Browsing by Author "Duran, M"

Now showing 1 - 6 of 6
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    Molecular structure and bonding of copper cluster monocarbonyls CunCO (n=1-9)
    (AMER CHEMICAL SOC, 2006) Poater, A; Duran, M; Jaque, P; Toro Labbe, A; Sola, M
    In this work we analyze CO binding on small neutral copper clusters, Cu-n (n = 1-9). Molecular structures and reactivity descriptors of copper clusters are computed and discussed. The results show that the condensed Fukui functions and the frontier molecular orbital theory are useful tools to predict the selectivity of CO adsorption on these small clusters. To get further insight into the CO binding to copper clusters, an energy decomposition analysis of the CO binding energy is performed. The CS symmetry of the formed CunCO clusters (n = 1-8) allows the separation between the orbital interaction terms corresponding to donation and back-donation. It is found that, energetically, the donation is twice as important as back-donation.
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    Numerical modeling of saline intrusion in Salar de Atacama
    (ASCE-AMER SOC CIVIL ENGINEERS, 2003) Tejeda, I; Cienfuegos, R; Munoz, JF; Duran, M
    This paper presents the results of numerical simulations of groundwater circulation and solute transport at the Salar de Atacama through use of a numerical model to solve the two-dimensional problem of flow in an aquifer when considering the effects of variable density. The phenomena associated with solute transport are modeled by means of an advection-dispersion equation, and a linear relationship is assumed between fluid density and concentration of the dissolved solids. Simulations considered conditions of high groundwater evaporation, which depends on the depth of the phreatic surface. Results indicate that the discharge of groundwater occurs essentially in freshwater-saline water interface zones, where a number of lagunas begin. Different freshwater recharge scenarios were simulated, while it was verified that the effects of evaporation are important and minimize or buffer the variations in the phreatic surface and the discharges of groundwater that are the source of water supply for the lagunas.
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    Numerical stability in the calculation of eigenfrequencies using integral equations
    (ELSEVIER SCIENCE BV, 2001) Duran, M; Miguez, M; Nedelec, JC
    We comment on a phenomenon of instability that appears while computing eigenfrequencies using the integral equation framework. More precisely, it is currently known that the real symmetric matrices are well, and sometimes the best, adapted to numerical treatment. However, we show that this is not the case, if we wish to determine with high accuracy the spectrum of elliptic, and other related operators, using integral representations. (C) 2001 Elsevier Science B.V. All rights reserved.
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    Rate of convergence estimates for the spectral approximation of a generalized eigenvalue problem
    (1998) Conca, C; Duran, M; Rappaz, J
    The aim of this work is to derive rate of convergence estimates for the spectral approximation of a mathematical model which describes the vibrations of a solid-fluid type structure. First, we summarize the main theoretical results and the discretization of this variational eigenvalue problem. Then, we state some well known abstract theorems on spectral approximation and apply them to our specific problem, which allow us to obtain the desired spectral convergence. By using classical regularity results, we are able to establish estimates for the rate of convergence of the approximated eigenvalues and for the gap between generalized eigenspaces.
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    The Helmholtz equation with impedance in a half-plane
    (ELSEVIER FRANCE-EDITIONS SCIENTIFIQUES MEDICALES ELSEVIER, 2005) Duran, M; Muga, I; Nedelec, JC
    This Note gives answers to the uniqueness and existence questions for solutions of the Helmholtz equation in an half-plane with an impedance or mixed boundary condition. We deal with unbounded domains which boundaries are unbounded too. The radiation conditions are different from the ones that we found in an usual exterior problem due to the appearance of surface waves. We first compute and study the half-plane Green's function to see how the solutions behave at infinity, and second obtain integral representation for these solutions. (c) 2005 Academie des sciences. Published by Elsevier SAS. All rights reserved.
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    The Helmholtz equation with impedance in a half-space
    (ELSEVIER FRANCE-EDITIONS SCIENTIFIQUES MEDICALES ELSEVIER, 2005) Duran, M; Muga, I; Nedelec, JC
    In this Note we obtain existence and uniqueness results for the Helmholtz equation in the half-space R-+(3) with an impedance or Robin boundary condition. Basically, we follow the procedure we have already used in the bi-dimensional case (the half-plane). Thus, we compute the associated Green's function with the help of a double Fourier transform and we analyze its far field in order to obtain radiation conditions that allow us to prove the uniqueness of an outgoing solution. Again, these radiation conditions are somewhat unusual due to the appearance of a surface wave guided by the boundary. An integral representation of the solution is presented by means of the Green's function and the boundary data.