190,982 research outputs found

    Disassortativity of random critical branching trees

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    Random critical branching trees (CBTs) are generated by the multiplicative branching process, where the branching number is determined stochastically, independent of the degree of their ancestor. Here we show analytically that despite this stochastic independence, there exists the degree-degree correlation (DDC) in the CBT and it is disassortative. Moreover, the skeletons of fractal networks, the maximum spanning trees formed by the edge betweenness centrality, behave similarly to the CBT in the DDC. This analytic solution and observation support the argument that the fractal scaling in complex networks originates from the disassortativity in the DDC.Comment: 3 pages, 2 figure

    Electronic structures of Zn1x_{1-x}Cox_xO using photoemission and x-ray absorption spectroscopy

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    Electronic structures of Zn1x_{1-x}Cox_xO have been investigated using photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). The Co 3d states are found to lie near the top of the O 2p2p valence band, with a peak around 3\sim 3 eV binding energy. The Co 2p2p XAS spectrum provides evidence that the Co ions in Zn1x_{1-x}Cox_{x}O are in the divalent Co2+^{2+} (d7d^7) states under the tetrahedral symmetry. Our finding indicates that the properly substituted Co ions for Zn sites will not produce the diluted ferromagnetic semiconductor property.Comment: 3 pages, 2 figure

    Charmless Non-Leptonic B Decays and R-parity Violating Supersymmetry

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    We examine the charmless hadronic B decay modes in the context of R-parity violating (\rpv) supersymmetry. We try to explain the large branching ratio (compared to the Standard Model (SM) prediction) of the decay B±ηK±B^{\pm}\to \eta' K^{\pm}. There exist data for other observed η()\eta^{(\prime)} modes and among these modes, the decay B0ηK0B^{0}\to \eta K^{*0} is also found to be large compared to the SM prediction. We investigate all these modes and find that only two pairs of \rpv coupling can satisfy the requirements without affecting the other B\ra PP and B\ra VP decay modes barring the decay B\ra\phi K. From this analysis, we determine the preferred values of the \rpv couplings and the effective number of color NcN_c. We also calculate the CP asymmetry for the observed decay modes affected by these new couplings.Comment: 14 pages, 7 figures; revtex; version published in Phys. Lett.