1,303 research outputs found
Electron Positron Annihilation Radiation from SgrA East at the Galactic Center
Maps of the Galactic electron-positron annihilation radiation show evidence
for three distinct and significant features: (1) a central bulge source, (2)
emission in the Galactic plane, and (3) an enhancement of emission at positive
latitudes above the Galactic Center. In this paper, we explore the possibility
that Sgr A East, a very prominent radio structure surrounding the Galactic
nucleus, may be a significant contributer to the central bulge feature. The
motivation for doing so stems from a recently proposed link between this radio
object and the EGRET gamma-ray source 2EG J1746-2852. If this association is
correct, then Sgr A East is also expected to be a source of copious positron
production. The results presented here show that indeed Sgr A East must have
produced a numerically significant population of positrons, but also that most
of them have not yet had sufficient time to thermalize and annihilate. As such,
Sgr A East by itself does not appear to be the dominant current source of
annihilation radiation, but it will be when the positrons have cooled
sufficiently and they have become thermalized. This raises the interesting
possibility that the bulge component may be due to the relics of earlier
explosive events like the one that produced Sgr A East.Comment: This manuscript was prepared with the AAS Latex macros v4.0 It is 37
pages long and has 16 figure
Structure and Phase Transitions of Metastable Hexagonal Uranium Thin Films
We report a simple technique for the synthesis of uniaxially textured,
metastable hexagonal close-packed-like uranium thin films with thicknesses
between 175-2800 \r{A}. The initial structure and texture of the layers have
been studied via X-ray diffraction and reflectivity and the time-dependent
transitions of the samples into various orientations of orthorhombic
-U have been mapped by similar techniques. The final crystallographic
orientations of each system and the timescales on which the transitions occur
are found to depend on the lattice parameters of the original layer. The
absence of the -U (001) orientation in the transition products
suggests that the transitions in these layers are mediated by mechanisms other
than the [110] transverse acoustic phonon mode previously suggested for the
cubic -U(110) to hcp-U(00.1) to -U(001) displacive phase
transition. Alternative transition pathways are discussed
Linking adaptation science to action to build food secure Pacific Island communities
Climate change is a major threat to food security in Pacific Island countries, with declines in food production and increasing variability in food supplies already evident across the region. Such impacts have already led to observed consequences for human health, safety and economic prosperity. Enhancing the adaptive capacity of Pacific Island communities is one way to reduce vulnerability and is underpinned by the extent to which people can access, understand and use new knowledge to inform their decision-making processes. However, effective engagement of Pacific Island communities in climate adaption remains variable and is an ongoing and significant challenge. Here, we use a qualitative research approach to identify the impediments to engaging Pacific Island communities in the adaptations needed to safeguard food security. The main barriers include cultural differences between western science and cultural knowledge, a lack of trust among local communities and external scientists, inappropriate governance structures, and a lack of political and technical support. We identify the importance of adaptation science, local social networks, key actors (i.e., influential and trusted individuals), and relevant forms of knowledge exchange as being critical to overcoming these barriers. We also identify the importance of co-ordination with existing on-ground activities to effectively leverage, as opposed to duplicating, capacity
Enhancing cooperative responses by regional fisheries management organisations to climate-driven redistribution of tropical Pacific tuna stocks
