460 research outputs found
Dynamical transitions in incommensurate systems
In the dynamics of the undamped Frenkel-Kontorova model with kinetic terms,
we find a transition between two regimes, a floating incommensurate and a
pinned incommensurate phase. This behavior is compared to the static version of
the model. A remarkable difference is that, while in the static case the two
regimes are separated by a single transition (the Aubry transition), in the
dynamical case the transition is characterized by a critical region, in which
different phenomena take place at different times. In this paper, the
generalized angular momentum we have previously introduced, and the dynamical
modulation function are used to begin a characterization of this critical
region. We further elucidate the relation between these two quantities, and
present preliminary results about the order of the dynamical transition.Comment: 7 pages, 6 figures, file 'epl.cls' necessary for compilation
provided; subm. to Europhysics Letter
Systematic Improvement of Classical Nucleation Theory
We reconsider the applicability of classical nucleation theory (CNT) to the
calculation of the free energy of solid cluster formation in a liquid and its
use to the evaluation of interface free energies from nucleation barriers.
Using two different freezing transitions (hard spheres and NaCl) as test cases,
we first observe that the interface-free-energy estimates based on CNT are
generally in error. As successive refinements of nucleation-barrier theory, we
consider corrections due to a non-sharp solid-liquid interface and to a
non-spherical cluster shape. Extensive calculations for the Ising model show
that corrections due to a non-sharp and thermally fluctuating interface account
for the barrier shape with excellent accuracy. The experimental solid
nucleation rates that are measured in colloids are better accounted for by
these non-CNT terms, whose effect appears to be crucial in the interpretation
of data and in the extraction of the interface tension from them.Comment: 20 pages (text + supplementary material
Quantum coherence of discrete kink solitons in ion traps
We propose to realize quantized discrete kinks with cold trapped ions. We
show that long-lived solitonlike configurations are manifested as deformations
of the zigzag structure in the linear Paul trap, and are topologically
protected in a circular trap with an odd number of ions. We study the
quantum-mechanical time evolution of a high-frequency, gap separated internal
mode of a static kink and find long coherence times when the system is cooled
to the Doppler limit. The spectral properties of the internal modes make them
ideally suited for manipulation using current technology. This suggests that
ion traps can be used to test quantum-mechanical effects with solitons and
explore ideas for the utilization of the solitonic internal-modes as carriers
of quantum information.Comment: 5 pages, 4 figures ; minor correction
Energy flow of moving dissipative topological solitons
We study the energy flow due to the motion of topological solitons in
nonlinear extended systems in the presence of damping and driving. The total
field momentum contribution to the energy flux, which reduces the soliton
motion to that of a point particle, is insufficient. We identify an additional
exchange energy flux channel mediated by the spatial and temporal inhomogeneity
of the system state. In the well-known case of a DC external force the
corresponding exchange current is shown to be small but non-zero. For the case
of AC driving forces, which lead to a soliton ratchet, the exchange energy flux
mediates the complete energy flow of the system. We also consider the case of
combination of AC and DC external forces, as well as spatial discretization
effects.Comment: 24 pages, 5 figures, submitted to Chao
Plasmon signatures in high harmonic generation
High harmonic generation in polarizable multi-electron systems is
investigated in the framework of multi-configuration time-dependent
Hartree-Fock. The harmonic spectra exhibit two cut offs. The first cut off is
in agreement with the well established, single active electron cut off law. The
second cut off presents a signature of multi-electron dynamics. The strong
laser field excites non-linear plasmon oscillations. Electrons that are ionized
from one of the multi-plasmon states and recombine to the ground state gain
additional energy, thereby creating the second plateau.Comment: Major revision, 12 pages, 5 figures, submitted to J. Phys. B (2005),
accepte
Nonequilibrium evolution thermodynamics
A new approach - nonequilibrium evolution thermodynamics, is compared with
classical variant of Landau approachComment: 4 pages, 1 figur
Driven Dynamics: A Probable Photodriven Frenkel-Kontorova Model
In this study, we examine the dynamics of a one-dimensional Frenkel-Kontorova
chain consisting of nanosize clusters (the ''particles'') and photochromic
molecules (the ''bonds''), and being subjected to a periodic substrate
potential. Whether the whole chain should be running or be locked depends on
both the frequency and the wavelength of the light (keeping the other
parameters fixed), as observed through numerical simulation. In the locked
state, the particles are bound at the bottom of the external potential and
vibrate backwards and forwards at a constant amplitude. In the running state,
the initially fed energy is transformed into directed motion as a whole. It is
of interest to note that the driving energy is introduced to the system by the
irradiation of light, and the driven mechanism is based on the dynamical
competition between the inherent lengths of the moving object (the chain) and
the supporting carrier (the isotropic surface). However, the most important is
that the light-induced conformational changes of the chromophore lead to the
time-and-space dependence of the rest lengths of the bonds.Comment: 4 pages,5 figure
Formation of singularities on the surface of a liquid metal in a strong electric field
The nonlinear dynamics of the free surface of an ideal conducting liquid in a
strong external electric field is studied. It is establish that the equations
of motion for such a liquid can be solved in the approximation in which the
surface deviates from a plane by small angles. This makes it possible to show
that on an initially smooth surface for almost any initial conditions points
with an infinite curvature corresponding to branch points of the root type can
form in a finite time.Comment: 14 page
Master-equation approach to the study of phase-change processes in data storage media
We study the dynamics of crystallization in phase-change materials using a master-equation approach in which the state of the crystallizing material is described by a cluster size distribution function. A model is developed using the thermodynamics of the processes involved and representing the clusters of size two and greater as a continuum but clusters of size one (monomers) as a separate equation. We present some partial analytical results for the isothermal case and for large cluster sizes, but principally we use numerical simulations to investigate the model. We obtain results that are in good agreement with experimental data and the model appears to be useful for the fast simulation of reading and writing processes in phase-change optical and electrical memories
The Ehrenfest urn revisited: Playing the game on a realistic fluid model
The Ehrenfest urn process, also known as the dogs and fleas model, is
realistically simulated by molecular dynamics of the Lennard-Jones fluid. The
key variable is Delta z, i.e. the absolute value of the difference between the
number of particles in one half of the simulation box and in the other half.
This is a pure-jump stochastic process induced, under coarse graining, by the
deterministic time evolution of the atomic coordinates. We discuss the Markov
hypothesis by analyzing the statistical properties of the jumps and of the
waiting times between jumps. In the limit of a vanishing integration time-step,
the distribution of waiting times becomes closer to an exponential and,
therefore, the continuous-time jump stochastic process is Markovian. The random
variable Delta z behaves as a Markov chain and, in the gas phase, the observed
transition probabilities follow the predictions of the Ehrenfest theory.Comment: Accepted by Physical Review E on 4 May 200
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