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At least 541 records · Page 30

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NASA NTRS1980

Vegetation reflectance measurements as a function of solar zenith angle

An understanding of the behavior of vegetation canopy reflectance as a function of solar zenith angle is important to several remote sensing applications. Spectral hemispherical-conical reflectances of a nadir looking sensor were taken throughout the day of a lodgepole pine and two grass canopies. Mathematical simulations of both a spectral hemispherical-conical reflectance factor and a spectral bi-hemispherical reflectance were performed for two theoretical canopies of contrasting geometric structure. These results and results from literature studies showed a great amount of variability of vegetation canopy reflectances as a function of solar zenith angle. Explanations for this variability are discussed and recommendations for future measurements are proposed.

Kimes, D. S.↗

NASA NTRS1980

Thermal metamorphism of primitive meteorites. XI - The enstatite meteorites: Origin and evolution of a parent body

The neutron activation data for Ag, As, Bi, Cd, Co, Cs, Cu, Ga, In, Rb, Se, Te, Tl, and Zn were obtained in samples of Abee heated to 1000-1400 C at low pressures. In addition, these elements were reported in nine enstatite achondrites and in the silicate part of the Mt. Egerton stony-iron. The data show trace element losses above 1000 C by diffusion-controlled processes with apparent activation energies of 8 to 55 kcal/mol; these data together with abundances of aubrites, Mt. Egerton, and E4-6 chondrites, and isotopic results link all enstatite meteorites to a common parent body. The data also indicate that aubrites and the Mt. Egerton material reflect fractional crystallization of a magma produced from enstatite chondrite-like parent material (E6) and the late introduction of chalcophiles and mobile elements transported by an FeS-Fe eutectic from an E4-6 region undergoing open-system metamorphism.

Biswas, S.↗

NASA NTRS1980

Moon and earth - Compositional differences inferred from siderophiles, volatiles, and alkalis in basalts

A comparison of RNAA analyses of 18 trace elements in 25 low-Ti lunar and 10 terrestrial oceanic basalts indicated that the volatiles such as Ag, Bi, and Br are depleted in lunar basalts by nearly constant factors of 0.026 relative to terrestrial basalts. This constancy is not consistent with models that derive the moon's volatiles from partial recondensation of the earth's mantle or from partial degassing of a captured body; it is consistent with models which derive planetary volatiles from a thin veneer of C-chondrite material. Chalcogens (Se and Te) have almost constant and identical abundances in lunar and terrestrial basalts; siderophiles show abundant Ni in lunar basalts, while Ir, Re, Ge, and Au are depleted.

Wolf, R.↗

NASA NTRS1980

Trace elements in ocean ridge basalt glasses - Implications for fractionations during mantle evolution and petrogenesis

Seven documented and fresh glassy selvages from ocean floor basalt pillows were analyzed for trace elements including Ag, Au, Bi, Br, Ni, Pd, and Zn using radiochemical activation analysis. Glasses from DSDP leg 24, site 238 in the Indian Ocean have a trace element pattern which reflects secondary processes at a shallow depth. Chemical fractionations in petrogenesis of tholeiitic basalts indicate that (Ir, Os), Au, Pd, Ni, and Re are strongly fractionated in igneous processes; the unfractionated chondritic mantle pattern thus imposes constraints on mantle evolution models. Finally, the limited Rb/Cs fractionation in oceanic tholeiites reflects the low abundance of volatiles and hydrous silicates in normal ocean ridge basalts.

Hertogen, J.↗

NASA NTRS1981

Chemical studies of L-chondrites. I - A study of possible chemical sub-groups

Radiochemical neutron activation analysis of Ag, As, Au, Bi, Co, Cs, Ga, In, Rb, Sb, Te, Tl and Zn and major element data in 14 L4-6 and 3 LL5 chondrites indicates that the L-group is unusually variable and may represent at least 2 sub-groups differing in formation history. Chemical trends in the S/Fe-rich sub-group support textural evidence indicating late loss of a shock-formed Fe-Ni-S melt; the S/Fe-poor sub-group seemingly reflects nebular fractionation only. Highly mobile In and Zn apparently reflect shock-induced loss from L-chondrites. Data for L5 chondrites suggest higher formation temperatures and/or degrees of shock than for LL5 chondrites.

Neal, C. W.↗

NASA NTRS1981

Composition of the earth's upper mantle. I - Siderophile trace elements in ultramafic nodules

The considered investigation is concerned with a reexamination of the question of the distribution of siderophile elements in the earth's upper mantle, taking into account a more unified data base which is now available. A comprehensive suite of ultramafic inclusions was collected as part of the Basaltic Volcanism Study Project and has been analyzed by instrument neutron activation analysis for major, minor, and some lithophile trace elements. In addition, 18 of these rocks and the important sheared garnet lherzolite PHN 1611 have been analyzed by means of radiochemical neutron activation analysis for 7 siderophile elements (Au, Ge, Ir, Ni, Os, Pd, and Re) and 9 volatile elements (Ag, Bi, Cd, In, Sb, Se, Te, Tl, and Zn). The siderophile element data reveal interesting inter-element correlations, which were not apparent from the compiled abundance tables of Ringwood and Kesson (1976) and Chou (1978).

