5,190 research outputs found
The Evolution of Radio Galaxies at Intermediate Redshift
We describe a new estimate of the radio galaxy 1.4 GHz luminosity function
and its evolution at intermediate redshifts (z~0.4). Photometric redshifts and
color selection have been used to select Bj<23.5 early-type galaxies from the
Panoramic Deep Fields, a multicolor survey of two 25 sq deg fields.
Approximately 230 radio galaxies have then been selected by matching early-type
galaxies with NVSS radio sources brighter than 5 mJy. Estimates of the 1.4 GHz
luminosity function of radio galaxies measure significant evolution over the
observed redshift range. For an Omega_M=1 cosmology the evolution of the radio
power is consistent with luminosity evolution where P(z)=P(0)(1+z)^{k_L} and
3<k_L<5. The observed evolution is similar to that observed for UVX and X-ray
selected AGN and is consistent with the same physical process being responsible
for the optical and radio luminosity evolution of AGN.Comment: 26 pages, 9 Figures, Accepted for Publication in A
The Effect of Variability on the Estimation of Quasar Black Hole Masses
We investigate the time-dependent variations of ultraviolet (UV) black hole
mass estimates of quasars in the Sloan Digital Sky Survey (SDSS). From SDSS
spectra of 615 high-redshift (1.69 < z < 4.75) quasars with spectra from two
epochs, we estimate black hole masses, using a single-epoch technique which
employs an additional, automated night-sky-line removal, and relies on UV
continuum luminosity and CIV (1549A) emission line dispersion. Mass estimates
show variations between epochs at about the 30% level for the sample as a
whole. We determine that, for our full sample, measurement error in the line
dispersion likely plays a larger role than the inherent variability, in terms
of contributing to variations in mass estimates between epochs. However, we use
the variations in quasars with r-band spectral signal-to-noise ratio greater
than 15 to estimate that the contribution to these variations from inherent
variability is roughly 20%. We conclude that these differences in black hole
mass estimates between epochs indicate variability is not a large contributer
to the current factor of two scatter between mass estimates derived from low-
and high-ionization emission lines.Comment: 76 pages, 15 figures, 2 (long) tables; Accepted for publication in
ApJ (November 10, 2007
Are routinely collected NHS administrative records suitable for endpoint identification in clinical trials? Evidence from the West of Scotland coronary prevention study
Background: Routinely collected electronic patient records are already widely used in epidemiological research. In this work we investigated the potential for using them to identify endpoints in clinical trials.<p></p>
Methods: The events recorded in the West of Scotland Coronary Prevention Study (WOSCOPS), a large clinical trial of pravastatin in middle-aged hypercholesterolaemic men in the 1990s, were compared with those in the record-linked deaths and hospitalisations records routinely collected in Scotland.<p></p>
Results: We matched 99% of fatal study events by date. We showed excellent matching (97%) of the causes of fatal
endpoint events and good matching (.80% for first events) of the causes of nonfatal endpoint events with a slightly lower
rate of mismatching of record linkage than study events (19% of first study myocardial infarctions (MI) and 4% of first record linkage MIs not matched as MI). We also investigated the matching of non-endpoint events and showed a good level of matching, with .78% of first stroke/TIA events being matched as stroke/TIA. The primary reasons for mismatches were record linkage data recording readmissions for procedures or previous events, differences between the diagnoses in the routinely collected data and the conclusions of the clinical trial expert adjudication committee, events occurring outside Scotland and therefore being missed by record linkage data, miscoding of cardiac events in hospitalisations data as âunspecified chest painâ, some general miscoding in the record linkage data and some record linkage errors.<p></p>
Conclusions: We conclude that routinely collected data could be used for recording cardiovascular endpoints in clinical
trials and would give very similar results to rigorously collected clinical trial data, in countries with unified health systems such as Scotland. The endpoint types would need to be carefully thought through and an expert endpoint adjudication committee should be involved.<p></p>
Spectral Variability of Quasars in the Sloan Digital Sky Survey. II: The C IV Line
We examine the variability of the high-ionizaton C IV line in a sample of 105
quasars observed at multiple epochs by the Sloan Digital Sky Survey. We find a
strong correlation between the change in the C IV line flux and the change in
the line width, but no correlations between the change in flux and changes in
line center and skewness. The relation between line flux change and line width
change is consistent with a model in which a broad line base varies with
greater amplitude than the line core. The objects studied here are more
luminous and at higher redshift than those normally studied for variability,
ranging in redshift from 1.65 to 4.00 and in absolute r-band magnitude from
roughly -24 to -28. Using moment analysis line-fitting techniques, we measure
line fluxes, centers, widths and skewnesses for the C IV line at two epochs for
each object. The well-known Baldwin Effect is seen for these objects, with a
slope beta = -0.22. The sample has a median intrinsic Baldwin Effect slope of
beta = -0.85; the C IV lines in these high-luminosity quasars appear to be less
responsive to continuum variations than those in lower luminosity AGN.
