6,153 research outputs found
A Practical Theorem on Gravitational Wave Backgrounds
There is an extremely simple relationship between the spectrum of the
gravitational wave background produced by a cosmological distribution of
discrete gravitational wave sources, the total time-integrated energy spectrum
of an individual source, and the present-day comoving number density of
remnants. Stated in this way, the background is entirely independent of the
cosmology, and only weakly dependent on the evolutionary history of the
sources. This relationship allows one easily to compute the amplitude and
spectrum of cosmic gravitational wave backgrounds from a broad range of
astrophysical sources, and to evaluate the uncertainties therein.Comment: 7 pages, no figures, uses mn2e.cls; submitted to MNRA
Preliminary evaluation of the Environmental Research Institute of Michigan crop calendar shift algorithm for estimation of spring wheat development stage
An algorithm for estimating spectral crop calendar shifts of spring small grains was applied to 1978 spring wheat fields. The algorithm provides estimates of the date of peak spectral response by maximizing the cross correlation between a reference profile and the observed multitemporal pattern of Kauth-Thomas greenness for a field. A methodology was developed for estimation of crop development stage from the date of peak spectral response. Evaluation studies showed that the algorithm provided stable estimates with no geographical bias. Crop development stage estimates had a root mean square error near 10 days. The algorithm was recommended for comparative testing against other models which are candidates for use in AgRISTARS experiments
Large Area Crop Inventory Experiment (LACIE). Experiment plan for evaluation of LANDSAT agronomic variables using wheat intensive test sites
There are no author-identified significant results in this report
Slip ring experience in long duration space applications
Ball Aerospace experience with slip rings in space extends back to 1962. Over 40 multi-ring assemblies have been flown and continuous operating lifetimes greater than 8 years at up to 60 rpm have been demonstrated. Slip rings provide multi-channel transfer of electrical power and signals in assemblies that are small in size and weight, and low in cost. By use of multiple brushes and sufficient copper within the assembly, power transfer efficiency better than 99.95 percent for high voltage circuits can be achieved. A low slip ring failure rate based on actual space operation totalling billions of ring revolutions has been established. Well qualified suppliers who have been making slip rings for space use for over 25 years are available. It is hoped that the suspected problem in SEASAT will not be allowed to prejudice space system designer against these very useful mechanisms
Feasibility of estimation of surface air temperature from meteorological satellite data test plan
A conceptual system designed to estimate daily surface air temperatures utilizing radiometric data obtained from polar orbiting meteorological satellites is discussed in this memorandum. The Surface Air Temperature Estimation System is an outgrowth of previous developmental and operational systems. The system represents an effort to integrate both satellite and surface meteorological observations into an operational framework which would be usable worldwide
Anatomy of a bearing torque problem
In the early 1970s, an antenna despin drive was developed for MBB solar science satellite HELIOS. A problem with high bearing drag torque that was encountered on the two flight models of this drive, after successful tests were completed on twelve bearings, an engineering model, and the qualification unit is discussed
Workshop on Early Crustal Genesis: Implications from Earth
Ways to foster increased study of the early evolution of the Earth, considering the planet as a whole, were explored and recommendations were made to NASA with the intent of exploring optimal ways for integrating Archean studies with problems of planetary evolution. Major themes addressed include: (1) Archean contribution to constraints for modeling planetary evolution; (2) Archean surface conditions and processes as clues to early planetary history; and (3) Archean evidence for physical, chemical and isotopic transfer processes in early planetary crusts. Ten early crustal evolution problems are outlined
Dynamics and Interactions of Binaries and Neutron Stars in Globular Clusters
We model the dynamics of test binaries in isotropic, multi-mass models of
galactic globular clusters. The evolution of binary orbits through the cluster
potentials is modeled, including second order diffusion terms, and
probabilities for close encounters with field stars are calculated. We carry
out Monte Carlo simulations of the effects of the binary--single star
encounters on the binary population and distribution in the cluster, and
estimate the collision rate for different stellar populations in globular
clusters with different structural parameters. Assuming a Salpeter IMF, for low
concentration clusters the core encounter rate is dominated by turnoff mass
main--sequence stars and medium mass white dwarfs. For high concentration, high
density clusters the encounter probabilities are increasingly dominated by
neutron stars and heavy white dwarfs. Hence we predict a smaller ratio of blue
stragglers and cataclysmic variables to pulsars in high concentration clusters.
The total number of millisecond pulsars, and the ratio of single to binary
pulsars, is broadly consistent with the observed population, suggesting the
binary--single star encounters contribute significantly to the pulsar formation
rate in globular clusters, for the whole range of globular cluster types. The
number of millisecond pulsars and the ratio of pulsars in different globular
clusters is best explained by a total binary fraction comparable to that of the
galaxy, and a modest number of primordial neutron stars in the globular
clusters.Comment: 59 pages, uuencoded compressed postscript, including 18 figures.
Astrophysical Journal Supplements, in pres
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