The possibility of a metal insulator transition in antidot arrays induced by an external driving

It is shown that a family of models associated with the kicked Harper model is relevant for cyclotron resonance experiments in an antidot array. For this purpose a simplified model for electronic motion in a related model system in presence of a magnetic field and an AC electric field is developed. In the limit of strong magnetic field it reduces to a model similar to the kicked Harper model. This model is studied numerically and is found to be extremely sensitive to the strength of the electric field. In particular, as the strength of the electric field is varied a metal -- insulator transition may be found. The experimental conditions required for this transition are discussed.Comment: 6 files: kharp.tex, fig1.ps fig2.ps fi3.ps fig4.ps fig5.p

Fisheries interactions of Delphinus delphis in the north-east Atlantic with an emphasis on Galicia, north-west Spain.

Bycatch from interactions with fisherie s remains the biggest global threat to marine mammals. Galicia, north - west Spain, is one of the world’s main fishing regions and a high level of cetacean - fisheries interactions has been reported from on - board observers, interviews with fisheries stakeholde rs and analysis of stranded and by - caught carcasses. Delphinus delphis is the most abundant cetacean in the area and since 1990 necropsies of over 1800 stranded and by - caught Delphinus have been conducted. Life history data (age, maturity, and pregnancy ra te data) from stranded and by - caught cetaceans can be used to construct life tables and to estimate overall mortality and fisheries mortality rates. Age and maturity were determined from stranded and by - caught Delphinus between 1990 and 2009. Males and fem ales reach sexual maturity at 8.5 and 7.5 years of age, respectively, and no temporal difference in age at sexual maturity was observed. Results indicate 13% annual mortality in the Delphinus delphis north - east Atlantic population and necropsy data suggest s that 60% of mortality (i.e. 7.2% annual mortality) is attributable to fisheries interactions, predominantly from pair trawls and gillnets. By - caught Delphinus were found to die significantly younger than non - by - caught animals (p=<0.001) although no sex - r elated difference in bycatch rate was observed (p=0.051). The estimated annual mortality due to fisheries interactions greatly exceeds the 2% limit set by ASCOBANS and the IWC and high bycatch rates are also reported for other countries e.g. the UK, France and Portugal. Although Delphinus delphis in the north - east Atlantic is one continuous population, the high level of bycatch occurring in parts of the range is most likely unsustainable and will be discussed. There is a need to carry out on - board monitorin g, notably in the north - west Iberian Peninsula (Galicia and Portugal), to incorporate cetacean bycatch into fisheries advice and, above all, to start introducing mitigation measures

Chaos and flights in the atom-photon interaction in cavity QED

We study dynamics of the atom-photon interaction in cavity quantum electrodynamics (QED), considering a cold two-level atom in a single-mode high-finesse standing-wave cavity as a nonlinear Hamiltonian system with three coupled degrees of freedom: translational, internal atomic, and the field. The system proves to have different types of motion including L\'{e}vy flights and chaotic walkings of an atom in a cavity. It is shown that the translational motion, related to the atom recoils, is governed by an equation of a parametric nonlinear pendulum with a frequency modulated by the Rabi oscillations. This type of dynamics is chaotic with some width of the stochastic layer that is estimated analytically. The width is fairly small for realistic values of the control parameters, the normalized detuning $\delta$ and atomic recoil frequency $\alpha$. It is demonstrated how the atom-photon dynamics with a given value of $\alpha$ depends on the values of $\delta$ and initial conditions. Two types of L\'{e}vy flights, one corresponding to the ballistic motion of the atom and another one corresponding to small oscillations in a potential well, are found. These flights influence statistical properties of the atom-photon interaction such as distribution of Poincar\'{e} recurrences and moments of the atom position $x$. The simulation shows different regimes of motion, from slightly abnormal diffusion with $\sim\tau^{1.13}$ at $\delta =1.2$ to a superdiffusion with $\sim \tau^{2.2}$ at $\delta=1.92$ that corresponds to a superballistic motion of the atom with an acceleration. The obtained results can be used to find new ways to manipulate atoms, to cool and trap them by adjusting the detuning $\delta$.Comment: 16 pages, 7 figures. To be published in Phys. Rev.

