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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Role of minerals in the thermal alteration of organic matter. I - Generation of gases and condensates under dry condition

Pyrolysis experiments conducted at 200 and 300 C on kerogen and bitumen from the Monterey formation and on the Green River Formation kerogen with montmorillonite, illite, and calcite added are described. The pyrolysis products are identified and gas and condensate analyses are performed. A catalytic effect is detected in the pyrolysis of kerogen with montmorillonite; however, illite and calcite display no catalytic activity. The increased production of C1-C6 hydrocarbons and the dominance of branched hydrocarbons in the C4-C6 range reveals a catalytic influence. It is observed that the catalysis of montmorillonite is greater during bitumen pyrolysis than for kerogen, and catalysis with minerals affects the production of CO2. It is concluded that a mineral matrix is important in determining the type and amount of gases and condensates forming from organic matter under thermal stress.

Tannenbaum, E.↗
NASA NTRS1987

Part 2: Sedimentary geology of the Valles, Marineris, Mars and Antarctic dry valley lakes

Detailed mapping of the layered deposits in the Valles Marineris, Mars from high-resolution Viking orbiter images revealed that they from plateaus of rhythmically layered material whose bases are in the lowest elevations of the canyon floors, and whose tops are within a few hundred meters in elevation of the surrounding plateaus. Four hypotheses for the origin of the layered deposits were considered: that they are eolian deposits; that they are remnants of the same material as the canyon walls; that they are explosive volcanic deposits; or that they were deposited in standing bodies of water. There are serious morphologic objections to each of the first three. The deposition of the layered deposits in standing bodies of water best explains their lateral continuity, horizontality, great thickness, rhythmic nature, and stratigraphic relationships with other units within the canyons. The Martian climatic history indicated that any ancient lakes were ice covered. Two methods for transporting sediment through a cover of ice on a martian lake appear to be feasible. Based on the presently available data, along with the theoretical calculations presented, it appears most likely that the layered deposits in the Valles Marineris were laid down in standing bodies of water.

Nedell, Susan S.↗
NASA NTRS1987

Numerical simulation of polar lows and comma clouds using simple dry models

Linear and nonlinear numerical channel models are used to simulate polar low/comma cloud evolution. The basic state of the model is idealized and can be specified analytically. It has strong horizontal as well as vertical wind shear and implicitly includes the effect of sensible heat fluxes from the lower boundary. This is done by having a layer of reduced stability present in the lower troposphere. The results of the linear model study are presented and used to provide input for the nonlinear model integration. It is shown that, given sufficient horizontal resolution, many features of polar low/comma clouds can be simulated by the nonlinear primitive equations model and the idealized basic state, in particular a rapidly growing disturbance with a wavelength on the order of 1000 km.

Mudrick, Stephen E.↗
NASA NTRS1988

Formic and acetic acid over the central Amazon region, Brazil. I - Dry season

The concentrations of formic and acetic acids in the gas phase, atmospheric aerosol, and rainwater samples collected in Amazonia at ground level and in the atmosphere during the Amazon Boundary Layer Experiment in July/August 1985 were analyzed by ion exchange chromatography. The diurnal behavior of both acids at ground level and their vertical distribution in the forest canopy point to the existence of vegetative sources as well as to production by chemical reactions in the atmosphere. The concentrations of formic and acetic acids in the gas phase were about 2 orders of magnitude higher than the corresponding concentrations in the atmospheric aerosol. In rainwater, the total formate and acetate represented about one half of the anion equivalents, in contrast to less than 10 percent of the soluble anionic equivalents contributed by these acids in the atmospheric aerosol. The observed levels of these ions in rainwater are considered to be the result of a combination of chemical reactions in hydrometeors and the scavenging of the gaseous acids by cloud droplets.

Andreae, M. O.↗
NASA NTRS1989

The Antarctic dry valley lakes: Relevance to Mars

The similarity of the early environments of Mars and Earth, and the biological evolution which occurred on early Earth, motivates exobiologists to seriously consider the possiblity of an early Martian biota. Environments are being identified which could contain Martian life and areas which may presently contain evidence of this former life. Sediments which were thought to be deposited in large ice-covered lakes are present on Mars. Such localities were identified within some of the canyons of the Valles Marineris and more recently in the ancient terrain in the Southern Hemisphere. Perennially ice-covered Antarctic lakes are being studied in order to develop quantitative models that relate environmental factors to the nature of the biological community and sediment forming processes. These models will be applied to the Martian paleolakes to establish the scientific rationale for the exobiological study of ancient Martian sediments.

Wharton, R. A., Jr.↗
NASA NTRS1989

Stereological characterization of dry alpine snow for microwave remote sensing

A persistent problem in investigations of electromagnetic properties of snow, from reflectance at visible wavelengths to emission and backscattering in the microwave, has been the proper characterization of the snow's physical properties. It is suggested that the granular and laminar structure of snow can be measured in its aggregated state by stereology performed on sections prepared from snow specimens, and that these kinds of measurements can be incorporated into models of the electromagnetic properties. With careful sampling, anisotropy in the snow microstructure at various scales can be quantified. It is shown how stereological parameters can be averaged over orientation and optical depth for radiative transfer modeling.

