64,555 research outputs found

    Axion hot dark matter bounds

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    We derive cosmological limits on two-component hot dark matter consisting of neutrinos and axions. We restrict the large-scale structure data to the safely linear regime, excluding the Lyman-alpha forest. We derive Bayesian credible regions in the two-parameter space consisting of m_a and sum(m_nu). Marginalizing over sum(m_nu) provides m_a<1.02 eV (95% CL). In the absence of axions the same data and methods give sum(m_nu)< 0.63 eV (95% CL).Comment: Contribution to Proc. 4th Patras Workshop on Axions, WIMPs and WISPs (18-21 June 2008, DESY

    Television signal processing system Patent

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    Video signal processing system for sampling video brightness level

    Improved television signal processing system

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    Digital system processes spacecraft television pictures by converting images sensed on a photostorage vidicon to pulses which can be transmitted by telemetry. This system can be applied in the processing of medical X ray photographs and in electron microscopy

    Video signal enhancement system with dynamic range compression and modulation index expansion Patent

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    Video signal enhancement of signal component representing brightness of scene element in low contras

    Application of Pad\'{e} interpolation to stationary state problems

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    If the small and large coupling behavior of a physical system can be computed perturbatively and expressed respectively as power series in a coupling parameter gg and 1/g1/g, a Pad\'{e} approximant embracing the two series can interpolate between these two limits and provide an accurate estimate of the system's behavior in the generally intractable intermediate coupling regime. The methodology and validity of this approach are illustrated by considering several stationary state problems in quantum mechanics.Comment: RevTeX4, 7 pages (including 7 tables); v4 typos correcte

    How CMB and large-scale structure constrain chameleon interacting dark energy

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    We explore a chameleon type of interacting dark matter-dark energy scenario in which a scalar field adiabatically traces the minimum of an effective potential sourced by the dark matter density. We discuss extensively the effect of this coupling on cosmological observables, especially the parameter degeneracies expected to arise between the model parameters and other cosmological parameters, and then test the model against observations of the cosmic microwave background (CMB) anisotropies and other cosmological probes. We find that the chameleon parameters α\alpha and β\beta, which determine respectively the slope of the scalar field potential and the dark matter-dark energy coupling strength, can be constrained to α<0.17\alpha < 0.17 and β<0.19\beta < 0.19 using CMB data alone. The latter parameter in particular is constrained only by the late Integrated Sachs-Wolfe effect. Adding measurements of the local Hubble expansion rate H0H_0 tightens the bound on α\alpha by a factor of two, although this apparent improvement is arguably an artefact of the tension between the local measurement and the H0H_0 value inferred from Planck data in the minimal Λ\LambdaCDM model. The same argument also precludes chameleon models from mimicking a dark radiation component, despite a passing similarity between the two scenarios in that they both delay the epoch of matter-radiation equality. Based on the derived parameter constraints, we discuss possible signatures of the model for ongoing and future large-scale structure surveys.Comment: 25 pages, 6 figure
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