Phase Transitions in Generalised Spin-Boson (Dicke) Models

We consider a class of generalised single mode Dicke Hamiltonians with arbitrary boson coupling in the pseudo-spin $x$-$z$ plane. We find exact solutions in the thermodynamic, large-spin limit as a function of the coupling angle, which allows us to continuously move between the simple dephasing and the original Dicke Hamiltonians. Only in the latter case (orthogonal static and fluctuating couplings), does the parity-symmetry induced quantum phase transition occur.Comment: 6 pages, 5 figue

Coherent control of population transfer between communicating defects

Population transfer between two identical, communicating defects in a one-dimensional tight-binding lattice can be systematically controlled by external time-periodic forcing. Employing a force with slowly changing amplitude, the time it takes to transfer a particle from one defect to the other can be altered over several orders of magnitude. An analytical expression is derived which shows how the forcing effectively changes the energy splitting between the defect states, and numerical model calculations illustrate the possibility of coherent control of the transfer.Comment: 7 pages, 6 figures, to appear in Phys. Rev.

A progressive diagonalization scheme for the Rabi Hamiltonian

A diagonalization scheme for the Rabi Hamiltonian, which describes a qubit interacting with a single-mode radiation field via a dipole interaction, is proposed. It is shown that the Rabi Hamiltonian can be solved almost exactly using a progressive scheme that involves a finite set of one variable polynomial equations. The scheme is especially efficient for lower part of the spectrum. Some low-lying energy levels of the model with several sets of parameters are calculated and compared to those provided by the recently proposed generalized rotating-wave approximation and full matrix diagonalization.Comment: 8pages, 1 figure, LaTeX. Accepted for publication in J. Phys. B: At. Mol. Opt. Phy

Multiplexed long-range electrohydrodynamic transport and nano-optical trapping with cascaded bowtie photonic crystal cavities

Photonic crystal cavities have been widely studied for optical trapping due to their ability to generate high quality factor resonances. However, prior photonic crystal nanotweezers possess mode volumes significantly larger than those of plasmonic nanotweezers, which limit the gradient force. Additionally, they also suffer from low particle capture rates. In this paper, we propose a nanotweezer system based on a 1D bowtie photonic crystal nanobeam that achieves extreme mode confinement and an electromagnetic field enhancement factor of 68 times, while supporting a high-quality factor of 15,000 in water. Furthermore, by harnessing the localized heating of a water layer near the bowtie cavity region, combined with an applied alternating current electric field, our system provides long-range transport of particles with average velocities of 5 ${\mu}$m/s towards the bowtie cavities on demand. Once transported to the bowtie cavity region, our results show that a 20 nm quantum dot will be confined in a potential well with a depth of 35 ${k_B}$T. Thus, our approach effectively addresses the challenge of limited capture rate in photonic crystal nanotweezers for the first time. Finally, we present the concept of multiplexed long-range transport for hand-off of a single emitter from one cavity to the next by simply switching the wavelength of the input light. This novel multiplexed integrated particle trapping platform is expected to open new opportunities in directed assembly of nanoscale quantum emitters and ultrasensitive sensors for single particle spectroscopy.Comment: 11 pages, 4 figure

Risky bodies, risky spaces, maternal ‘instincts’: swimming and motherhood

Swimming and aquatic activity are fields in which gendered, embodied identities are brought to the fore, and the co-presence of other bodies can have a significant impact upon lived experiences. To date, however, there has been little research on sport and physical cultures that investigates how meanings associated with space impact upon women’s embodied experiences of participating in swimming, specifically in the presence of their young children. Using semi-structured interviews and non-participant observations, this qualitative study employed a Foucauldian-feminist framework to explore self-perceptions and embodied experiences of aquatic activity amongst 20 women, who were swimming with children aged under 4. Results highlight that through ‘felt’ maternal responsibilities, the co-presence of babies’ and children’s bodies shifted women’s intentionality away from the self towards their child. Mothers’ embodied experiences were grounded in perceptions of space-specific ‘maternal instincts’ and focused upon disciplining their children’s bodies in the lived-space of the swimming pool. Key findings cohere around mothers’ felt concerns about hygiene, water temperature and safety, and elements of intercorporeality and ‘somatic empathy’

