87 research outputs found
The Ultraviolet Imaging Telescope: Instrument and Data Characteristics
The Ultraviolet Imaging Telescope (UIT) was flown as part of the Astro
observatory on the Space Shuttle Columbia in December 1990 and again on the
Space Shuttle Endeavor in March 1995. Ultraviolet (1200-3300 Angstroms) images
of a variety of astronomical objects, with a 40 arcmin field of view and a
resolution of about 3 arcsec, were recorded on photographic film. The data
recorded during the first flight are available to the astronomical community
through the National Space Science Data Center (NSSDC); the data recorded
during the second flight will soon be available as well. This paper discusses
in detail the design, operation, data reduction, and calibration of UIT,
providing the user of the data with information for understanding and using the
data. It also provides guidelines for analyzing other astronomical imagery made
with image intensifiers and photographic film.Comment: 44 pages, LaTeX, AAS preprint style and EPSF macros, accepted by PAS
High Precision Astrometry with MICADO at the European Extremely Large Telescope
In this article we identify and discuss various statistical and systematic
effects influencing the astrometric accuracy achievable with MICADO, the
near-infrared imaging camera proposed for the 42-metre European Extremely Large
Telescope (E-ELT). These effects are instrumental (e.g. geometric distortion),
atmospheric (e.g. chromatic differential refraction), and astronomical
(reference source selection). We find that there are several phenomena having
impact on ~100 micro-arcsec scales, meaning they can be substantially larger
than the theoretical statistical astrometric accuracy of an optical/NIR
42m-telescope. Depending on type, these effects need to be controlled via
dedicated instrumental design properties or via dedicated calibration
procedures. We conclude that if this is done properly, astrometric accuracies
of 40 micro-arcsec or better - with 40 micro-arcsec/year in proper motions
corresponding to ~20 km/s at 100 kpc distance - can be achieved in one epoch of
actual observationsComment: 15 pages, 9 figures, 3 tables. Accepted by MNRA
Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Sky Maps, Systematic Errors, and Basic Results
(Abridged) New full sky temperature and polarization maps based on seven
years of data from WMAP are presented. The new results are consistent with
previous results, but have improved due to reduced noise from the additional
integration time, improved knowledge of the instrument performance, and
improved data analysis procedures. The improvements are described in detail.
The seven year data set is well fit by a minimal six-parameter flat Lambda-CDM
model. The parameters for this model, using the WMAP data in conjunction with
baryon acoustic oscillation data from the Sloan Digital Sky Survey and priors
on H_0 from Hubble Space Telescope observations, are: Omega_bh^2 = 0.02260
+-0.00053, Omega_ch^2 = 0.1123 +-0.0035, Omega_Lambda = 0.728 +0.015 -0.016,
n_s = 0.963 +-0.012, tau = 0.087 +-0.014 and sigma_8 = 0.809 +-0.024 (68 % CL
uncertainties). The temperature power spectrum signal-to-noise ratio per
multipole is greater that unity for multipoles < 919, allowing a robust
measurement of the third acoustic peak. This measurement results in improved
constraints on the matter density, Omega_mh^2 = 0.1334 +0.0056 -0.0055, and the
epoch of matter- radiation equality, z_eq = 3196 +134 -133, using WMAP data
alone. The new WMAP data, when combined with smaller angular scale microwave
background anisotropy data, results in a 3 sigma detection of the abundance of
primordial Helium, Y_He = 0.326 +-0.075.The power-law index of the primordial
power spectrum is now determined to be n_s = 0.963 +-0.012, excluding the
Harrison-Zel'dovich-Peebles spectrum by >3 sigma. These new WMAP measurements
provide important tests of Big Bang cosmology.Comment: 42 pages, 9 figures, Submitted to Astrophysical Journal Supplement
Serie
Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Planets and Celestial Calibration Sources
(Abridged) We present WMAP seven-year observations of bright sources which
are often used as calibrators at microwave frequencies. Ten objects are studied
in five frequency bands (23 - 94 GHz): the outer planets (Mars, Jupiter,
Saturn, Uranus and Neptune) and five fixed celestial sources (Cas A, Tau A, Cyg
A, 3C274 and 3C58). The seven-year analysis of Jupiter provides temperatures
which are within 1-sigma of the previously published WMAP five-year values,
with slightly tighter constraints on variability with orbital phase, and limits
(but no detections) on linear polarization. Scaling factors are provided which,
when multiplied by the Wright Mars thermal model predictions at 350 micron,
reproduce WMAP seasonally averaged observations of Mars within ~2%. An
empirical model is described which fits brightness variations of Saturn due to
geometrical effects and can be used to predict the WMAP observations to within
3%. Seven-year mean temperatures for Uranus and Neptune are also tabulated.
