1,484 research outputs found
The Luminosity Dependence of Quasar Clustering
We investigate the luminosity dependence of quasar clustering, inspired by
numerical simulations of galaxy mergers that incorporate black hole growth.
These simulations have motivated a new interpretation of the quasar luminosity
function. In this picture, the bright end of the quasar luminosity function
consists of quasars radiating nearly at their peak luminosities, while the
faint end consists mainly of very similar sources, but at dimmer phases in
their evolution. We combine this model with the statistics of dark matter halos
that host quasar activity. We find that, since bright and faint quasars are
mostly similar sources seen in different evolutionary stages, a broad range in
quasar luminosities corresponds to only a narrow range in the masses of quasar
host halos. On average, bright and faint quasars reside in similar host halos.
Consequently, we argue that quasar clustering should depend only weakly on
luminosity. This prediction is in qualitative agreement with recent
measurements of the luminosity dependence of the quasar correlation function
(Croom et al. 2005) and the galaxy-quasar cross-correlation function
(Adelberger & Steidel 2005). Future precision clustering measurements from SDSS
and 2dF, spanning a large range in luminosity, should provide a strong test of
our model.Comment: 9 pages, 4 figures, submitted to Ap
R&R: Retirements from and Retentions in the Popularly-Elected Senate
While there has been a good bit of scholarly attention paid to career dynamics in—including retirements from—the U. S. House of Representatives, relatively less attention has been paid to the Senate. The few studies of career decisions in the upper chamber (e.g., Bernstein and Wolak 2002; Masthay and Overby 2017) have focused on the more or less modern Senate. In this study, we extend the time series back to the early 1900s, taking in the entire century of the popularly elected Senate. In doing so, we increase our analytical leverage to explore dynamics in the frequency, ratio (compared to electoral defeats), and direction (i.e., progressive ambition or retirement from public life) of voluntary departures from the upper chamber. We are particularly interested in the ability of the parties to retain Senate seats opened up by voluntary departures and focus our multivariate analysis on that question. Among our most noteworthy findings are 1) that the partisan differential in retirements so obvious in the House (with Republicans outpacing Democrats in voluntary departures) is absent not only in the modern Senate but over the entire history of the elected chamber, and 2) that the GOP is systemically better at retaining open seats in the upper chamber, a finding consistent with other work on party asymmetries
EPR identification of defects responsible for thermoluminescence in Cu-doped lithium tetraborate (Li2B4O7) crystals
Electron paramagnetic resonance (EPR) is used to identify the electron and hole traps responsible for thermoluminescence (TL) peaks occurring near 100 and 200 â—¦C in copper-doped lithium tetraborate (Li2B4O7) crystals. As-grown crystals have Cu+ and Cu2+ ions substituting for lithium and have Cu+ ions at interstitial sites. All of the substitutional Cu2+ ions in the as-grown crystals have an adjacent lithium vacancy and give rise to a distinct EPR spectrum. Exposure to ionizing radiation at room temperature produces a second and different Cu2+ EPR spectrum when a hole is trapped by substitutional Cu+ ions that have no nearby defects. These two Cu2+ trapped-hole centers are referred to as Cu2+-VLi and Cu2+active, respectively. Also during the irradiation, two trapped-electron centers in the form of interstitial Cu0 atoms are produced when interstitial Cu+ ions trap electrons. They are observed with EPR and are labeled Cu0A and Cu0B. When an irradiated crystal is warmed from 25 to 150 â—¦C, the Cu2+active centers have a partial decay step that correlates with the TL peak near 100 â—¦C. The concentrations of Cu0A and Cu0B centers, however, increase as the crystal is heated through this range. As the crystal is futher warmed between 150 and 250 â—¦C, the EPR signals from the Cu2+active hole centers and Cu0A and Cu0B electron centers decay simultaneously. This decay step correlates with the intense TL peak near 200 â—¦C
Probing the Electronic Structure of Bilayer Graphene by Raman Scattering
The electronic structure of bilayer graphene is investigated from a resonant
Raman study using different laser excitation energies. The values of the
parameters of the Slonczewski-Weiss-McClure model for graphite are measured
experimentally and some of them differ significantly from those reported
previously for graphite, specially that associated with the difference of the
effective mass of electrons and holes. The splitting of the two TO phonon
branches in bilayer graphene is also obtained from the experimental data. Our
results have implications for bilayer graphene electronic devices.Comment: 4 pages, 4 figure
Small animal disease surveillance: respiratory disease 2017
This report focuses on surveillance for respiratory disease in companion animals. It begins with an analysis of data from 392 veterinary practices contributing to the Small Animal Veterinary Surveillance Network (SAVSNET) between January and December 2017.
The following section describes canine respiratory coronavirus infections in dogs, presenting results from laboratory-confirmed cases across the country between January 2010 and December 2017. This is followed by an update on the temporal trends of three important syndromes in companion animals, namely gastroenteritis, pruritus and respiratory disease, from 2014 to 2017.
