363 research outputs found

    Flash-Heating of Circumstellar Clouds by Gamma Ray Bursts

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    The blast-wave model for gamma-ray bursts (GRBs) has been called into question by observations of spectra from GRBs that are harder than can be produced through optically thin synchrotron emission. If GRBs originate from the collapse of massive stars, then circumstellar clouds near burst sources will be illuminated by intense gamma radiation, and the electrons in these clouds will be rapidly scattered to energies as large as several hundred keV. Low-energy photons that subsequently pass through the hot plasma will be scattered to higher energies, hardening the intrisic spectrum. This effect resolves the "line-of-death" objection to the synchrotron shock model. Illuminated clouds near GRBs will form relativistic plasmas containing large numbers of electron-positron pairs that can be detected within ~ 1-2 days of the explosion before expanding and dissipating. Localized regions of pair annihilation radiation in the Galaxy would reveal past GRB explosions.Comment: 9 pages, 1 figure, submitted to ApJ Letter

    Coastal Wetland Restoration through the lens of Odum\u27s theory of ecosystem development

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    Advancing ecological restoration assessments requires a more detailed consideration of species interactions and ecosystem processes. Most restoration projects rely on a few metrics not always directly linked with ecological theory. Here, we used Odum\u27s theory of ecosystem development to assess and compare the ecosystem structure and services of created marshes (4–6 years old) with preexisting, reference marshes in a brackish water region of the Mississippi River Delta. We built ecosystem models for created and reference marshes that integrated large datasets of stomach contents, stable isotopes, and taxa abundances. Despite strong resemblance in community structure, created marshes were at an earlier succession stage compared to the reference marshes, having lower biomass (including exploited species), higher biomass turnover and production, less dependence on detritus, lower material cycling, and less energy flowing through specialist pathways. Although preserving preexisting marshes should be a priority, created marshes may still be an important tool for the restoration of coastal areas and their ecosystem services. In addition, our results show that comparisons of species biodiversity alone may fail to capture essential differences in ecosystem processes between habitats, which reinforces the importance of ecosystem modeling approaches to assess restoration projects

    Neutrino, Neutron, and Cosmic Ray Production in the External Shock Model of Gamma Ray Bursts

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    The hypothesis that ultra-high energy (>~ 10^19 eV) cosmic rays (UHECRs) are accelerated by gamma-ray burst (GRB) blast waves is assumed to be correct. Implications of this assumption are then derived for the external shock model of gamma-ray bursts. The evolving synchrotron radiation spectrum in GRB blast waves provides target photons for the photomeson production of neutrinos and neutrons. Decay characteristics and radiative efficiencies of the neutral particles that escape from the blast wave are calculated. The diffuse high-energy GRB neutrino background and the distribution of high-energy GRB neutrino events are calculated for specific parameter sets, and a scaling relation for the photomeson production efficiency in surroundings with different densities is derived. GRBs provide an intense flux of high-energy neutrons, with neutron-production efficiencies exceeding ~ 1% of the total energy release. The radiative characteristics of the neutron beta-decay electrons from the GRB "neutron bomb" are solved in a special case. Galaxies with GRB activity should be surrounded by radiation halos of ~ 100 kpc extent from the outflowing neutrons, consisting of a nonthermal optical/X-ray synchrotron component and a high-energy gamma-ray component from Compton-scattered microwave background radiation. The luminosity of sources of GRBs and relativistic outflows in L* galaxies such as the Milky Way is at the level of ~10^40+-1 ergs/s. This is sufficient to account for UHECR generation by GRBs. We briefly speculate on the possibility that hadronic cosmic rays originate from the subset of supernovae that collapse to form relativistic outflows and GRBs. (abridged)Comment: 53 pages, 8 figures, ApJ, in press, 574, July 20, 2002. Substantial revision, previous Appendix expanded to ApJ, 556, 479; cosmic ray origin speculations to Heidelberg (astro-ph/001054) and Hamburg ICRC (astro-ph/0202254) proceeding

    Patients’ use of information about medicine side effects in relation to experiences of suspected adverse drug reactions

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    Background Adverse drug reactions (ADRs) are common, and information about medicines is increasingly widely available to the public. However, relatively little work has explored how people use medicines information to help them assess symptoms that may be suspected ADRs. Objective Our objective was to determine how patients use patient information leaflets (PILs) or other medicines information sources and whether information use differs depending on experiences of suspected ADRs. Method This was a cross-sectional survey conducted in six National Health Service (NHS) hospitals in North West England involving medical in-patients taking at least two regular medicines prior to admission. The survey was administered via a questionnaire and covered use of the PIL and other medicines information sources, perceived knowledge about medicines risks/ADRs, experiences of suspected ADRs, plus demographic information. Results Of the 1,218 respondents to the survey, 18.8 % never read the PIL, whilst 6.5 % only do so if something unexpected happens. Educational level was related to perceived knowledge about medicines risks, but not to reading the PIL or seeking further information about medicines risks. Over half the respondents (56.0 %) never sought more information about possible side effects of medicines. A total of 57.2 % claimed they had experienced a suspected ADR. Of these 85.9 % were either very sure or fairly sure this was a reaction to a medicine. Over half of those experiencing a suspected ADR (53.8 %) had read the PIL, of whom 36.2 % did so before the suspected ADR occurred, the remainder afterwards. Reading the PIL helped 84.8 % of these respondents to decide they had experienced an ADR. Educational level, general knowledge of medicines risks and number of regular medicines used all increased the likelihood of experiencing an ADR. Conclusion More patients should be encouraged to read the PIL supplied with medicines. The results support the view that most patients feel knowledgeable about medicines risks and suspected ADRs and value information about side effects, but that reading about side effects in PILs or other medicines information sources does not lead to experiences of suspected ADRs

