26,475 research outputs found
Solitary waves of Bose-Einstein condensed atoms confined in finite rings
Motivated by recent progress in trapping Bose-Einstein condensed atoms in
toroidal potentials, we examine solitary-wave solutions of the nonlinear
Schr\"odinger equation subject to periodic boundary conditions. When the
circumference of the ring is much larger than the size of the wave, the density
profile is well approximated by that of an infinite ring, however the density
and the velocity of propagation cannot vanish simultaneously. When the size of
the ring becomes comparable to the size of the wave, the density variation
becomes sinusoidal and the velocity of propagation saturates to a constant
value.Comment: 6 pages, 2 figure
Measuring gravitational lens time delays using low-resolution radio monitoring observations
Obtaining lensing time delay measurements requires long-term monitoring
campaigns with a high enough resolution (< 1 arcsec) to separate the multiple
images. In the radio, a limited number of high-resolution interferometer arrays
make these observations difficult to schedule. To overcome this problem, we
propose a technique for measuring gravitational time delays which relies on
monitoring the total flux density with low-resolution but high-sensitivity
radio telescopes to follow the variation of the brighter image. This is then
used to trigger high-resolution observations in optimal numbers which then
reveal the variation in the fainter image. We present simulations to assess the
efficiency of this method together with a pilot project observing radio lens
systems with the Westerbork Synthesis Radio Telescope (WSRT) to trigger Very
Large Array (VLA) observations. This new method is promising for measuring time
delays because it uses relatively small amounts of time on high-resolution
telescopes. This will be important because instruments that have high
sensitivity but limited resolution, together with an optimum usage of followup
high-resolution observations from appropriate radio telescopes may in the
future be useful for gravitational lensing time delay measurements by means of
this new method.Comment: 10 pages, 7 figures, accepted by MNRA
Solitary-wave solutions in binary mixtures of Bose-Einstein condensates under periodic boundary conditions
We derive solitary-wave solutions within the mean-field approximation in
quasi-one-dimensional binary mixtures of Bose-Einstein condensates under
periodic boundary conditions, for the case of an effective repulsive
interatomic interaction. The particular gray-bright solutions that give the
global energy minima are determined. Their characteristics and the associated
dispersion relation are derived. In the case of weak coupling, we diagonalize
the Hamiltonian analytically to obtain the full excitation spectrum of
"quantum" solitary-wave solutions.Comment: 11 pages, 2 figure
Modelling the phase and chemical equilibria of aqueous solutions of alkanolamines and carbon dioxide using the SAFT-γ SW group contribution approach
p>All computational data for figures presented in the publication/p
Solitary waves in mixtures of Bose gases confined in annular traps
A two-component Bose-Einstein condensate that is confined in a
one-dimensional ring potential supports solitary-wave solutions, which we
evaluate analytically. The derived solutions are shown to be unique. The
corresponding dispersion relation that generalizes the case of a
single-component system shows interesting features.Comment: 4 pages, 1 figur
Solitary waves and yrast states in Bose-Einstein condensed gases of atoms
Considering a Bose-Einstein condensed gas confined in one dimension with
periodic boundary conditions, we demonstrate that, very generally,
solitary-wave and rotational excitations coincide. This exact equivalence
allows us to establish connections between a number of effects that are present
in these two problems, many of which have been studied using the mean-field
approximation.Comment: Revised version, where the generality of our arguments is presented
more clearl
New approach to the thermal Casimir force between real metals
The new approach to the theoretical description of the thermal Casimir force
between real metals is presented. It uses the plasma-like dielectric
permittivity that takes into account the interband transitions of core
electrons. This permittivity precisely satisfies the Kramers-Kronig relations.
The respective Casimir entropy is positive and vanishes at zero temperature in
accordance with the Nernst heat theorem. The physical reasons why the Drude
dielectric function, when substituted in the Lifshitz formula, is inconsistent
with electrodynamics are elucidated. The proposed approach is the single one
consistent with all measurements of the Casimir force performed up to date. The
application of this approach to metal-type semiconductors is considered.Comment: 14 pages, 6 figures. Proceedings of QFEXT07, to appear in J. Phys.
Magnetic levitation on a type-I superconductor as a practical demonstration experiment for students
We describe and discuss an experimental set-up which allows undergraduate and
graduate students to view and study magnetic levitation on a type-I
superconductor. The demonstration can be repeated many times using one readily
available 25 liter liquid helium dewar. We study the equilibrium position of a
magnet that levitates over a lead bowl immersed in a liquid hand-held helium
cryostat. We combine the measurement of the position of the magnet with simple
analytical calculations. This provides a vivid visualization of magnetic
levitation from the balance between pure flux expulsion and gravitation. The
experiment contrasts and illustrates the case of magnetic levitation with high
temperature type-II superconductors using liquid nitrogen, where levitation
results from partial flux expulsion and vortex physics
Kramers-Kronig relations for plasma-like permittivities and the Casimir force
The Kramers-Kronig relations are derived for the permittivity of the usual
plasma model which neglects dissipation and of a generalized model which takes
into account the interband transitions. The generalized plasma model is shown
to be consistent with all precision experiments on the measurement of the
Casimir force.Comment: 9 pages, 2 figures, 1 table; to appear in J. Phys. A: Math. Theor.
(fast track communication
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