Pressure-induced isostructural phase transition of metal-doped silicon clathrates

We propose an atomistic model for the pressure-induced isostructural phase transition of metal-doped silicon clathrates, Ba8Si46 and K8Si46, that has been observed at 14 GPa and 23 GPa, respectively. The model explains successfully the equation of state, transition pressure, change of Raman spectra and dependence on the doped cations as well as the effects of substituting Si(6c) atoms with noble metals.Comment: 5 pages, two coumn, 5 figures. See http://www.iitaka.org/down.html for more informatio

Cluster Property and Robustness of Ground States of Interacting Many Bosons

We study spatial correlation functions of local operators of interacting many bosons confined in a box of a large, but volume V, for various `ground states' whose energy densities are almost degenerate. The ground states include the coherent state of interacting bosons (CSIB), the number state of interacting bosons (NSIB), and the number-phase squeezed state of interacting bosons, which interpolates between the CSIB and NSIB. It was shown previously that only the CSIB is robust (i.e., does not decohere for a macroscopically long time) against the leakage of bosons into an environment. We show that for the CSIB the spatial correlation of any local operators A(r) and B(r') (which are localized around r and r', respectively) vanishes as |r - r' | \sim V^{1/3} \to \infty, i.e., the CSIB has the `cluster property.' In contrast, the other ground states do not possess the cluster property. Therefore, we have successfully shown that the robust state has the cluster property. This ensures the consistency of the field theory of bosons with macroscopic theories.Comment: We have replaced the manuscript in order to update the reference list and to fix typos. (5 pages, no figures) In the final manuscript, a few sentences have added for more detailed explanation. Journal PDF at http://jpsj.jps.or.jp/journal/JPSJ-71-1.htm

High-K Precession modes: Axially symmetric limit of wobbling motion

The rotational band built on the high-K multi-quasiparticle state can be interpreted as a multi-phonon band of the precession mode, which represents the precessional rotation about the axis perpendicular to the direction of the intrinsic angular momentum. By using the axially symmetric limit of the random-phase-approximation (RPA) formalism developed for the nuclear wobbling motion, we study the properties of the precession modes in $^{178}$W; the excitation energies, B(E2) and B(M1) values. We show that the excitations of such a specific type of rotation can be well described by the RPA formalism, which gives a new insight to understand the wobbling motion in the triaxial superdeformed nuclei from a microscopic view point.Comment: 14 pages, 8 figures (Spelling of the authors name was wrong at the first upload, so it is corrected

Generalized Phase Rules

For a multi-component system, general formulas are derived for the dimension of a coexisting region in the phase diagram in various state spaces.Comment: In the revised manuscript, physical meanings of D's are explained by adding three figures. 10 pages, 3 figure

Prediction of Ferromagnetic Ground State of NaCl-type FeN

Ab-initio results for structural and electronic properties of NaCl-type FeN are presented in a framework of plane-wave and ultrasoft pseudopotentials. Competition among different magnetic ordering is examined. We find the ferromagnetic phase stable overall. Stabilization over the unpolarized phase is obtained by splitting one flat t_2g-type band crossing the Fermi energy. A comparison with CrN is considered. We find large differences in the properties of the two systems that can be addressed to the smaller ionicity and magnetization of FeN.Comment: 5 pages, 4 figures, twocolumn latex style Sentence changed in Section III line 1

Photon-energy dissipation caused by an external electric circuit in "virtual" photo-excitation processes

We consider generation of an electrical pulse by an optical pulse in the ``virtual excitation'' regime. The electronic system, which is any electro-optic material including a quantum well structure biased by a dc electric field, is assumed to be coupled to an external circuit. It is found that the photon frequency is subject to an extra red shift in addition to the usual self-phase modulation, whereas the photon number is conserved. The Joule energy consumed in the external circuit is supplied only from the extra red shift.Comment: 4 pages, 1 fugur

1D Modeling for Temperature-Dependent Upflow in the Dimming Region Observed by Hinode/EIS

We have previously found a temperature-dependent upflow in the dimming region following a coronal mass ejection (CME) observed by the {\it Hinode} EUV Imaging Spectrometer (EIS). In this paper, we reanalyzed the observations along with previous work on this event, and provided boundary conditions for modeling. We found that the intensity in the dimming region dramatically drops within 30 minutes from the flare onset, and the dimming region reaches the equilibrium stage after $\sim$1 hour later. The temperature-dependent upflows were observed during the equilibrium stage by EIS. The cross sectional area of the fluxtube in the dimming region does not appear to expand significantly. From the observational constraints, we reconstructed the temperature-dependent upflow by using a new method which considers the mass and momentum conservation law, and demonstrated the height variation of plasma conditions in the dimming region. We found that a super radial expansion of the cross sectional area is required to satisfy the mass conservation and momentum equations. There is a steep temperature and velocity gradient of around 7 Mm from the solar surface. This result may suggest that the strong heating occurred above 7 Mm from the solar surface in the dimming region. We also showed that the ionization equilibrium assumption in the dimming region is violated especially in the higher temperature range.Comment: accepted for publication in The Astrophysical Journa

Simple model for decay of superdeformed nuclei

Recent theoretical investigations of the decay mechanism out of a superdeformed nuclear band have yielded qualitatively different results, depending on the relative values of the relevant decay widths. We present a simple two-level model for the dynamics of the tunneling between the superdeformed and normal-deformed bands, which treats decay and tunneling processes on an equal footing. The previous theoretical results are shown to correspond to coherent and incoherent limits of the full tunneling dynamics. Our model accounts for experimental data in both the A~150 mass region, where the tunneling dynamics is coherent, and in the A~190 mass region, where the tunneling dynamics is incoherent.Comment: 4 page

Spreading Width for Decay out of a Superdeformed Band

The attenuation factor F responsible for the decay out of a superdeformed (SD) band is calculated with the help of a statistical model. This factor is given by 1/F = (1 + Gamma(down) / Gamma(S)). Here, Gamma(S) is the width for the collective E2 transition within the superdeformed band, and Gamma(down) is the spreading width which describes the mixing between a state in the SD band and the normally deformed (ND) states of equal spin. The attenuation factor F is independent of the statistical E1 decay widths Gamma(N) of the ND states provided that the Gamma(N) are much larger than both Gamma(down) and Gamma(S). This condition is generically met. Previously measured values of F are used to determine Gamma(down).Comment: Submitted to Physical Review Letter