472 research outputs found
Running a distributed virtual observatory: US Virtual Astronomical Observatory operations
Operation of the US Virtual Astronomical Observatory shares some issues with
modern physical observatories, e.g., intimidating data volumes and rapid
technological change, and must also address unique concerns like the lack of
direct control of the underlying and scattered data resources, and the
distributed nature of the observatory itself. In this paper we discuss how the
VAO has addressed these challenges to provide the astronomical community with a
coherent set of science-enabling tools and services. The distributed nature of
our virtual observatory-with data and personnel spanning geographic,
institutional and regime boundaries-is simultaneously a major operational
headache and the primary science motivation for the VAO. Most astronomy today
uses data from many resources. Facilitation of matching heterogeneous datasets
is a fundamental reason for the virtual observatory. Key aspects of our
approach include continuous monitoring and validation of VAO and VO services
and the datasets provided by the community, monitoring of user requests to
optimize access, caching for large datasets, and providing distributed storage
services that allow user to collect results near large data repositories. Some
elements are now fully implemented, while others are planned for subsequent
years. The distributed nature of the VAO requires careful attention to what can
be a straightforward operation at a conventional observatory, e.g., the
organization of the web site or the collection and combined analysis of logs.
Many of these strategies use and extend protocols developed by the
international virtual observatory community.Comment: 7 pages with 2 figures included within PD
Contrast-Induced Nephropathy in Renal Transplant Recipients: A Single Center Experience
BACKGROUND: Contrast-induced nephropathy (CIN) in native kidneys is associated with a significant increase in mortality and morbidity. Data regarding CIN in renal allografts are limited, however. We retrospectively studied CIN in renal allografts at our institution: its incidence, risk factors, and effect on long-term outcomes including allograft loss and death.
METHODS: One hundred thirty-five renal transplant recipients undergoing 161 contrast-enhanced computed tomography (CT) scans or coronary angiograms (Cath) between years 2000 and 2014 were identified. Contrast agents were iso- or low osmolar. CIN was defined as a rise in serum creatinine (SCr) by \u3e0.3 mg/dl or 25% from baseline within 4 days of contrast exposure. After excluding 85 contrast exposures where patients had no SCr within 4 days of contrast administration, 76 exposures (CT:
RESULTS: Incidence of CIN was 13% following both, CT (6 out of 45) and Cath (4 out of 31). Significant bivariate predictors of CIN were IV fluid administration (
CONCLUSION: CIN is common in kidney transplant recipients, and there is room for quality improvement with regards to careful renal function monitoring post-contrast exposure. In our study
The Discovery of a Second Field Methane Brown Dwarf from Sloan Digital Sky Survey Commissioning Data
We report the discovery of a second field methane brown dwarf from the
commissioning data of the Sloan Digital Sky Survey (SDSS). The object, SDSS
J134646.45-003150.4 (SDSS 1346-00), was selected because of its very red color
and stellar appearance. Its spectrum between 0.8-2.5 mic is dominated by strong
absorption bands of H_2O and CH_4 and closely mimics those of Gliese 229B and
SDSS 162414.37+002915.6 (SDSS 1624+00), two other known methane brown dwarfs.
SDSS 1346-00 is approximately 1.5 mag fainter than Gliese 229B, suggesting that
it lies about 11 pc from the sun. The ratio of flux at 2.1 mic to that at 1.27
mic is larger for SDSS 1346-00 than for Gliese 229B and SDSS 1624+00, which
suggests that SDSS 1346-00 has a slightly higher effective temperature than the
others. Based on a search area of 130 sq. deg. and a detection limit of z* =
19.8, we estimate a space density of 0.05 pc^-3 for methane brown dwarfs with
T_eff ~ 1000 K in the 40 pc^3 volume of our search. This estimate is based on
small-sample statistics and should be treated with appropriate caution.Comment: 9 pages, 3 figures, AASTeX, to appear in ApJ Letters, authors list
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Outcomes following autologous hematopoietic stem cell transplant for patients with relapsed Wilms' tumor: a CIBMTR retrospective analysis.
