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NASA NTRS1975

Ultraviolet photometry from the Orbiting Astronomical Observatory. XX - The ultraviolet extinction bump

Ultraviolet extinction bumps are investigated in the interstellar extinction curves between 1800 and 3600 A for 36 stars which have (B-V) excesses ranging from 0.03 to 0.55 and are mostly confined to the brighter OB associations distributed along the galactic plane. Each extinction curve is found to have a broad bump which peaks near 2175 A and whose position and profile appear to be constant among all the stars. It is shown that the bump is probably interstellar in origin and that the constancy of its position and shape places such severe restrictions on grain geometrical parameters that classical scattering theory cannot be used to explain the feature unless the dust grains in widely separated regions of space and with very different physical conditions are assumed to have nearly identical size and shape distributions. Three extinction curves which extend to 1100 A are examined and found to have the same general characteristics as the others. Several extinction curves are analyzed for fine structure, but no convincing evidence is found in the present interval. Some processes are discussed which may be responsible for the bumps.

Savage, B. D.↗

NASA NTRS1980

Charge composition and energy spectra of ancient solar flare heavy nuclei

Nuclear tracks in olivine grains from three carbonaceous chondrites are analyzed to determine the energy spectra and charge compositions of solar flare heavy nuclei during the early history of the solar system. Track length measurements of grains irradiated before compaction into meteorites over 4 billion years ago were performed accompanied by calibration experiments using heavy ion beams from an accelerator to identify tracks formed by very heavy (Z between 20 and 28) and very very heavy (Z greater than or equal to 30) groups of nuclei in the Murchison, Murray and Cold Bokkeveld meteorite grains. The time-averaged spectral shape of the solar flare very heavy nuclei is found to be similar to that obtained in lunar sample studies and direct observations. The meteorite grains also reproduce the currently observed enrichment of low-energy heavy ions in solar cosmic rays with respect to photospheric levels, with enhancement factors from 2 to 12 in the energy interval 6-10 MeV/n. Variations of very very heavy/very heavy nuclei abundance ratios within individual kinetic energy intervals are interpreted as representing possible changes of solar flare activity on time scales of 10,000 years.

Goswami, J. N.↗

NASA NTRS1973

Some scattering problems of interstellar grains

Consideration of the general effects of size, shape, chemical composition, index of refraction, temperature, and other physical parameters of small particles upon their scattering properties. A determination of the relative importance of these effects to interstellar dust interpretations is attempted with the ultimate aim of a full definition of interstellar grain optics.

Greenberg, J. M.↗

NASA NTRS1978

Two-micron line emission from the H II region G 333.6-0.2

Spectrophotometry of the H II region G 333.6-0.2 with a resolution of approximately 100 shows strong emission lines of hydrogen and helium superimposed on a continuum. Spatial variations in the equivalent widths of the lines suggest the presence of very hot (at least 600 K) dust grains within the region. The shape of this very powerful H II region indicates that its dense ionized core is being continuously replenished from a reservoir of neutral gas.

Wynn-Williams, C. G.↗

NASA NTRS1981

Creep shear behavior of the oxide dispersion strengthened superalloy MA 6000E

The shear rupture life of the oxide dispersion strengthened (ODS) superalloy MA 6000E was determined at 650 and 760 C was 250 MPa. Comparisons were made at 760 C with the conventional cast superalloy B-1900+Hf, the ODS alloy MA 754, and the directionally solidified eutectic alloy gamma/gamma prime-delta was 170 MPa, and for B-1900+Hf was 360 MPa. The ODS alloy MA 6000E and gamma/gamma prime-delta failed with very little indication of ductile accommodation. Both MA 754 and B-1900+Hf showed some ductile tearing. Fracture surfaces of the ODS alloy MA 754 showed discontinuities similar size, shape, and roughness to its grain structure, but the fracture surfaces of MA 6000E were much smoother than its grain boundaries.

