76,606 research outputs found

    The Absolute Rate of LGRB Formation

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    We estimate the LGRB progenitor rate using our recent work on the effects of environmental metallically on LGRB formation in concert with SNe statistics via an approach patterned loosely off the Drake equation. Beginning with the cosmic star-formation history, we consider the expected number of broad-line Type Ic events (the SNe type associated with LGRBs) that are in low metallicity host environments adjusted by the contribution of high metallicity host environments at a much reduced rate. We then compare this estimate to the observed LGRB rate corrected for instrumental selection effects to provide a combined estimate of the efficiency fraction of these progenitors to produce LGRBs and the fraction of which are beamed in our direction. From this we estimate that an aligned LGRB occurs for approximately every 4000 low metallically broad-lined Type Ic Supernovae. Therefore if one assumes a semi-nominal beaming factor of 100 then only about one such supernova out of 40 produce an LGRB. Finally we propose an off-axis LGRB search strategy of targeting for radio observation broad-line Type Ic events that occur in low metallicity hosts.Comment: 9 pages, 3 figure

    The local supermassive black hole mass density: corrections for dependencies on the Hubble constant

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    We have investigated past measurements of the local supermassive black hole mass density, correcting for hitherto unknown dependencies on the Hubble constant, which, in some cases, had led to an underestimation of the mass density by factors of ~2. Correcting for this, we note that the majority of past studies yield a local supermassive black hole mas density that is consistent with the range 4.4-5.9 x 10^5 f(H_0) M_Sun / Mpc^3 (when using H_0 = 70 km/s/Mpc). In addition, we address a number of ways in which these past estimates can be further developed. In particular, we tabulate realistic bulge-to-total flux ratios which can be used to estimate the luminosity of bulges and subsequently their central black hole masses.Comment: MNRAS, accepte

    Pit latrines and their impacts on groundwater quality: a systematic review.

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    BackgroundPit latrines are one of the most common human excreta disposal systems in low-income countries, and their use is on the rise as countries aim to meet the sanitation-related target of the Millennium Development Goals. There is concern, however, that discharges of chemical and microbial contaminants from pit latrines to groundwater may negatively affect human health.ObjectivesOur goals were to a) calculate global pit latrine coverage, b) systematically review empirical studies of the impacts of pit latrines on groundwater quality, c) evaluate latrine siting standards, and d) identify knowledge gaps regarding the potential for and consequences of groundwater contamination by latrines.MethodsWe used existing survey and population data to calculate global pit latrine coverage. We reviewed the scientific literature on the occurrence of contaminants originating from pit latrines and considered the factors affecting transport of these contaminants. Data were extracted from peer-reviewed articles, books, and reports identified using Web of ScienceSM, PubMed, Google, and document reference lists.DiscussionWe estimated that approximately 1.77 billion people use pit latrines as their primary means of sanitation. Studies of pit latrines and groundwater are limited and have generally focused on only a few indicator contaminants. Although groundwater contamination is frequently observed downstream of latrines, contaminant transport distances, recommendations based on empirical studies, and siting guidelines are variable and not well aligned with one another.ConclusionsIn order to improve environmental and human health, future research should examine a larger set of contextual variables, improve measurement approaches, and develop better criteria for siting pit latrines

    Holonomy and Projective Equivalence in 4-Dimensional Lorentz Manifolds

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    A study is made of 4-dimensional Lorentz manifolds which are projectively related, that is, whose Levi-Civita connections give rise to the same (unparameterised) geodesics. A brief review of some relevant recent work is provided and a list of new results connecting projective relatedness and the holonomy type of the Lorentz manifold in question is given. This necessitates a review of the possible holonomy groups for such manifolds which, in turn, requires a certain convenient classification of the associated curvature tensors. These reviews are provided.Comment: Comments: 23 pages, LaTeX; typos corrected, page 9 last line corrected to $g'=e^{2\chi}a^{-1}

    Carbon in soils

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    Carbon is the fourth most common element in the galaxy(by mass) but does not even rank in the twelve most abundant elements on Earth. By far the most abundant source of carbon on Earth is in the crust as inorganic rocks such as calcite and limestone in marine and sedimentary deposits. These rocks have taken many millions of years to form. Other major inorganic sources are in the oceans and atmosphere

    A Hubble Space Telescope Survey of X-ray Luminous Galaxy Clusters: Gravitationally Lensed Arcs and EROs

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    We are conducting a systematic lensing survey of X-ray luminous galaxy clusters at z~0.2 using the Hubble Space Telescope and large ground-based telescopes. We summarize initial results from our survey, including a measurement of the inner slope of the mass profile of A383, and a search for gravitationally lensed Extremely Red Objects.Comment: 4 pages, 2 figures. To appear in "A New Era in Cosmology" (ASP Conference Proceedings), eds. T. Shanks and N. Metcalf

    Statistics and implications of substructure detected in a representative sample of X-ray clusters

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    We present a morphological study of 35 X-ray luminous galaxy clusters at 0.15<z<0.3, selected in a similar manner to the Local Cluster Substructure Survey (LoCuSS), for which deep XMM-Newton observations are available. We characterise the structure of the X-ray surface brightness distribution of each cluster by measuring both their power ratios and centroid shift, and thus rank the clusters by the degree of substructure. These complementary probes give a consistent description of the cluster morphologies with some well understood exceptions. We find a remarkably tight correlation of regular morphology with the occurrence of cool cores in clusters. We also compare our measurements of X-ray morphology with measurements of the luminosity gap statistics and ellipticity of the brightest cluster galaxy (BCG). We check how our new X-ray morphological analysis maps onto cluster scaling relations, finding that (i) clusters with relatively undisturbed X-ray morphologies are on average more luminous at fixed X-ray temperature than those with disturbed morphologies, and (ii) disturbed clusters have larger X-ray masses than regular clusters for a given temperature in the M-T relation. We also show that the scatter in the ratio of X-ray and weak lensing based cluster mass measurements is larger for disturbed clusters than for those of more regular morphology. Overall, our results demonstrate the feasibility of assembling a self-consistent picture of the physical structure of clusters from X-ray and optical data, and the potential to apply this in the measurement of cosmological cluster scaling relations.Comment: 12 pages, 13 figures, A&A accepte
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