1,462 research outputs found
Cosmic Reionization On Computers. Properties of the Post-reionization IGM
We present a comparison between several observational tests of the
post-reionization IGM and the numerical simulations of reionization completed
under the Cosmic Reionization On Computers (CROC) project. The CROC simulations
match the gap distribution reasonably well, and also provide a good match for
the distribution of peak heights, but there is a notable lack of wide peaks in
the simulated spectra and the flux PDFs are poorly matched in the narrow
redshift interval 5.5<z<5.7, with the match at other redshifts being
significantly better, albeit not exact. Both discrepancies are related:
simulations show more opacity than the data.Comment: Accepted by Ap
Adversarial Deep Structured Nets for Mass Segmentation from Mammograms
Mass segmentation provides effective morphological features which are
important for mass diagnosis. In this work, we propose a novel end-to-end
network for mammographic mass segmentation which employs a fully convolutional
network (FCN) to model a potential function, followed by a CRF to perform
structured learning. Because the mass distribution varies greatly with pixel
position, the FCN is combined with a position priori. Further, we employ
adversarial training to eliminate over-fitting due to the small sizes of
mammogram datasets. Multi-scale FCN is employed to improve the segmentation
performance. Experimental results on two public datasets, INbreast and
DDSM-BCRP, demonstrate that our end-to-end network achieves better performance
than state-of-the-art approaches.
\footnote{https://github.com/wentaozhu/adversarial-deep-structural-networks.git}Comment: Accepted by ISBI2018. arXiv admin note: substantial text overlap with
arXiv:1612.0597
The ensemble photometric variability of over quasars in the Dark Energy Camera Legacy Survey and the Sloan Digital Sky Survey
We present the ensemble variability analysis results of quasars using the
Dark Energy Camera Legacy Survey (DECaLS) and the Sloan Digital Sky Survey
(SDSS) quasar catalogs. Our dataset includes 119,305 quasars with redshifts up
to 4.89. Combining the two datasets provides a 15-year baseline and permits
analysis of the long timescale variability. Adopting a power-law form for the
variability structure function, , we use the
multi-dimensional parametric fitting to explore the relationships between the
quasar variability amplitude and a wide variety of quasar properties, including
redshift (positive), bolometric luminosity (negative), rest-frame wavelength
(negative), and black hole mass (uncertain). We also find that can be
also expressed as a function of redshift (negative), bolometric luminosity
(positive), rest-frame wavelength (positive), and black hole mass (positive).
Tests of the fitting significance with the bootstrap method show that, even
with such a large quasar sample, some correlations are marginally significant.
The typical value of for the entire dataset is ,
consistent with the results in previous studies on both the quasar ensemble
variability and the structure function. A significantly negative correlation
between the variability amplitude and the Eddington ratio is found, which may
be explained as an effect of accretion disk instability.Comment: 13 pages, 8 figures, 4 tables, accepted for publication in Ap
The Extremely Luminous Quasar Survey (ELQS) in the SDSS footprint I.: Infrared Based Candidate Selection
Studies of the most luminous quasars at high redshift directly probe the
evolution of the most massive black holes in the early Universe and their
connection to massive galaxy formation. However, extremely luminous quasars at
high redshift are very rare objects. Only wide area surveys have a chance to
constrain their population. The Sloan Digital Sky Survey (SDSS) has so far
provided the most widely adopted measurements of the quasar luminosity function
(QLF) at . However, a careful re-examination of the SDSS quasar sample
revealed that the SDSS quasar selection is in fact missing a significant
fraction of quasars at the brightest end. We have identified the
purely optical color selection of SDSS, where quasars at these redshifts are
strongly contaminated by late-type dwarfs, and the spectroscopic incompleteness
of the SDSS footprint as the main reasons. Therefore we have designed the