Davis, Robert E.↗
NASA NTRS1989

Neptune's Triton: A moon rich in dry ice and carbon

The encounter of the spacecraft Voyager 2 with Neptune and its large satellite Triton in August 1989 will provide a crucial test of ideas regarding the origin and chemical composition of the outer solar system. In this pre-encounter publication, the possibility is quantified that Titron is a captured moon which, like Pluto and Charon, originally condensed as a major planetesimal within the gas ring that was shed by the contracting protosolar cloud at Neptune's orbit. Ideas of supersonic convective turbulence are used to compute the gas pressure, temperature and rat of catalytic synthesis of CH4, CO2, and C(s) within the protosolar cloud, assuming that all C is initially present as CO. The calculations lead to a unique composition for Triton, Pluto, Charon: each body consists of, by mass, 18 1/2 percent solid CO2 ice, 4 percent graphite, 1/2 percent CH4 ice, 29 percent methanated water ice and 48 percent of anhydrous rock. This mix has a density consistent with that of the Pluto-Charon system and yields a predicted mean density for Triton of 2.20 + or - 0.5 g/cu cm, for satellite radius equal to 1,750 km.

Prentice, A. J. R.↗
NASA NTRS1990

Radiometric tests on wet and dry antenna reflector surface panels

The results of X-band noise temperature tests on two types of antenna surface panels are presented. The first type tested was a solid antenna panel, while the second type was a perforated panel with 3/16-in.-diameter holes. Measurements were made at 8.45 GHz using an X-band radiometric system. Included in this article are measured noise temperature contributions from: (1) thermal diffusive white paint on solid and perforated panels, and (2) water sprayed on both painted and unpainted perforated panels. Experiments on perforated panels were restricted to the 3/16-in.-diameter hole panels formerly used on Deep Space Network 64-m antennas. Rigorous calibration equations, applicable to a variety of antenna panel and dichroic plate test configurations, are presented. It was demonstrated that an accurate, stable radiometric measurement system of the type used for the results of this research makes it possible to obtain information that would be much more difficult to obtain using other techniques.

Otoshi, T. Y.↗
NASA NTRS1990

Single-ended output GaAs/AlGaAs single quantum well laser with a dry-etched corner reflector

GaAs/AlGaAs single quantum well lasers with integrated corner reflectors have been fabricated using chemically assisted ion beam etching. The air-GaAs interface is internally totally reflecting, and no coherent radiation is transmitted through the corner reflector. The corner reflector laser was compared with a conventional Fabry-Perot laser cleaved from the same wafer. An 11-percent reduction in threshold current and a reduction of the far-field angle from 4.4 deg to 0.7 deg was measured.

Hagberg, M.↗
NASA NTRS1990

Microwave dielectric properties of dry rocks

A combination of techniques was used to measure the dielectric properties of 80 rock samples in the microwave region. The real part (RP) of the relative dielectric constant was measured in 0.1-GHz steps from 0.5 to 18 GHz, and the imaginary part (IP) was measured at five frequencies between 1.6 and 16 GHz. The bulk density rho(b) was also measured for all the samples, and the bulk chemical composition (BCC) was determined for 56 of the samples. RP is found to be frequency-independent at 0.5-18 GHz for all samples, and rho(b) accounts for about 50 percent of the observed variance. For silicate rocks, as much as 78 percent of the variance is explained by the combination of rho(b) and the fractional contents of oxides when the silicates are subgrouped by genesis. In contrast, IP decreases with increasing frequency for most rock samples, and no statistically significant relationships are found between IP and rho(b). For subgrouped silicate rocks, 60 percent of the variance in IP can be explained by BCC.

Ulaby, Fawwaz T.↗
NASA NTRS1990

Electrostatic dry powder prepregging of carbon fiber

Ultrafine, 5-10 micron polymer-matrix resin powders are directly applied to carbon fiber tows by passing then in an air or nitrogen stream through an electrostatic potential; the particles thus charged will strongly adhere to grounded carbon fibers, and can be subsequently fused to the fiber in a continuously-fed radiant oven. This electrostatic technique derived significant end-use mechanical property advantages from the obviation of solvents, binders, and other adulterants. Additional matrix resins used to produce prepregs to date have been PMR-15, Torlon 40000, and LaRC TPI.

Throne, James L.↗
NASA NTRS1990

The effect of coatings and liners on heat transfer in a dry shaft-bush tribosystem

The temperatures due to frictional heating within a solid lubricated or coated journal bearing were analyzed by using a finite element method. A solid model of the shaft-bush tribocontact was generated with an eight-node, three-dimensional, first-order isoparametric heat-transfer element and the Patran solid modeler software. The Patmar (Patran-Marc) translator was used to help develop the Marc-based finite element program for the system; this software was used on the Cray X-MP supercomputer to perform a finite element analysis of the contact. The analysis was performed for various liner materials, for thin, hard, wear-resistant coated bearings, and for different geometries and thermal cooling boundary conditions. The analyses indicated that thermal conductivity of the liner or coating material is the most vital thermal parameter that controls the interface temperature. In addition to design variations, the proximity of the cooling source to the heat-flux-generating interface is critically important to the temperature control in the system.

Ghosh, Mihir K.↗
NASA NTRS1991

The rheology and hydrodynamics of dry powder lubrication

This paper conceptualizes a powder lubrication mechanisms which closely resembles that of a hydrodynamic fluid film. Based on the observations of past investigations and on the author's experiments, it is postulated that a layered shearing of the compacted powder generates velocity, density, and temperature profiles akin to fluid film bearings. Thus, a lubricant consisting of a fine powder unserted either deliberately or one generated by the water of the mating surfaces, constitutes a viable lubricant that generates the required flows and pressures to prevent contact between the surfaces.

Heshmat, Hooshang↗
NASA NTRS1992

Sorbent-Bed Crop-Drying System

Proposed aeration system helps reduce spoilage of stored grain or other crop stored in bulk. Air circulates through bin, sorbent bed, and heat exchanger. Outside air cools circulating air in heat exchanger. Sensors measure temperature and humidity, and adjust dampers to obtain requisite temperature and humidity. Suitable for grain bins and shipping barges.

Roberts, Barry C.↗