Observation of narrow-band noise accompanying the breakdown of insulating states in high Landau levels

Recent magnetotransport experiments on high mobility two-dimensional electron systems have revealed many-body electron states unique to high Landau levels. Among these are re-entrant integer quantum Hall states which undergo sharp transitions to conduction above some threshold field. Here we report that these transitions are often accompanied by narrow- and broad-band noise with frequencies which are strongly dependent on the magnitude of the applied dc current.Comment: 4 pages, 3 figure

Simulation studies of air transport operational problems

An experimental evaluation of the monitored approach procedure for conducting low visibility instrument approaches is described. Four airline crews each flew 16 approaches using the monitored procedure and 16 using a modified standard procedure in a DC-10 simulator under various conditions of visibility, wind shear and turbulence, and radar vectoring scenarios. In terms of system measures of aircrew performance, no major differences were found. Pilot opinion data indicate that there are some desirable characteristics of the monitored procedure, particularly with reference to the increased role of the flight engineer in conducting low visibility approaches. Rationale for developing approach procedures is discussed

Retrospective studies of operating problems in air transport

An epidemiological model for the study of human errors in aviation is presented. In this approach, retrospective data are used as the basis for formulation of hypotheses as to system factors which may have contributed to such errors. Prospective experimental studies of aviation operations are also required in order to prove or disprove the hypotheses, and to evaluate the effectiveness of intervention techniques designed to solve operational problems in the aviation system

Chaos in Time Dependent Variational Approximations to Quantum Dynamics

Dynamical chaos has recently been shown to exist in the Gaussian approximation in quantum mechanics and in the self-consistent mean field approach to studying the dynamics of quantum fields. In this study, we first show that any variational approximation to the dynamics of a quantum system based on the Dirac action principle leads to a classical Hamiltonian dynamics for the variational parameters. Since this Hamiltonian is generically nonlinear and nonintegrable, the dynamics thus generated can be chaotic, in distinction to the exact quantum evolution. We then restrict attention to a system of two biquadratically coupled quantum oscillators and study two variational schemes, the leading order large N (four canonical variables) and Hartree (six canonical variables) approximations. The chaos seen in the approximate dynamics is an artifact of the approximations: this is demonstrated by the fact that its onset occurs on the same characteristic time scale as the breakdown of the approximations when compared to numerical solutions of the time-dependent Schrodinger equation.Comment: 10 pages (12 figures), RevTeX (plus macro), uses epsf, minor typos correcte

Collective Oscillations of Vortex Lattices in Rotating Bose-Einstein Condensates

The complete low-energy collective-excitation spectrum of vortex lattices is discussed for rotating Bose-Einstein condensates (BEC) by solving the Bogoliubov-de Gennes (BdG) equation, yielding, e.g., the Tkachenko mode recently observed at JILA. The totally symmetric subset of these modes includes the transverse shear, common longitudinal, and differential longitudinal modes. We also solve the time-dependent Gross-Pitaevskii (TDGP) equation to simulate the actual JILA experiment, obtaining the Tkachenko mode and identifying a pair of breathing modes. Combining both the BdG and TDGP approaches allows one to unambiguously identify every observed mode.Comment: 5 pages, 4 figure

The decay of space charge in a glassy epoxy resin following voltage removal

The PEA technique is used to measure the distribution of space charge in an epoxy resin after polarisation for one week at an applied field of 7.14kV/mm over a range of temperatures. The decay of the space charge is followed for times up to 114 hours after removal of the voltage and analysed in terms of a number of alternative decay mechanisms. It is shown that the rate-determining stage of the decay mechanism is that of a thermally activated process that has been associated with charge de-trapping. At times greater than 102s the de-trapping process behaves as though the space charge field does not exist and the retention time of the space charge depends only upon the depth of the deepest occupied traps and the temperature

