1,332 research outputs found
Ultraviolet jets and bright points in the solar chromosphere : II : statistical correlations
We use HRTS{VI rocket observations of the solar chromosphere to search
for relationships between high-Dopplershift \jets" observed in the CI lines near
= 156 nm and internetwork \bright points" observed in the = 160 nm continuum,
in sequel to the analysis by Cook et al. (1996) which failed to find a direct
connection between these phenomena. We now use the same data to establish
statistical correlations between CI Dopplershift and 160 nm brightness modulation
in internetwork areas. These mean relations emerge only after extensive spatial
averaging and have small amplitude, but are definitely significant. They show that
both CI Dopplershift and 160 nm brightness participate in oscillatory behavior with
three-minute periodicity and mesoscale (8 Mm wavelength) as well as small-scale
(1.4 Mm wavelength) spatial patterning. We find spatial and temporal phase relations
between Dopplershift and brightness that confirm that jets and bright points should
not be interpreted as isolated entities. Rather, they are chromospheric manifestations,
with much pattern interference, of the oscillatory acoustic shock dynamics in the
internetwork which also cause Ca II K2V grains. Additional small-scale modulation is
present which we attribute to waves with f-mode character
Ultraviolet jets and bright points in the solar chromosphere: I : search for one-to-one relationships
Ultraviolet spectrograms and spectroheliograms of the solar chromosphere are
used to test the suggestion (Dere et al. 1986, Rutten & Uitenbroek 1991a) that
bright points observed at h = 1600 Ă…, chromospheric jets observed in CI lines
near h = 1560 Ă…, and Ca II K2V bright points are associated with each other and
that they are all manifestations of the same wave interaction in the non-magnetic
chromosphere. We search for spatio-temporal connections between 1600 Ă… bright
points and CI blue jets using data from the HRTS VI rocket mission, comparing
1600 Ă… spectroheliograms and a co-spatial CI Dopplershift map on a pixel-by-pixel
basis. We find no direct evidence for spatial co-location of bright points and jets, not
for instantaneous correspondence and also not when allowing for phase delays as long
as three minutes. Also, the average brightness evolution and its rms uctuation are
not obviously different between sites of large CI blueshift and the remaining surface
Corotating and irrotational binary black holes in quasi-circular orbits
A complete formalism for constructing initial data representing black-hole
binaries in quasi-equilibrium is developed. Radiation reaction prohibits, in
general, true equilibrium binary configurations. However, when the timescale
for orbital decay is much longer than the orbital period, a binary can be
considered to be in quasi-equilibrium. If each black hole is assumed to be in
quasi-equilibrium, then a complete set of boundary conditions for all initial
data variables can be developed. These boundary conditions are applied on the
apparent horizon of each black hole, and in fact force a specified surface to
be an apparent horizon. A global assumption of quasi-equilibrium is also used
to fix some of the freely specifiable pieces of the initial data and to
uniquely fix the asymptotic boundary conditions. This formalism should allow
for the construction of completely general quasi-equilibrium black hole binary
initial data.Comment: 13 pages, no figures, revtex4; Content changed slightly to reflect
fact that regularized shift solutions do satisfy the isometry boundary
condition
Extrinsic Curvature and the Einstein Constraints
The Einstein initial-value equations in the extrinsic curvature (Hamiltonian)
representation and conformal thin sandwich (Lagrangian) representation are
brought into complete conformity by the use of a decomposition of symmetric
tensors which involves a weight function. In stationary spacetimes, there is a
natural choice of the weight function such that the transverse traceless part
of the extrinsic curvature (or canonical momentum) vanishes.Comment: 8 pages, no figures; added new section; significant polishing of tex
Gauge conditions for binary black hole puncture data based on an approximate helical Killing vector
We show that puncture data for quasicircular binary black hole orbits allow a
special gauge choice that realizes some of the necessary conditions for the
existence of an approximate helical Killing vector field. Introducing free
parameters for the lapse at the punctures we can satisfy the condition that the
Komar and ADM mass agree at spatial infinity. Several other conditions for an
approximate Killing vector are then automatically satisfied, and the 3-metric
evolves on a timescale smaller than the orbital timescale. The time derivative
of the extrinsic curvature however remains significant. Nevertheless,
quasicircular puncture data are not as far from possessing a helical Killing
vector as one might have expected.Comment: 11 pages, 6 figures, 2 table
Comparing initial-data sets for binary black holes
We compare the results of constructing binary black hole initial data with
three different decompositions of the constraint equations of general
relativity. For each decomposition we compute the initial data using a
superposition of two Kerr-Schild black holes to fix the freely specifiable
data. We find that these initial-data sets differ significantly, with the ADM
energy varying by as much as 5% of the total mass. We find that all
initial-data sets currently used for evolutions might contain unphysical
gravitational radiation of the order of several percent of the total mass. This
is comparable to the amount of gravitational-wave energy observed during the
evolved collision. More astrophysically realistic initial data will require
more careful choices of the freely specifiable data and boundary conditions for
both the metric and extrinsic curvature. However, we find that the choice of
extrinsic curvature affects the resulting data sets more strongly than the
choice of conformal metric.Comment: 18 pages, 12 figures, accepted for publication in Phys. Rev.
