193 research outputs found
Topological pressure of simultaneous level sets
Multifractal analysis studies level sets of asymptotically defined quantities
in a topological dynamical system. We consider the topological pressure
function on such level sets, relating it both to the pressure on the entire
phase space and to a conditional variational principle. We use this to recover
information on the topological entropy and Hausdorff dimension of the level
sets.
Our approach is thermodynamic in nature, requiring only existence and
uniqueness of equilibrium states for a dense subspace of potential functions.
Using an idea of Hofbauer, we obtain results for all continuous potentials by
approximating them with functions from this subspace.
This technique allows us to extend a number of previous multifractal results
from the case to the case. We consider ergodic ratios
where the function need not be uniformly positive,
which lets us study dimension spectra for non-uniformly expanding maps. Our
results also cover coarse spectra and level sets corresponding to more general
limiting behaviour.Comment: 32 pages, minor changes based on referee's comment
Press shaping of arched components by means of a mobile tool
The best tool motion in a press is considered, when producing U-shaped components from sheet. The elastoplastic properties of the deformed material are taken into account. © 2013 Allerton Press, Inc
Oseledets' Splitting of Standard-like Maps
For the class of differentiable maps of the plane and, in particular, for
standard-like maps (McMillan form), a simple relation is shown between the
directions of the local invariant manifolds of a generic point and its
contribution to the finite-time Lyapunov exponents (FTLE) of the associated
orbit. By computing also the point-wise curvature of the manifolds, we produce
a comparative study between local Lyapunov exponent, manifold's curvature and
splitting angle between stable/unstable manifolds. Interestingly, the analysis
of the Chirikov-Taylor standard map suggests that the positive contributions to
the FTLE average mostly come from points of the orbit where the structure of
the manifolds is locally hyperbolic: where the manifolds are flat and
transversal, the one-step exponent is predominantly positive and large; this
behaviour is intended in a purely statistical sense, since it exhibits large
deviations. Such phenomenon can be understood by analytic arguments which, as a
by-product, also suggest an explicit way to point-wise approximate the
splitting.Comment: 17 pages, 11 figure
Fast numerical test of hyperbolic chaos
The effective numerical method is developed performing the test of the
hyperbolicity of chaotic dynamics. The method employs ideas of algorithms for
covariant Lyapunov vectors but avoids their explicit computation. The outcome
is a distribution of a characteristic value which is bounded within the unit
interval and whose zero indicate the presence of tangency between expanding and
contracting subspaces. To perform the test one needs to solve several copies of
equations for infinitesimal perturbations whose amount is equal to the sum of
numbers of positive and zero Lyapunov exponents. Since for high-dimensional
system this amount is normally much less then the full phase space dimension,
this method provide the fast and memory saving way for numerical hyperbolicity
test of such systems.Comment: 4 pages and 4 figure
Weak chaos detection in the Fermi-Pasta-Ulam- system using -Gaussian statistics
We study numerically statistical distributions of sums of orbit coordinates,
viewed as independent random variables in the spirit of the Central Limit
Theorem, in weakly chaotic regimes associated with the excitation of the first
() and last () linear normal modes of the Fermi-Pasta-Ulam-
system under fixed boundary conditions. We show that at low energies
(), when the linear mode is excited, chaotic diffusion occurs
characterized by distributions that are well approximated for long times
() by a -Gaussian Quasi-Stationary State (QSS) with .
On the other hand, when the mode is excited at the same energy, diffusive
phenomena are \textit{absent} and the motion is quasi-periodic. In fact, as the
energy increases to , the distributions in the former case pass through
\textit{shorter} -Gaussian states and tend rapidly to a Gaussian (i.e.
) where equipartition sets in, while in the latter we need to
reach to E=4 to see a \textit{sudden transition} to Gaussian statistics,
without any passage through an intermediate QSS. This may be explained by
different energy localization properties and recurrence phenomena in the two
cases, supporting the view that when the energy is placed in the first mode
weak chaos and "sticky" dynamics lead to a more gradual process of energy
sharing, while strong chaos and equipartition appear abruptly when only the
last mode is initially excited.Comment: 12 pages, 3 figures, submitted for publication to International
Journal of Bifurcation and Chaos. In honor of Prof. Tassos Bountis' 60th
birthda
Delocalization of slowly damped eigenmodes on Anosov manifolds
We look at the properties of high frequency eigenmodes for the damped wave
equation on a compact manifold with an Anosov geodesic flow. We study
eigenmodes with spectral parameters which are asymptotically close enough to
the real axis. We prove that such modes cannot be completely localized on
subsets satisfying a condition of negative topological pressure. As an
application, one can deduce the existence of a "strip" of logarithmic size
without eigenvalues below the real axis under this dynamical assumption on the
set of undamped trajectories.Comment: 28 pages; compared with version 1, minor modifications, add two
reference
Generalised dimensions of measures on almost self-affine sets
We establish a generic formula for the generalised q-dimensions of measures
supported by almost self-affine sets, for all q>1. These q-dimensions may
exhibit phase transitions as q varies. We first consider general measures and
then specialise to Bernoulli and Gibbs measures. Our method involves estimating
expectations of moment expressions in terms of `multienergy' integrals which we
then bound using induction on families of trees
Invariant manifolds and equilibrium states for non-uniformly hyperbolic horseshoes
In this paper we consider horseshoes containing an orbit of homoclinic
tangency accumulated by periodic points. We prove a version of the Invariant
Manifolds Theorem, construct finite Markov partitions and use them to prove the
existence and uniqueness of equilibrium states associated to H\"older
continuous potentials.Comment: 33 pages, 6 figure
A review of linear response theory for general differentiable dynamical systems
The classical theory of linear response applies to statistical mechanics
close to equilibrium. Away from equilibrium, one may describe the microscopic
time evolution by a general differentiable dynamical system, identify
nonequilibrium steady states (NESS), and study how these vary under
perturbations of the dynamics. Remarkably, it turns out that for uniformly
hyperbolic dynamical systems (those satisfying the "chaotic hypothesis"), the
linear response away from equilibrium is very similar to the linear response
close to equilibrium: the Kramers-Kronig dispersion relations hold, and the
fluctuation-dispersion theorem survives in a modified form (which takes into
account the oscillations around the "attractor" corresponding to the NESS). If
the chaotic hypothesis does not hold, two new phenomena may arise. The first is
a violation of linear response in the sense that the NESS does not depend
differentiably on parameters (but this nondifferentiability may be hard to see
experimentally). The second phenomenon is a violation of the dispersion
relations: the susceptibility has singularities in the upper half complex
plane. These "acausal" singularities are actually due to "energy
nonconservation": for a small periodic perturbation of the system, the
amplitude of the linear response is arbitrarily large. This means that the NESS
of the dynamical system under study is not "inert" but can give energy to the
outside world. An "active" NESS of this sort is very different from an
equilibrium state, and it would be interesting to see what happens for active
states to the Gallavotti-Cohen fluctuation theorem.Comment: 19 pages, 2 figure
Analyticity of the SRB measure of a lattice of coupled Anosov diffeomorphisms of the torus
We consider the "thermodynamic limit"of a d-dimensional lattice of hyperbolic
dynamical systems on the 2-torus, interacting via weak and nearest neighbor
coupling. We prove that the SRB measure is analytic in the strength of the
coupling. The proof is based on symbolic dynamics techniques that allow us to
map the SRB measure into a Gibbs measure for a spin system on a
(d+1)-dimensional lattice. This Gibbs measure can be studied by an extension
(decimation) of the usual "cluster expansion" techniques.Comment: 28 pages, 2 figure
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