1,893 research outputs found
Percolation study for the capillary ascent of a liquid through a granular soil
Capillary rise plays a crucial role in the construction of road embankments
in flood zones, where hydrophobic compounds are added to the soil to suppress
the rising of water and avoid possible damage of the pavement. Water rises
through liquid bridges, menisci and trimers, whose width and connectivity
depends on the maximal half-length {\lambda} of the capillary bridges among
grains. Low {\lambda} generate a disconnect structure, with small clusters
everywhere. On the contrary, for high {\lambda}, create a percolating cluster
of trimers and enclosed volumes that form a natural path for capillary rise.
Hereby, we study the percolation transition of this geometric structure as a
function of {\lambda} on a granular media of monodisperse spheres in a random
close packing. We determine both the percolating threshold {\lambda}_{c} =
(0.049 \pm 0.004)R (with R the radius of the granular spheres), and the
critical exponent of the correlation length {\nu} = (0.830 \pm 0.051),
suggesting that the percolation transition falls into the universality class of
ordinary percolation
Atomic Effective Pseudopotentials for Semiconductors
We derive an analytic connection between the screened self-consistent
effective potential from density functional theory (DFT) and atomic effective
pseudopotentials (AEPs). The motivation to derive AEPs is to address structures
with thousands to hundred thousand atoms, as given in most nanostructures. The
use of AEPs allows to bypass a self-consistent procedure and to address
eigenstates around a certain region of the spectrum (e.g., around the band
gap). The bulk AEP construction requires two simple DFT calculations of
slightly deformed elongated cells. The ensuing AEPs are given on a fine
reciprocal space grid, including the small reciprocal vector components, are
free of parameters, and involve no fitting procedure. We further show how to
connect the AEPs of different bulk materials, which is necessary to obtain
accurate band offsets. We derive a total of 20 AEPs for III-V, II-VI and group
IV semiconductors and demonstrate their accuracy and transferability by
comparison to DFT calculations of strained bulk structures, quantum wells with
varying thickness, and semiconductor alloys.Comment: 10 pages, 5 figures, submitted to PR
Resonance enhancement of particle production during reheating
We found a consistent equation of reheating after inflation, which shows that
for small quantum fluctuations the frequencies of resonance are slighted
different from the standard ones. Quantum interference is taken into account
and we found that at large fluctuations the process mimics very well the usual
parametric resonance but proceed in a different dynamical way. The analysis is
made in a toy quantum mechanical model and we discuss further its extension to
quantum field theory.Comment: 4 pages, 4 figures(eps), using RevTe
First record of Fistularia petimba Lacepéde, 1803 (Pisces, Fistulariidae) off the coast of Cadiz (southern Iberian Peninsula)
The capture of an individual from the family Fistulariidae (Fistularia petimba Lacepéde, 1803) off the coast of Cadiz (southern Iberian Peninsula) during the summer of 1996 is reported. Morphometric and meristic characteristics of this individual are also described.Se cita, por primera vez, la presencia de un individuo de la familia Fistulariidae (Fistularia petimba Lacepéde, 1803) en la costa de Cádiz (sur de la península Ibérica). Se describen las características morfobiométricas de este individuo.Instituto Español de Oceanografí
A study of local approximation for polarization potentials
We discuss the derivation of an equivalent \textit{l}-independent
polarization potential for use in the optical Schr\"{o}dinger equation that
describes the elastic scattering of heavy ions. Three diffferent methods are
used for this purpose. Application of our theory to the low energy scattering
of the halo nucleus Li from a C target is made. It is found that
the notion of \textit{l}-independent polarization potential has some validity
but can not be a good substitute for the \textit{l}-dependent local equivalent
Feshbach polarization potential.Comment: 8 pages, 4 figure
Inflation, Reheating and Dark Matter
In a recent paper, Liddle and Urena-Lopez suggested that to have a unified
model of inflation and dark matter is imperative to have a proper reheating
process where part of the inflaton field remains. In this paper I propose a
model where this is possible. I found that, incorporating the effect of plasma
masses generated by the inflaton products, enable us to stop the process. A
numerical estimated model is presented.Comment: 4 pages, 1 figur
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