6,199 research outputs found
Gapless finite- theory of collective modes of a trapped gas
We present predictions for the frequencies of collective modes of trapped
Bose-condensed Rb atoms at finite temperature. Our treatment includes a
self-consistent treatment of the mean-field from finite- excitations and the
anomolous average. This is the first gapless calculation of this type for a
trapped Bose-Einstein condensed gas. The corrections quantitatively account for
the downward shift in the excitation frequencies observed in recent
experiments as the critical temperature is approached.Comment: 4 pages Latex and 2 postscript figure
Quantum Vortex in a Vectorial Bose-Einstein Condensate
Quantum vortices in the multi-component Bose-Einstein condensation (BEC) are
investigated theoretically. It is found that three kinds of the vortex
configurations are possible and their physical properties are discussed in
details, including the density distribution and the spin texture. By using the
Bogoliubov theory extended to the three component BEC, the collective modes for
these vortices are evaluated. The local vortex stability for these vortices are
examined in light of the existence of the negative eigenvalue, yielding a
narrow magnetization window for the local intrinsic stable region where the
multi-components work together to stabilize a vortex in a self-organized way.Comment: 8 pages, 14 eps figure
Internal Vortex Structure of a Trapped Spinor Bose-Einstein Condensate
The internal vortex structure of a trapped spin-1 Bose-Einstein condensate is
investigated. It is shown that it has a variety of configurations depending on,
in particular, the ratio of the relevant scattering lengths and the total
magnetization.Comment: replacement; minor grammatical corrections but with additional
figure
Bound and resonance states of the nonlinear Schroedinger equation in simple model systems
The stationary nonlinear Schroedinger equation, or Gross-Pitaevskii equation,
is studied for the cases of a single delta potential and a delta-shell
potential. These model systems allow analytical solutions, and thus provide
useful insight into the features of stationary bound, scattering and resonance
states of the nonlinear Schroedinger equation. For the single delta potential,
the influence of the potential strength and the nonlinearity is studied as well
as the transition from bound to scattering states. Furthermore, the properties
of resonance states for a repulsive delta-shell potential are discussed.Comment: 19 pages, 10 figure
Mean-field dynamics of a Bose-Einstein condensate in a time-dependent triple-well trap: Nonlinear eigenstates, Landau-Zener models and STIRAP
We investigate the dynamics of a Bose--Einstein condensate (BEC) in a
triple-well trap in a three-level approximation. The inter-atomic interactions
are taken into account in a mean-field approximation (Gross-Pitaevskii
equation), leading to a nonlinear three-level model. New eigenstates emerge due
to the nonlinearity, depending on the system parameters. Adiabaticity breaks
down if such a nonlinear eigenstate disappears when the parameters are varied.
The dynamical implications of this loss of adiabaticity are analyzed for two
important special cases: A three level Landau-Zener model and the STIRAP
scheme. We discuss the emergence of looped levels for an equal-slope
Landau-Zener model. The Zener tunneling probability does not tend to zero in
the adiabatic limit and shows pronounced oscillations as a function of the
velocity of the parameter variation. Furthermore we generalize the STIRAP
scheme for adiabatic coherent population transfer between atomic states to the
nonlinear case. It is shown that STIRAP breaks down if the nonlinearity exceeds
the detuning.Comment: RevTex4, 7 pages, 11 figures, content extended and title/abstract
change
Microscopic Treatment of Binary Interactions in the Non-Equilibrium Dynamics of Partially Bose-condensed Trapped Gases
In this paper we use microscopic arguments to derive a nonlinear
Schr\"{o}dinger equation for trapped Bose-condensed gases. This is made
possible by considering the equations of motion of various anomalous averages.
