644 research outputs found
Measuring eccentricity in binary black-hole initial data
Initial data for evolving black-hole binaries can be constructed via many
techniques, and can represent a wide range of physical scenarios. However,
because of the way that different schemes parameterize the physical aspects of
a configuration, it is not alway clear what a given set of initial data
actually represents. This is especially important for quasiequilibrium data
constructed using the conformal thin-sandwich approach. Most initial-data
studies have focused on identifying data sets that represent binaries in
quasi-circular orbits. In this paper, we consider initial-data sets
representing equal-mass black holes binaries in eccentric orbits. We will show
that effective-potential techniques can be used to calibrate initial data for
black-hole binaries in eccentric orbits. We will also examine several different
approaches, including post-Newtonian diagnostics, for measuring the
eccentricity of an orbit. Finally, we propose the use of the ``Komar-mass
difference'' as a useful, invariant means of parameterizing the eccentricity of
relativistic orbits.Comment: 12 pages, 11 figures, submitted to Physical Review D, revtex
Delta nitrogen tetroxide fueling operations
The development of the Delta second stage nitrogen tetroxide fueling system is briefly summarized. The nitrogen tetroxide fueling system and the equipment used to protect the spacecraft environment from the toxic nitrogen tetroxide fumes are described. Topics covered include: the nitrogen tetroxide transfer system; loading operations; safety precautions; and chemical treatment of all toxic vapors
Development of fuel cell electrodes, Electrode improvement and life testing, tasks 1 and 3 Final report, 30 Jun. 1966 - 30 Apr. 1968
Volt-ampere characteristics improvement and life testing of electrodes for hydrogen oxygen fuel cell
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Development Of Third Harmonic Generation As A Short Pulse Probe Of Shock Heated Material
We are studying high-pressure laser produced shock waves in silicon (100). To examine the material dynamics, we are performing pump-probe style experiments utilizing 600 ps and 40 fs laser pulses from a Ti:sapphire laser. Two-dimensional interferometry reveals information about the shock breakout, while third harmonic light generated at the rear surface is used to infer the crystalline state of the material as a function of time. Sustained third harmonic generation (THG) during a similar to 100 kbar shock breakout indicate that the rear surface remains crystalline for at least 3 ns. However, a decrease in THG during a similar to 300 kbar shock breakout suggests a different behavior, which could include a change in crystalline structure.Mechanical Engineerin
Circular orbits and spin in black-hole initial data
The construction of initial data for black-hole binaries usually involves the
choice of free parameters that define the spins of the black holes and
essentially the eccentricity of the orbit. Such parameters must be chosen
carefully to yield initial data with the desired physical properties. In this
paper, we examine these choices in detail for the quasiequilibrium method
coupled to apparent-horizon/quasiequilibrium boundary conditions. First, we
compare two independent criteria for choosing the orbital frequency, the
"Komar-mass condition" and the "effective-potential method," and find excellent
agreement. Second, we implement quasi-local measures of the spin of the
individual holes, calibrate these with corotating binaries, and revisit the
construction of non-spinning black hole binaries. Higher-order effects, beyond
those considered in earlier work, turn out to be important. Without those,
supposedly non-spinning black holes have appreciable quasi-local spin;
furthermore, the Komar-mass condition and effective potential method agree only
when these higher-order effects are taken into account. We compute a new
sequence of quasi-circular orbits for non-spinning black-hole binaries, and
determine the innermost stable circular orbit of this sequence.Comment: 24 pages, 17 figures, accepted for publication in Physical Review D,
revtex4; Fixed error in computing proper separation and updated figures and
tables accordingly, added reference to Sec. IV.A, fixed minor error in Sec.
IV.B, added new data to Tables IV and V, fixed 1 reference, fixed error in
Eq. (A7b), included minor changes from PRD editin
Cultural Stressors, Identity Development, and Substance Use Attitudes Among Hispanic Immigrant Adolescents
The goal of this investigation was to determine whether various cultural stressors (bicultural stress, perceived discrimination, and perceived negative context of reception [PNCR]) predict positive and negative substance use attitudes, directly and indirectly through personal identity, in a sample of immigrant Hispanic adolescents. Data on cultural stressors, substance use attitudes, and covariates were collected from 302 Hispanic immigrant adolescents (152 from Miami [61% Cuban] and 150 from Los Angeles [70% Mexican]) at 3 time points. PNCR was associated with identity confusion (=.175, p=.033). Identity confusion significantly predicted higher positive attitudes toward alcohol and other drug (AOD; =.216, p\u3c.001) and cigarette use (=.191, p=.015) and mediated the relationship between PNCR with unfavorable AOD attitudes ( =-.019, 95% confidence interval [CI] [-0.052,-0.001]) and favorable AOD attitudes (=0.038, 95% CI [0.003, 0.086]). Perceptions of a negative context of reception may hinder successful personal identity formation and impact health outcomes for immigrant youth
Toward a dynamical shift condition for unequal mass black hole binary simulations
Moving puncture simulations of black hole binaries rely on a specific gauge
choice that leads to approximately stationary coordinates near each black hole.
Part of the shift condition is a damping parameter, which has to be properly
chosen for stable evolutions. However, a constant damping parameter does not
account for the difference in mass in unequal mass binaries. We introduce a
position dependent shift damping that addresses this problem. Although the
coordinates change, the changes in the extracted gravitational waves are small.Comment: 15 pages, submitted to CQG for NRDA 2009 conference proceeding
Economic evaluation strategies in telehealth: obtaining a more holistic valuation of telehealth interventions
Telehealth is an emerging area of medical research. Its translation from conception, to research and into practice requires tailored research and economic evaluation methods. Due to their nature telehealth interventions exhibit a number of extra-clinical benefits that are relevant when valuing their costs and outcomes. By incorporating methods to measure societal values such as patient preference and willingness-to-pay, a more holistic value can be placed on the extra-clinical outcomes associated with telehealth and evaluations can represent new interventions more effectively. Cost-benefit analysis is a method by which relevant costs and outcomes in telehealth can be succinctly valued and compared. When health economic methods are conducted using holistic approaches such as cost-benefit analysis they can facilitate the translation of telehealth research into policy and practice
Khovanov homology is an unknot-detector
We prove that a knot is the unknot if and only if its reduced Khovanov
cohomology has rank 1. The proof has two steps. We show first that there is a
spectral sequence beginning with the reduced Khovanov cohomology and abutting
to a knot homology defined using singular instantons. We then show that the
latter homology is isomorphic to the instanton Floer homology of the sutured
knot complement: an invariant that is already known to detect the unknot.Comment: 124 pages, 13 figure
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