1,034 research outputs found
Grain Physics and Rosseland Mean Opacities
Tables of mean opacities are often used to compute the transfer of radiation
in a variety of astrophysical simulations from stellar evolution models to
proto-planetary disks. Often tables, such as Ferguson et al. (2005), are
computed with a predetermined set of physical assumptions that may or may not
be valid for a specific application. This paper explores the effects of several
assumptions of grain physics on the Rosseland mean opacity in an oxygen rich
environment. We find that changing the distribution of grain sizes, either the
power-law exponent or the shape of the distribution, has a marginal effect on
the total mean opacity. We also explore the difference in the mean opacity
between solid homogenous grains and grains that are porous or conglomorations
of several species. Changing the amount of grain opacity included in the mean
by assuming a grain-to-gas ratio significantly affects the mean opacity, but in
a predictable way.Comment: 19 pages, 6 figures, accepted for publication in Ap
Generalized constraints on quantum amplification
We derive quantum constraints on the minimal amount of noise added in linear
amplification involving input or output signals whose component operators do
not necessarily have c-number commutators, as is the case for fermion currents.
This is a generalization of constraints derived for the amplification of
bosonic fields whose components posses c-number commutators.Comment: 4 pages, 1 figure, submitted to Physical Review Letter
Novel dynamic scaling regime in hole-doped La2CuO4
Only 3% hole doping by Li is sufficient to suppress the long-range
3-dimensional (3D) antiferromagnetic order in La2CuO4.
The spin dynamics of such a 2D spin liquid state at T << J was investigated
with measurements of the dynamic magnetic structure factor S(omega,q), using
cold neutron spectroscopy, for single crystalline La2Cu0.94Li0.06O4.
S(omega,q) peaks sharply at (pi,pi) and crosses over around 50K from omega/T
scaling to a novel low temperature regime characterized by a constant energy
scale. The possible connection to a crossover from the quantum critical to the
quantum disordered regime of the 2D antiferromagnetic spin liquid is discussed.Comment: 4 pages, 4 figure
PERIOD DETERMINATION FOR NEA (162421) 2000 ET70
Lightcurve analysis for (162421) 2000 ET70 was performed in collaboration with observers in Uruguay, Australia, and the United States from observations obtained during the asteroid’s favorable opposition in 2012. The synodic rotation period was found to be 8.947 ± 0.001 h and the lightcurve amplitude was 0.60 ± 0.07 mag
Imaging Three Dimensional Two-particle Correlations for Heavy-Ion Reaction Studies
We report an extension of the source imaging method for analyzing
three-dimensional sources from three-dimensional correlations. Our technique
consists of expanding the correlation data and the underlying source function
in spherical harmonics and inverting the resulting system of one-dimensional
integral equations. With this strategy, we can image the source function
quickly, even with the finely binned data sets common in three-dimensional
analyses.Comment: 13 pages, 11 figures, submitted to Physical Review
Identification of Non-unitary triplet pairing in a heavy Fermion superconductor UPt_3
A NMR experiment recently done by Tou et al. on a heavy Fermion
superconductor UPt is interpreted in terms of a non-unitary spin-triplet
pairing state which we have been advocating. The proposed state successfully
explains various aspects of the seemingly complicated Knight shift behaviors
probed for major orientations, including a remarkable d-vector rotation under
weak fields. This entitles UPt as the first example that a charged many
body system forms a spin-triplet odd-par ity pairing at low temperatures and
demonstrates unambiguously that the putative spin-orbit coupling in UPt is
weak.Comment: 4 pages, 2 eps figures, to be published in J. Phys. Soc. Jpn. 67
(1998) No.
Pd/Cu Site Interchange and Non-Fermi-Liquid Behavior in UCu_4Pd
X-ray-absorption fine-structure measurements of the local structure in
UCu_4Pd are described which indicate a probable lattice-disorder origin for
non-Fermi-liquid behavior in this material. Short Pd-Cu distances are observed,
consistent with 24 +/- 3% of the Pd atoms occupying nominally Cu sites. A
"Kondo disorder" model, based on the effect on the local Kondo temperature T_K
of this interchange and some additional bond-length disorder, agrees
quantitatively with previous experimental susceptibility data, and therefore
also with specific heat and magnetic resonance experiments.Comment: 4 pages, 3 PostScript figures, to be published in PR
8077 HOYLE: A SHORT PERIOD ASTEROID
The main-belt asteroid 8077 Hoyle was observed on 13 nights over a span of 47 days in 2012 April-May. A bimodal synodic period of 2.7454 ± 0.0002 h and an amplitude of 0.20 ± 0.02 mag. were obtained
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