15,578 research outputs found
The solar gravitational figure: J2 and J4
The theory of the solar gravitational figure is derived including the effects of differential rotation. It is shown that J sub 4 is smaller than J sub 2 by a factor of about 10 rather than being of order J sub 2 squared as would be expected for rigid rotation. The dependence of both J sub 2 and J sub 4 on envelope mass is given. High order p-mode oscillation frequencies provide a constraint on solar structure which limits the range in envelope mass to the range 0.01 M sub E/solar mass 0.04. For an assumed rotation law in which the surface pattern of differential rotation extends uniformly throughout the convective envelope, this structural constraint limits the ranges of J sub 2 and J sub 4 in units of 10 to the -8th power to 10 J sub 2 15 and 0.6 -J sub 4 1.5. Deviations from these ranges would imply that the rotation law is not constant with depth and would provide a measure of this rotation law
Scaling laws in spherical shell dynamos with free-slip boundaries
Numerical simulations of convection driven rotating spherical shell dynamos
have often been performed with rigid boundary conditions, as is appropriate for
the metallic cores of terrestrial planets. Free-slip boundaries are more
appropriate for dynamos in other astrophysical objects, such as gas-giants or
stars. Using a set of 57 direct numerical simulations, we investigate the
effect of free-slip boundary conditions on the scaling properties of heat flow,
flow velocity and magnetic field strength and compare it with earlier results
for rigid boundaries. We find that the nature of the mechanical boundary
condition has only a minor influence on the scaling laws. We also find that
although dipolar and multipolar dynamos exhibit approximately the same scaling
exponents, there is an offset in the scaling pre-factors for velocity and
magnetic field strength. We argue that the offset can be attributed to the
differences in the zonal flow contribution between dipolar and multipolar
dynamos.Comment: 10 pages, 9 figures, 1 table. To appear in ICARU
Interpretation of Solar Magnetic Field Strength Observations
This study based on longitudinal Zeeman effect magnetograms and spectral line
scans investigates the dependence of solar surface magnetic fields on the
spectral line used and the way the line is sampled in order to estimate the
magnetic flux emerging above the solar atmosphere and penetrating to the corona
from magnetograms of the Mt. Wilson 150-foot tower synoptic program (MWO). We
have compared the synoptic program \lambda5250\AA line of Fe I to the line of
Fe I at \lambda5233\AA since this latter line has a broad shape with a profile
that is nearly linear over a large portion of its wings. The present study uses
five pairs of sampling points on the \AA line. We recommend
adoption of the field determined with a line bisector method with a sampling
point as close as possible to the line core as the best estimate of the
emergent photospheric flux. The combination of the line profile measurements
and the cross-correlation of fields measured simultaneously with \lambda5250\AA
and \lambda5233\AA yields a formula for the scale factor 1/\delta that
multiplies the MWO synoptic magnetic fields. The new calibration shows that
magnetic fields measured by the MDI system on the SOHO spacecraft are equal to
0.619+/-0.018 times the true value at a center-to-limb position 30 deg. Berger
and Lites (2003) found this factor to be 0.64+/-0.013 based on a comparison the
the Advanced Stokes Polarimeter.Comment: Accepted by Solar Physic
Formation of starspots in self-consistent global dynamo models: Polar spots on cool stars
Observations of cool stars reveal dark spot-like features on their surfaces.
Compared to sunspots, starspots can be bigger or cover a larger fraction of the
stellar surface. While sunspots appear only at low latitudes, starspots are
also found in polar regions, in particular on rapidly rotating stars. Sunspots
are believed to result from the eruption of magnetic flux-tubes rising from the
deep interior of the Sun. The strong magnetic field locally reduces convective
heat transport to the solar surface. Such flux-tube models have also been
invoked to explain starspot properties. However, these models use several
simplifications and so far the generation of either sunspots or starspots has
not been demonstrated in a self-consistent simulation of stellar magnetic
convection. Here we show that direct numerical simulations of a distributed
dynamo operating in a density-stratified rotating spherical shell can
spontaneously generate cool spots. Convection in the interior of the model
produces a large scale magnetic field which interacts with near surface
granular convection leading to strong concentrations of magnetic flux and
formation of starspots. Prerequisites for the formation of sizeable
high-latitude spots in the model are sufficiently strong density stratification
and rapid rotation. Our model presents an alternate mechanism for starspot
formation by distributed dynamo action.Comment: 14 pages; Important additions in version 2; To appear in A&
Predominant utilization of V beta 8+ T cell receptor genes in the H-2Ld- restricted cytotoxic T cell response against the immediate-early protein pp89 of the murine cytomegalovirus
