576 research outputs found

### Enhancement of structural rearrangement in glassy systems under shear flow

We extend the analysis of the mean field schematic model recently introduced
for the description of glass forming liquids to the case of a supercooled fluid
subjected to a shear flow of rate $\gamma$. After quenching the system to a low
temperature $T$, a slow glassy regime is observed before stationarity is
achieved at the characteristic time $\tau_g$. $\tau_g$ is of the order of the
usual equilibration time without shear $\tau_g^o$ for weak shear, $\gamma
\tau_g ^o1$, local rearrangement of
dense regions is instead enhanced by the flow, and $\tau_g \simeq 1/(T\gamma)$.Comment: 8 pages, 3 figures, changed content Pacs{64}{70.Pf}{Glass
transitions} Pacs{05}{70.Ln}{Non-equilibrium thermodynamics, irreversible
processes} Pacs{83}{50.Ax}{Steady shear flows

### Evidence of aging in mean-field spin glass models

We study numerically the out of equilibrium dynamics of the hypercubic cell
spin glass in high dimensionalities. We obtain evidence of aging effects
qualitatively similar both to experiments and to simulations of low dimensional
models. This suggests that the Sherrington-Kirkpatrick model as well as other
mean-field finite connectivity lattices can be used to study these effects
analytically.Comment: 13 pages + 5 figures (upon request

### Fluctuation theorems and atypical trajectories

In this work, we have studied simple models that can be solved analytically
to illustrate various fluctuation theorems. These fluctuation theorems provide
symmetries individually to the distributions of physical quantities like the
classical work ($W_c$), thermodynamic work ($W$), total entropy ($\Delta
s_{tot}$) and dissipated heat ($Q$), when the system is driven arbitrarily out
of equilibrium. All these quantities can be defined for individual
trajectories. We have studied the number of trajectories which exhibit
behaviour unexpected at the macroscopic level. As the time of observation
increases, the fraction of such atypical trajectories decreases, as expected at
macroscale. Nature of distributions for the thermodynamic work and the entropy
production in nonlinear models may exhibit peak (most probable value) in the
atypical regime without violating the expected average behaviour. However,
dissipated heat and classical work exhibit peak in the regime of typical
behaviour only.Comment: 14 pages, 7 figure

### Fluctuation theorem for non-equilibrium relaxational systems driven by external forces

We discuss an extension of the fluctuation theorem to stochastic models that,
in the limit of zero external drive, are not able to equilibrate with their
environment, extending results presented by Sellitto (cond-mat/9809186). We
show that if the entropy production rate is suitably defined, its probability
distribution function verifies the Fluctuation Relation with the ambient
temperature replaced by a (frequency-dependent) effective temperature. We
derive modified Green-Kubo relations. We illustrate these results with the
simple example of an oscillator coupled to a nonequilibrium bath driven by an
external force. We discuss the relevance of our results for driven glasses and
the diffusion of Brownian particles in out of equilibrium media and propose a
concrete experimental strategy to measure the low frequency value of the
effective temperature using the fluctuations of the work done by an ac
conservative field. We compare our results to related ones that appeared in the
literature recently.Comment: 39 pages, 6 figure

### Dynamical transition of glasses: from exact to approximate

We introduce a family of glassy models having a parameter, playing the role
of an interaction range, that may be varied continuously to go from a system of
particles in d dimensions to a mean-field version of it. The mean-field limit
is exactly described by equations conceptually close, but different from, the
Mode-Coupling equations. We obtain these by a dynamic virial construction.
Quite surprisingly we observe that in three dimensions, the mean-field behavior
is closely followed for ranges as small as one interparticle distance, and
still qualitatively for smaller distances. For the original particle model, we
expect the present mean-field theory to become, unlike the Mode-Coupling
equations, an increasingly good approximation at higher dimensions.Comment: 44 pages, 19 figure

### A first principle computation of the thermodynamics of glasses

We propose a first principle computation of the equilibrium thermodynamics of
simple fragile glasses starting from the two body interatomic potential. A
replica formulation translates this problem into that of a gas of interacting
molecules, each molecule being built of m atoms, and having a gyration radius
(related to the cage size) which vanishes at zero temperature. We use a small
cage expansion, valid at low temperatures, which allows to compute the cage
size, the specific heat (which follows the Dulong and Petit law), and the
configurational entropy.Comment: Latex, 40 pages, 9 figures, corrected misprints, improved
presentatio

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