29,066 research outputs found
Brayton heat exchanger unit development program (alternate design)
A Brayton Heat Exchanger Unit Alternate Design (BHXU-Alternate) consisting of a recuperator, a heat sink heat exchanger, and a gas ducting system, was designed and fabricated. The design was formulated to provide a high performance unit suitable for use in a long-life Brayton-cycle powerplant. Emphasis was on double containment against external leakage and leakage of the organic coolant into the gas stream. A parametric analysis and design study was performed to establish the optimum component configurations to achieve low weight and size and high reliability, while meeting the requirements of high effectiveness and low pressure drop. Layout studies and detailed mechanical and structural design were performed to obtain a flight-type packaging arrangement, including the close-coupled integration of the BHXU-Alternate with the Brayton Rotating Unit (BRU)
Low-cycle fatigue evaluation for regeneratively cooled panels
Design data for regeneratively cooled panels from low cycle fatigue evaluation of Hastelloy X and Inconel 625 sheet and sandwich panel specimen
Large-area sheet task: Advanced dendritic-web-growth development
Thermally generated stresses in the growing web crystal were reduced. These stresses, which if too high cause the ribbon to degenerate, were reduced by a factor of three, resulting in the demonstrated growth of high-quality web crystals to widths of 5.4 cm. This progress was brought about chiefly by the application of thermal models to the development of low-stress growth configurations. A new temperature model was developed which can analyze the thermal effects of much more complex lid and top shield configurations than was possible with the old lumped shield model. Growth experiments which supplied input data such as actual shield temperature and melt levels were used to verify the modeling results. Desirable modifications in the melt level-sensing circuitry were made in the new experimental web growth furnace, and this furnace has been used to carry out growth experiments under steady-state conditions. New growth configurations were tested in long growth runs at Westinghouse AESD which produced wider, lower stress and higher quality web crystals than designs previously used
Prospective Analysis Spin- and CP-sensitive Variables in H -> ZZ -> l_1 l_1 l_2 l_2 with Atlas
A possibility to prove spin and CP-eigenvalue of a Standard Model (SM) Higgs
boson is presented. We exploit angular correlations in the subsequent decay H
-> ZZ -> 4l (muons or electrons) for Higgs masses above 200 GeV. We compare the
angular distributions of the leptons originating from the SM Higgs with those
resulting from decays of hypothetical particles with differing quantum numbers.
We restrict our analysis to the use of the Atlas-detector which is one of two
multi-purpose detectors at the upcoming 14 TeV proton-proton-collider (LHC) at
CERN. By applying a fast simulation of the Atlas detector it can be shown that
these correlations will be measured sufficiently well that consistency with the
spin-CP hypothesis 0+ of the Standard Model can be verified and the 0- and 1+-
can be ruled out with an integrated luminosity of 100 fb^-1.Comment: 25 pages, 9 figures Version 2: Minor changes made as requested by
Atlas referee and Springer editor. Added a chapter where background
subtraction is detaile
New Hope for the Working Poor: Effects After Eight Years for Families and Children
Implemented in 1994 in Milwaukee, New Hope provided full-time, low-wage workers with several benefits for three years: an earnings supplement, low-cost health insurance, and subsidized child care. A random assignment study shows positive effects for both adults and children, some of which persisted five years after the program ended
Physical Mechanisms for the Variable Spin-down of SGR 1900+14
We consider the physical implications of the rapid spindown of Soft Gamma
Repeater 1900+14, and of the apparent "braking glitch", \Delta P/P = l x 10^-4,
that was concurrent with the Aug. 27th giant flare. A radiation-hydrodynamical
outflow associated with the flare could impart the required torque, but only if
the dipole magnetic field is stronger than ~ 10^14 G and the outflow lasts
longer and/or is more energetic than the observed X-ray flare. A positive
period increment is also a natural consequence of a gradual, plastic
deformation of the neutron star crust by an intense magnetic field, which
forces the neutron superfluid to rotate more slowly than the crust. Sudden
unpinning of the neutron vortex lines during the August 27th event would then
induce a glitch opposite in sign to those observed in young pulsars, but of a
much larger magnitude as a result of the slower rotation.
