3,257 research outputs found
Report of the ultraviolet and visible sensors panel
In order to meet the science objectives of the Astrotech 21 mission set the Ultraviolet (UV) and Visible Sensors Panel made a number of recommendations. In the UV wavelength range of 0.01 to 0.3 micro-m the focus is on the need for large format high quantum efficiency, radiation hard 'solar-blind' detectors. Options recommended for support include Si and non-Si charge coupled devices (CCDs) as well as photocathodes with improved microchannel plate readouts. For the 0.3 to 0.9 micro-m range, it was felt that Si CCDs offer the best option for high quantum efficiencies at these wavelengths. In the 0.9 to 2.5 micro-m the panel recommended support for the investigation of monolithic arrays. Finally, the panel noted that the implementation of very large arrays will require new data transmission, data recording, and data handling technologies
Photoacclimatization by the coral Montastraea cavernosa in the mesophotic zone: light, food, and genetics
Most studies on coral reefs have focused on shallow reef (<30 m) systems due
to the technical limitations of conducting scientific diving deeper than 30 m. Compared to their
shallow-water counterparts, these mesophotic coral reefs (30–150 m) are understudied, which
has slowed our broader understanding of the biodiversity, ecology, and connectivity of
shallow and deep coral reef communities. We know that the light environment is an important
component of the productivity, physiology, and ecology of corals, and it restricts the
distribution of most species of coral to depths of 60 m or less. In the Bahamas, the coral
Montastraea cavernosa has a wide depth distribution, and it is one of the most numerous
corals at mesophotic depths. Using a range of optical, physiological, and biochemical
approaches, the relative dependence on autotrophy vs. heterotrophy was assessed for this
coral from 3 to 91 m. These measurements show that the quantum yield of PSII fluorescence
increases significantly with depth for M. cavernosa while gross primary productivity decreases
with depth. Both morphological and physiological photoacclimatization occurs to a depth of
91 m, and stable isotope data of the host tissues, symbionts, and skeleton reveal a marked
decrease in productivity and a sharp transition to heterotrophy between 45 and 61 m. Below
these depths, significant changes in the genetic composition of the zooxanthellae community,
including genotypes not previously observed, occur and suggest that there is strong selection
for zooxanthellae that are suited for survival in the light-limited environment where
mesophotic M. cavernosa are occurring
Metformin and Myocardial Injury in Patients With Diabetes and ST-Segment Elevation Myocardial Infarction: A Propensity Score Matched Analysis
BACKGROUND: Although animal studies have documented metformin's cardioprotective effects, the impact in humans remains elusive. The study objective was to explore the association between metformin and myocardial infarct size in patients with diabetes presenting with ST‐segment elevation myocardial infarction. METHODS AND RESULTS: Data extraction used the National Cardiovascular Data CathPCI Registry in all patients with diabetes aged >18 years presenting with ST‐segment elevation myocardial infarction at 2 academic medical centers from January 2010 to December 2013. The exposure of interest was ongoing metformin use before the event. Propensity score matching was used for the metformin and nonmetformin groups on key prognostic variables. All matched pairs had acceptable D scores of <10%, confirming an efficient matching procedure. The primary outcome was myocardial infarct size, reflected by peak serum creatine kinase–myocardial band, troponin T, and hospital discharge left ventricular ejection fraction. Of all 1726 ST‐segment elevation myocardial infarction cases reviewed, 493 patients had diabetes (28.5%), with 208 metformin users (42.1%) and 285 nonusers. Matched pairs analysis yielded 137 cases per group. The difference between metformin and nonmetformin groups was −18.1 ng/mL (95% CI −55.0 to 18.8; P=0.56) for total peak serum creatine kinase–myocardial band and −1.1 ng/mL (95% CI −2.8 to 0.5; P=0.41) for troponin T. Median discharge left ventricular ejection fraction in both groups was 45, and the difference between metformin and nonmetformin users was 0.7% (95% CI −2.2 to 3.6; P=0.99). CONCLUSIONS: No statistically significant association of cardioprotection was found between metformin and myocardial infarct size in patients with diabetes and acute ST‐segment elevation myocardial infarction
Advanced Camera for Surveys Observations of Young Star Clusters in the Interacting Galaxy UGC 10214
We present the first Advanced Camera for Surveys (ACS) observations of young
star clusters in the colliding/merging galaxy UGC 10214. The observations were
made as part of the Early Release Observation (ERO) program for the newly
installed ACS during service mission SM3B for the Hubble Space Telescope (HST).
