2,349 research outputs found
The Projected Gross-Pitaevskii Equation for harmonically confined Bose gases
We extend the Projected Gross Pitaevskii equation formalism of Davis et al.
[Phys. Rev. Lett. \bf{87}, 160402 (2001)] to the experimentally relevant case
of harmonic potentials. We outline a robust and accurate numerical scheme that
can efficiently simulate this system. We apply this method to investigate the
equilibrium properties of a harmonically trapped three-dimensional Bose gas at
finite temperature, and consider the dependence of condensate fraction,
position and momentum distributions, and density fluctuations on temperature.
We apply the scheme to simulate an evaporative cooling process in which the
preferential removal of high energy particles leads to the growth of a
Bose-Einstein condensate. We show that a condensate fraction can be inferred
during the dynamics even in this non-equilibrium situation.Comment: 11 pages, 7 figure
Critical temperature of a trapped Bose gas: comparison of theory and experiment
We apply the Projected Gross-Pitaevskii equation (PGPE) formalism to the
experimental problem of the shift in critical temperature of a
harmonically confined Bose gas as reported in Gerbier \emph{et al.} [Phys. Rev.
Lett. \textbf{92}, 030405 (2004)]. The PGPE method includes critical
fluctuations and we find the results differ from various mean-field theories,
and are in best agreement with experimental data. To unequivocally observe
beyond mean-field effects, however, the experimental precision must either
improve by an order of magnitude, or consider more strongly interacting
systems. This is the first application of a classical field method to make
quantitative comparison with experiment.Comment: revtex4, four pages, three figures. v2: updated to published version.
Several additions to figures, and better explanations in text in response to
referee comment
Tripodfish (Aulopiformes: Bathypterois) locomotion and landing behaviour from video observation at bathypelagic depths in the Campos Basin of Brazil
A video observation of a deep-sea tripodfish (Aulopiformes: Bathypterois) taken from a remotely-operated vehicle at a depth of 1443 m in the Campos Basin, Brazil is analysed for swimming and landing movements. The observed specimen is identified here as Bathypteroisgrallator, and this record is the first video observation of a tripodfish exhibiting periodic swimming followed by landing in a resting position on deep-sea substrate which we interpret as âbathypteroiformâ movement, a locomotive mode unique to taxa within Bathypterois. This observation describes the functional role of the fins associated with landing, including independent movements of the elongated fin ray elements. The specimen is observed to display subcarangiform body and/or caudal fin movement while swimming in a periodic state. Prior to landing, the specimen is observed to raise its elongated caudal fin element parallel to the body, a behaviour that has not been described previously. Following contact of the elongated pelvic fin elements with the deep-sea floor, the elongated caudal fin element is independently lowered, completing the tripod stance typically observed. Š 2011 Taylor & Francis Group, LLC
Modifying monolayer behaviour by incorporating subphase additives and improving LangmuirâBlodgett thin film deposition on optical fibres
Experiments showing the possibility of modifying the behaviour of calix[4]resorcinarene monolayers at the airâwater interface and optimising the deposition of multilayer coatings onto optical fibres are presented. The nature of the subphase is fundamental to the behaviour of monolayers and their utility in coating and sensing applications. Here we show initial studies exploring the modification of the calix[4]resorcinarene monolayerâwater interaction through the introduction of dipole altering alcohol additives to the aqueous subphase. We explored the effect of this modification for three small alcohols. The resulting isotherms of the materials showed a reduction in the surface pressure and area per molecule required in order for the monolayer to reach its point of collapse. Incorporation of alcohols shifted the point of collapse, leading to the application of ethanol being successful in improving the transfer of material via LangmuirâBlodgett coating onto optical fibres at lower pressures. This method may prove useful in allowing greater control over future sensor surface coatings
Synthesis and evaluation of a desymmetrised synthetic lectin:An approach to carbohydrate receptors with improved versatility
A new design for carbohydrate receptors features unmatched apolar surfaces, and could lead to selectivities for a broader range of substrates.</p
Formation of nonlinear X-waves in condensed matter systems
X-waves are an example of a localized wave packet solution of the homogeneous wave equation, and can potentially arise in any area of physics relating to wave phenomena, such as acoustics, electromagnetism, or quantum mechanics. They have been predicted in condensed matter systems such as atomic Bose-Einstein condensates in optical lattices, and were recently observed in exciton-polariton condensates. Here we show that polariton X-waves result from an interference between two separating wave packets that arise from the combination of a locally hyperbolic dispersion relation and nonlinear interactions. We show that similar X-wave structures could also be observed in expanding spin-orbit coupled Bose-Einstein condensates.Published onlin
The First Record of a Trans-Oceanic Sister-Group Relationship between Obligate Vertebrate Troglobites
We show using the most complete phylogeny of one of the most species-rich orders of vertebrates (Gobiiformes), and calibrations from the rich fossil record of teleost fishes, that the genus Typhleotris, endemic to subterranean karst habitats in southwestern Madagascar, is the sister group to Milyeringa, endemic to similar subterranean systems in northwestern Australia. Both groups are eyeless, and our phylogenetic and biogeographic results show that these obligate cave fishes now found on opposite ends of the Indian Ocean (separated by nearly 7,000 km) are each others closest relatives and owe their origins to the break up of the southern supercontinent, Gondwana, at the end of the Cretaceous period. Trans-oceanic sister-group relationships are otherwise unknown between blind, cave-adapted vertebrates and our results provide an extraordinary case of Gondwanan vicariance. Š 2012 Chakrabarty et al
Product Market Competition and Human Resource Practices: An Analysis of the Retail Food Sector
The rise of super-centers and the entry of Wal-Mart into food retailing have dramatically altered the competitive environment in the industry. This paper explores the impact of such changes on the labor market practices of traditional food retailers. We use longitudinal data on workers and firms to construct new measures of compensation and employment, and examine how these measures evolve within and across firms in response to changes in product market structure. An additional feature of the analysis is to combine rich case study knowledge about the retail food industry with the new matched employer-employee data from the Census Bureau.supermarkets, human resource practices, competition, internal labor market, wage growth, Labor and Human Capital, Marketing,
Classical Region of a Trapped Bose Gas
The classical region of a Bose gas consists of all single-particle modes that
have a high average occupation and are well-described by a classical field.
Highly-occupied modes only occur in massive Bose gases at ultra-cold
temperatures, in contrast to the photon case where there are highly-occupied
modes at all temperatures. For the Bose gas the number of these modes is
dependent on the temperature, the total number of particles and their
interaction strength. In this paper we characterize the classical region of a
harmonically trapped Bose gas over a wide parameter regime. We use a
Hartree-Fock approach to account for the effects of interactions, which we
observe to significantly change the classical region as compared to the
idealized case. We compare our results to full classical field calculations and
show that the Hartree-Fock approach provides a qualitatively accurate
description of classical region for the interacting gas.Comment: 6 pages, 5 figures; updated to include new results with interaction
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