3,634 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
Combined pressure and temperature distortion effects on internal flow of a turbofan engine
An additional data base for improving and verifying a computer simulation developed by an engine manufacturer was obtained. The multisegment parallel compressor simulation was designed to predict the effects of steady-state circumferential inlet total-pressure and total-temperature distortions on the flows into and through a turbofan compression system. It also predicts the degree of distortion that will result in surge of the compressor. The effect of combined 180 deg square-wave distortion patterns of total pressure and total temperature in various relative positions is reported. The observed effects of the combined distortion on a unitary bypass ratio turbofan engine are presented in terms of total and static pressure profiles and total temperature profiles at stations ahead of the inlet guide vanes as well as through the fan-compressor system. These observed profiles are compared with those predicted by the complex multisegment model. The effects of relative position of the two components comprising the combined distortion on the degree resulting in surge are discussed. Certain relative positions required less combined distortion than either a temperature or pressure distortion by itself
Search for Stable Magnetohydrodynamic Equilibria in Barotropic Stars
It is now believed that magnetohydrodynamic equilibria can exist in stably
stratified stars due to the seminal works of Braithwaite & Spruit (2004) and
Braithwaite & Nordlund (2006). What is still not known is whether
magnetohydrodynamic equilibria can exist in a barotropic star, in which stable
stratification is not present. It has been conjectured by Reisenegger (2009)
that there will likely not exist any magnetohydrodynamical equilibria in
barotropic stars. We aim to test this claim by presenting preliminary MHD
simulations of barotropic stars using the three dimensional stagger code of
Nordlund & Galsgaard (1995).Comment: 4 pages, 2 figures, to appear in the proceedings of IAUS 302:
"Magnetic Fields Throughout Stellar Evolution
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
Summary of investigations of engine response to distorted inlet conditions
A survey is presented of experimental and analytical experience of the NASA Lewis Research Center in engine response to inlet temperature and pressure distortions. This includes a description of the hardware and techniques employed, and a summary of the highlights of experimental investigations and analytical modeling. Distortion devices successfully simulated inlet distortion, and knowledge was gained about compression system response to different types of distortion. A list of NASA research references is included
Incorporating practitioner knowledge to test and improve a new conceptual framework for healthy urban design and planning
There are increasing arguments for bridging diverse knowledges and co-producing new knowledge between researchers, professional communities and citizens to create health-promoting built environments. The new THRIVES Framework (Towards Healthy uRbanism: InclusiVe, Equitable, Sustainable) echoes the call that healthy urbanism processes should be participatory and this principle informed the development of the Framework itself, which involved several stages of informal and formal testing with stakeholders, through a process of action research and ‘extended peer review’. Formal feedback about the design of the preliminary Framework and its implementation in built environment practice was gathered through a participatory workshop with 26 built environment and public health professionals in January 2020. Participants were encouraged to share their knowledge, ask questions, critique and provide recommendations. Overall, participants were supportive of the conceptual messages of the THRIVES Framework and more critical of the visual design of the preliminary version. They also questioned whether further resources would be required to implement the Framework. This research created a forum for stakeholders, who may typically be outside the research process, to shape the development of a conceptual framework for healthy urbanism. Further research and collaboration will create resources to bridge the gap between this new conceptualisation and practice
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
- …