Observation of vortex dipoles in an oblate Bose-Einstein condensate

We report experimental observations and numerical simulations of the formation, dynamics, and lifetimes of single and multiply charged quantized vortex dipoles in highly oblate dilute-gas Bose-Einstein condensates (BECs). We nucleate pairs of vortices of opposite charge (vortex dipoles) by forcing superfluid flow around a repulsive gaussian obstacle within the BEC. By controlling the flow velocity we determine the critical velocity for the nucleation of a single vortex dipole, with excellent agreement between experimental and numerical results. We present measurements of vortex dipole dynamics, finding that the vortex cores of opposite charge can exist for many seconds and that annihilation is inhibited in our highly oblate trap geometry. For sufficiently rapid flow velocities we find that clusters of like-charge vortices aggregate into long-lived dipolar flow structures.Comment: 4 pages, 4 figures, 1 EPAPS fil

Characteristics of Two-Dimensional Quantum Turbulence in a Compressible Superfluid

Under suitable forcing a fluid exhibits turbulence, with characteristics strongly affected by the fluid's confining geometry. Here we study two-dimensional quantum turbulence in a highly oblate Bose-Einstein condensate in an annular trap. As a compressible quantum fluid, this system affords a rich phenomenology, allowing coupling between vortex and acoustic energy. Small-scale stirring generates an experimentally observed disordered vortex distribution that evolves into large-scale flow in the form of a persistent current. Numerical simulation of the experiment reveals additional characteristics of two-dimensional quantum turbulence: spontaneous clustering of same-circulation vortices, and an incompressible energy spectrum with $k^{-5/3}$ dependence for low wavenumbers $k$ and $k^{-3}$ dependence for high $k$.Comment: 7 pages, 7 figures. Reference [29] updated for v

A Canadian-wide perspective on the essential conditions for taking a comprehensive school health approach

Background The primary purpose of this research was to explore Comprehensive School Health (CSH) stakeholders’ perceptions of the essential conditions for taking a CSH approach in other contexts across Canada. The secondary purpose was to examine the need for and development of an evaluative tool or resource to assess the implementation of the essential conditions. Methods Data were generated through individual semi-structured interviews (n = 38) and small group interviews (n = 3) with 45 participants across Canada involved in implementing policies or programs which take a CSH approach. Interviews were subjected to content analysis. Results There was positive support for the essential conditions and results indicated the essential conditions are relevant across Canada. Findings revealed the necessity for a new essential condition that reflected support and leadership from the school district and/or provincial/territorial governing bodies. Modifications to the description of each of the essential conditions were also suggested to provide clarity. Results also indicated that an evaluative tool that was concise, meaningful, and provided immediate feedback would be useful to school communities to establish readiness, assess, and improve ongoing implementation of CSH approaches. Conclusions This research contributes to the evidence-base of CSH by providing school communities across Canada with a set of refined and understandable essential conditions that support successful implementation. Further, the development of an evaluation tool will support school health champions, researchers, and policymakers in the optimization and implementation of policies or programs which take a CSH approach, ultimately supporting healthier school communities across the country

Dynamic Control of Laser Produced Proton Beams

The emission characteristics of intense laser driven protons are controlled using ultra-strong (of the order of 10^9 V/m) electrostatic fields varying on a few ps timescale. The field structures are achieved by exploiting the high potential of the target (reaching multi-MV during the laser interaction). Suitably shaped targets result in a reduction in the proton beam divergence, and hence an increase in proton flux while preserving the high beam quality. The peak focusing power and its temporal variation are shown to depend on the target characteristics, allowing for the collimation of the inherently highly divergent beam and the design of achromatic electrostatic lenses.Comment: 9 Pages, 5 figure

Optimization of double pulse pumping for Ni-like Sm x-ray lasers

We report a systematic study of double pulse pumping of the Ni-like Sm x-ray laser at 73 Angstrom, currently the shortest wavelength saturated x-ray laser. It is found that the Sm x-ray laser output can change by orders of magnitude when the intensity ratio of the pumping pulses and their relative delay are varied. Optimum pumping conditions are found and interpreted in terms of a simple model. (C) 1999 American Institute of Physics. [S0021-8979(99)07102-9]

Combination Forecasts of Bond and Stock Returns: An Asset Allocation Perspective

We investigate the out-of-sample forecasting ability of the HML, SMB, momentum, short-term and long-term reversal factors along with their size and value decompositions on U.S. bond and stock returns for a variety of horizons ranging from the short run (1 month) to the long run (2 years). Our findings suggest that these factors contain significantly more information for future bond and stock market returns than the typically employed financial variables. Combination of forecasts of the empirical factors turns out to be particularly successful, especially from an an asset allocation perspective. Similar findings pertain to the European and Japanese markets

Do women athletes’ experiences of menstrual function and dysfunction vary across competition levels? A mixed methods exploration

Menstrual dysfunction is a common phenomenon in sport and many women describe that their menstrual cycle can negatively impact their sport participation, performance, and experiences. However, there is little research examining if competition level plays a role in women athletes’ rates and experiences of menstrual function and dysfunction. Therefore, the purpose of this study was to explore and describe rates and experiences of menstrual function and dysfunction among athletes of differing competition levels. An online mixed methods approach was applied. Women athletes (N = 63), between 14 and 39 years of age (M = 24.20, SD = 6.53), competing in a range of sports from the local to international level completed an anonymous interview style survey to generate data. Data analysis for this project was an iterative and integrated process where quantitative and qualitative data were considered together and are represented through reported statistics and generated themes. Although group differences were hypothesized, no differences based on competition level in rates or experiences of menstrual dysfunction were observed. In addition to detailed descriptive statistics, five themes were generated: Normalizing Dysfunction; Menstrual Symptoms; Clothing as a Distraction; Participation Impact; and Regaining Control. In line with previous research, the women in this study experienced a range of menstrual dysfunctions that impacted their sport experiences. However, this study highlights that regardless of competition level or sport type women face challenges in sport regarding menstrual function and due to the normalization of dysfunction in sport women athletes’ health and well-being are not always supported