1,388 research outputs found

    Populating the Galaxy with low-mass X-ray binaries

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    We perform binary population synthesis calculations to investigate the incidence of low-mass X-ray binaries and their birth rate in the Galaxy. We use a binary evolution algorithm that models all the relevant processes including tidal circularization and synchronization. Parameters in the evolution algorithm that are uncertain and may affect X-ray binary formation are allowed to vary during the investigation. We agree with previous studies that under standard assumptions of binary evolution the formation rate and number of black-hole low-mass X-ray binaries predicted by the model are more than an order of magnitude less than what is indicated by observations. We find that the common-envelope process cannot be manipulated to produce significant numbers of black-hole low-mass X-ray binaries. However, by simply reducing the mass-loss rate from helium stars adopted in the standard model, to a rate that agrees with the latest data, we produce a good match to the observations. Including low-mass X-ray binaries that evolve from intermediate-mass systems also leads to favourable results. We stress that constraints on the X-ray binary population provided by observations are used here merely as a guide as surveys suffer from incompleteness and much uncertainty is involved in the interpretation of results.Comment: 17 pages and 9 figures; accepted by MNRA

    A study of the activation peptides of trypsinogen as indicators of severity in acute pancreatitis

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    The long and the short of it: modelling double neutron star and collapsar Galactic dynamics

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    The work presented here examines populations of double compact binary systems and tidally enhanced collapsars. We make use of BINPOP and BINKIN, two components of a recently developed population synthesis package. Results focus on correlations of both binary and spatial evolutionary population characteristics. Pulsar and long duration gamma-ray burst observations are used in concert with our models to draw the conclusions that: double neutron star binaries can merge rapidly on timescales of a few million years (much less than that found for the observed double neutron star population), common envelope evolution within these models is a very important phase in double neutron star formation, and observations of long gamma-ray burst projected distances are more centrally concentrated than our simulated coalescing double neutron star and collapsar Galactic populations. Better agreement is found with dwarf galaxy models although the outcome is strongly linked to the assumed birth radial distribution. The birth rate of the double neutron star population in our models range from 4-160 Myr^-1 and the merger rate ranges from 3-150 Myr^-1. The upper and lower limits of the rates results from including electron capture supernova kicks to neutron stars and decreasing the common envelope efficiency respectively. Our double black hole merger rates suggest that black holes should receive an asymmetric kick at birth.Comment: Accepted by MNRAS, 18 pages, 12 figures, 5 table

    Pruned Continuous Haar Transform of 2D Polygonal Patterns with Application to VLSI Layouts

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    We introduce an algorithm for the efficient computation of the continuous Haar transform of 2D patterns that can be described by polygons. These patterns are ubiquitous in VLSI processes where they are used to describe design and mask layouts. There, speed is of paramount importance due to the magnitude of the problems to be solved and hence very fast algorithms are needed. We show that by techniques borrowed from computational geometry we are not only able to compute the continuous Haar transform directly, but also to do it quickly. This is achieved by massively pruning the transform tree and thus dramatically decreasing the computational load when the number of vertices is small, as is the case for VLSI layouts. We call this new algorithm the pruned continuous Haar transform. We implement this algorithm and show that for patterns found in VLSI layouts the proposed algorithm was in the worst case as fast as its discrete counterpart and up to 12 times faster.Comment: 4 pages, 5 figures, 1 algorith

    The Hadamard circulant conjecture

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    It is shown that if HH is a circulant Hadamard 4n\ti 4n then n=1n=1. This proves the Hadamard circulant conjecture.Comment: This is post publication revision of on-line Bull. London Math. Soc. version which changes subsection 3.

    "Two Senses of Moral Verdict and Moral Overridingness"

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    I distinguish two different senses in which philosophers speak of moral verdicts, senses that in turn invite two different senses of moral overridingness. Although one of these senses, that upon which moral verdicts are taken to reflect decisive reasons from a distinctively moral standpoint, currently dominates the moral overridingness debate, my focus is the other sense, upon which moral verdicts are taken to reflect decisive reasons that are distinctively moral. I demonstrate that the recent tendency to emphasize the now dominant sense to the exclusion of the alternative, couple with the failure to disambiguate the two senses, has fundamentally skewed central debates in moral theory
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