130 research outputs found
Superfluid toroidal currents in atomic condensates
The dynamics of toroidal condensates in the presence of condensate flow and
dipole perturbation have been investigated. The Bogoliubov spectrum of
condensate is calculated for an oblate torus using a discrete-variable
representation and a spectral method to high accuracy. The transition from
spheroidal to toroidal geometry of the trap displaces the energy levels into
narrow bands. The lowest-order acoustic modes are quantized with the dispersion
relation with . A condensate
with toroidal current splits the co-rotating and
counter-rotating pair by the amount: . Radial dipole excitations are the lowest energy dissipation modes.
For highly occupied condensates the nonlinearity creates an asymmetric mix of
dipole circulation and nonlinear shifts in the spectrum of excitations so that
the center of mass circulates around the axis of symmetry of the trap. We
outline an experimental method to study these excitations.Comment: 8 pages, 8 figure
Carrier-induced refractive index in quantum dot structures due to transitions from discrete quantum dot levels to continuum states
The carrier-induced refractive index in quantum dot (QD) structures due to optical transitions from QD levels to continuum states is considered. It is shown that, for large photon energies, the refractive index change is given asymptotically by the Drude formula. Calculations of the linewidth enhancement factor, alpha, show that alphasimilar to1 due to this contribution to the total refractive index. Furthermore, for highly localized QD states, the absorption coefficient at the photon energies similar to0.8-1.0 eV due to these transitions can be on the order of 10(3) m(-1). (C) 2004 American Institute of Physics. (DOI: 10.1063/1.1639933
Gyroscopic motion of superfluid trapped atomic condensates
The gyroscopic motion of a trapped Bose gas containing a vortex is studied.
We model the system as a classical top, as a superposition of coherent
hydrodynamic states, by solution of the Bogoliubov equations, and by
integration of the time-dependent Gross-Pitaevskii equation. The frequency
spectrum of Bogoliubov excitations, including quantum frequency shifts, is
calculated and the quantal precession frequency is found to be consistent with
experimental results, though a small discrepancy exists. The superfluid
precession is found to be well described by the classical and hydrodynamic
models. However the frequency shifts and helical oscillations associated with
vortex bending and twisting require a quantal treatment. In gyroscopic
precession, the vortex excitation modes are the dominant features
giving a vortex kink or bend, while the is found to be the dominant
Kelvin wave associated with vortex twisting.Comment: 18 pages, 7 figures, 1 tabl
Collective excitations of trapped Bose condensates in the energy and time domains
A time-dependent method for calculating the collective excitation frequencies
and densities of a trapped, inhomogeneous Bose-Einstein condensate with
circulation is presented. The results are compared with time-independent
solutions of the Bogoliubov-deGennes equations. The method is based on
time-dependent linear-response theory combined with spectral analysis of
moments of the excitation modes of interest. The technique is straightforward
to apply, is extremely efficient in our implementation with parallel FFT
methods, and produces highly accurate results. The method is suitable for
general trap geometries, condensate flows and condensates permeated with vortex
structures.Comment: 6 pages, 3 figures small typos fixe
Electronic training devices: discussion on the pros and cons of their use in dogs as a basis for the position statement of the European Society of Veterinary Clinical Ethology (ESVCE)
In recent years, the affirmation of a greater ethical sense and research generating a better knowledge of the mechanisms of animal learning, evidence of the existence of an animal mind), and studies on the dog-human attachment bond have led to changes in the dog-human relationship. These changes have caused a notable improvement in dog training techniques. Increased emphasis on dog welfare, overall, led to questioning of many training techniques and tools that used aversive means. Recent research on the use of aversive training devices has been performed and, on this basis it has been possible to create guidelines to inform the public about utility and the possible detriments related to the use of these devices as a tool in dog training. The European Society of Clinical Animal Ethology (ESVCE) has released a public position statement based on the current scientific information available on e-collars, punitive training techniques and canine welfare. This paper elaborates and discusses the arguments âpro and contra the use of e-collars and aversive training methodsâ leading to the statement in more detail. As a conclusion, ESVCE strongly opposes the use of e-collars in dog training, and urges all European countries to take an interest in and position on this welfare matter
