6,590 research outputs found
Limb Darkening and Planetary Transits: Testing Center-to-limb Intensity Variations and Limb-Darkening Directly from Model Stellar Atmospheres
The transit method, employed by MOST, \emph{Kepler}, and various ground-based
surveys has enabled the characterization of extrasolar planets to unprecedented
precision. These results are precise enough to begin to measure planet
atmosphere composition, planetary oblateness, star spots, and other phenomena
at the level of a few hundred parts-per-million. However, these results depend
on our understanding of stellar limb darkening, that is, the intensity
distribution across the stellar disk that is sequentially blocked as the planet
transits. Typically, stellar limb darkening is assumed to be a simple
parameterization with two coefficients that are derived from stellar atmosphere
models or fit directly. In this work, we revisit this assumption and compute
synthetic planetary transit light curves directly from model stellar atmosphere
center-to-limb intensity variations (CLIV) using the plane-parallel
\textsc{Atlas} and spherically symmetric \textsc{SAtlas} codes. We compare
these light curves to those constructed using best-fit limb-darkening
parameterizations. We find that adopting parametric stellar limb-darkening laws
lead to systematic differences from the more geometrically realistic model
stellar atmosphere CLIV of about 50 -- 100 ppm at the transit center and up to
300 ppm at ingress/egress. While these errors are small they are systematic,
and appear to limit the precision necessary to measure secondary effects. Our
results may also have a significant impact on transit spectra.Comment: 12 pages, 14 figures, accepted for publication in ApJ after revision
Trust \u3ci\u3eThe Key to Leading When Lives Are on the Line\u3c/i\u3e
The Hostage Rescue Team (HRT) of the Federal Bureau of Investigation was called in to assist the bureau\u27s Special Weapons and Tactics (SWAT) team in Memphis to apprehend a married couple wanted on drug trafficking charges. The fugitive couple and an adult son, all with criminal records, were believed to be living in trailers in a mountain valley where outsiders would be easily noticed. The fugitives were known to stockpile weapons and had vowed never to be taken alive by law enforcement. Thus the FBI considered them to be armed and extremely dangerous.
Two HRT snipers along with two SWAT snipers were given the mission of positively identifying the fugitives and providing security and containment for the assault force. The snipers would have to travel several kilometers through wooded, mountainous terrain using night vision goggles (NVGs). The SWAT snipers did not have nighttime, overland movement capability, which is why HRT was brought in
Gold substrate-induced single-mode lasing of GaN nanowires
We demonstrate a method for mode-selection by coupling a GaN nanowire laser to an underlying gold substrate. Multimode lasing of GaN nanowires is converted to single-mode behavior following placement onto a gold film. A mode-dependent loss is generated by the absorbing substrate to suppress multiple transverse-mode operation with a concomitant increase in lasing threshold of only ā¼13%. This method provides greater flexibility in realizing practical single-mode nanowire lasers and offers insight into the design of metal-contacted nanoscale optoelectronics
Dopamine D_2-receptor activation elicits akinesia, rigidity, catalepsy, and tremor in mice expressing hypersensitive 4 nicotinic receptors via a cholinergic-dependent mechanism
Recent studies suggest that high-affinity neuronal nicotinic acetylcholine receptors (nAChRs) containing Ī±4 and Ī²2 subunits (Ī±4Ī²2*) functionally interact with G-protein-coupled dopamine (DA) D_2 receptors in basal ganglia. We hypothesized that if a functional interaction between these receptors exists, then mice expressing an M2 point mutation (Leu9'Ala) rendering 4 nAChRs hypersensitive to ACh may exhibit altered sensitivity to a D_2-receptor agonist. When challenged with the D_(2)R agonist, quinpirole (0.5ā10 mg/kg), Leu9'Ala mice, but not wild-type (WT) littermates, developed severe, reversible motor impairment characterized by rigidity, catalepsy, akinesia, and tremor. While striatal DA tissue content, baseline release, and quinpirole-induced DA depletion did not differ between Leu9'Ala and WT mice, quinpirole dramatically increased activity of cholinergic striatal interneurons only in mutant animals, as measured by increased c-Fos expression in choline acetyltransferase (ChAT)-positive interneurons. Highlighting the importance of the cholinergic system in this mouse model, inhibiting the effects of ACh by blocking muscarinic receptors, or by selectively activating hypersensitive nAChRs with nicotine, rescued motor symptoms. This novel mouse model mimics the imbalance between striatal DA/ACh function associated with severe motor impairment in disorders such as Parkinsonās disease, and the data suggest that a D_(2)RāĪ±4*-nAChR functional interaction regulates cholinergic interneuron activity.āZhao-Shea, R., Cohen, B. N., Just, H., McClure-Begley, T., Whiteaker, P., Grady, S. R., Salminen, O., Gardner, P. D., Lester, H. A., Tapper, A. R. Dopamine D2-receptor activation elicits akinesia, rigidity, catalepsy, and tremor in mice expressing hypersensitive Ī±4 nicotinic receptors via a cholinergic-dependent mechanism
Initial determination of the spins of the gluino and squarks at LHC
In principle particle spins can be measured from their production cross
sections once their mass is approximately known. The method works in practice
because spins are quantized and cross sections depend strongly on spins. It can
be used to determine, for example, the spin of the top quark. Direct
application of this method to supersymmetric theories will have to overcome the
challenge of measuring mass at the LHC, which could require high statistics. In
this article, we propose a method of measuring the spins of the colored
superpatners by combining rate information for several channels and a set of
kinematical variables, without directly measuring their masses. We argue that
such a method could lead to an early determination of the spin of gluino and
squarks. This method can be applied to the measurement of spin of other new
physics particles and more general scenarios.Comment: 23 pages, 8 figures, minor change
Mentoring Impact on Leader Efficacy Development: A Field Experiment
While practitioners and scholars tout the importance of mentorship in leader development, few studies have empirically determined whether mentoring actually positively impacts a leaderās development, and if so, in what ways. In a longitudinal field experiment, we examined how a targeted mentorship program that unfolded over 6 months enhanced the development of protĆ©gĆ©sā leader efficacy and performance. Results showed that the targeted mentorship intervention increased protĆ©gĆ©sā level of leader efficacy more than a comparison intervention that was based on a more eclectic leadership education program delivered in a group setting. Leader efficacy then predicted rated leader performance. Both protĆ©gĆ©sā preferences for feedback and trust in the mentor served as important moderators in contributing to the development of leader efficacy. Findings from this longitudinal field experiment could be used by educational institutions and other organizations to enhance their mentorship programs in content, focus, and evaluation of impact
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