10,136 research outputs found
Design and development of a solar array drive
The design and development of a dry lubricated direct drive solar array pointing mechanism is discussed for use on the Orbital Test Satellite (OTS), MAROTS, European Communication Satellite (ECS), and others. Results of life testing the original prototype and the OTS mechanism are presented together with an appraisal of expected future development
Kinematics of the Broad Line Region in M81
A new model is presented which explains the origin of the broad emission
lines observed in the LINER/Seyfert nucleus of M81 in terms of a steady state
spherically symmetric inflow, amounting to 1 x 10^-5 Msun/yr, which is
sufficient to explain the luminosity of the AGN. The emitting volume has an
outer radius of ~1 pc, making it the largest broad line region yet to be
measured, and it contains a total mass of ~ 5 x 10^-2 Msun of dense, ~ 10^8
cm^-3, ionized gas, leading to a very low filling factor of ~ 5 x 10^-9. The
fact that the BLR in M81 is so large may explain why the AGN is unable to
sustain the ionization seen there. Thus, the AGN in M81 is not simply a scaled
down quasar.Comment: Accepted for Publication in ApJ 7/21/0
Blood product transfusion in emergency department patients: A case-control study of practice patterns and impact on outcome
Definitions of comorbid conditions. (DOCX 13 kb
Border parasites: schistosomiasis control among Uganda's fisherfolk
Copyright @ 2012 Taylor & Francis. This article has been made publically available through the Brunel Open Access Publishing Fund.It is recognized that the control of schistosomisais in Uganda requires a focus on
fisherfolk. Large numbers suffer from this water-borne parasitic disease; notably along the shores of lakes Albert and Victoria and along the River Nile. Since 2004, a policy has been adopted of providing drugs, free of charge, to all those at risk. The strategy has been reported to be successful, but closer investigation reveals serious problems. This paper draws upon long-term research undertaken at three locations in northwestern and southeastern Uganda. It highlights consequences of not engaging with the day to day realities of fisherfolk
livelihoods; attributable, in part, to the fact that so many fisherfolk live and work in places located at the country’s international borders, and to a related
tendency to treat them as "feckless" and "ungovernable". Endeavours to roll out
treatment end up being haphazard, erratic and location-specific. In some places,
concerted efforts have been made to treat fisherfolk; but there is no effective
monitoring, and it is difficult to gauge what proportion have actually swallowed
the tablets. In other places, fisherfolk are, in practice, largely ignored, or are
actively harassed in ways that make treatment almost impossible. At all sites, the current reliance upon resident "community" drug distributors or staff based at static clinics and schools was found to be flawed.The Schistosomiasis Control Initiative, Imperial College, under the auspices of the Bill and Melinda Gates Foundation
The Expected Duration of Gamma-Ray Bursts in the Impulsive Hydrodynamic Models
Depending upon the various models and assumptions, the existing literature on
Gamma Ray Bursts (GRBs) mentions that the gross theoretical value of the
duration of the burst in the hydrodynamical models is tau~r^2/(eta^2 c), where
r is the radius at which the blastwave associated with the fireball (FB)
becomes radiative and sufficiently strong. Here eta = E/Mc^2, c is the speed of
light, E is initial lab frame energy of the FB, and M is the baryonic mass of
the same (Rees and Meszaros 1992). However, within the same basic framework,
some authors (like Katz and Piran) have given tau ~ r^2 /(eta c). We intend to
remove this confusion by considering this problem at a level deeper than what
has been considered so far. Our analysis shows that none of the previously
quoted expressions are exactly correct and in case the FB is produced
impulsively and the radiative processes responsible for the generation of the
GRB are sufficiently fast, its expected duration would be tau ~ar^2/(eta^2 c),
where a~O(10^1). We further discuss the probable change, if any, of this
expression, in case the FB propagates in an anisotropic fashion. We also
discuss some associated points in the context of the Meszaros and Rees
scenario.Comment: 21 pages, LATEX (AAMS4.STY -enclosed), 1 ps. Fig. Accepted in
Astrophysical Journa
Iron K Lines from Gamma Ray Bursts
We present models for reprocessing of an intense flux of X-rays and gamma
rays expected in the vicinity of gamma ray burst sources. We consider the
transfer and reprocessing of the energetic photons into observable features in
the X-ray band, notably the K lines of iron. Our models are based on the
assumption that the gas is sufficiently dense to allow the microphysical
processes to be in a steady state, thus allowing efficient line emission with
modest reprocessing mass and elemental abundances ranging from solar to
moderately enriched. We show that the reprocessing is enhanced by
down-Comptonization of photons whose energy would otherwise be too high to
absorb on iron, and that pair production can have an effect on enhancing the
line production. Both "distant" reprocessors such as supernova or wind remnants
and "nearby" reprocessors such as outer stellar envelopes can reproduce the
observed line fluxes with Fe abundances 30-100 times above solar, depending on
the incidence angle. The high incidence angles required arise naturally only in
nearby models, which for plausible values can reach Fe line to continuum ratios
close to the reported values.Comment: 37 pages, 10 figures. Ap. J in pres
Taming the Runaway Problem of Inflationary Landscapes
A wide variety of vacua, and their cosmological realization, may provide an
explanation for the apparently anthropic choices of some parameters of particle
physics and cosmology. If the probability on various parameters is weighted by
volume, a flat potential for slow-roll inflation is also naturally understood,
since the flatter the potential the larger the volume of the sub-universe.
However, such inflationary landscapes have a serious problem, predicting an
environment that makes it exponentially hard for observers to exist and giving
an exponentially small probability for a moderate universe like ours. A general
solution to this problem is proposed, and is illustrated in the context of
inflaton decay and leptogenesis, leading to an upper bound on the reheating
temperature in our sub-universe. In a particular scenario of chaotic inflation
and non-thermal leptogenesis, predictions can be made for the size of CP
violating phases, the rate of neutrinoless double beta decay and, in the case
of theories with gauge-mediated weak scale supersymmetry, for the fundamental
scale of supersymmetry breaking.Comment: 31 pages, including 3 figure
An identeification guide to the Mosquitoes of Utah
journal articleThe first detailed report on the mosquito fauna of Utah was published by pees (1943). In this bulletin Rees reported the occurrence in the state of 31 species, representing 4 genera, and discussed their biology, distribution, life history and importance. Subsequent publications by Rees (1944), Rees and Nielsen (1951, 1955), Nielsen and Rees (1959) and Richards et al. (1956) have added to the knowlgdge of the mosquito fauna of this state. A total of 45 species has been reported in the literature as occurring in Utah. Of this number five are records which the authors consider invalid or of uncertain status. These are discussed by Nielsen and Rees (1959). At present the known Utah mosquito fauna consists of 40 species, representing 6 genera. A list of the Utah species with their relative abundance is presented in Table I
An identification guide to the mosquitoes of Utah
journal articleThe first detailed report on the mosquito fauna of Utah was published by pees (1943). In this bulletin Rees reported the occurrence in the state of 31 s p e c ie s , representing 4 genera, and discussed their biology, distribution, life history and importance. Subsequent publications by Rees (1944), Rees and Nielsen (1951, 1955), Nielsen and Rees (1959) and Richards et al. (1956) have added to the knowlgdge of the mosquito fauna of this state. A total of 45 species has been reported in the literature as occurring in Utah. Of this number five are records which the authors consider invalid or of uncertain status. These are discussed by Nielsen and Rees (1959). At present the known Utah mosquito fauna consists of 40 species, representing 6 genera. A list of the Utah species with their relative abundance is presented in Table I
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