67,761 research outputs found
DEIMOS Observations of WISE-Selected, Optically Obscured AGNs
While there are numerous criteria for photometrically identifying active
galactic nuclei (AGNs), searches in the optical and UV tend to exclude galaxies
that are highly dust obscured. This is problematic for constraining models of
AGN evolution and estimating the AGN contribution to the cosmic X-ray and IR
backgrounds, as highly obscured objects tend to be underrepresented in
large-scale surveys. To address this, we identify potentially obscured AGNs
using mid-IR color colors from the Wide-field Infrared Survey Explorer (WISE)
catalog. This paper presents the results of optical spectroscopy of obscured
AGN candidates using Keck DEIMOS, and their physical properties derived from
these spectra. We find that a color criterion effectively selects
AGNs with a higher median level of extinction compared to the AGNs
found in the SDSS DR7 survey. This optical extinction can be measured using SED
modeling or by using as a measure of optical to IR flux. We find that
specific, targeted observations are necessary to find the most highly optically
obscured AGNs, and that additional far-IR photometry is necessary to further
constrain the dust properties of these AGNs.Comment: 20 pages, 25 figures, accepted by MNRA
Single stage experimental evaluation of variable geometry guide vanes and stators. Part 1 - Analysis and design
Variable geometry concepts applied to guide vanes and stators in single stage compressor
Bedrock geology of the northern Columbia Plateau and adjacent areas
The Columbia Plateau is surrounded by a complex assemblage of highly deformed Precambrian to lower Tertiary continental and oceanic rocks that reflects numerous episodes of continental accretion. The plateau itself is comprised of the Columbia River basalt group formed between about 16.5 x 1 million years B.P. and 6 x 1 million years B.P. Eruptions were infrequent between about 14 and 6 x 1 million years B.P., allowing time for erosion and deformation between successive outpourings. The present-day courses of much of the Snake River, and parts of the Columbia River, across the plateau date from this time. Basalt produced during this waning activity is more heterogeneous chemically and isotopically than older flows, reflecting its prolonged period of volcanism
Coulomb Distortion Effects for Electron or Positron Induced Reactions in the Quasielastic Region
In response to recent experimental studies we investigate Coulomb distortion
effects on reactions from medium and heavy nuclei for the case of
electrons and positrons. We extend our previously reported full DWBA treatment
of Coulomb distortions to the case of positrons for the
reaction in the quasielastic region for a particular nuclear model. In
addition, we use previously reported successful approaches to treating Coulomb
corrections in an approximate way to calculate the Coulomb distortion effects
for reactions for both electrons and positrons for the case of a
simple nuclear model for quasielastic knock-out of nucleons. With these results
in hand we develop a simple {\em ad-hoc} approximation for use in analyzing
experiments, and discuss methods of extracting the ``longitudinal structure
function" which enters into evaluation of the Coulomb sum rule. These
techniques are generally valid for lepton induced reactions on nuclei with
momentum transfers greater than approximately 300 .Comment: 18 pages, 6 figure
The Burundi Heart Centre: From concept to design.
Burundi is one of the worlds poorest nations, which is also reflected in its relative lack of cardiac facilities, particularly those catering to young children and adults. The authors discuss current efforts to build The Burundi Heart Centre to help address this challenge. In particular, they highlight how the project can act as a case study for a sustainable architecture that involves local people and uses locally available materials in a contemporary and innovative way
A solvable model of the evolutionary loop
A model for the evolution of a finite population in a rugged fitness
landscape is introduced and solved. The population is trapped in an
evolutionary loop, alternating periods of stasis to periods in which it
performs adaptive walks. The dependence of the average rarity of the population
(a quantity related to the fitness of the most adapted individual) and of the
duration of stases on population size and mutation rate is calculated.Comment: 6 pages, EuroLaTeX, 1 figur
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Effective Temperature Of Uranus
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