69 research outputs found
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
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
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
Simple Model for Attraction between Like-Charged Polyions
We present a simple model for the possible mechanism of appearance of
attraction between like charged polyions inside a polyelectrolyte solution. The
attraction is found to be short ranged, and exists only in presence of
multivalent counterions. The attraction is produced by the correlations in the
condensed layers of counterions surrounding each polyion, and appears only if
the number of condensed counterions exceeds the threshold, ,
where is the valence of counterions and is the polyion charge.Comment: 4 pages, 4 eps figures, also available at
http://www.if.ufrgs.br/~arenzon Figure added and a more detailed discussion
of conclusion
Kosterlitz-Thouless and Potts transitions in a generalized XY model
We present extensive numerical simulations of a generalized XY model with
nematic-like terms recently proposed by Poderoso {\it et al} [PRL
106(2011)067202]. Using finite size scaling and focusing on the case, we
locate the transitions between the paramagnetic (P), the nematic-like (N) and
the ferromagnetic (F) phases. The results are compared with the recently
derived lower bounds for the P-N and P-F transitions. While the P-N transition
is found to be very close to the lower bound, the P-F transition occurs
significantly above the bound. Finally, the transition between the nematic-like
and the ferromagnetic phases is found to belong to the 3-states Potts
universality class.Comment: Extended and updated version of arXiv:1207.3447v
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