Many young star clusters can be identified in the tails of UGC 10214, with ages
ranging from ~3 Myr to 10 Myr. The extreme blue V-I (F606W-F814W) colors of the
star clusters found in the tail of UGC 10214 can only be explained if strong
emission lines are included with a young stellar population. This has been
confirmed by our Keck spectroscopy of some of these bright blue stellar knots.
The most luminous and largest of these blue knots has an absolute magnitude of
M_V = -14.45, with a half-light radius of 161 pc, and if it is a single star
cluster, would qualify as a super star cluster (SSC). Alternatively, it could
be a superposition of multiple scaled OB associations or clusters. With an
estimated age of ~ 4-5 Myr, its derived mass is < 1.3 x 10^6 solar masses. Thus
the young stellar knot is unbound and will not evolve into a normal globular
cluster. The bright blue clusters and associations are much younger than the
dynamical age of the tail, providing strong evidence that star formation occurs
in the tail long after it was ejected. UGC 10214 provides a nearby example of
processes that contributed to the formation of halos and intra-cluster media in
the distant and younger Universe.Comment: 6 pages with embedded figures, ApJ in pres
Discovery of Globular Clusters in the Proto-Spiral NGC2915: Implications for Hierarchical Galaxy Evolution
We have discovered three globular clusters beyond the Holmberg radius in
Hubble Space Telescope Advanced Camera for Surveys images of the gas-rich dark
matter dominated blue compact dwarf galaxy NGC2915. The clusters, all of which
start to resolve into stars, have M_{V606} = -8.9 to -9.8 mag, significantly
brighter than the peak of the luminosity function of Milky Way globular
clusters. Their colors suggest a metallicity [Fe/H] ~ -1.9 dex, typical of
metal-poor Galactic globular clusters. The specific frequency of clusters is at
a minimum normal, compared to spiral galaxies. However, since only a small
portion of the system has been surveyed it is more likely that the luminosity
and mass normalized cluster content is higher, like that seen in elliptical
galaxies and galaxy clusters. This suggests that NGC2915 resembles a key phase
in the early hierarchical assembly of galaxies - the epoch when much of the old
stellar population has formed, but little of the stellar disk. Depending on the
subsequent interaction history, such systems could go on to build-up larger
elliptical galaxies, evolve into normal spirals, or in rare circumstances
remain suspended in their development to become systems like NGC2915.Comment: ApJ Letters accepted; 6 pages, 2 figures, 3 table
Internal Color Properties of Resolved Spheroids in the Deep HST/ACS field of UGC 10214
(Abridged) We study the internal color properties of a morphologically
selected sample of spheroidal galaxies taken from HST/ACS ERO program of UGC
10214 (``The Tadpole''). By taking advantage of the unprecedented high
resolution of the ACS in this very deep dataset we are able to characterize
spheroids at sub-arcseconds scales. Using the V_606W and I_814W bands, we
construct V-I color maps and extract color gradients for a sample of spheroids
at I_814W < 24 mag. We investigate the existence of a population of
morphologically classified spheroids which show extreme variation in their
internal color properties similar to the ones reported in the HDFs. These are
displayed as blue cores and inverse color gradients with respect to those
accounted from metallicity variations. Following the same analysis we find a
similar fraction of early-type systems (~30%-40%) that show non-homologous
internal colors, suggestive of recent star formation activity. We present two
statistics to quantify the internal color variation in galaxies and for tracing
blue cores, from which we estimate the fraction of non-homogeneous to
homogeneous internal colors as a function of redshift up to z<1.2. We find that
it can be described as about constant as a function of redshift, with a small
increase with redshift for the fraction of spheroids that present strong color
