10,159 research outputs found
The Luminosity Function and Surface Brightness Distribution of HI Selected Galaxies
We measure the z=0 B-band optical luminosity function (LF) for galaxies
selected in a blind HI survey. The total LF of the HI selected sample is flat,
with Schechter parameters M*=-19.38_{-0.62}^{+1.02} + 5 log h mag and
alpha=-1.03_{-0.15}^{+0.25}, in good agreement with LFs of optically selected
late-type galaxies. Bivariate distribution functions of several galaxy
parameters show that the HI density in the local Universe is more widely spread
over galaxies of different size, central surface brightness, and luminosity
than is the optical luminosity density. The number density of very low surface
brightness (>24.0 mag/arcsec^2) gas-rich galaxies is considerably lower than
that found in optical surveys designed to detect dim galaxies. This suggests
that only a part of the population of LSB galaxies is gas rich and that the
rest must be gas poor. However, we show that this gas-poor population must be
cosmologically insignificant in baryon content. The contribution of gas-rich
LSB galaxies (>23.0 mag/arcsec^2) to the local cosmological gas and luminosity
density is modest (18_{-5}^{+6} and 5_{-2}^{+2} per cent respectively); their
contribution to Omega_matter is not well-determined, but probably < 11 per
cent. These values are in excellent agreement with the low redshift results
from the Hubble Deep Field.Comment: Accepted for publication in MNRAS, 12 pages 6 figure
The credibility of health economic models for health policy decision-making: the case of population screening for abdominal aortic aneurysm
<i>Objectives</i>: To review health economic models of population screening for abdominal aortic aneurysm (AAA) among elderly males and assess their credibility for informing decision-making.
<i>Methods</i>: A literature review identified health economic models of ultrasound screening for AAA. For each model focussing on population screening in elderly males, model structure and input parameter values were critically appraised using published good practice guidelines for decision analytic models.
<i>Results</i>: Twelve models published between 1989 and 2003 were identified. Converting costs to a common currency and base year, substantial variability in cost-effectiveness results were revealed. Appraisals carried out for the nine models focusing on population screening showed differences in their complexity, with the simpler models generating results most favourable to screening. Eight of the nine models incorporated two or more simplifying structural assumptions favouring screening; uncertainty surrounding these assumptions was not investigated by any model. Quality assessments on a small number of parameters revealed input values varied between models, methods used to identify and incorporate input data were often not described, and few sensitivity analyses were reported.
<i>Conclusions</i>: Large variation exists in the cost-effectiveness results generated by AAA screening models. The substantial number of factors potentially contributing to such disparities means that reconciliation of model results is impossible. In addition, poor reporting of methods makes it difficult to identify the most plausible and thus most useful model of those developed
Wage and Occupational Differences Between Black and White Men: Labor Market Discrimination in the Rural South
The existence of labor market discrimination based on race is well established.However, study continues into a variety of aspects of discrimination-among them the extent to which it exists in different regions. Gwartney has estimated the ratio of black to white earnings to be between .83 and .88 for the North and between .68 and .74 for the South. Masters, in a study of earnings differentials between black and white men, found a ratio of .79 for the non-South and .69 for the South. Although considerable literature has developed concerning earnings differentials, wage discrimination in rural areas is one topic which has received relatively little attention. In an attempt to eliminate this oversight this paper concentrates on the extent of wage differences between black and white men in the rural South attributable to labor market discrimination
Modeling good research practices - overview: a report of the ISPOR-SMDM modeling good research practices task force - 1.
