380 research outputs found
Dissociative Adsorption: A Solvable Model
A model of "hot"-dimer deposition in one dimension, introduced by Pereyra and
Albano, is modified to have an unbounded dissociation range. The resulting
dynamical equations are solved exactly. A related k-mer dissociation model is
also introduced and its solution obtained as a quadrature.Comment: TeX (plain
Wang-Landau Algorithm: a Theoretical Analysis of the Saturation of the Error
In this work we present a theoretical analysis of the convergence of the
Wang-Landau algorithm [Phys. Rev. Lett. 86, 2050 (2001)] which was introduced
years ago to calculate the density of states in statistical models. We study
the dynamical behavior of the error in the calculation of the density of
states.We conclude that the source of the saturation of the error is due to the
decreasing variations of the refinement parameter. To overcome this limitation,
we present an analytical treatment in which the refinement parameter is scaled
down as a power law instead of exponentially. An extension of the analysis to
the N-fold way variation of the method is also discussed.Comment: 7 pages, 5 figure
Analysis of the convergence of the 1/t and Wang-Landau algorithms in the calculation of multidimensional integrals
In this communication, the convergence of the 1/t and Wang - Landau
algorithms in the calculation of multidimensional numerical integrals is
analyzed. Both simulation methods are applied to a wide variety of integrals
without restrictions in one, two and higher dimensions. The errors between the
exact and the calculated values of the integral are obtained and the efficiency
and accuracy of the methods are determined by their dynamical behavior. The
comparison between both methods and the simple sampling Monte Carlo method is
also reported. It is observed that the time dependence of the errors calculated
with 1/t algorithm goes as N^{-1/2} (with N the MC trials) in quantitative
agreement with the simple sampling Monte Carlo method. It is also showed that
the error for the Wang - Landau algorithm saturates in time evidencing the
non-convergence of the methods. The sources for the error are also determined.Comment: 8 pages, 5 figure
Optical polarimetric monitoring of the type II-plateau SN 2005af
Aims. Core-collapse supernovae may show significant polarization that implies
non-spherically symmetric explosions. We observed the type II-plateau SN 2005af
using optical polarimetry in order to verify whether any asphericity is present
in the supernova temporal evolution. Methods. We used the IAGPOL imaging
polarimeter to obtain optical linear polarization measurements in R (five
epochs) and V (one epoch) broadbands. Interstellar polarization was estimated
from the field stars in the CCD frames. The optical polarimetric monitoring
began around one month after the explosion and lasted ~30 days, between the
plateau and the early nebular phase. Results. The weighted mean observed
polarization in R band was [1.89 +/- 0.03]% at position angle (PA) 54 deg.
After foreground subtraction, the level of the average intrinsic polarization
for SN 2005af was ~0.5% with a slight enhancement during the plateau phase and
a decline at early nebular phase. A rotation in PA on a time scale of days was
also observed. The polarimetric evolution of SN 2005af in the observed epochs
is consistent with an overall asphericity of ~20% and an inclination of ~30
deg. Evidence for a more complex, evolving asphericity, possibly involving
clumps in the SN 2005af envelope, is found.Comment: 6 pages, 5 figures, to be published A&
La inclusión de la dimensión económica en la Evaluación de Impacto Ambiental
El objetivo de este trabajo es mostrar la importancia de incluir la dimensión económica en los Estudios deImpacto ambiental (EsIA). Dimensión económica que se incorpora a la evaluación “ex–ante” de inversiones a través del análisis beneficios costos (ABC) y la valoración económica de las externalidades (VEE). El trabajo muestra con ilustraciones y la presentación de dos casos las consecuencias no deseables de ignorar el ABC: a) Existencia de proyectos de eficiencia dudosa en términos de su resultado económico-social; y b) Escasez de proyectos ambientalmente eficientes, pero con escaso retorno económico privado
Fast Algorithm to Calculate Density of States
An algorithm to calculate the density of states, based on the well-known
Wang-Landau method, is introduced. Independent random walks are performed in
different restricted ranges of energy, and the resultant density of states is
modified by a function of time, F(t)=1/t, for large time. As a consequence, the
calculated density of state, gm(E,t), approaches asymptotically the exact value
gex(E) as 1/sqrt(t), avoiding the saturation of the error. It is also shown
that the growth of the interface of the energy histogram belongs to the random
deposition universality class.Comment: 5 pages, 5 figure
Random-Matrix Theory of Quantum Size Effects on Nuclear Magnetic Resonance in Metal Particles
The distribution function of the local density of states is computed exactly
for the Wigner-Dyson ensemble of random Hamiltonians. In the absence of
time-reversal symmetry, precise agreement is obtained with the "supersymmetry"
theory by Efetov and Prigodin of the NMR lineshape in disordered metal
particles. Upon breaking time-reversal symmetry, the variance of the Knight
shift in the smallest particles is reduced by a universal factor of 2/3. ***To
be published in Physical Review B.****Comment: 4 pages, REVTeX-3.0, 1 postscript figure, INLO-PUB-940819; [2017:
figure included in text
Magnetic field dependence of the exciton energy in a quantum disk
The groundstate energy and binding energy of an exciton, confined in a^M
quantum disk, are calculated as a function of an external magnetic field. The
confinement potential is a hard wall of finite height. The diamagnetic shift is
investigated for magnetic fields up to 40. Our results are applied to
self-assembled quantum dots and very good
agreement with experiments is obtained. Furthermore, we investigated the
influence of the dot size on the diamagnetic shift by changing the disk radius.
The exciton excited states are found as a function of the magnetic field. The
relative angular momentum is not a quantum number and changes with the magnetic
field strength.Comment: 10 pages, 17 figure
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