825 research outputs found
Asymmetric exclusion processes with constrained dynamics
Asymmetric exclusion processes with locally reversible kinetic constraints
are introduced to investigate the effect of non-conservative driving forces in
athermal systems. At high density they generally exhibit rheological-like
behavior, negative differential resistance, two-step structural relaxation,
dynamical heterogeneity and, possibly, a jamming transition driven by the
external field.Comment: 4 pages, 4 figures; revised version: minor changes, added references;
to be publishe
Facilitated spin models on Bethe lattice: bootstrap percolation, mode-coupling transition and glassy dynamics
We show that facilitated spin models of cooperative dynamics introduced by
Fredrickson and Andersen display on Bethe lattices a glassy behaviour similar
to the one predicted by the mode-coupling theory of supercooled liquids and the
dynamical theory of mean-field disordered systems. At low temperature such
cooperative models show a two-step relaxation and their equilibration time
diverges at a finite temperature according to a power-law. The geometric nature
of the dynamical arrest corresponds to a bootstrap percolation process which
leads to a phase space organization similar to the one of mean-field disordered
systems. The relaxation dynamics after a subcritical quench exhibits aging and
converges asymptotically to the threshold states that appear at the bootstrap
percolation transition.Comment: 7 pages, 6 figures, minor changes, final version to appear in
Europhys. Let
What is the temperature of a granular medium?
In this paper we discuss whether thermodynamical concepts and in particular
the notion of temperature could be relevant for the dynamics of granular
systems. We briefly review how a temperature-like quantity can be defined and
measured in granular media in very different regimes, namely the glassy-like,
the liquid-like and the granular gas. The common denominator will be given by
the Fluctuation-Dissipation Theorem, whose validity is explored by means of
both numerical and experimental techniques. It turns out that, although a
definition of a temperature is possible in all cases, its interpretation is far
from being obvious. We discuss the possible perspectives both from the
theoretical and, more importantly, from the experimental point of view
Spin-Glass Model for Inverse Freezing
We analyze the Blume-Emery-Griffiths model with disordered magnetic
interaction displaying the inverse freezing phenomenon. The behaviour of this
spin-1 model in crystal field is studied throughout the phase diagram and the
transition and spinodal lines for the model are computed using the Full Replica
Symmetry Breaking Ansatz that always yelds a thermodynamically stable phase. We
compare the results both with the quenched disordered model with Ising spins on
lattice gas - where no reentrance takes place - and with the model with
generalized spin variables recently introduced by Schupper and Shnerb [Phys.
Rev. Lett. 93, 037202 (2004)]. The simplest version of all these models, known
as Ghatak-Sherrington model, turns out to hold all the general features
characterizing an inverse transition to an amorphous phase, including the right
thermodynamic behavior.Comment: 6 pages, 4 figures, to appear in the Proceeding for the X
International Workshop on Disordered Systems (2006), Molveno, Ital
Driven lattice glass as a ratchet and pawl machine
Boundary-induced transport in particle systems with anomalous diffusion
exhibits rectification, negative resistance, and hysteresis phenomena depending
on the way the drive acts on the boundary. The solvable case of a 1D system
characterized by a power-law diffusion coefficient and coupled to two particles
reservoirs at different chemical potential is examined. In particular, it is
shown that a microscopic realisation of such a diffusion model is provided by a
3D driven lattice-gas with kinetic constraints, in which energy barriers are
absent and the local microscopic reversibility holds.Comment: 12 pages, 4 figures, minor change
Stable Solution of the Simplest Spin Model for Inverse Freezing
We analyze the Blume-Emery-Griffiths model with disordered magnetic
interaction that displays the inverse freezing phenomenon. The behavior of this
spin-1 model in crystal field is studied throughout the phase diagram and the
transition and spinodal lines for the model are computed using the Full Replica
Symmetry Breaking Ansatz that always yields a thermodynamically stable phase.
We compare the results both with the formulation of the same model in terms of
Ising spins on lattice gas, where no reentrance takes place, and with the model
with generalized spin variables recently introduced by Schupper and Shnerb
[Phys. Rev. Lett. {\bf 93} 037202 (2004)], for which the reentrance is enhanced
as the ratio between the degeneracy of full to empty sites increases. The
simplest version of all these models, known as the Ghatak-Sherrington model,
turns out to hold all the general features characterizing an inverse transition
to an amorphous phase, including the right thermodynamic behavior.Comment: 4 pages, 4 figure
Free-volume kinetic models of granular matter
We show that the main dynamical features of granular media can be understood
by means of simple models of fragile-glass forming liquid provided that gravity
alone is taken into account. In such lattice-gas models of cohesionless and
frictionless particles, the compaction and segregation phenomena appear as
purely non-equilibrium effects unrelated to the Boltzmann-Gibbs measure which
in this case is trivial. They provide a natural framework in which slow
relaxation phenomena in granular and glassy systems can be explained in terms
of a common microscopic mechanism given by a free-volume kinetic constraint.Comment: 4 pages, 6 figure
Dynamics of the frustrated Ising lattice gas
The dynamical properties of a three dimensional model glass, the frustrated
Ising lattice gas (FILG) are studied by Monte Carlo simulations. We present
results of compression experiments, where the chemical potential is either
slowly or abruptly changed, as well as simulations at constant density. One
time quantities like density and two time ones like correlations, responses and
mean square displacements are measured, and the departure from equilibrium
clearly characterized. The aging scenario, particularly in the case of density
autocorrelations is reminiscent of spin glass phenomenology with violations of
the Fluctuation-dissipation theorem, typical of systems with one replica
symmetry breaking. The FILG, as a valid on-lattice model of structural glasses
can be described with tools developed in spin glass theory and, being a finite
dimensional model, can open the way for a systematic study of activated
processes in glasses.Comment: to appear in Phys. Rev. E, november (2000
Kob-Andersen model: a non-standard mechanism for the glassy transition
We present new results reflecting the analogies between the Kob-Andersen
model and other glassy systems. Studying the stability of the blocked
configurations above and below the transition we also give arguments that
supports their relevance for the glassy behaviour of the model.
However we find, surprisingly, that the organization of the phase space of
the system is different from the well known organization of other mean-field
spin glasses and structural glasses.Comment: New reference added and one update
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