302 research outputs found
TC21/RRas2 regulates glycoprotein VI–FcRγ‐mediated platelet activation and thrombus stability
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145353/1/jth14197.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145353/2/jth14197_am.pd
Interferometric radii of bright Kepler stars with the CHARA Array: {\theta} Cygni and 16 Cygni A and B
We present the results of long-baseline optical interferometry observations
using the Precision Astronomical Visual Observations (PAVO) beam combiner at
the Center for High Angular Resolution Astronomy (CHARA) Array to measure the
angular sizes of three bright Kepler stars: {\theta} Cygni, and both components
of the binary system 16 Cygni. Supporting infrared observations were made with
the Michigan Infrared Combiner (MIRC) and Classic beam combiner, also at the
CHARA Array. We find limb-darkened angular diameters of 0.753+/-0.009 mas for
{\theta} Cyg, 0.539+/-0.007 mas for 16 Cyg A and 0.490+/-0.006 mas for 16 Cyg
B. The Kepler Mission has observed these stars with outstanding photometric
precision, revealing the presence of solar-like oscillations. Due to the
brightness of these stars the oscillations have exceptional signal-to-noise,
allowing for detailed study through asteroseismology, and are well constrained
by other observations. We have combined our interferometric diameters with
Hipparcos parallaxes, spectrophotometric bolometric fluxes and the
asteroseismic large frequency separation to measure linear radii ({\theta} Cyg:
1.48+/-0.02 Rsun, 16 Cyg A: 1.22+/-0.02 Rsun, 16 Cyg B: 1.12+/-0.02 Rsun),
effective temperatures ({\theta} Cyg: 6749+/-44 K, 16 Cyg A: 5839+/-42 K, 16
Cyg B: 5809+/-39 K), and masses ({\theta} Cyg: 1.37+/-0.04 Msun, 16 Cyg A:
1.07+/-0.05 Msun, 16 Cyg B: 1.05+/-0.04 Msun) for each star with very little
model dependence. The measurements presented here will provide strong
constraints for future stellar modelling efforts.Comment: 9 pages, 4 figures, and 5 tables, accepted for publication in Monthly
Notices of the Royal Astronomical Societ
Carbon nanotubes-semiconductor networks for organic electronics: The pickup stick transistor
We demonstrate an alternative path for achieving high transconductance organic transistors in spite of relatively large source to drain distances. The improvement of the electronic characteristic of such a scheme is equivalent to a 60-fold increase in mobility of the underlying organic semiconductor. The method is based on percolating networks, which we create from a dispersion of individual single-wall carbon nanotubes and narrow ropes within an organic semiconducting host. The majority of current paths between source and drain follow the metallic nanotubes but require a short, switchable semiconducting link to complete the circuit. With these nanotube-semiconducting composites we achieve effectively a 60X reduction in source to drain distance, which is equivalent to a 60-fold increase of the '' effective '' mobility of the starting semiconducting material with a minor decrease of the on/off current ratio. These field-induced percolating networks allow for the fabrication of high-transconductance transistors having relatively large source to drain distances that can be manufactured inexpensively by commercially available printing techniques. (c) 2005 American Institute of Physicsclose516
Toward Direct Detection of Hot Jupiters with Precision Closure Phase: Calibration Studies and First Results from the CHARA Array
Direct detection of thermal emission from nearby hot Jupiters has greatly
advanced our knowledge of extrasolar planets in recent years. Since hot Jupiter
systems can be regarded as analogs of high contrast binaries, ground-based
infrared long baseline interferometers have the potential to resolve them and
detect their thermal emission with precision closure phase - a method that is
immune to the systematic errors induced by the Earth's atmosphere. In this
work, we present closure phase studies toward direct detection of nearby hot
Jupiters using the CHARA interferometer array outfitted with the MIRC
instrument. We carry out closure phase simulations and conduct a large number
of observations for the best candidate {\upsion} And. Our experiments suggest
the method is feasible with highly stable and precise closure phases. However,
we also find much larger systematic errors than expected in the observations,
most likely caused by dispersion across different wavelengths. We find that
using higher spectral resolution modes (e.g., R=150) can significantly reduce
the systematics. By combining all calibrators in an observing run together, we
are able to roughly recalibrate the lower spectral resolution data, allowing us
to obtain upper limits of the star-planet contrast ratios of {\upsion} And b
across the H band. The data also allow us to get a refined stellar radius of
1.625\pm0.011 R\odot. Our best upper limit corresponds to a contrast ratio of
2.1\times10^3:1 with 90% confidence level at 1.52{\mu}m, suggesting that we are
starting to have the capability of constraining atmospheric models of hot
Jupiters with interferometry. With recent and upcoming improvements of
CHARA/MIRC, the prospect of detecting emission from hot Jupiters with closure
phases is promising.Comment: 30 pages, including 9 figures and 4 tables. Published in PASP in
August 201
Effects of red grape, wild grape and black raspberry wines on ground pork during refrigerated storage
The effects of red grape, wild grape and black raspberry wines on the quality of ground pork during a 15 days refrigerated storage period were investigated. The levels of phenolic compounds were the highest in black raspberry wine (P0.05). The addition of 5% and 10% wine influenced the quality of ground pork by decreasing pH, inhibiting the progression of lipid oxidation and the formation of total volatile basic nitrogen (TVB-N), and stabilizing the red colour of the ground pork compared to control samples to which no wine was added. In ground pork, addition of red grape wine led to lower concentrations of thiobarbituric acid reactive substances (TBARS, 0.19–0.39 mg kg−1) and TVB-N values (69.1–119.9 mg kg−1) than wild grape (0.16–0.43 mg kg−1 and 72.0–194.1 mg kg−1, respectively) or black raspberry wine (0.33–0.58 mg kg−1 and 81.7–225.4 mg kg−1, respectively) up to 10 days of storage. Results from the present study suggested that the quality of ground pork was affected by wine type and storage period. These effects could be due to phenolic compounds as well as other chemical components of the wines