Extremely Luminous Quasar Survey (ELQS), based on a novel near-infrared JKW2
color cut using WISE AllWISE and 2MASS all-sky photometry, to yield high
completeness for very bright () quasars in the redshift
range of . It effectively uses random forest machine-learning
algorithms on SDSS and WISE photometry for quasar-star classification and
photometric redshift estimation. The ELQS will spectroscopically follow-up
new quasar candidates in an area of in the
SDSS footprint, to obtain a well-defined and complete quasars sample for an
accurate measurement of the bright-end quasar luminosity function at . In this paper we present the quasar selection algorithm and the
quasar candidate catalog.Comment: 16 pages, 8 figures, 9 tables; ApJ in pres
Microarray sub-grid detection: A novel algorithm
This is the post print version of the article. The official published version can be obtained from the link below - Copyright 2007 Taylor & Francis LtdA novel algorithm for detecting microarray subgrids is proposed. The only input to the algorithm is the raw microarray image, which can be of any resolution, and the subgrid detection is performed with no prior assumptions. The algorithm consists of a series of methods of spot shape detection, spot filtering, spot spacing estimation, and subgrid shape detection. It is shown to be able to divide images of varying quality into subgrid regions with no manual interaction. The algorithm is robust against high levels of noise and high percentages of poorly expressed or missing spots. In addition, it is proved to be effective in locating regular groupings of primitives in a set of non-microarray images, suggesting potential application in the general area of image processing
An FeLoBAL Binary Quasar
In an ongoing infrared imaging survey of quasars at Keck Observatory, we have
discovered that the z=1.285 quasar SDSS J233646.2-010732.6 comprises two point
sources with a separation of 1.67". Resolved spectra show that one component is
a standard quasar with a blue continuum and broad emission lines; the other is
a broad absorption line (BAL) quasar, specifically, a BAL QSO with prominent
absorption from MgII and metastable FeII, making it a member of the ``FeLoBAL''
class. The number of known FeLoBALs has recently grown dramatically from a
single example to more than a dozen, including a gravitationally lensed example
and the binary member presented here, suggesting that this formerly rare object
may be fairly common. Additionally, the presence of this BAL quasar in a
relatively small separation binary adds to the growing evidence that the BAL
phenomenon is not due to viewing a normal quasar at a specific orientation, but
rather that it is an evolutionary phase in the life of many, if not all,
quasars, and is particularly associated with conditions found in interacting
systems.Comment: AASTEX 13 pp., 4 figs; accepted by ApJ Letter
Gemini Near-infrared Spectroscopy of Luminous z~6 Quasars: Chemical Abundances, Black Hole Masses, and MgII Absorption
We present Gemini near-infrared spectroscopic observations of six luminous
quasars at z=5.86.3. Five of them were observed using Gemini-South/GNIRS,
which provides a simultaneous wavelength coverage of 0.9--2.5 m in cross
dispersion mode. The other source was observed in K band with
Gemini-North/NIRI. We calculate line strengths for all detected emission lines
and use their ratios to estimate gas metallicity in the broad-line regions of
the quasars. The metallicity is found to be supersolar with a typical value of
4 Z_{\sun}, and a comparison with low-redshift observations shows no
strong evolution in metallicity up to z6. The FeII/MgII ratio of the
quasars is 4.9+/-1.4, consistent with low-redshift measurements. We estimate
central BH masses of 10^9 to 10^{10} M_{\sun} and Eddington luminosity ratios
of order unity. We identify two MgII 2796,2803 absorbers with
rest equivalent width W_0^{\lambda2796}>1 \AA at 2.2<z<3 and three MgII
absorbers with W_0^{\lambda2796}>1.5 \AA at z>3 in the spectra, with the two
most distant absorbers at z=4.8668 and 4.8823, respectively. The redshift
number densities (dN/dz) of MgII absorbers with W_0^{\lambda2796}>1.5 \AA are
consistent with no cosmic evolution up to z>4.Comment: 33 pages (including 7 figures and 6 tables), AJ in pres
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