Additionally, we find no evidence for variability of the well known blueshift
of the C IV line with respect to the low-ionization Mg II line in the highest
flux objects, indicating that this blueshift might be useful as a measure of
orientation.Comment: 52 pages, 14 figures, accepted for publication in Ap
A deep ROSAT survey - IV. The evolution of X-ray-selected QSOs
We report on a new estimate of the QSO X-ray luminosity function and its
evolution with redshift based on a sample of 107 QSOs detected at faint X-ray
fluxes, \ergcms , with the {\it ROSAT}
X-ray satellite. For , the X-ray evolution of QSOs in this sample is
consistent with strong luminosity evolution, , at low redshifts () and a constant comoving space
density at higher redshifts. The derived rate of evolution at low redshifts is
thus significantly higher than that obtained previously for the {\it Einstein}
Extended Medium Sensitivity Survey (EMSS). Indeed, most luminosity evolution
models provide a very poor fit (rejected at the 99 per cent confidence level)
when applied to the combined EMSS and {\it ROSAT} samples, although a
polynomial evolution model, , provides an adequate fit for . For , a simple
power-law luminosity evolution model with a redshift cut-off (,Comment: Accepted for publication in MNRAS. 10 pages including 4 figures;
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ROSAT Blank Field Sources I: Sample Selection and Archival Data
We have identified a population of blank field sources (or `blanks') among
the ROSAT bright unidentified X-ray sources with faint optical counterparts.
The extreme X-ray over optical flux ratio of blanks is not compatible with the
main classes of X-ray emitters except for extreme BL Lacertae objects. From the
analysis of ROSAT archival data we found no indication of variability and
evidence for only three sources, out of 16, needing absorption in excess of the
Galactic value. We also found evidence for an extended nature for only one of
the 5 blanks with a serendipitous HRI detection; this source (1WGAJ1226.9+3332)
was confirmed as a z=0.89 cluster of galaxies. Palomar images reveal the
presence of a red (O-E~2) counterpart in the X-ray error circle for 6 blanks.
The identification process brought to the discovery of another high z cluster
of galaxies, one (possibly extreme) BL Lac, two ultraluminous X-ray sources in
nearby galaxies and two apparently normal type1 AGNs. These AGNs, together with
4 more AGN-like objects seem to form a well defined group: they present
unabsorbed X-ray spectra but red Palomar counterparts. We discuss the possible
explanations for the discrepancy between the X-ray and optical data, among
which: a suppressed big blue bump emission, an extreme dust to gas (~40-60 the
Galactic ratio), a high redshift (z>3.5) QSO nature, an atypical dust grain
size distribution and a dusty warm absorber. These AGN-like blanks seem to be
the bright (and easier to study) analogs of the sources which are found in deep
Chandra observations. Three more blanks have a still unknown nature.Comment: 23 pages, 8 figures, accepted by ApJ main journa
Cognitive Information Processing
Contains reports on six research projects.National Institutes of Health (Grant 5 PO1 GM14940-03)National Institutes of Health (Grant 5 PO1 GM15006-03)Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U.S. Air Force) under Contract DA 28-043-AMC-02536(E)National Institutes of Health (Grant 5 TO1 GM01555-03
Pleiotropic genetic architecture and novel loci for C-reactive protein levels
C-reactive protein is involved in a plethora of pathophysiological conditions. Many genetic loci associated with C-reactive protein are annotated to lipid and glucose metabolism genes supporting common biological pathways between inflammation and metabolic traits. To identify novel pleiotropic loci, we perform multi-trait analysis of genome-wide association studies on C-reactive protein levels along with cardiometabolic traits, followed by a series of in silico analyses including colocalization, phenome-wide association studies and Mendelian randomization. We find 41 novel loci and 19 gene sets associated with C-reactive protein with various pleiotropic effects. Additionally, 41 variants colocalize between C-reactive protein and cardiometabolic risk factors and 12 of them display unexpected discordant effects between the shared traits which are translated into discordant associations with clinical outcomes in subsequent phenome-wide association studies. Our findings provide insights into shared mechanisms underlying inflammation and lipid metabolism, representing potential preventive and therapeutic targets
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