601 research outputs found

    Refractive effects in the scattering of loosely bound nuclei

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    A study of the interaction of loosely bound nuclei 6,7Li at 9 and 19 AMeV with light targets has been undertaken. With the determination of unambiguous optical potentials in mind, elastic data for four projectile-target combinations and one neutron transfer reaction 13C(7Li,8Li)12C have been measured on a large angular range. The kinematical regime encompasses a region where the mean field (optical potential) has a marked variation with mass and energy, but turns out to be sufficiently surface transparent to allow strong refractive effects to be manifested in elastic scattering data at intermediate angles. The identified exotic feature, a "plateau" in the angular distributions at intermediate angles, is fully confirmed in four reaction channels and interpreted as a pre-rainbow oscillation resulting from the interference of the barrier and internal barrier farside scattering subamplitudes.Comment: 19 pages, 14 figures, 3 tables to submit to Phys. Rev.

    Leche y queso en Oruro, Bolivia.

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    La papa nativa en norte Potosi, Bolivia.

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    Coherent states for a particle on a sphere

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    The coherent states for a particle on a sphere are introduced. These states are labelled by points of the classical phase space, that is the position on the sphere and the angular momentum of a particle. As with the coherent states for a particle on a circle discussed in Kowalski K {\em et al} 1996 {\em J. Phys. A} {\bf 29} 4149, we deal with a deformation of the classical phase space related with quantum fluctuations. The expectation values of the position and the angular momentum in the coherent states are regarded as the best possible approximation of the classical phase space. The correctness of the introduced coherent states is illustrated by an example of the rotator.Comment: LaTeX, 16 pages, 2 figure

    Dark Energy in an Axion Model with Explicit Z(N) Symmetry Breaking

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    We point out that a well known axion model with an explicit Z(N) symmetry breaking term predicts both dark energy and cold dark matter. We estimate the parameters of this model which fit the observed densities of the dark components of the universe. We find that the parameters do not conflict with any observations.Comment: 5 pages, minor change

    Nuevas citas de Eleutherodactylus Duméril y Bibron, 1841 (Anura, Leptodactylidae) para Bolivia

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    Five species of the genus Eleutherodactylus (Anura, Leptodactylidae) are reported from Bolivia for the first time: E. altamazonicus from Departments Pando and La Paz; E. carvalhoi from Cochabamba; and E. ockendeni, E. skydmainos and E. zimmermanae from Pando. New departmental records are provided for other species: E. cruralis for Department Pando, E. danae for Beni and La Paz, E. platydactylus for Beni, E. toftae for Pando and La Paz and E. ventrimarmoratus for La Paz. Currently, 25 species of Eleutherodactylus are known in Bolivia. The taxonomic status of some species remains uncertain, new species are being described and others are still to be discovered. Therefore, the actual number of Bolivian Eleutherodactylus species is still unknown.En este trabajo se publican los primeros registros de cinco especies del género Eleutherodactylus (Anura, Leptodactylidae) para Bolivia: E. altamazonicus en los Departamentos de Pando y La Paz; E. carvalhoi en Cochabamba; y E. ockendeni, E. skydmainos y E. zimmermanae en Pando. Además, se aportan las primeras citas de E. cruralis para el Departamento de Pando, de E. danae para Beni y La Paz, de E. platydactylus para Beni, de E. toftae para Pando y La Paz y de E. ventrimarmoratus para La Paz. La diversidad conocida de Eleutherodactylus en Bolivia es de 25 especies, aunque los problemas taxonómicos sin resolver, las especies en descripción y el alto número de especies aún no citadas que se considera probable encontrar, hacen que aún desconozcamos la verdadera diversidad de este género en Bolivia
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