3,902 research outputs found
Infection percolation: A dynamic network model of disease spreading
Models of disease spreading are critical for predicting infection growth in a
population and evaluating public health policies. However, standard models
typically represent the dynamics of disease transmission between individuals
using macroscopic parameters that do not accurately represent person-to-person
variability. To address this issue, we present a dynamic network model that
provides a straightforward way to incorporate both disease transmission
dynamics at the individual scale as well as the full spatiotemporal history of
infection at the population scale. We find that disease spreads through a
social network as a traveling wave of infection, followed by a traveling wave
of recovery, with the onset and dynamics of spreading determined by the
interplay between disease transmission and recovery. We use these insights to
develop a scaling theory that predicts the dynamics of infection for diverse
diseases and populations. Furthermore, we show how spatial heterogeneities in
susceptibility to infection can either exacerbate or quell the spread of
disease, depending on its infectivity. Ultimately, our dynamic network approach
provides a simple way to model disease spreading that unifies previous findings
and can be generalized to diverse diseases, containment strategies, seasonal
conditions, and community structures.Comment: In press, Frontiers in Physics (2021
Spectral Decomposition of Broad-Line AGNs and Host Galaxies
Using an eigenspectrum decomposition technique, we separate the host galaxy
from the broad line active galactic nucleus (AGN) in a set of 4666 spectra from
the Sloan Digital Sky Survey (SDSS), from redshifts near zero up to about 0.75.
The decomposition technique uses separate sets of galaxy and quasar
eigenspectra to efficiently and reliably separate the AGN and host
spectroscopic components. The technique accurately reproduces the host galaxy
spectrum, its contributing fraction, and its classification. We show how the
accuracy of the decomposition depends upon S/N, host galaxy fraction, and the
galaxy class. Based on the eigencoefficients, the sample of SDSS broad-line AGN
host galaxies spans a wide range of spectral types, but the distribution
differs significantly from inactive galaxies. In particular, post-starburst
activity appears to be much more common among AGN host galaxies. The
luminosities of the hosts are much higher than expected for normal early-type
galaxies, and their colors become increasingly bluer than early-type galaxies
with increasing host luminosity. Most of the AGNs with detected hosts are
emitting at between 1% and 10% of their estimated Eddington luminosities, but
the sensitivity of the technique usually does not extend to the Eddington
limit. There are mild correlations among the AGN and host galaxy
eigencoefficients, possibly indicating a link between recent star formation and
the onset of AGN activity. The catalog of spectral reconstruction parameters is
available as an electronic table.Comment: 18 pages; accepted for publication in A
Unbiased Cosmological Parameter Estimation from Emission Line Surveys with Interlopers
The galaxy catalogs generated from low-resolution emission line surveys often
contain both foreground and background interlopers due to line
misidentification, which can bias the cosmological parameter estimation. In
this paper, we present a method for correcting the interloper bias by using the
joint-analysis of auto- and cross-power spectra of the main and the interloper
samples. In particular, we can measure the interloper fractions from the
cross-correlation between the interlopers and survey galaxies, because the true
cross-correlation must be negligibly small. The estimated interloper fractions,
in turn, remove the interloper bias in the cosmological parameter estimation.
