695 research outputs found
Maximal width of the separatrix chaotic layer
The main goal of the paper is to find the {\it absolute maximum} of the width
of the separatrix chaotic layer as function of the frequency of the
time-periodic perturbation of a one-dimensional Hamiltonian system possessing a
separatrix, which is one of the major unsolved problems in the theory of
separatrix chaos. For a given small amplitude of the perturbation, the width is
shown to possess sharp peaks in the range from logarithmically small to
moderate frequencies. These peaks are universal, being the consequence of the
involvement of the nonlinear resonance dynamics into the separatrix chaotic
motion. Developing further the approach introduced in the recent paper by
Soskin et al. ({\it PRE} {\bf 77}, 036221 (2008)), we derive leading-order
asymptotic expressions for the shape of the low-frequency peaks. The maxima of
the peaks, including in particular the {\it absolute maximum} of the width, are
proportional to the perturbation amplitude times either a logarithmically large
factor or a numerical, still typically large, factor, depending on the type of
system. Thus, our theory predicts that the maximal width of the chaotic layer
may be much larger than that predicted by former theories. The theory is
verified in simulations. An application to the facilitation of global chaos
onset is discussed.Comment: 18 pages, 16 figures, submitted to PR
Landau equations and asymptotic operation
The pinched/non-pinched classification of intersections of causal
singularities of propagators in Minkowski space is reconsidered in the context
of the theory of asymptotic operation as a first step towards extension of the
latter to non-Euclidean asymptotic regimes. A highly visual
distribution-theoretic technique of singular wave fronts is tailored to the
needs of the theory of Feynman diagrams. Besides a simple derivation of the
usual Landau equations in the case of the conventional singularities, the
technique naturally extends to other types of singularities e.g. due to linear
denominators in non-covariant gauges etc. As another application, the results
of Euclidean asymptotic operation are extended to a class of quasi-Euclidean
asymptotic regimes in Minkowski space.Comment: 15p PS (GSview), IJMP-A (accepted
On the unconstrained expansion of a spherical plasma cloud turning collisionless : case of a cloud generated by a nanometer dust grain impact on an uncharged target in space
Nano and micro meter sized dust particles travelling through the heliosphere
at several hundreds of km/s have been repeatedly detected by interplanetary
spacecraft. When such fast moving dust particles hit a solid target in space,
an expanding plasma cloud is formed through the vaporisation and ionisation of
the dust particles itself and part of the target material at and near the
impact point. Immediately after the impact the small and dense cloud is
dominated by collisions and the expansion can be described by fluid equations.
However, once the cloud has reached micro-m dimensions, the plasma may turn
collisionless and a kinetic description is required to describe the subsequent
expansion. In this paper we explore the late and possibly collisionless
spherically symmetric unconstrained expansion of a single ionized ion-electron
plasma using N-body simulations. Given the strong uncertainties concerning the
early hydrodynamic expansion, we assume that at the time of the transition to
the collisionless regime the cloud density and temperature are spatially
uniform. We do also neglect the role of the ambient plasma. This is a
reasonable assumption as long as the cloud density is substantially higher than
the ambient plasma density. In the case of clouds generated by fast
interplanetary dust grains hitting a solid target some 10^7 electrons and ions
are liberated and the in vacuum approximation is acceptable up to meter order
cloud dimensions. ..
Space-Time Complexity in Hamiltonian Dynamics
New notions of the complexity function C(epsilon;t,s) and entropy function
S(epsilon;t,s) are introduced to describe systems with nonzero or zero Lyapunov
exponents or systems that exhibit strong intermittent behavior with
``flights'', trappings, weak mixing, etc. The important part of the new notions
is the first appearance of epsilon-separation of initially close trajectories.
The complexity function is similar to the propagator p(t0,x0;t,x) with a
replacement of x by the natural lengths s of trajectories, and its introduction
does not assume of the space-time independence in the process of evolution of
the system. A special stress is done on the choice of variables and the
replacement t by eta=ln(t), s by xi=ln(s) makes it possible to consider
time-algebraic and space-algebraic complexity and some mixed cases. It is shown
that for typical cases the entropy function S(epsilon;xi,eta) possesses
invariants (alpha,beta) that describe the fractal dimensions of the space-time
structures of trajectories. The invariants (alpha,beta) can be linked to the
transport properties of the system, from one side, and to the Riemann
invariants for simple waves, from the other side. This analog provides a new
meaning for the transport exponent mu that can be considered as the speed of a
Riemann wave in the log-phase space of the log-space-time variables. Some other
applications of new notions are considered and numerical examples are
presented.Comment: 27 pages, 6 figure
Giant acceleration in slow-fast space-periodic Hamiltonian systems
Motion of an ensemble of particles in a space-periodic potential well with a
weak wave-like perturbation imposed is considered. We found that slow
oscillations of wavenumber of the perturbation lead to occurrence of directed
particle current. This current is amplifying with time due to giant
acceleration of some particles. It is shown that giant acceleration is linked
with the existence of resonant channels in phase space
The possibility of a metal insulator transition in antidot arrays induced by an external driving
It is shown that a family of models associated with the kicked Harper model
is relevant for cyclotron resonance experiments in an antidot array. For this
purpose a simplified model for electronic motion in a related model system in
presence of a magnetic field and an AC electric field is developed. In the
limit of strong magnetic field it reduces to a model similar to the kicked
Harper model. This model is studied numerically and is found to be extremely
sensitive to the strength of the electric field. In particular, as the strength
of the electric field is varied a metal -- insulator transition may be found.
The experimental conditions required for this transition are discussed.Comment: 6 files: kharp.tex, fig1.ps fig2.ps fi3.ps fig4.ps fig5.p
Quantized Orbits and Resonant Transport
A tight binding representation of the kicked Harper model is used to obtain
an integrable semiclassical Hamiltonian consisting of degenerate "quantized"
orbits. New orbits appear when renormalized Harper parameters cross integer
multiples of . Commensurability relations between the orbit frequencies
are shown to correlate with the emergence of accelerator modes in the classical
phase space of the original kicked problem. The signature of this resonant
transport is seen in both classical and quantum behavior. An important feature
of our analysis is the emergence of a natural scaling relating classical and
quantum couplings which is necessary for establishing correspondence.Comment: REVTEX document - 8 pages + 3 postscript figures. Submitted to
Phys.Rev.Let
Chaotic and pseudochaotic attractors of perturbed fractional oscillator
We consider a nonlinear oscillator with fractional derivative of the order
alpha. Perturbed by a periodic force, the system exhibits chaotic motion called
fractional chaotic attractor (FCA). The FCA is compared to the ``regular''
chaotic attractor. The properties of the FCA are discussed and the
``pseudochaotic'' case is demonstrated.Comment: 20 pages, 7 figure
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