7,494 research outputs found
Metastable States, Relaxation Times and Free-energy Barriers in Finite Dimensional Glassy Systems
In this note we discuss metastability in a long-but-finite range disordered
model for the glass transition. We show that relaxation is dominated by
configuration belonging to metastable states and associate an in principle
computable free-energy barrier to the equilibrium relaxation time. Adam-Gibbs
like relaxation times appear naturally in this approach.Comment: 4 pages, 2 figures. Typos correcte
On nonlinear susceptibility in supercooled liquids
In this paper, we discuss theoretically the behavior of the four point
nonlinear susceptibility and its associated correlation length for supercooled
liquids close to the Mode Coupling instability temperature . We work in
the theoretical framework of the glass transition as described by mean field
theory of disordered systems, and the hypernetted chain approximation. Our
results give an interpretation framework for recent numerical findings on
heterogeneities in supercooled liquid dynamics.Comment: Proceedings of the Conference "Unifying Concepts in Glass Physics"
ICTP, Trieste, 15 - 18 September 199
First steps of a nucleation theory in disordered systems
We devise a field theoretical formalism for a microscopic theory of
nucleation processes and phase coexistence in finite dimensional glassy
systems. We study disordered -spin models with large but finite range of
interaction. We work in the framework of glassy effective potential theory
which in mean-field is a non-convex, two minima function of the overlap. We
will associate metastability and phase coexistence with the existence of space
inhomogeneous solution of suitable field equations and we will study the
simplest of such solutions.Comment: 31 pages, 4 figures. Content revised, typos correcte
Nonequilibrium dynamics of a simple stochastic model
We investigate the low-temperature dynamics of a simple stochastic model,
introduced recently in the context of the physics of glasses. The slowest
characteristic time at equilibrium diverges exponentially at low temperature.
On smaller time scales, the nonequilibrium dynamics of the system exhibits an
aging regime. We present an analytical study of the scaling behaviour of the
mean energy, of its local correlation and response functions, and of the
associated fluctuation-dissipation ratio throughout the regime of low
temperature and long times. This analysis includes the aging regime, the
convergence to equilibrium, and the crossover behaviour between them.Comment: 36 pages, plain tex, 7 figures, to be published by Journal of Physics
DYNAMICAL SOLUTION OF A MODEL WITHOUT ENERGY BARRIERS
In this note we study the dynamics of a model recently introduced by one of
us, that displays glassy phenomena in absence of energy barriers. Using an
adiabatic hypothesis we derive an equation for the evolution of the energy as a
function of time that describes extremely well the glassy behaviour observed in
Monte Carlo simulations.Comment: 11 pages, LaTeX, 3 uuencoded figure
Interface energies in Ising spin glasses
The replica method has been used to calculate the interface free energy
associated with the change from periodic to anti-periodic boundary conditions
in finite-dimensional spin glasses. At mean-field level the interface free
energy vanishes but after allowing for fluctuation effects, a non-zero
interface free energy is obtained which is significantly different from
numerical expectations.Comment: 4 pages. Minor changes and clarification
Correlation and response in the Backgammon model: the Ehrenfest legacy
We pursue our investigation of the non-equilibrium dynamics of the Backgammon
model, a dynamical urn model which exhibits aging and glassy behavior at low
temperature. We present an analytical study of the scaling behavior of the
local correlation and response functions of the density fluctuations of the
model, and of the associated fluctuation- dissipation ratios, throughout the
alpha regime of low temperatures and long times. This analysis includes the
aging regime, the convergence to equilibrium, sand the crossover behavior
between them.Comment: 30 pages, 2 figures. To appear in Journal of Physics
Nonequilibrium dynamics of urn models
Dynamical urn models, such as the Ehrenfest model, have played an important
role in the early days of statistical mechanics. Dynamical many-urn models
generalize the former models in two respects: the number of urns is
macroscopic, and thermal effects are included. These many-urn models are
exactly solvable in the mean-field geometry. They allow analytical
investigations of the characteristic features of nonequilibrium dynamics
referred to as aging, including the scaling of correlation and response
functions in the two-time plane and the violation of the
fluctuation-dissipation theorem. This review paper contains a general
presentation of these models, as well as a more detailed description of two
dynamical urn models, the backgammon model and the zeta urn model.Comment: 15 pages. Contribution to the Proceedings of the ESF SPHINX meeting
`Glassy behaviour of kinetically constrained models' (Barcelona, March 22-25,
2001). To appear in a special issue of J. Phys. Cond. Mat
Signatures of the impact of flare ejected plasma on the photosphere of a sunspot light-bridge
We investigate the properties of a sunspot light-bridge, focusing on the
changes produced by the impact of a plasma blob ejected from a C-class flare.
We observed a sunspot in active region NOAA 12544 using spectropolarimetric
raster maps of the four Fe I lines around 15655 \AA\ with the GREGOR Infrared
Spectrograph (GRIS), narrow-band intensity images sampling the Fe I 6173 \AA\
line with the GREGOR Fabry-P\'erot Interferometer (GFPI), and intensity broad
band images in G-band and Ca II H band with the High-resolution Fast Imager
(HiFI). All these instruments are located at the GREGOR telescope at the
Observatorio del Teide, Tenerife, Spain. The data cover the time before,
during, and after the flare event. The analysis is complemented with
Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI)
data from the Solar Dynamics Observatory (SDO). The physical parameters of the
atmosphere at differents heights were inferred using spectral-line inversion
techniques. We identify photospheric and chromospheric brightenings, heating
events, and changes in the Stokes profiles associated to the flare eruption and
the subsequent arrival of the plasma blob to the light bridge, after traveling
along an active region loop. The measurements suggest that these phenomena are
the result of reconnection events driven by the interaction of the plasma blob
with the magnetic field topology of the light bridge.Comment: Accepted for publication in A&
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