2,003 research outputs found
Bragg spectroscopy of an accelerating condensate with solitary-wave behaviour
We present a theoretical treatment of Bragg spectroscopy of an accelerating
condensate in a solitary-wave state. Our treatment is based on the
Gross-Pitaevskii equation with an optical potential representing the Bragg
pulse and an additional external time-dependent potential generating the
solitary-wave behaviour. By transforming to a frame translating with the
condensate, we derive an approximate set of equations that can be readily
solved to generate approximate Bragg spectra. Our analytic method is accurate
within a well defined parameter regime and provides physical insight into the
structure of the spectra. We illustrate our formalism using the example of
Bragg spectroscopy of a condensate in a time-averaged orbiting potential trap.Comment: 9 pages, 3 figure
Client self-assessment in community aged care: A comparative study involving older Australians and their case managers
Self-assessment of support needs is a relatively new and under-researched phenomenon in domiciliary aged care. This article outlines the results of a comparative study focusing on whether a self-assessment approach assists clients to identify support needs and the degree to which self-assessed needs differ from an assessment conducted by community care professionals. A total of 48 older people and their case managers completed a needs assessment tool. Twenty-two semi-structured interviews were used to ascertain older people’s views and preferences regarding the self-assessment process. The study suggests that while a co-assessment approach as outlined in this article has the potential to assist older people to gain a better understanding of their care needs as well as the assessment process and its ramifications, client self-assessment should be seen as part of a co-assessment process involving care professionals. Such a co-assessment process allows older people to gain a better understanding of their support needs and the wider community aged care context. The article suggests that a co-assessment process involving both clients and care professionals contains features that have the capacity to enhance domiciliary aged care
Solitary-wave description of condensate micro-motion in a time-averaged orbiting potential trap
We present a detailed theoretical analysis of micro-motion in a time-averaged
orbiting potential trap. Our treatment is based on the Gross-Pitaevskii
equation, with the full time dependent behaviour of the trap systematically
approximated to reduce the trapping potential to its dominant terms. We show
that within some well specified approximations, the dynamic trap has
solitary-wave solutions, and we identify a moving frame of reference which
provides the most natural description of the system. In that frame eigenstates
of the time-averaged orbiting potential trap can be found, all of which must be
solitary-wave solutions with identical, circular centre of mass motion in the
lab frame. The validity regime for our treatment is carefully defined, and is
shown to be satisfied by existing experimental systems.Comment: 12 pages, 2 figure
Bragg scattering of Cooper pairs in an ultra-cold Fermi gas
We present a theoretical treatment of Bragg scattering of a degenerate Fermi
gas in the weakly interacting BCS regime. Our numerical calculations predict
correlated scattering of Cooper pairs into a spherical shell in momentum space.
The scattered shell of correlated atoms is centered at half the usual Bragg
momentum transfer, and can be clearly distinguished from atoms scattered by the
usual single-particle Bragg mechanism. We develop an analytic model that
explains key features of the correlated-pair Bragg scattering, and determine
the dependence of this scattering on the initial pair correlations in the gas.Comment: Manuscript substantially revised. Version 2 contains a more detailed
discussion of the collisional interaction used in our theory, and is based on
three-dimensional solution
The NDE of Complex Liquids Containing Suspended Particles
Many products of commercial significance exist as suspensions of particles in a liquid or will have consisted as such as suspension at a stage during manufacture; the particles may be solid or liquid. It is necessary to determine the physical state of such suspensions both in the development laboratory and for the purposes of quality and process control at plant level. Reliable estimates are required of the size distribution and concentration of the dispersed phase, as well as indications of flocculation, and network formation. Dynamic measures may be required in support of reaction processes such as crystallization. Techniques that can be used for the characterisation of suspensions are optical scattering or turbidity tests, sedimentation rate tests, ionizing radiation, electrical tests, electroacoustic measurements, and acoustic (ultrasonic) methods alone. Ultrasonic methods have the advantages that they can be used on mixtures that are too opaque for optical techniques, and that they can be incorporated into robust and low cost instrumentation. This paper gives a brief overview of the physics of the interactions of ultrasonic waves with particulate suspensions and a brief review of measurement methods and errors. Recent results that show agreement or otherwise between theory and experiment are given for silica sols. Examples are also given of the use of ultrasound to track flocculation in an aqueous emulsion, and to track a crystallization reaction
Nonlinear atom-optical delta-kicked harmonic oscillator using a Bose-Einstein condensate
We experimentally investigate the atom-optical delta-kicked harmonic
oscillator for the case of nonlinearity due to collisional interactions present
in a Bose-Einstein condensate. A Bose condensate of rubidium atoms tightly
confined in a static harmonic magnetic trap is exposed to a one-dimensional
optical standing-wave potential that is pulsed on periodically. We focus on the
quantum anti-resonance case for which the classical periodic behavior is simple
and well understood. We show that after a small number of kicks the dynamics is
dominated by dephasing of matter wave interference due to the finite width of
the condensate's initial momentum distribution. In addition, we demonstrate
that the nonlinear mean-field interaction in a typical harmonically confined
Bose condensate is not sufficient to give rise to chaotic behavior.Comment: 4 pages, 3 figure
Magnetoroton scattering by phonons in the fractional quantum Hall regime
Motivated by recent phonon spectroscopy experiments in the fractional quantum
Hall regime we consider processes in which thermally excited magnetoroton
excitations are scattered by low energy phonons. We show that such scattering
processes can never give rise to dissociation of magnetorotons into unbound
charged quasiparticles as had been proposed previously. In addition we show
that scattering of magnetorotons to longer wavelengths by phonon absorption is
possible because of the shape of the magnetoroton dispersion curve and it is
shown that there is a characteristic cross-over temperature above which the
rate of energy transfer to the electron gas changes from an exponential
(activated) to a power law dependence on the effective phonon temperature.Comment: LaTex document, 3 eps figures. submitted to Phys Rev
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