8,252 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
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
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
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
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Effect of side chains on the dielectric properties of alkyl esters derived from palm kernel oil
Alkyl ester derivatives were synthesized from laboratory purified palm kernel oil. The steps in the synthesis involved transesterification of palm kernel oil to produce a methyl ester, followed by epoxidation and then the grafting of side chains by esterification with propionic and butyric anhydride. The dielectric and thermal properties of the ester derivatives were analyzed and compared with the methyl ester. The melting point of the ester derivatives were found to reduce with side chain attachment and antioxidant improved its thermal stability. The dielectric loss was dominated by mobile charged particles and the chemical modification appeared to increase the rate at which electric double layer was formed at the electrode-liquid interface. The esters possessed excellent breakdown strengths suggesting that the processing to optimize their physical properties did not have a negative influence on their electrical breakdown strength. This product may prove useful as an insulation fluid in Electrical Power Transformers
The influence of pig carcass processing of the efficacy of sponge swab sampling
The efficacy of different methods of sampling have been widely compared in the literature. Whilst it is recognised that swabbing and sponging leave a residual bacterial population, the levels that are left are difficult to evaluate and may be Influenced by other factors such as changes to the skin due to processing. In this Food Standards Agency funded study we have used bacterial bioluminescence as a visual marker of the presence of bacteria to evaluate the efficacy of different sampling methods on the removal of bacteria. Pig skin was spiked with a strain of E. coli or Salmonella Typhimurium made bioluminescent by the introduction of the luxCDABE genes from Photorhabdus luminescens on a plasmid construct. Samples were visualized under a light sensitive camera before and after sponging or swabbing and the levels of the bacteria removed evaluated. Methods compared were agitated sponging, using cellulose acetate sponges, against traditional sponging and a double-swabbing techmque, using cotton tipped bud swabs. Results indicate that damage to skin can lead to \u27hot spots\u27 of contamination, here residual bacteria are not easily removed by further physical abrasion
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
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
Long-range sound-mediated dark soliton interactions in trapped atomic condensates
A long-range soliton interaction is discussed whereby two or more dark
solitons interact in an inhomogeneous atomic condensate, modifying their
respective dynamics via the exchange of sound waves without ever coming into
direct contact. An idealized double well geometry is shown to yield perfect
energy transfer and complete periodic identity reversal of the two solitons.
Two experimentally relevant geometries are analyzed which should enable the
observation of this long-range interaction
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