1,527 research outputs found
Self-Trapping, Quantum Tunneling and Decay Rates for a Bose Gas with Attractive Nonlocal Interaction
We study the Bose-Einstein condensation for a cloud of Li atoms with
attractive nonlocal (finite-range) interaction in a harmonic trap. In addition
to the low-density metastable branch, that is present also in the case of local
interaction, a new stable branch appears at higher densities. For a large
number of atoms, the size of the cloud in the stable high-density branch is
independent of the trap size and the atoms are in a macroscopic quantum
self-trapped configuration. We analyze the macroscopic quantum tunneling
between the low-density metastable branch and the high-density one by using the
istanton technique. Moreover we consider the decay rate of the Bose condensate
due to inelastic two- and three-body collisions.Comment: 5 pages, 4 figures, submitted to Phys. Rev.
Quantum Dynamics of Three Coupled Atomic Bose-Einstein Condensates
The simplest model of three coupled Bose-Einstein Condensates (BEC) is
investigated using a group theoretical method. The stationary solutions are
determined using the SU(3) group under the mean field approximation. This
semiclassical analysis using the system symmetries shows a transition in the
dynamics of the system from self trapping to delocalization at a critical value
for the coupling between the condensates. The global dynamics are investigated
by examination of the stable points and our analysis shows the structure of the
stable points depends on the ratio of the condensate coupling to the
particle-particle interaction, undergoes bifurcations as this ratio is varied.
This semiclassical model is compared to a full quantum treatment, which also
displays the dynamical transition. The quantum case has collapse and revival
sequences superposed on the semiclassical dynamics reflecting the underlying
discreteness of the spectrum. Non-zero circular current states are also
demonstrated as one of the higher dimensional effects displayed in this system.Comment: Accepted to PR
Intermittent implosion and pattern formation of trapped Bose-Einstein condensates with attractive interaction
The collapsing dynamics of a trapped Bose-Einstein condensate (BEC) with
attractive interaction are revealed to exhibit two previously unknown
phenomena. During the collapse, BEC undergoes a series of rapid implosions that
occur {\it intermittently} within a very small region. When the sign of the
interaction is suddenly switched from repulsive to attractive, e.g., by the
Feshbach resonance, density fluctuations grow to form various patterns such as
a shell structure.Comment: 5 pages, 2 figures, RevTeX, epsf.sty, corrected loss rate
Experiment Data Report for Semiscale Mod-1 Tests S-01-4 and S-01-4A (Isothermal Blowdown With Core Resistance Simulator)
Quantum Mechanical Aspects of Cell Microtubules: Science Fiction or Realistic Possibility?
Recent experimental research with marine algae points towards quantum
entanglement at ambient temperature, with correlations between essential
biological units separated by distances as long as 20 Angstr\"oms. The
associated decoherence times, due to environmental influences, are found to be
of order 400 fs. This prompted some authors to connect such findings with the
possibility of some kind of quantum computation taking place in these
biological entities: within the decoherence time scales, the cell "quantum
calculates" the optimal "path" along which energy and signal would be
transported more efficiently. Prompted by these experimental results, in this
talk I remind the audience of a related topic proposed several years ago in
connection with the possible r\^ole of quantum mechanics and/or field theory on
dissipation-free energy transfer in microtubules (MT), which constitute
fundamental cell substructures. Quantum entanglement between tubulin dimers was
argued to be possible, provided there exists sufficient isolation from other
environmental cell effects. The model was based on certain ferroelectric
aspects of MT. In the talk I review the model and the associated experimental
tests so far and discuss future directions, especially in view of the algae
photo-experiments.Comment: 31 pages latex, 11 pdf figures, uses special macros, Invited Plenary
Talk at DICE2010, Castello Pasquini, Castiglioncello (Italy), September 13-18
201
Power laws and collapsing dynamics of a trapped Bose-Einstein condensate with attractive interactions
The critical behavior of collective modes and the collapsing dynamics of
trapped Bose-Einstein condensates with attractive interactions are studied
analytically and numerically. The time scales of these dynamics both below and
above the critical point of the collapse are found to obey power laws with a
single parameter of N/N_c - 1, where N is the number of condensate atoms and
N_c is the critical number. The collapsing condensate eventually undergoes
rapid implosion, which occurs several times intermittently, and then the
implosion turns to an explosion. The release energy of the explosion is found
to be proportional to the square of the interaction strength, inversely
proportional to the three-body recombination rate, and independent of the
number of condensate atoms and the trap frequency.Comment: 9 pages, RevTeX, 7 figures, epsf.sty, corrected loss rate
Methods for identifying surgical wound infection after discharge from hospital: a systematic review.
