164 research outputs found
Broad Absorption Line Quasars in the Sloan Digital Sky Survey with VLA-FIRST Radio Detections
We present 13 Broad Absorption Line (BAL) quasars, including 12 new objects,
which were identified in the Sloan Digital Sky Survey (SDSS) and matched within
2'' to sources in the FIRST radio survey catalog. The surface density of this
sample of radio-detected BAL quasars is 4.5 +- 1.2 per 100 deg^2, i.e.
approximately 4 times larger than previously found by the shallower FIRST
Bright Quasar Survey (FBQS). A majority of these radio-detected BAL quasars are
moderately radio-loud objects. The fraction of BAL quasars in the entire radio
quasar sample, 4.8 +- 1.3 %, is comparable to the fraction of BAL quasars among
the SDSS optical quasar sample (ignoring selection effects). We estimate that
the true fraction of BAL quasars (mostly HiBALs) in the radio sample is 9.2 +-
2.6 % once selection effects are accounted for. We caution that the absorption
troughs of 4 of the 13 radio-detected quasars considered do not strictly
satisfy the standard BALnicity criterion. One or possibly two of the new
radio-detected BAL quasars are of the rare ``iron LoBAL'' type. BAL quasars are
generally redder than the median SDSS quasar at the same redshift.Comment: 10 pages, 3 figures, accepted for publication in Ap
The Late Eocene 187Os / 188Os excursion : chemostratigraphy, cosmic dust flux and the early Oligocene glaciation
Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 241 (2006): 477-492, doi:10.1016/j.epsl.2005.11.035.High resolution records (ca. 100 kyr) of Os isotope composition (187Os/188Os) in bulk sediments from two tropical Pacific sites (ODP Sites 1218 and 1219) capture the complete Late Eocene 187Os/188Os excursion and confirm that the Late Eocene 187Os/188Os minimum, earlier reported by Ravizza and Peucker-Ehrenbrink [Earth Planet. Sci. Lett. 210 (2003) 151-165], is a global feature. Using the astronomically tuned age models available for these sites, it is suggested that the Late Eocene 187Os/188Os minimum can be placed at 34.5±0.1 Ma in the marine records. In addition, two other distinct features of the 187Os/188Os excursion that are correlatable among sections are proposed as chemostratigraphic markers which can serve as age control points with a precision of ca. ±0.1 Myr. We propose a speculative hypothesis that higher cosmic dust flux in the Late Eocene may have contributed to global cooling and early Oligocene glaciation (Oi-1) by supplying bio-essential trace elements to the oceans and thereby resulting in higher ocean productivity, enhanced burial of organic carbon and draw down of atmospheric CO2. To determine if the hypothesis that enhanced cosmic dust flux in the Late Eocene was a cause for the 187Os/188Os excursion can be tested by using the paired bulk sediment and leachate Os isotope composition, 187Os/188Os were also measured in sediment leachates. Results of analyses of leachates are inconsistent between the south Atlantic and the Pacific sites, and therefore do not yield a robust test of this hypothesis. Comparison of 187Os/188Os records with high resolution benthic foraminiferal δ18O records across the Eocene-Oligocene transition suggests that 187Os flux to the oceans decreased during cooling and ice growth leading to the Oi-1 glaciation, whereas subsequent decay of ice-sheets and deglacial weathering drove seawater 187Os/188Os to higher values. Although the precise timing and magnitude of these changes in weathering fluxes and their effects on the marine 187Os/188Os records are obscured by recovery from the Late Eocene 187Os/188Os excursion, evidence of the global influence of glaciation on supply of Os to the ocean is robust as it has now been documented in both Pacific and Atlantic records.This study was supported by NSF awards OCE-0118380, EAR-0215297 and EAR-0215297
LSST: from Science Drivers to Reference Design and Anticipated Data Products
(Abridged) We describe here the most ambitious survey currently planned in
the optical, the Large Synoptic Survey Telescope (LSST). A vast array of
science will be enabled by a single wide-deep-fast sky survey, and LSST will
have unique survey capability in the faint time domain. The LSST design is
driven by four main science themes: probing dark energy and dark matter, taking
an inventory of the Solar System, exploring the transient optical sky, and
mapping the Milky Way. LSST will be a wide-field ground-based system sited at
Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m
effective) primary mirror, a 9.6 deg field of view, and a 3.2 Gigapixel
camera. The standard observing sequence will consist of pairs of 15-second
exposures in a given field, with two such visits in each pointing in a given
night. With these repeats, the LSST system is capable of imaging about 10,000
square degrees of sky in a single filter in three nights. The typical 5
point-source depth in a single visit in will be (AB). The
project is in the construction phase and will begin regular survey operations
by 2022. The survey area will be contained within 30,000 deg with
, and will be imaged multiple times in six bands, ,
covering the wavelength range 320--1050 nm. About 90\% of the observing time
will be devoted to a deep-wide-fast survey mode which will uniformly observe a
18,000 deg region about 800 times (summed over all six bands) during the
anticipated 10 years of operations, and yield a coadded map to . The
remaining 10\% of the observing time will be allocated to projects such as a
Very Deep and Fast time domain survey. The goal is to make LSST data products,
including a relational database of about 32 trillion observations of 40 billion
objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures
available from https://www.lsst.org/overvie
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
Variability-selected active galactic nuclei from supernova search in the Chandra deep field south
Variability is a property shared by virtually all active galactic nuclei
(AGNs), and was adopted as a criterion for their selection using data from
multi epoch surveys. Low Luminosity AGNs (LLAGNs) are contaminated by the light
of their host galaxies, and cannot therefore be detected by the usual colour
techniques. For this reason, their evolution in cosmic time is poorly known.
