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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
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NASA NTRS1974

Results on the two population feature selection problem using probability of correct classification as a criterion

Variational equations are presented for maximizing the probability of correct classification as a function of a 1xn feature selection matrix B for the two-population problem. For the special case of equal covariance matrices the optimal B is unique up to scalar multiples and rank one sufficient. For equal population means, the best 1xn B is an eigenvector corresponding either to the largest or smallest eigenvalue of sigma sub 2 to the minus 1 power sigma sub 1 where sigma sub 1 and sigma sub 2 are the nxn covariance matrices of the two populations. The transformed probability of correct classification depends only on the eigenvalue. Finally, a procedure is proposed for constructing an optimal or nearly optimal kxn matrix of rank k without solving the k-dimensional variational equation.

Peters, B. C.↗
NASA NTRS1974

Microcrater populations on Apollo 17 rocks

Approximately 6000 microcraters were investigated using binocular microscope techniques on Apollo 17 rocks 70215, 72215, 72235, 72395, 72435, 73216, 73218, 73275, 74275, 76135, 76136, and 79155. The crater populations observed have identical characteristics to those obtained from previous missions. Special emphasis was placed on assessing the influence of target properties on the observable crater populations. Although these properties cannot be quantitatively evaluated at present, the empirical results indicate that crater populations on glass, breccia, and crystalline rock surfaces may differ fundamentally. As a consequence, lunar surface exposure ages of individual rocks based on micrometeoroid craters may be subject to criticism.

Schneider, E.↗
NASA NTRS1976

Crater populations in the early history of Mercury

Crater populations on two major geologic units of Mercury have been classified into three morphologic types which characterize their state of degradation. The results indicate that one or more processes either prior to or contemporary with the formation of the 1300-km-diameter Caloris Planitia reduced the population of fresh craters smaller than 70 to 80 km in diameter and totally erased the population of fresh craters smaller than 20 to 30 km.

Guest, J. E.↗
NASA NTRS1976

New galactic population class

It has been found that galactic gamma rays come from regions in which molecular hydrogen is dense and in which 'population I' objects are predominantly found. An interpretation of the existence of such regions leads to a proposal for a change in the Baade classification scheme. 'Population I' is to include all the objects associated with the H2 clouds. A new class, 'population 0' is to refer to the regions, relatively richer in atomic hydrogen, which lie further from the galactic center.

Stecker, F. W.↗
NASA NTRS1978

Meteorological limits on the growth and development of screwworm populations

A program to evaluate the use of remotely sensed data as an additional tool in existing and projected efforts to eradicate the screwworm began in 1973. Estimating weather conditions by use of remotely sensed data was part of the study. Next, the effect of weather on screwworm populations was modeled. A significant portion of the variation in screwworm population growth and development has been traced to weather-related parameters. This report deals with the salient points of the weather and the screwworm population interaction.

Phinney, D. E.↗
NASA NTRS1978

Observations of two distinct populations of bow shock ions in the upstream solar wind

Observations upstream of the earth's bow shock with the LASL/MPI fast plasma experiments on ISEE 1 and 2 reveal the presence of two distinct and mutually exclusive populations of low energy (no more than 40 keV) ions apparently accelerated at the bow shock. The first of these, the 'reflected' population, is characterized by (1) sharply peaked spectra seldom extending much above about 10 keV/ion and (2) relatively collimated flow coming from the direction of the shock. On the other hand, the 'diffuse' ions are distinguished by relatively flat energy spectra above about 10 keV and broad angular distributions. They are by far the most commonly observed upstream ion event. A close causal association is suggested between the diffuse ion population in the upstream solar wind and energetic plasma ions observed within the magnetosheath.

Gosling, J. T.↗
NASA NTRS1979

Satellite-aided evaluation of population exposure to air pollution

The evaluation of population exposure to air pollution through the computer processing of Landsat digital land use data, along with total suspended particulate estimates and population data by census tracts, is demonstrated. Digital image processing was employed to analyze simultaneously data from Landsat MSS bands 4 through 7 in order to extract land use and land cover information. The three data sets were spatially registered in a digital format, compatible with integrated computer processing, and cross-tabulated. A map illustrating relative air quality by 2-sq km cells for the residential population in the Portland, Oregon area is obtained.

