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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Retrograde, charnockite- gneiss relations in Southern India

The high-pressure charnockites (P = 8 to 9 Kb., T = 700 to 800 C CO2-rich fluid regime) of the Nilgiri hills show evidence of retrogression related to shear deformation within the Moyar and Bhavani shear belts. Two types of retrogression have been noticed: (1) retrogression along shear planes, and (2) retrogression along pegmatitic veins. Initial stages of retrogression results in the formation of irregular, 2 to 3 cm to one meter wide bleached zones with the removal of greasy grey color of charnockites. Minor structures which were earlier obscured in charnockites are clearly seen in bleached areas. In intensely shear areas, formation of highly fissile grey gneiss results often with the development of flaser and mylonitic structures. Fluid inclusion studies and geochemical investigations carried out for serial samples collected from charnockite to gneiss indicate following features: (1) there is a gradual decrease in density of CO2-rich fluids from 1.073 to 0.821 g/cu cm; (2) interestingly, in many sections of the gneisses studied, there is almost complete absence of fluid inclusions suggesting that they would have decrepitated (this may be due to large pressure difference (2 to 3 Kb.) created between the interior and exterior of the fluid inclusions); and (3) presence of mixed CO2-H2O inclusions were noticed.

Srikantappa, C.↗
NASA NTRS1987

The effect of fluid mechanical stress on cellular arachidonic acid metabolism

The effect of sublytic levels of mechanical perturations of cells on cell metabolism were investigated by analyzing the products of arachidonic acid (used as a marker metabolite) in blood platelets, polymorphonuclear leucocytes, and cultured umbilical-vein endothelial cells after the suspensions of these cells were subjected to a shear stress in a modified viscometer. It is shown that the sublytic levels of mechanical stress stimulated the arachidonic acid metabolism in all these cell types. Possible biological implications of this stress-metabolism coupling are discussed.

Mcintire, L. V.↗
NASA NTRS1988

Ongonite and topazite dikes in the Flying W ranch area, Tonto basin, Arizona

The petrogenesis of the topaz-rich ongonite and topazite dikes in the Flying W ranch area (Tonto basin, Arizona) was investigated, and the possible origin of the topaz in the Flying W rhyolite is discussed. The field, textural geochemical, and mineralogical characteristics of the topaz-bearing dikes in the Flying W ranch area all were found to support the genesis of the topaz-bearing bodies from a magma. The evidence obtained contradicts an origin for these rock types by greisenization or veining.

Kortemeier, Winifred T.↗
NASA NTRS1990

Intraocular pressure, retinal vascular, and visual acuity changes during 48 hours of 10-deg head-down tilt

Intraocular pressures, retinal vascular diameters, and visual acuities of nine men, were repeatedly measured while the subjects were tilted 10 deg head-down for 48 h and while they were seated before (baseline), and after the tilt. An immediate increase in intraocular pressure, measured by pneumatonometer was recorded when subjects assumed the head-down position, and diurnal variations in intraocular pressures were observed for the 48 h. The initial and final head-down intraocular pressures were not significantly different. However, when subjects resumed the sitting position, intraocular pressures fell below the initial sitting values. Computer image analysis of the retinal vasculature detected a 6 percent and 2 percent reduction in the caliber of arteries and veins, respectively, as compared with sitting baseline values. No changes in visual acuity were documented during the 48 h of head-down tilt. The data suggest that the choroidal blood reservoir increases in volume over 48 h at continuous head-down position with a compensatory decrease in aqueous volume. These findings may explain intraocular pressure changes noted in astronauts during previous space missions and in studies associated with change in body position.

Mader, Thomas H.↗
NASA NTRS1990

A discussion of 'Anomalous quartz from the Roter Kamm impact crater, Namibia - Evidence for post-impact hydrothermal activity?'

This paper presents arguments against the statement made by Koeberl et al. (1989) to the effect that various differences between the quartz of the three quartz pebbles from the Roter Kamm impact crater (Namibia) and the quartz of the pegmatites present in the basement rocks of this crater can be best interpreted as evidence that the pebbles were formed (or 'recrystallized') by a post-impact hydrothermal system. Arguments are presented that suggest that the three quartz pebbles are, most likely, fragments of a preimpact vein quartz of hydrothermal origin.

