7,163 research outputs found

    Gravitational Coset Models

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    The algebra A(D-3)+++ dimensionally reduces to the E(D-1) symmetry algebra of (12-D)-dimensional supergravity. An infinite set of five-dimensional gravitational objects trivially embedded in D-dimensions is constructed by identifying the null geodesic motion on cosets embedded in the generalised Kac-Moody algebra A(D-3)+++. By analogy with supergravity these are bound states of dual gravitons. The metric interpolates continuously between exotic gravitational solutions generated by the action of the Geroch group but is not a continuously transforming solution of the Einstein-Hilbert action. We investigate mixed-symmetry fields in the brane sigma model, identify actions for the full interpolating bound state and understand the obstruction to the bound state being a solution of the Einstein-Hilbert action.Comment: 46 page

    Transition stages of Rayleigh–Taylor instability between miscible fluids

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    Direct numerical simulations (DNS) are presented of three-dimensional, Rayleigh–Taylor instability (RTI) between two incompressible, miscible fluids, with a 3:1 density ratio. Periodic boundary conditions are imposed in the horizontal directions of a rectangular domain, with no-slip top and bottom walls. Solutions are obtained for the Navier–Stokes equations, augmented by a species transport-diffusion equation, with various initial perturbations. The DNS achieved outer-scale Reynolds numbers, based on mixing-zone height and its rate of growth, in excess of 3000. Initial growth is diffusive and independent of the initial perturbations. The onset of nonlinear growth is not predicted by available linear-stability theory. Following the diffusive-growth stage, growth rates are found to depend on the initial perturbations, up to the end of the simulations. Mixing is found to be even more sensitive to initial conditions than growth rates. Taylor microscales and Reynolds numbers are anisotropic throughout the simulations. Improved collapse of many statistics is achieved if the height of the mixing zone, rather than time, is used as the scaling or progress variable. Mixing has dynamical consequences for this flow, since it is driven by the action of the imposed acceleration field on local density differences

    G+++ and Brane Solutions

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    We demonstrate that the very extended G+++ group element of the form gA=exp(1(β,β)lnNβH)exp((1N)Eβ)g_A=\exp(-{\frac{1}{(\beta,\beta)}\ln N}\beta \cdot H)\exp((1-N)E_\beta) describes the usual BPS, electric, single brane solutions found in G+++ theories.Comment: One new equation, added references, corrected typos and minor changes, 42 pages, 6 figures, LaTeX2

    A casemix analysis of hospital admissions in six specialties for Barking & Havering Health Authority.

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    To examine admission rates for Barking & Havering residents to six surgical specialties by first looking at elective, emergency and total workloads, then at the casemix of elective work using Healthcare Resource Groups. To compare findings to other London areas

    Off-Shell Hodge Dualities in Linearised Gravity and E11

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    In a spacetime of dimension n, the dual graviton is characterised by a Young diagram with two columns, the first of length n-3 and the second of length one. In this paper we perform the off-shell dualisation relating the dual graviton to the double-dual graviton, displaying the precise off-shell field content and gauge invariances. We then show that one can further perform infinitely many off-shell dualities, reformulating linearised gravity in an infinite number of equivalent actions. The actions require supplementary mixed-symmetry fields which are contained within the generalised Kac-Moody algebra E11 and are associated with null and imaginary roots.Comment: 33 pages, 2 figures, nomenclature changed and comments added to the conclusion

    New Anomalies in Topological String Theory

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    We show that the topological string partition function with D-branes on a compact Calabi-Yau manifold has new anomalies that spoil the recursive structure of the holomorphic anomaly equation and introduce dependence on wrong moduli (such as complex structure moduli in the A-model), unless the disk one-point functions vanish. This provides a microscopic explanation for the recent result of Walcher in arXiv:0712.2775 on counting of BPS states in M-theory using the topological string partition function. The relevance of vanishing disk one-point functions to large N duality for compact Calabi-Yau manifolds is noted

    WHAT IS "THE BASIS," HOW IS IT MEASURED, AND WHY DOES IT MATTER?

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    Basis behavior is generally considered to be the major determinant of hedging success or failure. In the course of our work as contract designers for Chicago Mercantile Exchange Inc., we have come to the conclusion that there are many misconceptions and incorrect statements made about "the basis" among practitioners and academics alike. Our work suggests that basis values, how they are measured, what they represent and how they are interpreted may differ widely from one commodity contract to another due to differences in the specifications of the underlying futures market, as well as differences in the structure of the underlying cash market.Marketing,

    Zero gravity tissue-culture laboratory

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    Hardware was developed for performing experiments to detect the effects that zero gravity may have on living human cells. The hardware is composed of a timelapse camera that photographs the activity of cell specimens and an experiment module in which a variety of living-cell experiments can be performed using interchangeable modules. The experiment is scheduled for the first manned Skylab mission

    Pique

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    The Gangsters

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