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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Thermal control of low-pressure fractionation processes

Thermal models detailing the solidification paths for shallow basaltic magma chambers (both open and closed systems) were calculated using finite-difference techniques. The total solidification time for closed chambers are comparable to previously published calculations; however, the temperature-time paths are not. These paths are dependent on the phase relations and the crystallinity of the system, because both affect the manner in which the latent heat of crystallization is distributed. In open systems, where a chamber would be periodically replenished with additional parental liquid, calculations indicate that the possibility is strong that a steady-state temperature interval is achieved near a major phase boundary. In these cases it is straightforward to analyze fractionation models of the basaltic liquid evolution and their corresponding cumulate sequences. This steady thermal fractionating state can be invoked to explain large amounts of erupted basalts of similar composition over long time periods from the same volcanic center and some rhythmically layered basic cumulate sequences.

Usselman, T. M.↗
NASA NTRS1979

Large impact basins on Mercury and relative crater production rates

A search for impact basins on Mercury having diameters greater than 200 km revealed evidence for 40 such structures on the 47% of Mercury mapped at sufficient resolution by Mariner 10. This is similar to the number (35) found by Schaber et al. (1977), although there is disagreement in the details of both diameters (for basins observed by them and by the authors) and in the existence of individual basins. The differences are described in detail. A log (cumulative number/unit area)-log (diameter) plot for mercurian basins has a least squares slope of -2; basins show somewhat less scatter about this line than do the Schaber et al. basins. Mercury has (in cumulative number/unit area) only 37% as many basins as does the moon over the entire range of diameters greater than 300 km. If both the moon and Mercury have had similar preservation times for craters and if common populations of impactors are involved, then Mars-crossers may have been a dominant contribution to the basin-forming objects.

Frey, H.↗
NASA NTRS1980

The nature and origin of ureilites

A theory of the origin of ureilites is presented based on mineralogical and petrological investigation of eight species including Kenna, Novo Urei, and Goalpara. The theory suggests that ureilites are primarily olivine-pigeonite cumulates crystallized from a silicate liquid which also contained suspended solid carbon phases. The carbon induced reduction of the melt and affected the ureilite mineral compositions. Petrofabric analyses show that mafic silicates are oriented in lineated and foliated patterns similar to cumulate rocks; strain rate of silicates suggests that ureilites were deformed after lithification by a mild tectonic stress and a moderate to severe shock.

Berkley, J. L.↗
NASA NTRS1981

The Antarctic achondrite ALHA 76005 - A polymict eucrite

ALHA 76005 is a basaltic achondrite containing few, if any, orthopyroxenes. Its bulk major and trace element composition is like that of a non-cumulate eucrite, and unlike that of a howardite. It contains a variety of igneous clasts which differ in their textures, pyroxene/plagioclase ratios and pyroxene and plagioclase compositions. One clast, No. 4, was found to have the REE pattern of a cumulate eucrite and an oxygen isotopic composition different from that of the bulk meteorite. Both the chemical and oxygen isotopic composition of clast No. 4 suggest that it was derived from a source different from its host. These observations lead to the conclusion that ALHA 76005 is a polymict eucrite.

Grossman, L.↗
NASA NTRS1982

Interconnect fatigue design for terrestrial photovoltaic modules

The results of comprehensive investigation of interconnect fatigue that has led to the definition of useful reliability-design and life-prediction algorithms are presented. Experimental data indicate that the classical strain-cycle (fatigue) curve for the interconnect material is a good model of mean interconnect fatigue performance, but it fails to account for the broad statistical scatter, which is critical to reliability prediction. To fill this shortcoming the classical fatigue curve is combined with experimental cumulative interconnect failure rate data to yield statistical fatigue curves (having failure probability as a parameter) which enable (1) the prediction of cumulative interconnect failures during the design life of an array field, and (2) the unambiguous--ie., quantitative--interpretation of data from field-service qualification (accelerated thermal cycling) tests. Optimal interconnect cost-reliability design algorithms are derived based on minimizing the cost of energy over the design life of the array field.

Mon, G. R.↗
NASA NTRS1980

Ground cloud related weather modification effects

The principal concerns about inadvertent weather modification by the solar power satellite system rocket effluents are discussed, namely the possibility that the ground cloud might temporarily modify local weather and the cumulative effects of nearly 500 launches per year. These issues are discussed through the consideration of (1) the possible alteration of the microphysical processes of clouds in the general area due to rocket effluents and debris and cooling water entrained during the launch and (2) the direct dynamical and thermodynamical responses to the inputs of thermal energy and moisture from the rocket exhaust for given ambient meteorological conditions. The huge amount of thermal energy contained in the exhaust of the proposed launch vehicle would in some situations induce a saturated, wet convective cloud or enhance an existing convective activity. Nevertheless, the effects would be limited to the general area of the launch site. The observed long lasting high concentrations of cloud condensation nuclei produced during and after a rocket launch may appreciably affect the frequency of occurrence and persistence of fogs and haze. In view of the high mission frequency proposed for the vehicle launches, a potential exists for a cumulative effect.

