1,936 research outputs found
How to discriminate easily between Directed-percolation and Manna scaling
Here we compare critical properties of systems in the directed-percolation
(DP) universality class with those of absorbing-state phase transitions
occurring in the presence of a non-diffusive conserved field, i.e. transitions
in the so-called Manna or C-DP class. Even if it is clearly established that
these constitute two different universality classes, most of their universal
features (exponents, moment ratios, scaling functions,...) are very similar,
making it difficult to discriminate numerically between them. Nevertheless, as
illustrated here, the two classes behave in a rather different way upon
introducing a physical boundary or wall. Taking advantage of this, we propose a
simple and fast method to discriminate between these two universality classes.
This is particularly helpful in solving some existing discrepancies in
self-organized critical systems as sandpiles.Comment: 7 Pages, 4 Figure
Field theory of self-organized fractal etching
We propose a phenomenological field theoretical approach to the chemical
etching of a disordered-solid. The theory is based on a recently proposed
dynamical etching model. Through the introduction of a set of Langevin
equations for the model evolution, we are able to map the problem into a field
theory related to isotropic percolation. To the best of the authors knowledge,
it constitutes the first application of field theory to a problem of chemical
dynamics. By using this mapping, many of the etching process critical
properties are seen to be describable in terms of the percolation
renormalization group fixed point. The emerging field theory has the
peculiarity of being ``{\it self-organized}'', in the sense that without any
parameter fine-tuning, the system develops fractal properties up to certain
scale controlled solely by the volume, , of the etching solution.
In the limit the upper cut-off goes to infinity and the system
becomes scale invariant. We present also a finite size scaling analysis and
discuss the relation of this particular etching mechanism with Gradient
Percolation.
Finally, the possibility of considering this mechanism as a new generic path
to self-organized criticality is analyzed, with the characteristics of being
closely related to a real physical system and therefore more directly
accessible to experiments.Comment: 9 pages, 3 figures. Submitted to Phys. Rev.
JOB MATCHING QUALITY EFFECTS OF EMPLOYMENT PROMOTION MEASURES FOR PEOPLE WITH DISABILITIES
In this article, we evaluate the influence that employment promotion measures designed for disabled people have on the latterâs job matching quality through the use of matching analysis. We focus on two aspects of quality: the type of contract held (either permanent or temporary) and whether or not the individual is searching for another job. We find that employment promotion measures do not improve the matchâs job quality. Furthermore, the use of specialized labour market intermediation services by disabled individuals does not affect their job matching quality. As an additional contribution, our definition of disability eludes the self-justification bias.
Working career progress in the tourism industry: Temp-to-perm transitions in Spain
In this article, we analyze the dynamics of temporary workersâ transitions into permanent contracts for workers related to the tourism industry. For this purpose, we use an administrative retrospective dataset from Spanish Social security records. Results show that while individuals with a weaker attachment to the tourism industry achieve open-ended contracts sooner than in most other industries, on the contrary, it takes more time to those with a greater attachment to the tourism industry to exit from the temporary status. In addition, we find that for workers substantially engaged in the tourism industry, it takes more time to reach an open-ended contract when they have held between six and ten contracts in the past (as opposed to holding only one previous contract). On the contrary, for individuals with a weaker attachment to the tourism industry, holding between two and ten previous contracts implies a quicker exit from temporality.Temporary employment, Temporality trap, Spanish tourism industry
Mean-field solution of the parity-conserving kinetic phase transition in one dimension
A two-offspring branching annihilating random walk model, with finite
reaction rates, is studied in one-dimension. The model exhibits a transition
from an active to an absorbing phase, expected to belong to the
universality class embracing systems that possess two symmetric absorbing
states, which in one-dimensional systems, is in many cases equivalent to parity
conservation. The phase transition is studied analytically through a mean-field
like modification of the so-called {\it parity interval method}. The original
method of parity intervals allows for an exact analysis of the
diffusion-controlled limit of infinite reaction rate, where there is no active
phase and hence no phase transition. For finite rates, we obtain a surprisingly
good description of the transition which compares favorably with the outcome of
Monte Carlo simulations. This provides one of the first analytical attempts to
deal with the broadly studied DP2 universality class.Comment: 4 Figures. 9 Pages. revtex4. Some comments have been improve
Critical behavior of a bounded Kardar-Parisi-Zhang equation
A host of spatially extended systems, both in physics and in other
disciplines, are well described at a coarse-grained scale by a Langevin
equation with multiplicative-noise. Such systems may exhibit non-equilibrium
phase transitions, which can be classified into universality classes. Here we
study in detail one of such classes that can be mapped into a
Kardar-Parisi-Zhang (KPZ) interface equation with a positive (negative)
non-linearity in the presence of a bounding lower (upper) wall. The wall limits
the possible values taken by the height variable, introducing a lower (upper)
cut-off, and induce a phase transition between a pinned (active) and a depinned
(absorbing) phase. This transition is studied here using mean field and field
theoretical arguments, as well as from a numerical point of view. Its main
properties and critical features, as well as some challenging theoretical
difficulties, are reported. The differences with other multiplicative noise and
bounded-KPZ universality classes are stressed, and the effects caused by the
introduction of ``attractive'' walls, relevant in some physical contexts, are
also analyzed.Comment: Invited paper to a special issue of the Brazilian J. of Physics. 5
eps Figures. 9 pagres. Revtex
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