Compact magneto-optical sources of slow atoms

Three different configurations of compact magneto-optical sources of slow Rb atoms(LVIS, 2D(+)-MOT and 2D-MOT) were compared with each other at fixed geometry of cooling laser beams. A precise control of the intensity balances between the four separate transverse cooling laser beams provided a total continuous flux of cold atoms from the LVIS and 2D(+)-MOT sources about 8x10^9 atoms/s at total laser power of 60 mW. The flux was measured directly from the loading rate of a 3D-MOT, placed 34 cm downstream from the sources. Average velocities of the cooled atomic beam for the LVIS and 2D(+)-MOT sources were about 8.5 m/s and 11 m/s respectively. An essential advantage of the compact magneto-optical sources is that their background flux of thermal atoms is two to three orders of the magnitude smaller than the flux of slow atoms.Comment: 12 pages, 10 figures. to be published in Optics Communication

Volunteer Delivery of a Community-Based Strength Training Program: Comparison of Adopting and Nonadopting Extension Educator Perspectives

Volunteer leaders are increasingly being utilized to deliver community strength training classes, but the factors affecting adoption of volunteer delivery approaches by educators or program managers have not been well explored. This study sought to identify these factors by comparing perspectives of adopting and nonadopting county Extension educators for a group strength training program delivered through county Cooperative Extension offices. Semistructured interviews were conducted with a purposive sample of adopting (n=6) and nonadopting (n=13) educators. Interviews were recorded, transcribed verbatim, and coded using thematic content analysis. Review of codes related to adoption or nonadoption of volunteer delivery approaches produced common themes. Both groups acknowledged role differences between educators and volunteers and expressed concerns about maintaining program quality. Adopters expressed greater comfort with volunteer-led program approaches and understanding of the educator-volunteer role. Nonadopters were hesitant to request program participants serve as leaders but felt participants were capable. Both groups were motivated to offer the program for dual personal and community benefit, but nonadopters expressed reliance on the program to maintain physical activity habits and for social support. Findings can inform others seeking to adapt community programs for volunteer delivery or engage volunteers in existing program delivery

Motivations of Volunteer Leaders in an Extension Exercise Program

This article describes findings from a qualitative study of volunteer leaders in the StrongWomen strength training program in Arkansas. The study explored reasons volunteers initially agreed to serve, perceptions of volunteer role, and motivations for continuing to lead strength training groups long-term. Findings suggest a combination of factors supporting volunteer engagement: personal benefit of program, desire to continue program combined with a personal invitation to volunteer extended by the agent, desire to support a co-leader, and exercise and social support needs met through volunteer service. Motivations of Extension health program volunteers are important to address to maximize program impact

Absence of histones from the chromosomal proteins of fungi

Interphase chromosomes were isolated in good yield from four species of fungi. In no case does the chromatin contain histones such as are characteristic of the chromosomes of other eukaryotic organisms

Market conditions, trader types and price–volume relation in energy futures markets

We investigate the asymmetric relations between trading volume and price changes, and trading volume and price volatility of energy futures contracts across maturities and under different market conditions. Using a relatively long sample of daily observations, we examine whether the impact of trading volume on returns and volatility of futures contracts can be time-varying and dependent on the market condition. We differentiate the market condition based on the slope of the forward curve into backwardation and contango. The results indicate that trading volume and returns are positively related when the market is in backwardation and negatively related when the market is in contango. In addition, the positive relation between changes in trading volume and volatility of futures contracts seem to be stronger when the market is in backwardation than when it is in contango. Finally, the results indicate that, to a certain extent, trade participation and trading activities of agents in energy futures markets can be explained by the slope of the forward curve which reflects the market condition and sentiment

Adaptable-radius, time-orbiting magnetic ring trap for Bose-Einstein condensates

We theoretically investigate an adjustable-radius magnetic storage ring for laser-cooled and Bose-condensed atoms. Additionally, we discuss a novel time-dependent variant of this and other ring traps. Time-orbiting ring traps provide a high optical access method for spin-flip loss prevention near a storage ring's circular magnetic field zero. Our scalable storage ring will allow one to probe the fundamental limits of condensate Sagnac interferometry.Comment: 5 pages, 3 figures. accepted in J Phys

