287 research outputs found
Interaction of Vortices in Complex Vector Field and Stability of a ``Vortex Molecule''
We consider interaction of vortices in the vector complex Ginzburg--Landau
equation (CVGLE). In the limit of small field coupling, it is found
analytically that the interaction between well-separated defects in two
different fields is long-range, in contrast to interaction between defects in
the same field which falls off exponentially. In a certain region of parameters
of CVGLE, we find stable rotating bound states of two defects -- a ``vortex
molecule".Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let
Model of coarsening and vortex formation in vibrated granular rods
Neicu and Kudrolli observed experimentally spontaneous formation of the
long-range orientational order and large-scale vortices in a system of vibrated
macroscopic rods. We propose a phenomenological theory of this phenomenon,
based on a coupled system of equations for local rods density and tilt. The
density evolution is described by modified Cahn-Hilliard equation, while the
tilt is described by the Ginzburg-Landau type equation. Our analysis shows
that, in accordance to the Cahn-Hilliard dynamics, the islands of the ordered
phase appear spontaneously and grow due to coarsening. The generic vortex
solutions of the Ginzburg-Landau equation for the tilt correspond to the
vortical motion of the rods around the cores which are located near the centers
of the islands.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let
Nucleation of Spontaneous Vortices in Trapped Fermi Gases Undergoing a BCS-BEC Crossover
We study the spontaneous formation of vortices during the superfluid
condensation in a trapped fermionic gas subjected to a rapid thermal quench via
evaporative cooling. Our work is based on the numerical solution of the time
dependent crossover Ginzburg-Landau equation coupled to the heat diffusion
equation. We quantify the evolution of condensate density and vortex length as
a function of a crossover phase parameter from BCS to BEC. The more interesting
phenomena occur somewhat nearer to the BEC regime and should be experimentally
observable; during the propagation of the cold front, the increase in
condensate density leads to the formation of supercurrents towards the center
of the condensate as well as possible condensate volume oscillations.Comment: 5 pages, 3 figure
Nonequilibrium dislocation dynamics and instability of driven vortex lattices in two dimensions
We consider dislocations in a vortex lattice that is driven in a
two-dimensional superconductor with random impurities. The structure and
dynamics of dislocations is studied in this genuine nonequilibrium situation on
the basis of a coarse-grained equation of motion for the displacement field.
The presence of dislocations leads to a characteristic anisotropic distortion
of the vortex density that is controlled by a Kardar-Parisi-Zhang nonlinearity
in the coarse-grained equation of motion. This nonlinearity also implies a
screening of the interaction between dislocations and thereby an instability of
the vortex lattice to the proliferation of free dislocations.Comment: published version with minor correction
Theory of pattern-formation of metallic microparticles in poorly conducting liquid
We develop continuum theory of self-assembly and pattern formation in
metallic microparticles immersed in a poorly conducting liquid in DC electric
field. The theory is formulated in terms of two conservation laws for the
densities of immobile particles (precipitate) and bouncing particles (gas)
coupled to the Navier-Stokes equation for the liquid. This theory successfully
reproduces correct topology of the phase diagram and primary patterns observed
in the experiment [Sapozhnikov et al, Phys. Rev. Lett. v. 90, 114301 (2003)]:
static crystals and honeycombs and dynamic pulsating rings and rotating
multi-petal vortices.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let
Doppler Effect of Nonlinear Waves and Superspirals in Oscillatory Media
Nonlinear waves emitted from a moving source are studied. A meandering spiral
in a reaction-diffusion medium provides an example, where waves originate from
a source exhibiting a back-and-forth movement in radial direction. The periodic
motion of the source induces a Doppler effect that causes a modulation in
wavelength and amplitude of the waves (``superspiral''). Using the complex
Ginzburg-Landau equation, we show that waves subject to a convective Eckhaus
instability can exhibit monotonous growth or decay as well as saturation of
these modulations away from the source depending on the perturbation frequency.
Our findings allow a consistent interpretation of recent experimental
observations concerning superspirals and their decay to spatio-temporal chaos.Comment: 4 pages, 4 figure
- …