Uncertainties in Uranus temperatures are 3%-4% in the 41, 61 and 94 GHz bands;
the smallest uncertainty for Neptune is ~8% for the 94 GHz band. Intriguingly,
the spectrum of Uranus appears to show a dip at ~30 GHz of unidentified origin,
although the feature is not of high statistical significance. Flux densities
for the five selected fixed celestial sources are derived from the seven-year
WMAP sky maps, and are tabulated for Stokes I, Q and U, along with polarization
fraction and position angle. Fractional uncertainties for the Stokes I fluxes
are typically 1% to 3%. Source variability over the seven-year baseline is also
estimated. Significant secular decrease is seen for Cas A and Tau A: our
results are consistent with a frequency independent decrease of about 0.53% per
year for Cas A and 0.22% per year for Tau A.Comment: 72 pages, 21 figures; accepted to ApJS; (v2) corrected Mars model
scaling factors, added figure 21, added text to Mars, Saturn and celestial
sources section
Two-year outcomes after transcatheter or surgical aortic-valve replacement.
BACKGROUND: The Placement of Aortic Transcatheter Valves (PARTNER) trial showed that among high-risk patients with aortic stenosis, the 1-year survival rates are similar with transcatheter aortic-valve replacement (TAVR) and surgical replacement. However, longer-term follow-up is necessary to determine whether TAVR has prolonged benefits. METHODS: At 25 centers, we randomly assigned 699 high-risk patients with severe aortic stenosis to undergo either surgical aortic-valve replacement or TAVR. All patients were followed for at least 2 years, with assessment of clinical outcomes and echocardiographic evaluation. RESULTS: The rates of death from any cause were similar in the TAVR and surgery groups (hazard ratio with TAVR, 0.90; 95% confidence interval [CI], 0.71 to 1.15; P=0.41) and at 2 years (Kaplan-Meier analysis) were 33.9% in the TAVR group and 35.0% in the surgery group (P=0.78). The frequency of all strokes during follow-up did not differ significantly between the two groups (hazard ratio, 1.22; 95% CI, 0.67 to 2.23; P=0.52). At 30 days, strokes were more frequent with TAVR than with surgical replacement (4.6% vs. 2.4%, P=0.12); subsequently, there were 8 additional strokes in the TAVR group and 12 in the surgery group. Improvement in valve areas was similar with TAVR and surgical replacement and was maintained for 2 years. Paravalvular regurgitation was more frequent after TAVR (P<0.001), and even mild paravalvular regurgitation was associated with increased late mortality (P<0.001). CONCLUSIONS: A 2-year follow-up of patients in the PARTNER trial supports TAVR as an alternative to surgery in high-risk patients. The two treatments were similar with respect to mortality, reduction in symptoms, and improved valve hemodynamics, but paravalvular regurgitation was more frequent after TAVR and was associated with increased late mortality. (Funded by Edwards Lifesciences; ClinicalTrials.gov number, NCT00530894.)
Transcatheter or surgical aortic-valve replacement in intermediate-risk patients
BACKGROUND:
Previous trials have shown that among high-risk patients with aortic stenosis, survival
rates are similar with transcatheter aortic-valve replacement (TAVR) and surgical aorticvalve
replacement. We evaluated the two procedures in a randomized trial involving
intermediate-risk patients.
METHODS:
We randomly assigned 2032 intermediate-risk patients with severe aortic stenosis, at 57
centers, to undergo either TAVR or surgical replacement. The primary end point was death
from any cause or disabling stroke at 2 years. The primary hypothesis was that TAVR would
not be inferior to surgical replacement. Before randomization, patients were entered into
one of two cohorts on the basis of clinical and imaging findings; 76.3% of the patients were
included in the transfemoral-access cohort and 23.7% in the transthoracic-access cohort.