    TADPOL: A 1.3 mm Survey of Dust Polarization in Star-forming Cores and Regions

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    We present {\lambda}1.3 mm CARMA observations of dust polarization toward 30 star-forming cores and 8 star-forming regions from the TADPOL survey. We show maps of all sources, and compare the ~2.5" resolution TADPOL maps with ~20" resolution polarization maps from single-dish submillimeter telescopes. Here we do not attempt to interpret the detailed B-field morphology of each object. Rather, we use average B-field orientations to derive conclusions in a statistical sense from the ensemble of sources, bearing in mind that these average orientations can be quite uncertain. We discuss three main findings: (1) A subset of the sources have consistent magnetic field (B-field) orientations between large (~20") and small (~2.5") scales. Those same sources also tend to have higher fractional polarizations than the sources with inconsistent large-to-small-scale fields. We interpret this to mean that in at least some cases B-fields play a role in regulating the infall of material all the way down to the ~1000 AU scales of protostellar envelopes. (2) Outflows appear to be randomly aligned with B-fields; although, in sources with low polarization fractions there is a hint that outflows are preferentially perpendicular to small-scale B-fields, which suggests that in these sources the fields have been wrapped up by envelope rotation. (3) Finally, even at ~2.5" resolution we see the so-called "polarization hole" effect, where the fractional polarization drops significantly near the total intensity peak. All data are publicly available in the electronic edition of this article.Comment: 53 pages, 37 figures -- main body (13 pp., 3 figures), source maps (32 pp., 34 figures), source descriptions (8 pp.). Accepted by the Astrophysical Journal Supplemen

    Justice Stevens: The First Three Terms

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    This Special Project undertakes an examination of Justice Stevens\u27 Supreme Court opinions in an effort to identify his philosophical orientations, to evaluate the consistency of his views, and to determine the extent to which he has developed workable analytical methods. To achieve these goals, Justice Stevens\u27 opinions are examined in three contexts: first, the area of federal-state relations,including commerce clause and supremacy clause questions; second, the individual rights area, emphasizing criminal constitutional and first amendment issues, and problems of fifth and fourteenth amendment analysis; and third, questions concerning the proper role of the Supreme Court in the constitutional scheme. Even though any vote cast by a Supreme Court Justice may illustrate a significant aspect of his ideology, this Special Project limits attention to opinions authored by Justice Stevens on the assumption that they most accurately represent his views.\u2

    Can biodiversity of preexisting and created salt marshes match across scales? An assessment from microbes to predators

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    Coastal wetlands are rapidly disappearing worldwide due to a variety of processes, including climate change and flood control. The rate of loss in the Mississippi River Delta is among the highest in the world and billions of dollars have been allocated to build and restore coastal wetlands. A key question guiding assessment is whether created coastal salt marshes have similar biodiversity to preexisting, reference marshes. However, the numerous biodiversity metrics used to make these determinations are typically scale dependent and often conflicting. Here, we applied ecological theory to compare the diversity of different assemblages (surface and below-surface soil microbes, plants, macroinfauna, spiders, and on-marsh and off-marsh nekton) between two created marshes (4–6 years old) and four reference marshes. We also quantified the scale-dependent effects of species abundance distribution, aggregation, and density on richness differences and explored differences in species composition. Total, between-sample, and within-sample diversity (γ, β, and α, respectively) were not consistently lower at created marshes. Richness decomposition varied greatly among assemblages and marshes (e.g., soil microbes showed high equitability and α diversity, but plant diversity was restricted to a few dominant species with high aggregation). However, species abundance distribution, aggregation, and density patterns were not directly associated with differences between created and reference marshes. One exception was considerably lower density for macroinfauna at one of the created marshes, which was drier because of being at a higher elevation and having coarser substrate compared with the other marshes. The community compositions of created marshes were more dissimilar than reference marshes for microbe and macroinfauna assemblages. However, differences were small, particularly for microbes. Together, our results suggest generally similar taxonomic diversity and composition between created and reference marshes. This provides support for the creation of marsh habitat as tools for the maintenance and restoration of coastal biodiversity. However, caution is needed when creating marshes because specific building and restoration plans may lead to different colonization patterns
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