126 research outputs found
Kovacs effect in facilitated spin models of strong and fragile glasses
We investigate the Kovacs (or crossover) effect in facilitated -spin
models of glassy dynamics. Although the Kovacs hump shows a behavior
qualitatively similar for all cases we have examined (irrespective of the
facilitation parameter and the spatial dimension ), we find that the
dependence of the Kovacs peak time on the temperature of the second quench
allows to distinguish among different microscopic mechanisms responsible for
the glassy relaxation (e.g. cooperative vs defect diffusion). We also analyze
the inherent structure dynamics underlying the Kovacs protocol, and find that
the class of facilitated spin models with and shows features
resembling those obtained recently in a realistic model of fragile glass
forming liquid.Comment: 7 pages, final version to appear in EPJB, new results and an extended
discussio
Heterogeneities in Aging Models of Granular Compaction
Kinetically constrained models (KCM) are systems with trivial thermodynamics
but often complex dynamical behavior due to constraints on the accessible paths
followed by the system. Exploring these properties, the Kob-Andersen (KA) model
was introduced to study the slow dynamics of glass forming liquids and later
extended to granular materials. In this last context, we present new results on
the heterogeneous character of both in and out of equilibrium dynamics, further
stretching the granular-glass analogy.Comment: Final version appearing on the Proceedings of the IV Brazilian
Meeting on Simulational Physics (Ouro Preto
The Blume-Emery-Griffiths Spin Glass Model
We study the equilibrium properties of the Blume-Emery-Griffiths model with
bilinear quenched disorder in the case of attractive as well as repulsive
biquadratic interactions. The global phase diagram of the system is calculated
in the context of the replica symmetric mean field approximation.Comment: 22 pages and 9 figures. REVTeX. To appear on Journal de Physiqu
Rumor propagation meets skepticism: a parallel with zombies
We propose a model of rumor spreading in which susceptible, but skeptically
oriented individuals may oppose the rumor. Resistance may be implemented either
by skeptical activists trying to convince spreaders to stop their activity,
becoming stiflers or, passively (non-reactive) as a consequence, for example,
of fact-checking. Interestingly, these two mechanisms, when combined, are
similar to the (assumed) spreading of a fictitious zombie outbreak, where
survivors actively target infected people. We analyse the well-mixed
(mean-field) description and obtain the conditions for rumors (zombies) to
spread through the whole population. The results show that when the skepticism
is strong enough, the model predicts the coexistence of two fixed points (such
bistability may be related to polarized situations), with the fate of rumors
depending on the initial exposure to it
Equilibrium properties of the Ising frustrated lattice gas
We study the equilibrium properties of an Ising frustrated lattice gas with a
mean field replica approach. This model bridges usual {\em Spin Glasses} and a
version of {\em Frustrated Percolation} model, and has proven relevant to
describe the glass transition. It shows a rich phase diagram which in a
definite limit reduces to the known Sherrington-Kirkpatrick spin glass model.Comment: To appear in J.Physique I (september 96). All figures included in an
one-page postscript fil
Off equilibrium dynamics of the Frustrated Ising Lattice Gas
We study by means of Monte Carlo simulations the off equilibrium properties
of a model glass, the Frustrated Ising Lattice Gas (FILG) in three dimensions.
We have computed typical two times quantities, like density-density
autocorrelations and the autocorrelation of internal degrees of freedom. We
find an aging scenario particularly interesting in the case of the density
autocorrelations in real space which is very reminiscent of spin glass
phenomenology. While this model captures the essential features of structural
glass dynamics, its analogy with spin glasses may bring the possibility of its
complete description using the tools developed in spin glass theory.Comment: Phys. Rev. E (Rapid Communication), 1999 (probably May
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