DISCUSSION: CONSEJO MEXICANO DE PORCICULURA

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Quasi-Ballistic Electron Transport in Random Superlattices

We theoretically study electron transport in disordered, quantum-well based, semiconductor superlattices with structural short-range correlations. Our system consists of equal width square barriers and quantum wells with two different thicknesses. The two kinds of quantum wells are randomly distributed along the growth direction. Structural correlations are introduced by adding the constraint that one of the wells always appears in pairs. We show that such correlated disordered superlattices exhibit a strong enhancement of their dc conductance as compared to usual random ones, giving rise to quasi-ballistic electron transport. Our predictions can be used to demonstrate experimentally that structural correlations inhibit the localization effects of disorder. We specifically describe the way superlattices should be built and experiments should be carried out for that purpose.Comment: REVTeX 3.0, 7 pages, 4 figures on request from FD-A ([email protected]). Submitted to Physical Review B. Preprint MA/UC3M/12/199

Absence of localization and large dc conductance in random superlattices with correlated disorder

We study how the influence of structural correlations in disordered systems manifests itself in experimentally measurable magnitudes, focusing on dc conductance of semiconductor superlattices with general potential profiles. We show that the existence of bands of extended states in these structures gives rise to very noticeable peaks in the finite temperature dc conductance as the chemical potential is moved through the bands or as the temperature is increased from zero. On the basis of these results we discuss how dc conductance measurements can provide information on the location and width of the bands of extended states. Our predictions can be used to demonstrate experimentally that structural correlations inhibit the localization effects of disorder.Comment: REVTeX 3.0, 14 pages, 11 figures available on request from ED ([email protected]). Submitted to Phys Rev B. MA/UC3M/06/9

Excitation decay in one-dimensional disordered systems with paired traps

Incoherent transport of excitations in one-dimensional disordered lattices with pairs of traps placed at random is studied by numerically solving the corresponding master equation. Results are compared to the case of lattices with the same concentration of unpaired traps, and it is found that pairing of traps causes a slowdown of the decay rate of both the mean square displacement and the survival probability of excitations. We suggest that this result is due to the presence of larger trap-free segments in the lattices with paired disorder, which implies that pairing of traps causes less disruption on the dynamics of excitations. In the conclusion we discuss the implications of our work, placing it in a more general context.Comment: REVTeX 3.0, 10 pages, 7 figures available on request from FD-A ([email protected]), Universidad Carlos III preprint MA/UC3M/08/9

Incoherent Exciton Trapping in Self-Similar Aperiodic Lattices

Incoherent exciton dynamics in one-dimensional perfect lattices with traps at sites arranged according to aperiodic deterministic sequences is studied. We focus our attention on Thue-Morse and Fibonacci systems as canonical examples of self-similar aperiodic systems. Excitons progressively extend over the lattice on increasing time and, in this sense, they act as a probe of the particular arrangements of traps in each system considered. The analysis of the characteristic features of their time decay indicates that exciton dynamics in self-similar aperiodic arrangements of traps is quite close to that observed in periodic ones, but differs significatively from that corresponding to random lattices. We also report on characteristic features of exciton motion suggesting that Fibonacci and Thue-Morse orderings might be clearly observed by appropriate experimental measurements. In the conclusions we comment on the implications of our work on the way towards a unified theory of the orderings of matter.Comment: REVTeX 3.0, 10 pages, 2 figures on request from FD-A ([email protected]). Submitted to Phys Rev B. MA/UC3M/11/9

Manifolds with corners modeled on convenient vector spaces

The authors of the present paper realize a quite systematic study of infinite-dimensional Banach manifolds with corners in [8]. Here, we extend some features of the manifolds with corners modeled on Banach spaces to manifolds with corners modeled on convenient vector spaces, that have arisen as important, in the last years, in Global Analysis

Método de los Elementos de Contorno en algunos problemas de interacción suelo-estructura

Los problemas del comportamiento sismico de estructuras masivas de gran responsabilidad y edificios de gran altura asi como el clásico problema del cimiento de las maquinas vibrantes, hacen que el estudio de la interacci6n suelo- estructura adquiera una gran actualidad. Estos problemas, que implican formas y propiedades complicadas, suponen siempre la necesidad de utilizar un modelo numerico del medio considerado. Aqui se emplea el metodo de los elementos de contorno que dadas sus caracteristicas resulta una alternativa muy sugestiva para modelar el suelo y que hace posible el estudio de problemas tridimensionales a un precio razonable. Se introduce un tipo de elementos para problenas bidimensionales , que incluye una singularidad de tipo logaritmico en uno de sus extremos.Se muestran distribuciones de tensiones obtenidas con este tipo de elementos

Determinación de las tensiones en cabezas de anclaje

El problema de la concentración de tensiones en las proximidades de las cabezas de anclaje ha sido tratado utilizando diversos procedimientos basados en la teoría de la elasticidad, tanto en el caso de anclajes en bloques extremos de vigas pretensadas, como en anclajes pasivos incluidos dentro del material, ya sea este hormigón o suelo en el caso de tablestacas. Los procedimientos más utilizados envuelven un elevado grado de aproximación ante la necesidad de reducir un problema de esta complejidad a los niveles normales en la ingeniería. El presente trabajo analiza el problema bajo dos ópticas diferentes: Primero, un estudio analítico de las tensiones en las proximidades de un anclaje sumergido dentro de un medio cuyos contornos libres se encuentran alejados de él; en segundo lugar se estudia el problema utilizando un método numérico, el Método de los Elementos de Contorno, que hace posible la obtención de la solución no sólo en tensiones sino en desplazamientos y permite tener en cuenta el espesor real de la placa de anclaje, la existencia de bordes libres próximos a un anclaje incluida en el material o el caso de anclajes en los bloques extremos de vigas. El método de los elementos de contorno está siendo objeto de atención en los últimos años por parte de investigadores de muchos países y sus características lo hacen muy indicado frente al método de los Elementos Finitos para problemas como este donde existen zonas de concentración de tensiones o grandes zonas que modelar