1,797 research outputs found
Negative Particle Planar and Axial Channeling and Channeling Collimation
While information exists on high energy negative particle channeling there
has been little study of the challenges of negative particle bending and
channeling collimation. Partly this is because negative dechanneling lengths
are relatively much shorter. Electrons are not particularly useful for
investigating negative particle channeling effects because their material
interactions are dominated by channeling radiation. Another important factor is
that the current central challenge in channeling collimation is the
proton-proton Large Hadron Collider (LHC) where both beams are positive. On the
other hand in the future the collimation question might reemerge for
electron-positron or muon colliders. Dechanneling lengths increase at higher
energies so that part of the negative particle experimental challenge
diminishes. In the article different approaches to determining negative
dechanneling lengths are reviewed. The more complicated case for axial
channeling is also discussed. Muon channeling as a tool to investigate
dechanneling is also discussed. While it is now possible to study muon
channeling it will probably not illuminate the study of negative dechanneling.Comment: 15 pages, 1 figure, docx fil
No-vent fill pressurization tests using a cryogen simulant
The results are described of an experimental program which studied the performance of various no-vent fill techniques for tank-to-tank liquid transfer. The tests were performed using a cryogen simulant (Freon-114) and a test bed consisting of a multiple tank/plumbing network that enabled studies of a variety of different inlet flow and active mixing regimes. Several results and conclusions were drawn from the 26 transfer experiments comprising the program. Most notable was the significant improvement in fill performance (i.e., minimized fill time and maximized fill fraction) with increased agitation of the liquid surface. Another was the close correlation between measured condensation rates and those predicted by recent theories which express condensation as a function of turbulent eddy effects on the liquid surface. In most cases, test data exhibited strong agreement with an analytical model which accounts for tank heat transfer and thermodynamics in a 1 g environment
The HIV/AIDS Epidemic in Miami: Perspectives of Stakeholders and Frontline Providers
Background: Miami, Florida persists as an epicenter of HIV/AIDS nationally and has been more delayed than other areas with high HIV burden in implementing public health measures that mitigate transmission risk. These issues among other social and structural-level determinants have complicated progress in addressing HIV/AIDS in Miami.
Purpose: The stagnated progress in improving HIV outcomes in Miami necessitated a more comprehensive understanding of the experiences and insights of stakeholders within the system. We used a stakeholder analysis approach to understand the complexity of driving factors and key challenges facing this HIV epidemic.
Methods: A stakeholder analysis was conducted through 11 focus groups (64 participants) with front line workers working in non-profit, community-based agencies in Miami. The interview guide was designed to elicit a broad discussion on the social and intermediary determinants of HIV/AIDS, as well as the context surrounding barriers to treatment. Data were analyzed using qualitative software for thematic analysis.
Results: Participants highlighted particular populations vulnerable to HIV/AIDS and insufficiently engaged in treatment, including immigrants and people who use drugs. Stigma surrounding HIV/AIDS as well as sexual orientation, mental health, and drug use was a noted persisting barrier. Participants expressed needs for more targeted outreach and education for both prevention and treatment. Numerous systemic gaps were identified as barriers to treatment engagement and retention. Other comorbidities and socioeconomic challenges, including criminal justice histories, housing instability and low educational attainment, also hamper HIV/AIDS management.
Discussion: Through these discussions with stakeholders representing a diversity of voices, findings can inform comprehensive and coordinated strategies for curbing the HIV/AIDS epidemic in Miami. The development of prevention and treatment interventions should consider cultural contexts of health behaviors, multi-level stigma related to HIV/AIDS and other comorbid and socioeconomic challenges, and increased implementation of harm reduction programs such as PrEP delivery and syringe exchange programs
Hominids adapted to metabolize ethanol long before human-directed fermentation
Paleogenetics is an emerging field that resurrects ancestral proteins from now-extinct organisms to test, in the laboratory, models of protein function based on natural history and Darwinian evolution. Here, we resurrect digestive alcohol dehydrogenases (ADH4) from our primate ancestors to explore the history of primate-ethanol interactions. The evolving catalytic properties of these resurrected enzymes show that our ape ancestors gained a digestive dehydrogenase enzyme capable of metabolizing ethanol near the time that they began using the forest floor, about 10 million y ago. The ADH4 enzyme in our more ancient and arboreal ancestors did not efficiently oxidize ethanol. This change suggests that exposure to dietary sources of ethanol increased in hominids during the early stages of our adaptation to a terrestrial lifestyle. Because fruit collected from the forest floor is expected to contain higher concentrations of fermenting yeast and ethanol than similar fruits hanging on trees, this transition may also be the first time our ancestors were exposed to (and adapted to) substantial amounts of dietary ethanol
A Framework to Manage the Complex Organisation of Collaborating: Its Application to Autonomous Systems
In this paper we present an analysis of the complexities of large group
collaboration and its application to develop detailed requirements for
collaboration schema for Autonomous Systems (AS). These requirements flow from
our development of a framework for collaboration that provides a basis for
designing, supporting and managing complex collaborative systems that can be
applied and tested in various real world settings. We present the concepts of
"collaborative flow" and "working as one" as descriptive expressions of what
good collaborative teamwork can be in such scenarios. The paper considers the
application of the framework within different scenarios and discuses the
utility of the framework in modelling and supporting collaboration in complex
organisational structures
Exploring the Galaxy at TeV energies: Latest results from the H.E.S.S. Galactic Plane Survey
The High Energy Stereoscopic System (H.E.S.S.) is an array of four imaging
atmospheric-Cherenkov telescopes located in Namibia and designed to detect
extensive air showers initiated by gamma-rays in the very-high-energy domain.
