Frenkel Excitons in Random Systems With Correlated Gaussian Disorder

Optical absorption spectra of Frenkel excitons in random one-dimensional systems are presented. Two models of inhomogeneous broadening, arising from a Gaussian distribution of on-site energies, are considered. In one case the on-site energies are uncorrelated variables whereas in the second model the on-site energies are pairwise correlated (dimers). We observe a red shift and a broadening of the absorption line on increasing the width of the Gaussian distribution. In the two cases we find that the shift is the same, within our numerical accuracy, whereas the broadening is larger when dimers are introduced. The increase of the width of the Gaussian distribution leads to larger differences between uncorrelated and correlated disordered models. We suggest that this higher broadening is due to stronger scattering effects from dimers.Comment: 9 pages, REVTeX 3.0, 3 ps figures. To appear in Physical Review

Notes on proper homotopy theories associated with compact PL-manifolds

The purpose of this note is to present a bigraded sequence of functors associated with compact PL-manifolds . These functors are invariant of proper homotopy type, and distinguish topological spaces which have the same homotopy type. On the category of compact topological spaces these functors agree with the Hurewicz homotopy groups, hence the principal interest of these functors is for noncompact spaces

Broadband telecom transparency of semiconductor-coated metal nanowires: more transparent than glass

Metallic nanowires (NW) coated with a high permittivity dielectric are proposed as means to strongly reduce the light scattering of the conducting NW, rendering them transparent at infrared wavelengths of interest in telecommunications. Based on a simple, universal law derived from electrostatics arguments, we find appropriate parameters to reduce the scattering efficiency of hybrid metal-dielectric NW by up to three orders of magnitude as compared with the scattering efficiency of the homogeneous metallic NW. We show that metal@dielectric structures are much more robust against fabrication imperfections than analogous dielectric@metal ones. The bandwidth of the transparent region entirely covers the near IR telecommunications range. Although this effect is optimum at normal incidence and for a given polarization, rigorous theoretical and numerical calculations reveal that transparency is robust against changes in polarization and angle of incidence, and also holds for relatively dense periodic or random arrangements. A wealth of applications based on metal-NWs may benefit from such invisibility

Evaluación de las integrales singulares del M.E.C. tridimensional mediante transformaciones no lineales

Se presenta en este trabajo una técnica para la evaluación de las integrales singulares que aparecen en el Método de los Elementos de Contorno en Elasticidad tridimensional, basada en la utilización de transformaciones de coordenadas no lineales, tales como las utilizadas en el caso bidimensional.Peer Reviewe

Effects of thermal fluctuations on the magnetic behavior of mesoscopic superconductors

We study the influence of thermal fluctuations on the magnetic behavior of square mesoscopic superconductors. The strength of thermal fluctuations are parameterized using the Ginzburg number, which is small ($G_i \approx 10^{-10}$) in low-$T_c$ superconductors and large in high-$T_c$ superconductors ($G_i \approx 10^{-4}$). For low-$T_c$ mesoscopic superconductors we found that the meta-stable states due to the surface barrier have a large half-life time, which leads to the hysteresis in the magnetization curves as observed experimentally. A very different behavior appears for high-$T_c$ mesoscopic superconductors where thermally activated vortex entrance/exit through surface barriers is frequent. This leads to a reduction of the magnetization and a non-integer average number of flux quanta penetrating the superconductor. The magnetic field dependence of the probability for the occurrence of the different vortex states and the fluctuations in the number of vortices are studied.Comment: 9 pages, 6 figures, submitted to Phys. Rev.

Evaluación de las integrales singulares del M.E.C. tridimensional mediante transformaciones no lineales

Se presenta en este trabajo una técnica para la evaluación de las integrales singulares que aparecen en el Método de los Elementos de Contorno en Elasticidad tridimensional, basada en la utilización de transformaciones de coordenadas no lineales, tales como las utilizadas en el caso bidimensional.Peer Reviewe