. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Eigenfunction expansions associated with the one‐dimensional Schroedinger operator
Authors: Gilbert Daphne
Published: October 2015

We consider the one‐dimensional Schroedinger operator H on L2(−∞, ∞) associated with

where q(r) : R → R is locally integrable, λ ∈ R is a spectral parameter, and the differential expression is in Weyl's limit point cases at both endpoints. Starting from the well known Weyl‐Kodaira formulation of the eigenfunction expansion associated with H [1], an alternative formulation can be derived in such a way that the principal features contributing to it, namely a scalar spectral density function, the location and multiplicity of the spectrum, and the spectral types of the generalised eigenfunctions, can be explicitly exhibited in the resulting expansion. The proof is based on classical work of Kac [2] and the theory of subordinacy [3], [4]. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On a Particular Construction of Skew‐Selfadjoint Operator Matrices
Authors: Picard Rainer , Seidler Stefan , Trostorff Sascha , Waurick Marcus
Published: October 2015

We consider a particular construction for skew‐selfadjoint operator matrices, which are of central importance in initial boundary value problems of mathematical physics. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Exponential stability of a second‐order integro‐differential equation with delay
Authors: Trostorff Sascha
Published: October 2015

We consider a second order integro‐differential equation with time‐delay and show that this equation can be written as an evolutionary equation. Within the framework of evolutionary equations we show the well‐posedness and the exponential stability of the equation. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the graphic statics for the analysis of masonry domes
Authors: Cavalagli Nicola , Gusella Vittorio
Published: October 2015

The graphic statics applied to constructions has been characterized by a rapid development between the end of the 19th century and the first decades of the 20th century. In this paper the application of the graphic statics to masonry domes is show. In particular three different methods are applied to a specific case study and the results discussed. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Beltrami's continuum mechanics in non‐Euclidean spaces
Authors: Capecchi Danilo , Ruta Giuseppe
Published: October 2015

Eugenio Beltrami investigated if ambient space, where physical phenomena occur, is Euclidean: such a subject was trendy in the mathematical scientific community at the end of the 19th century. Beltrami, along with Riemann, was interested also on how non‐Euclidean geometry affects elasticity and electro‐magnetism. Beltrami opened new paths for mathematical physics; his pupils Ernesto Cesaro, Ernesto Padova, Carlo Somigliana also studied elasticity in non‐Euclidean spaces. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The role of virtual work in Levi‐Civita's parallel transport
Authors: Iurato Giuseppe , Ruta Giuseppe
Published: October 2015

According to current history of science, Levi‐Civita introduced parallel transport solely to give a geometrical interpretation to the covariant derivative of absolute differential calculus. Levi‐Civita, however, searched a simple computation of the curvature of a Riemannian manifold, basing on notions of the Italian school of mathematical physics of his time: holonomic constraints, virtual displacements and work, which so have a remarkable, if not dominant, role in the origin of parallel transport. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adjoint Error Estimation for a Pseudo‐Spectral Approach to Stochastic Field‐Circuit Coupled Problems
Authors: Römer Ulrich , Schöps Sebastian
Published: October 2015

This work is concerned with the numerical approximation of random differential‐algebraic equations (DAE), arising from electric field‐circuit coupled problems. Using the adjoint DAE, the stochastic collation error is analyzed. The error can be evaluated using a collocation method of the same polynomial degree for the adjoint DAE. In particular, there is no need for constructing a solution of higher polynomial degree. The accuracy of the estimator is illustrated by a numerical example. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A finite element phase field model for relaxor ferroelectrics
Authors: Xu Bai‐Xiang , Wang Shuai , Yi Min
Published: October 2015

A mechanically coupled phase field model is presented for the domain evolution and mesoscopic response of relaxor ferroelectrics. In the model the spontaneous polarization is treated as order parameter. The model is derived from thermodynamic analysis including the material force theory. Random field theory is adopted to take the disorder of relaxor ferroelectrics into account. Results show that the model is capable of reproducing relaxor features, such as domain miniaturization, small remnant polarization and large piezoelectric response. Dependence of these features on the random field strength is discussed. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Block triangular preconditioning for time‐dependent Stokes control
Authors: Pearson John W.
Published: October 2015

We consider the numerical solution of time‐dependent Stokes control problems, an important class of flow control problems within the field of PDE‐constrained optimization. The problems we examine lead to large and sparse matrix systems which, with suitable rearrangement, can be written in block tridiagonal form, with the diagonal blocks given by saddle point systems. Using previous results for preconditioning PDE‐constrained optimization and fluid dynamics problems, along with well‐studied saddle point theory, we construct a block triangular preconditioner for the matrix systems. Numerical experiments verify the effectiveness of our solver. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Achieving optimal convergence order for FEM in control constrained optimal control problems
Authors: Schneider René , Wachsmuth Gerd
Published: October 2015

