Nonlinear coupling between scissors modes of a Bose-Einstein condensate

We explore the nonlinear coupling of the three scissors modes of an anisotropic Bose-Einstein condensate. We show that only when the frequency of one of the scissors modes is twice the frequency of another scissors mode, these two modes can be resonantly coupled and a down conversion can occur. We perform the calculation variationally using a gaussian trial wave function. This enables us to obtain simple analytical results that describe the oscillation and resonance behaviour of the two coupled modes.Comment: 12 pages, 3 figures, submitted to Phys. Rev.

Phase fluctuations in atomic Bose gases

We improve on the Popov theory for partially Bose-Einstein condensed atomic gases by treating the phase fluctuations exactly. As a result, the theory becomes valid in arbitrary dimensions and is able to describe the low-temperature crossover between three, two and one-dimensional Bose gases, which is currently being explored experimentally. We consider both homogeneous and trapped Bose gases.Comment: 4 pages. Title changed Major changes involve extension of theory to include trapped Bose gases. Deletion of reference to and comparison with hydrogen experiment. Due to these changes, second author added. Modified manuscript accepted for PR

A Cross-Sectional Study Exploring the Physical Activity Levels of Afghans and Other South Asian Youth in the UK

Introduction: Participating in regular physical activity (PA) has numerous benefits, such as reducing obesity, chronic degenerative conditions, and depression. Despite many health-related benefits, physical inactivity is increasing in young people worldwide, especially in ethnic minority groups, such as British South Asians (BSAs). The aim of this study was to explore the PA levels of BSAs, specifically focusing on youth from Afghan, Pakistani, Bangladeshi, and Indian groups. Methods: A total of 191 (Afghans N = 44; Bangladeshi N = 39; Indian N = 56, Pakistani N = 52) youth from the West Midlands (UK) participated in this study (mean age 15.4 ± 0.5). The International Physical Activity Questionnaire—Short Form was used to measure PA levels. Data were modelled using a Bayesian approach to determine differences in PA levels. Results: The results indicated that 88.5% Afghans, 80% Bangladeshi, 78.6% Indians and 63% Pakistani reported engaging in <30 min of PA per day. Additionally, boys were more active than girls across all ethnic groups. Discussion: This study highlighted an alarmingly low proportion of young people from each BSA ethnic group meeting the PA guidelines. To the authors’ knowledge, this is the first study to explore and compare PA levels of the young British Afghan population, thus contributing novel findings to the area of BSA PA. Conclusion: Overall, the vast majority of BSA young people failed to meet the recommended PA guidelines of 60 min per day. Future research could utilise objective methods, such as Global Positioning System, pedometers and accelerometery to track and monitor PA levels, and could adopt an ecological approach to explore determinants of PA within each ethnic and gender group

The Psychobiological Correlates Of Panic Attacks During In Vivo Exposure

This study examined in detail the psychobiological correlates of panic attacks experienced in panic disorder with agoraphobia. The cognitions, affect, and physiology of the six patients were monitored during in vivo exposure to their phobic situations. The results from these case studies showed that catastrophic cognitions are the key component of panic attacks. However, there was no clear-cut evidence to support an interaction among cognitions, affect, and physiology, which has been postulated by cognitive theories to be the central component of panic attacks and panic disorder with agoraphobia

Bright soliton trains of trapped Bose-Einstein condensates

We variationally determine the dynamics of bright soliton trains composed of harmonically trapped Bose-Einstein condensates with attractive interatomic interactions. In particular, we obtain the interaction potential between two solitons. We also discuss the formation of soliton trains due to the quantum mechanical phase fluctuations of a one-dimensional condensate.Comment: 4 pages, 2 figures, submitted to PR

Spinor Bose-Einstein Condensates with Many Vortices

Vortex-lattice structures of antiferromagnetic spinor Bose-Einstein condensates with hyperfine spin F=1 are investigated theoretically based on the Ginzburg-Pitaevskii equations near $T_{c}$. The Abrikosov lattice with clear core regions are found {\em never stable} at any rotation drive $\Omega$. Instead, each component $\Psi_{i}$ $(i=0,\pm 1)$ prefers to shift the core locations from the others to realize almost uniform order-parameter amplitude with complicated magnetic-moment configurations. This system is characterized by many competing metastable structures so that quite a variety of vortices may be realized with a small change in external parameters.Comment: 4 page

Extension of valuations in skew fields

The aim of this thesis is to study the extension of valuations in skew field extensions. In Chapter I we look at the following problem. Let K be a field and V a valuation ring of rank 1 in K. Let H be a crossed product division algebra over K. Then we study conditions under which there exists a matrix local ring R in H lying over V and generating H as K-space. We then find that R is a valuation ring in H lying over V iff R is local. Moreover if V is discrete of rank 1, then R is a maximal order in H. In Chapter II we study directly conditions under which a valuation on the centre of a finite dimensional central division algebra can be extended to the whole algebra. In particular if H = (E/K; sigma, a) is a cyclic division algebra and v is a discrete rank 1 valuation on K, then the extension of v to H depends on v(a). We then carry on the study of the extension problem for the tensor product of algebras. In particular if [special characters omitted] and V a rank 1 valuation ring in K and if there exists a valuation ring W in H lying over V with W &cap; Hi = wi (i = 1,...,r), we study conditions under which [special characters omitted]. In Chapter III we look at infinite skew field extensions. We study valuations in skew function fields. The application will include among others, free algebras, universal associative envelopes of Lie algebras and generic crossed product. However our main concern in this chapter is the following question raised by P.M. Cohn. Let K1, K2 be two skew fields with a common subfield K and let v1, v2 be real valued valuations on K 1 and K2 respectively such that v1|K = v 2|K = v. Do v1, v2 have a common extension to H = K 1 OK K2 (the field coproduct of K1 and K2)?. We show that in general the answer is no. Nevertheless we find conditions under which v1,v2 have a common extension to H. <p

Mermin-Ho vortex in ferromagnetic spinor Bose-Einstein condensates

The Mermin-Ho and Anderson-Toulouse coreless non-singular vortices are demonstrated to be thermodynamically stable in ferromagnetic spinor Bose-Einstein condensates with the hyperfine state F=1. The phase diagram is established in a plane of the rotation drive vs the total magnetization by comparing the energies for other competing non-axis-symmetric or singular vortices. Their stability is also checked by evaluating collective modes.Comment: 4 pages, 4 figure

Skyrmion Excitation in Two-Dimensional Spinor Bose-Einstein Condensate

We study the properties of coreless vortices(skyrmion) in spinor Bose-Einstein condensate. We find that this excitation is always energetically unstable, it always decays to an uniform spin texture. We obtain the skyrmion energy as a function of its size and position, a key quantity in understanding the decay process. We also point out that the decay rate of a skyrmion with high winding number will be slower. The interaction between skyrmions and other excitation modes are also discussed.Comment: 5 pages, 4 figures, final version published in Phys. Rev.