30,646 research outputs found

    The rheology of dense, polydisperse granular fluids under shear

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    The solution of the Enskog equation for the one-body velocity distribution of a moderately dense, arbitrary mixture of inelastic hard spheres undergoing planar shear flow is described. A generalization of the Grad moment method, implemented by means of a novel generating function technique, is used so as to avoid any assumptions concerning the size of the shear rate. The result is illustrated by using it to calculate the pressure, normal stresses and shear viscosity of a model polydisperse granular fluid in which grain size, mass and coefficient of restitution varies amoungst the grains. The results are compared to a numerical solution of the Enskog equation as well as molecular dynamics simulations. Most bulk properties are well described by the Enskog theory and it is shown that the generalized moment method is more accurate than the simple (Grad) moment method. However, the description of the distribution of temperatures in the mixture predicted by Enskog theory does not compare well to simulation, even at relatively modest densities.Comment: 8 postscript figures Replaced with new version correcting an error in the SME calculations and misc. small corrections. Second replacement with final correction of SME calculation

    Sub-mm counterparts to Lyman-break galaxies

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    We summarize the main results from our SCUBA survey of Lyman-break galaxies (LBGs) at z~3. Analysis of our sample of LBGs reveals a mean flux of S850=0.6±\pm0.2 mJy, while simple models of emission based on the UV properties predict a mean flux about twice as large. Known populations of LBGs are expected to contribute flux to the weak sub-mm source portion of the far-IR background, but are not likely to comprise the bright source (S850>5 mJy) end of the SCUBA-detected source count. The detection of the LBG, Westphal-MM8, at 1.9 mJy suggests that deeper observations of individual LBGs in our sample could uncover detections at similar levels, consistent with our UV-based predictions. By the same token, many sub-mm selected sources with S850<2 mJy could be LBGs. The data are also consistent with the FarIR/β\beta relation holding at z=3.Comment: 6 pages, 1 figure, contributed talk at UMass/INAOE Conference ``Deep Millimeter Surveys'

    Asymptotic analysis of a secondary bifurcation of the one-dimensional Ginzburg-Landau equations of superconductivity

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    The bifurcation of asymmetric superconducting solutions from the normal solution is considered for the one-dimensional Ginzburg--Landau equations by the methods of formal asymptotics. The behavior of the bifurcating branch depends on the parameters d, the size of the superconducting slab, and κ\kappa, the Ginzburg--Landau parameter. The secondary bifurcation in which the asymmetric solution branches reconnect with the symmetric solution branch is studied for values of (κ,d)(\kappa,d) for which it is close to the primary bifurcation from the normal state. These values of (κ,d)(\kappa,d) form a curve in the κd\kappa d-plane, which is determined. At one point on this curve, called the quintuple point, the primary bifurcations switch from being subcritical to supercritical, requiring a separate analysis. The results answer some of the conjectures of [A. Aftalion and W. C. Troy, Phys. D, 132 (1999), pp. 214--232]

    Statistical summary: Study to determine the IFR operational profile of the general aviation single pilot

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    The statistical summary of data resulting from a mail questionnaire survey designed to develop information on the general aviation single pilot operating under instrument flight rules is presented

    Modelling the measured local time evolution of strongly nonlinear heat pulses in the Large Helical Device

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    In some magnetically confined plasmas, an applied pulse of rapid edge cooling can trigger either a positive or negative excursion in the core electron temperature from its steady state value. We present a new model which captures the time evolution of the transient, non-diffusive local dynamics in the core plasma. We show quantitative agreement between this model and recent spatially localized measurements (Inagaki et al 2010 Plasma Phys. Control. Fusion 52 075002) of the local time-evolving temperature pulse in cold pulse propagation experiments in the Large Helical Device
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