7,044 research outputs found

    The Role of Governmental Credit in Hemispheric Trade

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    Vortex Stability in a Trapped Bose Condensate

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    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

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    The Bogoliubov approximation is used to study the excited states of a dilute gas of NN atomic bosons trapped in an isotropic harmonic potential characterized by a frequency ω0\omega_0 and an oscillator length d0=/mω0d_0 = \sqrt{\hbar/m\omega_0}. The self-consistent static Bose condensate has macroscopic occupation number N01N_0 \gg 1, with nonuniform spherical condensate density n0(r)n_0(r); by assumption, the depletion of the condensate is small (NNN0N0N' \equiv N - N_0\ll N_0). The linearized density fluctuation operator ρ^\hat \rho' and velocity potential operator Φ^\hat\Phi' satisfy coupled equations that embody particle conservation and Bernoulli's theorem. For each angular momentum ll, introduction of quasiparticle operators yields coupled eigenvalue equations for the excited states; they can be expressed either in terms of Bogoliubov coherence amplitudes ul(r)u_l(r) and vl(r)v_l(r) that determine the appropriate linear combinations of particle operators, or in terms of hydrodynamic amplitudes ρl(r)\rho_l'(r) and Φl(r)\Phi_l'(r). The hydrodynamic picture suggests a simple variational approximation for l>0l >0 that provides an upper bound for the lowest eigenvalue ωl\omega_l and an estimate for the corresponding zero-temperature occupation number NlN_l'; 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

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    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

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    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
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