256 research outputs found
Instabilities of wave function monopoles in Bose-Einstein condensates
We present analytic and numerical results for a class of monopole solutions
to the two-component Gross-Pitaevski equation for a two-species Bose condensate
in an effectively two-dimensional trap. We exhibit dynamical instabilities
involving vortex production as one species pours through another, from which we
conclude that the sub-optical sharpness of potentials exerted by matter waves
makes condensates ideal tools for manipulating condensates. We also show that
there are two equally valid but drastically different hydrodynamic descriptions
of a two-component condensate, and illustrate how different phenomena may
appear simpler in each.Comment: 4 pages, 9 figures (compressed figures become legible when zoomed or
when paper is actually printed
Low noise amplication of an optically carried microwave signal: application to atom interferometry
In this paper, we report a new scheme to amplify a microwave signal carried
on a laser light at =852nm. The amplification is done via a
semiconductor tapered amplifier and this scheme is used to drive stimulated
Raman transitions in an atom interferometer. Sideband generation in the
amplifier, due to self-phase and amplitude modulation, is investigated and
characterized. We also demonstrate that the amplifier does not induce any
significant phase-noise on the beating signal. Finally, the degradation of the
performances of the interferometer due to the amplification process is shown to
be negligible
Soliton Squeezing in a Mach-Zehnder Fiber Interferometer
A new scheme for generating amplitude squeezed light by means of soliton
self-phase modulation is experimentally demonstrated. By injecting 180-fs
pulses into an equivalent Mach-Zehnder fiber interferometer, a maximum noise
reduction of dB is obtained ( dB when corrected for
losses). The dependence of noise reduction on the interferometer splitting
ratio and fiber length is studied in detail.Comment: 5 pages, 4 figure
Lyapunov Potential Description for Laser Dynamics
We describe the dynamical behavior of both class A and class B lasers in
terms of a Lyapunov potential. For class A lasers we use the potential to
analyze both deterministic and stochastic dynamics. In the stochastic case it
is found that the phase of the electric field drifts with time in the steady
state. For class B lasers, the potential obtained is valid in the absence of
noise. In this case, a general expression relating the period of the relaxation
oscillations to the potential is found. We have included in this expression the
terms corresponding to the gain saturation and the mean value of the
spontaneously emitted power, which were not considered previously. The validity
of this expression is also discussed and a semi-empirical relation giving the
period of the relaxation oscillations far from the stationary state is proposed
and checked against numerical simulations.Comment: 13 pages (including 7 figures) LaTeX file. To appear in Phys Rev.A
(June 1999
Exact dipole solitary wave solution in metamaterials with higher-order dispersion
We present an exact dipole solitary wave solution in a mutual modulation form of bright and dark
solitons for a higher-order nonlinear Schrödinger equation with third- and fourth-order dispersion
in metamaterials (MMs) using an ansatz method. Based on the Drude model, the formation
conditions, existence regions and propagation properties are discussed. The results reveal that the
solitary wave may exist in a few parameter regions of MMs, different from those in optical fibres, and
its propagation properties can be controlled by adjusting the frequency of incident waves in each
existence region
Identifying Heavy Goods Vehicle Driving Styles in the United Kingdom
Although driving behavior has been largely studied amongst private motor vehicles drivers, the literature addressing heavy goods vehicle (HGV) drivers is scarce. Identifying the existing groups of driving stereotypes and their proportions enables researchers, companies, and policy makers to establish group-specific strategies to improve safety and economy. In addition, insight into driving styles can help predict drivers' reactions and therefore enable the modeling of interactions between vehicles and the possible obstacles encountered on a journey. Consequently, there are also contributions to the research and development of autonomous vehicles and smart roads. In this paper, our interest lies in investigating driving behavior within the HGV community in the United Kingdom (U.K.). We conduct analysis of a telematics dataset containing the incident information on 21 193 HGV drivers across the U.K. We are interested in answering two research questions: 1) What groups of behavior are we able to uncover? 2) How do these groups complement current findings in the literature? To answer these questions, we apply a two-stage data analysis methodology involving consensus clustering and ensemble classification to the dataset. Through the analysis, eight patterns of behavior are uncovered. It is also observed that although our findings have similarities to those from previous work on driving behavior, further knowledge is obtained, such as extra patterns and driving traits arising from vehicle and road characteristics
Distinguishing WH and WBBbar production at the Fermilab Tevatron
The production of a Higgs boson in association with a W-boson is the most
likely process for the discovery of a light Higgs at the Fermilab Tevatron.
Since it decays primarily to b-quark pairs, the principal background for this
associated Higgs production process is WBBbar, where the BBbar pair comes from
the splitting of an off mass shell gluon. In this paper we investigate whether
the spin angular correlations of the final state particles can be used to
separate the Higgs signal from the WBBbar background. We develop a general
numerical technique which allows one to find a spin basis optimized according
to a given criterion, and also give a new algorithm for reconstructing the W
longitudinal momentum which is suitable for the WH and WBBbar processes.Comment: latex, 12 pages, 19 postscript figure
Spectral Dependence of Polarized Radiation due to Spatial Correlations
We study the polarization of light emitted by spatially correlated sources.
We show that in general polarization acquires nontrivial spectral dependence
due to spatial correlations. The spectral dependence is found to be absent only
for a special class of sources where the correlation length scales as the
wavelength of light. We further study the cross correlations between two
spatially distinct points that are generated due to propagation. It is found
that such cross correlation leads to sufficiently strong spectral dependence of
polarization which can be measured experimentally.Comment: 5 pages, 4 figure
Stationary solutions of the one-dimensional nonlinear Schroedinger equation: I. Case of repulsive nonlinearity
All stationary solutions to the one-dimensional nonlinear Schroedinger
equation under box and periodic boundary conditions are presented in analytic
form. We consider the case of repulsive nonlinearity; in a companion paper we
treat the attractive case. Our solutions take the form of stationary trains of
dark or grey density-notch solitons. Real stationary states are in one-to-one
correspondence with those of the linear Schr\"odinger equation. Complex
stationary states are uniquely nonlinear, nodeless, and symmetry-breaking. Our
solutions apply to many physical contexts, including the Bose-Einstein
condensate and optical pulses in fibers.Comment: 11 pages, 7 figures -- revised versio
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