Glasgow, T. K.↗

NASA NTRS1985

Structural characterization and gas reactions of small metal particles by high-resolution TEM and TED

The interaction of 100 and 200 keV electron beams with amorphous alumina, titania, and aluminum nitride substrates and nanometer-size palladium particulate deposits was investigated for the two extreme cases of (1) large-area electron-beam flash-heating and (2) small-area high-intensity electron-beam irradiation. The former simulates a short-term heating effect with minimum electron irradiation exposure, the latter simulates high-dosage irradiation with minimum heating effect. All alumina and titania samples responded to the flash-heating treatment with significant recrystallization. However, the size, crystal structure, shape, and orientation of the grains depended on the type and thickness of the films and the thickness of the Pd deposit. High-dosage electron irradiation also readily crystallized the alumina substrate films but did not affect the titania films. The alumina recrystallization products were usually either all in the alpha phase, or they were a mixture of small grains in a number of low-temperature phases including gamma, delta, kappa, beta, theta-alumina. Palladium deposits reacted heavily with the alumina substrates during either treatment, but they were very little effected when supported on titania. Both treatments had the same, less prominent localized crystallization effect on aluminum nitride films.

Heinemann, K.↗

NASA NTRS1991

Grain growth kinetics in liquid-phase-sintered zinc oxide-barium oxide ceramics

Grain growth of ZnO in the presence of a liquid phase of the ZnO-BaO system has been studied for temperatures from 1300 to 1400 C. The specimens were treated in boiling water and the grains were separated by dissolving the matrix phase in an ultrasonic bath. As a consequence 3D grain size measurements were possible. Microstructural examination shows some grain coalescence with a wide range of neck size ratios and corresponding dihedral angles, however, most grains are isolated. Lognormal grain size distributions show similar shapes, indicating that the growth mechanism is invariant over this time and temperature. All regressions between G exp n and time for n = 2 and 3 proved statistically significant. The rate constants calculated with the growth exponent set to n = 3 are on the same order of magnitude as in metallic systems. The apparent activation energy for growth is estimated between 355 and 458 kJ/mol.

Yang, Sung-Chul↗

NASA NTRS1992

Aerodynamics of a finite wing with simulated ice

The effect of a simulated glaze ice accretion on the aerodynamic performance of a three-dimensional wing is studied experimentally. Results are reviewed from earlier two-dimensional tests which show the character of the large leading-edge separation bubbles caused by the simulated ice accretion. The 2-D bubbles are found to closely resemble well known airfoil laminar separation bubbles. For the 3-D experiments a semispan wing of effective aspect ratio five was mounted from the sidewall of the UIUC subsonic wind tunnel. The model uses a NACA 0012 airfoil section on a rectangular planform with interchangeable tip and root sections to allow for 0- and 30-degree sweep. A three-component sidewall balance was used to measure lift, drag and pitching moment on the clean and iced model. Fluorescent oil flow visualization has been performed on the iced model and reveals extensive spanwise and vortical flow in the separation bubble aft of the upper surface horn. Sidewall interaction and spanwise nonuniformity are also seen on the unswept model. Comparisons to the computed flow fields are shown. Results are also shown for roughness effects on the straight wing. Sand grain roughness on the ice shape is seen to have a different effect than isolated 3-D roughness elements.

Bragg, M. B.↗

NASA NTRS1996

Ultralow Friction in a Superconducting Magnetic Bearing

Passive levitation by superconducting magnetic bearings can be utilized in flywheels for energy storage. Basic design criteria of such a bearing are high levitation force, sufficient vertical and horizontal stability and low friction. A test facility was built for the measurement and evaluation of friction in a superconducting magnetic bearing as a function of operating temperature and pressure in the vacuum vessel. The bearing consists of a commercial disk shaped magnet levitated above single grain, melt-textured YBCO high-temperature superconductor material. The superconductor was conduction cooled by an integrated AEG tactical cryocooler. The temperature could be varied from 50 K to 80 K. The pressure in the vacuum chamber was varied from 1 bar to 10(exp -5) mbar. At the lowest pressure setting, the drag torque shows a linear frequency dependence over the entire range investigated (0 less than f less than 40 Hz). Magnetic friction, the frequency independent contribution, is very low. The frequency dependent drag torque is generated by molecular friction from molecule-surface collisions and by eddy currents. Given the specific geometry of the set-up and gas pressure, the molecular drag torque can be estimated. At a speed of 40 Hz, the coefficient of friction (drag-to-lift ratio) was measured to be mu = 1.6 x 10(exp -7) at 10(exp -5) mbar and T = 60 K. This is equivalent to a drag torque of 7.6 x 10(exp -10) Nm. Magnetic friction causes approx. 1% of the total losses. Molecular friction accounts for about 13% of the frequency dependent drag torque, the remaining 87% being due to eddy currents and losses from rotor unbalance. The specific energy loss is only 0.3% per hour.

