1,433,848 research outputs found
Mean Field Theory of the Morphology Transition in Stochastic Diffusion Limited Growth
We propose a mean-field model for describing the averaged properties of a
class of stochastic diffusion-limited growth systems. We then show that this
model exhibits a morphology transition from a dense-branching structure with a
convex envelope to a dendritic one with an overall concave morphology. We have
also constructed an order parameter which describes the transition
quantitatively. The transition is shown to be continuous, which can be verified
by noting the non-existence of any hysteresis.Comment: 16 pages, 5 figure
Vector solitons in (2+1) dimensions
We address the problem of existence and stability of vector spatial solitons
formed by two incoherently interacting optical beams in bulk Kerr and saturable
media. We identify families of (2+1)-dimensional two-mode self-trapped beams,
with and without a topological charge, and describe their properties
analytically and numerically.Comment: 3 pages, 5 figures, submitted to Opt. Let
Spatiotemporal chaotic dynamics of solitons with internal structure in the presence of finite-width inhomogeneities
We present an analytical and numerical study of the Klein-Gordon kink-soliton
dynamics in inhomogeneous media. In particular, we study an external field that
is almost constant for the whole system but that changes its sign at the center
of coordinates and a localized impurity with finite-width. The soliton solution
of the Klein-Gordon-like equations is usually treated as a structureless
point-like particle. A richer dynamics is unveiled when the extended character
of the soliton is taken into account. We show that interesting spatiotemporal
phenomena appear when the structure of the soliton interacts with finite-width
inhomogeneities. We solve an inverse problem in order to have external
perturbations which are generic and topologically equivalent to well-known
bifurcation models and such that the stability problem can be solved exactly.
We also show the different quasiperiodic and chaotic motions the soliton
undergoes as a time-dependent force pumps energy into the traslational mode of
the kink and relate these dynamics with the excitation of the shape modes of
the soliton.Comment: 10 pages Revtex style article, 22 gziped postscript figures and 5 jpg
figure
Square patterns in Rayleigh-Benard convection with rotation about a vertical axis
We present experimental results for Rayleigh-Benard convection with rotation
about a vertical axis at dimensionless rotation rates in the range 0 to 250 and
upto 20% above the onset. Critical Rayleigh numbers and wavenumbers agree with
predictions of linear stability analysis. For rotation rates greater than 70
and close to onset, the patterns are cellular with local four-fold coordination
and differ from the theoretically expected Kuppers-Lortz unstable state. Stable
as well as intermittent defect-free square lattices exist over certain
parameter ranges. Over other ranges defects dynamically disrupt the lattice but
cellular flow and local four-fold coordination is maintained.Comment: ReVTeX, 4 pages, 7 eps figures include
Thermally Induced Fluctuations Below the Onset of Rayleigh-B\'enard Convection
We report quantitative experimental results for the intensity of
noise-induced fluctuations below the critical temperature difference for Rayleigh-B\'enard convection. The structure factor of the fluctuating
convection rolls is consistent with the expected rotational invariance of the
system. In agreement with predictions based on stochastic hydrodynamic
equations, the fluctuation intensity is found to be proportional to
where . The
noise power necessary to explain the measurements agrees with the prediction
for thermal noise. (WAC95-1)Comment: 13 pages of text and 4 Figures in a tar-compressed and uuencoded file
(using uufiles package). Detailed instructions of unpacking are include
Diffusion-induced vortex filament instability in 3-dimensional excitable media
We studied the stability of linear vortex filaments in 3-dimensional (3D)
excitable media, using both analytical and numerical methods. We found an
intrinsic 3D instability of vortex filaments that is diffusion-induced, and is
due to the slower diffusion of the inhibitor. This instability can result
either in a single helical filament or in chaotic scroll breakup, depending on
the specific kinetic model. When the 2-dimensional dynamics were in the chaotic
regime, filament instability occurred via on-off intermittency, a failure of
chaos synchronization in the third dimension.Comment: 5 pages, 5 figures, to appear in PRL (September, 1999
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