Lee, J.↗
NASA NTRS1980

A pristine eucrite-like gabbro from Descartes and its exotic kindred

A coarse-grained plagioclase-pyroxene gabbro (61224,6) with a cumulate texture suggestive of a slowly cooled plutonic rock was recovered from the 4-10 mm fraction of an Apollo 16 soil. The rock is uncommonly poor in feldspar and rich in Na for a lunar highlands lithology. Trace element analyses show extremely low siderophile element concentrations which confirm the pristine character indicated by the texture. The composition of 61224,6 is compared with those of 3 other pristine, exceptionally mafic, nonmare gabbros and of certain eucrites. 61224,6 and the three other gabbros have notable chemical differences but share relatively high ratios of Ti/Sm and Sc/Sm which suggest a possible genetic relationship. We conclude that 61224,6 represents a Na-rich cumulate from a layered intrusion within the highlands crust.

Marvin, U. B.↗
NASA NTRS1980

Modal studies of mesosiderites and related achondrites, including the new mesosiderite ALHA 77219

The Antarctic meteorite ALHA 77219 is found to be a new mesosiderite. It contains about 25% metal + troilite (+ rust) and the brecciated silicate portion is dominated by orthopyroxene (En 68-71). These features, together with the presence of olivine surrounded by coronas, and abundant tridymite + phosphate conform to the characteristics of mesosiderites. A comparison of the modal abundances of minerals in 77219 with modes of 20 mesosiderites, 14 howardites, six basaltic eucrites, three feldspar cumulate eucrites, and one orthopyroxene cumulate eucrite shows that there are major differences between mesosiderites and howardites. These differences are described in detail.

Prinz, M.↗
NASA NTRS1980

Comparative petrology and origin of Governador Valadares and other nakhlites

The Governador Valadares is a cumulate augite achondrite showing many petrographic and geochemical similarities to the other known nakhlites, Nakhla and Lafayette. However, subtle differences in minor-element composition and textures suggest that each nakhlite is unique and probably represents a separate meteorite fall. Cumulus clinopyroxene compositions (En39FS23WO38) suggest crystallization from a common silica-saturated (tholeiite-like) liquid. Intercumulus mesostasis material shows evidence for a two-stage cooling history (slow, followed by quenching) and may represent highly fractionated, foreign pore liquid filtered into present nakhlites by compaction of lower-level cumulates.

Berkley, J. L.↗
NASA NTRS1982

Fragmentation of ice by low velocity impact

Low-velocity impact experiments (0.14 to 1 km/s) carried out in polycrystalline water ice targets at 257 and 81 K reveal interactions which are assigned to four fragmentation classes: cratering, erosion, disruption, and total fragmentation. The specific kinetic energies for the transitions between these classes are found to be about one to two orders of magnitude below those for silicate rocks. The mass vs. cumulative number distribution of fragments in the experiments is described by a simple power law, similar to that observed in fragmented rocks both in the laboratory and in nature. The logarithmic slopes of cumulative number vs. fragment weight range from -0.9 to -1.8; they decrease with increasing projectile energy and are approximately independent of target temperature. The shapes of fragments resulting from erosion and disruption of ice targets are found to be significantly less spherical for 257 K targets than for 81 K targets. Fragment sphericity increases with increasing projectile energy at 257 K; however, no similar trend is observed for 81 K ice.

Lange, M. A.↗
NASA NTRS1982

Steady state volcanism - Evidence from eruption histories of polygenetic volcanoes

Cumulative volcano volume curves are presented as evidence for steady-state behavior at certain volcanoes and to develop a model of steady-state volcanism. A minimum criteria of five eruptions over a year was chosen to characterize a steady-state volcano. The subsequent model features a constant head of magmatic pressure from a reservoir supplied from depth, a sawtooth curve produced by the magma arrivals or discharge from the subvolcanic reservoir, large volume eruptions with long repose periods, and conditions of nonsupply of magma. The behavior of Mts. Etna, Nyamuragira, and Kilauea are described and show continuous levels of plasma output resulting in cumulative volume increases. Further discussion is made of steady-state andesitic and dacitic volcanism, long term patterns of the steady state, and magma storage, and the lack of a sufficient number of steady-state volcanoes in the world is taken as evidence that further data is required for a comprehensive model.