We propose a new heuristic approach to overcome convergence order restrictions implied by the low regularity of the optimal control due to the activity interface of control constraints. Aligning the mesh with the interface yields an improved approximation of the control. Utility of the approach is demonstrated by numerical experiments. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Equivalence of Linear Programming and Basis Pursuit
Authors: Tillmann Andreas M.
Published: October 2015

In this note, we show that linear programming and the prominent Basis Pursuit problem (i.e., minimizing the ℓ1‐norm of a vector x subject to an underdetermined linear equation system Ax = b) are theoretically equivalent, and briefly discuss possible ramifications regarding computational complexity and practical applicability. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Approximation of Singularities by Quantized‐Tensor FEM
Authors: Kazeev Vladimir , Schwab Christoph
Published: October 2015

In d dimensions, first‐order tensor‐product finite‐element (FE) approximations of the solutions of second‐order elliptic problems are well known to converge algebraically, with rate at most 1/d in the energy norm and with respect to the number of degrees of freedom. On the other hand, FE methods of higher regularity may achieve exponential convergence, e.g. global spectral methods for analytic solutions and hp methods for solutions from certain countably normed spaces, which may exhibit singularities.

In this note, we revisit, in one dimension, the tensor‐structured approach to the h‐FE approximation of singular functions. We outline a proof of the exponential convergence of such approximations represented in the quantized‐tensor‐train (QTT) format. Compared to special approximation techniques, such as hp, that approach is fully adaptive in the sense that it finds suitable approximation spaces algorithmically. The convergence is measured with respect to the number of parameters used to represent the solution, which is not the dimension of the first‐order FE space, but depends only polylogarithmically on that. We demonstrate the convergence numerically for a simple model problem and find the rate to be approximately the same as for hp approximations. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Psychosocial Late Effects in Pediatric Cancer Survivors: A Report From the Children's Oncology Group
Authors: Bitsko Matthew J. , Cohen Debra , Dillon Robyn , Harvey Jeanne , Krull Kevin , Klosky James L.
Published: October 2015

Background

This review was conducted to update the Children's Oncology Group (COG) Long‐Term Follow‐Up Guidelines (COG‐LTFU Guidelines, version 4.0) regarding screening for psychosocial late effects of pediatric cancer.

Procedure

Articles published between August 2009 and January 2011 that addressed psychosocial late effects of long‐term survivors of pediatric cancer (n = 35) were reviewed by a multidisciplinary team of COG late effect experts.

Results

The majority of studies in this time period indicate that survivors experience few psychosocial problems in long‐term survivorship. A critical subset, however, is at increased risk for psychosocial late effects secondary to the treatment. Highlighted findings from this review include increased rates of suicidal ideation (SI), and health beliefs as robust predictors of SI, anxiety, and global distress. Survivors’ health beliefs were associated with their perceptions of physical limitations, overall late effects, and cancer‐related pain. While many survivorship studies continue to specify risk factors for anxiety and posttraumatic stress symptoms/posttraumatic stress disorder, others outcomes (e.g., developmental, interpersonal, and familial factors) appear to be emerging in importance.

Conclusions

Although the majority of childhood cancer survivors do not experience psychosocial problems, a subset will. The recent research findings have been included in the new COG‐LTFU Guidelines that will assist in the targeted assessment and the treatment of survivors’ psychosocial health.
Cyclic peptide–polymer conjugates: Grafting‐to vs grafting‐from
Authors: Larnaudie Sophie C. , Brendel Johannes C. , Jolliffe Katrina A. , Perrier Sébastien
Published: October 2015

A systematic comparison between the grafting‐to (convergent) and grafting‐from (divergent) synthetic routes leading to cyclic peptide–polymer conjugates is described. The reversible addition–fragmentation chain transfer (RAFT) process was used to control the polymerizations and the couplings between cyclic peptide and polymer or RAFT agent were performed using N‐hydroxysuccinimide (NHS) active ester ligation. The kinetics of polymerization and polymer conjugation to cyclic peptides were studied for both grafting‐to and grafting‐from synthetic routes, using N‐acryloyl morpholine as a model monomer. The cyclic peptide chain transfer agent was able to mediate polymerization as efficiently as a traditional RAFT agent, reaching high conversion in the same time scale while maintaining excellent control over the molecular weight distribution. The conjugation of polymers to cyclic peptides proceeded to high conversion, and the nature of the carbon at the α‐position to the NHS group was found to play a crucial role in the reaction kinetics. The study was extended to a wider range of monomers, including hydrophilic and temperature responsive acrylamides, hydrophilic and hydrophobic acrylates, and hydrophobic and pH responsive methacrylates. Both approaches lead to similar peptide–polymer conjugates in most cases, while some exceptions highlight the advantages of one or the other method, thereby demonstrating their complementarity. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1003–1011
Efficient fabrication of polymer nanoparticles via sonogashira cross‐linking of linear polymers in dilute solution
Authors: Prasher Alka , Loynd Conor M. , Tuten Bryan T. , Frank Peter G. , Chao Danming , Berda Erik B.
Published: October 2015

