66,016 research outputs found

    Globalisation and public health policy

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    Session 1B

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    Kohonen Self Organizing Map for Analyzing Rainfall and Inflow Patterns with Indiana Reservoir Sites, Chandra Viswanathan and Nimisha Gupta, Dept Civil Engineering, Purdue University Calumet, Hammond, IN Watershed Clustering Based on Geomorphic and Human Induced Landscape Modifications: A Central Kentucky Example, Brian Lee, Angela Schörgendorfer, and Collin Linebach, College of Agriculture, UK “True Relief”? Asynchronous Topographic Change Detection and Concomitant Land Cover and Hydrologic Implications, Demetrio Zourarakis, Kentucky Division of Geographic Information Cumulative Impacts Assessments for 404 Mining Permits, A Watershed Approach, J. Steven Gardner, Engineering Consulting Services, Inc., Lexington, K

    Transmission-Line Analysis of Epsilon-Near-Zero (ENZ)-Filled Narrow Channels

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    Following our recent interest in metamaterial-based devices supporting resonant tunneling, energy squeezing and supercoupling through narrow waveguide channels and bends, here we analyze the fundamental physical mechanisms behind this phenomenon using a transmission-line model. These theoretical findings extend our theory, allowing us to take fully into account frequency dispersion and losses and revealing the substantial differences between this unique tunneling phenomenon and higher-frequency Fabry-Perot resonances. Moreover, they represent the foundations for other possibilities to realize tunneling through arbitrary waveguide bends, both in E and H planes of polarization, waveguide connections and sharp abruptions and to obtain analogous effects with geometries arguably simpler to realize.Comment: 35 pages, 9 figure

    Are quasars accreting at super-Eddington rates?

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    In a previous paper, Collin & Hur\'e (2001), using a sample of Active Galactic Nuclei (AGN) where the mass has been determined by reverberation studies (Kaspi et al. 2000), have shown that if the optical luminosity is emitted by a steady accretion disc, about half of the objects are accreting close to or higher than the Eddington rate. We conclude here that this result is unavoidable, unless the masses are strongly underestimated by reverberation studies, which does not seem to be the case. There are three issues to the problem: 1. Accretion proceeds at Eddington or super-Eddington rates through thick discs. Several consequences follow: an anti-correlation between the line widths of the lines and the Eddington ratios, and a decrease of the Eddington ratio with an increasing black hole mass. Extrapolated to all quasars, these results imply that the amount of mass locked in massive black holes should be larger than presently thought. 2. The optical luminosity is not produced directly by the gravitational release of energy, and super-Eddington rates are not required. The optical luminosity has to be emitted by a dense and thick medium located at large distances from the center (103^3 to 10410^4 gravitational radii). It can be due to reprocessing of the X-ray photons from the central source in a geometrically thin warped disc, or in dense "blobs" forming a geometrically thick system, which can be a part of the accretion flow or the basis of an outflow. 3. Accretion discs are completely "non standard". Presently neither the predictions of models nor the observed spectral distributions are sufficient to help choosing between these solutions.Comment: 16 pages, 11 figures, accepted in A&
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