7,177 research outputs found
Differential Rotation and Magnetism in Simulations of Fully Convective Stars
Stars of sufficiently low mass are convective throughout their interiors, and
so do not possess an internal boundary layer akin to the solar tachocline.
Because that interface figures so prominently in many theories of the solar
magnetic dynamo, a widespread expectation had been that fully convective stars
would exhibit surface magnetic behavior very different from that realized in
more massive stars. Here I describe how recent observations and theoretical
models of dynamo action in low-mass stars are partly confirming, and partly
confounding, this basic expectation. In particular, I present the results of
3--D MHD simulations of dynamo action by convection in rotating spherical
shells that approximate the interiors of 0.3 solar-mass stars at a range of
rotation rates. The simulated stars can establish latitudinal differential
rotation at their surfaces which is solar-like at ``rapid'' rotation rates
(defined within) and anti-solar at slower rotation rates; the differential
rotation is greatly reduced by feedback from strong dynamo-generated magnetic
fields in some parameter regimes. I argue that this ``flip'' in the sense of
differential rotation may be observable in the near future. I also briefly
describe how the strength and morphology of the magnetic fields varies with the
rotation rate of the simulated star, and show that the maximum magnetic
energies attained are compatible with simple scaling arguments.Comment: 9 pages, 2 color figures, to appear in Proc. IAU Symposium 271,
"Astrophysical Dynamics: from Stars to Galaxies
India's Mineral Sands Industry - A Global Perspective
India is in a very fortunate position, poised to become a leader in the global TiO2 minerals industry. It has ample mineral sand resources, competitive labour costs, improving
infrastructure and growing domestic and regional markets. Adopting global standards in assessing markets, establish-ing modern process flowsheets and above all, knowing the ultimate details of the resource, can push India' to the status of industry leader
Gz, a guanine nucleotide-binding protein with unique biochemical properties
Cloning of a complementary DNA (cDNA) for Gz alpha, a newly appreciated member of the family of guanine nucleotide-binding regulatory proteins (G proteins), has allowed preparation of specific antisera to identify the protein in tissues and to assay it during purification from bovine brain. Additionally, expression of the cDNA in Escherichia coli has resulted in the production and purification of the recombinant protein. Purification of Gz from bovine brain is tedious, and only small quantities of protein have been obtained. The protein copurifies with the beta gamma subunit complex common to other G proteins; another 26- kDa GTP-binding protein is also present in these preparations. The purified protein could not serve as a substrate for NAD-dependent ADP- ribosylation catalyzed by either pertussis toxin or cholera toxin. Purification of recombinant Gz alpha (rGz alpha) from E. coli is simple, and quantities of homogeneous protein sufficient for biochemical analysis are obtained. Purified rGz alpha has several properties that distinguish it from other G protein alpha subunit polypeptides. These include a very slow rate of guanine nucleotide exchange (k = 0.02 min^-1), which is reduced greater than 20-fold in the presence of mM concentrations of Mg2+. In addition, the rate of the intrinsic GTPase activity of Gz alpha is extremely slow. The hydrolysis rate (kcat) for rGz alpha at 30 degrees C is 0.05 min^-1, or 200-fold slower than that determined for other G protein alpha subunits. rGz alpha can interact with bovine brain beta gamma but does not serve as a substrate for ADP-ribosylation catalyzed by either pertussis toxin or cholera toxin. These studies suggest that Gz may play a role in signal transduction pathways that are mechanistically distinct from those controlled by the other members of the G protein family
Dynamics of the fast solar tachocline: I. Dipolar field
One possible scenario for the origin of the solar tachocline, known as the
"fast tachocline", assumes that the turbulent diffusivity exceeds eta>10^9
cm^2/s. In this case the dynamics will be governed by the dynamo-generated
oscillatory magnetic field on relatively short timescales. Here, for the first
time, we present detailed numerical models for the fast solar tachocline with
all components of the magnetic field calculated explicitly, assuming axial
symmetry and a constant turbulent diffusivity eta and viscosity nu. We find
that a sufficiently strong oscillatory poloidal field with dipolar latitude
dependence at the tachocline-convective zone boundary is able to confine the
tachocline. Exploring the three-dimensional parameter space defined by the
viscosity in the range log(nu)=9-11, the magnetic Prandtl number in the range
Prm=0.1-10, and the meridional flow amplitude (-3 to +3 cm/s), we also find
that the confining field strength B_conf, necessary to reproduce the observed
thickness of the tachocline, increases with viscosity nu, with magnetic Prandtl
number nu/eta, and with equatorward meridional flow speed. Nevertheless, the
resulting B_conf values remain quite reasonable, in the range 10^3-10^4 G, for
all parameter combinations considered here. The thickness of the tachocline
shows a marked dependence on both time and latitude. A comparison with seismic
constraints suggests that best agreement with our models is achieved for the
highest values of nu and Prm considered here.Comment: 11 page
Differential rotation and meridional flow in the solar supergranulation layer: Measuring the eddy viscosity
We measure the eddy viscosity in the outermost layers of the solar convection
zone by comparing the rotation law computed with the Reynolds stress resulting
from f-plane simulations of the angular momentum transport in rotating
convection with the observed differential rotation pattern. The simulations
lead to a negative vertical and a positive horizontal angular momentum
transport. The consequence is a subrotation of the outermost layers, as it is
indeed indicated both by helioseismology and the observed rotation rates of
sunspots. In order to reproduce the observed gradient of the rotation rate a
value of about 1.5 x 10^{13} cm/s for the eddy viscosity is necessary.
Comparison with the magnetic eddy diffusivity derived from the sunspot decay
yields a surprisingly large magnetic Prandtl number of 150 for the
supergranulation layer. The negative gradient of the rotation rate also drives
a surface meridional flow towards the poles, in agreement with the results from
Doppler measurements. The successful reproduction of the abnormally positive
horizontal cross correlation (on the northern hemisphere) observed for bipolar
groups then provides an independent test for the resulting eddy viscosity.Comment: 6 pages, 8 figures, Astronomy and Astrophysics (subm.
The Different Flavors of Research Impact: A Tasting of Traditional and Alternative Bibliometric Assessment Tools
This workshop introduces researchers to a variety of traditional and alternative bibliometric assessment tools. These metric tools are each defined and their potential uses, abuses, benefits, and drawbacks discussed. Researchers are then shown how to effectively utilize these metric tools to best fit their personal research needs and assess their research impact
Management of migraine in adolescents
Headaches in children and adolescents are still under-diagnosed. 75% of children are affected by primary headache by the age of 15 with 28% fitting the ICHD2 criteria of migraine. Migraine is considered a chronic disorder that can severely impact a child’s daily activities, including schooling and socializing. Early recognition and aggressive therapy, with acute and prophylactic treatments, as well as intensive biobehavioral interventions, are essential to control the migraine attacks and reverse the progression into intractable disabling headache
Creators for the Earth: The Academic Library’s Role in Supporting Sustainability Creators and Practitioners Across All Disciplines
The image of a creator often brings to mind individuals that can take an abstract or unique idea and transform it into an impressive, tangible creation. Whether it’s an architect crafting a new building design, an artist painting on canvas, or an interior designer mapping out a new room layout, creators are generally seen as those who can formulate conceptual ideas that are then realized to showcase amazing ingenuity. In the world of higher education, this type of work is often first associated with disciplines like art, design, architecture, and engineering—fields where acts of “making,” “creating,” or “building” are integral to their purposes. However, this chapter invites readers to think beyond these more well-established creator fields to consider another field where creators are equally needed, supported, and produced: the field of sustainability and sustainable development
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