283,785 research outputs found
2007 Disability Status Reports: United States
The Annual Disability Status Reports provide policy makers, disability advocates, reporters, and the public with a summary of the most recent demographic and economic statistics on the working-age (ages 21-64) population with disabilities. They contain information on the population size, prevalence, employment, earnings, poverty, household income, home ownership, and activity limitations of working-age people with disabilities, as well as the composition of this population by age, race, gender, and educational attainment
Vortex description of the fractionalized phase in exciton bose condensate
As a sequel to the previous work [Phys. Rev. B 72, 235104 (2005)] we present
a vortex description of the fractionalized phase in exciton bose condensate.
Magnetic flux line and monopole of the 3+1D emergent U(1) gauge theory are
identified in the exciton picture. A bundle of vortex/anti-vortex pairs of all
flavors of excitons corresponds to the magnetic flux line and a point at which
the vortices and anti-vortices recombine is identified as magnetic monopole.
This completes the magnetic sector of the low energy excitation in the
fractionalized phase.Comment: 8 pages, 6 figures; clarification made in introductio
A Theory of Gamma-Ray Bursts
We present a specific scenario for the link between GRB and hypernovae, based
on Blandford-Znajek extraction of black-hole spin energy. Such a mechanism
requires a high angular momentum in the progenitor object. The observed
association of gamma-ray bursts with type Ibc supernovae leads us to consider
massive helium stars that form black holes at the end of their lives as
progenitors. We combine the numerical work of MacFadyen & Woosley with analytic
calculations, to show that about 1E53 erg each are available to drive the fast
GRB ejecta and the supernova. The GRB ejecta are driven by the power output
through the open field lines, whereas the supernova is powered by closed filed
lines and jet shocks. We also present a much simplified approximate derivation
of these energetics.
Helium stars that leave massive black-hole remnants in special ways, namely
via soft X-ray transients or very massive WNL stars. Since binaries naturally
have high angular momentum, we propose a link between black-hole transients and
gamma-ray bursts. Recent observations of one such transient, GRO J1655-40/Nova
Scorpii 1994, explicitly support this connection: its high space velocity
indicates that substantial mass was ejected in the formation of the black hole,
and the overabundance of alpha-nuclei, especially sulphur, indicates that the
explosion energy was extreme, as in SN 1998bw/GRB 980425. (abstract shortened)Comment: 32 pages, 8 figures, accepted for publication in New Astronom
Threshold Regression for Survival Analysis: Modeling Event Times by a Stochastic Process Reaching a Boundary
Many researchers have investigated first hitting times as models for survival
data. First hitting times arise naturally in many types of stochastic
processes, ranging from Wiener processes to Markov chains. In a survival
context, the state of the underlying process represents the strength of an item
or the health of an individual. The item fails or the individual experiences a
clinical endpoint when the process reaches an adverse threshold state for the
first time. The time scale can be calendar time or some other operational
measure of degradation or disease progression. In many applications, the
process is latent (i.e., unobservable). Threshold regression refers to
first-hitting-time models with regression structures that accommodate covariate
data. The parameters of the process, threshold state and time scale may depend
on the covariates. This paper reviews aspects of this topic and discusses
fruitful avenues for future research.Comment: Published at http://dx.doi.org/10.1214/088342306000000330 in the
Statistical Science (http://www.imstat.org/sts/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Transverse Quark Distribution in Mesons - QCD Sum Rule Approach -
QCD sum rules are used to compute the first few moments of the mesonic quark
momentum. Transverse, longitudinal and mixed transverse-longitudinal components
are examined. The transverse size of the pion is shown to be dictated by the
gluon condensate, even though the mass and the longitudinal distribution are
dominated by the quark condensate. The implications of our results for color
transparency physics and finite temperature QCD are discussed.Comment: 8 pages, Latex, Univ. of Washington preprint DOE/ER/40427-24-N9
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