Collaborative International Research in Clinical and Longitudinal Experience Study in NMOSD
Objective
To develop a resource of systematically collected, longitudinal clinical data and biospecimens for assisting in the
investigation into neuromyelitis optica spectrum disorder (NMOSD) epidemiology, pathogenesis, and treatment.
Methods
To illustrate its research-enabling purpose, epidemiologic patterns and disease phenotypes were assessed among enrolled
subjects, including age at disease onset, annualized relapse rate (ARR), and time between the first and second attacks.
Results
As of December 2017, the Collaborative International Research in Clinical and Longitudinal Experience Study
(CIRCLES) had enrolled more than 1,000 participants, of whom 77.5% of the NMOSD cases and 71.7% of the
controls continue in active follow-up. Consanguineous relatives of patients with NMOSD represented 43.6% of the
control cohort. Of the 599 active cases with complete data, 84% were female, and 76% were anti-AQP4 seropositive.
The majority were white/Caucasian (52.6%), whereas blacks/African Americans accounted for 23.5%, Hispanics/
Latinos 12.4%, and Asians accounted for 9.0%. The median age at disease onset was 38.4 years, with a median ARR of
0.5. Seropositive cases were older at disease onset, more likely to be black/African American or Hispanic/Latino, and
more likely to be female.
Conclusions
Collectively, the CIRCLES experience to date demonstrates this study to be a useful and readily accessible resource to
facilitate accelerating solutions for patients with NMOSD
Comparing Criteria for Circular Orbits in General Relativity
We study a simple analytic solution to Einstein's field equations describing
a thin spherical shell consisting of collisionless particles in circular orbit.
We then apply two independent criteria for the identification of circular
orbits, which have recently been used in the numerical construction of binary
black hole solutions, and find that both yield equivalent results. Our
calculation illustrates these two criteria in a particularly transparent
framework and provides further evidence that the deviations found in those
numerical binary black hole solutions are not caused by the different criteria
for circular orbits.Comment: 4 pages; to appear in PRD as a Brief Report; added and corrected
reference
Binary black hole initial data for numerical general relativity based on post-Newtonian data
With the goal of taking a step toward the construction of astrophysically
realistic initial data for numerical simulations of black holes, we for the
first time derive a family of fully general relativistic initial data based on
post-2-Newtonian expansions of the 3-metric and extrinsic curvature without
spin. It is expected that such initial data provide a direct connection with
the early inspiral phase of the binary system. We discuss a straightforward
numerical implementation, which is based on a generalized puncture method.
Furthermore, we suggest a method to address some of the inherent ambiguity in
mapping post-Newtonian data onto a solution of the general relativistic
constraints.Comment: 13 pages, 8 figures, RevTex
Time-symmetric initial data for binary black holes in numerical relativity
We look for physically realistic initial data in numerical relativity which
are in agreement with post-Newtonian approximations. We propose a particular
solution of the time-symmetric constraint equation, appropriate to two
momentarily static black holes, in the form of a conformal decomposition of the
spatial metric. This solution is isometric to the post-Newtonian metric up to
the 2PN order. It represents a non-linear deformation of the solution of Brill
and Lindquist, i.e. an asymptotically flat region is connected to two
asymptotically flat (in a certain weak sense) sheets, that are the images of
the two singularities through appropriate inversion transformations. The total
ADM mass M as well as the individual masses m_1 and m_2 (when they exist) are
computed by surface integrals performed at infinity. Using second order
perturbation theory on the Brill-Lindquist background, we prove that the
binary's interacting mass-energy M-m_1-m_2 is well-defined at the 2PN order and
in agreement with the known post-Newtonian result.Comment: 27 pages, to appear in Phys. Rev.
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