A Numerical Investigation of the Effects of Classical Phase Space Structure on a Quantum System

We present a detailed numerical study of a chaotic classical system and its quantum counterpart. The system is a special case of a kicked rotor and for certain parameter values possesses cantori dividing chaotic regions of the classical phase space. We investigate the diffusion of particles through a cantorus; classical diffusion is observed but quantum diffusion is only significant when the classical phase space area escaping through the cantorus per kicking period greatly exceeds Planck's constant. A quantum analysis confirms that the cantori act as barriers. We numerically estimate the classical phase space flux through the cantorus per kick and relate this quantity to the behaviour of the quantum system. We introduce decoherence via environmental interactions with the quantum system and observe the subsequent increase in the transport of quantum particles through the boundary.Comment: 15 pages, 22 figure

Dressing Up the Kink

Many quantum field theoretical models possess non-trivial solutions which are stable for topological reasons. We construct a self-consistent example for a self-interacting scalar field--the quantum (or dressed) kink--using a two particle irreducible effective action in the Hartree approximation. This new solution includes quantum fluctuations determined self-consistently and nonperturbatively at the 1-loop resummed level and allowed to backreact on the classical mean-field profile. This dressed kink is static under the familiar Hartree equations for the time evolution of quantum fields. Because the quantum fluctuation spectrum is lower lying in the presence of the defect, the quantum kink has a lower rest energy than its classical counterpart. However its energy is higher than well-known strict 1-loop results, where backreaction and fluctuation self-interactions are omitted. We also show that the quantum kink exists at finite temperature and that its profile broadens as temperature is increased until it eventually disappears.Comment: 13 pages, latex, 3 eps figures; revised with yet additional references, minor rewordin

Controlling collapse in Bose-Einstein condensates by temporal modulation of the scattering length

We consider, by means of the variational approximation (VA) and direct numerical simulations of the Gross-Pitaevskii (GP) equation, the dynamics of 2D and 3D condensates with a scattering length containing constant and harmonically varying parts, which can be achieved with an ac magnetic field tuned to the Feshbach resonance. For a rapid time modulation, we develop an approach based on the direct averaging of the GP equation,without using the VA. In the 2D case, both VA and direct simulations, as well as the averaging method, reveal the existence of stable self-confined condensates without an external trap, in agreement with qualitatively similar results recently reported for spatial solitons in nonlinear optics. In the 3D case, the VA again predicts the existence of a stable self-confined condensate without a trap. In this case, direct simulations demonstrate that the stability is limited in time, eventually switching into collapse, even though the constant part of the scattering length is positive (but not too large). Thus a spatially uniform ac magnetic field, resonantly tuned to control the scattering length, may play the role of an effective trap confining the condensate, and sometimes causing its collapse.Comment: 7 figure

Breakdown of correspondence in chaotic systems: Ehrenfest versus localization times

Breakdown of quantum-classical correspondence is studied on an experimentally realizable example of one-dimensional periodically driven system. Two relevant time scales are identified in this system: the short Ehrenfest time t_h and the typically much longer localization time scale T_L. It is shown that surprisingly weak modification of the Hamiltonian may eliminate the more dramatic symptoms of localization without effecting the more subtle but ubiquitous and rapid loss of correspondence at t_h.Comment: 4 pages, 5 figures, replaced with a version submitted to PR

What trial participants need to be told about placebo effects to give informed consent: a survey to establish existing knowledge among patients with back pain.

INTRODUCTION: Patients require an accurate knowledge about placebos and their possible effects to ensure consent for placebo-controlled clinical trials is adequately informed. However, few previous studies have explored patients' baseline (ie, pretrial recruitment) levels of understanding and knowledge about placebos. The present online survey aimed to assess knowledge about placebos among patients with a history of back pain. DESIGN: A 15-item questionnaire was constructed to measure knowledge about placebos. Additional questions assessed sociodemographic characteristics, duration and severity of back pain, and previous experience of receiving placebos. SETTING: Participants recruited from community settings completed the study online. RESULTS: 210 participants completed the questionnaire. 86.7% had back pain in the past 6 months, 44.3% currently had back pain. 4.3% had received a placebo intervention as part of a clinical trial and 68.1% had previously read or heard information about placebos. Overall knowledge of placebos was high, with participants on average answering 12.07 of 15 questions about placebos correctly (SD=2.35). However, few participants correctly answered questions about the nocebo effect (31.9% correct) and the impact of the colour of a placebo pill (55.2% correct). CONCLUSIONS: The findings identified key gaps in knowledge about placebos. The lack of understanding of the nocebo effect in particular has implications for the informed consent of trial participants. Research ethics committees and investigators should prioritise amending informed consent procedures to incorporate the fact that participants in the placebo arm might experience adverse side effects

Chaos in a double driven dissipative nonlinear oscillator

We propose an anharmonic oscillator driven by two periodic forces of different frequencies as a new time-dependent model for investigating quantum dissipative chaos. Our analysis is done in the frame of statistical ensemble of quantum trajectories in quantum state diffusion approach. Quantum dynamical manifestation of chaotic behavior, including the emergence of chaos, properties of strange attractors, and quantum entanglement are studied by numerical simulation of ensemble averaged Wigner function and von Neumann entropy.Comment: 9 pages, 18 figure