743 research outputs found
Bouncing droplets on a billiard table
In a set of experiments, Couder et. al. demonstrate that an oscillating fluid
bed may propagate a bouncing droplet through the guidance of the surface waves.
We present a dynamical systems model, in the form of an iterative map, for a
droplet on an oscillating bath. We examine the droplet bifurcation from
bouncing to walking, and prescribe general requirements for the surface wave to
support stable walking states. We show that in addition to walking, there is a
region of large forcing that may support the chaotic bouncing of the droplet.
Using the map, we then investigate the droplet trajectories for two different
wave responses in a square (billiard ball) domain. We show that for waves which
are quickly damped in space, the long time trajectories in a square domain are
either non-periodic dense curves, or approach a quasiperiodic orbit. In
contrast, for waves which extend over many wavelengths, at low forcing,
trajectories tend to approach an array of circular attracting sets. As the
forcing increases, the attracting sets break down and the droplet travels
throughout space
Flux-splitting schemes for parabolic problems
To solve numerically boundary value problems for parabolic equations with
mixed derivatives, the construction of difference schemes with prescribed
quality faces essential difficulties. In parabolic problems, some possibilities
are associated with the transition to a new formulation of the problem, where
the fluxes (derivatives with respect to a spatial direction) are treated as
unknown quantities. In this case, the original problem is rewritten in the form
of a boundary value problem for the system of equations in the fluxes. This
work deals with studying schemes with weights for parabolic equations written
in the flux coordinates. Unconditionally stable flux locally one-dimensional
schemes of the first and second order of approximation in time are constructed
for parabolic equations without mixed derivatives. A peculiarity of the system
of equations written in flux variables for equations with mixed derivatives is
that there do exist coupled terms with time derivatives
Self-Similar Solutions to a Density-Dependent Reaction-Diffusion Model
In this paper, we investigated a density-dependent reaction-diffusion
equation, . This equation is known as the
extension of the Fisher or Kolmogoroff-Petrovsky-Piscounoff equation which is
widely used in the population dynamics, combustion theory and plasma physics.
By employing the suitable transformation, this equation was mapped to the
anomalous diffusion equation where the nonlinear reaction term was eliminated.
Due to its simpler form, some exact self-similar solutions with the compact
support have been obtained. The solutions, evolving from an initial state,
converge to the usual traveling wave at a certain transition time. Hence, it is
quite clear the connection between the self-similar solution and the traveling
wave solution from these results. Moreover, the solutions were found in the
manner that either propagates to the right or propagates to the left.
Furthermore, the two solutions form a symmetric solution, expanding in both
directions. The application on the spatiotemporal pattern formation in
biological population has been mainly focused.Comment: 5 pages, 2 figures, accepted by Phys. Rev.
Probing the hydrogen melting line at high pressures by dynamic compression
We investigate the capabilities of dynamic compression by intense heavy ion beams to yield information about the high pressure phases of hydrogen. Employing ab initio simulations and experimental data, a new wide range equation of state for hydrogen is constructed. The results show that the melting line up to its maximum as well as the transition from molecular fluids to fully ionized plasmas can be tested with the beam parameters soon to be available. We demonstrate that x-ray scattering can distinguish between phases and dissociation states
Regularized extremal shift in problems of stable control
We discuss a technical approach, based on the method of regularized extremal shift (RES), intended to help solve problems of stable control of uncertain dynamical systems. Our goal is to demonstrate the essence and abilities of the RES technique; for this purpose we construct feedback controller for approximate tracking a prescribed trajectory of an inaccurately observed system described by a parabolic equation. The controller is "resource-saving" in a sense that control resource spent for approximate tracking do not exceed those needed for tracking in an "ideal" situation where the current values of the input disturbance are fully observable. © 2013 IFIP International Federation for Information Processing.German Sci. Found. (DFG) Eur. Sci. Found. (ESF);Natl. Inst. Res. Comput. Sci. Control France (INRIA);DFG Research Center MATHEON;Weierstrass Institute for Applied Analysis and Stochastics (WIAS);European Patent Offic
Conditional Lie-B\"acklund symmetry and reduction of evolution equations.
We suggest a generalization of the notion of invariance of a given partial
differential equation with respect to Lie-B\"acklund vector field. Such
generalization proves to be effective and enables us to construct principally
new Ans\"atze reducing evolution-type equations to several ordinary
differential equations. In the framework of the said generalization we obtain
principally new reductions of a number of nonlinear heat conductivity equations
with poor Lie symmetry and obtain their exact solutions.
It is shown that these solutions can not be constructed by means of the
symmetry reduction procedure.Comment: 12 pages, latex, needs amssymb., to appear in the "Journal of Physics
A: Mathematical and General" (1995
Flame fronts in Supernovae Ia and their pulsational stability
The structure of the deflagration burning front in type Ia supernovae is
considered. The parameters of the flame are obtained: its normal velocity and
thickness. The results are in good agreement with the previous works of
different authors. The problem of pulsation instability of the flame, subject
to plane perturbations, is studied. First, with the artificial system with
switched-off hydrodynamics the possibility of secondary reactions to stabilize
the front is shown. Second, with account of hydrodynamics, realistic EOS and
thermal conduction we can obtain pulsations when Zeldovich number was
artificially increased. The critical Zeldovich numbers are presented. These
results show the stability of the flame in type Ia supernovae against
pulsations because its effective Zeldovich number is small.Comment: 12 pages, 11 figure
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