Consistency with the evolution derived from X-ray detected samples has not been
clearly established so far, also because the low luminosity population consists
of a mixture of different object types. LLAGNs can be detected by the nuclear
optical variability of extended objects. Several variability surveys have been,
or are being, conducted for the detection of supernovae (SNe). We propose to
re-analyse these SNe data using a variability criterion optimised for AGN
detection, to select a new AGN sample and study its properties. We analysed
images acquired with the wide field imager at the 2.2 m ESO/MPI telescope, in
the framework of the STRESS supernova survey. We selected the AXAF field
centred on the Chandra Deep Field South where, besides the deep X-ray survey,
various optical data exist, originating in the EIS and COMBO-17 photometric
surveys and the spectroscopic database of GOODS. We obtained a catalogue of 132
variable AGN candidates. Several of the candidates are X-ray sources. We
compare our results with an HST variability study of X-ray and IR detected
AGNs, finding consistent results. The relatively high fraction of confirmed
AGNs in our sample (60%) allowed us to extract a list of reliable AGN
candidates for spectroscopic follow-up observations.Comment: language revised, table reformatted. To Appear on A&
Comparison of heat-sensitive moxibustion versus fluticasone/salmeterol (seretide) combination in the treatment of chronic persistent asthma: design of a multicenter randomized controlled trial
Genome-wide association study of endometrial cancer in E2C2
Endometrial cancer (EC), a neoplasm of the uterine epithelial lining, is the most common gynecological malignancy in developed countries and the fourth most common cancer among US women. Women with a family history of EC have an increased risk for the disease, suggesting that inherited genetic factors play a role. We conducted a two-stage genome-wide association study of Type I EC. Stage 1 included 5,472 women (2,695 cases and 2,777 controls) of European ancestry from seven studies. We selected independent single-nucleotide polymorphisms (SNPs) that displayed the most significant associations with EC in Stage 1 for replication among 17,948 women (4,382 cases and 13,566 controls) in a multiethnic population (African America, Asian, Latina, Hawaiian and European ancestry), from nine studies. Although no novel variants reached genome-wide significance, we replicated previously identified associations with genetic markers near the HNF1B locus. Our findings suggest that larger studies with specific tumor classification are necessary to identify novel genetic polymorphisms associated with EC susceptibility. Electronic supplementary material The online version of this article (doi:10.1007/s00439-013-1369-1) contains supplementary material, which is available to authorized users
ROCK Inhibitor Is Not Required for Embryoid Body Formation from Singularized Human Embryonic Stem Cells
We report a technology to form human embryoid bodies (hEBs) from singularized human embryonic stem cells (hESCs) without the use of the p160 rho-associated coiled-coil kinase inhibitor (ROCKi) or centrifugation (spin). hEB formation was tested under four conditions: +ROCKi/+spin, +ROCKi/-spin, -ROCKi/+spin, and -ROCKi/-spin. Cell suspensions of BG01V/hOG and H9 hESC lines were pipetted into non-adherent hydrogel substrates containing defined microwell arrays. hEBs of consistent size and spherical geometry can be formed in each of the four conditions, including the -ROCKi/-spin condition. The hEBs formed under the -ROCKi/-spin condition differentiated to develop the three embryonic germ layers and tissues derived from each of the germ layers. This simplified hEB production technique offers homogeneity in hEB size and shape to support synchronous differentiation, elimination of the ROCKi xeno-factor and rate-limiting centrifugation treatment, and low-cost scalability, which will directly support automated, large-scale production of hEBs and hESC-derived cells needed for clinical, research, or therapeutic applications
International mobility, sexual behaviour and HIV-related characteristics of men who have sex with men residing in Belgium
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