Studies of group velocity reduction and pulse regeneration with and without the adiabatic approximation

We present a detailed semiclassical study on the propagation of a pair of optical fields in resonant media with and without adiabatic approximation. In the case of near and on resonance excitation, we show detailed calculation, both analytically and numerically, on the extremely slowly propagating probe pulse and the subsequent regeneration of a pulse via a coupling laser. Further discussions on the adiabatic approximation provide many subtle understandings of the process including the effect on the band width of the regenerated optical field. Indeed, all features of the optical pulse regeneration and most of the intricate details of the process can be obtained with the present treatment without invoke a full field theoretical method. For very far off resonance excitation, we show that the analytical solution is nearly detuning independent, a surprising result that is vigorously tested and compared to numerical calculations with very good agreement.Comment: 13 pages, 15 figures, submitted to Phys. Rev.

Predicting global habitat suitability for stony corals on seamounts

Aim Globally, species distribution patterns in the deep sea are poorly resolved, with spatial coverage being sparse for most taxa and true absence data missing. Increasing human impacts on deep-sea ecosystems mean that reaching a better understanding of such patterns is becoming more urgent. Cold-water stony corals (Order Scleractinia) form structurally complex habitats (dense thickets or reefs) that can support a diversity of other associated fauna. Despite their widely accepted ecological importance, records of scleractinian corals on seamounts are patchy and simply not available for most of the global ocean. The objective of this paper is to model the global distribution of suitable habitat for stony corals on seamounts. Location Seamounts worldwide. Methods We compiled a database containing all accessible records of scleractinian corals on seamounts. Two modelling approaches developed for presence-only data were used to predict global habitat suitability for seamount scleractinians: maximum entropy modelling (Maxent) and environmental niche factor analysis (ENFA). We generated habitat-suitability maps and used a cross-validation process with a threshold-independent metric to evaluate the performance of the models. Results Both models performed well in cross-validation, although the Maxent method consistently outperformed ENFA. Highly suitable habitat for seamount stony corals was predicted to occur at most modelled depths in the North Atlantic, and in a circumglobal strip in the Southern Hemisphere between 20° and 50° S and shallower than around 1500 m. Seamount summits in most other regions appeared much less likely to provide suitable habitat, except for small near-surface patches. The patterns of habitat suitability largely reflect current biogeographical knowledge. Environmental variables positively associated with high predicted habitat suitability included the aragonite saturation state, and oxygen saturation and concentration. By contrast, low levels of dissolved inorganic carbon, nitrate, phosphate and silicate were associated with high predicted suitability. High correlation among variables made assessing individual drivers difficult. Main conclusions Our models predict environmental conditions likely to play a role in determining large-scale scleractinian coral distributions on seamounts, and provide a baseline scenario on a global scale. These results present a first-order hypothesis that can be tested by further sampling. Given the high vulnerability of cold-water corals to human impacts, such predictions are crucial tools in developing worldwide conservation and management strategies for seamount ecosystems. © 2009 Blackwell Publishing Ltd

Synchronization of Hamiltonian motion and dissipative effects in optical lattices: Evidence for a stochastic resonance

We theoretically study the influence of the noise strength on the excitation of the Brillouin propagation modes in a dissipative optical lattice. We show that the excitation has a resonant behavior for a specific amount of noise corresponding to the precise synchronization of the Hamiltonian motion on the optical potential surfaces and the dissipative effects associated with optical pumping in the lattice. This corresponds to the phenomenon of stochastic resonance. Our results are obtained by numerical simulations and correspond to the analysis of microscopic quantities (atomic spatial distributions) as well as macroscopic quantities (enhancement of spatial diffusion and pump-probe spectra). We also present a simple analytical model in excellent agreement with the simulations