De-excitation of the strongly coupled band in 177Au and implications for core intruder configurations in the light Hg isotopes
Excited states in the proton-unbound nuclide 177Au were populated in the 92Mo(88Sr, p2n) reaction and identified using the Jurogam-II and GREAT spectrometers in conjunction with the RITU gas-filled separator at the University of JyvĂ€skylĂ€ Accelerator Laboratory. A strongly coupled band and its decay path to the 11/2â α-decaying isomer have been identified using recoil-decay tagging. Comparisons with cranked HartreeFock-Bogoliubov (HFB) calculations based on Skyrme energy functionals suggest that the band has a prolate deformation and is based upon coupling the odd 1h11/2 proton hole to the excited 0+ 2 configuration in the 178Hg core. Although these configurations might be expected to follow the parabolic trend of core Hg(0+2 ) states as a function of neutron number, the electromagnetic decay paths from the strongly coupled band in 177Au are markedly different from those observed in the heavier isotopes above the midshell. This indicates that a significant change in the structure of the underlying A+1Hg core occurs below the neutron midshell
Direct observation of the Ba 114 â Xe 110 â Te 106 â Sn 102 triple α -decay chain using position and time correlations
The triple α-decay chain 114Ba â 110Xe â 106Te â 102Sn has been directly observed for the first time,
following the 58Ni(58Ni ,2n) reaction. Implantation of 114Ba nuclei into a double-sided silicon-strip detector has
allowed their α decays to be correlated in position and time with the α decays of the daughter (110Xe) and
granddaughter (106Te) nuclei. In total, 17 events have been assigned to the 114Ba â 110Xe â 106Te â 102Sn
triple α-decay chain. The energy of the 114Ba α decay has been measured to be Eα = 3480(20) keV, which is
70 keV higher than the previously measured value, and the half-life of 114Ba has been measured with improved
accuracy, to be 380+190
â110 ms. A revised Q12C value of 19 035(45) keV for 114Ba is presented.peerReviewe
Long Covid in adults discharged from UK hospitals after Covid-19: A prospective, multicentre cohort study using the ISARIC WHO Clinical Characterisation Protocol.
Background: This study sought to establish the long-term effects of Covid-19 following hospitalisation. Methods: 327 hospitalised participants, with SARS-CoV-2 infection were recruited into a prospective multicentre cohort study at least 3 months post-discharge. The primary outcome was self-reported recovery at least ninety days after initial Covid-19 symptom onset. Secondary outcomes included new symptoms, disability (Washington group short scale), breathlessness (MRC Dyspnoea scale) and quality of life (EQ5D-5L). Findings: 55% of participants reported not feeling fully recovered. 93% reported persistent symptoms, with fatigue the most common (83%), followed by breathlessness (54%). 47% reported an increase in MRC dyspnoea scale of at least one grade. New or worse disability was reported by 24% of participants. The EQ5D-5L summary index was significantly worse following acute illness (median difference 0.1 points on a scale of 0 to 1, IQR: -0.2 to 0.0). Females under the age of 50 years were five times less likely to report feeling recovered (adjusted OR 5.09, 95% CI 1.64 to 15.74), were more likely to have greater disability (adjusted OR 4.22, 95% CI 1.12 to 15.94), twice as likely to report worse fatigue (adjusted OR 2.06, 95% CI 0.81 to 3.31) and seven times more likely to become more breathless (adjusted OR 7.15, 95% CI 2.24 to 22.83) than men of the same age. Interpretation: Survivors of Covid-19 experienced long-term symptoms, new disability, increased breathlessness, and reduced quality of life. These findings were present in young, previously healthy working age adults, and were most common in younger females. Funding: National Institute for Health Research, UK Medical Research Council, Wellcome Trust, Department for International Development and the Bill and Melinda Gates Foundation
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