413 research outputs found
The Nonequilibrium Thermodynamics of Small Systems
The interactions of tiny objects with their environment are dominated by
thermal fluctuations. Guided by theory and assisted by micromanipulation tools,
scientists have begun to study such interactions in detail.Comment: PDF file, 13 pages. Long version of the paper published in Physics
Toda
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
Work distribution functions in polymer stretching experiments
We compute the distribution of the work done in stretching a Gaussian
polymer, made of N monomers, at a finite rate. For a one-dimensional polymer
undergoing Rouse dynamics, the work distribution is a Gaussian and we
explicitly compute the mean and width. The two cases where the polymer is
stretched, either by constraining its end or by constraining the force on it,
are examined. We discuss connections to Jarzynski's equality and the
fluctuation theorems.Comment: 5 pages, 2 figure
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
The disordered Backgammon model
In this paper we consider an exactly solvable model which displays glassy
behavior at zero temperature due to entropic barriers. The new ingredient of
the model is the existence of different energy scales or modes associated to
different relaxational time-scales. Low-temperature relaxation takes place by
partial equilibration of successive lower energy modes. An adiabatic scaling
solution, defined in terms of a threshold energy scale \eps^*, is proposed.
For such a solution, modes with energy \eps\gg\eps^* are equilibrated at the
bath temperature, modes with \eps\ll\eps^* remain out of equilibrium and
relaxation occurs in the neighborhood of the threshold \eps\sim \eps^*. The
model is presented as a toy example to investigate conditions related to the
existence of an effective temperature in glassy systems and its possible
dependence on the energy sector probed by the corresponding observable.Comment: 24 pages, 11 figure
Dynamic force spectroscopy of DNA hairpins. II. Irreversibility and dissipation
We investigate irreversibility and dissipation in single molecules that
cooperatively fold/unfold in a two state manner under the action of mechanical
force. We apply path thermodynamics to derive analytical expressions for the
average dissipated work and the average hopping number in two state systems. It
is shown how these quantities only depend on two parameters that characterize
the folding/unfolding kinetics of the molecule: the fragility and the
coexistence hopping rate. The latter has to be rescaled to take into account
the appropriate experimental setup. Finally we carry out pulling experiments
with optical tweezers in a specifically designed DNA hairpin that shows
two-state cooperative folding. We then use these experimental results to
validate our theoretical predictions.Comment: 28 pages, 12 figure
Aging effects and dynamic scaling in the 3d Edwards-Anderson spin glasses: a comparison with experiments
We present a detailed study of the scaling behavior of correlations functions
and AC susceptibility relaxations in the aging regime in three dimensional spin
glasses. The agreement between simulations and experiments is excellent
confirming the validity of the full aging scenario with logarithmic corrections
which manifests as weak sub-aging effects.Comment: 6 pages, 6 figures. Previously appeared as a part of cond-mat/000554
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
Replica Field Theory for Deterministic Models: Binary Sequences with Low Autocorrelation
We study systems without quenched disorder with a complex landscape, and we
use replica symmetry theory to describe them. We discuss the
Golay-Bernasconi-Derrida approximation of the low autocorrelation model, and we
reconstruct it by using replica calculations. Then we consider the full model,
its low properties (with the help of number theory) and a Hartree-Fock
resummation of the high-temperature series. We show that replica theory allows
to solve the model in the high phase. Our solution is based on one-link
integral techniques, and is based on substituting a Fourier transform with a
generic unitary transformation. We discuss this approach as a powerful tool to
describe systems with a complex landscape in the absence of quenched disorder.Comment: 42 pages, uufile with eps figures added in figures, ROM2F/94/1
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