Bornemann, Hans J.↗

NASA NTRS1994

Plant Responses to Increased UV-B Radiation: A Research Project

Ozone decrease implies more ultraviolet-B (UV-B) radiation reaching the surface of the Earth. Increased UV-B radiation triggers responses by living organisms. Despite the large potential impacts on vegetation, little is known about UV-B effects on terrestrial ecosystems. Long-term ecological studies are needed to quantify the effects of increased UV radiation on terrestrial ecosystems, asses the risks, and produce reliable data for prediction. Screening pigments are part of one of the protective mechanism in plants. Higher concentrations of screening pigments in leaves may be interpreted as a response to increased UV radiation. If the screening effect is not sufficient, important molecules will be disturbed by incoming radiation. Thus, genetics, photosynthesis, growth, plant and leaf shape and size, and pollen grains may be affected. This will have an impact on ecosystem dynamics, structure and productivity. It is necessary to monitor selected terrestrial ecosystems to permit detection and interpretation of changes attributable to global climate change and depleted ozone shield. The objectives of this project are: (1) To identify and measure indicators of the effects of increased solar UV-B radiation on terrestrial plants; (2) to select indicators with the greatest responses to UV-B exposure; (3) to test, adapt or create ecosystem models that use the information gathered by this project for prediction and to enhance our understanding of the effects of increased UV-B radiation on terrestrial ecosystems. As a first step to achieve these objectives we propose a three-year study of forest and steppe vegetation on the North slope of the Brooks Range (within the Arctic circle, in Alaska), in the Saguaro National Monument (near Tucson, Arizona) and in the forests and steppes of Patagonia (Argentina). We selected (1) vegetation north of the Polar Circle because at 70N there is 8% risk of plant damage due to increased UV-B radiation; (2) the foothills of Catalina Mountains because there is anecdotal evidence of plant damage on the saguaros that has been linked to increased UV radiation, and (3) the forests of Nothofagus spp. and the steppe of Patagonia where the risk of plant damage at 35S is 5% and increases to as much as 15% at 55S due to increased UV-B radiation. Measurements of UV-B radiation impinging on the surface at 55S largely exceed the predicted UV-B radiation values at 50 latitude and 0% ozone depletion. Preliminary HPLC analyses of UV-B absorbing compounds in Nothofagus antartica, N. pumilio, N. betuloides and Rumex sp. in natural conditions show species-specific patterns. The spectrum of N. antartica grown at 38S differs significantly from that of N. antartica in natural conditions in Ushuaia (55S). These results suggest that the selected main area (Patagonia) is appropriate for assessing the problem and its magnitude and that Nothofagus is appropriate for our study.

DAntoni, H. L.↗

NASA NTRS1997

Structure of potato tubers formed during spaceflight

Potato (Solanum tuberosum L. cv. Norland) explants, consisting of a leaf, axillary bud, and small stem segment, were used as a model system to study the influence of spaceflight on the formation of sessile tubers from axillary buds. The explants were flown on the space shuttle Columbia (STS-73, 20 October to 5 November 1995) in the ASTROCULTURE (TM) flight package, which provided a controlled environment for plant growth. Light and scanning electron microscopy were used to compare the precisely ordered tissues of tubers formed on Earth with those formed during spaceflight. The structure of tubers produced during spaceflight was similar to that of tubers produced in a control experiment. The size and shape of tubers, the geometry of tuber tissues, and the distribution of starch grains and proteinaceous crystals were comparable in tubers formed in both environments. The shape, surface texture, and size range of starch grains from both environments were similar, but a greater percentage of smaller starch grains formed in spaceflight than on Earth. Since explant leaves must be of given developmental age before tubers form, instructions regarding the regular shape and ordered tissue geometry of tubers may have been provided in the presence of gravity. Regardless of when the signalling occurred, gravity was not required to produce a tuber of typical structure.

manned↗

NASA NTRS1984

Fabrication development for ODS-superalloy, air-cooled turbine blades

MA-600 is a gamma prime and oxide dispersion strengthened superalloy made by mechanical alloying. At the initiation of this program, MA-6000 was available as an experimental alloy only and did not go into production until late in the program. The objective of this program was to develop a thermal-mechanical-processing approach which would yield the necessary elongated grain structure and desirable mechanical properties after conventional press forging. Forging evaluations were performed to select optimum thermal-mechanical-processing conditions. These forging evaluations indicated that MA-6000 was extremely sensitive to die chilling. In order to conventionally hot forge the alloy, an adherent cladding, either the original extrusion can or a thick plating, was required to prevent cracking of the workpiece. Die design must reflect the requirement of cladding. MA-6000 was found to be sensitive to the forging temperature. The correct temperature required to obtain the proper grain structure after recrystallization was found to be between 1010-1065 C (1850-1950 F). The deformation level did not affect subsequent crystallization; however, sharp transition areas in tooling designs should be avoided in forming a blade shape because of the potential for grain structure discontinuities. Starting material to be used for forging should be processed so that it is capable of being zone annealed to a coarse elongated grain structure as bar stock. This conclusion means that standard processed bar materials can be used.