Todd, W. J.↗
NASA NTRS1981

Crater populations on Ganymede and Callisto

Voyager 1 observations reveal heavily cratered surfaces on Ganymede and Callisto which suggest that a period of heavy bombardment occurred in the outer solar system. The overall crater density on Ganymede indicates that the oldest regions began recording the observed crater population at a later time than Callisto. A diameter-dependent loss of craters from 10-40 km occurs on Ganymede and may be due to ice formation or the formation of arcuate troughs. Evidence is given which suggests that the population of bodies responsible for the period of late heavy bombardment in the inner solar system is very different from that responsible for the late heavy bombardment in the outer solar system. In addition, it is postulated that Ganymede and Callisto may principally record a population of bodies that never penetrated the inner solar system in numbers great enough to leave a recognizable signature.

Strom, R. G.↗
NASA NTRS1984

Stellar populations in local group dwarf elliptical galaxies. II - NGC 205

NGC 205, a dwarf elliptical companion of M31, was studied using deep CCD photometry on the VRI system. Consideration is given to a comparison between the giant branch and the Galactic globular clusters, the degree of chemical enrichment in the outer parts of NGC 204, and the setting of constraints on the stellar population of NGC 205. Should the distance of the galaxy be that of M31, this field's stellar population is extremely old. If star formation in NGC 205 is a recurring phenomenon, it is confined to the interior of the galaxy. Should the stellar population of NGC 205 be as old as Galactic globular clusters, its distance modulus is 24.3 + or - 0.2. The giant branch location corresponds to a mean metallicity greater than or equal to -0.9 + or - 0.2, and a metallicity dispersion is determined to be sigma greater than or equal to 0.5 dex. Also noted is that the color distribution at a given luminosity appears to be positively skewed.

Mould, J.↗
NASA NTRS1984

Intense low-energy ion populations at low equatorial altitudes

The ISEE 1 satellite trajectory often passed through the magnetospheric region during the time from November 1977 to April 1978. On every occasion, the medium energy particles instrument (MEPI) of the satellite recorded an intense ion population in a region corresponding to low equatorial altitudes. An intensity peak was observed in the lowest MEPI energy channel. A comparison of high bit rate MEPI data with simultaneous data from the LEPEDEA plasma instrument on Nov. 29, 1977 1930-2000 UT shows additional peaks in the ion population existing in the L of 2 to at least 4. In the present report, data characterizing these ion populations are presented, and implications are discussed in terms of source and loss mechanisms.

Williams, D. J.↗
NASA NTRS1985

The hidden ion population - Revisited

In an investigation conducted by Olsen (1982) on the basis of particle data taken with an electrostatic analyzer, it was found that a cold plasma population with a density between 10 and 100 per cu cm appeared suddenly when the satellite was eclipsed, but was hidden in sunlight. The present paper has the objective to show further measurements of ordinarily 'hidden' ion populations, in order to resolve some of the questions raised in connection with the Scatha satellite data reported by Olsen. It is found that the retarding ion mass spectrometer (RIMS) detector is capable of measuring the core of the plasma distribution in sunlight and eclipse, though the task is more easily done in eclipse. There are, however, limitations concerning the ability of the detector to measure all the plasma, all the time. It is, therefore, pointed out that continuous effective measurements of the 'hidden' ion population of the magnetosphere still awaits satellites with effective means of potential control.

Olsen, R. C.↗
NASA NTRS1986

Supernova nucleosynthesis in low-metallicity populations

The mass loss rate in low-metallicity stars is discussed, and the consequences of that rate for the fate of such stars are considered. It is shown that, if radiation pressure on dust is important in driving the mass loss from red giants, and if these stars do not dredge up large amounts of processed material during their evolution, then the total amount of mass lost by Population II stars with low metallicity is small. Consequently, the rate of supernovae in populations of low metallicity is much higher than in populations of solar abundances. This conclusion leads to the prediction that the supernova rate should be high in galaxies that have some intermediate mass stars and have metallicity less than about 0.1 of the solar value.

