37,715 research outputs found
An open-system approach for the characterization of spatio-temporal chaos
We investigate the structure of the invariant measure of space-time chaos by
adopting an "open-system" point of view. We consider large but finite windows
of formally infinite one-dimensional lattices and quantify the effect of the
interaction with the outer region by mapping the problem on the dynamical
characterization of localized perturbations. This latter task is performed by
suitably generalizing the concept of Lyapunov spectrum to cope with
perturbations that propagate outside the region under investigation. As a
result, we are able to introduce a "volume"-propagation velocity, i.e. the
velocity with which ensembles of localized perturbations tend to fill volumes
in the neighbouring regions.Comment: Submitted to J.Stat.Phys. - 26 pages, 7 eps-figures included.
Keywords: High-dimensional Chaos; Fractals; Coupled map lattices; Numerical
simulations of chaotic model
Production of three-body Efimov molecules in an optical lattice
We study the possibility of associating meta-stable Efimov trimers from three
free Bose atoms in a tight trap realised, for instance, via an optical lattice
site or a microchip. The suggested scheme for the production of these molecules
is based on magnetically tunable Feshbach resonances and takes advantage of the
Efimov effect in three-body energy spectra. Our predictions on the energy
levels and wave functions of three pairwise interacting 85Rb atoms rely upon
exact solutions of the Faddeev equations and include the tightly confining
potential of an isotropic harmonic atom trap. The magnetic field dependence of
these energy levels indicates that it is the lowest energetic Efimov trimer
state that can be associated in an adiabatic sweep of the field strength. We
show that the binding energies and spatial extents of the trimer molecules
produced are comparable, in their magnitudes, to those of the associated
diatomic Feshbach molecule. The three-body molecular state follows Efimov's
scenario when the pairwise attraction of the atoms is strengthened by tuning
the magnetic field strength.Comment: 21 pages, 8 figures (final version
Positive Feedback, Memory and the Predictability of Earthquakes
We review the "critical point" concept for large earthquakes and enlarge it
in the framework of so-called "finite-time singularities". The singular
behavior associated with accelerated seismic release is shown to result from a
positive feedback of the seismic activity on its release rate. The most
important mechanisms for such positive feedback are presented. We introduce and
solve analytically a novel simple model of geometrical positive feedback in
which the stress shadow cast by the last large earthquake is progressively
fragmented by the increasing tectonic stress. Finally, we present a somewhat
speculative figure that tends to support a mechanism based on the decay of
stress shadows. This figure suggests that a large earthquake in Southern
California of size similar to the 1812 great event is maturing.Comment: PostScript document of 18 pages + 2 eps figure
Noise-guided evolution within cyclical interactions
We study a stochastic predator-prey model on a square lattice, where each of
the six species has two superior and two inferior partners. The invasion
probabilities between species depend on the predator-prey pair and are
supplemented by Gaussian noise. Conditions are identified that warrant the
largest impact of noise on the evolutionary process, and the results of Monte
Carlo simulations are qualitatively reproduced by a four-point cluster
dynamical mean-field approximation. The observed noise-guided evolution is
deeply routed in short-range spatial correlations, which is supported by
simulations on other host lattice topologies. Our findings are conceptually
related to the coherence resonance phenomenon in dynamical systems via the
mechanism of threshold duality. We also show that the introduced concept of
noise-guided evolution via the exploitation of threshold duality is not limited
to predator-prey cyclical interactions, but may apply to models of evolutionary
game theory as well, thus indicating its applicability in several different
fields of research.Comment: to be published in New J. Phy
Calibration of Smearing and Cooling Algorithms in SU(3)-Color Gauge Theory
The action and topological charge are used to determine the relative rates of
standard cooling and smearing algorithms in pure SU(3)-color gauge theory. We
consider representative gauge field configurations on lattices
at and lattices at . We find the
relative rate of variation in the action and topological charge under various
algorithms may be succinctly described in terms of simple formulae. The results
are in accord with recent suggestions from fat-link perturbation theory.Comment: RevTeX, 25 pages, 22 figures, full resolution jpeg version of Fig. 22
can be obtained from
http://www.physics.adelaide.edu.au/cssm/papers_etc/SmearingComp.jp
Autonomous Energy Transducer: Proposition, Example, Basic Characteristics
We propose a concept of autonomous energy transducer at a molecular scale,
where output is produced with small input energy, of the same order of the
thermal energy, without restriction of magnitude or timing of input, and
without any control after the input. As an example that satisfies these
requisites, a dynamical systems model with several degrees of freedom is
proposed, which transduces input energy to output motion on the average. It is
shown that this transduction is robust and the coupling between the input and
output is generally loose. How this transducer works is analyzed in terms of
dynamical systems theory, where chaotic dynamics of the internal degrees of
freedom, as well as duration of active state which is self-organized with the
energy flow, is essential. We also discuss possible relationships to enzyme
dynamics or protein motors.Comment: 14 pages, 12 figure
Surface code fidelity at finite temperatures
We study the dependence of the fidelity of the surface code in the presence
of a single finite-temperature massless bosonic environment after a quantum
error correction cycle. The three standard types of environment are considered:
super-Ohmic, Ohmic, and sub-Ohmic. Our results show that, for regimes relevant
to current experiments, quantum error correction works well even in the
presence of environment-induced, long-range inter-qubit interactions. A
threshold always exists at finite temperatures, although its temperature
dependence is very sensitive to the type of environment. For the super-Ohmic
case, the critical coupling constant separating high- from low-fidelity
decreases with increasing temperature. For both Ohmic and super-Ohmic cases,
the dependence of the critical coupling on temperature is weak. In all cases,
the critical coupling is determined by microscopic parameters of the
environment. For the sub-Ohmic case, it also depends strongly on the duration
of the QEC cycle.Comment: 13 pages, 6 figure
Summary: Working Group on QCD and Strong Interactions
In this summary of the considerations of the QCD working group at Snowmass
2001, the roles of quantum chromodynamics in the Standard Model and in the
search for new physics are reviewed, with empahsis on frontier areas in the
field. We discuss the importance of, and prospects for, precision QCD in
perturbative and lattice calculations. We describe new ideas in the analysis of
parton distribution functions and jet structure, and review progress in
small- and in polarization.Comment: Snowmass 2001. Revtex4, 34 pages, 4 figures, revised to include
additional references on jets and lattice QC
- …