231 research outputs found
Chandra Observation of an X-ray Flare at Saturn: Evidence for Direct Solar Control on Saturn's Disk X-ray Emissions
Saturn was observed by Chandra ACIS-S on 20 and 26-27 January 2004 for one
full Saturn rotation (10.7 hr) at each epoch. We report here the first
observation of an X-ray flare from Saturn's non-auroral (low-latitude) disk,
which is seen in direct response to an M6-class flare emanating from a sunspot
that was clearly visible from both Saturn and Earth. Saturn's disk X-ray
emissions are found to be variable on time scales of hours to weeks to months,
and correlated with solar F10.7 cm flux. Unlike Jupiter, X-rays from Saturn's
polar (auroral) region have characteristics similar to those from its disk.
This report, combined with earlier studies, establishes that disk X-ray
emissions of the giant planets Saturn and Jupiter are directly regulated by
processes happening on the Sun. We suggest that these emissions could be
monitored to study X-ray flaring from solar active regions when they are on the
far side and not visible to Near-Earth space weather satellites.Comment: Total 12 pages including 4 figure
Validation of Kepler's Multiple Planet Candidates. III: Light Curve Analysis & Announcement of Hundreds of New Multi-planet Systems
The Kepler mission has discovered over 2500 exoplanet candidates in the first
two years of spacecraft data, with approximately 40% of them in candidate
multi-planet systems. The high rate of multiplicity combined with the low rate
of identified false-positives indicates that the multiplanet systems contain
very few false-positive signals due to other systems not gravitationally bound
to the target star (Lissauer, J. J., et al., 2012, ApJ 750, 131). False
positives in the multi- planet systems are identified and removed, leaving
behind a residual population of candidate multi-planet transiting systems
expected to have a false-positive rate less than 1%. We present a sample of 340
planetary systems that contain 851 planets that are validated to substantially
better than the 99% confidence level; the vast majority of these have not been
previously verified as planets. We expect ~2 unidentified false-positives
making our sample of planet very reliable. We present fundamental planetary
properties of our sample based on a comprehensive analysis of Kepler light
curves and ground-based spectroscopy and high-resolution imaging. Since we do
not require spectroscopy or high-resolution imaging for validation, some of our
derived parameters for a planetary system may be systematically incorrect due
to dilution from light due to additional stars in the photometric aperture.
None the less, our result nearly doubles the number of verified exoplanets.Comment: 138 pages, 8 Figures, 5 Tables. Accepted for publications in the
Astrophysical Journa
Planetary Candidates Observed by Kepler V: Planet Sample from Q1-Q12 (36 Months)
The Kepler mission discovered 2842 exoplanet candidates with 2 years of data.
We provide updates to the Kepler planet candidate sample based upon 3 years
(Q1-Q12) of data. Through a series of tests to exclude false-positives,
primarily caused by eclipsing binary stars and instrumental systematics, 855
additional planetary candidates have been discovered, bringing the total number
known to 3697. We provide revised transit parameters and accompanying posterior
distributions based on a Markov Chain Monte Carlo algorithm for the cumulative
catalogue of Kepler Objects of Interest. There are now 130 candidates in the
cumulative catalogue that receive less than twice the flux the Earth receives
and more than 1100 have a radius less than 1.5 Rearth. There are now a dozen
candidates meeting both criteria, roughly doubling the number of candidate
Earth analogs. A majority of planetary candidates have a high probability of
being bonafide planets, however, there are populations of likely
false-positives. We discuss and suggest additional cuts that can be easily
applied to the catalogue to produce a set of planetary candidates with good
fidelity. The full catalogue is publicly available at the NASA Exoplanet
Archive.Comment: Accepted for publication, ApJ
Holographic Measurement and Improvement of the Green Bank Telescope Surface
We describe the successful design, implementation, and operation of a 12 GHz
holography system installed on the Robert C. Byrd Green Bank Telescope (GBT).
