Density functional method for nonequilibrium electron transport

We describe an ab initio method for calculating the electronic structure, electronic transport, and forces acting on the atoms, for atomic scale systems connected to semi-infinite electrodes and with an applied voltage bias. Our method is based on the density functional theory (DFT) as implemented in the well tested Siesta approach (which uses non-local norm-conserving pseudopotentials to describe the effect of the core electrons, and linear combination of finite-range numerical atomic orbitals to describe the valence states). We fully deal with the atomistic structure of the whole system, treating both the contact and the electrodes on the same footing. The effect of the finite bias (including selfconsistency and the solution of the electrostatic problem) is taken into account using nonequilibrium Green's functions. We relate the nonequilibrium Green's function expressions to the more transparent scheme involving the scattering states. As an illustration, the method is applied to three systems where we are able to compare our results to earlier ab initio DFT calculations or experiments, and we point out differences between this method and existing schemes. The systems considered are: (1) single atom carbon wires connected to aluminum electrodes with extended or finite cross section, (2) single atom gold wires, and finally (3) large carbon nanotube systems with point defects.Comment: 18 pages, 23 figure

La pugna de poderes : análisis crítico del sistema político ecuatoriano

1.- Pugna, conflicto y régimen político 2.- La producción de los poderes en pugna 3.- La pugna legislativa entre Gobierno y Congreso 4.- La pugna fiscalizadora 5.- Las apuestas políticas en pugna 6.- Bibliografia, índice de listas de cuadros, anexos: cuadros 7.- Pugna entre violencia y crisis polític

Projet politique ethnique et pouvoirs locaux. Les secteurs indigènes de la Sierra en équateur

1. LE PHÉNOMÈNE DU POLITIQUE DANS LES GROUPES INDIGENES Le fait politique chez les groupes indigènes andins est traversé par deux phénomènes complexes, apparemment contradictoires mais qui définissent l'originalité spécifique du pouvoir et du politique dans la communauté andine : l'un se réfère à l'ordre socio-organisateur tandis que l'autre se rapporte plus directement à la réalité même du pouvoir au sein des sociétés indigènes a) L'organisation andine : entre la solidarité et le factionnali..

Kinetics and Energy Consumption for a Three-Stage Electrocoagulation Process for the Recovery of Au and Ag from Cyanide Leachates

The most common processes used for the recovery of gold and silver from cyanide leachates are Merril-Crowe, activated carbon in pulp, and ion exchange resins; the process of electrocoagulation (EC) also is a promising new technique. EC is an electrochemical process whose mechanisms include oxidation, reduction, decomposition, deposition, coagulation, absorption, flotation, and precipitation. It has been used for the treatment of water and wastewater with different degrees of success. This study aimed to determine the kinetics of the reaction and the energy consumption at constant voltage, and at constant current using aluminum electrodes with two different distances between electrodes. EC was run in three stages for the removal of gold and silver from aqueous cyanide solutions from samples supplied by a Mexican mining company. Characterization of the sample showed initial concentrations of 49.48 and 383 mg/L of gold and silver, respectively. Results showed the effectiveness of the process by achieving removals up to 98.59% of gold and 99.43% of silver. Additionally, it was determined that the kinetics of the reaction is of zero order and that the lowest energy consumption can be achieved when working at constant voltage and with a separation of 0.8 cm between electrodes

Pouvoir local, régionalismes, décentralisation

En Amérique latine, depuis le début des années quatre-vingt, deux phénomènes majeurs, l'approfondissement de la crise financière-économique et l'évolution démocratique, ont renouvelé les termes et les enjeux d'un débat désormais généralisé sur les rapports entre pouvoirs centraux, pouvoirs régionaux et pouvoirs locaux. En France, dans la même période, mais dans un contexte politique différent, la discussion puis l'application des lois de décentralisation ont répondu à la volonté des sociétés locales de prendre une plus grande part dans la détermination de leur destin et de celui de leur territoire. Démocratisation et modernisation, modernisation et démocratisation sont ainsi devenues, tant en France (en Europe devrait-on dire) qu'en Amérique latine les mots-clés, les références incontournables pour toute réflexion sur les voies et moyens permettant d'affronter les mutations imposées par la compétition internationale

Democracia formal, cultura política informal e capital social no Brasil

Este artigo analisa as distorções teóricas que surgem quando se examina o processo e construção democrática no Brasil unicamente por meio do enfoque institucional. Esta abordagem não consegue explicar a ambigüidade entre o surgimento de uma economia de mercado e uma sociedade passiva e desconfiada dos representantes eleitos e das instituições políticas. Tal situação produz condições adversas para o fortalecimento democrático e a institucionalização de uma cultura política participativa. Nesse contexto, é possível desenvolver a capacitação política dos cidadãos via capital social como dispositivo alternativo de cidadania? Os resultados aqui apresentados não são muito alentadores a esse respeito.<br>In this article we analyse the theoretical distortions that emerge when the Brazilian democratic construction process is analyzed utilizing exclusively the institutional approach. This approach does not explain the ambiguities between the emergence of a market economy and a passive and distrustful society of their elected officials and political institutions. In that context, adverse political conditions are produced that do not contribute for the democratic strengthening and the institutionalization of a participative political culture. The question to answer is: is it possible to develop political capacity of citizens through social capital as an alternative mechanism of citizenship? The results of the data examined in this paper are not too convincing