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Browsing by Issue Date, starting with "2010-09-30"

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  • Formulations for the Weight-Constrained Minimum Spanning Tree Problem
    Publication . Requejo, Cristina; Agra, Agostinho; Cerveira, Adelaide; Santos, Eulália
    We consider the Weight-constrained Minimum Spanning Tree problem (WMST). The WMST aims at finding a minimum spanning tree such that the overall tree weight does not exceed a specified limit on a graph with costs and weights associated with each edge. We present and compare, from the computational point of view, several formulations for the WMST. From preliminary computational results we propose a model that combines a formulation similar to the well known Miller-Tucker-Zemlin formulation with the cut-set inequalities.
    2010-09-30Journal article Open access Show more
  • The Importance of the Numerical Resolution of the Laplace Equation in the optimization of a Neuronal Stimulation Technique
    Publication . Faria, Paula
    For the past few years, the potential of transcranial direct current stimulation (tDCS) for the treatment of several pathologies has been investigated. Knowledge of the current density distribution is an important factor in optimizing such applications of tDCS. For this goal, we used the finite element method to solve the Laplace equation in a spherical head model in order to investigate the three dimensional distribution of the current density and the variation of its intensity with depth using different electrodes montages: the traditional one with two sponge electrodes and new electrode montages: with sponge and EEG electrodes and with EEG electrodes varying the numbers of electrodes. The simulation results confirm the effectiveness of the mixed system which may allow the use of tDCS and EEG recording concomitantly and may help to optimize this neuronal stimulation technique. The numerical results were used in a promising application of tDCS in epilepsy.
    2010-09-30Journal article Open access Show more
  • Asymptotic Analysis of the Method of Fundamental Solutions for Acoustic Wave Propagation
    Publication . Valtchev, Svilen S.
    The asymptotic behavior of the Method of Fundamental Solutions (MFS) is analyzed, for the numerical solution of acoustic wave propagation problems in 2D and 3D bounded domains. As a consequence, a meshfree method, based on superposition of plane acoustic waves, referred to as the Plane Waves Method (PWM), is developed. Numerical examples are included in order to illustrate the relation between the two methods and the accuracy of the PWM.
    2010-09-30Journal article Restricted access Show more