5,958 research outputs found

    High efficiency thermionic converter studies

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    Research in thermionic energy conversion technology is reported. The objectives were to produce converters suitable for use in out of core space reactors, radioisotope generators, and solar satellites. The development of emitter electrodes that operate at low cesium pressure, stable low work function collector electrodes, and more efficient means of space charge neutralization were investigated to improve thermionic converter performance. Potential improvements in collector properties were noted with evaporated thin film barium oxide coatings. Experiments with cesium carbonate suggest this substance may provide optimum combinations of cesium and oxygen for thermionic conversion

    La relación personal en el tratamiento de la diversidad

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    El autor centra su aportación en diferentes características de los organismos vivos, para incorporarlas a las perspectivas interpretativas y operativas, y de los métodos actuales de intervención educativa. En el texto también se trata el enfoque positivo desde la dimensión técnica y no «voluntarista», teniendo en cuenta que los especialistas que adoptan la perspectiva del enfoque positivo dan mucha importancia al tema de la calidad de vida.L'autor centra la seva aportació en diferents característiques dels organismes vius, per incorporar- les a les perspectives interpretatives i operatives, i dels mètodes actuals d'intervenció educativa. Al text també es tracta l'enfocament positiu des de la seva dimensió tècnica i no «voluntarista», tenint en compte que els especialistes que adopten la perspectiva de l'enfocament positiu donen molta importància al tema de la qualitat de vida.The author focuses on the different characteristics of the alive organisms in order to include them into the interpretative and operative views of the current methods of educational intervention. He also deals with the positive focus, from the technical and «no voluntary» dimension, taking into account that those specialists having this kind of view do emphasize a lot on the quality of life issue

    A Microscopic T-Violating Optical Potential: Implications for Neutron-Transmission Experiments

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    We derive a T-violating P-conserving optical potential for neutron-nucleus scattering, starting from a uniquely determined two-body ρ\rho-exchange interaction with the same symmetry. We then obtain limits on the T-violating ρ\rho-nucleon coupling g‾ρ\overline{g}_{\rho} from neutron-transmission experiments in 165^{165}Ho. The limits may soon compete with those from measurements of atomic electric-dipole moments.Comment: 8 pages, 2 uuencoded figures in separate files (replaces version sent earlier in the day with figures attached), in RevTeX 3, submitted to PR

    Solid deuterium surface degradation at ultracold neutron sources

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    Solid deuterium (sD_2) is used as an efficient converter to produce ultracold neutrons (UCN). It is known that the sD_2 must be sufficiently cold, of high purity and mostly in its ortho-state in order to guarantee long lifetimes of UCN in the solid from which they are extracted into vacuum. Also the UCN transparency of the bulk sD_2 material must be high because crystal inhomogeneities limit the mean free path for elastic scattering and reduce the extraction efficiency. Observations at the UCN sources at Paul Scherrer Institute and at Los Alamos National Laboratory consistently show a decrease of the UCN yield with time of operation after initial preparation or later treatment (`conditioning') of the sD_2. We show that, in addition to the quality of the bulk sD_2, the quality of its surface is essential. Our observations and simulations support the view that the surface is deteriorating due to a build-up of D_2 frost-layers under pulsed operation which leads to strong albedo reflections of UCN and subsequent loss. We report results of UCN yield measurements, temperature and pressure behavior of deuterium during source operation and conditioning, and UCN transport simulations. This, together with optical observations of sD_2 frost formation on initially transparent sD_2 in offline studies with pulsed heat input at the North Carolina State University UCN source results in a consistent description of the UCN yield decrease.Comment: 15 pages, 22 figures, accepted by EPJ-

    Witnessing (co)datatypes

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    Datatypes and codatatypes are useful for specifying and reasoning about (possibly infinite) computational processes. The Isabelle/HOL proof assistant has recently been extended with a definitional package that supports both. We describe a complete procedure for deriving nonemptiness witnesses in the general mutually recursive, nested case—nonemptiness being a proviso for introducing types in higher-order logic
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