Background: Wound infections are a common complication of surgery that add significantly to the morbidity of patients and costs of treatment. The global trend towards reducing length of hospital stay post-surgery and the increase in day case surgery means that surgical site infections (SSI) will increasingly occur after hospital discharge. Surveillance of SSIs is important because rates of SSI are viewed as a measure of hospital performance, however accurate detection of SSIs post-hospital discharge is not straightforward. Methods: We conducted a systematic review of methods of post discharge surveillance for surgical wound infection and undertook a national audit of methods of post-discharge surveillance for surgical site infection currently used within United Kingdom NHS Trusts. Results: Seven reports of six comparative studies which examined the validity of post-discharge surveillance methods were located; these involved different comparisons and some had methodological limitations, making it difficult to identify an optimal method. Several studies evaluated automated screening of electronic records and found this to be a useful strategy for the identification of SSIs that occurred post discharge. The audit identified a wide range of relevant post-discharge surveillance programmes in England, Scotland and Wales and Northern Ireland; however, these programmes used varying approaches for which there is little supporting evidence of validity and/or reliability. Conclusion: In order to establish robust methods of surveillance for those surgical site infections that occur post discharge, there is a need to develop a method of case ascertainment that is valid and reliable post discharge. Existing research has not identified a valid and reliable method. A standardised definition of wound infection ( e. g. that of the Centres for Disease Control) should be used as a basis for developing a feasible, valid and reliable approach to defining post discharge SSI. At a local level, the method used to ascertain post discharge SSI will depend upon the purpose of the surveillance, the nature of available routine data and the resources available
ROM-based quantum computation: Experimental explorations using Nuclear Magnetic Resonance, and future prospects
ROM-based quantum computation (QC) is an alternative to oracle-based QC. It
has the advantages of being less ``magical'', and being more suited to
implementing space-efficient computation (i.e. computation using the minimum
number of writable qubits). Here we consider a number of small (one and
two-qubit) quantum algorithms illustrating different aspects of ROM-based QC.
They are: (a) a one-qubit algorithm to solve the Deutsch problem; (b) a
one-qubit binary multiplication algorithm; (c) a two-qubit controlled binary
multiplication algorithm; and (d) a two-qubit ROM-based version of the
Deutsch-Jozsa algorithm. For each algorithm we present experimental
verification using NMR ensemble QC. The average fidelities for the
implementation were in the ranges 0.9 - 0.97 for the one-qubit algorithms, and
0.84 - 0.94 for the two-qubit algorithms. We conclude with a discussion of
future prospects for ROM-based quantum computation. We propose a four-qubit
algorithm, using Grover's iterate, for solving a miniature ``real-world''
problem relating to the lengths of paths in a network.Comment: 11 pages, 5 figure
Development and validation of the ACE tool: Assessing medical trainees' competency in evidence based medicine
BACKGROUND: While a variety of instruments have been developed to assess knowledge and skills in evidence based medicine (EBM), few assess all aspects of EBM - including knowledge, skills attitudes and behaviour - or have been psychometrically evaluated. The aim of this study was to develop and validate an instrument that evaluates medical traineesâ competency in EBM across knowledge, skills and attitude. METHODS: The âAssessing Competency in EBMâ (ACE) tool was developed by the authors, with content and face validity assessed by expert opinion. A cross-sectional sample of 342 medical trainees representing ânoviceâ, âintermediateâ and âadvancedâ EBM trainees were recruited to complete the ACE tool. Construct validity, item difficulty, internal reliability and item discrimination were analysed. RESULTS: We recruited 98 EBM-novice, 108 EBM-intermediate and 136 EBM-advanced participants. A statistically significant difference in the total ACE score was observed and corresponded to the level of training: on a 0-15-point test, the mean ACE scores were 8.6 for EBM-novice; 9.5 for EBM-intermediate; and 10.4 for EBM-advanced (pâ<â0.0001). Individual item discrimination was excellent (Item Discrimination Index ranging from 0.37 to 0.84), with internal reliability consistent across all but three items (Item Total Correlations were all positive ranging from 0.14 to 0.20). CONCLUSION: The 15-item ACE tool is a reliable and valid instrument to assess medical traineesâ competency in EBM. The ACE tool provides a novel assessment that measures user performance across the four main steps of EBM. To provide a complete suite of instruments to assess EBM competency across various patient scenarios, future refinement of the ACE instrument should include further scenarios across harm, diagnosis and prognosis
A white-light trap for Bose-Einstein condensates
We propose a novel method for trapping Bose-condensed atoms using a
white-light interference fringe. Confinement frequencies of tens of kHz can be
achieved in conjunction with trap depths of only a few micro-K. We estimate
that lifetimes on the order of 10 s can be achieved for small numbers of atoms.
The tight confinement and shallow depth permit tunneling processes to be used
for studying interaction effects and for applications in quantum information.Comment: 10 pages with 3 figure
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