Cytotoxic T cell responses to the murine Cytomegalovirus (MCMV) were elicited in BALB/c mice (H-2d) by infectious virus. Eight days after infection, MCMV-primed local lymph node T cells were either depleted for T cells expressing a V beta 8+ TCR or separated into V beta 8+ and V beta 8- subpopulations by a cell sorter using the mAb F23.1. T cells were then expanded in vitro under limiting dilution conditions in the presence of IL-2 and in the absence of viral Ag to avoid selection by Ag in vitro. Frequencies of CTL precursors specific for the Immediate- Early-Ag 1 of MCMV and restricted to H-2Ld were determined. L cells of the endogenous haplotype H-2k cotransfected with the genes for MCMV-IE 1 and H-2Ld were used as target cells. Detection of a CTL response required previous priming of the animals by infection in vivo (less than 1/10(6) for nonimmunized animals). In primed animals CTL precursors of this specificity and restriction were three to fivefold more frequent in the V beta 8+ population (1/9.900 to 1/22.300) than in the V beta 8- population (1/57.000 to 1/87.200). Control experiments showed that frequencies were not influenced by the treatment with the anti-V beta 8-antibody and the fluorescein-labeled anti-Ig itself. V beta 8+ and V beta 8- T cells did not reveal any frequency differences when several other responses were determined (TNP-specific self- restricted CTL precursor; Th cells specific for keyhole limpet hemocyanin or Listeria monocytogenes)
Bridging planets and stars using scaling laws in anelastic spherical shell dynamos
Dynamos operating in the interiors of rapidly rotating planets and low-mass
stars might belong to a similar category where rotation plays a vital role. We
quantify this similarity using scaling laws. We analyse direct numerical
simulations of Boussinesq and anelastic spherical shell dynamos. These dynamos
represent simplified models which span from Earth-like planets to rapidly
rotating low-mass stars. We find that magnetic field and velocity in these
dynamos are related to the available buoyancy power via a simple power law
which holds over wide variety of control parameters.Comment: 2 pages; Proceedings of IAUS 302: Magnetic fields throughout stellar
evolution (August 2013, Biarritz, France
Kinematic analysis of handwriting movements in patients with Alzheimer's disease, mild cognitive impairment, depression and healthy subjects
A variety of studies have demonstrated that motor disorders, parkinsonism and extrapyramidal motor symptoms (EPMS) are common in patients with Alzheimer's disease (AD). Several studies have reported an association of EPMS with severity, progression and poor prognosis of AD. The majority of these studies used clinical assessments for the rating of EPMS. In this study, kinematic handwriting analysis was used to quantify differences in fine hand motor function in patients with probable AD and mild cognitive impairment (MCl, as an assumed initial stage of AD) compared to depressed patients and healthy controls. Both patients with MCl and patients with probable AD exhibited loss of fine motor performance. Movements of AD patients were significantly less regular than those of healthy controls. Copyright (C) 2003 S. Karger AG, Basel
Characteristics of Magnetohydrodynamic Oscillations Observed with Michelson Doppler Imager
We report on the spatial distribution of magnetogram oscillatory power and
phase angles between velocity and magnetogram signals as observed with the
Michelson Doppler Imager. The dataset is 151.25 arcsec times 151.25 arcsec
containing sunspot from Dec 2, 1997 with a temporal sampling interval of 60
seconds and spatial sampling of 0.605 arcsec. Simultaneously observed continuum
intensity and surface velocity accompany the magnetic information. We focus on
three frequency regimes: 0.5-1.0, 3.0-3.5 and 5.5-6.0 mHz corresponding roughly
to timescales of magnetic evolution, p-modes and the 3 minute resonant sunspot
oscillation. Significant low frequency magnetogram power is found in lower flux
pixels, 100-300 Gauss, in a striking ring with filamentary structure
surrounding sunspot. Five minute magnetogram power peaks in extended regions of
flux 600-800 Gauss. The 3 minute oscillation is observed in sunspot umbra in
pixels whose flux measures 1300-1500 Gauss. Phase angles of approximately -90
degrees between velocity and magnetic flux in the 3.0-3.5 and 5.5-6.0 mHz
regimes are found in regions of significant cross amplitude.Comment: 4 Pages, 4 Figures -- For better Figure files see:
http://www.astro.ucla.edu/~norton/pub_list.htm
Solar Seismology from Space. a Conference at Snowmass, Colorado
The quality of the ground based observing environment suffers from several degrading factors: diurnal interruptions and thermal variations, atmospheric seeing and transparency fluctuations and adverse weather interruptions are among the chief difficulties. The limited fraction of the solar surface observable from only one vantage point is also a potential limitation to the quality of the data available without going to space. Primary conference goals were to discuss in depth the scientific return from current observations and analyses of solar oscillations, to discuss the instrumental and site requirements for realizing the full potential of the seismic analysis method, and to help bring new workers into the field by collecting and summarizing the key background theory. At the conclusion of the conference there was a clear consensus that ground based observation would not be able to provide data of the quality required to permit a substantial analysis of the solar convection zone dynamics or to permit a full deduction of the solar interior structure
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