7,215 research outputs found
Application of Dressing Method for Long Wave-Short Wave Resonance Interaction Equation
In this paper we investigate the application of Zakharov - Shabat dressing
method to (2+1) - dimensional long wave - short wave resonance interaction
equation (LSRI). Using this method we can construct the exact N - soliton
solution of this equation depending on arbitrary constants. It contains both
solutions which don't decay along N different directions in space infinity, and
"dromion" ones, or localized solutions that decay exponentially in all
directions.Comment: 8 page
Nonlinear Band Gap Transmission in Optical Waveguide Arrays
The effect of nonlinear transmission in coupled optical waveguide arrays is
theoretically investigated via numerical simulations on the corresponding model
equations. The realistic experimental setup is suggested injecting the beam in
a single boundary waveguide, linear refractive index of which () is larger
than one () of other identical waveguides in the array. Particularly, the
effect holds if , where is a linear coupling constant
between array waveguides, is a carrier wave frequency and is a
light velocity. Making numerical experiments in case of discrete nonlinear
Schr\"odinger equation it is shown that the energy transfers from the boundary
waveguide to the waveguide array above certain threshold intensity of the
injected beam. This effect is explained by means of the creation and
propagation of gap solitons in full analogy with the similar phenomenon of
nonlinear supratransmission [F. Geniet, J. Leon, PRL, {\bf 89}, 134102, (2002)]
in case of discrete sine-Gordon lattice.Comment: 4 pages, 6 figures. Phys. Rev. Lett. (in press
Surface losses and self-pumping effects in a long Josephson junction - a semi-analytical approach
The flux-flow dynamics in a long Josephson junction is studied both
analytically and numerically. A realistic model of the junction is considered
by taking into account a nonuniform current distribution, surface losses and
self-pumping effects. An approximate analytical solution of the modified
sine-Gordon equation is derived in the form of a unidirectional dense fluxon
train accompanied by two oppositely directed plasma waves. Next, some
macroscopic time-averaged quantities are calculated making possible to evaluate
the current-voltage characteristic of the junction. The results obtained by the
present method are compared with direct numerical simulations both for the
current-voltage characteristics and for the loss factor modulated spatially due
to the self-pumping. The comparison shows very good agreement for typical
junction parameters but indicates also some limitations of the method.Comment: 7 pages, 5 figure
Collective excitations of atomic Bose-Einstein condensates
We apply linear-response analysis of the Gross-Pitaevskii equation to obtain
the excitation frequencies of a Bose-Einstein condensate confined in a
time-averaged orbiting potential trap. Our calculated values are in excellent
agreement with those observed in a recent experiment.Comment: 11 pages, 2 Postscript figures, uses psbox.tex for automatic figure
inclusion. More info at http://amo.phy.gasou.edu/bec.htm
Harmonic generation of gravitational wave induced Alfven waves
Here we consider the nonlinear evolution of Alfven waves that have been
excited by gravitational waves from merging binary pulsars. We derive a wave
equation for strongly nonlinear and dispersive Alfven waves. Due to the weak
dispersion of the Alfven waves, significant wave steepening can occur, which in
turn implies strong harmonic generation. We find that the harmonic generation
is saturated due to dispersive effects, and use this to estimate the resulting
spectrum. Finally we discuss the possibility of observing the above process.Comment: 7 page
Two point correlations of a trapped interacting Bose gas at finite temperature
We develop a computationally tractable method for calculating correlation
functions of the finite temperature trapped Bose gas that includes the effects
of s-wave interactions. Our approach uses a classical field method to model the
low energy modes and treats the high energy modes using a Hartree-Fock
description. We present results of first and second order correlation
functions, in position and momentum space, for an experimentally realistic
system in the temperature range of to . We also characterize
the spatial coherence length of the system. Our theory should be applicable in
the critical region where experiments are now able to measure first and second
order correlations.Comment: 9 pages, 4 figure
Energy Flow Puzzle of Soliton Ratchets
We study the mechanism of directed energy transport for soliton ratchets. The
energy flow appears due to the progressive motion of a soliton (kink) which is
an energy carrier. However, the energy current formed by internal system
deformations (the total field momentum) is zero. We solve the underlying puzzle
by showing that the energy flow is realized via an {\it inhomogeneous} energy
exchange between the system and the external ac driving. Internal kink modes
are unambiguously shown to be crucial for that transport process to take place.
We also discuss effects of spatial discretization and combination of ac and dc
external drivings.Comment: 4 pages, 3 figures, submitted to PR
Discrete surface solitons in two dimensions
We investigate fundamental localized modes in 2D lattices with an edge
(surface). Interaction with the edge expands the stability area for ordinary
solitons, and induces a difference between perpendicular and parallel dipoles;
on the contrary, lattice vortices cannot exist too close to the border.
Furthermore, we show analytically and numerically that the edge stabilizes a
novel wave species, which is entirely unstable in the uniform lattice, namely,
a "horseshoe" soliton, consisting of 3 sites. Unstable horseshoes transform
themselves into a pair of ordinary solitons.Comment: 6 pages, 4 composite figure
Parametrically controlling solitary wave dynamics in modified Kortweg-de Vries equation
We demonstrate the control of solitary wave dynamics of modified Kortweg-de
Vries (MKdV) equation through the temporal variations of the distributed
coefficients. This is explicated through exact cnoidal wave and localized
soliton solutions of the MKdV equation with variable coefficients. The solitons
can be accelerated and their propagation can be manipulated by suitable
variations of the above parameters. In sharp contrast with nonlinear
Schr\"{o}dinger equation, the soliton amplitude and widths are time
independent.Comment: 4 pages, 5 eps figure
User needs, benefits and integration of robotic systems in a space station laboratory
The methodology, results and conclusions of the User Needs, Benefits, and Integration Study (UNBIS) of Robotic Systems in the Space Station Microgravity and Materials Processing Facility are summarized. Study goals include the determination of user requirements for robotics within the Space Station, United States Laboratory. Three experiments were selected to determine user needs and to allow detailed investigation of microgravity requirements. A NASTRAN analysis of Space Station response to robotic disturbances, and acceleration measurement of a standard industrial robot (Intelledex Model 660) resulted in selection of two ranges of low gravity manipulation: Level 1 (10-3 to 10-5 G at greater than 1 Hz.) and Level 2 (less than = 10-6 G at 0.1 Hz). This included an evaluation of microstepping methods for controlling stepper motors and concluded that an industrial robot actuator can perform milli-G motion without modification. Relative merits of end-effectors and manipulators were studied in order to determine their ability to perform a range of tasks related to the three low gravity experiments. An Effectivity Rating was established for evaluating these robotic system capabilities. Preliminary interface requirements were determined such that definition of requirements for an orbital flight demonstration experiment may be established
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