Climate change is predicted to alter the distributions of tropical tuna stocks in the Pacific Ocean. Recent modelling projects significant future shifts in tuna biomass from west to east, and from national jurisdictions to high seas areas. As the distributions of these stocks change, the relevant regional fisheries management organisations (RFMOs)—the Western and Central Pacific Fisheries Commission (WCPFC) and the Inter-American Tropical Tuna Commission (IATTC)—will need to develop an expanded framework for cooperation and collaboration to fulfil their conservation and management responsibilities under international law. The key elements of a possible expanded framework for cooperation can be developed, and fundamental areas for collaboration identified, by applying and adapting principles established in the United Nations Convention on the Law of the Sea, the United Nations Fish Stocks Agreement, and the constituent instruments of the RFMOs themselves. Our analysis reveals a wide range of important issues requiring cooperation, and three clear priorities. First, a formal mechanism for cooperation is needed to enable effective and efficient decision-making and action by the two RFMOs on key issues. Second, further cooperation is required in scientific research and modelling to better understand the biology and distributions of Pacific tuna stocks and how they will respond to climate change, and to inform stock assessments and harvest strategies. Third, the RFMOs must cooperate to define appropriate limits on fishing for each stock in a way that ensures they are compatible across the two organisations, taking into account their different members and management regimes
Effect of Oral Alendronate on Bone Mineral Density and the Incidence of Fractures in Postmenopausal Osteoporosis
BACKGROUND
Postmenopausal osteoporosis is a serious health problem, and additional treatments are needed. METHODS
We studied the effects of oral alendronate, an aminobisphosphonate, on bone mineral density and the incidence of fractures and height loss in 994 women with postmenopausal osteoporosis. The women were treated with placebo or alendronate (5 or 10 mg daily for three years, or 20 mg for two years followed by 5 mg for one year); all the women received 500 mg of calcium daily. Bone mineral density was measured by dual-energy x-ray absorptiometry. The occurrence of new vertebral fractures and the progression of vertebral deformities were determined by an analysis of digitized radiographs, and loss of height was determined by sequential height measurements. RESULTS
The women receiving alendronate had significant, progressive increases in bone mineral density at all skeletal sites, whereas those receiving placebo had decreases in bone mineral density. At three years, the mean (±SE) differences in bone mineral density between the women receiving 10 mg of alendronate daily and those receiving placebo were 8.8±0.4 percent in the spine, 5.9±0.5 percent in the femoral neck, 7.8±0.6 percent in the trochanter, and 2.5±0.3 percent in the total body (P CONCLUSIONS
Daily treatment with alendronate progressively increases the bone mass in the spine, hip, and total body and reduces the incidence of vertebral fractures, the progression of vertebral deformities, and height loss in postmenopausal women with osteoporosis
Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial
Background
Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy
Macroscopic quantum resonators (MAQRO)
Quantum physics challenges our understanding of the nature of physical
reality and of space-time and suggests the necessity of radical revisions of
their underlying concepts. Experimental tests of quantum phenomena involving
massive macroscopic objects would provide novel insights into these fundamental
questions. Making use of the unique environment provided by space, MAQRO aims
at investigating this largely unexplored realm of macroscopic quantum physics.
MAQRO has originally been proposed as a medium-sized fundamental-science space
mission for the 2010 call of Cosmic Vision. MAQRO unites two experiments:
DECIDE (DECoherence In Double-Slit Experiments) and CASE (Comparative
Acceleration Sensing Experiment). The main scientific objective of MAQRO, which
is addressed by the experiment DECIDE, is to test the predictions of quantum
theory for quantum superpositions of macroscopic objects containing more than
10e8 atoms. Under these conditions, deviations due to various suggested
alternative models to quantum theory would become visible. These models have
been suggested to harmonize the paradoxical quantum phenomena both with the
classical macroscopic world and with our notion of Minkowski space-time. The
second scientific objective of MAQRO, which is addressed by the experiment
CASE, is to demonstrate the performance of a novel type of inertial sensor
based on optically trapped microspheres. CASE is a technology demonstrator that
shows how the modular design of DECIDE allows to easily incorporate it with
other missions that have compatible requirements in terms of spacecraft and
orbit. CASE can, at the same time, serve as a test bench for the weak
equivalence principle, i.e., the universality of free fall with test-masses
differing in their mass by 7 orders of magnitude.Comment: Proposal for a medium-sized space mission, 28 pages, 9 figures - in
v2, we corrected some minor mistakes and replaced fig. 9 with a
higher-resolution version; Experimental Astronomy, March 2012, Online, Open
Acces
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