7,350 research outputs found
Far-from-equilibrium dynamics of a strongly coupled non-Abelian plasma with non-zero charge density or external magnetic field
Using holography, we study the evolution of a spatially homogeneous, far from
equilibrium, strongly coupled N=4 supersymmetric Yang-Mills plasma with a
non-zero charge density or a background magnetic field. This gauge theory
problem corresponds, in the dual gravity description, to an initial value
problem in Einstein-Maxwell theory with homogeneous but anisotropic initial
conditions. We explore the dependence of the equilibration process on different
aspects of the initial departure from equilibrium and, while controlling for
these dependencies, examine how the equilibration dynamics are affected by the
presence of a non-vanishing charge density or an external magnetic field. The
equilibration dynamics are remarkably insensitive to the addition of even large
chemical potentials or magnetic fields; the equilibration time is set primarily
by the form of the initial departure from equilibrium. For initial deviations
from equilibrium which are well localized in scale, we formulate a simple model
for equilibration times which agrees quite well with our results.Comment: 54 pages, 18 figures, published version, ref. update
Psychosocial mediators of change in physical activity in the Welsh national exercise referral scheme: secondary analysis of a randomised controlled trial
Objective:
While an increasing number of randomised controlled trials report impacts of exercise referral schemes (ERS) on physical activity, few have investigated the mechanisms through which increases in physical activity are produced. This study examines whether a National Exercise Referral Scheme (NERS) in Wales is associated with improvements in autonomous motivation, self-efficacy and social support, and whether change in physical activity is mediated by change in these psychosocial processes.<p></p>
Methods:
A pragmatic randomised controlled trial of NERS across 12 LHBs in Wales. Questionnaires measured demographic data and physical activity at baseline. Participants (N = 2160) with depression, anxiety or CHD risk factors were referred by health professionals and randomly assigned to control or intervention. At six months psychological process measures were collected by questionnaire. At 12 months physical activity was assessed by 7 Day PAR telephone interview. Regressions tested intervention effects on psychosocial variables, physical activity before and after adjusting for mediators and socio demographic patterning.<p></p>
Results:
Significant intervention effects were found for autonomous motivation and social support for exercise at 6 months. No intervention effect was observed for self-efficacy. The data are consistent with a hypothesis of partial mediation of the intervention effect by autonomous motivation. Analysis of moderators showed significant improvements in relative autonomy in all subgroups. The greatest improvements in autonomous motivation were observed among patients who were least active at baseline.<p></p>
Discussion:
The present study offered key insights into psychosocial processes of change in an exercise referral scheme, with effects on physical activity mediated by autonomous motivation. Findings support the use of self-determination theory as a framework for ERS. Further research is required to explain socio-demographic patterning in responses to ERS, with changes in motivation occurring among all sub-groups of participants, though not always leading to higher adherence or behavioural change. This highlights the importance of socio-ecological approaches to developing and evaluating behaviour change interventions, which consider factors beyond the individual, including conditions in which improved motivation does or does not produce behavioural change
Sub-Optimal Allocation of Time in Sequential Movements
The allocation of limited resources such as time or energy is a core problem that organisms face when planning complex
actions. Most previous research concerning planning of movement has focused on the planning of single, isolated
movements. Here we investigated the allocation of time in a pointing task where human subjects attempted to touch two
targets in a specified order to earn monetary rewards. Subjects were required to complete both movements within a limited time but could freely allocate the available time between the movements. The time constraint presents an allocation
problem to the subjects: the more time spent on one movement, the less time is available for the other. In different
conditions we assigned different rewards to the two tokens. How the subject allocated time between movements affected
their expected gain on each trial. We also varied the angle between the first and second movements and the length of the
second movement. Based on our results, we developed and tested a model of speed-accuracy tradeoff for sequential
movements. Using this model we could predict the time allocation that would maximize the expected gain of each subject
in each experimental condition. We compared human performance with predicted optimal performance. We found that all
subjects allocated time sub-optimally, spending more time than they should on the first movement even when the reward
of the second target was five times larger than the first. We conclude that the movement planning system fails to maximize
expected reward in planning sequences of as few as two movements and discuss possible interpretations drawn from
economic theory
The use of phenol and myodil in the treatment of trigeminal neuralgia and atypical face pain
No Abstrac
Chandra and XMM-Newton Observations of the Double Cluster Abell 1758
Abell 1758 was classified as a single rich cluster of galaxies by Abell, but
a ROSAT observation showed that this system consists of two distinct clusters
(A1758N and A1758S) separated by approximately 8\arcmin (a projected
separation of 2 Mpc in the rest frame of the clusters). Only a few galaxy
redshifts have been published for these two clusters, but the redshift of the
Fe lines in the Chandra and XMM-Newton spectra shows that the recessional
velocities of A1758N and A1758S are within 2,100 km s. Thus, these two
clusters most likely form a gravitationally bound system, but our imaging and
spectroscopic analyses of the X-ray data do not reveal any sign of interaction
between the two clusters. The Chandra and XMM-Newton observations show that
A1758N and A1758S are both undergoing major mergers.
A1758N is in the late stages of a large impact parameter merger between two 7
keV clusters. The two remnant cores have a projected separation of 800 kpc.
Based on the measured pressure jumps preceding the two cores, they are receding
from one another at less than 1,600 km s. The two cores are surrounded
by hotter gas (--12 keV) that was probably shock heated during
the early stages of the merger. The gas entropy in the two remnant cores is
comparable with the central entropy observed in dynamically relaxed clusters,
indicating that the merger-induced shocks stalled as they tried to penetrate
the high pressure cores of the two merging systems.Each core also has a wake of
low entropy gas indicating that this gas was ram pressure stripped without
being strongly shocked (abridged). (A copy of the paper with higher resolution
images is available at http://asc.harvard.edu/~lpd/a1758.ps).Comment: paper plus 13 figure
Measuring Value in Primary Care: Enhancing Quality or Checking the Box?
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109581/1/hesr12256-sup-0001-AuthorMatrix.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109581/2/hesr12256.pd
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