4,401 research outputs found
Adsorption of a binary mixture of monomers with nearest-neighbour cooperative effects
A model for the adsorption of a binary mixture on a one-dimensional infinite
lattice with nearest neighbour cooperative effects is considered. The particles
of the two species are both monomers but differ in the repulsive interaction
experienced by them when trying to adsorb. An exact expression for the coverage
of the lattice is derived. In the jamming limit, it is a monotonic function of
the ratio between the attempt frequencies of the two species, varying between
the values corresponding to each of the two single species. This is in contrast
with the results obtained in other models for the adsorption of particles of
different sizes. The structure of the jamming state is also investigated.Comment: v2: Errors in the figures fixed; same text; 23 pages, 5 figures.
Accepted for publication in Journal of Physics A: Mathematical and Genera
Memory effects in vibrated granular systems
Granular materials present memory effects when submitted to tapping
processes. These effects have been observed experimentally and are discussed
here in the context of a general kind of model systems for compaction
formulated at a mesoscopic level. The theoretical predictions qualitatively
agree with the experimental results. As an example, a particular simple model
is used for detailed calculations.Comment: 12 pages, 5 figures; to appear in Journal of Physics: Condensed
Matter (Special Issue: Proceedings of ESF SPHINX Workshop on ``Glassy
behaviour of kinetically constrained models.''
Analytical solution of a one-dimensional Ising model with zero temperature dynamics
The one-dimensional Ising model with nearest neighbour interactions and the
zero-temperature dynamics recently considered by Lefevre and Dean -J. Phys. A:
Math. Gen. {\bf 34}, L213 (2001)- is investigated. By introducing a
particle-hole description, in which the holes are associated to the domain
walls of the Ising model, an analytical solution is obtained. The result for
the asymptotic energy agrees with that found in the mean field approximation.Comment: 6 pages, no figures; accepted in J. Phys. A: Math. Gen. (Letter to
the Editor
Enhancement of ferromagnetism by nickel doping in the 112 cobaltite EuBaCo2O5.50
The study of the ordered oxygen deficient perovskite EuBaCo2-xNixO5.50 shows
that the doping of cobalt sites by nickel induces a strong ferromagnetic
component at low temperature in the antiferromagnetic matrix of EuBaCo2O5.50.
This system exhibits indeed phase separation, i.e. consists of ferromagnetic
domains embedded in the antiferromagnetic matrix of EuBaCo2O5.50. Besides, a
magnetic transition is observed for the first time at 40K in the undoped and
nickel doped phases, which can be attributed to the ferromagnetic ordering of
the Eu3+ moments below this temperature. Moreover sharp ultra magnetization
multisteps are observed below 5K, characteristic of motion of domain walls in a
strong pinning system and very different from any metamagnetic transition
2-Dust : a Dust Radiative Transfer Code for an Axisymmetric System
We have developed a general purpose dust radiative transfer code for an
axisymmetric system, 2-Dust, motivated by the recent increasing availability of
high-resolution images of circumstellar dust shells at various wavelengths.
This code solves the equation of radiative transfer following the principle of
long characteristic in a 2-D polar grid while considering a 3-D radiation field
at each grid point. A solution is sought through an iterative scheme in which
self-consistency of the solution is achieved by requiring a global luminosity
constancy throughout the shell. The dust opacities are calculated through Mie
theory from the given size distribution and optical properties of the dust
grains. The main focus of the code is to obtain insights on (1) the global
energetics of dust grains in the shell (2) the 2-D projected morphologies that
are strongly dependent on the mixed effects of the axisymmetric dust
distribution and inclination angle of the shell. Here, test models are
presented with discussion of the results. The code can be supplied with a
user-defined density distribution function, and thus, is applicable to a
variety of dusty astronomical objects possessing the axisymmetric geometry.Comment: To be published in ApJ, April 2003 issue; 13 pages, 4 tables, 17
figures, 5-page appendix (no figures for the main text included in this
preprint). For the complete preprint and code distribution, contact the
author
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