Wadge, G.↗
NASA NTRS1982

A Poisson process approximation for generalized K-5 confidence regions

One-sided confidence regions for continuous cumulative distribution functions are constructed using empirical cumulative distribution functions and the generalized Kolmogorov-Smirnov distance. The band width of such regions becomes narrower in the right or left tail of the distribution. To avoid tedious computation of confidence levels and critical values, an approximation based on the Poisson process is introduced. This aproximation provides a conservative confidence region; moreover, the approximation error decreases monotonically to 0 as sample size increases. Critical values necessary for implementation are given. Applications are made to the areas of risk analysis, investment modeling, reliability assessment, and analysis of fault tolerant systems.

Arsham, H.↗
NASA NTRS1981

Workshop on Magmatic Processes of Early Planetary Crusts: Magma Oceans and Stratiform Layered Intrusions

The significance of the lunar highland pristine cumulate samples were reevaluated with the aid of the additional insights provided by geologically constrained terrestrial investigations. This exercise involved a review of the state of knowledge about terrestrial and lunar cumulate rocks as well as an enumeration and reevaluation of the processes hypothesized to have been responsible for their formation, both classically and at present.

Walker, D.↗
NASA NTRS1982

Comments on the gamma-ray burst log N /greater than S/ log S point of Beurle et al

Statistical improbability is demonstrated for the Beurle et al (1981) determination of an isotropic cumulative burst rate of 7030 + 10,000 or - 6000/year, at a fluence of 8.47 x to the -9th/erg per sq cm, from their observation of two gamma-ray bursts. The difficulty identified is Beurle's assumption that the power law cumulative distribution function index equals one. Reconsideration of the Beurle observations is undertaken, and an alternative upper limit of the annual number of bursts at the fluence cited of less than 5400/year is proposed.

Jennings, M. C.↗
NASA NTRS1983

The magma ocean from the Fra Mauro shoreline - An overview of the Apollo 14 crust

Petrographic and mineralogical studies of coarse grained, polymineralic, texturally monominct igneous clasts from the Apollo 14 breccias show troctolite and troctolitic anorthosite to be the most abundant rock types. The second most abundant group consists of plagioclase cumulates with more evolved mineral compositions than the Mg-rich trend anorthosite cumulates. Coarse grained ilmenite gabbros and mineralogically evolved monzonoritic and granitic clasts are widespread in occurrence, but not abundant. The present data provide further support for widespread regional heterogeneities within the early lunar crust.

Hunter, R. H.↗
NASA NTRS1982

Optimization technique for improved microwave transmission from multi-solar power satellites

An optimization technique for generating antenna illumination tapers allows improved microwave transmission efficiencies from proposed solar power satellite (SPS) systems and minimizes sidelobe levels to meet preset environmental standards. The cumulative microwave power density levels from 50 optimized SPS systems are calculated at the centroids of each of the 3073 counties in the continental United States. These cumulative levels are compared with Environmental Protection Agency (EPA) measured levels of electromagnetic radiation in seven eastern cities. Effects of rectenna relocations upon the power levels/population exposure rates are also studied.

Arndt, G. D.↗
NASA NTRS1983

Impact cratering and spall failure at gabbro

Both hypervelocity impact and dynamic spall experiments were carried out on a series of well-indurated samples of gabbro. The impact experiments carried out with 0.04 to 0.2g, 5-6 km/sec projectiles produced deci-centimeter-sized craters and demonstrated crater efficiencies of 6/10 to the - 9 g/erg, and order of magnitude greater than in metal and some two to three times that of previous experiments on less strong igneous rocks. Most of the crater volume (some 60 to 80%) is due to spall failure. Distribution of cumulative fragment number, as a function of mass of fragments with masses greater than 0.1 gram yield values of b = d(log10N sub f)dlog10(m)of -0.5 to -0.6, where N sub f is the cumulate number of fragments and m is the mass of fragments. These values are in agreement or slightly higher than those obtained for less strong rocks and indicate that a large fraction of the ejectra resides in a few large fragments.

Lange, M. A.↗
NASA NTRS1983

Use of olivine and plagioclase saturation surfaces for the petrogenetic modeling of recrystallized basic plutonic systems

During petrogenetic studies of basic plutonic rocks, there are at least three major questions to be considered: (1) what were the relative proportions of cumulate crystals and intercumulus melt in a given sample? (2) what is the composition and variation in composition of the melts within the pluton? and (3) what is the original composition of the liquids, their source and evolution prior to the time of emplacement? Use of both saturation surfaces can place strong limits on the compositions of potential cumulate phases and intercumulus melts. Consideration of appropriate trace elements can indicate whether a sample is an orthocumulate, adcumulate or mesocumulate. Thus, when trace element and petrographic data are considered together with the saturation surfaces, it should be possible to begin to answer the three major questions given above, even for strongly recrystallized basic plutons.

Hanson, G. N.↗