Jura, M.↗
NASA NTRS1986

Systematics of the CHON and other light-element particle populations in Comet Halley

Based on chemical signatures measured by the PIA experiment during the Giotto flyby of comet Halley, particle classifications were designated. In addition to silicate-like grains and particles of mixed (cosmic) composition, there appear to be several light-element rich populations, including the CHON, (H,C), (H,C,O), and (H,C,N) particle types. These compositional classes are further distinguished by differences in mass distributions, a density indicator, and variations in relative abundance within the coma. These particle populations are evidence for chemical heterogeneity in the surface of the cometary nucleus. Particles found mainly in the inner coma may be volatile icy grains. Most of the N of the comet may be found in up to three different populations of grains; one or more of these may be responsible for the observation of cyanojets.

Clark, Benton↗
NASA NTRS1986

The ABC of Population III

The author discusses the circumstances in which Population III stars are expected to form and examines their cosmological consequences. Consideration of their production of light, metals, and remnants places a strong constraint on their formation epoch and mass spectrum. However, these constraints would still allow Population III stars to provide the dark matter in galactic halos, a helium abundance of around 25 percent, a detectable background of gravitational waves, a possible infrared background, and the generation of large-scale cosmological structure through explosions. All of these features could be achieved by VMOs in the range 100 to 100,000 solar masses. On the other hand, the Population III scenario would be most compatible with the standard Big Bang picture if the stars were SMOs with mass around a million solar masses. Such stars could still provide the dark matter and detectable gravitational waves.

Carr, B. J.↗
NASA NTRS1987

The spatial distribution and population of novae in M31

Results from an H-alpha survey for novae in the bulge of M31 are reported, and the spatial distribution of the nova population is analyzed. It is shown that in M31's central bulge the distribution of novae follows that of the light to within about 10 arcsec of the nucleus, refuting the notion that there is a nova 'hole' near the center of the galaxy. The Hubble-Arp nova sample is reanalyzed, concluding that the novae observed in the central 30 arcmin x 15 arcmin region belong almost exclusively to the bulge population. This result is compared to the observed cataclysmic variable distribution in the Galaxy, concluding that M31's spheroidal nova population is still compatible with the thin disk distribution of cataclysmic variables measured in the solar neighborhood. Possible explanations for the high specific nova rate of the bulge are discussed.

Ciardullo, Robin↗
NASA NTRS1987

Electrophoretic enzyme analysis of North American and eastern Asian populations of Agastache sect. Agastache (Labiatae)

Genetic relationships among the seven species of Agastache sect. Agastache common in North America and the one found in eastern Asia were assessed using starch-gel electrophoresis of twelve enzymatic proteins. Nei's (1976) genetic distance and identity values, calculated among the 32 populations used in this study, partitioned the Agastache section into four discrete groups: (1) A. nepetoides (eastern North America), (2) A. scrophulariifolia and A. foeniculum (eastern and central North America), (3) the four species of the western U.S. (A. urticifolia, A. occidentalis, A. parvifolia, and A. cusickii), and (4) A. rugosa (eastern Asia). The Asian Agastache, separated from its American congeners for over 12 million years, differed from American populations at only two (the IDH-1 and LAP-1 alleles) of the fifteen loci surveyed; these alleles were not found in any of the North American plants. Nei's genetic distances between the Asian and North American populations ranged from 0.2877 to 0.6734.

Vogelmann, James E.↗
NASA NTRS1988

Observational test of shock drift and Fermi acceleration on a seed particle population upstream of earth's bow shock

The efficiency of proposed shock acceleration mechanisms as they operate at the bow shock in the presence of a seed energetic particle population was examined using data from simultaneous observations of energetic solar-origin protons, carried out by the IMP 7 and 8 spacecraft in the vicinity of the quasi-parallel (dawn) and quasi-perpendicular (dusk) regions of the earth's bow shock, respectively. The results of observations (which include acceleration effects in the intensities of the energetic protons with energies as high as 4 MeV observed at the vicinity of the dusk bow shock, but no evidence for any particle acceleration at the energy equal to or above 50 keV at the dawn side of the bow shock) indicate that the acceleration of a seed particle population occurs only at the quasi-perpendicular bow shock through shock drift acceleration and that the major source of observed upstream ion populations is the leakage of magnetospheric ions of energies not less than 50 keV, rather than in situ acceleration.

Anagnostopoulos, G. C.↗