21,495 research outputs found

    Experimental probes of axions

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    Experimental searches for axions or axion-like particles rely on semiclassical phenomena resulting from the postulated coupling of the axion to two photons. Sensitive probes of the extremely small coupling constant can be made by exploiting familiar, coherent electromagnetic laboratory techniques, including resonant enhancement of transitions using microwave and optical cavities, Bragg scattering, and coherent photon-axion oscillations. The axion beam may either be astrophysical in origin as in the case of dark matter axion searches and solar axion searches, or created in the laboratory from laser interactions with magnetic fields. This note is meant to be a sampling of recent experimental results.Comment: 6 pages, 7 figures, proceedings of XXIX Physics in Collision Conference, Kobe, Japan, August 30-September 2, 2009. An incorrect file was accidentally submitted as V1. V2 is the version in the actual proceedings. Difference: axion-fermion scattering is always suppressed by the Yukawa coupling m_f/f_a. High kinetic energies do not overcome this suppressio

    Manifestations of Dynamical Facilitation in Glassy Materials

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    By characterizing the dynamics of idealized lattice models with a tunable kinetic constraint, we explore the different ways in which dynamical facilitation manifests itself within the local dynamics of glassy materials. Dynamical facilitation is characterized both by a mobility transfer function, the propensity for highly-mobile regions to arise near regions that were previously mobile, and by a facilitation volume, the effect of an initial dynamical event on subsequent dynamics within a region surrounding it. Sustained bursts of dynamical activity -- avalanches -- are shown to occur in kinetically constrained models, but, contrary to recent claims, we find that the decreasing spatiotemporal extent of avalanches with increased supercooling previously observed in granular experiments does not imply diminishing facilitation. Viewed within the context of existing simulation and experimental evidence, our findings show that dynamical facilitation plays a significant role in the dynamics of systems investigated over the range of state points accessible to molecular simulations and granular experiments.Comment: 10 pages, 5 figure

    Cadillac Contracts and Up-Front Payments: Efficient Investment Under Expectation Damages

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    This paper shows that up-front payments can play a crucial role in providing efficient investment incentives when contracts are incomplete. They can eliminate the overinvestment effect identified by Rogerson [1984] and Shavell [1980] when courts use an expectation damage remedy. This method extends to complex contracting situations if parties combine up-front payments with what we call 'Cadillac' contracts (contracts for a very high quality or quantity). This combination provides efficient investment incentives in complex contracting problems when an expectation damage remedy is accompanied by a broad duty to mitigate damages. This indicates that an expectation remedy is well-suited to multidimensional, but one-sided, investment problems, in contrast to specific performance, which Edlin and Reichelstein [1993] showed is well-suited to two-sided, but unidimensional, investment problems.


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    Replaced with revised version of paper 07/27/04.Marketing,

    Low-noise nozzle valve

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    A low noise, variable discharage area, valve is constructed having opposed recesses within which a pair of gates are slidably disposed. Each of the gates is provided with upstream edges having a radius thereon, the radius enabling smooth, accelerated, low noise flow therebetween. The gates are further provided with tracks along each side, which in turn slide along splines set in the side walls of the valve. A threaded rod which rotates in a threaded insert in a rear wall of each of the gates, serves to move the gates within their respective recesses
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