9,155 research outputs found
First-principles study on dielectric properties of NaCl crystal and ultrathin NaCl films under finite external electric field
We present a first-principles study on the dielectric properties of an NaCl
crystal and ultrathin NaCl films under a finite external electric field. Our
results show that the high-frequency dielectric constant of the films is not
affected by the finite size effect from crystal surfaces and is close to that
of the crystal, whereas the static one is sensitive to the thickness of the
film due to the difference in the atomic configurations between the surface and
inside of the film.Comment: 11 pages and 4 figure
Angular instability due to radiation pressure in the LIGO gravitational-wave detector
We observed the effect of radiation pressure on the angular sensing and control system of the Laser Interferometer Gravitational-Wave Observatory (LIGO) interferometer’s core optics at LIGO Hanford Observatory. This is the first measurement of this effect in a complete gravitational-wave interferometer. Only one of the two angular modes survives with feedback control, because the other mode is suppressed when the control gain is sufficiently large. We developed a mathematical model to understand the physics of the system. This model matches well with the dynamics that we observe
Direct administration of 2-hydroxypropyl-beta-cyclodextrin into guinea pig cochleae: Effects on physiological and histological measurements
<p>Cochlear response measurements from two different animals made before (red) and after (blue) treatment with HPβCD (Panel A) and TTX (Panel B) to 80 dB SPL 4 kHz tone bursts. Cochlear response waveform maintained CAP-like morphology after HPβCD treatment, consistent with reduced mechanical drive to neural excitation (Panel B, blue). In contrast, response waveform is EPSP-like following TTX treatment. Unlike TTX, results from HPβCD do not support the hypothesis that the auditory nerve is a site of action for 13 mM HPβCD.</p
Magnetically Driven Accretion in the Kerr Metric III: Unbound Outflows
We have carried out fully relativistic numerical simulations of accretion
disks in the Kerr metric. In this paper we focus on the unbound outflows that
emerge self-consistently from the accretion flow. These outflows are found in
the axial funnel region and consist of two components: a hot, fast, tenuous
outflow in the axial funnel proper, and a colder, slower, denser jet along the
funnel wall. Although a rotating black hole is not required to produce these
unbound outflows, their strength is enhanced by black hole spin. The
funnel-wall jet is excluded from the axial funnel due to elevated angular
momentum, and is also pressure-confined by a magnetized corona. The tenuous
funnel outflow accounts for a significant fraction of the energy transported to
large distances in the higher-spin simulations. We compare the outflows
observed in our simulations with those seen in other simulations.Comment: 33 pages, 8 figures, ApJ submitte
Imprint of Gravitational Lensing by Population III Stars in Gamma Ray Burst Light Curves
We propose a novel method to extract the imprint of gravitational lensing by
Pop III stars in the light curves of Gamma Ray Bursts (GRBs). Significant
portions of GRBs can originate in hypernovae of Pop III stars and be
gravitationally lensed by foreground Pop III stars or their remnants. If the
lens mass is on the order of and the lens redshift is
greater than 10, the time delay between two lensed images of a GRB is s and the image separation is as. Although it is difficult to
resolve the two lensed images spatially with current facilities, the light
curves of two images are superimposed with a delay of s. GRB light
curves usually exhibit noticeable variability, where each spike is less than
1s. If a GRB is lensed, all spikes are superimposed with the same time delay.
Hence, if the autocorrelation of light curve with changing time interval is
calculated, it should show the resonance at the time delay of lensed images.
