11,691 research outputs found
A simple stochastic model for the dynamics of condensation
We consider the dynamics of a model introduced recently by Bialas, Burda and
Johnston. At equilibrium the model exhibits a transition between a fluid and a
condensed phase. For long evolution times the dynamics of condensation
possesses a scaling regime that we study by analytical and numerical means. We
determine the scaling form of the occupation number probabilities. The
behaviour of the two-time correlations of the energy demonstrates that aging
takes place in the condensed phase, while it does not in the fluid phase.Comment: 8 pages, plain tex, 2 figure
Fractionalization in a square-lattice model with time-reversal symmetry
We propose a two-dimensional time-reversal invariant system of essentially
non-interacting electrons on a square lattice that exhibits configurations with
fractional charges e/2. These are vortex-like topological defects in the
dimerization order parameter describing spatial modulation in the electron
hopping amplitudes. Charge fractionalization is established by a simple
counting argument, analytical calculation within the effective low-energy
theory, and by an exact numerical diagonalization of the lattice Hamiltonian.
We comment on the exchange statistics of fractional charges and possible
realizations of the system.Comment: 4 pages, 3 figures, RevTex 4. (v2) improved discussion of lattice
effects and confinement; clearer figure
Magnetoelectric Response of the Time-Reversal Invariant Helical Metal
We derive compact analytical expressions for the coupled spin-charge
susceptibility of a clean helical metal at the surface of a three dimensional
topological insulator (TI). These expressions lead to unconventional
non-collinear RKKY interactions between two impurity magnetic moments placed on
the surface of a TI, and predict the generation of electric currents by
time-dependent magnetic moments. We determine the influence of gate and bias
voltages on the interlayer exchange coupling between two single-domain
ferromagnetic monolayers deposited on top of a TI.Comment: 4 pages, 2 figures; submitted to Phys. Rev. B R
Impurity scattering and localization in -wave superconductors
Strong evidence is presented for the localization of low energy quasiparticle
states in disordered -wave superconductors. Within the framework of the
Bogoliubov-de Gennes (BdG) theory applied to the extended Hubbard model with a
finite concentration of non-magnetic impurities, we carry out a fully
self-consistent numerical diagonalization of the BdG equations on finite
clusters containing up to sites. Localized states are identified
by probing their sensitivity to the boundary conditions and by analyzing the
finite size dependence of inverse participation ratios.Comment: 4 pages REVTeX with 2 embedded .ps figures; submitted to PRB as Rapid
Communicatio
On nonlinear susceptibility in supercooled liquids
In this paper, we discuss theoretically the behavior of the four point
nonlinear susceptibility and its associated correlation length for supercooled
liquids close to the Mode Coupling instability temperature . We work in
the theoretical framework of the glass transition as described by mean field
theory of disordered systems, and the hypernetted chain approximation. Our
results give an interpretation framework for recent numerical findings on
heterogeneities in supercooled liquid dynamics.Comment: Proceedings of the Conference "Unifying Concepts in Glass Physics"
ICTP, Trieste, 15 - 18 September 199
Metastable States, Relaxation Times and Free-energy Barriers in Finite Dimensional Glassy Systems
In this note we discuss metastability in a long-but-finite range disordered
model for the glass transition. We show that relaxation is dominated by
configuration belonging to metastable states and associate an in principle
computable free-energy barrier to the equilibrium relaxation time. Adam-Gibbs
like relaxation times appear naturally in this approach.Comment: 4 pages, 2 figures. Typos correcte
Local Spin Glass Order in 1D
We study the behavior of one dimensional Kac spin glasses as function of the
interaction range. We verify by Montecarlo numerical simulations the crossover
from local mean field behavior to global paramagnetism. We investigate the
behavior of correlations and find that in the low temperature phase
correlations grow at a faster rate then the interaction range. We completely
characterize the growth of correlations in the vicinity of the mean-field
critical region
Using all-sky differential photometry to investigate how nocturnal clouds darken the night sky in rural areas
Artificial light at night has affected most of the natural nocturnal
landscapes worldwide and the subsequent light pollution has diverse effects on
flora, fauna and human well-being. To evaluate the environmental impacts of
light pollution, it is crucial to understand both the natural and artificial
components of light at night under all weather conditions. The night sky
brightness for clear skies is relatively well understood and a reference point
for a lower limit is defined. However, no such reference point exists for
cloudy skies. While some studies have examined the brightening of the night sky
by clouds in urban areas, the published data on the (natural) darkening by
clouds is very sparse. Knowledge of reference points for the illumination of
natural nocturnal environments however, is essential for experimental design
and ecological modeling to assess the impacts of light pollution. Here we use
differential all-sky photometry with a commercial digital camera to investigate
how clouds darken sky brightness at two rural sites. The spatially resolved
data enables us to identify and study the nearly unpolluted parts of the sky
and to set an upper limit on ground illumination for overcast nights at sites
without light pollution.Comment: 17 pages, 6 figure
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