Roedder, Edwin↗
NASA NTRS1991

Calcic micas in the Allende meteorite - Evidence for hydration reactions in the early solar nebula

Two calcic micas, clintonite and margarite, have been identified in alteration products in a calcium- and aluminum-rich inclusion (CAI) in the Allende meteorite. Clintonite replaces grossular in alteration veins, and margarite occurs as lamellae in anorthite. Their occurrence suggests that, in addition to undergoing high-temperature alteration by a volatile and iron-rich vapor that produced the grossular and anorthite, some CAIs underwent alteration at moderate temperatures (400 K or less). Petrographic evidence suggests that the calcic micas formed before accretion but after the formation of the layered rim sequences that surround the CAI. These calcic micas provide strong evidence that, contrary to theoretical calculations, some hydration reactions occurred in the early solar nebula.

Keller, Lindsay P.↗
NASA NTRS1991

Aqueous alteration of the Nakhla meteorite

Interior samples of three different Nakhla specimens contain an iron-rich silicate 'rust' (which includes a tentatively identified smectite), Ca-carbonate (probably calcite), Ca-sulfate (possibly gypsum or bassanite), Mg-sulfate (possibly epsomite or kieserite), and NaCl (halite); the total abundance of these phases is estimated as less than 0.01 weight percent of the bulk meteorite. Rust veins are truncated and decrepitated by fusion crust and are preserved as faulted segments in partially healed olivine crystals, indicating that the rust is preterrestrial in origin. Because Ca-carbonate and Ca-sulfate are intergrown with the rust, they are also indicated to be of preterrestrial origin. Similar textural evidence regarding origins of the NaCl and Mg-sulfate is lacking. Impure and poorly crystallized sulfates and halides on the fusion crust of the meteorite suggest leaching of interior (preterrestrial) salts from the interior after Makhla arrived on earth, but coincidental addition of these same salts by terrestrial contamination cannot be exluded. At least the clay-like silicate 'rust', Ca-carbonate, and Ca-sulfate were formed by precipitation from water-based solutions on the Nakhla parent planet, although temperature and pressure conditions of aqueous precipitation are unconstrained by currently available data. It is possible that aqueous alteration on the parent body was responsible for the previously observed disturbance of the Rb-Sr geochronometer in Nakhla at or near 1.3 Ga.

Gooding, James L.↗
NASA NTRS1991

Physical properties of cryovolcanic brines: Applications to the evolution of Ganymede

Carbonaceous chondrites contain abundant veins of water soluble salts, including carbonates and hydrated sulfates of Mg, Ca, Na, Ni, and Fe. These constitute over 1/4 of the mass of the meteorite Orgueil. Magnesium sulfate is the most abundant salt, constituting nearly half the mass of all salt components combined (anhydrous), and 73 pct. of the highly water soluble salts. The assumption that icy satellites and asteroids contain rock compositionally similar to carbonaceous chondrites suggests that salts may be important in the cryoigneous evolution of icy satellites and asteroids. Ordinary chondrites, an alternative rock component of icy satellites, lack abundant salts, although their anhydrous silicate assemblages are unstable with respect to water and would react to produce salts upon initial melting of ice. Some basic physiochemical properties are reviewed of likely cryovolcanic brines and how the existence of soluble salts in Ganymede might affect its structure and evolution is considered. Observations indicate late stage (post heavy bombardment and post tectonic) volcanism on Ganymede. The highly fluid character of Ganymedian volcanism is consistent with extrusions of either water or salt water brines.

Kargel, Jeffrey S.↗
NASA NTRS1992

Measurement of venous compliance (8-IML-1)

The prime objective of this International Microgravity Laboratory (IML-1) investigation is to measure the bulk compliance (distensibility) of the veins in the lower leg before, during, and after spaceflight. It is of particular interest whether venous compliance over the range of both positive and negative transmural pressures (various states of venous distention and collapse) changes throughout the duration of spaceflight. Information concerning the occurrence and character of compliance changes could have implications for the design of improved antigravity suits and further the understanding of inflight and postflight venous hemodynamics.

Thirsk, R. B.↗
NASA NTRS1992

Effects of CSF hormones and ionic composition on salt/water metabolism

This collaborative agreement between Drs. Severs and Keil began in 1981, arising from a continuing interest in the issue of what, exactly, are the consequences of headward fluid shifts during manned spaceflight. Such shifts were recognized early by both U.S. and Soviet Scientists because of signs and symptoms referable to the head. Some of these include disturbed vision, puffiness in the face and periorbital areas, headache, vestibular dysfunction and distended jugular veins. We posited that the fluid shift had an immediate effect on the brain, and a long-term action requiring a neural interpretation of the flight environment. This would re-adjust both efferent neural as well as hormonal mechanisms to sustain cardiovascular and fluid/electrolyte balance consonent with survival in microgravity. Work along these lines is summarized.