Dynamical transitions and sliding friction in the two-dimensional Frenkel-Kontorova model

The nonlinear response of an adsorbed layer on a periodic substrate to an external force is studied via a two dimensional uniaxial Frenkel-Kontorova model. The nonequlibrium properties of the model are simulated by Brownian molecular dynamics. Dynamical phase transitions between pinned solid, sliding commensurate and incommensurate solids and hysteresis effects are found that are qualitatively similar to the results for a Lennard-Jones model, thus demonstrating the universal nature of these features.Comment: 11 pages, 12 figures, to appear in Phys. Rev.

Sporting embodiment: sports studies and the (continuing) promise of phenomenology

Whilst in recent years sports studies have addressed the calls ‘to bring the body back in’ to theorisations of sport and physical activity, the ‘promise of phenomenology’ remains largely under-realised with regard to sporting embodiment. Relatively few accounts are grounded in the ‘flesh’ of the lived sporting body, and phenomenology offers a powerful framework for such analysis. A wide-ranging, multi-stranded, and interpretatively contested perspective, phenomenology in general has been taken up and utilised in very different ways within different disciplinary fields. The purpose of this article is to consider some selected phenomenological threads, key qualities of the phenomenological method, and the potential for existentialist phenomenology in particular to contribute fresh perspectives to the sociological study of embodiment in sport and exercise. It offers one way to convey the ‘essences’, corporeal immediacy and textured sensuosity of the lived sporting body. The use of Interpretative Phenomenological Analysis (IPA) is also critically addressed. Key words: phenomenology; existentialist phenomenology; interpretative phenomenological analysis (IPA); sporting embodiment; the lived-body; Merleau-Pont

Primary Defects in β-Cell Function Further Exacerbated by Worsening of Insulin Resistance Mark the Development of Impaired Glucose Tolerance in Obese Adolescents

OBJECTIVE—Impaired glucose tolerance (IGT) is a pre-diabetic state of increasing prevalence among obese adolescents. The purpose of this study was to determine the natural history of progression from normal glucose tolerance (NGT) to IGT in obese adolescents

Exclusion of enrolled participants in randomised controlled trials: what to do with ineligible participants?

OBJECTIVE: Post-randomisation exclusions in randomised controlled trials are common and may include participants identified as not meeting trial eligibility criteria after randomisation. We report how a decision might be reached and reported on, to include or exclude these participants. We illustrate using a motivating scenario from the BREATHE trial (Trial registration ClinicalTrials.gov, NCT02426112) evaluating azithromycin for the treatment of chronic lung disease in people aged 6-19 years with HIV in Zimbabwe and Malawi. KEY POINTS: Including all enrolled and randomised participants in the primary analysis of a trial ensures an unbiased estimate of the intervention effect using intention-to-treat principles, and minimises the effects of confounding through balanced allocation to trial arm. Ineligible participants are sometimes enrolled, due to measurement or human error. Of 347 participants enrolled into the BREATHE trial, 11 (3.2%) were subsequently found to be ineligible based on lung function criteria. We assumed no safety risk of azithromycin treatment; their inclusion in the trial and subsequent analysis of the intervention effect therefore mirrors clinical practice. Senior trial investigators considered diurnal variations in the measurement of lung function, advantages of retaining a higher sample size and advice from the Data Safety and Monitoring Board and Trial Steering Committee, and decided to include these participants in primary analysis. We planned and reported analyses including and excluding these participants, and in our case the interpretation of treatment effect was consistent. CONCLUSION: The decision, by senior investigators, on whether to exclude enrolled participants, should reflect issues of safety, treatment efficacy, statistical power and measurement error. As long as decisions are made prior to finalising the statistical analysis plan for the trial, the risk of exclusions creating bias should be minimal. The decision taken should be transparently reported and a sensitivity analysis can present the opposite decision