5,821 research outputs found
Atomically straight steps on vicinal Si (111) surfaces prepared by step-parallel current in the kink-up direction
We demonstrate that annealing of a vicinal Si(111) surface at about 800 C
with a direct current in the direction that ascends the kinks enhances the
formation of atomically straight step edges over micrometer lengths, while
annealing with a current in the opposite direction does not. Every straight
step edge has the same atomic configuration U(2,0), which is useful as a
template for the formation of a variety of nanostructures. A phenomenological
model based on electromigration of charged mobile atoms explains the observed
current-polarity dependent behavior.Comment: Accepted for publication in Appl. Phys. Lett. Numbers of pages and
figures are 12 and 4, respectivel
Gravitational waves and neutrino emission from the merger of binary neutron stars
Numerical simulations for the merger of binary neutron stars are performed in
full general relativity incorporating a finite-temperature (Shen's) equation of
state (EOS) and neutrino cooling for the first time. It is found that for this
stiff EOS, a hypermassive neutron star (HMNS) with a long lifetime (
ms) is the outcome for the total mass \alt 3.0M_{\odot}. It is shown that the
typical total neutrino luminosity of the HMNS is --
ergs/s and the effective amplitude of gravitational waves from the HMNS is
4-- at --2.5 kHz for a source distance of 100 Mpc. We
also present the neutrino luminosity curve when a black hole is formed for the
first time.Comment: 4 pages, 4 figures (Fig.2 is in low resolution), Accepted for
publication in PR
A Theoretical Light-Curve Model for the Recurrent Nova V394 Coronae Austrinae
A theoretical light curve for the 1987 outburst of V394 Coronae Austrinae
(V394 CrA) is modeled to obtain various physical parameters of this recurrent
nova. We then apply the same set of parametersto a quiescent phase and confirm
that these parameters give a unified picture of the binary. The early visual
light curve (1-10 days after the optical maximum) is well reproduced by a
thermonuclear runaway model on a very massive WD close to the Chandrasekhar
limit (1.37 +- 0.01 M_sun). The ensuing plateau phase (10-30 days) is also
reproduced by the combination of a slightly irradiated MS and a fully
irradiated flaring-up disk with a radius ~1.4 times the Roche lobe size. The
best fit parameters are the WD mass 1.37 M_sun, the companion mass 1.5 M_sun
(0.8-2.0 M_sun is acceptable), the inclination angle of the orbit i~65-68
degree, and the flaring-up rim ~0.30 times the disk radius. The envelope mass
at the optical peak is estimated to be ~6 x 10^{-6} M_sun, which indicates an
average mass accretion rate of 1.5 x 10^{-7} M_sun yr^{-1} during the quiescent
phase between the 1949 and 1987 outbursts. In the quiescent phase, the observed
light curve can be reproduced with a disk size of 0.7 times the Roche lobe size
and a rather slim thickness of 0.05 times the accretion disk size at the rim.
About 0.5 mag sinusoidal variation of the light curve requires the mass
accretion rate higher than ~1.0 x 10^{-7} M_sun yr^{-1}, which is consistent
with the above estimation from the 1987 outburst. These newly obtained
quantities are exactly the same as those predicted in a new progenitor model of
Type Ia supernovae.Comment: 9 pages including 4 figures, to appear in the Astrophysical Journal,
Part
Spin dependent recombination based magnetic resonance spectroscopy of bismuth donor spins in silicon at low magnetic fields
Low-field (6-110 mT) magnetic resonance of bismuth (Bi) donors in silicon has
been observed by monitoring the change in photoconductivity induced by spin
dependent recombination. The spectra at various resonance frequencies show
signal intensity distributions drastically different from that observed in
conventional electron paramagnetic resonance, attributed to different
recombination rates for the forty possible combinations of spin states of a
pair of a Bi donor and a paramagnetic recombination center. An excellent
tunability of Bi excitation energy for the future coupling with superconducting
flux qubits at low fields has been demonstrated.Comment: 5 pages, 4 figure
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