The resulting equation explicitly includes the effect of repeated binary
interactions (in particular ladders) between the atoms. Moreover, under the
conditions that dressing of the intermediate states of a collision can be
ignored, this equation is shown to reduce to the conventional Gross-Pitaevskii
equation in the pseudopotential limit. Extending the treatment, we show first
how the occupation of excited (bare particle) states affects the collisions,
and thus obtain the many-body T-matrix approximation in a trap. In addition, we
discuss how the bare particle many-body T-matrix gets dressed by mean fields
due to condensed and excited atoms. We conclude that the most commonly used
version of the Gross-Pitaevskii equation can only be put on a microscopic basis
for a restrictive range of conditions. For partial condensation, we need to
take account of interactions between condensed and excited atoms, which, in a
consistent formulation, should also be expressed in terms of the many-body
T-matrix. This can be achieved by considering fluctuations around the
condensate mean field beyond those included in the conventional finite
temperature mean field, i.e. Hartree-Fock-Bogoliubov (HFB), theory.Comment: Resolved some problems with printing of figure
Wave envelopes with second-order spatiotemporal dispersion : I. Bright Kerr solitons and cnoidal waves
We propose a simple scalar model for describing pulse phenomena beyond the conventional slowly-varying envelope approximation. The generic governing equation has a cubic nonlinearity and we focus here mainly on contexts involving anomalous group-velocity dispersion. Pulse propagation turns out to be a problem firmly rooted in frames-of-reference considerations. The transformation properties of the new model and its space-time structure are explored in detail. Two distinct representations of exact analytical solitons and their associated conservation laws (in both integral and algebraic forms) are presented, and a range of new predictions is made. We also report cnoidal waves of the governing nonlinear equation. Crucially, conventional pulse theory is shown to emerge as a limit of the more general formulation. Extensive simulations examine the role of the new solitons as robust attractors
Prevalence and co-infection of Toxoplasma gondii and Neospora caninum in Apodemus sylvaticus in an area relatively free of cats
The protozoan parasite Toxoplasma gondii is prevalent worldwide and can infect a remarkably wide range of hosts despite
felids being the only definitive host. As cats play a major role in transmission to secondary mammalian hosts, the interaction
between cats and these hosts should be a major factor determining final prevalence in the secondary host. This study
investigates the prevalence of T. gondii in a natural population of Apodemus sylvaticus collected from an area with low cat
density (<2·5 cats/km2). A surprisingly high prevalence of 40·78% (95% CI: 34·07%–47·79%) was observed despite this.
A comparable level of prevalence was observed in a previously published study using the same approaches where a
prevalence of 59% (95% CI: 50·13%–67·87%) was observed in a natural population of Mus domesticus from an area with high
cat density (>500 cats/km2). Detection of infected foetuses frompregnant dams in both populations suggests that congenital
transmission may enable persistence of infection in the absence of cats. The prevalences of the related parasite, Neospora
caninum were found to be low in both populations (A. sylvaticus: 3·39% (95% CI: 0·12%–6·66%); M. domesticus: 3·08%
(95% CI: 0·11%–6·05%)). These results suggest that cat density may have a lower than expected effect on final prevalence in
these ecosystems
Lung cancer screening program factors that influence psychosocial outcomes: A systematic review.
OBJECTIVES: Lung cancer screening (LCS) programs are being designed and implemented globally. Early data suggests that the psychosocial impacts of LCS are influenced by program factors, but evidence synthesis is needed. This systematic review aimed to elucidate the impact of service-level factors on psychosocial outcomes to inform optimal LCS program design and future implementation. METHODS: Four databases were searched from inception to July 2023. Inclusion criteria were full-text articles published in English that reported an association between any program factors and psychosocial outcomes experienced during LCS. Study quality was appraised, and findings were synthesised narratively. RESULTS: Thirty-two articles were included; 29 studies were assessed at high or moderate risk of bias. Study designs were RCT (n = 3), pre-post (n = 6), cross-sectional (n = 12), mixed-methods (n = 1), and qualitative (n = 10) studies, and conducted primarily in the USA (n = 25). Findings suggested that targeted interventions can improve smoking-related or decisional psychosocial outcomes (e.g., smoking cessation interventions increase readiness/motivation to quit) but impacts of interventions on other psychological outcomes were varied. There was limited evidence reporting association between service delivery components and psychological outcomes, and results suggested moderation by individual aspects (e.g., expectation of results, baseline anxiety). Opportunities for discussion were key in reducing psychological harm. CONCLUSIONS: Certain program factors are reportedly associated with psychosocial impacts of LCS, but study heterogeneity and quality necessitate more real-world studies. Future work should examine (a) implementation of targeted interventions and high-value discussion during LCS, and (b) optimal methods and timing of risk and result communication, to improve psychosocial outcomes while reducing time burden for clinicians
Adiabaticity Criterion for Moving Vortices in Dilute Bose-Einstein Condensates
Considering a moving vortex line in a dilute atomic Bose-Einstein condensate
within time-dependent Hartree-Fock-Bogoliubov-Popov theory, we derive a
criterion for the quasiparticle excitations to follow the vortex core rigidly.
The assumption of adiabaticity, which is crucial for the validity of the
stationary self-consistent theories in describing such time-dependent
phenomena, is shown to imply a stringent criterion for the velocity of the
vortex line. Furthermore, this condition is shown to be violated in the recent
vortex precession experiments.Comment: 4 pages, 1 figur
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