1,942 research outputs found
Thermal stress response of General Purpose Heat Source (GPHS) aeroshell material
A thermal stress test was conducted to determine the ability of the GPHS aeroshell 3 D FWPF material to maintain physical integrity when exposed to a severe heat flux such as would occur from prompt reentry of GPHS modules. The test was performed in the Giant Planetary Facility at NASA's Ames Research Center. Good agreement was obtained between the theoretical and experimental results for both temperature and strain time histories. No physical damage was observed in the test specimen. These results provide initial corroboration both of the analysis techniques and that the GPHS reentry member will survive the reentry thermal stress levels expected
Degradation and reuse of radiative thermal protection system materials for the space shuttle
Three silicide coated columbium alloys and two cobalt alloys were subjected to identical simulated reentry profiling exposures in both static (controlled vacuum leak) and dynamic (hypersonic plasma shear) environments. Primary emphasis in the columbium alloy evaluation was on the Cb752 and C129Y alloys with a lesser amount on FS85. Commercial silicide coatings of the R512E and VH109 formulations were used. The coated specimens were intentionally defected to provide the types of coating flaws that are expected in service. Temperatures were profiled up to peak temperatures of either 2350 F or 2500 F for 15 minutes in each cycle
X-ray Reflection Spectroscopy of the Black Hole GX 339-4: Exploring the Hard State with Unprecedented Sensitivity
We analyze {\it simultaneously} six composite {\it RXTE} spectra of GX 339--4
in the hard state comprising 77 million counts collected over 196 ks. The
source spectra are ordered by luminosity and spanthe range 1.6\% to 17\% of the
Eddington luminosity. Crucially, using our new tool {\tt pcacorr}, we
re-calibrate the data to a precision of 0.1\%, an order of magnitude
improvement over all earlier work. Using our advanced reflection model {\tt
relxill}, we target the strong features in the component of emission reflected
from the disk, namely, the relativistically-broadened Fe K emission line, the
Fe K edge and the Compton hump. We report results for two joint fits to the six
spectra: For the first fit, we fix the spin parameter to its maximal value
() and allow the inner disk radius to vary. Results
include (i) precise measurements of , with evidence that the disk
becomes slightly truncated at a few percent of Eddington; and (ii) an
order-of-magnitude swing with luminosity in the high energy cutoff, which
reaches keV at our lowest luminosity. For the second fit, we make the
standard assumption in estimating spin that the inner edge of the accretion
disk is located at the innermost stable circular orbit () and find (90\% confidence,
statistical). For both fits, and at the same level of statistical confidence,
we estimate that the disk inclination is deg and that the Fe
abundance is super-solar, .Comment: Accepted for publication in ApJ, 20 pages, 13 figure
Photovoltage in curved 1D systems
Curvature of quantum wire results in intrasubband absorption of
IR radiation that induces stationary photovoltage in presence of circular
polarization. This effect is studied in ballistic (collisionless) and kinetic
regimes. The consideration is concentrated on quantum wires with curved central
part. It is shown, that if mean free path is shorter than length of the curved
part the photovoltage does not depend on the wire shape, but on the total angle
of rotation of wire tangent. It is not the case when mean free path is finite
or large. This situation was studied for three specific shapes of wires: "hard
angle", "open book" and "-like".Comment: 12 pages, 1 figur
Saturation of a nonuniformly broadened line under phonon bottleneck conditions
Using the methods of nonequilibrium statistics, equations are obtained that describe the saturation of a nonuniformly broadened ESR line taking into account the phenomenon of spectral diffusion under phonon bottleneck conditions. It is shown that the width and depth of the "holes," burnt out by the saturation in the line, increase as the phonon bottleneck sector increases. The temperature dependence of the width of the "holes" burnt out in the line is studied. © 1979 Plenum Publishing Corporation
Estimates for measures of sections of convex bodies
A estimate in the hyperplane problem with arbitrary measures has
recently been proved in \cite{K3}. In this note we present analogs of this
result for sections of lower dimensions and in the complex case. We deduce
these inequalities from stability in comparison problems for different
generalizations of intersection bodies
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