Chromosphere of K giant stars Geometrical extent and spatial structure detection
We aim to constrain the geometrical extent of the chromosphere of non-binary
K giant stars and detect any spatial structures in the chromosphere. We
performed observations with the CHARA interferometer and the VEGA beam combiner
at optical wavelengths. We observed seven non-binary K giant stars. We measured
the ratio of the radii of the photosphere to the chromosphere using the
interferometric measurements in the Halpha and the Ca II infrared triplet line
cores. For beta Ceti, spectro-interferometric observations are compared to an
non-local thermal equilibrium (NLTE) semi-empirical model atmosphere including
a chromosphere. The NLTE computations provide line intensities and contribution
functions that indicate the relative locations where the line cores are formed
and can constrain the size of the limb-darkened disk of the stars with
chromospheres. We measured the angular diameter of seven K giant stars and
deduced their fundamental parameters: effective temperatures, radii,
luminosities, and masses. We determined the geometrical extent of the
chromosphere for four giant stars. The chromosphere extents obtained range
between 16% to 47% of the stellar radius. The NLTE computations confirm that
the Ca II/849 nm line core is deeper in the chromosphere of ? Cet than either
of the Ca II/854 nm and Ca II/866 nm line cores. We present a modified version
of a semi-empirical model atmosphere derived by fitting the Ca II triplet line
cores of this star. In four of our targets, we also detect the signature of a
differential signal showing the presence of asymmetries in the chromospheres.
Conclusions. It is the first time that geometrical extents and structure in the
chromospheres of non-binary K giant stars are determined by interferometry.
These observations provide strong constrains on stellar atmosphere models.Comment: 10 pages, 12 figure
Enhanced Halpha activity at periastron in the young and massive spectroscopic binary HD200775
Young close binaries clear central cavities in their surrounding circumbinary
disk from which the stars can still accrete material. This process takes place
within the very first astronomical units, and is still not well constrained as
the observational evidence has been gathered, until now, only by means of
spectroscopy. The young object HD200775 (MWC361) is a massive spectroscopic
binary (separation of ~15.9mas, ~5.0~AU), with uncertain classification
(early/late Be), that shows a strong and variable Halpha emission. We aim to
study the mechanisms that produce the Halpha line at the AU-scale. Combining
the radial velocity measurements and astrometric data available in the
literature, we determined new orbital parameters. With the VEGA instrument on
the CHARA array, we spatially and spectrally resolved the Halpha emission of
HD200775, at low and medium spectral resolutions (R~1600 and 5000) over a full
orbital period (~3.6 years). We observe that the Halpha equivalent width varies
with the orbital phase, and increases close to periastron, as expected from
theoretical models that predict an increase of the mass transfer from the
circumbinary disk to the primary disk. In addition, using spectral visibilities
and differential phases, we find marginal variations of the typical extent of
the Halpha emission (at 1 to 2-sigma level) and location (at 1 to 5-sigma
level). The spatial extent of the Halpha emission, as probed by a Gaussian
FWHM, is minimum at the ascending node (0.67+/-0.20 mas, i.e., 0.22+/-0.06 AU),
and more than doubles at periastron. In addition, the Gaussian photocenter is
slightly displaced in the direction opposite to the secondary, ruling out the
scenario in which all or most of the Halpha emission is due to accretion onto
the secondary. These findings, together with the wide Halpha line profile, may
be due to a non-spherical wind enhanced at periastron.Comment: Accepted by Astronomy & Astrophysic
A Tale of Two Herbig Ae stars -MWC275 and AB Aurigae: Comprehensive Models for SED and Interferometry
We present comprehensive models for the Herbig Ae stars MWC275 and AB Aur
that aim to explain their spectral energy distribution (from UV to millimeter)
and long baseline interferometry (from near-infrared to millimeter)
simultaneously. Data from the literature, combined with new mid-infrared (MIR)
interferometry from the Keck Segment Tilting Experiment, are modeled using an
axisymmetric Monte Carlo radiative transfer code. Models in which most of the
near-infrared (NIR) emission arises from a dust rim fail to fit the NIR
spectral energy distribution (SED) and sub-milli-arcsecond NIR CHARA
interferometry. Following recent work, we include an additional gas emission
component with similar size scale to the dust rim, inside the sublimation
radius, to fit the NIR SED and long-baseline NIR interferometry on MWC275 and
AB Aur. In the absence of shielding of star light by gas, we show that the
gas-dust transition region in these YSOs will have to contain highly refractory
dust, sublimating at ~1850K. Despite having nearly identical structure in the
thermal NIR, the outer disks of MWC275 and AB Aur differ substantially. In
contrast to the AB Aur disk, MWC275 lacks small grains in the disk atmosphere
capable of producing significant 10-20micron emission beyond ~7AU, forcing the
outer regions into the "shadow" of the inner diskComment: Accepted for publication in Ap
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