3,960 research outputs found
Nonlinear broadening of the plasmon linewidth in a graphene stripe
In contrast to semiconductor structures, the experimentally observed plasma
resonances in graphene show an asymmetrical and rather broad linewidth. We show
that this can be explained by the linear electron energy dispersion in this
material and is related to the violation of the generalized Kohn theorem in
graphene.Comment: 5 pages, 3 figure
Dynamical clustering in oscillator ensembles with time-dependent interactions
We consider an ensemble of coupled oscillators whose individual states, in
addition to the phase, are characterized by an internal variable with
autonomous evolution. The time scale of this evolution is different for each
oscillator, so that the ensemble is inhomogeneous with respect to the internal
variable. Interactions between oscillators depend on this variable and thus
vary with time. We show that as the inhomogeneity of time scales in the
internal evolution grows, the system undergoes a critical transition between
ordered and incoherent states. This transition is mediated by a regime of
dynamical clustering, where the ensemble recurrently splits into groups formed
by varying subpopulations.Comment: 4 pages, 3 figure
Nonequilibrium pattern formation in chiral Langmuir monolayers with transmembrane flows
Nonequilibrium Langmuir monolayers including a fraction of chiral molecules
and subject to transmembrane flow are considered. The flow induces coherent
collective precession of chiral molecules. Our theoretical study shows that
splay interactions in this system lead to spatial redistribution of chiral
molecules and formation of spiral waves and target patterns observed in
experiments
Noise-induced breakdown of coherent collective motion in swarms
We consider swarms formed by populations of self-propelled particles with
attractive long-range interactions. These swarms represent multistable
dynamical systems and can be found either in coherent traveling states or in an
incoherent oscillatory state where translational motion of the entire swarm is
absent. Under increasing the noise intensity, the coherent traveling state of
the swarms is destroyed and an abrupt transition to the oscillatory state takes
place.Comment: 6 pages, 5 figures; to appear in Phys. Rev.
On complete integrability of the Mikhailov-Novikov-Wang system
We obtain compatible Hamiltonian and symplectic structure for a new
two-component fifth-order integrable system recently found by Mikhailov,
Novikov and Wang (arXiv:0712.1972), and show that this system possesses a
hereditary recursion operator and infinitely many commuting symmetries and
conservation laws, as well as infinitely many compatible Hamiltonian and
symplectic structures, and is therefore completely integrable. The system in
question admits a reduction to the Kaup--Kupershmidt equation.Comment: 5 pages, no figure
Zero curvature representation for a new fifth-order integrable system
In this brief note we present a zero-curvature representation for one of the
new integrable system found by Mikhailov, Novikov and Wang in nlin.SI/0601046.Comment: 2 pages, LaTeX 2e, no figure
Plane wave limit of local conserved charges
We study the plane wave limit of the Backlund transformations for the
classical string in AdS space times a sphere and obtain an explicit expression
for the local conserved charges. We show that the Pohlmeyer charges become in
the plane wave limit the local integrals of motion of the free massive field.
This fixes the coefficients in the expansion of the anomalous dimension as the
sum of the Pohlmeyer charges.Comment: v2: added explanation
Magnetic fields near the peripheries of galactic discs
Magnetic fields are observed beyond the peripheries of optically detected
galactic discs, while numerical models of their origin and the typical
magnitudes are still absent. Previously, studies of galactic dynamo have
avoided considering the peripheries of galactic discs because of the very
limited (though gradually growing) knowledge about the local properties of the
interstellar medium. Here we investigate the possibility that magnetic fields
can be generated in the outskirts of discs, taking the Milky Way as an example.
We consider a simple evolving galactic dynamo model in the "no-z" formulation,
applicable to peripheral regions of galaxies, for various assumptions about the
radial and vertical profiles of the ionized gas disc. The magnetic field may
grow as galaxies evolve, even in the more remote parts of the galactic disc,
out to radii of 15 to 30 kpc, becoming substantial after times of about 10 Gyr.
This result depends weakly on the adopted distributions of the half thickness
and surface density of the ionized gas component. The model is robust to
changes in the amplitude of the initial field and the position of its maximum
strength. The magnetic field in the remote parts of the galactic disc could be
generated in situ from a seed field by local dynamo action. Another possibility
is field production in the central regions of a galaxy, followed by transport
to the disc's periphery by the joint action of the dynamo and turbulent
diffusivity. Our results demonstrate the possibilities for the appearance and
strengthening of magnetic fields at the peripheries of disc galaxies and
emphasize the need for observational tests with new and anticipated radio
telescopes (LOFAR, MWA, and SKA).Comment: 8 pages, 5 figure
Noise-Induced Transition from Translational to Rotational Motion of Swarms
We consider a model of active Brownian agents interacting via a harmonic
attractive potential in a two-dimensional system in the presence of noise. By
numerical simulations, we show that this model possesses a noise-induced
transition characterized by the breakdown of translational motion and the onset
of swarm rotation as the noise intensity is increased. Statistical properties
of swarm dynamics in the weak noise limit are further analytically
investigated.Comment: 7 pages, 7 figure
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