97,224 research outputs found
Catastrophe versus instability for the eruption of a toroidal solar magnetic flux rope
The onset of a solar eruption is formulated here as either a magnetic
catastrophe or as an instability. Both start with the same equation of force
balance governing the underlying equilibria. Using a toroidal flux rope in an
external bipolar or quadrupolar field as a model for the current-carrying flux,
we demonstrate the occurrence of a fold catastrophe by loss of equilibrium for
several representative evolutionary sequences in the stable domain of parameter
space. We verify that this catastrophe and the torus instability occur at the
same point; they are thus equivalent descriptions for the onset condition of
solar eruptions.Comment: V2: update to conform to the published article; new choice for
internal inductance of torus; updated Fig. 2; new Figs. 3, 5, and
PRICE, YIELD, AND GROSS REVENUE VARIABILITY FOR SELECTED GEORGIA CROPS
Demand and Price Analysis,
Optical Spectroscopy of K-selected Extremely Red Galaxies
We have obtained spectroscopic redshifts for 24 red galaxies from a sample
with median Ks=18.7 and F814W - Ks > 4, using the Keck telescope. These
EROshave high resolution morphologies from HST (Yan & Thompson 2003). Among the
24 redshifts, the majority (92%) are at . We derived the
rest-frame J-band luminosity function at . Our result
suggests that the luminosity evolution between bright EROs at and the
present-day L massive galaxies is at most about 0.7 magnitude. Combining
the morphologies and deep spectroscopy revealed the following properties: (1)
86% of the spectra have absorption features from old stars, suggesting that the
dominant stellar populations seen in the rest-frame UV are old stars. 50% of
the sources have pure absorption lines, while the remaining 50% have emission
lines, indicating recent star formation. We conclude that the color criterion
for EROs is very effective in selecting old stellar populations at ,
and a large fraction of these systems with prominent old stellar populations
also have recent star formation. (2) The 12 emission line systems have the same
number of disk and bulge galaxies as in the remaining 12 pure absorption line
systems. We conclude that spectral classes do not have a simple, direct
correspondence with morphological types. (3) Three EROs could be isolated, pure
passively evolving early-type galaxies at . This implies that only a
small fraction (10%--15%) of early-type galaxies are formed in a rapid burst of
star formation at high redshifts and evolved passively since then. (Abridged).Comment: 27 pages, 8 figures. Accepted for publication in Astronomical
Journal, issue March 200
Premature recruitment of oocyte pool and increased mTOR activity in Fmr1 knockout mice and reversal of phenotype with rapamycin.
While mutations in the fragile X mental retardation-1 (FMR1) gene are associated with varying reproductive outcomes in females, the effects of a complete lack of FMR1 expression are not known. Here, we studied the ovarian and reproductive phenotypes in an Fmr1 knockout (KO) mouse model and the role of mammalian target of rapamycin (mTOR) signaling. Breeding, histologic and mTOR signaling data were obtained at multiple time points in KO and wild type (WT) mice fed a control or rapamycin (mTOR inhibitor) diet. KO mice showed an earlier decline in ovarian reserve than WT mice with an increased proportion of activated follicles. mTOR and phosphorylated S6 kinase (p-S6K) levels, a measure of downstream mTOR signaling, were elevated in the KO ovaries. Rapamycin blocked these effects in KO mice, and increased the primordial follicle pool and age of last litter in WT mice. Our data demonstrates an early decline in reproductive capacity in Fmr1 KO mice and proposes that premature recruitment of the primordial pool via altered mTOR signaling may be the mechanism. Reversal of phenotypes and protein levels in rapamycin-treated KO mice, as well as increased reproductive lifespan of rapamycin-fed WT mice, suggest the mTOR pathway as a potential therapeutic target
Tau Neutrino Astronomy in GeV Energies
We point out the opportunity of the tau neutrino astronomy for the neutrino
energy E ranging between 10 GeV and 10^3 GeV. In this energy range, the
intrinsic tau neutrino production is suppressed relative to the intrinsic muon
neutrino production. Any sizable tau neutrino flux may thus arise because of
the \nu_{\mu}\to \nu_{\tau} neutrino oscillations only. It is demonstrated
that, in the presence of the neutrino oscillations, consideration of the
neutrino flavor dependence in the background atmospheric neutrino flux leads to
the drastically different prospects between the observation of the
astrophysical muon neutrinos and that of the astrophysical tau neutrinos.
