5,959 research outputs found
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 () in low- superconductors and large in high- superconductors
(). For low- 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- 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
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