It is an ideal instrument for surveying the Galactic plane in search of new
sources, thanks to its location in the Southern Hemisphere, its excellent
sensitivity, and its large field-of-view. The efforts of the H.E.S.S. Galactic
Plane Survey, the first comprehensive survey of the inner Galaxy at TeV
energies, have contributed to the discovery of an unexpectedly large and
diverse population of over 60 sources of VHE gamma rays within its current
range of l=250 to 65 degrees in longitude and |b|<=3.5 degrees in latitude. The
population of VHE gamma-ray emitters is dominated by the pulsar wind nebula and
supernova remnant source classes, although nearly a third remain unidentified
or confused.
The sensitivity of H.E.S.S. to sources in the inner Galaxy has improved
significantly over the past two years, from continued survey observations,
dedicated follow-up observations of interesting source candidates, and from the
development of advanced methods for discrimination of gamma-ray-induced showers
from the dominant background of hadron-induced showers. The latest maps of the
Galaxy at TeV energies will be presented, and a few remarkable new sources will
be highlighted.Comment: 4 pages, 2 figures, appears in the Proceedings of the 32nd
International Cosmic Ray Conference (ICRC 2011), Beijing, China, 11th to 18th
August 201
The influence of the dechanneling process on the photon emission by an ultra-relativistc positron channeling in a periodically bent crystal
We investigate, both analytically and numerically, the influence of the
dechanneling process on the parameters of undulator radiation generated by
ultra-relativistic positron channelling along a crystal plane, which is
periodically bent. The bending might be due either to the propagation of a
transverse acoustic wave through the crystal, or due to the static strain as it
occurs in superlattices. In either case the periodically bent crystal serves as
an undulator which allows to generate X-ray and gamma-radiation.
We propose the scheme for accurate quantitative treatment of the radiation in
presence of the dechanneling. The scheme includes (i) the analytic expression
for spectral-angular distribution which contains, as a parameter, the
dechanneling length, (ii) the simulation procedure of the dechanneling process
of a positron in periodically bent crystals. Using these we calculate the
dechanneling lengths of 5 GeV positrons channeling in Si, Ge and W crystals,
and the spectral-angular and spectral distributions of the undulator over broad
ranges of the photons. The calculations are performed for various parameters of
the channel bending.Comment: published in J. Phys. G: Nucl. Part. Phys. 27 (2001) 95-125,
http://www.iop.or
Electron-based crystalline undulator
We discuss the features of a crystalline undulator of the novel type based on
the effect of a planar channeling of ultra-relativistic electrons in a
periodically bent crystals. It is demonstrated that an electron-based undulator
is feasible in the tens of GeV range of the beam energies, which is noticeably
higher than the energy interval allowed in a positron-based undulator.
Numerical analysis of the main parameters of the undulator as well as the
characteristics of the emitted undulator radiation is carried out for 20 and 50
GeV electrons channeling in diamond and silicon crystals along the (111)
crystallographic planes.Comment: 16 pages, 8 figures, Latex, IOP styl
Improved Experimental Limits on the Production of Magnetic Monopoles
We present new limits on low mass accelerator-produced point-like Dirac
magnetic monopoles trapped and bound in matter surrounding the D\O collision
region of the Tevatron at Fermilab (experiment E-882). In the context of a
Drell-Yan mechanism, we obtain cross section limits for the production of
monopoles with magnetic charge values of 1, 2, 3, and 6 times the minimum Dirac
charge of the order of picobarns, some hundred times smaller than found in
similar previous Fermilab searches. Mass limits inferred from these cross
section limits are presented.Comment: 5 pages, 4 eps figures, REVTe
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