2,190 research outputs found
Relativistic models of magnetars: the twisted-torus magnetic field configuration
We find general relativistic solutions of equilibrium magnetic field
configurations in magnetars, extending previous results of Colaiuda et al.
(2008). Our method is based on the solution of the relativistic Grad-Shafranov
equation, to which Maxwell's equations can be reduced in some limit. We obtain
equilibrium solutions with the toroidal magnetic field component confined into
a finite region inside the star, and the poloidal component extending to the
exterior. These so-called twisted-torus configurations have been found to be
the final outcome of dynamical simulations in the framework of Newtonian
gravity, and appear to be more stable than other configurations. The solutions
include higher order multipoles, which are coupled to the dominant dipolar
field. We use arguments of minimal energy to constrain the ratio of the
toroidal to the poloidal field.Comment: 13 pages, 12 figures. Minor changes to match the version published on
MNRA
An investigative study of a spectrum-matching imaging system Final report
Evaluation system for classification of remote objects and materials identified by solar and thermal radiation emissio
Structure and deformations of strongly magnetized neutron stars with twisted torus configurations
We construct general relativistic models of stationary, strongly magnetized
neutron stars. The magnetic field configuration, obtained by solving the
relativistic Grad-Shafranov equation, is a generalization of the twisted torus
model recently proposed in the literature; the stellar deformations induced by
the magnetic field are computed by solving the perturbed Einstein's equations;
stellar matter is modeled using realistic equations of state. We find that in
these configurations the poloidal field dominates over the toroidal field and
that, if the magnetic field is sufficiently strong during the first phases of
the stellar life, it can produce large deformations.Comment: 10 pages, 5 figures. Minor changes to match the version published on
MNRA
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Visualising gas heating from an RF plasma loudspeaker
In an electro-acoustic transduction mechanism, an ac modulation (here in the audio frequency range) of the electric field in an atmospheric pressure air plasma gives rise to a rapid increase in the gas temperature and dimensions of the gas volume. As in natural lightning, the rapid expansion in the ionised column though the air produces external pressure variations at the modulation frequency.
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Spatial and temporal measurement of the gas temperature can identify the nature of the thermal expansion and provide a direct approach to understanding its relationship to the sound pressure wave that is generated. However, the established method through spectroscopic measurement of rotational line emission from nitrogen molecules is limited to the main current channel where relaxation and subsequent optical emission of the excited nitrogen molecules occurs. The wider picture is revealed through the use of the Schlieren method where the refractive index gradients caused by gas heating in the plasma are imaged
Correlation between Boldness and Body Mass in Natural Populations of the Poeciliid Brachyrhaphis episcopi
The boldness of individual Brachyrhaphis episcopi, collected from regions of high and low predation, was investigated using two independent assays: (1) the time to emerge from cover and (2) the propensity to leave shoal mates and investigate a novel object. A strong correlation between the two assays was revealed such that fish that emerged from shelter sooner were also more likely to approach a novel object. This is indicative of a boldness personality axis acting across both behavioural contexts. Fish from high-predation areas were bolder than those from low-predation areas and males were bolder than females. A significant correlation between body mass, standard length (LS) and boldness score was also found. In general, bold fish had a greater body mass at a given LS than shy fish. These results suggest that personality traits are strongly influenced by population-specific ecological variables and may have fitness consequences in wild populations
The MiMeS Project: Magnetism in Massive Stars
The Magnetism in Massive Stars (MiMeS) Project is a consensus collaboration
among the foremost international researchers of the physics of hot, massive
stars, with the basic aim of understanding the origin, evolution and impact of
magnetic fields in these objects. The cornerstone of the project is the MiMeS
Large Program at the Canada-France-Hawaii Telescope, which represents a
dedication of 640 hours of telescope time from 2008-2012. The MiMeS Large
Program will exploit the unique capabilities of the ESPaDOnS spectropolarimeter
to obtain critical missing information about the poorly-studied magnetic
properties of these important stars, to confront current models and to guide
theory.Comment: 6 pages, 3 figures, proceedings of IAUS 259: Cosmic Magnetic Field
Valence Instability of YbCuSi through its quantum critical point
We report Resonant inelastic x-ray scattering measurements (RIXS) in
YbCuSi at the Yb L edge under high pressure (up to 22 GPa) and at
low temperatures (down to 7 K) with emphasis on the vicinity of the transition
to a magnetic ordered state. We find a continuous valence change towards the
trivalent state with increasing pressure but with a pronounced change of slope
close to the critical pressure. Even at 22 GPa the Yb state is not fully
achieved. The pressure where this feature is observed decreases as the
temperature is reduced to 9 GPa at 7K, a value close to the critical pressure
(\itshape{p\normalfont{}}\normalfont 7.5 GPa) where magnetic
order occurs. The decrease in the valence with decreasing temperature
previously reported at ambient pressure is confirmed and is found to be
enhanced at higher pressures. We also compare the f electron occupancy between
YbCuSi and its Ce-counterpart, CeCuSi
Motivational climate interventions in school based physical education: A meta Analysis
This article was published in the journal Psychology of Sport and Exercise [© Elsevier Ltd]. The definitive version is available at: http://dx.doi.org/10.1016/j.psychsport.2011.06.005Objective: The purpose of this study was to synthesize findings from motivational climate interventions
employing Ames (1992a, 1992b) and Epstein’s (1988, 1989) TARGET framework within school-based
physical education contexts.
Design: The present study employed a quantitative research synthesis design. Meta-analysis uses
empirical studies to summarize past research by drawing overall conclusions from separate investigations.
This research design highlights important and unsolved issues related to motivational climate
interventions within physical education.
Methods: Standard meta-analytic procedures incorporating inclusion and exclusion criteria, literature
search, coding procedures, and statistical methods were used to identify and synthesize 22 studies with
24 independent samples. Cohen’s (1988) criteria for effect sizes were used to interpret and evaluate
results.
Results: There was an overall small positive treatment effect (g ¼ 0.103) for groups exposed to mastery
motivational climates. Outcome analyses identified the most consistent and largest overall treatment
effects for behavioral outcomes (g ¼ 0.39e0.49) followed by affective outcomes (g¼ 0.27 to 0.59) and
cognitive outcomes (g¼ 0.25 to 0.32). Moderator analyses were directed by study heterogeneity and
identified several trends in intervention features and study features with the most substantial trend for
participant features as elementary students had the largest overall treatment effect (g¼ 0.41).
Conclusions: Outcome and moderator analyses identified several trends in methodological features,
participant features, and study features that should be addressed in future physical education motivational
climate interventions
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