A fourth section presents a brief update on Streptococcus equi subspecies zooepidemicus in companion animals. The final section summarises some recent developments pertinent to companion animal health, namely eyeworm (Thelazzia callipaeda) infestations in dogs imported to the UK and canine influenza virus in the USA and Canada
A Case-Mix System for Children and Youth With Developmental Disabilities
Limited funding across health and social service programs presents a challenge regarding how to best match resources to the needs of the population. There is increasing consensus that differences in individual characteristics and care needs should be reflected in variations in service costs, which has led to the development of case-mix systems. The present study sought to develop a new approach to allocate resources among children and youth with intellectual and developmental disabilities (IDD) as part of a system-wide Medicaid payment reform initiative in Arkansas. To develop the system, assessment data collected using the interRAI Child and Youth Mental Health-Developmental Disability instrument was matched to paid service claims. The sample consisted of 346 children and youth with developmental disabilities in the home setting. Using automatic interactions detection, individuals were sorted into unique, clinically relevant groups (ie, based on similar resource use) and a standardized relative measure of the cost of services provided to each group was calculated. The resulting case-mix system has 8 distinct, final groups and explains 30% of the variance in per diem costs. Our analyses indicate that this case-mix classification system could provide the foundation for a future prospective payment system that is centered around stability and equitability in the allocation of limited resources within this vulnerable population
The Evolution in the Faint-End Slope of the Quasar Luminosity Function
(Abridged) Based on numerical simulations of galaxy mergers that incorporate
black hole (BH) growth, we predict the faint end slope of the quasar luminosity
function (QLF) and its evolution with redshift. Our simulations have yielded a
new model for quasar lifetimes where the lifetime depends on both the
instantaneous and peak quasar luminosities. This motivates a new interpretation
of the QLF in which the bright end consists of quasars radiating at nearly
their peak luminosities, but the faint end is mostly made up of quasars in less
luminous phases of evolution. The faint-end QLF slope is then determined by the
faint-end slope of the quasar lifetime for quasars with peak luminosities near
the observed break. We determine this slope from the quasar lifetime as a
function of peak luminosity, based on a large set of simulations spanning a
wide variety of host galaxy, merger, BH, and ISM gas properties. Brighter peak
luminosity (higher BH mass) systems undergo more violent evolution, and expel
and heat gas more rapidly in the final stages of quasar evolution, resulting in
a flatter faint-end slope (as these objects fall below the observed break in
the QLF more rapidly). Therefore, as the QLF break luminosity moves to higher
luminosities with increasing redshift, implying a larger typical quasar peak
luminosity, the faint-end QLF slope flattens. From the quasar lifetime as a
function of peak luminosity and this interpretation of the QLF, we predict the
faint-end QLF slope and its evolution with redshift in good agreement with
observations. Although BHs grow anti-hierarchically (with lower-mass BHs formed
primarily at lower redshifts), the observed change in slope and differential or
luminosity dependent density evolution in the QLF is completely determined by
the luminosity-dependent quasar lifetime and physics of quasar feedback.Comment: 13 pages, 4 figures, submitted to ApJ (Replacement with minor
revisions and changed sign convention
A Case-Mix System for Adults with Developmental Disabilities
Effective management of publicly funded services matches the provision of needed services with cost-efficient payment methods. Payment systems that recognize differences in care needs (eg, case-mix systems) allow for greater proportions of available funds to be directed to providers supporting individuals with more needs. We describe a new way to allocate funds spent on adults with intellectual disabilities (ID) as part of a system-wide Medicaid payment reform initiative in Arkansas. Analyses were based on population-level data for persons living at home, collected using the interRAI ID assessment system, which were linked to paid service claims. We used automatic interactions detection to sort individuals into unique groups and provide a standardized relative measure of the cost of the services provided to each group. The final case-mix system has 33 distinct final groups and explains 26% of the variance in costs, which is similar to other systems in health and social services sectors. The results indicate that this system could be the foundation for a future case-mix approach to reimbursement and stand the test of “fairness” when examined by stakeholders, including parents, advocates, providers, and political entities
Diffractive Photoproduction in the Framework of Fracture Functions
Recent data on diffractive photoproduction of dijets are analyzed within the
framework of fracture functions and paying special attention to the
consequences of the use of different rapidity gap definitions in order to
identify diffractive events. Although these effects are found to be
significant, it is shown that once they are properly taken into account, a very
precise agreement between diffractive DIS and diffractive dijet photoproduction
emerges without any significant hint of hard factorization breaking.Comment: 13 pages, 4 figures. To appear in Phys.Rev.
The Relation Between Quasar and Merging Galaxy Luminosity Functions and the Merger-Induced Star Formation Rate of the Universe
Using a model for self-regulated growth of black holes (BHs) in mergers
involving gas-rich galaxies, we study the relationship between quasars and the
population of merging galaxies and predict the merger-induced star formation
rate density of the Universe. Mergers drive nuclear gas inflows, fueling
starbursts and 'buried quasars' until accretion feedback expels the gas,
rendering a briefly visible optical quasar. Star formation is shut down and
accretion declines, leaving a passively evolving remnant with properties
typical of red, elliptical galaxies. Based on evolution of these events in our
simulations, we demonstrate that the observed statistics of merger rates,
luminosity functions (LFs) and mass functions, SFR distributions, specific
SFRs, quasar and quasar host galaxy LFs, and elliptical/red galaxy LFs are
self-consistent and follow from one another as predicted by the merger
hypothesis. We use our simulations to de-convolve both quasar and merging
galaxy LFs to determine the birthrate of black holes of a given final mass and
merger rates as a function of stellar mass. We use this to predict the merging
galaxy LF in several observed wavebands, color-magnitude relations, mass
functions, absolute and specific SFR distributions and SFR density, and quasar
host galaxy LFs, as a function of redshift from z=0-6. We invert this and
predict e.g. quasar LFs from observed merger LFs or SFR distributions. Our
results agree well with observations, but idealized models of quasar
lightcurves are ruled out by comparison of merger and quasar observations at
>99.9% confidence. Using only observations of quasars, we estimate the
contribution of mergers to the SFR density of the Universe even to high
redshifts z~4.Comment: 26 pages, 15 figures, matches version accepted to Ap
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