Applying this autocorrelation method to GRB light curves which are archived as
the {\it BATSE} catalogue, we demonstrate that more than half light curves can
show the recognizable resonance, if they are lensed. Furthermore, in 1821 GRBs
we actually find one candidate of GRB lensed by a Pop III star, which may be
located at redshift 20-200. The present method is quite straightforward and
therefore provides an effective tool to search for Pop III stars at redshift
greater than 10. Using this method, we may find more candidates of GRBs lensed
by Pop III stars in the data by the {\it Swift} satellite.Comment: 13 pages, 13 figures, accepted for publication in Ap
Structure and evolution of circumbinary disks around supermassive black hole (SMBH) binaries
It is generally believed that gaseous disks around supermassive black hole
(SMBH) binaries in centers of galaxies can facilitate binary merger and give
rise to observational signatures both in electromagnetic and gravitational wave
domains. We explore general properties of circumbinary disks by reformulating
standard equations for the viscous disk evolution in terms of the viscous
angular momentum flux F_J. In steady state F_J is a linear function of the
specific angular momentum, which is a generalization of (but is not equivalent
to) the standard constant \dot M disk solution. If the torque produced by the
central binary is effective at stopping gas inflow and opening a gap (or
cavity) in the disk, then the inner part of the circumbinary disk can be
approximated as a constant F_J disk. We compute properties of such disks in
different physical regimes relevant for SMBH binaries and use these results to
understand the gas-assisted evolution of SMBH pairs starting at separations
10^{-4}-10^{-2} pc. We find the following. (1) Pile-up of matter at the inner
edge of the disk leads to continuous growth of the torque acting on the binary
and can considerably accelerate its orbital evolution compared to the
gravitational wave-driven decay. (2) Torque on the binary is determined
non-locally and does not in general reflect the disk properties in the vicinity
of the binary. (3) Binary evolution depends on the past history of the disk
evolution. (4) Eddington limit can be important in circumbinary disks even if
they accrete at sub-Eddington rates at late stages of binary evolution. (5)
Circumbinary disk self-consistently evolved under the action of the binary
torque emits more power and has spectrum different from the spectrum of
constant \dot M disk - it is steeper (\nu F_\nu\propto \nu^{12/7}) and extends
to shorter wavelength, facilitating its detection.Comment: Discussion of overflow across the orbit of the secondary added in
section 5.2.6. 23 pages, 10 figures, submitted to Ap
Ground-state energy and spin in disordered quantum dots
We investigate the ground-state energy and spin of disordered quantum dots
using spin-density-functional theory. Fluctuations of addition energies
(Coulomb-blockade peak spacings) do not scale with average addition energy but
remain proportional to level spacing. With increasing interaction strength, the
even-odd alternation of addition energies disappears, and the probability of
non-minimal spin increases, but never exceeds 50%. Within a two-orbital model,
we show that the off-diagonal Coulomb matrix elements help stabilize a ground
state of minimal spin.Comment: 10 pages, 2 figure
Superhumps in a Peculiar SU UMa-Type Dwarf Nova ER Ursae Majoris
We report the photometry of a peculiar SU UMa-type dwarf nova - ER UMa for
ten nights during 1998 December and 1999 March covering a complete rise to the
supermaximum and a normal outburst cycle. Superhumps have been found during the
rise to the superoutburst. A negative superhump appeared in Dec.22 light curve,
while the superhump on the next night became positive and had large amplitude
and distinct waveform from that of the previous night. In the normal outburst
we captured, superhumps with larger or smaller amplitudes seem to always exist,
although it is not necessarily true for every normal outburst. These results
show great resemblance with V1159 Ori (Patterson et al. 1995). It is more
likely that superhumps occasionally exist at essentially all phases of the
eruption cycles of ER UMa stars, which should be considered in modeling.Comment: 4 pages, 5 figures, Accepted by ApJ Letter
Density functional theory of spin-polarized disordered quantum dots
Using density functional theory, we investigate fluctuations of the ground
state energy of spin-polarized, disordered quantum dots in the metallic regime.
To compare to experiment, we evaluate the distribution of addition energies and
find a convolution of the Wigner-Dyson distribution, expected for noniteracting
electrons, with a narrower Gaussian distribution due to interactions. The tird
moment of the total distribution is independent of interactions, and so is
predicted to decrease by a factor of 0.405 upon application of a magnetic field
which transforms from the Gaussian orthogonal to the Gaussian unitary ensemble.Comment: 13 pages, 2 figure
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