1,721,030 research outputs found
Numerical study of the effectivity index for an anisotropic error indicator based on Zienkiewicz-Zhu error estimator
No full textThe framework of Formaggia and Perotto (Numerische Mathematik 2001; 89:641-667) is considered to derive a new anisotropic error indicator for a Laplace problem in the energy norm. The matrix containing the error gradient is approached using a Zienkiewicz-Zhu error estimator. A numerical study of the effectivity index is proposed for anisotropic unstructured meshes, showing that our indicator is sharp. An anisotropic adaptive algorithm is implemented, aiming at controlling the estimated relative error. Copyright (C) 2003 John Wiley Sons, Ltd.ASNEcole Polytech Fed Lausanne, Dept Math, CH-1015 Lausanne, Switzerland. Picasso, M, Ecole Polytech Fed Lausanne, Dept Math, CH-1015 Lausanne, Switzerland.ISI Document Delivery No.: 640JCCited Reference Count: 1
Adaptive finite elements for a linear parabolic problem
No full textA posteriori error estimates for the heat equation in two space dimensions are presented. A classical discretization is used, Euler backward in time, and continuous, piecewise linear triangular finite elements in space. The error is bounded above and below by an explicit error estimator based on the residual. Numerical results are presented for uniform triangulations and constant time steps. The quality of our error estimator is discussed. An adaptive algorithm is then proposed. Successive Delaunay triangulations are generated, so that the estimated relative error is close to a preset tolerance. Again, numerical results demonstrate the efficiency of our approach. (C) 1998 Elsevier Science S.A. All rights reserved.ASNEcole Polytech Fed Lausanne, Dept Math, CH-1015 Lausanne, Switzerland. Picasso, M, Ecole Polytech Fed Lausanne, Dept Math, CH-1015 Lausanne, Switzerland.ISI Document Delivery No.: 156KWCited Reference Count: 2
Anisotropic error indicator based on Zienkiewicz-Zhu error estimator: Application to elliptic and parabolic problems
No full textThe anisotropic error indicator presented in [M. Picasso, Comm. Numer. Methods Engrg., 19 (2003), pp. 13-23.] in the frame of the Laplace equation is extended to elliptic and parabolic problems. Our error indicator is derived using the anisotropic interpolation estimates of [L. Formaggia and S. Perotto, Numer. Math., 89 (2001), pp. 641-667; L. Formaggia and S. Perotto, Numer. Math., (2002), DOI 10.1007/s002110200415], together with a Zienkiewicz-Zhu error estimator to approach the error gradient. A numerical study of the effectivity index is proposed for elliptic, diffusion-convection, and parabolic problems. An adaptive algorithm is implemented, aimed at controlling the relative estimated error.ASNEcole Polytech Fed Lausanne, Dept Math, CH-1015 Lausanne, Switzerland. Picasso, M, Ecole Polytech Fed Lausanne, Dept Math, CH-1015 Lausanne, Switzerland.ISI Document Delivery No.: 665PGCited Reference Count: 3
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variance reduction methods for CONNFFESSIT-like simulations
No full textThe aim of this paper is to present simple but efficient variance reduction methods for CONNFFESSIT-like simulations, extending the ideas of Hulsen et al. [J. Non-Newtonian Fluid Mech. 70 (1997) 79-101] and Ottinger et al. [J. Non-Newtonian Fluid Mech. 70 (1997) 255-261]. Strongly correlated local ensembles of dumbells were used, and equilibrium ensembles of dumbbells were subtracted. This idea is extended here to non-equilibrium ensembles of dumbbells. The methods are first presented in the frame of the plane Couette flow for Hookean and FENE dumbbells. Extensions to two-dimensional flows are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.ASNEcole Polytech Fed Lausanne, Dept Math, CH-1015 Lausanne, Switzerland. Picasso, M, Ecole Polytech Fed Lausanne, Dept Math, CH-1015 Lausanne, Switzerland.ISI Document Delivery No.: 207WNCited Reference Count: 1
Existence, a priori and a posteriori error estimates for a nonlinear three-field problem arising from Oldroyd-B viscoelastic flows
No full textIn this paper, a nonlinear problem corresponding to a simplified Oldroyd-B model without convective terms is considered. Assuming the domain to be a convex polygon, existence of a solution is proved for small relaxation times. Continuous piecewise linear finite elements together with a Galerkin Least Square (GLS) method are studied for solving this problem. Existence and a priori error estimates are established using a Newton-chord fixed point theorem, a posteriori error estimates are also derived. An Elastic Viscous Split Stress (EVSS) scheme related to the GLS method is introduced. Numerical results confirm the theoretical predictions.ASNEcole Polytech Fed Lausanne, Dept Math, CH-1015 Lausanne, Switzerland. Picasso, M, Ecole Polytech Fed Lausanne, Dept Math, CH-1015 Lausanne, Switzerland.ISI Document Delivery No.: 498FUCited Reference Count: 2
Stability of time-splitting schemes for the Stokes problem with stabilized finite elements
No full textThe time-dependent Stokes problem is solved using continuous, piecewise linear finite elements and a classical stabilization procedure. Four order-one methods are proposed for the time discretization. The first one is nothing but the Euler backward scheme and requires a large linear system involving the velocity and pressure unknowns to be solved. The other three schemes allow velocity and pressure computations to be decoupled, namely the pressure-matrix method, a method based on an inexact LU factorization, and an operator splitting method. Stability and condition number estimates are derived. Numerical experiments in two space dimensions confirm the theoretical predictions. (C) 2001 John Wiley & Sons, Inc.ASNEcole Polytech Fed Lausanne, Dept Math, CH-1015 Lausanne, Switzerland. Picasso, M, Ecole Polytech Fed Lausanne, Dept Math, CH-1015 Lausanne, Switzerland.ISI Document Delivery No.: 484GFCited Reference Count: 2
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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