12,768 research outputs found
The BCS-BEC Crossover
This chapter presents the crossover from the Bardeen-Cooper-Schrieffer (BCS)
state of weakly-correlated pairs of fermions to the Bose-Einstein condensation
(BEC) of diatomic molecules in the atomic Fermi gas. Our aim is to provide a
pedagogical review of the BCS-BEC crossover, with an emphasis on the basic
concepts, particularly those that are not generally known or are difficult to
find in the literature. We shall not attempt to give an exhaustive survey of
current research in the limited space here; where possible, we will direct the
reader to more extensive reviews.Comment: 19 pages, 6 figures. This article will be published as Chapter 9 in
"Quantum gas experiments - exploring many-body states", edited by P. Torma
and K. Sengstock, Imperial College Press, London, to be published 201
Microgravity fluid management in two-phase thermal systems
Initial studies have indicated that in comparison to an all liquid single phase system, a two-phase liquid/vapor thermal control system requires significantly lower pumping power, demonstrates more isothermal control characteristics, and allows greater operational flexibility in heat load placement. As a function of JSC's Work Package responsibility for thermal management of space station equipment external to the pressurized modules, prototype development programs were initiated on the Two-Phase Thermal Bus System (TBS) and the Space Erectable Radiator System (SERS). JSC currently has several programs underway to enhance the understanding of two-phase fluid flow characteristics. The objective of one of these programs (sponsored by the Microgravity Science and Applications Division at NASA-Headquarters) is to design, fabricate, and fly a two-phase flow regime mapping experiment in the Shuttle vehicle mid-deck. Another program, sponsored by OAST, involves the testing of a two-phase thermal transport loop aboard the KC-135 reduced gravity aircraft to identify system implications of pressure drop variation as a function of the flow quality and flow regime present in a representative thermal system
Three-body correlations in a two-dimensional SU(3) Fermi gas
We consider a three-component Fermi gas that has SU(3) symmetry and is
confined to two dimensions (2D). For realistic cold atomic gas experiments, we
show that the phase diagram of the quasi-2D system can be characterized using
two 2D scattering parameters: the scattering length and the effective range.
Unlike the case in 3D, we argue that three-body bound states (trimers) in the
quasi-2D system can be stable against three-body losses. Using a low-density
expansion coupled with a variational approach, we investigate the fate of such
trimers in the many-body system as the attractive interactions are decreased
(or, conversely, as the density of particles is increased). We find that
remnants of trimers can persist in the form of strong three-body correlations
in the weak-coupling (high-density) limit.Comment: 13 pages, 4 figure
Aerodynamic investigations of ventilated brake discs.
The heat dissipation and performance of a ventilated brake disc strongly depends
on the aerodynamic characteristics of the flow through the rotor passages. The
aim of this investigation was to provide an improved understanding of ventilated
brake rotor flow phenomena, with a view to improving heat dissipation, as well
as providing a measurement data set for validation of computational fluid
dynamics methods. The flow fields at the exit of four different brake rotor
geometries, rotated in free air, were measured using a five-hole pressure probe
and a hot-wire anemometry system. The principal measurements were taken using
two-component hot-wire techniques and were used to determine mean and unsteady
flow characteristics at the exit of the brake rotors. Using phase-locked data
processing, it was possible to reveal the spatial and temporal flow variation
within individual rotor passages. The effects of disc geometry and rotational
speed on the mean flow, passage turbulence intensity, and mass flow were
determined. The rotor exit jet and wake flow were clearly observed as
characterized by the passage geometry as well as definite regions of high and
low turbulence. The aerodynamic flow characteristics were found to be reasonably
independent of rotational speed but highly dependent upon rotor geometry
Why Medical (and Dermatologic) Practice Has Become So Convoluted: The Complexity/Convolutional/Obfuscatory Kleptocracies.
Consider dermatology (or medical) practice from the aspect of those who manage, and seek to glean a profit from, medical management corporations, including but not limited to third party payers. Although much of the complexity burden thrust upon doctors’ offices is borne by the offices and doctors, there is also much that is borne by the companies, and the entire process appears to make no sense whatsoever. How can the business professionals who run these outfits make such blunders? Let us approach this question by examining another industry: fast food franchising
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