12,782 research outputs found
Optical observations of NEA 162173 (1999 JU3) during the 2011-2012 apparition
Near-Earth asteroid 162173 (1999 JU3) is a potential target of two asteroid
sample return missions, not only because of its accessibility but also because
of the first C-type asteroid for exploration missions. The lightcurve-related
physical properties of this object were investigated during the 2011-2012
apparition. We aim to confirm the physical parameters useful for JAXA's
Hayabusa 2 mission, such as rotational period, absolute magnitude, and phase
function. Our data complement previous studies that did not cover low phase
angles. With optical imagers and 1-2 m class telescopes, we acquired the
photometric data at different phase angles. We independently derived the
rotational lightcurve and the phase curve of the asteroid. We have analyzed the
lightcurve of 162173 (1999 JU3), and derived a synodic rotational period of
7.625 +/- 0.003 h, the axis ratio a/b = 1.12. The absolute magnitude H_R =
18.69 +/- 0.07 mag and the phase slope of G = -0.09 +/- 0.03 were also obtained
based on the observations made during the 2011-2012 apparition.Comment: 4 pages, 3 figure
Compaction and dilation rate dependence of stresses in gas-fluidized beds
A particle dynamics-based hybrid model, consisting of monodisperse spherical
solid particles and volume-averaged gas hydrodynamics, is used to study
traveling planar waves (one-dimensional traveling waves) of voids formed in
gas-fluidized beds of narrow cross sectional areas. Through ensemble-averaging
in a co-traveling frame, we compute solid phase continuum variables (local
volume fraction, average velocity, stress tensor, and granular temperature)
across the waves, and examine the relations among them. We probe the
consistency between such computationally obtained relations and constitutive
models in the kinetic theory for granular materials which are widely used in
the two-fluid modeling approach to fluidized beds. We demonstrate that solid
phase continuum variables exhibit appreciable ``path dependence'', which is not
captured by the commonly used kinetic theory-based models. We show that this
path dependence is associated with the large rates of dilation and compaction
that occur in the wave. We also examine the relations among solid phase
continuum variables in beds of cohesive particles, which yield the same path
dependence. Our results both for beds of cohesive and non-cohesive particles
suggest that path-dependent constitutive models need to be developed.Comment: accepted for publication in Physics of Fluids (Burnett-order effect
analysis added
Quantum Numbers of Textured Hall Effect Quasiparticles
We propose a class of variational wave functions with slow variation in spin
and charge density and simple vortex structure at infinity, which properly
generalize both the Laughlin quasiparticles and baby Skyrmions. We argue that
the spin of the corresponding quasiparticle has a fractional part related in a
universal fashion to the properties of the bulk state, and propose a direct
experimental test of this claim. We show that certain spin-singlet quantum Hall
states can be understood as arising from primary polarized states by Skyrmion
condensation.Comment: 13 pages, no figures, Phyzz
Discovery of Coupling between Periodic and Aperiodic Variability and X-ray Quasi-periodic Oscillations from Her X-1
We report the discovery of coupling between periodic and aperiodic
variability and ~12-mHz X-ray quasi-periodic oscillations (QPOs) from the X-ray
binary pulsar Her X-1 using data from the Rossi X-Ray Timing Explorer. We found
two different couplings, one during the pre-eclipse dips and the other during
the normal state of the source, using a method which directly compares the
low-frequency power-density spectra (PDS) with those of the sidebands around
the coherent pulse frequency. The pre-eclipse dip lightcurves show significant
time variation of photon counts, and this variation appears in the PDS as both
strong mHz powers and well-developed sidebands around the coherent pulse
frequency. The linear correlation coefficients between the mHz PDS and the
sideband PDS obtained from two pre-eclipse dip data segments are 0.880 +- 0.003
and 0.982 +- 0.001, respectively. This very strong coupling demonstrates that
the amplitudes of the coherent pulsations are almost exactly modulated by the
aperiodic variabilities, suggesting that both the periodic and aperiodic
variabilities are related to time variation of obscuration of X-rays from the
central pulsar by an accretion disk during pre-eclipse dips. We also found weak
coupling during the normal state of the source, together with ~12-mHz QPOs. The
normal state coupling seems to reconcile with the prediction that the aperiodic
variabilities from X-ray binary pulsars are due to time-varying accretion flows
onto the pulsar's magnetic poles. If the ~12-mHz QPOs are due to global-normal
disk oscillations caused by the gravitational interactions between the central
pulsar and the accretion disk, the inferred inner-disk radius is roughly
comparable to the magnetospheric radius, ~1 10^8 cm.Comment: 13 pages (including 5 figures), submitted to ApJL (revised after
referee's report
The black hole final state for the Dirac fields In Schwarzschild spacetime
We show that the internal stationary state of a black hole for massless Dirac
fields can be represented by an entangled state of collapsing matter and
infalling Hawking radiation. This implies that the Horowitz-Maldacena
conjecture for the black hole final state originally proposed for the massless
scalar fields is also applicable to fermionic fields as well. For an initially
mixed state we find that the measure of mixedness is expected to decrease under
evaporation
Strain-controlled band engineering and self-doping in ultrathin LaNiO films
We report on a systematic study of the temperature-dependent Hall coefficient
and thermoelectric power in ultra-thin metallic LaNiO films that reveal a
strain-induced, self-doping carrier transition that is inaccessible in the
bulk. As the film strain varies from compressive to tensile at fixed
composition and stoichiometry, the transport coefficients evolve in a manner
strikingly similar to those of bulk hole-doped superconducting cuprates with
varying doping level. Density functional calculations reveal that the
strain-induced changes in the transport properties are due to self-doping in
the low-energy electronic band structure. The results imply that thin-film
epitaxy can serve as a new means to achieve hole-doping in other (negative)
charge-transfer gap transition metal oxides without resorting to chemical
substitution
Lorenz-like systems and classical dynamical equations with memory forcing: a new point of view for singling out the origin of chaos
A novel view for the emergence of chaos in Lorenz-like systems is presented.
For such purpose, the Lorenz problem is reformulated in a classical mechanical
form and it turns out to be equivalent to the problem of a damped and forced
one dimensional motion of a particle in a two-well potential, with a forcing
term depending on the ``memory'' of the particle past motion. The dynamics of
the original Lorenz system in the new particle phase space can then be
rewritten in terms of an one-dimensional first-exit-time problem. The emergence
of chaos turns out to be due to the discontinuous solutions of the
transcendental equation ruling the time for the particle to cross the
intermediate potential wall. The whole problem is tackled analytically deriving
a piecewise linearized Lorenz-like system which preserves all the essential
properties of the original model.Comment: 48 pages, 25 figure
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