22,644 research outputs found
SSME main combustion chamber life prediction
Typically, low cycle fatigue life is a function of the cyclic strain range, the material properties, and the operating temperature. The reusable life is normally defined by the number of strain cycles that can be accrued before severe material degradation occurs. Reusable life is normally signified by the initiation or propagation of surface cracks. Hot-fire testing of channel wall combustors has shown significant mid-channel wall thinning or deformation during accrued cyclic testing. This phenomenon is termed cyclic-creep and appears to be significantly accelerated at elevated surface temperatures. This failure mode was analytically modelled. The cyclic life of the baseline SSME-MCC based on measured calorimeter heat transfer data, and the life sensitivity of local hot spots caused by injector effects were determined. Four life enhanced designs were assessed
Results of AC loss tests on twisted and untwisted HTSC tape exposed to an external field
This paper presents the results of magnetic losstests on twisted and untwisted 37 multifilaments tapes exposed to an alternating field at power frequencies. The losses are measured using calorimetric methods, which are capable of measuring losses in short tapes with the accuracy of several microwatts per centimeter of tape. The losses of the tape due to the longitudinal field of the untwisted tape agree well with theoretical calculations. The measurement results on the twisted filament tape, with 50-mm twist pitch, show that the losses are slightly lower than that in the untwisted tape. This is due to the reduction of the coupling losses between the filaments in the tape. It is also shown that in the presence of normal fields, the losses are about one order higher than for longitudinal fields because of the anisotropic properties of the superconducting parts and because of the existence of eddy current loss in the silver sheath
Development of Uniform CdTe Pixel Detectors Based on Caltech ASIC
We have developed a large CdTe pixel detector with dimensions of 23.7 x 13.0
mm and a pixel size of 448 x 448 um^2. The detector is based on recent
technologies of an uniform CdTe single crystal, a two-dimensional ASIC, and
stud bump-bonding to connect pixel electrodes on the CdTe surface to the ASIC.
Good spectra are obtained from 1051 pixels out of total 1056 pixels. When we
operate the detector at -50 C, the energy resolution is 0.67 keV and 0.99 keV
at 14 keV and 60 keV, respectively. Week-long stability of the detector is
confirmed at operating temperatures of both -50 C and -20 C. The detector also
shows high uniformity: the peak positions for all pixels agree to within 0.82%,
and the average of the energy resolution is 1.04 keV at a temperature of -50 C.
When we normalized the peak area by the total counts detected by each pixel, a
variation of 2.1 % is obtained.Comment: 11pages, 17figures, accepted for publication in Proc. SPIE 200
Can a combination of the conformal thin-sandwich and puncture methods yield binary black hole solutions in quasi-equilibrium?
We consider combining two important methods for constructing
quasi-equilibrium initial data for binary black holes: the conformal
thin-sandwich formalism and the puncture method. The former seeks to enforce
stationarity in the conformal three-metric and the latter attempts to avoid
internal boundaries, like minimal surfaces or apparent horizons. We show that
these two methods make partially conflicting requirements on the boundary
conditions that determine the time slices. In particular, it does not seem
possible to construct slices that are quasi-stationary and avoid physical
singularities and simultaneously are connected by an everywhere positive lapse
function, a condition which must obtain if internal boundaries are to be
avoided. Some relaxation of these conflicting requirements may yield a soluble
system, but some of the advantages that were sought in combining these
approaches will be lost.Comment: 8 pages, LaTeX2e, 2 postscript figure
Combined observations of meteors by image-orthicon television camera and multi-station radar
Observations from multiple sites of a radar network and by television of 29 individual meteors from February 1969 through June 1970 are reported. Only 12 of the meteors did not appear to fragment over all the observed portion of their trajectories. From these 12, the relation for the radar magnitude to the panchromatic absolute magnitude was found in terms of velocity of the meteor. A very tentative fit to the data on the duration of long enduring echoes versus visual absolute magnitude is made. The exponential decay characteristics of the later parts of several of the light curves are pointed out as possible evidence of mutual coalescence of droplets into which the meteoroid has completely broken
Detection Techniques of Microsecond Gamma-Ray Bursts using Ground-Based Telescopes
Gamma-ray observations above 200 MeV are conventionally made by
satellite-based detectors. The EGRET detector on the Compton Gamma Ray
Observatory (CGRO) has provided good sensitivity for the detection of bursts
lasting for more than 200 ms. Theoretical predictions of high-energy gamma-ray
bursts produced by quantum-mechanical decay of primordial black holes (Hawking
1971) suggest the emission of bursts on shorter time scales. The final stage of
a primordial black hole results in a burst of gamma-rays, peaking around 250
MeV and lasting for a tenth of a microsecond or longer depending on particle
physics. In this work we show that there is an observational window using
ground-based imaging Cherenkov detectors to measure gamma-ray burst emission at
energies E greater than 200 MeV. This technique, with a sensitivity for bursts
lasting nanoseconds to several microseconds, is based on the detection of
multi-photon-initiated air showers.Comment: accepted for publication in the Astrophysical Journa
Stability and collapse of rapidly rotating, supramassive neutron stars: 3D simulations in general relativity
We perform 3D numerical simulations in full general relativity to study the
stability of rapidly rotating, supramassive neutron stars at the mass-shedding
limit to dynamical collapse. We adopt an adiabatic equation of state with
and focus on uniformly rotating stars. We find that the onset of
dynamical instability along mass-shedding sequences nearly coincides with the
onset of secular instability. Unstable stars collapse to rotating black holes
within about one rotation period. We also study the collapse of stable stars
which have been destabilized by pressure depletion (e.g. via a phase
transition) or mass accretion. In no case do we find evidence for the formation
of massive disks or any ejecta around the newly formed Kerr black holes, even
though the progenitors are rapidly rotating.Comment: 16 pages, to appear in Phys. Rev.
Funding Shortfall for Housing Vouchers Could Have Serious Health Consequences for Children
In the fourth brief in its Policy Action series, Children's HealthWatch finds that unaffordable housing endangers the health and development of young children. Due to a federal funding shortfall, state and local housing agencies will be forced to reduce or eliminate rental assitance to thousands of families starting this month. Voucher cuts will push more families into the ranks of the "hidden homeless" -- families that move frequently, crowd into apartments that are too small, or live doubled up with other households when they cannot find affordable housing. Children in hidden homeless families are at increased risk for poor health, nutrition, and growth, as well as developmental delays. Timely Congressional action to protect the Housing Choice Voucher Program will ensure that families have stable, affordable housing essential to children's health
Must naive realists be relationalists?
Relationalism maintains that perceptual experience involves, as part of its nature, a distinctive kind of conscious perceptual relation between a subject of experience and an object of experience. Together with the claim that perceptual experience is presentational, relationalism is widely believed to be a core aspect of the naive realist outlook on perception. This is a mistake. I argue that naive realism about perception can be upheld without a commitment to relationalism
Pyridine Thioamides as Analytical Reagents for lron
Thiopicolinamide and pyridine-2, 6-dithioamide were investigated as spectrophotometric reagents for iron. Both reagents form soluble blue colored species with iron (II) ion in basic solutions. The tris-thiopicolfuarnide-iron (II) complex exhibits a wavelength of maximum absorption at 615 mμ with a molar absorptivity of 13,600. The bispyridine-2, 6-dithioarnide-iron (II) complex exhibits a wavelength of maximum absorption at 600 mμ with a molar absorptivity of 21,000. A sensitive method for the determination of iron based upon the latter complex is proposed
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