2,347 research outputs found
An Empirical Calibration of the Completeness of the SDSS Quasar Survey
Spectra of nearly 20000 point-like objects to a Galactic reddening corrected
magnitude of i=19.1 have been obtained to test the completeness of the SDSS
quasar survey. The spatially-unresolved objects were selected from all regions
of color space, sparsely sampled from within a 278 sq. deg. area of sky covered
by this study. Only ten quasars were identified that were not targeted as
candidates by the SDSS quasar survey (including both color and radio source
selection). The inferred density of unresolved quasars on the sky that are
missed by the SDSS algorithm is 0.44 per sq. deg, compared to 8.28 per sq. deg.
for the selected quasar density, giving a completeness of 94.9(+2.6,-3.8) to
the limiting magnitude. Omitting radio selection reduces the color-only
selection completeness by about 1%. Of the ten newly identified quasars, three
have detected broad absorption line systems, six are significantly redder than
other quasars at the same redshift, and four have redshifts between 2.7 and 3.0
(the redshift range where the SDSS colors of quasars intersect the stellar
locus). The fraction of quasars missed due to image defects and blends is
approximately 4%, but this number varies by a few percent with magnitude.
Quasars with extended images comprise about 6% of the SDSS sample, and the
completeness of the selection algorithm for extended quasars is approximately
81%, based on the SDSS galaxy survey. The combined end-to-end completeness for
the SDSS quasar survey is approximately 89%. The total corrected density of
quasars on the sky to i=19.1 is estimated to be 10.2 per sq. deg.Comment: 37 pages, 10 figures, accepted for publication in A
Evaluating future risk of NAFLD in adolescents:a prediction and decision curve analysis
BACKGROUND: Non-alcoholic fatty liver disease (NAFLD) is the commonest liver condition in the western world and is directly linked to obesity and the metabolic syndrome. Elevated body mass index is regarded as a major risk factor of NAFL (steatosis) and NAFLD fibrosis. Using data from the Avon Longitudinal Study of Parents and Children (ALSPAC), we sought to investigate whether other variables from adolescence could improve prediction of future NAFL and NAFLD fibrosis risk at 24Â years, above BMI and sex. METHODS: Aged 24Â years, 4018 ALSPAC participants had transient elastography (TE) and controlled attenuation parameter (CAP) measurement using Echosens 502 Touch. 513 participants with harmful alcohol consumption were excluded. Logistic regression models examined which variables measured at 17Â years were predictive of NAFL and NAFLD fibrosis in young adults. Predictors included sex, BMI, central adiposity, lipid profile, blood pressure, liver function tests, homeostatic model assessment for insulin resistance (HOMA-IR), and ultrasound defined NAFL at 17Â years (when examining fibrosis outcomes). A model including all these variables was termed âroutine clinical measuresâ. Models were compared using area under the receiver operator curve (AUROC) and Bayesian Information Criterion (BIC), analysis, which penalises model complexity. Models were tested in all participants and those with overweight or obese standardised BMIs (BMI SDS) centiles at the 17-year time point. A decision curve analysis (DCA) was performed to evaluate the clinical utility of models in overweight and obese adolescents predicting NAFLD fibrosis at a threshold probability of 0.1. RESULTS: The âroutine clinical measuresâ model had the highest AUROC for predicting NAFL in all adolescent participants (AUROC 0.79 [SD 0.00]) and those with an overweight/obese BMI SDS centile (AUROC 0.77 [SD 0.01]). According to BIC analysis, insulin resistance was the best predictor of NAFL in all adolescents, whilst central adiposity was the best predictor in those with an overweight/obese BMI SDS centile. The âroutine clinical measuresâ model also had the highest AUROC for predicting NAFLD fibrosis in all adolescent participants (AUROC 0.78 [SD 0.02]) and participants with an overweight/obese BMI SDS centile (AUROC 0.84 [SD 0.03]). However, following BIC analysis, BMI was the best predictor of NAFLD fibrosis in all adolescents including those with an overweight/obese BMI SDS centile. A decision curve analysis examining overweight/obese adolescent participants showed the model that had the greatest net benefit for increased NAFLD fibrosis detection, above a treat all overweight and obese adolescentsâ assumption, was the âroutine clinical measuresâ model. However, the net benefit was marginal (0.0054 [0.0034â0.0075]). CONCLUSION: In adolescents, routine clinical measures were not superior to central adiposity and BMI at predicting NAFL and NAFLD fibrosis respectively in young adulthood. Additional routine clinical measurements do provide incremental benefit in detecting true positive fibrosis cases, but the benefit is small. Thus, to reduce morbidity and mortality associated with NASH cirrhosis in adults, the ultimate end point of NAFLD, the focus must be on obesity management at a population level. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12876-022-02401-y
Double-Peaked Low-Ionization Emission Lines in Active Galactic Nuclei
We present a new sample of 116 double-peaked Balmer line Active Galactic
Nuclei (AGN) selected from the Sloan Digital Sky Survey. Double-peaked emission