We have used a geostationary satellite beacon to construct high-resolution
holographic images of the telescope mirror surface irregularities. These images
have allowed us to infer and apply improved position offsets for the 2209
actuators which control the active surface of the primary mirror, thereby
achieving a dramatic reduction in the total surface error (from 390 microns to
~240 microns, rms). We have also performed manual adjustments of the corner
offsets for a few panels. The expected improvement in the radiometric aperture
efficiency has been rigorously modeled and confirmed at 43 GHz and 90 GHz. The
improvement in the telescope beam pattern has also been measured at 11.7 GHz
with greater than 60 dB of dynamic range. Symmetric features in the beam
pattern have emerged which are consistent with a repetitive pattern in the
aperture due to systematic panel distortions. By computing average images for
each tier of panels from the holography images, we confirm that the magnitude
and direction of the panel distortions, in response to the combination of
gravity and thermal gradients, are in general agreement with finite-element
model predictions. The holography system is now fully integrated into the GBT
control system, and by enabling the telescope staff to monitor the health of
the individual actuators, it continues to be an essential tool to support
high-frequency observations.Comment: Accepted for publication in PASP. Contains 28 pages with 2 tables and
9 figures (several at reduced quality). The full resolution version is
available at http://wwwlocal.gb.nrao.edu/ptcs/papers/Hunter2011/gbtholo.ps.gz
(34MB gzip file unpacks to 134MB postscript
Muslim Integration into Western Cultures: Between Origins and Destinations
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91196/1/j.1467-9248.2012.00951.x.pd
Masses, radii, and orbits of small Kepler planets : The transition from gaseous to rocky planets
We report on the masses, sizes, and orbits of the planets orbiting 22 Kepler stars. There are 49 planet candidates around these stars, including 42 detected through transits and 7 revealed by precise Doppler measurements of the host stars. Based on an analysis of the Kepler brightness measurements, along with high-resolution imaging and spectroscopy, Doppler spectroscopy, and (for 11 stars) asteroseismology, we establish low false-positive probabilities (FPPs) for all of the transiting planets (41 of 42 have an FPP under 1%), and we constrain their sizes and masses. Most of the transiting planets are smaller than three times the size of Earth. For 16 planets, the Doppler signal was securely detected, providing a direct measurement of the planet's mass. For the other 26 planets we provide either marginal mass measurements or upper limits to their masses and densities; in many cases we can rule out a rocky composition. We identify six planets with densities above 5 g cm-3, suggesting a mostly rocky interior for them. Indeed, the only planets that are compatible with a purely rocky composition are smaller than 2 R ⊕. Larger planets evidently contain a larger fraction of low-density material (H, He, and H2O).Peer reviewedFinal Accepted Versio
Genetically-controlled Vesicle-Associated Membrane Protein 1 expression may contribute to Alzheimer’s pathophysiology and susceptibility
Background
Alzheimer’s disease is a neurodegenerative disorder in which extracellular deposition of β-amyloid (Aβ) oligomers causes synaptic injury resulting in early memory loss, altered homeostasis, accumulation of hyperphosphorylated tau and cell death. Since proteins in the SNAP (Soluble N-ethylmaleimide-sensitive factor Attachment Protein) REceptors (SNARE) complex are essential for neuronal Aβ release at pre-synaptic terminals, we hypothesized that genetically controlled SNARE expression could alter neuronal Aß release at the synapse and hence play an early role in Alzheimer’s pathophysiology.
Results
Here we report 5 polymorphisms in Vesicle-Associated Membrane Protein 1 (VAMP1), a gene encoding a member of the SNARE complex, associated with bidirectionally altered cerebellar VAMP1 transcript levels (all p < 0.05). At the functional level, we demonstrated that control of VAMP1 expression by heterogeneous knockdown in mice resulted in up to 74% reduction in neuronal Aβ exocytosis (p < 0.001). We performed a case-control association study of the 5 VAMP1 expression regulating polymorphisms in 4,667 Alzheimer’s disease patients and 6,175 controls to determine their contribution to Alzheimer’s disease risk. We found that polymorphisms associated with increased brain VAMP1 transcript levels conferred higher risk for Alzheimer’s disease than those associated with lower VAMP1 transcript levels (p = 0.03). Moreover, we also report a modest protective association for a common VAMP1 polymorphism with Alzheimer’s disease risk (OR = 0.88, p = 0.03). This polymorphism was associated with decreased VAMP1 transcript levels (p = 0.02) and was functionally active in a dual luciferase reporter gene assay (p < 0.01).
Conclusions
Genetically regulated VAMP1 expression in the brain may modify both Alzheimer’s disease risk and may contribute to Alzheimer’s pathophysiology
Incidence of AIDS-Defining Opportunistic Infections in a Multicohort Analysis of HIV-infected Persons in the United States and Canada, 2000–2010
Background. There are few recent data on the rates of AIDS-defining opportunistic infections (OIs) among human immunodeficiency virus (HIV)–infected patients in care in the United States and Canada
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