Taking the galactic-plane neutrino flux as the targeted astrophysical source,
we have found that the galactic-plane tau neutrino flux dominates over the
atmospheric tau neutrino flux for E > 10 GeV. Hence, the galactic-plane can at
least in principle be seen through the tau neutrinos with energies just greater
than 10 GeV. In a sharp contrast, the galactic-plane muon neutrino flux is
overwhelmed by its atmospheric background until E > 10^6 GeV.Comment: major revision of text and two new figures, to appear in PR
Effect of the Milky Way on Magellanic Cloud structure
A combination of analytic models and n-body simulations implies that the
structural evolution of the Large Magellanic Cloud (LMC) is dominated by its
dynamical interaction with the Milky Way. Although expected at some level, the
scope of the involvement has significant observational consequences. First, LMC
disk orbits are torqued out of the disk plane, thickening the disk and
populating a spheroid. The torque results from direct forcing by the Milky Way
tide and, indirectly, from the drag between the LMC disk and its halo resulting
from the induced precession of the LMC disk. The latter is a newly reported
mechanism that can affect all satellite interations. However, the overall
torque can not isotropize the stellar orbits and their kinematics remains
disk-like. Such a kinematic signature is observed for nearly all LMC
populations. The extended disk distribution is predicted to increase the
microlensing toward the LMC. Second, the disk's binding energy slowly decreases
during this process, puffing up and priming the outer regions for subsequent
tidal stripping. Because the tidally stripped debris will be spatially
extended, the distribution of stripped stars is much more extended than the HI
Magellanic Stream. This is consistent with upper limits to stellar densities in
the gas stream and suggests a different strategy for detecting the stripped
stars. And, finally, the mass loss over several LMC orbits is predicted by
n-body simulation and the debris extends to tens of kiloparsecs from the tidal
boundary. Although the overall space density of the stripped stars is low,
possible existence of such intervening populations have been recently reported
and may be detectable using 2MASS.Comment: 15 pages, color Postscript figures, uses emulateapj.sty. Also
available from http://www-astro.phast.umass.edu/~weinberg/weinberg-pubs.htm
Use of Standardized Assessments and Online Resources in Stroke Rehabilitation
Background: The extent to which movement-related standardized assessments and online resources are used in stroke rehabilitation is unclear in the United States.
Method: The researchers used a cross-sectional descriptive survey that examined (a) therapists use of movement-related standardized assessments, (b) factors influencing learning of new assessments, and (c) use of frequency of online resources by occupational therapists and physical therapists in the United States.
Results: Of 151 respondents (46.4% occupational therapists, 53.6% physical therapists), the most frequently used movement-related assessments by occupational and physical therapists were the Berg and Fugl-Meyer Assessment, respectively. More physical therapists use motor-related standardized assessments regularly than occupational therapists, and physical therapists showed more consensus among standardized assessments. Both professions cited quality of patient care for motivating them to integrate outcome measures into practice. Most therapists in stroke rehabilitation used online resources to access movement-related standardized assessment content at least 25% of the time. The Rehabilitation Measures Database was the most frequently used website.
Conclusion: Both occupational and physical therapists use online resources for movement-related standardized assessments on a regular basis. However, occupational therapists do not use standardized assessments as frequently as physical therapists. A systematic study of factors that impact the integration of standardized assessments is needed to further identify barriers and inform clinical practice change
Effect of an InP/InGaAs Interface on Spin-orbit Interaction in InAlAs/InGaAs Heterostructures
We report the effect of the insertion of an InP/InGaAs
Interface on Rashba spin-orbit interaction in
InAlAs/InGaAs quantum wells. A small spin
split-off energy in InP produces a very intriguing band lineup in the valence
bands in this system. With or without this InP layer above the
InGaAs well, the overall values of the spin-orbit coupling
constant turned out to be enhanced or diminished for samples with the
front- or back-doping position, respectively. These experimental results, using
weak antilocalization analysis, are compared with the results of the
theory. The actual conditions of the interfaces and
materials should account for the quantitative difference in magnitude between
the measurements and calculations.Comment: Submitted for publication; v2 to adjust Eq.6; v3 to correct the
figure file name; v4, a revised version accepted for publication in Phys.
Rev.
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