The synthesis of single‐chain nanoparticles by palladium‐catalyzed Sonogashira coupling between a terminal alkyne and a di‐halo aryl cross‐linker is reported. Statistical copolymers with trimethylsilyl protected alkyne groups pendent to the linear methacrylate back bones were synthesized using reversible addition‐fragmentation chain transfer polymerization post polymerization de‐protection providing terminal alkyne functionalized linear polymer chains. These linear polymer chains were intramolecularly cross‐linked via bifunctional cross‐linkers. The resulting well‐defined covalently bonded nanoparticles were characterized via triple‐detection size exclusion chromatography where MALS detector provided molecular weight information and viscometric detection characterizes particle size and conformations. The particle size could be readily tuned through polymer molecular weight and by degree of cross‐linking. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 209–217
Arborescent micelles: Dendritic poly(γ‐benzyl l‐glutamate) cores grafted with hydrophilic chain segments
Authors: Whitton Greg , Gauthier Mario
Published: October 2015

Amphiphilic copolymers were obtained by grafting arborescent poly(γ‐benzyl l‐glutamate) (PBG) cores of generations G1–G3 with polyglycidol, poly(ethylene oxide) (PEO), or poly(l‐glutamic acid) (PGA) chain segments. The PBG substrates were synthesized by two methods: (1) subjecting PBG samples with a dispersity Đ = Mw/Mn < 1.1 to partial acidolysis of the benzyl ester groups, to produce randomly distributed carboxylic acid functionalities, and (2) using PBG chains containing a glutamic acid di‐tert‐butyl ester initiator fragment in the last grafting cycle of the PBG core synthesis, and selective acidolysis of the tert‐butyl ester groups to obtain substrates with carboxylic acid termini. Linear polymers with Đ < 1.20 and a primary amine terminus were also synthesized to serve as hydrophilic shell materials: Polyglycidol and PEO by anionic polymerization, and PGA by N‐carboxyanhydride ring‐opening polymerization. These polymers, combined with the two different PGB substrate types, allowed the evaluation of the usefulness of random versus chain‐end grafting in producing arborescent copolymers useful as unimolecular micelles in organic and aqueous media. Size exclusion chromatography served to determine the grafting yield, molar mass, dispersity, and branching functionality of the copolymers. Dynamic light scattering measurements provided information on their aggregation behavior in aqueous environments. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1197–1209
Influence of ligand exchange on the electrical transport properties of PbS nanocrystals
Authors: Borriello Carmela , Miscioscia Riccardo , Mansour Shehab A. , Di Luccio Tiziana , Bruno Annalisa , Loffredo Fausta , Villani Fulvia , Minarini Carla
Published: October 2015

In this work, FETs are used as a research tool to study charge carrier mobilities in PbS nanocrystals (NCs) thin‐films employed as semiconducting layer in bottom‐gate bottom‐contact (BGBC) field‐effect transistors (FETs). The as‐synthesised NCs are surrounded by long alkyl chain ligands which act as electrical insulators. Therefore, a ligand exchange process with shorter molecules is necessary to enhance the free charges generation and transport. We used two different ligands: 1,2 ethandithiol (EDT) and 1,2,3,4‐tetrabutylammonium iodide (TBAI) and studied the charge mobility of PbS NCs comparing the electrical characteristics of FETs made by exchanged NCs. We analysed also the contemporary presence of both exchanged nanocrystals on the device. All the transistors showed p‐type transport behaviour, enhanced by an annealing process at 100 °C for 10 min. After this, only the TBAI‐treated NCs devices showed a n‐type transport, resulting in an ambipolar behaviour. Inkjet printing deposition techniques was also successfully used to deposit PbS‐(TBAI) NCs and ambipolar devices were obtained. In addition, for printed devices it was found that it is possible to modulate the charge transport properties by applying surface treatment to the substrate with a pentafluorothiophenol (PFTP). Indeed in this case, the p‐type transport was suppressed while n‐type behaviour was induced.
Nanometer size pores in ionic liquid loaded silica gel characterized by positron lifetime spectroscopy
Authors: Herold Christian , Ceeh Hubert , Gigl Thomas , Reiner Markus , Haumann Marco , Schönweiz Andreas , Hugenschmidt Christoph
Published: October 2015