Moracz, D. J.↗

NASA NTRS1995

Solid Carbonyl Sulphide (OCS) in W33A

We present ground-based observations of the 2041/cm (4.9 micrometer) absorption feature toward the deeply embedded protostar W33A. We attribute this interstellar feature to solid carbonyl sulphide (OCS) embedded in icy grain mantles along the line of sight. We have made an extensive laboratory study of the infrared characteristics of OCS in various ice mixtures. Studies of the 2041/cm band of solid OCS and solid mixtures containing OCS show that its shape and peak position are sensitive to the molecular environment of the OCS molecule. Mie scattering calculations show that the peak position and profile of the OCS band depend on the shape and size of the absorbing grain when the OCS concentration is larger than 0.05. For lower OCS concentrations, laboratory-measured bulk spectra agree very well with the absorption spectra of small grains. We have compared the observed feature with laboratory and theoretical spectra of astrophysically relevant mixtures. The best agreement is obtained for mixtures with traces of OCS in a methanol-rich matrix. This would suggest the presence of independent grain components and in particular of a minor fraction of methanol-rich icy grain mantles in which OCS is embedded. From the strength of the absorption feature we deduce a OCS/H 20 ratio, along the line of sight, of 4 x 10(exp -4).

Palumbo, M. E.↗

NASA NTRS1995

Solid Carbonyl Sulphide (OCS) in W33A

We present ground-based observations of the 2041 cm(exp -1) (4.9 mm) absorption feature toward the deeply embedded protostar W33A. We attribute this interstellar feature to solid carbonyl sulphide (OCS) embedded in icy grain mantles along the line of sight. We have made an extensive laboratory study of the infrared characteristics of OCS in various ice mixtures. Studies of the 2041 cm(exp -1) band of solid OCS and solid mixtures containing OCS show that its shape and peak position are sensitive to the molecular environment of the OCS molecule. Mie scattering calculations show that the peak position and profile of the OCS band depend on the shape and size of the absorbing grain when the OCS concentration is larger than 0.05. For lower OCS concentrations, laboratory-measured bulk spectra agree very well with the absorption spectra of small grains. We have compared the observed feature with laboratory and theoretical spectra of astrophysically relevant mixtures. The best agreement is obtained for mixtures with traces of OCS in a methanol-rich matrix. This would suggest the presence of independent grain components and in particular of a minor fraction of methanol-rich icy grain mantles in which OCS is embedded. From the strength of the absorption feature we deduce a OCS/H2O ratio, along the line of sight, of 4 x 10(exp -4).

