113,920 research outputs found
Synchronization of Chaotic Maps by Symmetric Common Noise
Synchronization of identical chaotic systems subjected to common noise has
been the subject of recent research. Studies on several chaotic systems have
shown that, the synchronization is actually induced by the non-zero mean of the
noise, and symmetric noise with zero-mean cannot lead to synchronization. Here
it is presented that synchronization can be achieved by {\sl zero-mean} noise
in some chaotic maps with large convergence regions.Comment: 5 pages, 4 figure
Dynamics of a hole in the large--U Hubbard model: a Feynman diagram approach
We study the dynamics of a single hole in an otherwise half--filled
two--dimensional Hubbard model by introducing a nonlocal Bogolyubov
transformation in the antiferromagnetic state. This allows us to rewrite the
Hamiltonian in a form that makes a separation between high--energy processes
(involving double--occupancy) and low--energy physics possible. A diagrammatic
scheme is developped that allows for a systematic study of the different
processes delocalizing a carrier in the antiferromagnetic state. In particular,
the so--called Trugman process, important if transverse spin fluctuations are
neglected, is studied and is shown to be dominated by the leading vertex
corrections. We analyze the dynamics of a single hole both in the Ising limit
and with spin fluctuations. The results are compared with previous theories as
well as with recent exact small--cluster calculations, and we find good
agreement. The formalism establishes a link between weak and strong coupling
methodologies.Comment: Latex 34pages, Orsay Preprint, submitted to Phys. Rev.
Non-linear Plasma Wake Growth of Electron Holes
An object's wake in a plasma with small Debye length that drifts
\emph{across} the magnetic field is subject to electrostatic electron
instabilities. Such situations include, for example, the moon in the solar wind
wake and probes in magnetized laboratory plasmas. The instability drive
mechanism can equivalently be considered drift down the potential-energy
gradient or drift up the density-gradient. The gradients arise because the
plasma wake has a region of depressed density and electrostatic potential into
which ions are attracted along the field. The non-linear consequences of the
instability are analysed in this paper. At physical ratios of electron to ion
mass, neither linear nor quasilinear treatment can explain the observation of
large-amplitude perturbations that disrupt the ion streams well before they
become ion-ion unstable. We show here, however, that electron holes, once
formed, continue to grow, driven by the drift mechanism, and if they remain in
the wake may reach a maximum non-linearly stable size, beyond which their
uncontrolled growth disrupts the ions. The hole growth calculations provide a
quantitative prediction of hole profile and size evolution. Hole growth appears
to explain the observations of recent particle-in-cell simulations
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