5,788 research outputs found
The Deep Diffuse Extragalactic Radio Sky at 1.75 GHz
We present a study of diffuse extragalactic radio emission at GHz
from part of the ELAIS-S1 field using the Australia Telescope Compact Array.
The resulting mosaic is deg, with a roughly constant noise region
of deg used for analysis. The image has a beam size of arcsec and instrumental Jy beam. Using point-source models from the ATLAS survey, we
subtract the discrete emission in this field for Jy
beam. Comparison of the source-subtracted probability distribution, or
\pd, with the predicted distribution from unsubtracted discrete emission and
noise, yields an excess of Jy beam. Taking this as
an upper limit on any extended emission we constrain several models of extended
source counts, assuming arcmin. The best-fitting
models yield temperatures of the radio background from extended emission of
mK, giving an upper limit on the total temperature at
GHz of mK. Further modelling shows that our data are
inconsistent with the reported excess temperature of ARCADE2 to a source-count
limit of Jy. Our new data close a loop-hole in the previous
constraints, because of the possibility of extended emission being resolved out
at higher resolution. Additionally, we look at a model of cluster halo emission
and two WIMP dark matter annihilation source-count models, and discuss general
constraints on any predicted counts from such sources. Finally, we report the
derived integral count at GHz using the deepest discrete count plus our
new extended-emission limits, providing numbers that can be used for planning
future ultra-deep surveys.Comment: 18 pages, 15 figures, 7 tables, Accepted by MNRA
U.S. Coast Guard Boat Recovery Simulation at NASA Ames Vertical Motion Simulator
The Boat Recovery Simulation was a collaboration between the U.S. Coast Guard and NASA. The experiment was conducted at the NASA Ames Vertical Motion Simulator (VMS). The goals were to (1) design a VMS experiment that can accurately simulate the motion of high sea conditions and to (2) collect data for the U.S. Coast Guard on human performance related to small boat recovery operations. The experiment setup included a software operation model designed around empirical boat position data; a replica boat section manufactured to incorporate real-world task elements; and the means to collect objective and subjective data from human participants. The VMS provided a viable testbed to assess certified U.S. Coast Guard crewmembers task performance while in motion
Multiple populations in Omega Centauri: a cluster analysis of spectroscopic data
Omega Cen is composed of several stellar populations. Their history might
allow us to reconstruct the evolution of this complex object. We performed a
statistical cluster analysis on the large data set provided by Johnson and
Pilachowski (2010). Stars in Omega Cen divide into three main groups. The
metal-poor group includes about a third of the total. It shows a moderate O-Na
anticorrelation, and similarly to other clusters, the O-poor second generation
stars are more centrally concentrated than the O-rich first generation ones.
This whole population is La-poor, with a pattern of abundances for n-capture
elements which is very close to a scaled r-process one. The metal-intermediate
group includes the majority of the cluster stars. This is a much more complex
population, with an internal spread in the abundances of most elements. It
shows an extreme O-Na anticorrelation, with a very numerous population of
extremely O-poor and He-rich second generation stars. This second generation is
very centrally concentrated. This whole population is La-rich, with a pattern
of the abundances of n-capture elements that shows a strong contribution by the
s-process. The spread in metallicity within this metal-intermediate population
is not very large, and we might attribute it either to non uniformities of an
originally very extended star forming region, or to some ability to retain a
fraction of the ejecta of the core collapse SNe that exploded first, or both.
As previously noticed, the metal-rich group has an Na-O correlation, rather
than anticorrelation. There is evidence for the contribution of both massive
stars ending their life as core-collapse SNe, and intermediate/low mass stars,
producing the s-capture elements. Kinematics of this population suggests that
it formed within the cluster rather than being accreted.Comment: Accepted for publication in Astronomy and Astrophysic
Site investigation for the effects of vegetation on ground stability
The procedure for geotechnical site investigation is well established but little attention is currently given to investigating the potential of vegetation to assist with ground stability. This paper describes how routine investigation procedures may be adapted to consider the effects of the vegetation. It is recommended that the major part of the vegetation investigation is carried out, at relatively low cost, during the preliminary (desk) study phase of the investigation when there is maximum flexibility to take account of findings in the proposed design and construction. The techniques available for investigation of the effects of vegetation are reviewed and references provided for further consideration. As for general geotechnical investigation work, it is important that a balance of effort is maintained in the vegetation investigation between (a) site characterisation (defining and identifying the existing and proposed vegetation to suit the site and ground conditions), (b) testing (in-situ and laboratory testing of the vegetation and root systems to provide design parameters) and (c) modelling (to analyse the vegetation effects)
Bio-degradable Escape Panel Research on Fish Pots in Dominica: A Fisheries Resources Management Tool
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