2,525 research outputs found
Stabilized Kuramoto-Sivashinsky system
A model consisting of a mixed Kuramoto - Sivashinsky - KdV equation, linearly
coupled to an extra linear dissipative equation, is proposed. The model applies
to the description of surface waves on multilayered liquid films. The extra
equation makes its possible to stabilize the zero solution in the model,
opening way to the existence of stable solitary pulses (SPs). Treating the
dissipation and instability-generating gain in the model as small
perturbations, we demonstrate that balance between them selects two
steady-state solitons from their continuous family existing in the absence of
the dissipation and gain. The may be stable, provided that the zero solution is
stable. The prediction is completely confirmed by direct simulations. If the
integration domain is not very large, some pulses are stable even when the zero
background is unstable. Stable bound states of two and three pulses are found
too. The work was supported, in a part, by a joint grant from the Israeli
Minsitry of Science and Technology and Japan Society for Promotion of Science.Comment: A text file in the latex format and 20 eps files with figures.
Physical Review E, in pres
On the shape of a D-brane bound state and its topology change
As is well known, coordinates of D-branes are described by NxN matrices. From
generic non-commuting matrices, it is difficult to extract physics, for
example, the shape of the distribution of positions of D-branes. To overcome
this problem, we generalize and elaborate on a simple prescription, first
introduced by Hotta, Nishimura and Tsuchiya, which determines the most
appropriate gauge to make the separation between diagonal components (D-brane
positions) and off-diagonal components. This prescription makes it possible to
extract the distribution of D-branes directly from matrices. We verify the
power of it by applying it to Monte-Carlo simulations for various lower
dimensional Yang-Mills matrix models. In particular, we detect the topology
change of the D-brane bound state for a phase transition of a matrix model; the
existence of this phase transition is expected from the gauge/gravity duality,
and the pattern of the topology change is strikingly similar to the counterpart
in the gravity side, the black hole/black string transition. We also propose a
criterion, based on the behavior of the off-diagonal components, which
determines when our prescription gives a sensible definition of D-brane
positions. We provide numerical evidence that our criterion is satisfied for
the typical distance between D-branes. For a supersymmetric model, positions of
D-branes can be defined even at a shorter distance scale. The behavior of
off-diagonal elements found in this analysis gives some support for previous
studies of D-brane bound states.Comment: 29 pages, 16 figure
Radial velocity eclipse mapping of exoplanets
Planetary rotation rates and obliquities provide information regarding the
history of planet formation, but have not yet been measured for evolved
extrasolar planets. Here we investigate the theoretical and observational
perspective of the Rossiter-McLauglin effect during secondary eclipse (RMse)
ingress and egress for transiting exoplanets. Near secondary eclipse, when the
planet passes behind the parent star, the star sequentially obscures light from
the approaching and receding parts of the rotating planetary surface. The
temporal block of light emerging from the approaching (blue-shifted) or
receding (red-shifted) parts of the planet causes a temporal distortion in the
planet's spectral line profiles resulting in an anomaly in the planet's radial
velocity curve. We demonstrate that the shape and the ratio of the
ingress-to-egress radial velocity amplitudes depends on the planetary
rotational rate, axial tilt and impact factor (i.e. sky-projected planet
spin-orbital alignment). In addition, line asymmetries originating from
different layers in the atmosphere of the planet could provide information
regarding zonal atmospheric winds and constraints on the hot spot shape for
giant irradiated exoplanets. The effect is expected to be most-pronounced at
near-infrared wavelengths, where the planet-to-star contrasts are large. We
create synthetic near-infrared, high-dispersion spectroscopic data and
demonstrate how the sky-projected spin axis orientation and equatorial velocity
of the planet can be estimated. We conclude that the RMse effect could be a
powerful method to measure exoplanet spins.Comment: 7 pages, 3 figures, 1 table, accepted for publication in ApJ on 2015
June 1
X-ray study of the double radio relic Abell 3376 with Suzaku
We present an X-ray spectral analysis of the nearby double radio relic merging cluster Abell 3376 ( z = 0.046), observed with the Suzaku XIS instrument. These deep (similar to 360 ks) observations cover the entire double relic region in the outskirts of the cluster. These diffuse radio structures are amongst the largest and arc-shaped relics observed in combination with large-scale X-ray shocks in a merging cluster. We confirm the presence of a stronger shock (M-W = 2.8 +/- 0.4) in the western direction at r similar to 26 0, derived from a temperature and surface brightness discontinuity across the radio relic. In the east, we detect a weaker shock ( M-E = 1.5 +/- 0.1) at r similar to 8', possibly associated with the "notch" of the eastern relic, and a cold front at r similar to 3'. Based on the shock speed calculated from the Mach numbers, we estimate that the dynamical age of the shock front is similar to 0.6 Gyr after core passage, indicating that Abell 3376 is still an evolving merging cluster and that the merger is taking place close to the plane of the sky. These results are consistent with simulations and optical and weak lensing studies from the literature
Studies of Phase Turbulence in the One Dimensional Complex Ginzburg-Landau Equation
The phase-turbulent (PT) regime for the one dimensional complex
Ginzburg-Landau equation (CGLE) is carefully studied, in the limit of large
systems and long integration times, using an efficient new integration scheme.
