2,764 research outputs found
Vortex Stability in a Trapped Bose Condensate
A vortex in a trapped Bose-Einstein condensate can experience at least two
types of instabilities. (1). Macroscopic hydrodynamic motion of the vortex core
relative to the center of mass of the condensate requires some process to
dissipate energy. (2). Microscopic small-amplitude normal modes can also induce
an instability. In one specific example, the vortex core again moves relative
to the overall center of mass, suggesting that there may be only a single
physical mechanism.Comment: Latex, 6 pages, no figures, to appear in Proceedings of International
Symposium on Quantum Fluids and Solids, 1998 (J. Low Temp. Phys.
Excited states of a static dilute spherical Bose condensate in a trap
The Bogoliubov approximation is used to study the excited states of a dilute
gas of atomic bosons trapped in an isotropic harmonic potential
characterized by a frequency and an oscillator length . The self-consistent static Bose condensate has
macroscopic occupation number , with nonuniform spherical condensate
density ; by assumption, the depletion of the condensate is small (). The linearized density fluctuation operator and velocity potential operator satisfy coupled equations
that embody particle conservation and Bernoulli's theorem. For each angular
momentum , introduction of quasiparticle operators yields coupled eigenvalue
equations for the excited states; they can be expressed either in terms of
Bogoliubov coherence amplitudes and that determine the
appropriate linear combinations of particle operators, or in terms of
hydrodynamic amplitudes and . The hydrodynamic picture
suggests a simple variational approximation for that provides an upper
bound for the lowest eigenvalue and an estimate for the
corresponding zero-temperature occupation number ; both expressions
closely resemble those for a uniform bulk Bose condensate.Comment: 5 pages, RevTeX, contributed paper accepted for Low Temperature
Conference, LT21, August, 199
Finite temperature analysis of a quasi2D dipolar gas
We present finite temperature analysis of a quasi2D dipolar gas. To do this,
we use the Hartree Fock Bogoliubov method within the Popov approximation. This
formalism is a set of non-local equations containing the dipole-dipole
interaction and the condensate and thermal correlation functions, which are
solved self-consistently. We detail the numerical method used to implement the
scheme. We present density profiles for a finite temperature dipolar gas in
quasi2D, and compare these results to a gas with zero-range interactions.
Additionally, we analyze the excitation spectrum and study the impact of the
thermal exchange
A communications system for the terminal area effectiveness program
The terminal area effectiveness program has the broad scope of evaluating air traffic control (ATC) procedures. One area of interest is pilot acceptance of complex ATC procedures. A means to measure this acceptance is described by studying the impact on pilots of meeting the ATC procedural requirements. The concept-testing system configuration, its operation, and its performance are discussed
Superfluid Vortex Dynamics on Planar Sectors and Cones
We study the dynamics of vortices formed in a superfluid film adsorbed on the
curved two-dimensional surface of a cone. To this aim, we observe that a cone
can be unrolled to a sector on a plane with periodic boundary conditions on the
straight sides. The sector can then be mapped conformally to the whole plane,
leading to the relevant stream function. In this way, we show that a superfluid
vortex on the cone precesses uniformly at fixed distance from the apex. The
stream function also yields directly the interaction energy of two vortices on
the cone. We then study the vortex dynamics on unbounded and bounded cones. In
suitable limits, we recover the known results for dynamics on cylinders and
planar annuli.Comment: 10 pages, 8 figure
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