Long-term evolution of accretion discs in Be/X-ray binaries

We numerically study the long-term evolution of the accretion disc around the neutron star in a coplanar Be/X-ray binary with a short period and a moderate eccentricity. From three dimensional Smoothed Particle Hydrodynamics simulations, we find that the disc evolves through three distinct phases, each characterized by different mass accretion patterns. In the first "developing phase", the disc is formed and develops towards a nearly Keplerian disc. It has a relatively large, double-peaked mass-accretion rate with the higher peak by the direct accretion at periastron, which is followed by the lower peak by the accretion induced by a one-armed spiral wave. In the second "transition phase", the disc is approximately Keplerian and grows with time. The mass-accretion rate increases as the disc grows. In the second phase, there is a transition in the mass accretion rate from a double peaked to a single peaked pattern. In the final quasi-steady state, the mass-accretion rate is on average balanced with the mass-transfer rate from the Be disc and exhibits a regular orbital modulation. In the quasi-steady state, the mass-accretion rate has a single peak by the wave-induced accretion as in a later stage of the transition phase. The orbital modulation of X-ray maxima could provide not only a circumstantial evidence for the persistent disc but also an observational diagnosis of the disc evolutionary state.Comment: 10 pages, 7 figures, Accepted for publication in MNRA

Aging of poled ferroelectric ceramics due to relaxation of random depolarization fields by space-charge accumulation near grain boundaries

Migration of charged point defects triggered by the local random depolarization field is shown to plausibly explain aging of poled ferroelectric ceramics providing reasonable time and acceptor concentration dependences of the emerging internal bias field. The theory is based on the evaluation of the energy of the local depolarization field caused by mismatch of the polarizations of neighbor grains. The kinetics of charge migration assumes presence of mobile oxygen vacancies in the material due to the intentional or unintentional acceptor doping. Satisfactory agreement of the theory with experiment on the Fe-doped lead zirconate titanate is demonstrated.Comment: theory and experiment, 22 pages, 3 figure

Phonon, Two-Magnon and Electronic Raman Scattering of Fe1+yTe1-xSex

We have measured Raman scattering spectra of single-crystalline FeTe0.6Se0.4 (T_c ~ 14.5 K) and its parent compound Fe1.074Te at various temperatures. In the parent compound Fe1.074Te, A1g and B1g modes have been observed at 157.5 and 202.3 cm-1, respectively, at 5 K. These frequencies qualitatively agree with the calculated results. Two-magnon excitation has been observed around 2300 cm-1 for both compounds. Temperature dependence between the electronic Raman spectra below and above T_c has been observed and 2\Delta and 2\Delta/k_BT_C have been estimated as 5.0 meV and 4.0, respectively.Comment: 8 pages, 8 figures, to be published in Phys. Rev.

Magnetization Plateau of an S=1 Frustrated Spin Ladder

We study the magnetization plateau at 1/4 of the saturation magnetization of the S=1 antiferromagnetic spin ladder both analytically and numerically, with the aim of explaining recent experimental results on BIP-TENO by Goto et al. We propose two mechanisms for the plateau formation and clarify the plateau phase diagram on the plane of the coupling constants between spins

Equivalence between Schwinger and Dirac schemes of quantization

This paper introduces the modified version of Schwinger's quantization method, in which the information on constraints and the choice of gauge conditions are included implicitly in the choice of variations used in quantization scheme. A proof of equivalence between Schwinger- and Dirac-methods for constraint systems is given.Comment: 12pages, No figures, Latex, The proof is improved and one reference is adde