Severs, Walter B.↗
NASA NTRS1991

A ferroan region of the lunar highlands as recorded in meteorites MAC88104 and MAC88105

MAC88104 and 88105, paired meteorites of noritic anorthosite composition, are examined. Results indicate that these meteorites contain a variety of materials including impact-melt breccias, igneous and metamorphosed bressia clasts, glass clasts and veins, mineral clasts, and extralunar meteoritic debris. Compositions of the bulk meteorite and its components suggest that it came from a region of the moon's crust that was highly aluminous, low in incompatible trace elements, and ferroan in character.

Jolliff, Bradley L.↗
NASA NTRS1992

CI chondrite-like clasts in the Nilpena polymict ureilite - Implications for aqueous alteration processes in CI chondrites

Petrographic studies of Nilpena polymict ureilite have revealed the presence of small quantities of carbonaceous chondrite matrix clasts. Detailed electron microprobe and TEM studies show that the chemistry and fine-scale mineralogy of one of these clasts is consistent with CI carbonaceous chondrite matrix. Compared to Orgeuil, the phyllosilicate, sulfide, and oxide mineralogy suggests that the Nilpena clasts may represent a less altered type of CI matrix. It is suggested that increased oxidation and aqueous alteration of Nilpena-type materials could result in the formation of the type of mineral assemblage observed in Orgueil. Increased alteration produces progressive more Mg-rich phyllosilicates and more Fe(3+)-rich iron oxides, such as ferrihydrite. As a function of increased alteration, Ca is also progressively leached from the matrix material to form carbonate veins. The depletion of Ca in CI chondrite matrices suggests the Ivuna and Alais may be intermediate in their degree of alteration to Nilpena and Orgueil.

Brearley, Adrian J.↗
NASA NTRS1992

Search for a meteoritic component at the Beaverhead impact structure, Montana

The Beaverhead impact structure, in southwestern Montana, was identified recently by the presence of shatter cones and impactites in outcrops of Proterozoic sandstones of the Belt Supergroup. The cones occur over an area greater than 100 sq km. Because the geologic and tectonic history of this region is long and complex, the outline of the original impact crater is no longer identifiable. The extent of the area over which shatter cones occur suggests, however, that the feature may have been at least 60 km in diameter. The absence of shatter cones in younger sedimentary units suggests that the impact event occurred in late Precambrian or early Paleozoic time. We have collected samples of shocked sandstone from the so-called 'Main Site' of dark-matrix breccias, and of impact breccias and melts from the south end of Island Butte. The melts, occurring often as veins through brecciated sandstone, exhibit a distinctive fluidal texture, a greenish color, and a cryptocrystalline matrix, with small inclusions of deformed sandstone. Samples of the same type, along with country rock, were analyzed previously for major- and trace-element abundances. It was found that, although the major-element composition as relatively uniform, trace-element composition showed variations between the melt material and the adjacent sandstone. These variations were attributed to extensive weathering and hydrothermal alteration. In a more specific search for a possible meteoritic signature in the breccia and the melt material we have conducted a new series of trace-element analyses on powders of our own samples by thermal neutron activation analysis. Our results indicate that Ir abundances in the breccia, the melts, and the adjacent sandstone clasts are no greater than about 0.1 ppb, suggesting no Ir enrichment of the breccia or the melts relative to the country rock. However, both the breccia and the melt material exhibit notable enrichments in Cr (8- and 10-fold), in U (9- and 5-fold), and in the heavy REE's (1.5- and 3-fold), respectively.

Lee, Pascal↗
NASA NTRS1992

The pseudotachylites from the Vredefort structure and the Witwatersrand basin

Pseudotachylite (PT) from both the Sudbury structure in Ontario and the Vredefort Dome in South Africa have been widely cited as the result of shock (impact)-induced brecciation. In the scientific and popular literature PT has been described as shock melt or even as impact melt rock. In contrast, others have for years requested that a clarification of the definitions for PT and impact melt rock be pursued. We have suggested that, until that time when well-defined criteria for genetically different melt rock types (e.g., generated by impact or tectonic processes) will have been established, the term PT should only be used as a descriptive one and that, wherever genetic implications are discussed, other terms, such as impact melt (rock) or friction melt, should be applied. It is obvious that these suggestions are not only of value for the discussion of terrestrial melt rocks of controversial origin, but also apply to the characterization of melt veins in extraterrestrial materials. Important observations on Vredefort and Witwatersrand pseudotachylite are summarized.