lines are believed to originate in the accretion disks of AGN, a few hundred
gravitational radii (Rg) from the supermassive black hole. We investigate the
properties of the candidate disk emitters with respect to the full sample of
AGN over the same redshifts, focusing on optical, radio and X-ray flux, broad
line shapes and narrow line equivalent widths and line flux-ratios. We find
that the disk-emitters have medium luminosities (~10^44erg/s) and FWHM on
average six times broader than the AGN in the parent sample. The double-peaked
AGN are 1.6 times more likely to be radio-sources and are predominantly (76%)
radio quiet, with about 12% of the objects classified as LINERs. Statistical
comparison of the observed double-peaked line profiles with those produced by
axisymmetric and non-axisymmetric accretion disk models allows us to impose
constraints on accretion disk parameters. The observed Halpha line profiles are
consistent with accretion disks with inclinations smaller than 50 deg, surface
emissivity slopes of 1.0-2.5, outer radii larger than ~2000 Rg, inner radii
between 200-800Rg, and local turbulent broadening of 780-1800 km/s. The
comparison suggests that 60% of accretion disks require some form of asymmetry
(e.g., elliptical disks, warps, spiral shocks or hot spots).Comment: 60 pages, 19 figures, accepted for publication in AJ. For high
quality figures and full tables, please see
http://astro.princeton.edu/~iskra/disks.htm
Chandra Observations of the Highest Redshift Quasars from the Sloan Digital Sky Survey
We present new Chandra observations of 21 z>4 quasars, including 11 sources
at z>5. These observations double the number of X-ray detected quasars at z>5,
allowing investigation of the X-ray spectral properties of a substantial sample
of quasars at the dawn of the modern Universe. By jointly fitting the spectra
of 15 z>5 radio-quiet quasars (RQQs), including sources from the Chandra
archive, with a total of 185 photons, we find a mean X-ray power-law photon
index of Gamma=1.95^{+0.30}_{-0.26}, and a mean neutral intrinsic absorption
column density of N_H<~6x10^{22} cm^{-2}. These results show that quasar X-ray
spectral properties have not evolved up to the highest observable redshifts. We
also find that the mean optical-X-ray spectral slope (alpha_ox) of
optically-selected z>5 RQQs, excluding broad absorption line quasars, is
alpha_ox=-1.69+/-0.03, which is consistent with the value predicted from the
observed relationship between alpha_ox and ultraviolet luminosity. Four of the
sources in our sample are members of the rare class of weak emission-line
quasars, and we detect two of them in X-rays. We discuss the implications our
X-ray observations have for the nature of these mysterious sources and, in
particular, whether their weak-line spectra are a consequence of continuum
boosting or a deficit of high-ionization line emitting gas.Comment: 15 pages (emulateapj), 8 figures. Accepted by Ap
A Survey of z>5.7 Quasars in the Sloan Digital Sky Survey II: Discovery of Three Additional Quasars at z>6
We present the discovery of three new quasars at z>6 in 1300 deg^2 of SDSS
imaging data, J114816.64+525150.3 (z=6.43), J104845.05+463718.3 (z=6.23) and
J163033.90+401209.6 (z=6.05). The first two objects have weak Ly alpha emission
lines; their redshifts are determined from the positions of the Lyman break.
They are only accurate to 0.05 and could be affected by the presence of broad
absorption line systems. The last object has a Ly alpha strength more typical
of lower redshift quasars. Based on a sample of six quasars at z>5.7 that cover
2870 deg^2 presented in this paper and in Paper I, we estimate the comoving
density of luminous quasars at z 6 and M_{1450} < -26.8 to be (8 +/-
3)x10^{-10} Mpc^{-3} (for H_0 = 50 km/s/Mpc, Omega = 1). HST imaging of two
z>5.7 quasars and high-resolution ground-based images (seeing 0.4'') of three
additional z>5.7 quasars show that none of them is gravitationally lensed. The
luminosity distribution of the high-redshfit quasar sample suggests the bright
end slope of the quasar luminosity function at z 6 is shallower than Psi
L^{-3.5} (2-sigma), consistent with the absence of strongly lensed objects.Comment: AJ in press (Apr 2003), 26 pages, 9 figure
Civic republican social justice and the case of state grammar schools in England
The aim of this paper is to consider the ways in which civic republican theory can provide a meaningful and useful account of social justice, one that is which holds resonance for educational debates. Recognising the need for educationalists interested in civic republicanism to pay greater attention to ideas of justice â and in particular social justice as it concerns relationships between citizens (citizen to citizen, group to group or citizen to group) â it is argued that a form of civic republicanism committed to freedom as non-domination is capable of providing a substantive model for analysing social (in)justice within educational arenas. After positioning the contribution offered here within existing educational literature on civic republicanism, salient elements of social justice as freedom as non-domination are identified. On this basis, debates concerning the existence and potential expansion of state (public) grammar schools in England are considered in relation to the account of republican social justice as non-domination.
