27,167 research outputs found

    Effect of applied DC voltages and temperatures on space charge behaviour of multi-layer oil-paper insulation

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    In this paper, space charge in a multi-layer oil-paper insulation system was investigated using the pulsed electroacoustic (PEA) technique. A series of measurements had been carried following subjection of the insulation system to different applied voltages and different temperatures. Charge behaviours in the insulation system were analyzed and the influence of temperature on charge dynamics was discussed. The test results shows that homocharge injection takes place under all the test conditions, the applied DC voltage mainly affects the amount of space charge, while the temperature has greater influence on the distribution and mobility of space charge inside oil-paper samples

    On C*-algebras related to constrained representations of a free group

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    We consider representations of the free group F2F_2 on two generators such that the norm of the sum of the generators and their inverses is bounded by μ∈[0,4]\mu\in[0,4]. These μ\mu-constrained representations determine a C*-algebra AμA_{\mu} for each μ∈[0,4]\mu\in[0,4]. We prove that these C*-algebras form a continuous bundle of C*-algebras over [0,4][0,4] and calculate their K-groups.Comment: 9 page

    Exclusive Lambda_b -> Lambda l^+ l^- decay in two Higgs doublet model

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    Rare Lambda_b -> Lambda l^+ l^- decay is investigated in framework of general two Higgs doublet model, in which a new source of CP violation exists (model III). The polarization parameter, CP asymmetry and decay width are calculated. It is shown that CP asymmetry is a very sensitive tool for establishing model III.Comment: 16 pages, 3 figures, LaTeX formatte

    Coherence freeze in an optical lattice investigated via pump-probe spectroscopy

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    Motivated by our observation of fast echo decay and a surprising coherence freeze, we have developed a pump-probe spectroscopy technique for vibrational states of ultracold 85^{85}Rb atoms in an optical lattice to gain information about the memory dynamics of the system. We use pump-probe spectroscopy to monitor the time-dependent changes of frequencies experienced by atoms and to characterize the probability distribution of these frequency trajectories. We show that the inferred distribution, unlike a naive microscopic model of the lattice, correctly predicts the main features of the observed echo decay.Comment: 4 pages, 5 figure

    Critical Phenomena and Thermodynamic Geometry of RN-AdS Black Holes

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    The phase transition of Reissner-Nordstr\"om black holes in (n+1)(n+1)-dimensional anti-de Sitter spacetime is studied in details using the thermodynamic analogy between a RN-AdS black hole and a van der Waals liquid gas system. We first investigate critical phenomena of the RN-AdS black hole. The critical exponents of relevant thermodynamical quantities are evaluated. We find identical exponents for a RN-AdS black hole and a Van der Waals liquid gas system. This suggests a possible universality in the phase transitions of these systems. We finally study the thermodynamic behavior using the equilibrium thermodynamic state space geometry and find that the scalar curvature diverges exactly at the van der Waals-like critical point where the heat capacity at constant charge of the black hole diverges.Comment: 18 pages, 5 figure

    Decays of the Meson BcB_c to a PP-Wave Charmonium State χc\chi_c or hch_c

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    The semileptonic decays, Bc⟶χc(hc)+ℓ+νℓB_{c}{\longrightarrow}{\chi_c}(h_c)+{\ell}+{{\nu}}_{\ell}, and the two-body nonleptonic decays, Bc⟶χc(hc)+hB_{c}{\longrightarrow}{\chi_c}(h_c)+h, (here χc\chi_c and hch_c denote (ccˉ[3PJ])(c\bar c[^3P_J]) and (ccˉ[1P1])(c\bar c[^1P_1]) respectively, and hh indicates a meson) were computed. All of the form factors appearing in the relevant weak-current matrix elements with BcB_c as its initial state and a PP-wave charmonium state as its final state for the decays were precisely formulated in terms of two independent overlapping-integrations of the wave-functions of BcB_c and the PP-wave charmonium and with proper kinematics factors being `accompanied'. We found that the decays are quite sizable, so they may be accessible in Run-II at Tevatron and in the foreseen future at LHC, particularly, when BTeV and LHCB, the special detectors for B-physics, are borne in mind. In addition, we also pointed out that the decays Bc→hc+...B_c\to h_c+... may potentially be used as a fresh window to look for the hch_c charmonium state, and the cascade decays, Bc→χc[3P1,2]+l+νlB_c\to \chi_c[^3P_{1,2}]+l+\nu_l (Bc→χc[3P1,2]+hB_c\to \chi_c[^3P_{1,2}]+h) with one of the radiative decays χc[3P1,2]→J/ψ+γ\chi_c[^3P_{1,2}] \to J/\psi+\gamma being followed accordingly, may affect the observations of BcB_c meson through the decays Bc→J/ψ+l+νlB_{c}\to {J/\psi}+{l}+\nu_{l} (Bc→J/ψ+hB_c\to J/\psi+h) substantially.Comment: 24 pages, 3 figures, the replacement for improving the presentation and adding reference
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