1,598 research outputs found
A glass transition scenario based on heterogeneities and entropy barriers
We propose a scenario for the glass transition based on the cooperative
nature of nucleation processes and entropic effects. The main point is the
relation between the off-equilibrium energy dissipation and nucleation
processes in off-equilibrium supercooled liquids which leads to a natural
definition of the complexity. From the absence of coarsening growth we can
derive an entropy based fluctuation formula which relates the free energy
dissipation rate in the glass with the nucleation rate of the largest
cooperative regions. As by-product we obtain a new phenomenological relation
between the largest relaxation time in the supercooled liquid phase and an
effective temperature. This differs from the Adam-Gibbs relation in that
predicts no divergence of the primary relaxation time at the Kauzmann
temperature and the existence of a crossover from fragile to strong behavior.Comment: 8th International Workshop on Disordered Systems, Andalo (Trento),
Italy, 12-15 March 200
Inherent Structures, Configurational Entropy and Slow Glassy Dynamics
We give a short introduction to the inherent structure approach, with
particular emphasis on the Stillinger and Weber decomposition, of glassy
systems. We present some of the results obtained in the framework of spin-glass
models and Lennard-Jones glasses. We discuss how to generalize the standard
Stillinger and Weber approach by including the entropy of inherent structures.
Finally we discuss why this approach is probably insufficient to describe the
behavior of some kinetically constrained models.Comment: 16 pages, 8 figures, Contribution to the ESF SPHINX meeting `Glassy
behaviour of kinetically constrained models' (Barcelona, March 22-25, 2001
Is the Stillinger and Weber decomposition relevant for coarsening models?
We study three kinetic models with constraint, namely the Symmetrically
Constrained Ising Chain, the Asymmetrically Constrained Ising Chain, and the
Backgammon Model. All these models show glassy behavior and coarsening. We
apply to them the Stillinger and Weber decomposition, and find that they share
the same configurational entropy, despite of their different nonequilibrium
dynamics. We conclude therefore that the Stillinger and Weber decomposition is
not relevant for this type of models.Comment: 14 pages, 12 figure
Frequency-domain study of relaxation in a spin glass model for the structural glass transition
We have computed the time-dependent susceptibility for the finite-size
mean-field Random Orthogonal model (ROM). We find that for temperatures above
the mode-coupling temperature the imaginary part of the susceptibility
obeys the scaling forms proposed for glass-forming liquids.
Furthermore, as the temperature is lowered the peak frequency of
decreases following a Vogel-Fulcher law with a critical temperature remarkably
close to the known critical temperature where the configurational entropy
vanishes.Comment: 7 pages, 4 figures, epl LaTeX packag
Barriers in the p-spin interacting spin-glass model. The dynamical approach
We investigate the barriers separating metastable states in the spherical
p-spin glass model using the instanton method. We show that the problem of
finding the barrier heights can be reduced to the causal two-real-replica
dynamics. We find the probability for the system to escape one of the highest
energy metastable states and the energy barrier corresponding to this process.Comment: 4 pages, 1 figur
Inherent structures and non-equilibrium dynamics of 1D constrained kinetic models: a comparison study
e discuss the relevance of the Stillinger and Weber approach to the glass
transition investigating the non-equilibrium behavior of models with
non-trivial dynamics, but with simple equilibrium properties. We consider a
family of 1D constrained kinetic models, which interpolates between the
asymmetric chain introduced by Eisinger and J\"ackle [Z. Phys. {\bf B84}, 115
(1991)] and the symmetric chain introduced by Fredrickson and Andersen [Phys.
Rev. Lett {\bf 53}, 1244 (1984)], and the 1D version of the Backgammon model
[Phys. Rev. Lett. {\bf 75}, 1190 (1995)]. We show that the configurational
entropy obtained from the inherent structures is the same for all models
irrespective of their different microscopic dynamics. We present a detailed
study of the coarsening behavior of these models, including the relation
between fluctuations and response. Our results suggest that any approach to the
glass transition inspired by mean-field ideas and resting on the definition of
a configurational entropy must rely on the absence of any growing
characteristic coarsening pattern.Comment: 32 pages, 28 figures, RevTe
Activated processes and Inherent Structure dynamics of finite-size mean-field models for glasses
We investigate the inherent structure (IS) dynamics of mean-field {\it
finite-size} spin-glass models whose high-temperature dynamics is described in
the thermodynamic limit by the schematic Mode Coupling Theory for super-cooled
liquids. Near the threshold energy the dynamics is ruled by activated processes
which induce a logarithmic slow relaxation. We show the presence of aging in
both the IS correlation and integrated response functions and check the
validity of the one-step replica symmetry breaking scenario in the presence of
activated processes. Our work shows: 1) The violation of the
fluctuation-dissipation theorem is given by the configurational entropy, 2) The
intermediate time regime () in mean-field theory automatically
includes activated processes opening the way to analytically investigate
activated processes by computing corrections beyond mean-field.Comment: 8 pages, 3 postscript figures, EPL format, improved versio
Slow and fast dynamics in coupled systems: A time series analysis view
We study the dynamics of systems with different time scales, when access only
to the slow variables is allowed. We use the concept of Finite Size Lyapunov
Exponent (FSLE) and consider both the case when the equations of motion for the
slow components are known, and the situation when a scalar time series of one
of the slow variables has been measured. A discussion on the effects of
parameterizing the fast dynamics is given. We show that, although the
computation of the largest Lyapunov exponent can be practically infeasible in
complex dynamical systems, the computation of the FSLE allows to extract
information on the characteristic time and on the predictability of the
large-scale, slow-time dynamics even with moderate statistics and unresolved
small scales.Comment: 17 pages RevTeX, 6 PostScript figures, tarred, gzipped, uuencoded.
Submitted to Physica
Intermittency of glassy relaxation and the emergence of a non-equilibrium spontaneous measure in the aging regime
We consider heat exchange processes between non-equilibrium aging systems (in
their activated regime) and the thermal bath in contact. We discuss a scenario
where two different heat exchange processes concur in the overall heat
dissipation: a stimulated fast process determined by the temperature of the
bath and a spontaneous intermittent process determined by the fact that the
system has been prepared in a non-equilibrium state. The latter is described by
a probability distribution function (PDF) that has an exponential tail of width
given by a parameter , and satisfies a fluctuation theorem (FT)
governed by that parameter. The value of is proportional to the
so-called effective temperature, thereby providing a practical way to
experimentally measure it by analyzing the PDF of intermittent events.Comment: Latex file, 8 pages + 5 postscript figure
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