Morgan, J. W.↗

NASA NTRS1981

Infrared charge-injection-device array performance at low background

Low-background tests of a 1 x 32 Si:Bi charge-injection-device (CID) IR detector are carried out to evaluate its feasibility for space-based astronomical observations. Optimum performance is obtained at a temperature of 11 K. The sensitivity is found to compare well with that of discrete extrinsic silicon photoconductors. The measured sensitivity and the apparent absence of anomalous effects make extrinsic silicon CID arrays very promising for astronomical applications.

Mccreight, C. R.↗

NASA NTRS1981

Metal and Bi/Pb microdistribution studies of an L3 chondrite - Their implications for a meteorite parent body

Strong localizations relative to bulk are reported of Bi, and to a lesser extent Pb, in some of the kamacite grains in Khohar, while other kamacite grains show no such enrichments. Distinctive and correlated differences in the Ni content are found in the two kamacite populations, with the Bi/Pb-rich kamacite grains having consistently lower Ni levels than the 6-7% typical of the Bi/Pb-poor kamacite. The Bi/Pb-rich kamacite grains also exhibit a highly reactive attack upon etching, which may be due to a finely polycrystaline microstructure. It is concluded that the trace element microdistributions were not established in the nebula, and that the enrichments were not likely to have occurred with slow cooling in the presence of a vapor phase during the kamacite-taenite phase transitions.

Woolum, D. S.↗

NASA NTRS1981

Study of foldable elastic tubes for large space structure applications, phase 3

A bi-convex foldable elastic tube, suitable for use in self deploying space structures, was subjected to a series of buckling tests to deterine initial buckling loads, collapse loads, and the buckling mode. The tube is cylindrical with a cross-section that is lenticular-like with flared edges. It is capable of being flattened in the center and folded compactly, storing up strain energy in the process. Upon removal of constraint, it springs back to its original straight configuration, releasing the stored strain energy. The tests showed that this type of tube has good resistance to buckling, with the initial buckling loads all falling within or above the range of those for comparable circular cylindrical tubes.

Jones, I. W.↗

NASA NTRS1982

Aircraft geometry verification with enhanced computer generated displays

A method for visual verification of aerodynamic geometries using computer generated, color shaded images is described. The mathematical models representing aircraft geometries are created for use in theoretical aerodynamic analyses and in computer aided manufacturing. The aerodynamic shapes are defined using parametric bi-cubic splined patches. This mathematical representation is then used as input to an algorithm that generates a color shaded image of the geometry. A discussion of the techniques used in the mathematical representation of the geometry and in the rendering of the color shaded display is presented. The results include examples of color shaded displays, which are contrasted with wire frame type displays. The examples also show the use of mapped surface pressures in terms of color shaded images of V/STOL fighter/attack aircraft and advanced turboprop aircraft.

Cozzolongo, J. V.↗

NASA NTRS1981

Template-directed synthesis of oligoguanylic acids - Metal ion catalysis

The effects of Zn(2+), Pb(2+) and other metal ions on the efficiency and stereo-selectivity of the template-directed oligomerization of guanosine 5'-phosphorimidazolide are investigated. Reactions were run in the presence of a polyC template in a 2,6-lutidine buffer, and products analyzed by high-performance liquid chromatography on an RPC-5 column. The presence of the Pb(2+) ion is found to lead to the formation of 2'-5' linked oligomers up to the 40-mer, while Zn(2+) favors the formation of predominantly 3'-5' linked oligomers up to the 35-mer. When amounts of uracil, cytidine or adenosine 5'-phosphorimidazole equal to those of the guanosine derivative are included in the reaction mixture, the incorrect base is incorporated into the oligomer about 10% of the time with a Pb(2+) catalyst, but less than 0.5% of the time with Zn(2+). The Sn(2+), Sb(3+) and Bi(3+) ions are also found to promote the formation of 2'-5' oligomers, although not as effectively as Pb(2+), while no metal ions other than Zn(2+) promote the formation of the 3'-5' oligomers. The results may be important for the understanding of the evolution of nucleic acid replication in the absence of enzymes.

Bridson, P. K.↗

NASA NTRS1980

Composition of the earth's upper mantle. II - Volatile trace elements in ultramafic xenoliths

Radiochemical neutron activation analysis was used to determine the nine volatile elements Ag, Bi, Cd, In, Sb, Se, Te, Tl, and Zn in 19 ultramafic rocks, consisting mainly of spinel and garnet lherzolites. A sheared garnet lherzolite, PHN 1611, may approximate undepleted mantle material and tends to have a higher volatile element content than the depleted mantle material represented by spinel lherzolites. Comparisons of continental basalts with PHN 1611 and of oceanic ridge basalts with spinel lherzolites show similar basalt: source material partition factors for eight of the nine volatile elements, Sb being the exception. The strong depletion of Te and Se in the mantle, relative to lithophile elements of similar volatility, suggests that 97% of the earth's S, Se and Te may be in the outer core.