For example, in the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX)
low-redshift () [O II] {\AA} emitters contaminate
high-redshift () Lyman- line emitters. We demonstrate that
the joint-analysis method yields a high signal-to-noise ratio measurement of
the interloper fractions while only marginally increasing the uncertainties in
the cosmological parameters relative to the case without interlopers. We also
show the same is true for the high-latitude spectroscopic survey of Wide-Field
Infrared Survey Telescope (WFIRST) mission where contamination occurs between
the Balmer- line emitters at lower redshifts () and Oxygen
([O III] {\AA}) line emitters at higher redshifts ().Comment: 36 pages, 26 figure
Dust Reddening in SDSS Quasars
We explore the form of extragalactic reddening toward quasars using a sample
of 9566 quasars with redshifts 0<z<2.2, and accurate optical colors from the
Sloan Digital Sky Survey (SDSS). We confirm that dust reddening is the primary
explanation for the red ``tail'' of the color distribution of SDSS quasars. Our
fitting to 5-band photometry normalized by the modal quasar color as a function
of redshift shows that this ``tail'' is well described by SMC-like reddening
but not by LMC-like, Galactic, or Gaskell et al. (2004) reddening. Extension to
longer wavelengths using a subset of 1886 SDSS-2MASS matches confirms these
results at high significance. We carry out Monte-Carlo simulations that match
the observed distribution of quasar spectral energy distributions using a
Lorentzian dust reddening distribution; 2% of quasars selected by the main SDSS
targeting algorithm (i.e., which are not extincted out of the sample) have
E_{B-V} > 0.1; less than 1% have E_{B-V} > 0.2, where the extinction is
relative to quasars with modal colors. Reddening is uncorrelated with the
presence of intervening narrow-line absorption systems, but reddened quasars
are much more likely to show narrow absorption at the redshift of the quasar
than are unreddened quasars. Thus the reddening towards quasars is dominated by
SMC-like dust at the quasar redshift.Comment: 29 pages including 8 figures. AJ, September 2004 issu
The High-Mass End of the Red Sequence at z~0.55 from SDSS-III/BOSS: completeness, bimodality and luminosity function
We have developed an analytical method based on forward-modeling techniques
to characterize the high-mass end of the red sequence (RS) galaxy population at
redshift , from the DR10 BOSS CMASS spectroscopic sample, which
comprises galaxies. The method, which follows an unbinned maximum
likelihood approach, allows the deconvolution of the intrinsic CMASS
colour-colour-magnitude distributions from photometric errors and selection
effects. This procedure requires modeling the covariance matrix for the i-band
magnitude, g-r colour and r-i colour using Stripe 82 multi-epoch data. Our
results indicate that the error-deconvolved intrinsic RS distribution is
consistent, within the photometric uncertainties, with a single point
() in the colour-colour plane at fixed magnitude, for a
narrow redshift slice. We have computed the high-mass end () of the -band RS Luminosity Function (RS LF) in several redshift
slices within the redshift range . In this narrow redshift range,
the evolution of the RS LF is consistent, within the uncertainties in the
modeling, with a passively-evolving model with Mpc mag, fading at a rate of mag per
unit redshift. We report RS completeness as a function of magnitude and
redshift in the CMASS sample, which will facilitate a variety of
galaxy-evolution and clustering studies using BOSS. Our forward-modeling method
lays the foundations for future studies using other dark-energy surveys like
eBOSS or DESI, which are affected by the same type of photometric
blurring/selection effects.Comment: 27 pages, 20 figures, accepted for publication in MNRA
Magnetic White Dwarfs from the SDSS II. The Second and Third Data Releases
Fifty-two magnetic white dwarfs have been identified in spectroscopic
observations from the Sloan Digital Sky Survey (SDSS) obtained between mid-2002
and the end of 2004, including Data Releases 2 and 3. Though not as numerous
nor as diverse as the discoveries from the first Data Release, the collection
exhibits polar field strengths ranging from 1.5MG to ~1000MG, and includes two
new unusual atomic DQA examples, a molecular DQ, and five stars that show
hydrogen in fields above 500MG. The highest-field example, SDSSJ2346+3853, may
be the most strongly magnetic white dwarf yet discovered. Analysis of the
photometric data indicates that the magnetic sample spans the same temperature
range as for nonmagnetic white dwarfs from the SDSS, and support is found for
previous claims that magnetic white dwarfs tend to have larger masses than
their nonmagnetic counterparts. A glaring exception to this trend is the
apparently low-gravity object SDSSJ0933+1022, which may have a history
involving a close binary companion.Comment: 20 pages, 4 figures Accepted for publication in the Astronomical
Journa
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