4,838 research outputs found
Persistent current formation in a high-temperature Bose-Einstein condensate: an experimental test for c-field theory
Experimental stirring of a toroidally trapped Bose-Einstein condensate at
high temperature generates a disordered array of quantum vortices that decays
via thermal dissipation to form a macroscopic persistent current [T. W. Neely
em et al. arXiv:1204.1102 (2012)]. We perform 3D numerical simulations of the
experimental sequence within the Stochastic Projected Gross-Pitaevskii equation
using ab initio determined reservoir parameters. We find that both damping and
noise are essential for describing the dynamics of the high-temperature Bose
field. The theory gives a quantitative account of the formation of a persistent
current, with no fitted parameters.Comment: v2: 7 pages, 3 figures, new experimental data and numerical
simulation
INVISQUE as a tool for intelligence analysis: the construction of explanatory narratives
We report an exploratory user-study in which a group of civil servants with experience of, or involvement in, intelligence analysis used the tool INVISQUE to address a problem using the 2011 VAST dataset. INVISQUE uses a visual metaphor that combines searching, clustering and sorting of document surrogates with free-form manipulation on an infinite canvas. We were interested in exposing the behaviours and related cognitive strategies that users would employ to better understand how this and similar environments might better support intelligence type work. Our results include the observation that the search and spatial features of the system supported participants in establishing, elaborating and systematically evaluating explanatory narratives that accounted for the data. Also, visual persistence at the interface allowed them to keep track of searches and to re-find documents when their importance became apparent. We conclude with reflections on our findings and propose a set of guidelines for developing systems that support sensemaking
Suppression of Kelvon-induced decay of quantized vortices in oblate Bose-Einstein Condensates
We study the Kelvin mode excitations on a vortex line in a three-dimensional
trapped Bose-Einstein condensate at finite temperature. Our stochastic
Gross-Pitaevskii simulations show that the activation of these modes can be
suppressed by tightening the confinement along the direction of the vortex
line, leading to a strong suppression in the vortex decay rate as the system
enters a regime of two-dimensional vortex dynamics. As the system approaches
the condensation transition temperature we find that the vortex decay rate is
strongly sensitive to dimensionality and temperature, observing a large
enhancement for quasi-two-dimensional traps. Three-dimensional simulations of
the recent vortex dipole decay experiment of Neely et al. [Phys. Rev. Lett.
104, 160401 (2010)] confirm two-dimensional vortex dynamics, and predict a
dipole lifetime consistent with experimental observations and suppression of
Kelvon-induced vortex decay in highly oblate condensates.Comment: 8 pages, 8 figure
Indexing Giving: Examining State-level Data about Itemized Charitable Deductions Using Known Determinants of Giving
Average itemized charitable deductions by state are widely used as a measure of giving yet grossly misstate “generosity.” Extending a model initially developed by Gittell and Tebaldi (2004), this work finds that when considering state-level measures of economic and social factors determinant of individual giving at the micro-level, six of the 20 states said to be most generous on the popular “generosity index” have average itemized contributions at least 5 percent LOWER than their predicted giving capacity. Nine states in the bottom 20 on the “generosity index” have average itemized giving at or above the predicted levels.
Further analysis using household-level survey data from the Center on Philanthropy Panel Study (a part of the Panel Study of Income Dynamics conducted by the University of Michigan) reveals significant differences in total secular and total religious giving by households in different Census regions (analysis is not possible at the state level using this data set). The secular and religious differences in giving largely account for the differing total amounts reported. The paper concludes with an appeal that generosity be evaluated as a percentage of income donated combined with percentage of households that donate in a given region
An Investigation into the Role of Coping in Preventing Depression Associated with Perfectionism in Preadolescent Children
The relationships between self-oriented and socially prescribed perfectionism (SPP) and maladaptive and adaptive coping strategies and their collective impact on depression symptoms were examined in the context of a randomized controlled universal trial of the Aussie Optimism Positive Thinking Skills Program. Five hundred and forty-one children aged 8-12 completed a battery of self-reports, of which responses for measures of depression symptoms, perfectionism, and coping strategies were examined for the purposes of this study. Structural equation modeling tested whether coping mediated the effects of perfectionism on depression. Results indicated that SPP had both a direct and an indirect relationship with depression symptoms through a moderate association with maladaptive coping. Implications for prevention of depression were discussed and recommendations for future research were proposed
- …