Examinando por Autor "Restrepo, A."

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    Dynamic server allocation in virtual environments, using quadtrees for dynamic space partition
    (2003-01-01) Restrepo, A.; Montoya, A.; Trefftz, H.; Universidad EAFIT. Departamento de Ingeniería de Sistemas; I+D+I en Tecnologías de la Información y las Comunicaciones
    In actual applications of virtual environments, one of the problems that has received attention is the way to assign computational resources to those who participate in the system. In most cases, static resource allocation is used. Static allocation is simple but has several limitations, among them, the missutilization of resources. In this paper we present a proof-of-concept of a new system and report the results of experiments with a system that accomplishes dynamic resource allocation by using Quadtrees for space partitioning, in a Shared Virtual Environment.
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    Hydrogen bonding in the binary water/ammonia complex
    (IOS Press, 2014-01-01) Guerra, D.; David, J.; Restrepo, A.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
    A detailed study of the interactions leading to stabilization of the NH3(H2O){n =1,2} clusters is presented in this work. The Potential Energy Surface for the trimers was explored using an adapted version of the simulated annealing optimization procedure that produced cluster candidate structures that were further optimized, refined, and characterized at the MP2/6-311++G(d, p) level. Our results indicate that hydrogen bonding of the N-H type is stronger and more covalent than of the O-H type. We provide evidence that suggests that the topological complexity of the electron distributions is directly correlated with cluster stability and that most of the stabilization energy originates in electrostatic and exchange contributions. Our calculated trimerization enthalpy, H° 298-41.75 kJ/mol, is in excellent agreement with the experimental enthalpy of adsorption of NH3 into surface water, reported to be-(41 ± 5) kJ/mol. © 2014-IOS Press.
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    Microsolvation of methylmercury: structures, energies, bonding and NMR constants (Hg-199, C-13 and O-17)
    (ROYAL SOC CHEMISTRY, 2016-01-21) Flórez, E.; Maldonado, A.F.; Aucar, G.A.; David, J.; Restrepo, A.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
    Hartree-Fock (HF) and second order perturbation theory (MP2) calculations within the scalar and full relativistic frames were carried out in order to determine the equilibrium geometries and interaction energies between cationic methylmercury (CH3Hg+) and up to three water molecules. A total of nine structures were obtained. Bonding properties were analyzed using the Quantum Theory of Atoms In Molecules (QTAIM). The analyses of the topology of electron densities reveal that all structures exhibit a partially covalent Hg center dot center dot center dot O interaction between methylmercury and one water molecule. Consideration of additional water molecules suggests that they solvate the (CH3Hg center dot center dot center dot OH2)(+) unit. Nuclear magnetic shielding constants sigma(Hg-199), sigma(C-13) and sigma(O-17), as well as indirect spin-spin coupling constants J(Hg-199-C-13), J(Hg-199-O-17) and J(C-13-O-17), were calculated for each one of the geometries. Thermodynamic stability and the values of NMR constants correlate with the ability of the system to directly coordinate oxygen atoms of water molecules to the mercury atom in methylmercury and with the formation of hydrogen bonds among solvating water molecules. Relativistic effects account for 11% on sigma(C-13) and 14% on sigma(O-17), which is due to the presence of Hg (heavy atom on light atom, HALA effect), while the relativistic effects on sigma(Hg-199) are close to 50% (heavy atom on heavy atom itself, HAHA effect). J-coupling constants are highly influenced by relativity when mercury is involved as in J(Hg-199-C-13) and J(Hg-199-O-17). On the other hand, our results show that the values of NMR constants for carbon and oxygen, atoms which are connected through mercury (C-Hg center dot center dot center dot O), are highly correlated and are greatly influenced by the presence of water molecules. Water molecules introduce additional electronic effects to the relativistic effects due to the mercury atom.