273,448 research outputs found

    Comment on "Potential Energy Landscape for Hot Electrons in Periodically Nanostructured Graphene"

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    In a recent letter [Phys. Rev. Lett. 105 (2010) 036804] the unoccupied electronic states of single layers of graphene on ruthenium are investigated. Here we comment on the interpretation, which deviates in four points from [J. Phys.: Condens. Matter 22 (2010) 302001] and outline the corresponding consequences

    Ergodicity and Mixing in Quantum Dynamics

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    After a brief historical review of ergodicity and mixing in dynamics, particularly in quantum dynamics, we introduce definitions of quantum ergodicity and mixing using the structure of the system's energy levels and spacings. Our definitions are consistent with usual understanding of ergodicity and mixing. Two parameters concerning the degeneracy in energy levels and spacings are introduced. They are computed for right triangular billiards and the results indicate a very close relation between quantum ergodicity (mixing) and quantum chaos. At the end, we argue that, besides ergodicity and mixing, there may exist a third class of quantum dynamics which is characterized by a maximized entropy.Comment: 10 pages, 6 figures and 1 tabl

    NLTE study of scandium in the Sun

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    We investigate the formation of neutral and singly ionized scandium lines in the solar photospheres. The research is aimed derive solar loggfϵ\log gf\epsilon_{\odot}(Sc) values for scandium lines, which will later be used in differential abundance analyses of metal-poor stars. Extensive statistical equilibrium calculations were carried out for a model atom, which comprises 92 terms for \ion{Sc}{i} and 79 for \ion{Sc}{ii}. Photoionization cross-sections are assumed to be hydrogenic. Synthetic line profiles calculated from the level populations according to the NLTE departure coefficients were compared with the observed solar spectral atlas. Hyperfine structure (HFS) broadening is taken into account. The statistical equilibrium of scandium is dominated by a strong underpopulation of \ion{Sc}{i} caused by missing strong lines. It is nearly unaffected by the variation in interaction parameters and only marginally sensitive to the choice of the solar atmospheric model. Abundance determinations using the ODF model lead to a solar Sc abundance of between logϵ=3.07\log\epsilon_\odot = 3.07 and 3.13, depending on the choice of ff values. The long known difference between photospheric and meteoritic scandium abundances is confirmed for the experimental ff-values.Comment: 10 pages, 6 figures, A&A accepte
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