120 research outputs found
Solvable dynamics in a system of interacting random tops
In this letter a new solvable model of synchronization dynamics is
introduced. It consists of a system of long range interacting tops with random
precession frequencies. The model allows for an explicit study of orientational
effects in synchronized phenomena. A stability analysis of the incoherent
solution is performed for different types of orientational disorder. A system
with only orientational disorder always synchronizes in the absence of external
noise.Comment: 6 Pages including 1 figure, Revte
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
Configurational entropy and the one-step RSB scenario in glasses
In this talk we discuss the possibility of constructing a fluctuation theory
for structural glasses in the non-equilibrium aging state. After reviewing well
known results in a toy model we discuss some of the key assumptions which
support the validity of this theory, in particular the role of the
configurational entropy and its relation to the effective temperature. Recent
numerical results for mean-field finite-size glasses agree with this scenario.Comment: Disordered and Complex Systems, 10-14 July 2000, Conference
Proceedings, 7 pages + 1 figur
Numerical study of the Ising spin glass in a magnetic field
We study the order parameter distribution P(q) in the 4d Ising spin glass
with couplings in a magnetic field. We also compare these results with
simulations for the infinite ranged model (i.e. SK model.) Then we analyse our
numerical results in the framework of the droplet picture as well as in the
mean field approach.Comment: 11 pages + 3 figures, LateX, figures uuencoded at the end of fil
Improving free-energy estimates from unidirectional work measurements: theory and experiment
We derive analytical expressions for the bias of the Jarzynski free-energy
estimator from N nonequilibrium work measurements, for a generic work
distribution. To achieve this, we map the estimator onto the Random Energy
Model in a suitable scaling limit parametrized by (log N)/m, where m measures
the width of the lower tail of the work distribution, and then compute the
finite-N corrections to this limit with different approaches for different
regimes of (log N)/m. We show that these expressions describe accurately the
bias for a wide class of work distributions, and exploit them to build an
improved free-energy estimator from unidirectional work measurements. We apply
the method to optical tweezers unfolding/refolding experiments on DNA hairpins
of varying loop size and dissipation, displaying both near-Gaussian and
non-Gaussian work distributions.Comment: 4 pages, 3 figure
Glassy dynamics of kinetically constrained models
We review the use of kinetically constrained models (KCMs) for the study of
dynamics in glassy systems. The characteristic feature of KCMs is that they
have trivial, often non-interacting, equilibrium behaviour but interesting slow
dynamics due to restrictions on the allowed transitions between configurations.
The basic question which KCMs ask is therefore how much glassy physics can be
understood without an underlying ``equilibrium glass transition''. After a
brief review of glassy phenomenology, we describe the main model classes, which
include spin-facilitated (Ising) models, constrained lattice gases, models
inspired by cellular structures such as soap froths, models obtained via
mappings from interacting systems without constraints, and finally related
models such as urn, oscillator, tiling and needle models. We then describe the
broad range of techniques that have been applied to KCMs, including exact
solutions, adiabatic approximations, projection and mode-coupling techniques,
diagrammatic approaches and mappings to quantum systems or effective models.
Finally, we give a survey of the known results for the dynamics of KCMs both in
and out of equilibrium, including topics such as relaxation time divergences
and dynamical transitions, nonlinear relaxation, aging and effective
temperatures, cooperativity and dynamical heterogeneities, and finally
non-equilibrium stationary states generated by external driving. We conclude
with a discussion of open questions and possibilities for future work.Comment: 137 pages. Additions to section on dynamical heterogeneities (5.5,
new pages 110 and 112), otherwise minor corrections, additions and reference
updates. Version to be published in Advances in Physic
Single-domain protein folding: a multi-faceted problem
We review theoretical approaches, experiments and numerical simulations that
have been recently proposed to investigate the folding problem in single-domain
proteins. From a theoretical point of view, we emphasize the energy landscape
approach. As far as experiments are concerned, we focus on the recent
development of single-molecule techniques. In particular, we compare the
results obtained with two main techniques: single protein force measurements
with optical tweezers and single-molecule fluorescence in studies on the same
protein (RNase H). This allows us to point out some controversial issues such
as the nature of the denatured and intermediate states and possible folding
pathways. After reviewing the various numerical simulation techniques, we show
that on-lattice protein-like models can help to understand many controversial
issues.Comment: 26 pages, AIP Conference Proceeding
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