The change in the persistent X-ray lightcurve following the August 27 event
is ascribed to continued particle heating in the active region of that
outburst. The enhanced X-ray output can be powered by a steady current flowing
through the magnetosphere, induced by the twisting motion of the crust. The
long term rate of spindown appears to be accelerated with respect to a simple
magnetic dipole torque. Accelerated spindown of a seismically-active magnetar
will occur when its persistent output of Alfven waves and particles exceeds its
spindown luminosity. We suggest that SGRs experience some episodes of relative
inactivity, with diminished spindown rates, and that such inactive magnetars
are observed as Anomalous X-ray Pulsars (AXPs). The rapid reappearence of
persistent X-ray emission following August 27 flare gives evidence against
accretion-powered models.Comment: 24 pages, no figure
Large-area sheet task advanced dendritic web growth development
The thermal models used for analyzing dendritic web growth and calculating the thermal stress were reexamined to establish the validity limits imposed by the assumptions of the models. Also, the effects of thermal conduction through the gas phase were evaluated and found to be small. New growth designs, both static and dynamic, were generated using the modeling results. Residual stress effects in dendritic web were examined. In the laboratory, new techniques for the control of temperature distributions in three dimensions were developed. A new maximum undeformed web width of 5.8 cm was achieved. A 58% increase in growth velocity of 150 micrometers thickness was achieved with dynamic hardware. The area throughput goals for transient growth of 30 and 35 sq cm/min were exceeded
Planets in Spin-Orbit Misalignment and the Search for Stellar Companions
The discovery of giant planets orbiting close to their host stars was one of
the most unexpected results of early exoplanetary science. Astronomers have
since found that a significant fraction of these 'Hot Jupiters' move on orbits
substantially misaligned with the rotation axis of their host star. We recently
reported the measurement of the spin-orbit misalignment for WASP-79b by using
data from the 3.9 m Anglo-Australian Telescope. Contemporary models of
planetary formation produce planets on nearly coplanar orbits with respect to
their host star's equator. We discuss the mechanisms which could drive planets
into spin-orbit misalignment. The most commonly proposed being the Kozai
mechanism, which requires the presence of a distant, massive companion to the
star-planet system. We therefore describe a volume-limited direct-imaging
survey of Hot Jupiter systems with measured spin-orbit angles, to search for
the presence of stellar companions and test the Kozai hypothesis.Comment: Accepted for publication in the peer-reviewed proceedings of the 13th
annual Australian Space Science Conferenc
The (In)Stability of Planetary Systems
We present results of numerical simulations which examine the dynamical
stability of known planetary systems, a star with two or more planets. First we
vary the initial conditions of each system based on observational data. We then
determine regions of phase space which produce stable planetary configurations.
For each system we perform 1000 ~1 million year integrations. We examine
upsilon And, HD83443, GJ876, HD82943, 47UMa, HD168443, and the solar system
(SS). We find that the resonant systems, 2 planets in a first order mean motion
resonance, (HD82943 and GJ876) have very narrow zones of stability. The
interacting systems, not in first order resonance, but able to perturb each
other (upsilon And, 47UMa, and SS) have broad regions of stability. The
separated systems, 2 planets beyond 10:1 resonance, (we only examine HD83443
and HD168443) are fully stable. Furthermore we find that the best fits to the
interacting and resonant systems place them very close to unstable regions. The
boundary in phase space between stability and instability depends strongly on
the eccentricities, and (if applicable) the proximity of the system to perfect
resonance. In addition to million year integrations, we also examined stability
on ~100 million year timescales. For each system we ran ~10 long term
simulations, and find that the Keplerian fits to these systems all contain
configurations which may be regular on this timescale.Comment: 37 pages, 49 figures, 13 tables, submitted to Ap
Optimal indicators of socioeconomic status for health research
Objectives: This paper examines the relationship between various measures of SES and mortality for a representative sample of individuals. ; Methods: Data are from the Panel Study of Income Dynamics. Sample includes 3,734 individuals aged 45 and above who participated in the 1984 interview. Mortality was tracked between 1984 and 1994 and is related to SES indicators using Cox event-history regression models. ; Results: Wealth has the strongest associations with subsequent mortality, and these associations differ little by age and sex. Other economic measures, especially family-size-adjusted household income, have significant associations with mortality, particularly for nonelderly women. ; Conclusions: By and large, the economic components of SES have associations with mortality that are at least as strong as, and often stronger than, more conventional components (e.g., completed schooling, occupation).Income distribution
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