4,286 research outputs found
Magnetic fields in non-convective regions of stars
We review the current state of knowledge of magnetic fields inside stars,
concentrating on recent developments concerning magnetic fields in stably
stratified (zones of) stars, leaving out convective dynamo theories and
observations of convective envelopes. We include the observational properties
of A, B and O-type main-sequence stars, which have radiative envelopes, and the
fossil field model which is normally invoked to explain the strong fields
sometimes seen in these stars. Observations seem to show that Ap-type stable
fields are excluded in stars with convective envelopes. Most stars contain both
radiative and convective zones, and there are potentially important effects
arising from the interaction of magnetic fields at the boundaries between them.
Related to this, we discuss whether the Sun could harbour a magnetic field in
its core. Recent developments regarding the various convective and radiative
layers near the surfaces of early-type stars and their observational effects
are examined. We look at possible dynamo mechanisms that run on differential
rotation rather than convection. Finally we turn to neutron stars with a
discussion of the possible origins for their magnetic fields.Comment: 48 pages + 21 figures, to appear in Royal Society Open Science. This
arXiv version includes internal links, external links to ADS abstracts, and
uses standard astrophysical citation style. [The RSOS version uses the
cumbersome numbered citations, and does without internal or external links
Stability of toroidal magnetic fields in stellar interiors
We present 3D MHD simulations of purely toroidal and mixed poloidal-toroidal
magnetic field configurations to study the behavior of the Tayler instability.
For the first time the simultaneous action of rotation and magnetic diffusion
are taken into account and the effects of a poloidal field on the dynamic
evolution of unstable toroidal magnetic fields is included. In the absence of
diffusion, fast rotation (rotation rate compared to Alfv\'en frequency) is able
to suppress the instability when the rotation and magnetic axes are aligned and
when the radial field strength gradient p < 1.5. When diffusion is included,
this system turns unstable for diffusion dominated and marginally diffusive
dominated regions. If the magnetic and rotation axes are perpendicular to each
other the stabilizing effect induced by the Coriolis force is scale dependent
and decreases with increasing wavenumber. In toroidal fields with radial field
gradients bigger than p > 1.5, rapid rotation does not suppress the instability
but instead introduces a damping factor to the growth rate in agreement with
the analytic predictions. For the mixed poloidal-toroidal fields we find an
unstable axisymmetric mode, not predicted analytically, right at the stability
threshold for the non-axisymmetric modes; it has been argued that an
axisymmetric mode is necessary for the closure of the Tayler-Spruit dynamo
loop.Comment: 12 pages, 12 figures. Accepted for publication in A&
Evolution of the magnetic field in magnetars
We use numerical MHD to look at the stability of a possible poloidal field in
neutron stars (Flowers & Ruderman 1977), and follow its unstable evolution,
which leads to the complete decay of the field. We then model a neutron star
after the formation of a solid crust of high conductivity. As the initial
magnetic field we use the stable `twisted torus' field which was the result of
our earlier work (Braithwaite & Nordlund 2005), since this field is likely to
exist in the interior of the star at the time of crust formation. We follow the
evolution of the field under the influence of diffusion, and find that large
stresses build up in the crust, which will presumably lead to cracking. We put
this forward as a model for outbursts in soft gamma repeaters.Comment: 11 pages, 12 figures, submitted to A&
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
Recommended from our members
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
Indirect age- and sex-standardisation of COVID-19-related mortality rates for the prison population of England and Wales
This paper estimates a standardised mortality ratio (SMR) for death due to COVID-19 among people in prisons in England and Wales between 1 March 2020 and 26 February 2021. Over this period, prisons in England and Wales reported 121 deaths related to COVID-19. The SMR is 3.33 (95% C.I. 2.77–3.98), meaning there were 3.33 times more deaths among people in prisons than expected given the age and sex of the population
Energy loss rates of two-dimensional hole gases in inverted Si/Si0.8Ge0.2 heterostructures
We have investigated the energy loss rate of hot holes as a function of carrier temperature TC in p-type inverted modulation-doped (MD) Si/SiGe heterostructures over the carrier sheet density range (3.5–13)×1011 cm–2, at lattice temperatures of 0.34 and 1.8 K. It is found that the energy loss rate (ELR) depends significantly upon the carrier sheet density, n2D. Such an n2D dependence of ELR has not been observed previously in p-type SiGe MD structures. The extracted effective mass decreases as n2D increases, which is in agreement with recent measurements on a gated inverted sample. It is shown that the energy relaxation of the two-dimensional hole gases is dominated by unscreened acoustic phonon scattering and a deformation potential of 3.0±0.4 eV is deduced
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
Network structure and the role of key players in a translational cancer research network: a study protocol
Introduction: Translational research networks are a deliberate strategy to bridge the gulf between biomedical research and clinical practice through interdisciplinary collaboration, supportive funding and infrastructure. The social network approach examines how the structure of the network and players who hold important positions within it constrain or enable function. This information can be used to guide network management and optimise its operations. The aim of this study was to describe the structure of a translational cancer research network (TCRN) in Australia over its first year, identify the key players within the network and explore these players'opportunities and constraints in maximising important network collaborations. Methods and analysis: This study deploys a mixed-method longitudinal design using social network analysis augmented by interviews and review of TCRN documents. The study will use network documents and interviews with governing body members to explore the broader context into which the network is embedded as well as the perceptions and expectations of members. Of particular interest are the attitudes and perceptions of clinicians compared with those of researchers. A co-authorship network will be constructed of TCRN members using journal and citation databases to assess the success of past pre-network collaborations. Two whole network social network surveys will be administered 12 months apart and parameters such as density, clustering, centrality and betweenness centrality computed and compared using UCINET and Netdraw. Key players will be identified and interviewed to understand the specific activities, barriers and enablers they face in that role. Ethics and dissemination: Ethics approvals were obtained from the University of New South Wales, South Eastern Sydney Northern Sector Local Health Network and Calvary Health Care Sydney. Results will be discussed with members of the TCRN, submitted to relevant journals and presented as oral presentations to clinicians, researchers and policymakers.8 page(s
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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