Non-equilibrium dynamics in quantum field theory at high density: the tsunami

The dynamics of a dense relativistic quantum fluid out of thermodynamic equilibrium is studied in the framework of the Phi^4 scalar field theory in the large N limit. The time evolution of a particle distribution in momentum space (the tsunami) is computed. The effective mass felt by the particles in such a high density medium equals the tree level mass plus the expectation value of the squared field. The case of negative tree level squared mass is particularly interesting. In such case dynamical symmetry restoration as well as dynamical symmetry breaking can happen. Furthermore, the symmetry may stay broken with vanishing asymptotic squared mass showing the presence of out of equilibrium Goldstone bosons. We study these phenomena and identify the set of initial conditions that lead to each case. We compute the equation of state which turns to depend on the initial state. Although the system does not thermalize, the equation of state for asymptotically broken symmetry is of radiation type. We compute the correlation functions at equal times. The two point correlator for late times is the sum of different terms. One stems from the initial particle distribution. Another term accounts for the out of equilibrium Goldstone bosons created by spinodal unstabilities when the symmetry is asymptotically broken.Both terms are of the order of the inverse of the coupling for distances where causal signals can connect the two points. The contribution of the out of equilibrium Goldstones exhibits scaling behaviour in a generalized sense.Comment: LaTex, 49 pages, 15 .ps figure

Classical Nucleation Theory of the One-Component Plasma

We investigate the crystallization rate of a one-component plasma (OCP) in the context of classical nucleation theory. From our derivation of the free energy of an arbitrary distribution of solid clusters embedded in a liquid phase, we derive the steady-state nucleation rate of an OCP as a function of the Coulomb coupling parameter. Our result for the rate is in accord with recent molecular dynamics simulations, but it is greater than that of previous analytical estimates by many orders of magnitude. Further molecular dynamics simulations of the nucleation rate of a supercooled liquid OCP for several values of the coupling parameter would clarify the physics of this process.Comment: 6 pages, 1 figure, accepted by PR

Development of a complex intervention to support exercise self-management for people with Parkinson's.

Purpose: The value of exercise for people with Parkinson's (PwP) is undisputed, and is associated with improved health outcomes and potential to slow down the rate of symptom decline. However, the optimum means to support long-term participation in exercise remains undetermined. Current exercise provision within physiotherapy is commonly time limited. Moreover, research has shown that when current services cease, adherence declines and the effects on outcomes diminish. Therefore, a sustainable means of maintaining activity, beyond the end of normal physiotherapy care, is required, which necessitates a different approach to support People PwP to be more active. Aims: To develop an evidence based intervention to equip PwP to self-manage their exercise participation. Methods: A multi-step mixed methods approach was adopted. A systematic review of the literature exploring barriers and motivators to exercise and a comprehensive review of the exercise literature for PwP was conducted. Consultation with a convenience sample drawn from UK wide specialist physiotherapists and the Parkinson's community was conducted to explore barriers and facilitators to exercise delivery and participation. The findings were used to inform the development of a multi-component intervention aimed at promoting exercise self-management. PwP were involved in refining the intervention. Results: The literature review identified that simply prescribing exercise in isolation is ineffective to promote long-term changes in exercise behaviour. Amalgamating findings from the systematic and comprehensive literature reviews with consultation finding identified key ingredients to support long-term exercise self-management were identified. These included: individualised exercise programmes, contextualised education, and the provision of strategies to support PwP to develop an exercise habit. While the benefits of exercise were widely acknowledged, a need was identified for services to develop exercise self-confidence, to empower PwP with the knowledge and skills they need to embed exercise within their everyday routine. Access to professionals with specialist Parkinson's training was highly valued, either on a 1:1 basis or within a group. 1:1 interventions were thought to develop confidence, whereas group-based exercise provided opportunity for shared learning and development of a social network. Transport and costs were reported as key barriers; accessibility and sustainability were key to long-term participation. This process informed the development of the PDConnect programme. PDConnect is an evidence-informed exercise intervention underpinned by empowerment theory, with the aim of providing PwP with a toolkit of behaviour change techniques to promote participation in exercise and exercise self-management. The PDConnect combines specialist physiotherapy, group-based exercise and self-management support, with education and behaviour change strategies threaded throughout. The programme consists of three components: (i) six sessions of 1-1-specialist physiotherapy delivered at home; (ii) 12 sessions of group-based exercise, delivered once a week for 12 weeks; (iii) 12 weeks of self-management, with a support session each month. Conclusion(s): Aligning with the Medical Research Council guidelines for developing complex interventions, the feasibility and acceptability of the PDConnect programme is currently being tested and evaluated by those delivering and receiving the intervention. Impact: Promoting exercise self-management is beneficial to the NHS to reduce health service utilisation and prevent secondary complications related to sedentary behaviour. Funding acknowledgements: This development of the PDConnect intervention was not funded. Current work to explore the feasibility and acceptability of the PDConnect intervention is jointly funded by Parkinson's UK and the Chief Scientist Office, Scotland