Finite element approximation of Maxwell’s equations with Debye memory

Copyright © 2010 Simon Shaw. All rights reserved.This article has been made available through the Brunel Open Access Publishing Fund.Maxwell’s equations in a bounded Debye medium are formulated in terms of the standard partial differential equations of electromagnetism with a Volterra-type history dependence of the polarization on the electric field intensity. This leads to Maxwell’s equations with memory. We make a correspondence between this type of constitutive law and the hereditary integral constitutive laws from linear viscoelasticity, and are then able to apply known results from viscoelasticity theory to this Maxwell system. In particular we can show long-time stability by shunning Gronwall’s lemma and estimating the history kernels more carefully by appeal to the underlying physical fading memory. We also give a fully discrete scheme for the electric field wave equation and derive stability bounds which are exactly analagous to those for the continuous problem, thus providing a foundation for long-time numerical integration. We finish by also providing error bounds for which the constant grows, at worst, linearly in time (excluding the time dependence in the norms of the exact solution). Although the first (mixed) finite element error analysis for the Debye problem was given by Jichun Li (in Comp. Meth. Appl. Mech. Eng., 196, (2007), pp. 3081–3094) this seems to be the the first time sharp constants have been given for this problem.This article is available through the Brunel Open Access Publishing Fund

Finite element approximation of a non-local problem in non-fickian polymer diffusion

This is the post-print version of the Article. Copyright @ 2011 Institute for Scientific Computing and InformationThe problem of non-local nonlinear non-Fickian polymer diffusion as modelled by a diffusion equation with a nonlinearly coupled boundary value problem for a viscoelastic ‘pseudostress’ is considered (see, for example, DA Edwards in Z. angew. Math. Phys., 52, 2001, pp. 254—288). We present two numerical schemes using the implicit Euler method and also the Crank-Nicolson method. Each scheme uses a Galerkin finite element method for the spatial discretisation. Special attention is paid to linearising the discrete equations by extrapolating the value of the nonlinear terms from previous time steps. A priori error estimates are given, based on the usual assumptions that the exact solution possesses certain regularity properties, and numerical experiments are given to support these error estimates. We demonstrate by example that although both schemes converge at their optimal rates the Euler method may be more robust than the Crank-Nicolson method for problems of practical relevance

The Subversion of Traditional Gender Roles in Thomas Hardy’s \u27The Mayor of Casterbridge\u27

This essay examines Thomas Hardy\u27s understanding and subversion of gender roles in The Mayor of Casterbridge by focusing on the novel\u27s two most prominent characters and their respective progressions over the course of the narrative. Michael Henchard’s hypermasculine behavior and eventual undoing is juxtaposed with Elizabeth-Jane’s active rejection of the male gaze, as well as her unique role as a proxy for the reader. In his 1886 novel, Hardy questions the legitimacy of gender expectations by acknowledging and subsequently undermining patriarchal traditions

Time-decoupled high order continuous space-time finite element schemes for the heat equation

Copyright © by SIAMIn Comput. Methods Appl. Mech. Engrg., 190 (2001), pp. 6685—6708 Werder et al. demonstrated that time discretizations of the heat equation by a temporally discontinuous Galerkin finite element method could be decoupled by diagonalising the temporal ‘Gram matrices’. In this article we propose a companion approach for the heat equation by using a continuous Galerkin time discretization. As a result, if piecewise polynomials of degree d are used as the trial functions in time and the spatial discretization produces systems of dimension M then, after decoupling, d systems of size M need to be solved rather than a single system of sizeMd. These decoupled systems require complex arithmetic, as did Werder et al.’s technique, but are amenable to parallel solution on modern multi-core architectures. We give numerical tests for temporal polynomial degrees up to six for three different model test problems, using both Galerkin and spectral element spatial discretizations, and show convergence and temporal superconvergence rates that accord with the bounds given by Aziz and Monk, Math. Comp. 52:186 (1989), pp. 255—274. We also interpret error as a function of computational time and see that our high order schemes may offer greater efficiency that the Crank-Nicolson method in terms of accuracy per unit of computational time—although in a multi-core world, with highly tuned iterative solvers, one has to be cautious with such claims. We close with a speculation on the application of these ideas to the Navier-Stokes equations for incompressible fluids

An initial-boundary value problem for the Korteweg-de Vries equation on the negative quarter-plane

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Finite element approximation of non-Fickian polymer diffusion

The problem of nonlinear non-Fickian polymer diffusion as modelled by a diffusion equation with an adjoined spatially local evolution equation for a viscoelastic stress is considered (see, for example, Cohen, White & Witelski, SIAM J. Appl. Math. 55, pp. 348–368, 1995). We present numerical schemes based, spatially, on the Galerkin finite element method and, temporally, on the Crank-Nicolson method. Special attention is paid to linearising the discrete equations by extrapolating the value of the nonlinear term from previous time steps. Optimal a priori error estimates are given, based on the assumption that the exact solution possesses certain regularity properties, and numerical experiments are given to support these error estimates

Schemes and estimates for the long-time numerical solution of Maxwell’s equations for Lorentz metamaterials

We consider time domain formulations of Maxwell's equations for the Lorentz model for metamaterials. The field equations are considered in two different forms which have either six or four unknown vector fields. In each case we use arguments tuned to the physical laws to derive data-stability estimates which do not require Gronwall's inequality. The resulting estimates are, in this sense, sharp. We also give fully discrete formulations for each case and extend the sharp data-stability to these. Since the physical problem is linear it follows (and we show this with examples) that this stability property is also reflected in the constants appearing in the a priori error bounds. By removing the exponential growth in time from these estimates we conclude that these schemes can be used with confidence for the long-time numerical simulation of Lorentz metamaterials.This work was supported in part by NSFC Project 11271310, NSF grant DMS-1416742, and a grant from the Simons Foundation (#281296 to Li), in part by scheme 4 London Mathematical Society funding and in part by the Engineering and Physical Sciences Research Council (EP/H011072/1 to Shaw)

International money and international inflation, 1958-1973

Inflation (Finance) ; United Nations Monetary and Financial Conference ; Monetary theory ; International finance