RESULTS:
The rate of death from any cause or disabling stroke was similar in the TAVR group and
the surgery group (P=0.001 for noninferiority). At 2 years, the Kaplan–Meier event rates
were 19.3% in the TAVR group and 21.1% in the surgery group (hazard ratio in the TAVR
group, 0.89; 95% confidence interval [CI], 0.73 to 1.09; P=0.25). In the transfemoralaccess
cohort, TAVR resulted in a lower rate of death or disabling stroke than surgery
(hazard ratio, 0.79; 95% CI, 0.62 to 1.00; P=0.05), whereas in the transthoracic-access
cohort, outcomes were similar in the two groups. TAVR resulted in larger aortic-valve
areas than did surgery and also resulted in lower rates of acute kidney injury, severe bleeding,
and new-onset atrial fibrillation; surgery resulted in fewer major vascular complications
and less paravalvular aortic regurgitation.
CONCLUSIONS:
In intermediate-risk patients, TAVR was similar to surgical aortic-valve replacement with
respect to the primary end point of death or disabling stroke. (Funded by Edwards Lifesciences;
PARTNER 2 ClinicalTrials.gov number, NCT01314313
Three-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Temperature Analysis
We present new full-sky temperature maps in five frequency bands from 23 to
94 GHz, based on the first three years of the WMAP sky survey. The new maps,
which are consistent with the first-year maps and more sensitive, incorporate
improvements in data processing made possible by the additional years of data
and by a more complete analysis of the polarization signal. These include
refinements in the gain calibration and beam response models. We employ two
forms of multi-frequency analysis to separate astrophysical foreground signals
from the CMB, each of which improves on our first-year analyses. First, we form
an improved 'Internal Linear Combination' map, based solely on WMAP data, by
adding a bias correction step and by quantifying residual uncertainties in the
resulting map. Second, we fit and subtract new spatial templates that trace
Galactic emission; in particular, we now use low-frequency WMAP data to trace
synchrotron emission. The WMAP point source catalog is updated to include 115
new sources. We derive the angular power spectrum of the temperature anisotropy
using a hybrid approach that combines a maximum likelihood estimate at low l
(large angular scales) with a quadratic cross-power estimate for l>30. Our best
estimate of the CMB power spectrum is derived by averaging cross-power spectra
from 153 statistically independent channel pairs. The combined spectrum is
cosmic variance limited to l=400, and the signal-to-noise ratio per l-mode
exceeds unity up to l=850. The first two acoustic peaks are seen at l=220.8 +-
0.7 and l=530.9 +- 3.8, respectively, while the first two troughs are seen at
l=412.4 +- 1.9 and l=675.1 +- 11.1, respectively. The rise to the third peak is
unambiguous; when the WMAP data are combined with higher resolution CMB
measurements, the existence of a third acoustic peak is well established.Comment: 116 pgs, 24 figs. Accepted version of the 3-year paper as posted to
http://lambda.gsfc.nasa.gov/product/map/dr2/map_bibliography.cfm in January
200
Transapical transcatheter aortic valve replacement in patients with or without prior coronary artery bypass graft operation
Non-Gaussian Inflationary Perturbations from the dS/CFT Correspondence
We use the dS/CFT correspondence and bulk gravity to predict the form of the
renormalized holographic three-point correlation function of the operator which
is dual to the inflaton field perturbation during single-field, slow-roll
inflation. Using Maldcaena's formulation of the correspondence, this correlator
can be related to the three-point function of the curvature perturbation
generated during single-field inflation, and we find exact agreement with
previous bulk QFT calculations. This provides a consistency check on existing
derivations of the non-Gaussianity from single-field inflation and also yields
insight into the nature of the dS/CFT correspondence. As a result of our
calculation, we obtain the properly renormalized dS/CFT one-point function,
including boundary contributions where derivative interactions are present in
the bulk. In principle, our method may be employed to derive the n-point
correlators of the inflationary curvature perturbation within the context of
(n-1)th-order perturbation theory, rather than nth-order theory as in
conventional approaches.Comment: 23 pages, uses iopart.cls. Replaced with version accepted by JCAP;
some clarifications in the introduction, and references adde
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