Particular attention is paid to solutions with a non-zero phase gradient. For
fixed control parameters, solutions with conserved average phase gradient
exist only for less than some upper limit. The transition from phase to
defect-turbulence happens when this limit becomes zero. A Lyapunov analysis
shows that the system becomes less and less chaotic for increasing values of
the phase gradient. For high values of the phase gradient a family of
non-chaotic solutions of the CGLE is found. These solutions consist of
spatially periodic or aperiodic waves travelling with constant velocity. They
typically have incommensurate velocities for phase and amplitude propagation,
showing thereby a novel type of quasiperiodic behavior. The main features of
these travelling wave solutions can be explained through a modified
Kuramoto-Sivashinsky equation that rules the phase dynamics of the CGLE in the
PT phase. The latter explains also the behavior of the maximal Lyapunov
exponents of chaotic solutions.Comment: 16 pages, LaTeX (Version 2.09), 10 Postscript-figures included,
submitted to Phys. Rev.
Non-Gaussian Velocity Distribution Function in a Vibrating Granular Bed
The simulation of granular particles in a quasi two-dimensional container
under the vertical vibration as an experimental accessible model for granular
gases is performed. The velocity distribution function obeys an
exponential-like function during the vibration and deviates from the
exponential function in free-cooling states. It is confirmed that this
exponential-like distribution function is produced by Coulomb's friction force.
A Langevin equation with Coulomb's friction is proposed to describe the motion
of such the system.Comment: 4 pages, 4 figures. to be published in Journal of Physical Society of
Japan Vol.73 No.
Pseudogap-less high T superconductivity in BaCoFeAs
The pseudogap state is one of the peculiarities of the cuprate high
temperature superconductors. Here we investigate its presence in
BaCoFeAs, a member of the pnictide family, with temperature
dependent scanning tunneling spectroscopy. We observe that for under, optimally
and overdoped systems the gap in the tunneling spectra always closes at the
bulk T, ruling out the presence of a pseudogap state. For the underdoped
case we observe superconducting gaps over large fields of view, setting a lower
limit of tens of nanometers on the length scale of possible phase separated
regions.Comment: 5 pages, 3 figure
Order-of-magnitude speedup for steady states and traveling waves via Stokes preconditioning in Channelflow and Openpipeflow
Steady states and traveling waves play a fundamental role in understanding
hydrodynamic problems. Even when unstable, these states provide the
bifurcation-theoretic explanation for the origin of the observed states. In
turbulent wall-bounded shear flows, these states have been hypothesized to be
saddle points organizing the trajectories within a chaotic attractor. These
states must be computed with Newton's method or one of its generalizations,
since time-integration cannot converge to unstable equilibria. The bottleneck
is the solution of linear systems involving the Jacobian of the Navier-Stokes
or Boussinesq equations. Originally such computations were carried out by
constructing and directly inverting the Jacobian, but this is unfeasible for
the matrices arising from three-dimensional hydrodynamic configurations in
large domains. A popular method is to seek states that are invariant under
numerical time integration. Surprisingly, equilibria may also be found by
seeking flows that are invariant under a single very large Backwards-Euler
Forwards-Euler timestep. We show that this method, called Stokes
preconditioning, is 10 to 50 times faster at computing steady states in plane
Couette flow and traveling waves in pipe flow. Moreover, it can be carried out
using Channelflow (by Gibson) and Openpipeflow (by Willis) without any changes
to these popular spectral codes. We explain the convergence rate as a function
of the integration period and Reynolds number by computing the full spectra of
the operators corresponding to the Jacobians of both methods.Comment: in Computational Modelling of Bifurcations and Instabilities in Fluid
Dynamics, ed. Alexander Gelfgat (Springer, 2018
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