Modelsâmathematical frameworks that facilitate estimation of the consequences of health care decisionsâhave become essential tools for health technology assessment. Evolution of the methods since the first ISPOR modeling task force reported in 2003 has led to a new task force, jointly convened with the Society for Medical Decision Making, and this series of seven papers presents the updated recommendations for best practices in conceptualizing models; implementing stateâtransition approaches, discrete event simulations, or dynamic transmission models; dealing with uncertainty; and validating and reporting models transparently. This overview introduces the work of the task force, provides all the recommendations, and discusses some quandaries that require further elucidation. The audience for these papers includes those who build models, stakeholders who utilize their results, and, indeed, anyone concerned with the use of models to support decision making
Enhanced electron correlations, local moments, and Curie temperature in strained MnAs nanocrystals embedded in GaAs
We have studied the electronic structure of hexagonal MnAs, as epitaxial
continuous film on GaAs(001) and as nanocrystals embedded in GaAs, by Mn 2p
core-level photoemission spectroscopy. Configuration-interaction analyses based
on a cluster model show that the ground state of the embedded MnAs nanocrystals
is dominated by a d5 configuration that maximizes the local Mn moment.
Nanoscaling and strain significantly alter the properties of MnAs. Internal
strain in the nanocrystals results in reduced p-d hybridization and enhanced
ionic character of the Mn-As bonding interactions. The spatial confinement and
reduced p-d hybridization in the nanocrystals lead to enhanced d-electron
localization, triggering d-d electron correlations and enhancing local Mn
moments. These changes in the electronic structure of MnAs have an advantageous
effect on the Curie temperature of the nanocrystals, which is measured to be
remarkably higher than that of bulk MnAs.Comment: 4 figures, 2 table
Detailed Analysis of the Pulsations During and After Bursts from the Bursting Pulsar (GRO J1744-28)
The hard X-ray bursts observed during both major outbursts of the Bursting
Pulsar (GRO J1744-28) show pulsations near the neutron star spin frequency with
an enhanced amplitude relative to that of the persistent emission. Consistent
with previous work, we find that the pulsations within bursts lag behind their
expected arrival times based upon the persistent pulsar ephemeris. For an
ensemble of 1293 bursts recorded with the Burst and Transient Source
Experiment, the average burst pulse time delay is 61.0 +/- 0.8 ms in the 25 -
50 keV energy range and 72 +/- 5 ms in the 50 - 100 keV band. The residual time
delay from 10 to 240 s following the start of the burst is 18.1 +/- 0.7 ms (25
- 50 keV). A significant correlation of the average burst time delay with burst
peak flux is found. Our results are consistent with the model of the pulse time
lags presented by Miller (1996).Comment: 11 pages, accepted for publication in Ap
GBM Observations of V404 Cyg During its 2015 Outburst
V404 Cygni was discovered in 1989 by the X-ray satellite during its
only previously observed X-ray outburst and soon after confirmed as a black
hole binary. On June 15, 2015, the Gamma Ray Burst Monitor (GBM) triggered on a
new outburst of V404 Cygni. We present 13 days of GBM observations of this
outburst including Earth occultation flux measurements, spectral and temporal
analysis. The Earth occultation fluxes reached 30 Crab with detected emission
to 100 keV and determined, via hardness ratios, that the source was in a hard
state. At high luminosity, spectral analysis between 8 and 300 keV showed that
the electron temperature decreased with increasing luminosity. This is expected
if the protons and electrons are in thermal equilibrium during an outburst with
the electrons cooled by the Compton scattering of softer seed photons from the
disk. However, the implied seed photon temperatures are unusually high,
suggesting a contribution from another source, such as the jet. No evidence of
state transitions is seen during this time period. The temporal analysis
reveals power spectra that can be modeled with two or three strong, broad
Lorentzians, similar to the power spectra of black hole binaries in their hard
state
Air Traffic Simulation Technology for High-Population Metroplexes
IAI's MetroSim optimizes air traffic by simulating departures, arrivals, and activity in air and onthe ground in busy metroplexes, where flights impact each other at a single airport and among traffic at nearby airports. MetroSim evolved out of several NASA SBIR/STTR Awards and has since been used by NASA for flight simulation analysis. MetroSim has also been integrated with FAA and DOT technology, has produced studies for the Port Authority of New York and New Jersey, and is under development to support the Nav
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