108,747 research outputs found

    Light Collimation and Focussing by a Thin Flat Metallic Slab

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    We present experimental and theoretical work showing that a flat metallic slab can collimate and focus light impinging on the slab from a punctual source. The effect is optimised when the radiation is around the bulk, not at the surface, plasma frequency. And the smaller the imaginary part of the permittivity is, the better the collimation. Experiments for Ag in the visible as well as calculations are presented. We also discuss the interesting case of the Aluminium whose imaginary part of the permittivity is very small at the plasma frequency in UV radiation. Generalization to other materials and radiations are also discussed.Comment: 6 pages, 3 figures. To be published on Optics Lette

    Do Transaction Costs and Risk Preferences Influence Marketing Arrangements in the Illinois Hog Industry?

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    Risk reduction and transaction costs are often used to explain contracting in the U.S. hog industry with little empirical support. Using a unified conceptual framework that draws from risk behavior and transaction cost theories, in combination with unique survey and accounting data, we demonstrate that risk preferences and asset specificity impact Illinois producers’ use of contracts and spot markets. In particular, producers’ investments in specific hog genetics and human capital are related to selection of long-term marketing contracts over spot markets. Producers who perceive greater levels of price risk and/or are more averse are more (less) likely to use contracts (spot markets). Key words: asset specificity, contracts, hogs, risk attitude, risk behavior, risk perception, transaction costs economic

    Convergent sequences of perturbative approximations for the anharmonic oscillator II. Compact time approach

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    We present an alternative pathway in the application of the variation improvement of ordinary perturbation theory exposed in [1] which can preserve the internal symmetries of a model by means of a time compactification.Comment: 21 pages, 4 Postscript figures available through anonymous ftp at ftp://algol.lpm.univ-montp2.fr ; replaces version which could not be postscripted presumably for lack of figures.uu fil
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