14,947 research outputs found
Achieving a BCS transition in an atomic Fermi gas
We consider a gas of cold fermionic atoms having two spin components with
interactions characterized by their s-wave scattering length . At positive
scattering length the atoms form weakly bound bosonic molecules which can be
evaporatively cooled to undergo Bose-Einstein condensation, whereas at negative
scattering length BCS pairing can take place. It is shown that, by
adiabatically tuning the scattering length from positive to negative
values, one may transform the molecular Bose-Einstein condensate into a highly
degenerate atomic Fermi gas, with the ratio of temperature to Fermi temperature
. The corresponding critical final value of
which leads to the BCS transition is found to be about one half, where is
the Fermi momentum.Comment: 4 pages, 1 figure. Phys. Rev. Lett. in pres
Quantum Entangled Dark Solitons Formed by Ultracold Atoms in Optical Lattices
Inspired by experiments on Bose-Einstein condensates in optical lattices, we
study the quantum evolution of dark soliton initial conditions in the context
of the Bose-Hubbard Hamiltonian. An extensive set of quantum measures is
utilized in our analysis, including von Neumann and generalized quantum
entropies, quantum depletion, and the pair correlation function. We find that
quantum effects cause the soliton to fill in. Moreover, soliton-soliton
collisions become inelastic, in strong contrast to the predictions of
mean-field theory. These features show that the lifetime and collision
properties of dark solitons in optical lattices provide clear signals of
quantum effects.Comment: 4 pages, 4 figures; version appearing in PRL, only minor changes from
v
An Empirical Analysis of Community Center Rents
This article is the winner of the Retail Real Estate manuscript prize (sponsored by the International Council of Shopping Centers) presented at the 2001 American Real Estate Society Annual Meeting. This study empirically models the determinants of community center rent. It employs a two-stage model that estimates center vacancy in the first stage and then includes predicted vacancy in a second stage demand model investigating endogenous and exogenous determinants of community center rent. The data includes information on maximum and minimum square foot rent for 118 community centers in Atlanta, Georgia. Maximum community center rent is highly correlated with a center’s predicted vacancy rate and location within the Atlanta area. Additionally, rent at both maximum and minimum levels is influenced by trade area purchasing power, property age and to a lesser extent by proximity to a regional mall, center design and neighborhood factors.
Review: emerging concepts in the pathogenesis of tendinopathy
Tendinopathy is a common clinical problem and has a significant disease burden attached, not only in terms of health care costs, but also for patients directly in terms of time off work and impact upon quality of life. Controversy surrounds the pathogenesis of tendinopathy, however the recent systematic analysis of the evidence has demonstrated that many of the claims of an absence of inflammation in tendinopathy were more based around belief than robust scientific data. This review is a summary of the emerging research in this topical area, with a particular focus on the role of neuronal regulation and inflammation in tendinopathy
Bose-Einstein condensates with attractive interactions on a ring
Considering an effectively attractive quasi-one-dimensional Bose-Einstein
condensate of atoms confined in a toroidal trap, we find that the system
undergoes a phase transition from a uniform to a localized state, as the
magnitude of the coupling constant increases. Both the mean-field
approximation, as well as a diagonalization scheme are used to attack the
problem.Comment: 4 pages, 4 ps figures, RevTex, typographic errors correcte
Dynamic behavior of an unsteady trubulent boundary layer
Experiments on an unsteady turbulent boundary layer are reported in which the upstream portion of the flow is steady (in the mean) and in the downstream region, the boundary layer sees a linearly decreasing free stream velocity. This velocity gradient oscillates in time, at frequencies ranging from zero to approximately the bursting frequency. For the small amplitude, the mean velocity and mean turbulence intensity profiles are unaffected by the oscillations. The amplitude of the periodic velocity component, although as much as 70% greater than that in the free stream for very low frequencies, becomes equal to that in the free stream at higher frequencies. At high frequencies, both the boundary layer thickness and the Reynolds stress distribution across the boundary layer become frozen. The behavior at higher amplitude is quite similar. At sufficiently high frequencies, the boundary layer thickness remains frozen at the mean value over the oscillation cycle, even though flow reverses near the wall during a part of the cycle
Formation of a Matter-Wave Bright Soliton
We report the production of matter-wave solitons in an ultracold lithium 7
gas. The effective interaction between atoms in a Bose-Einstein condensate is
tuned with a Feshbach resonance from repulsive to attractive before release in
a one-dimensional optical waveguide. Propagation of the soliton without
dispersion over a macroscopic distance of 1.1 mm is observed. A simple
theoretical model explains the stability region of the soliton. These
matter-wave solitons open fascinating possibilities for future applications in
coherent atom optics, atom interferometry and atom transport.Comment: 11 pages, 5 figure
Calculation of two-dimensional turbulent flow fields
Navier-Stokes equation solutions for two- dimensional turbulent flow fields of compressible viscous flui
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