It is argued that from this republican position grammar schools (1) represent an arbitrary domination of the interests of those less well off by those with greater material and cultural capital and (2) in doing so lead to advantages for some at the expense of others.
Though the focus of the paper is on grammar schools in England, it is suggested that republican justice may be a useful frame for considering similar educational cases in England and elsewhere
The Sloan Digital Sky Survey Quasar Catalog I. Early Data Release
We present the first edition of the Sloan Digital Sky Survey (SDSS) Quasar
Catalog. The catalog consists of the 3814 objects (3000 discovered by the SDSS)
in the initial SDSS public data release that have at least one emission line
with a full width at half maximum larger than 1000 km/s, luminosities brighter
than M_i^* = -23, and highly reliable redshifts. The area covered by the
catalog is 494 square degrees; the majority of the objects were found in SDSS
commissioning data using a multicolor selection technique. The quasar redshifts
range from 0.15 to 5.03. For each object the catalog presents positions
accurate to better than 0.2" rms per coordinate, five band (ugriz) CCD-based
photometry with typical accuracy of 0.05 mag, radio and X-ray emission
properties, and information on the morphology and selection method. Calibrated
spectra of all objects in the catalog, covering the wavelength region 3800 to
9200 Angstroms at a spectral resolution of 1800-2100, are also available. Since
the quasars were selected during the commissioning period, a time when the
quasar selection algorithm was undergoing frequent revisions, the sample is not
homogeneous and is not intended for statistical analysis.Comment: 27 pages, 4 figures, 4 tables, accepted by A
Colors of 2625 Quasars at 0<z<5 Measured in the Sloan Digital Sky Survey Photometric System
We present an empirical investigation of the colors of quasars in the Sloan
Digital Sky Survey (SDSS) photometric system. The sample studied includes 2625
quasars with SDSS photometry. The quasars are distributed in a 2.5 degree wide
stripe centered on the Celestial Equator covering square degrees.
Positions and SDSS magnitudes are given for the 898 quasars known prior to SDSS
spectroscopic commissioning. New SDSS quasars represent an increase of over
200% in the number of known quasars in this area of the sky. The ensemble
average of the observed colors of quasars in the SDSS passbands are well
represented by a power-law continuum with (). However, the contributions of the bump
and other strong emission lines have a significant effect upon the colors. The
color-redshift relation exhibits considerable structure, which may be of use in
determining photometric redshifts for quasars. The range of colors can be
accounted for by a range in the optical spectral index with a distribution
(95% confidence), but there is a red tail in the
distribution. This tail may be a sign of internal reddening. Finally, we show
that there is a continuum of properties between quasars and Seyfert galaxies
and we test the validity of the traditional division between the two classes of
AGN.Comment: 66 pages, 15 figures (3 color), accepted by A
Addressing disparities in cancer clinical trials: a roadmap to more equitable accrual
The Georgia Center for Oncology Research and Education (Georgia CORE) and the Georgia Society of Clinical Oncology (GASCO) held a one-day summit exploring opportunities and evidence-based interventions to address disparities in cancer clinical trials. The purpose of the summit was to identify clear and concise recommendations aimed at decreasing clinical trial accrual disparities in Georgia for rural and minority populations. The summit included expert presentations, panel discussions with leaders from provider organizations throughout Georgia, and breakout sessions to allow participants to critically discuss the information presented. Over 120 participants attended the summit. Recognizing the need for evidence-based interventions to improve clinical trial accrual among rural Georgians and persons of color, summit participants identified four key areas of focus that included: improving clinical trial design, providing navigation for all, enhancing public education and awareness of cancer clinical trials, and identifying potential policy and other opportunities. A comprehensive list of takeaways and action plans was developed in the four key areas of focus with the expectation that implementation of the strategies that emerged from the summit will enhance cancer clinical trial accrual for all Georgians
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