37,477 research outputs found

    Monopole Excitation to Cluster States

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    We discuss strength of monopole excitation of the ground state to cluster states in light nuclei. We clarify that the monopole excitation to cluster states is in general strong as to be comparable with the single particle strength and shares an appreciable portion of the sum rule value in spite of large difference of the structure between the cluster state and the shell-model-like ground state. We argue that the essential reasons of the large strength are twofold. One is the fact that the clustering degree of freedom is possessed even by simple shell model wave functions. The detailed feature of this fact is described by the so-called Bayman-Bohr theorem which tells us that SU(3) shell model wave function is equivalent to cluster model wave function. The other is the ground state correlation induced by the activation of the cluster degrees of freedom described by the Bayman-Bohr theorem. We demonstrate, by deriving analytical expressions of monopole matrix elements, that the order of magnitude of the monopole strength is governed by the first reason, while the second reason plays a sufficient role in reproducing the data up to the factor of magnitude of the monopole strength. Our explanation is made by analysing three examples which are the monopole excitations to the 02+0^+_2 and 03+0^+_3 states in 16^{16}O and the one to the 02+0^+_2 state in 12^{12}C. The present results imply that the measurement of strong monopole transitions or excitations is in general very useful for the study of cluster states.Comment: 11 pages, 1 figure: revised versio

    Electrical switching in cadmium boracite single crystals

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    Cadmium boracite single crystals at high temperatures ( 300 C) were found to exhibit a reversible electric field-induced transition between a highly insulative and a conductive state. The switching threshold is smaller than a few volts for an electrode spacing of a few tenth of a millimeter corresponding to an electric field of 100 to 1000 V/cm. This is much smaller than the dielectric break-down field for an insulator such as boracite. The insulative state reappears after voltage removal. A pulse technique revealed two different types of switching. Unstable switching occurs when the pulse voltage slightly exceeds the switching threshold and is characterized by a pre-switching delay and also a residual current after voltage pulse removal. A stable type of switching occurs when the voltage becomes sufficiently high. Possible device applications of this switching phenomenon are discussed

    Crystal-field-induced magnetostrictions in the spin reorientation process of Nd2_2Fe14_{14}B-type compounds

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    Volume expansion ΔV/V\Delta V / V associated with the spin reorientation process of Nd2_2Fe14_{14}B-type compounds has been investigated in terms of simple crystalline-electric-field (CEF) model. In this system, ΔV/V\Delta V / V is shown to be a direct measure of second order CEF energy. Calculated anomalies in ΔV/V\Delta V / V associated with the first-order magnetization process of Nd2_2Fe14_{14}B are presented, which well reproduced the observations.Comment: 2 pages, 2 figures, to appear in J. Magn. Magn. Mate

    Chiral dynamics of Σ\Sigma-hyperons in the nuclear medium

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    Using SU(3) chiral perturbation theory we calculate the density-dependent complex mean field UΣ(kf)+iWΣ(kf)U_\Sigma(k_f)+ i W_\Sigma(k_f) of a Σ\Sigma-hyperon in isospin-symmetric nuclear matter. The leading long-range ΣN\Sigma N -interaction arises from one-kaon exchange and from two-pion exchange with a Σ\Sigma- or a Λ\Lambda-hyperon in the intermediate state. We find from the ΣNΛN\Sigma N\to \Lambda N conversion process at nuclear matter saturation density ρ0=0.16\rho_0 = 0.16 fm3^{-3} an imaginary single-particle potential of WΣ(kf0)=21.5W_\Sigma(k_{f0}) =-21.5 MeV, in fair agreement with existing empirical determinations. The genuine long-range contributions from iterated (second order) one-pion exchange with an intermediate Σ\Sigma- or Λ\Lambda-hyperon sum up to a moderately repulsive real single-particle potential of UΣ(kf0)=59U_\Sigma(k_{f0})= 59 MeV. Recently measured (π,K+(\pi^-,K^+) inclusive spectra related to Σ\Sigma^--formation in heavy nuclei give evidence for a Σ\Sigma-nucleus repulsion of similar size. Our results suggest that the net effect of the short-range ΣN\Sigma N-interaction on the Σ\Sigma-nuclear mean field could be small.Comment: 7 pages, 2 figures, published in: Phys. Rev. C 71, 068201 (2005

    On the Genus Expansion in the Topological String Theory

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    A systematic formulation of the higher genus expansion in topological string theory is considered. We also develop a simple way of evaluating genus zero correlation functions. At higher genera we derive some interesting formulas for the free energy in the A1A_1 and A2A_2 models. We present some evidence that topological minimal models associated with Lie algebras other than the A-D-E type do not have a consistent higher genus expansion beyond genus one. We also present some new results on the CP1CP^1 model at higher genera.Comment: 36 pages, phyzzx, UTHEP-27