24,273 research outputs found
Hypervelocity scramjet combustor-nozzle analysis and design
The progress report for the grant entitled 'Hypervelocity of Scramjet Combustor-Nozzle Analysis and Design' is presented. The three main tasks in the program are combustor modeling study, development of anaylsis capabilities for hypersonic scramjet nozzles, and development of optimum design methods for hypersonic scramjet nozzles. The research performed was documented in a series of technical publications and presentations at various conferences. A brief description of the research in each of the above three areas and a list of the resulting technical publications are included
The Production of Ti44 and Co60 in Supernova
The production of the radioactive isotopes Ti and Co in all
types of supernovae is examined and compared to observational constraints
including Galactic --ray surveys, measurements of the diffuse 511 keV
radiation, --ray observations of Cas A, the late time light curve of SN
1987A, and isotopic anomalies found in silicon carbide grains in meteorites.
The (revised) line flux from Ti decay in the Cas A supernova remnant
reported by COMPTEL on the Compton Gamma-Ray Observatory is near the upper
bound expected from our models. The necessary concurrent ejection of Ni
would also imply that Cas A was a brighter supernova than previously thought
unless extinction in the intervening matter was very large. Thus, if confirmed,
the reported amount of Ti in Cas A provides very interesting constraints
on both the supernova environment and its mechanism. The abundances of
Ti and Co ejected by Type II supernovae are such that
gamma-radiation from Ti decay SN 1987A could be detected by a future
generation of gamma-ray telescopes and that the decay of Co might
provide an interesting contribution to the late time light curve of SN 1987A
and other Type II supernovae. To produce the solar Ca abundance and
satisfy all the observational constraints, nature may prefer at least the
occasional explosion of sub-Chandrasekhar mass white dwarfs as Type Ia
supernovae. Depending on the escape fraction of positrons due to Co made
in all kinds of Type Ia supernovae, a significant fraction of the steady state
diffuse 511 keV emission may arise from the annihilation of positrons produced
during the decay of Ti to Ca. The Ca and Ti isotopic anomalies in
pre-solar grains confirm the production of Ti in supernovae and thatComment: 27 pages including 7 figures. uuencoded, compressed, postscript. in
press Ap
Effect of environment on biological burden during spacecraft assembly
Determining effects of environment on accumulation of biological burden on spacecraft during assembl
Off-lattice Monte Carlo Simulation of Supramolecular Polymer Architectures
We introduce an efficient, scalable Monte Carlo algorithm to simulate
cross-linked architectures of freely-jointed and discrete worm-like chains.
Bond movement is based on the discrete tractrix construction, which effects
conformational changes that exactly preserve fixed-length constraints of all
bonds. The algorithm reproduces known end-to-end distance distributions for
simple, analytically tractable systems of cross-linked stiff and freely jointed
polymers flawlessly, and is used to determine the effective persistence length
of short bundles of semi-flexible worm-like chains, cross-linked to each other.
It reveals a possible regulatory mechanism in bundled networks: the effective
persistence of bundles is controlled by the linker density.Comment: 4 pages, 4 figure
Experimental Heat Transfer Supporting Simulated Water Well Performance on Mars
Favorable indications of massive quantities of water on Mars have initiated studies of potential changes to human Mars missions. Using a technique known as a Rodriguez Well to melt the ice, store the resulting water in a subsurface ice cavity until needed, and then pump water to the surface for use is one potential means to effect these changes. A computer simulation of the Rodriguez Well in a terrestrial environment is one of the engineering tools being used to characterize the performance of this type of well on Mars. An experiment at the NASA Johnson Space Center is gathering data for convective heat transfer and evaporation rates at Mars surface conditions so that this computer simulation can be properly modified to predict performance on Mars. While quantitative results await processing, tests have indicated that a pool of water can be maintained at 1C to 2 C while at Mars surface temperatures and pressures
Results of a study of the stability of cointegrating relations comprised of broad monetary aggregates
There is strong evidence of a stable “money demand” relationship for MZM and M2 through the 1990s. Though the M2 relationship breaks down somewhere around 1990, evidence has been accumulating that the disturbance is well characterized as a permanent upward shift in M2 velocity that began around 1990 and was largely over by 1994. This paper’s results support the hypothesis that households permanently reallocated a portion of their wealth from time deposits to mutual funds. This reallocation may have been induced by depository restructuring, but it could also be explained by appropriately measured opportunity cost.Demand for money
The swept angle retarding mass spectrometer: Initial results from the Michigan auroral probe sounding rocket
Data from a sounding rocket flight of the swept angle retarding ion mass spectrometer (SARIMS) are presented to demonstrate the capability of the instrument to make measurements of thermal ions which are differential in angle, energy, and mass. The SARIMS was flown on the Michigan auroral probe over regions characterized first by discrete auroral arcs and later by diffuse precipitation. The instrument measured the temperature, densities, and flow velocities of the ions NO(+) and O(+). Measured NO(+) densities ranged from 10 to the 5th power up to 3 x 10 to the 5th power ions/cu cm, while the measured O(+) densities were a factor of 5-10 less. Ion temperatures ranged from 0.15 up to 0.33 eV. Eastward ion flows approximately 0.5 km/sec were measured near the arcs, and the observed flow magnitude decreased markedly inside the arcs
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