Morgan, J. W.↗

NASA NTRS1982

The effect of grooves in amorphous substrates on the orientation of metal deposits. I - Carbon substrates

The graphoepitaxial alignment of vapor-deposited discrete metal crystallites is investigated in the nucleation and growth stages and during annealing by in situ UHV/TEM techniques. Various stages of nucleation, growth and coalescence of vapor deposits of Au, Ag, Pb, Sn, and Bi on amorphous, topographically structured C substrates are analyzed by advanced dark-field techniques to detect preferred local orientations. It is found that the topography-induced orientation of metal crystallites depends strongly on their mobility and their respective tendency to develop pronounced crystallographic shapes. Lowering of the average surface free energies and increasing the crystallographic surface energy anisotropies cause generally improved graphoepitaxial alignments.

Anton, R.↗

NASA NTRS1982

Aircraft geometry verification with enhanced computer-generated displays

A method for visual verification of aerodynamic geometries using computer-generated, color-shaded images is described. The mathematical models representing aircraft geometries are created for use in theoretical aerodynamic analyses and in computer-aided manufacturing. The aerodynamic shapes are defined using parametric bi-cubic splined patches. This mathematical representation is then used as input to an algorithm that generates a color-shaded image of the geometry. A discussion of the techniques used in the mathematical representation of the geometry and in the rendering of the color-shaded display is presented. The results include examples of color-shaded displays, which are contrasted with wire-frame-type displays. The examples also show the use of mapped surface pressures in terms of color-shaded images of V/STOL fighter/attack aircraft and advanced turboprop aircraft.

Cozzolongo, J. V.↗

NASA NTRS1982

Self-heated thermocouples for far-infrared detection

A novel self-heated Bi-Sb thermocouple for far-infrared detection has been developed. The detector is suitable for integration with monolithic antennas and imaging arrays. The device is fabricated in a single photolithography masking step using a photoresist-bridge technique. This bridge technique has also been used to make microbolometers with lower 1/f noise than those made by two conventional masking steps. The thermocouples have a noise equivalent power of 7 x 10 to the -10th W/sq rt of Hz and a 3-dB frequency response of 150 kHz.

Neikirk, D. P.↗

NASA NTRS1980

MRS proof-of-concept on atmospheric corrections. Atmospheric corrections using an orbital pointable imaging system

The feasibility of using a pointable imager to determine atmospheric parameters was studied. In particular the determination of the atmospheric extinction coefficient and the path radiance, the two quantities that have to be known in order to correct spectral signatures for atmospheric effects, was simulated. The study included the consideration of the geometry of ground irradiance and observation conditions for a pointable imager in a LANDSAT orbit as a function of time of year. A simulation study was conducted on the sensitivity of scene classification accuracy to changes in atmospheric condition. A two wavelength and a nonlinear regression method for determining the required atmospheric parameters were investigated. The results indicate the feasibility of using a pointable imaging system (1) for the determination of the atmospheric parameters required to improve classification accuracies in urban-rural transition zones and to apply in studies of bi-directional reflectance distribution function data and polarization effects; and (2) for the determination of the spectral reflectances of ground features.

Slater, P. N.↗

NASA NTRS1982

A broadband VLF burst associated with ring current electrons

A determination is made of the source of a broadband VLF burst observed during the inbound plasmapause crossing of the explorer 45 spacecraft on April 2, 1972 in the late stage of a geomagnetic storm. Electric and magnetic receiver data from the satellite were spectrally analyzed, showing a 1-3 kHz whistler component and an emission broadening event comprising enhancement of the 1.0 and 1.78 kHz electric field intensities by several orders of magnitude. A corresponding and simulaneous enhancement of the ring current electrons was observed. The emission band spreading was attributed to the generation of quasi-electrostatic short wavelength whistler mode emissions by hot bi-maxwellian electrons surging into the domain of low density magnetized cold plasma. The inner edge of the plasma sheet, which was the source of the electrons, was not far from the event.

Maeda, K.↗

NASA NTRS1983

High-energy tail distributions and resonant wave particle interaction

High-energy tail distributions (k distributions) are used as an alternative to a bi-Lorentzian distribution to study the influence of energetic protons on the right- and left-hand cyclotron modes in a hot two-temperature plasma. Although the parameters are chosen to be in a range appropriate to solar wind or magnetospheric configurations, the results apply not only to specific space plasmas. The presence of energetic particles significantly alters the behavior of the electromagnetic ion cyclotron modes, leading to a wide range of unstable frequencies and increased growth rates. From the strongly enhanced growth rates it can be concluded that high-energy tail distributions should not show major temperature anisotropies, which is consistent with observations.

Leubner, M. P.↗