We present studies on the free volume of silica gel dependent on water absorption and on loading with a different amount of the ionic liquid (IL) [C2 MIM][NTf2] using positron lifetime spectroscopy (PLS). The found two long lifetime components (2 and 10–20 ns) are attributed to the annihilation of ortho‐positronium (o‐Ps) in micropores of different size. The application of a semi‐empirical quantum mechanical model allowed us to correlate the measured o‐Ps lifetimes to the absolute mean size of the micropores by approximation with a spherical shape. The mean diameter of the pores in the pure silica gel could, hence, be determined to 1.72(6) nm. IL loading with up to 70 vol% lead to the formation of smaller voids with a mean diameter of 1.28(4) nm according to a reduction of the mean pore volume by about 60%. In addition, the accumulation of H2 O molecules from the surrounding air inside the pores could be observed in‐situ by time dependent PLS.
Grain size and Fe2+ concentration‐dependent magnetic, dielectric, and magnetodielectric properties of Y3Fe5O12 ceramics
Authors: Wu Huarui , Huang Fengzhen , Lu Xueliang , Xu Tingting , Lu Xiaomei , Ti Ruixia , Jin Yaming , Zhu Jinsong
Published: October 2015

Y3Fe5O12 ceramics are prepared by the solid state reaction method. Grain size and Fe2+ concentration‐dependent magnetic, dielectric, and magnetodielectric properties are investigated systematically. It is found that grain size and Fe2+ concentration increase with increasing sintering temperature, which thus results in increased saturation magnetization while decreased coercive field and remanent magnetization. Three sets of dielectric relaxation are observed in temperature range from 10 to 500 K, which are considered to be originated from quantum tunneling effect of electrons, electron hopping between Fe2+ and Fe3+, and the migration of oxygen vacancies, respectively. Cole–Cole fitting results of relaxation II indicate that a correlation exists among the hopping electrons, and the correlation is strengthened as Fe2+ concentration increases, which in turn results in easier hopping process and decreased activation energy. More interesting, YIG ceramics sintered at 1350 °C show both considerable magnetic and dielectric properties at room temperature, opening a new window for the application of YIG as a possible multi‐susceptibile single‐phase material.
Cellular and chromatin dynamics of antibody‐secreting plasma cells
Authors: Bortnick Alexandra , Murre Cornelis
Published: October 2015

Plasma cells are terminally differentiated B cells responsible for maintaining protective serum antibody titers. Despite their clinical importance, our understanding of the linear genomic features and chromatin structure of plasma cells is incomplete. The plasma cell differentiation program can be triggered by different signals and in multiple, diverse peripheral B cell subsets. This heterogeneity raises questions about the gene regulatory circuits required for plasma cell specification. Recently, new regulators of plasma cell differentiation have been identified and the enhancer landscapes of naïve B cells have been described. Other studies have revealed that the bone marrow niche harbors heterogeneous plasma cell subsets. Still undefined are the minimal requirements to become a plasma cell and what molecular features make peripheral B cell subsets competent to become antibody‐secreting plasma cells. New technologies promise to reveal underlying chromatin configurations that promote efficient antibody secretion. WIREs Dev Biol 2016, 5:136–149. doi: 10.1002/wdev.213

This article is categorized under:

Gene Expression and Transcriptional Hierarchies > Gene Networks and Genomics

Gene Expression and Transcriptional Hierarchies > Cellular Differentiation
Analysis of a Study of Lead Wheel Weight Deposition and Abrasion in New Jersey
Authors: Root Robert A.
Published: October 2015

This paper analyzes the implications for children’s health of shortcomings in the methods and results of a study of lead in the environment, “Quantity of Lead Released to the Environment in New Jersey in the Form of Motor Vehicle Wheel Weights,” by the New Jersey Department of Environmental Protection (Aucott and Caldarelli, Water, Air, & Soil Pollution, 223, 1743–1752, 2012). The study significantly understates the amount of lead deposited in New Jersey streets as 12 metric tons per year and incorrectly concludes that only 40 kg per year of the lead from wheel weights is abraded into small particles. The 2012 New Jersey Department of Environmental Protection (NJDEP) study misleads regulators and the public into believing that little toxic particulate lead from abraded wheel weights occurs on the streets of New Jersey and by implication that little occurs elsewhere in the United States, thus minimizing the potential health risk that lead wheel weights may have to our nation’s children and indeed all of us.