494 research outputs found
Polaron features of the one-dimensional Holstein Molecular Crystal Model
The polaron features of the one-dimensional Holstein Molecular Crystal Model
are investigated by improving a variational method introduced recently and
based on a linear superposition of Bloch states that describe large and small
polaron wave functions. The mean number of phonons, the polaron kinetic energy,
the electron-phonon local correlation function, and the ground state spectral
weight are calculated and discussed. A crossover regime between large and small
polaron for any value of the adiabatic parameter is found and a
polaron phase diagram is proposed.Comment: 12 pages, 2 figure
Integrated random processes exhibiting long tails, finite moments and 1/f spectra
A dynamical model based on a continuous addition of colored shot noises is
presented. The resulting process is colored and non-Gaussian. A general
expression for the characteristic function of the process is obtained, which,
after a scaling assumption, takes on a form that is the basis of the results
derived in the rest of the paper. One of these is an expansion for the
cumulants, which are all finite, subject to mild conditions on the functions
defining the process. This is in contrast with the Levy distribution -which can
be obtained from our model in certain limits- which has no finite moments. The
evaluation of the power spectrum and the form of the probability density
function in the tails of the distribution shows that the model exhibits a 1/f
spectrum and long tails in a natural way. A careful analysis of the
characteristic function shows that it may be separated into a part representing
a Levy processes together with another part representing the deviation of our
model from the Levy process. This allows our process to be viewed as a
generalization of the Levy process which has finite moments.Comment: Revtex (aps), 15 pages, no figures. Submitted to Phys. Rev.
Point-occurrence self-similarity in crackling-noise systems and in other complex systems
It has been recently found that a number of systems displaying crackling
noise also show a remarkable behavior regarding the temporal occurrence of
successive events versus their size: a scaling law for the probability
distributions of waiting times as a function of a minimum size is fulfilled,
signaling the existence on those systems of self-similarity in time-size. This
property is also present in some non-crackling systems. Here, the uncommon
character of the scaling law is illustrated with simple marked renewal
processes, built by definition with no correlations. Whereas processes with a
finite mean waiting time do not fulfill a scaling law in general and tend
towards a Poisson process in the limit of very high sizes, processes without a
finite mean tend to another class of distributions, characterized by double
power-law waiting-time densities. This is somehow reminiscent of the
generalized central limit theorem. A model with short-range correlations is not
able to escape from the attraction of those limit distributions. A discussion
on open problems in the modeling of these properties is provided.Comment: Submitted to J. Stat. Mech. for the proceedings of UPON 2008 (Lyon),
topic: crackling nois
Liquid-liquid equilibrium for monodisperse spherical particles
A system of identical particles interacting through an isotropic potential
that allows for two preferred interparticle distances is numerically studied.
When the parameters of the interaction potential are adequately chosen, the
system exhibits coexistence between two different liquid phases (in addition to
the usual liquid-gas coexistence). It is shown that this coexistence can occur
at equilibrium, namely, in the region where the liquid is thermodynamically
stable.Comment: 6 pages, 8 figures. Published versio
Effect of the Complete Health Improvement Program on Neutrophil Phagocytic Activity
The increased incidence of lifestyle diseases has led to the development of health intervention programs. These lifestyle programs have the potential to greatly change one’s overall health. One of such program is the Complete Health Improvement Program (CHIP). Although offered in various locations worldwide, this study involved CHIP participants held at Adventist Medical Center-Manila, Pasay City, Manila (AMCM). The goal of this study was to determine the effect of participating in the CHIP on the innate immune system particularly the neutrophil phagocytic activity. Using pre-experimental design, incidental quota sampling was used to conduct a pre-post intervention study design. The phagocytic activity of neutrophils was determined through microscopic examination of slides prepared from the participants’ heparinized whole blood, inoculated with a bacterial suspension of Staphylococcus aureus and stained with Wright’s stain. Statistical comparison using dependent t-test of the pre- and post-CHIP neutrophil phagocytic activity of the participants who joined the program showed significant changes. Phagocytic percent, phagocytic index and phagocytic activity are significantly higher after the completion of the program. Further study on whether these results would be consistent in participants who can maintain the lifestyle and the effect on the adaptive immune system may be explored
The dynamic stability and nonlinear resonance of a flexible connecting rod: Continuous parameter model
The transverse vibrations of a flexible connecting rod in an otherwise rigid slider-crank mechanism are considered. An analytical approach using the method of multiple scales is adopted and particular emphasis is placed on nonlinear effects which arise from finite deformations. Several nonlinear resonances and instabilities are investigated, and the influences of important system parameters on these resonances are examined in detail.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43330/1/11071_2004_Article_BF00162233.pd
Polaron and bipolaron formation in the Hubbard-Holstein model: role of next-nearest neighbor electron hopping
The influence of next-nearest neighbor electron hopping, , on the
polaron and bipolaron formation in a square Hubbard-Holstein model is
investigated within a variational approach. The results for electron-phonon and
electron-electron correlation functions show that a negative value of
induces a strong anisotropy in the lattice distortions favoring
the formation of nearest neighbor intersite bipolaron. The role of
, electron-phonon and electron-electron interactions is briefly
discussed in view of the formation of charged striped domains.Comment: 4 figure
F-term Uplift in Heterotic M-theory
We investigate the viability of F-term uplift in heterotic M-theory. With
this aim we explore a natural ingredient of heterotic compactifications, namely
vector bundle moduli. It is shown that it is generically possible to obtain
stable de Sitter vacua with broken supersymmetry provided the little Kahler
potential and the prefactors of the non-perturbative superpotential are
suitably tuned. An additional requirement is the existence of non-trivial gauge
instantons both at the visible and hidden sectors. This is illustrated with
analytical and numerical examples.Comment: 21 pages, 1 figure, references added, typos correcte
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