7,505 research outputs found
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
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