Reimold, W. U.↗
NASA NTRS1992

Viscosity determinations of some frictionally generated silicate melts: Implications for slip zone rheology during impact-induced faulting

Analytical scanning electron microscopy, using combined energy dispersive and wavelength dispersive spectrometry, was used to determine the major-element compositions of some natural and artificial glasses and their crystalline equivalents derived by the frictional melting of acid to intermediate protoliths. The major-element compositions are used to calculate the viscosities of their melt precursors using the model of Shaw at temperatures of 800-1400 C, with Fe(2+)/Fe(tot) = 0.5 and for 1-3 wt percent H2O. These results are then modified to account for suspension effects in order to determine viscosities. The results have implications for the generation of pseudotachylitic breccias as seen in the basement lithologies of the Sudbury and Vredefort structures and possibly certain dimict lunar breccias. Many of these breccias show similarities with the more commonly developed pseudotachylite fault and injection veins seen in endogenic fault zones that typically occur in thicknesses of a few centimeters or less. The main difference is one of scale: Impact-induced pseudotachylite breccias can attain several meters in thickness. This would suggest that they were generated under exceptionally high slip rates and hence high strain rates and that the friction melts generated possessed extremely low viscosities.

Spray, John G.↗
NASA NTRS1992

A comparison of the chemistry of pseudotachylyte breccias in the Archean Levack Gneisses of the Sudbury structure, Ontario

The Archean Levack Gneisses of the North Range host millimeter-thick veins and centimeter-thick lenses of pseudotachylyte, as well as substantially larger meter-wide, dykelike bodies of pseudotachylytic 'breccia'. The 'breccia' occurs up to several tens of kilometers away from the Sudbury Igneous Complex and is commonly sited within or near joints and other natural weaknesses such as bedding, dyke contacts, and lithological boundaries. The larger 'breccia' dykes comprise a generally dark matrix containing rounded to subrounded and occasionally angular rock fragments derived predominantly from Levack Gneiss. Selected samples of bulk Sudbury Breccia and Sudbury Breccia matrices were chemically analyzed and compared to existing data on the Levack Gneisses and Sudbury Breccia. The matrices are apparently enriched in Fe and, to a lesser extent, Mg, Ti, and Ca compared to the wallrocks and the majority of clasts. This enrichment can be partly explained by the preferential cataclasis and/or frictional melting of hydrous ferromagnesian wallrock minerals, but also appear to require contamination by more basic exotic lithologies. This suggests that certain components of pseudotachylitic Sudbury Breccia have undergone significant transport during their formation.

Thompson, Lucy M.↗
NASA NTRS1992

The effects of Venusian mantle convection with multiple phase transitions

Recently there was a flurry of activities in studying the effects of phase transitions in the Earth's mantle. From petrological and geophysical considerations, phase-transitions would also play an important role in venusian dynamics. The basic differences between the two planets are the surface boundary conditions, both thermally and mechanically. In this vein we have studied time-dependent mantle convection with multiple phase transitions and depth-dependent thermal expansivity (alpha is approximately rho(exp -6)), based on high-pressure and temperature measurements. Both the olivine-spinel and spinel-perovskite transitions were simulated by introducing an effective thermal expansivity, as described. Used together with the extended Boussinesq Approximation this method serves as a powerful tool to examine the effects of phase transitions on convection at relatively low computational costs.

Steinbach, V.↗
NASA NTRS1993

Explosive volcanism and the compositions of cores of differentiated asteroids

Eleven iron meteorite groups show correlations between Ni and siderophile trace elements that are predictable by distribution coefficients between liquid and solid metal in fractionally crystallizing metal magmas. These meteorites are interpreted to be fragments of the fractionally crystallized cores of eleven differentiated asteroids. Many of these groups crystallized from S-depleted magmas which we propose resulted from removal of the first partial melt (the Fe,Ni-FeS cotectic melt) by explosive pyroclastic volcanism of the type envisaged by Wilson and Keil (1991). We show that these dense, negatively buoyant melts can be driven to asteroidal surfaces due to the presence of excess pressure in the melt and the presence of buoyant bubbles of gas which decrease the density of the melt. We also show that, in typical asteroidal materials, veins will form which grow into dikes and serve as pathways for migration of melt and gas to asteroidal surfaces. Since cotectic Fe, Ni-FeS melt consists of about 85 wt pct FeS and 15 wt pct Fe, Ni, removal of small volumes of eutectic melts results in major loss of S but only minor loss of Fe,Ni, thus leaving sufficient Fe,Ni to form sizeable asteroidal cores.

Keil, Klaus↗