Despite the marked improvement in the overall survival (OS) for patients diagnosed with Wilms' tumor (WT), the outcomes for those who experience relapse have remained disappointing. We describe the outcomes of 253 patients with relapsed WT who received high-dose chemotherapy (HDT) followed by autologous hematopoietic stem cell transplant (HCT) between 1990 and 2013, and were reported to the Center for International Blood and Marrow Transplantation Research. The 5-year estimates for event-free survival (EFS) and OS were 36% (95% confidence interval (CI); 29-43%) and 45% (95 CI; 38-51%), respectively. Relapse of primary disease was the cause of death in 81% of the population. EFS, OS, relapse and transplant-related mortality showed no significant differences when broken down by disease status at transplant, time from diagnosis to transplant, year of transplant or conditioning regimen. Our data suggest that HDT followed by autologous HCT for relapsed WT is well tolerated and outcomes are similar to those reported in the literature. As attempts to conduct a randomized trial comparing maintenance chemotherapy with consolidation versus HDT followed by stem cell transplant have failed, one should balance the potential benefits with the yet unknown long-term risks. As disease recurrence continues to be the most common cause of death, future research should focus on the development of consolidation therapies for those patients achieving complete response to therapy
Five High-Redshift Quasars Discovered in Commissioning Imaging Data of the Sloan Digital Sky Survey
We report the discovery of five quasars with redshifts of 4.67 - 5.27 and
z'-band magnitudes of 19.5-20.7 M_B ~ -27. All were originally selected as
distant quasar candidates in optical/near-infrared photometry from the Sloan
Digital Sky Survey (SDSS), and most were confirmed as probable high-redshift
quasars by supplementing the SDSS data with J and K measurements. The quasars
possess strong, broad Lyman-alpha emission lines, with the characteristic sharp
cutoff on the blue side produced by Lyman-alpha forest absorption. Three
quasars contain strong, broad absorption features, and one of them exhibits
very strong N V emission. The amount of absorption produced by the Lyman-alpha
forest increases toward higher redshift, and that in the z=5.27 object (D_A ~
0.7) is consistent with a smooth extrapolation of the absorption seen in lower
redshift quasars. The high luminosity of these objects relative to most other
known objects at z >~ 5 makes them potentially valuable as probes of early
quasar properties and of the intervening intergalactic medium.Comment: 13 pages in LaTex format, two postscirpt figures. Submitted to the
Astronomical Journa
Evidence for Reionization at z ~ 6: Detection of a Gunn-Peterson Trough in a z=6.28 Quasar
We present moderate resolution Keck spectroscopy of quasars at z=5.82, 5.99
and 6.28, discovered by the Sloan Digital Sky Survey (SDSS). We find that the
Ly Alpha absorption in the spectra of these quasars evolves strongly with
redshift. To z~5.7, the Ly Alpha absorption evolves as expected from an
extrapolation from lower redshifts. However, in the highest redshift object,
SDSSp J103027.10+052455.0 (z=6.28), the average transmitted flux is
0.0038+-0.0026 times that of the continuum level over 8450 A < lambda < 8710 A
(5.95<z(abs)<6.16), consistent with zero flux. Thus the flux level drops by a
factor of >150, and is consistent with zero flux in the Ly Alpha forest region
immediately blueward of the Ly Alpha emission line, compared with a drop by a
factor of ~10 at z(abs)~5.3. A similar break is seen at Ly Beta; because of the
decreased oscillator strength of this transition, this allows us to put a
considerably stronger limit, tau(eff) > 20, on the optical depth to Ly Alpha
absorption at z=6.
This is a clear detection of a complete Gunn-Peterson trough, caused by
neutral hydrogen in the intergalactic medium. Even a small neutral hydrogen
fraction in the intergalactic medium would result in an undetectable flux in
the Ly Alpha forest region. Therefore, the existence of the Gunn-Peterson
trough by itself does not indicate that the quasar is observed prior to the
reionization epoch. However, the fast evolution of the mean absorption in these
high-redshift quasars suggests that the mean ionizing background along the line
of sight to this quasar has declined significantly from z~5 to 6, and the
universe is approaching the reionization epoch at z~6.Comment: Revised version (2001 Sep 4) accepted by the Astronomical Journal
(minor changes
Early-type galaxies in the SDSS. I. The sample
A sample of nearly 9000 early-type galaxies, in the redshift range 0.01 < z <
0.3, was selected from the Sloan Digital Sky Survey using morphological and
spectral criteria. This paper describes how the sample was selected, presents
examples of images and seeing corrected fits to the observed surface brightness
profiles, describes our method for estimating K-corrections, and shows that the
SDSS spectra are of sufficiently high quality to measure velocity dispersions
accurately. It also provides catalogs of the measured photometric and
spectroscopic parameters. In related papers, these data are used to study how
early-type galaxy observables, including luminosity, effective radius, surface
brightness, color, and velocity dispersion, are correlated with one another.Comment: 63 pages, 21 figures. Accepted by AJ (scheduled for April 2003). This
paper is part I of a revised version of astro-ph/0110344. The full version of
Tables 2 and 3, i.e. the tables listing the photometric and spectroscopic
parameters of ~ 9000 galaxies, are available at
http://astrophysics.phys.cmu.edu/~bernardi/SDSS/Etypes/TABLE
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