dispersions. The implications of a constant fraction at all redshifts suggests
the existence of a relatively permanent population of evolving spheroids up to
z~1. We discuss the implications of this in the context of spheroidal
formation.Comment: Fixed URL for high resolution version. 13 Pages, 10 Figures. Accepted
for Publication in ApJ. Sep 1st issue. Higher resolution version and complete
table3B at http://acs.pha.jhu.edu/~felipe/e-prints/Tadpol
Star Formation at z~6: i-dropouts in the ACS GTO fields
Using an i-z dropout criterion, we determine the space density of z~6
galaxies from two deep ACS GTO fields with deep optical-IR imaging. A total of
23 objects are found over 46 arcmin^2, or ~0.5 objects/arcmin^2 down to z~27.3
(6 sigma; all AB mag) (including one probable z~6 AGN). Combining deep ISAAC
data for our RDCS1252-2927 field (J~25.7 and Ks~25.0 (5 sigma)) and NICMOS data
for the HDF North (JH~27.3 (5 sigma)), we verify that these dropouts have flat
spectral slopes. i-dropouts in our sample range in luminosity from ~1.5 L*
(z~25.6) to ~0.3 L* (z~27.3) with the exception of one very bright candidate at
z~24.2. The half-light radii vary from 0.09" to 0.29", or 0.5 kpc to 1.7 kpc.
We derive the z~6 rest-frame UV luminosity density using three different
procedures, each utilizing simulations based on a CDF South V dropout sample.
First, we compare our findings with a no-evolution projection of this V-dropout
sample. We find 23+/-25% more i-dropouts than we predict. Adopting previous
results to z~5, this works out to a 20+/-29% drop in the luminosity density
from z~3 to z~6. Second, we use these same V-dropout simulations to derive a
selection function for our i-dropout sample and compute the UV-luminosity
density (7.2+/-2.5 x 10^25 ergs/s/Hz/Mpc^3 down to z~27). We find a 39+/-21%
drop over the same redshift range. This is our preferred value and suggests a
star formation rate of 0.0090+/-0.0031 M_sol/yr/Mpc^3 to z~27, or ~0.036+/-
0.012 M_sol/yr/Mpc^3 extrapolating the LF to the faint limit. Third, we follow
a very similar procedure, but assume no incompleteness, finding a luminosity
density which is ~2-3X lower. This final estimate constitutes a lower limit.
All three estimates are within the canonical range of luminosity densities
necessary for reionization of the universe at this epoch. (abridged)Comment: 36 pages, 13 figures, 2 tables, accepted for publication in ApJ,
postscript version with high-resolution figures can be downloaded at
http://www.ucolick.org/~bouwens/idropout.p
The Luminosity Function of Early-Type Galaxies at z~0.75
We measure the luminosity function of morphologically selected E/S0 galaxies
from to using deep high resolution Advanced Camera for Surveys
imaging data. Our analysis covers an area of 48\Box\arcmin (8 the
area of the HDF-N) and extends 2 magnitudes deeper ( mag) than was
possible in the Deep Groth Strip Survey (DGSS). At , we find
and , and at
, we find . These luminosity
functions are similar in both shape and number density to the luminosity
function using morphological selection (e.g., DGSS), but are much steeper than
the luminosity functions of samples selected using morphological proxies like
the color or spectral energy distribution (e.g., CFRS, CADIS, or COMBO-17). The
difference is due to the `blue', , E/S0 galaxies, which make up to
of the sample at all magnitudes and an increasing proportion of faint
galaxies. We thereby demonstrate the need for {\it both morphological and
structural information} to constrain the evolution of galaxies.
We find that the `blue' E/S0 galaxies have the same average sizes and Sersic
parameters as the `red', , E/S0 galaxies at brighter luminosities
(), but are increasingly different at fainter magnitudes where
`blue' galaxies are both smaller and have lower Sersic parameters. Fits of the
colors to stellar population models suggest that most E/S0 galaxies have short
star-formation time scales ( Gyr), and that galaxies have formed at an
increasing rate from until after which there has been a
gradual decline.Comment: 39 pages, 21 figures, accepted in A
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