1,158 research outputs found

### Phase Transitions in Granular Packings

We describe the contact network of granular packings by a frustrated lattice
gas that contains steric frustration as essential ingredient. Two transitions
are identified, a spin glass transition at the onset of Reynolds dilatancy and
at lower densities a percolation transition. We describe the correlation
functions that give rise to the singularities and propose some dynamical
experiments

### Dynamics and thermodynamics of the spherical frustrated Blume-Emery-Griffiths model

We introduce a spherical version of the frustrated Blume-Emery-Griffiths
model and solve exactly the statics and the Langevin dynamics for zero
particle-particle coupling (K=0). In this case the model exhibits an
equilibrium transition from a disordered to a spin glass phase which is always
continuous for nonzero temperature. The same phase diagram results from the
study of the dynamics. Furthermore, we notice the existence of a nonequilibrium
time regime in a region of the disordered phase, characterized by aging as
occurs in the spin glass phase. Due to a finite equilibration time, the system
displays in this region the pattern of interrupted aging.Comment: 19 pages, 8 figure

### A Geometrical Interpretation of Hyperscaling Breaking in the Ising Model

In random percolation one finds that the mean field regime above the upper
critical dimension can simply be explained through the coexistence of infinite
percolating clusters at the critical point. Because of the mapping between
percolation and critical behaviour in the Ising model, one might check whether
the breakdown of hyperscaling in the Ising model can also be intepreted as due
to an infinite multiplicity of percolating Fortuin-Kasteleyn clusters at the
critical temperature T_c. Preliminary results suggest that the scenario is much
more involved than expected due to the fact that the percolation variables
behave differently on the two sides of T_c.Comment: Lattice2002(spin

### Phase coexistence and relaxation of the spherical frustrated Blume-Emery-Griffiths model with attractive particles coupling

We study the equilibrium and dynamical properties of a spherical version of
the frustrated Blume-Emery-Griffiths model at mean field level for attractive
particle-particle coupling (K>0). Beyond a second order transition line from a
paramagnetic to a (replica symmetric) spin glass phase, the density-temperature
phase diagram is characterized by a tricritical point from which,
interestingly, a first order transition line starts with coexistence of the two
phases. In the Langevin dynamics the paramagnetic/spin glass discontinuous
transition line is found to be dependent on the initial density; close to this
line, on the paramagnetic side, the correlation-response plot displays
interrupted aging.Comment: to be published on Europhysics Letter

### Relaxation properties in a lattice gas model with asymmetrical particles

We study the relaxation process in a two-dimensional lattice gas model, where
the interactions come from the excluded volume. In this model particles have
three arms with an asymmetrical shape, which results in geometrical frustration
that inhibits full packing. A dynamical crossover is found at the arm
percolation of the particles, from a dynamical behavior characterized by a
single step relaxation above the transition, to a two-step decay below it.
Relaxation functions of the self-part of density fluctuations are well fitted
by a stretched exponential form, with a $\beta$ exponent decreasing when the
temperature is lowered until the percolation transition is reached, and
constant below it. The structural arrest of the model seems to happen only at
the maximum density of the model, where both the inverse diffusivity and the
relaxation time of density fluctuations diverge with a power law. The dynamical
non linear susceptibility, defined as the fluctuations of the self-overlap
autocorrelation, exhibits a peak at some characteristic time, which seems to
diverge at the maximum density as well.Comment: 7 pages and 9 figure

### Preasymptotic multiscaling in the phase-ordering dynamics of the kinetic Ising model

The evolution of the structure factor is studied during the phase-ordering
dynamics of the kinetic Ising model with conserved order parameter. A
preasymptotic multiscaling regime is found as in the solution of the
Cahn-Hilliard-Cook equation, revealing that the late stage of phase-ordering is
always approached through a crossover from multiscaling to standard scaling,
independently from the nature of the microscopic dynamics.Comment: 11 pages, 3 figures, to be published in Europhys. Let

### Invaded Cluster Dynamics for Frustrated Models

The Invaded Cluster (IC) dynamics introduced by Machta et al. [Phys. Rev.
Lett. 75 2792 (1995)] is extended to the fully frustrated Ising model on a
square lattice. The properties of the dynamics which exhibits numerical
evidence of self-organized criticality are studied. The fluctuations in the IC
dynamics are shown to be intrinsic of the algorithm and the
fluctuation-dissipation theorem is no more valid. The relaxation time is found
very short and does not present critical size dependence.Comment: notes and refernences added, some minor changes in text and fig.3,5,7
16 pages, Latex, 8 EPS figures, submitted to Phys. Rev.

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