Palumbo, M. E.↗

NASA NTRS2005

Lunar and Planetary Science XXXVI, Part 14

Contents include the following: Destruction of Presolar Silicates by Aqueous Alteration Observed in Murchison CM2 Chondrite. Generation of Chondrule Forming Shock Waves in Solar Nebula by X-Ray Flares. TEM and NanoSIMS Study of Hydrated/Anhydrous Phase Mixed IDPs: Cometary or Asteroidal Origin? Inflight Calibration of Asteroid Multiband Imaging Camera Onboard Hayabusa: Preliminary Results. Corundum and Corundum-Hibonite Grains Discovered by Cathodoluminescence in the Matrix of Acfer 094 Meteorite. Spatial Extent of a Deep Moonquake Nest A Preliminary Report of Reexamination. Modal Abundances of Carbon in Ureilites: Implications for the Petrogenesis of Ureilites. Trapped Noble Gas Components and Exposure History of the Enstatite Chondrite ALH84206. Deep-seated Crustal Material in Dhofar Lunar Meteorites: Evidence from Pyroxene Chemistry. Numerical Investigations of Kuiper Belt Binaries. Dust Devils on Mars: Effects of Surface Roughness on Particle Threshold. Hecates Tholus, Mars: Nighttime Aeolian Activity Suggested by Thermal Images and Mesoscale Atmospheric Model Simulations. Are the Apollo 14 High-Al Basalts Really Impact Melts? Garnet in the Lunar Mantle: Further Evidence from Volcanic Glass Beads. The Earth/Mars Dichotomy in Mg/Si and Al/Si Ratios: Is It Real? Dissecting the Polar Asymmetry in the Non-Condensable Gas Enhancement on Mars: A Numerical Modeling Study. Cassini VIMS Preliminary Exploration of Titan s Surface Hemispheric Albedo Dichotomy. An Improved Instrument for Investigating Planetary Regolith Microstructure. Isotopic Composition of Oxygen in Lunar Zircons Preliminary Design of Visualization Tool for Hayabusa Operation. Size and Shape Distributions of Chondrules and Metal Grains Revealed by X-Ray Computed Tomography Data. Properties of Permanently Shadowed Regolith. Landslides in Interior Layered Deposits, Valles Marineris, Mars: Effects of Water and Ground Shaking on Slope Stability. Mars: Recent and Episodic Volcanic, Hydrothermal, and Glacial Activity Revealed by Mars Express High Resolution Stereo Camera (HRSC). The Cratering Record of the Saturnian Satellites Phoebe, Tethys, Dione and Iapetus in Comparison: First Results from Analysis of the Cassini ISS Imaging Data. Joint Crossover Solutions of Altimetry and Image Data on 433 Eros. The Martian Soil as a Geochemical Sink for.

Source record↗

NASA NTRS1993

Thermal conductivity measurements of particulate materials under Martian conditions

The mean particle diameter of surficial units on Mars has been approximated by applying thermal inertia determinations from the Mariner 9 Infrared Radiometer and the Viking Infrared Thermal Mapper data together with thermal conductivity measurement. Several studies have used this approximation to characterize surficial units and infer their nature and possible origin. Such interpretations are possible because previous measurements of the thermal conductivity of particulate materials have shown that particle size significantly affects thermal conductivity under martian atmospheric pressures. The transfer of thermal energy due to collisions of gas molecules is the predominant mechanism of thermal conductivity in porous systems for gas pressures above about 0.01 torr. At martian atmospheric pressures the mean free path of the gas molecules becomes greater than the effective distance over which conduction takes place between the particles. Gas particles are then more likely to collide with the solid particles than they are with each other. The average heat transfer distance between particles, which is related to particle size, shape and packing, thus determines how fast heat will flow through a particulate material.The derived one-to-one correspondence of thermal inertia to mean particle diameter implies a certain homogeneity in the materials analyzed. Yet the samples used were often characterized by fairly wide ranges of particle sizes with little information about the possible distribution of sizes within those ranges. Interpretation of thermal inertia data is further limited by the lack of data on other effects on the interparticle spacing relative to particle size, such as particle shape, bimodal or polymodal mixtures of grain sizes and formation of salt cements between grains. To address these limitations and to provide a more comprehensive set of thermal conductivities vs. particle size a linear heat source apparatus, similar to that of Cremers, was assembled to provide a means of measuring the thermal conductivity of particulate samples. In order to concentrate on the dependence of the thermal conductivity on particle size, initial runs will use spherical glass beads that are precision sieved into relatively small size ranges and thoroughly washed.

Presley, M. A.↗

NASA NTRS2003

Evolution and Transport of Water in the Upper Regolith of Mars

Long standing theoretical predictions [1-3], as well as recent spacecraft observations [4] indicate that large quantities of ice is present in the high latitudes upper decimeters to meters of the Martian regolith. At shallower depths and warmer locations small amounts of H2O, either adsorbed or free, may be present transiently. An understanding of the evolution of water based on theoretical and experimental considerations of the processes operating at the Martian environment is required. In particular, the porosity, diffusivity, and permeability of soils and their effect on water vapor transport under Mars-like conditions have been estimated, but experimental validation of such models is lacking. Goal: Three related mechanisms may affect water transport in the upper Martian regolith. 1) diffusion along a concentration gradient under isobaric conditions, 2) diffusion along a thermal gradient, which may give rise to a concentration gradient as ice sublimes or molecules desorb from the regolith, and 3) hydraulic flow, or mass motion in response to a pressure gradient. Our combined theoretical and experimental investigation seeks to disentangle these mechanisms and determine which process(es) are dominant in the upper regolith over various timescales. A detailed one-dimensional model of the upper regolith is being created which incorporates water adsorption/ desorption, condensation, porosity, diffusivity, and permeability effects. Certain factors such as diffusivity are difficult to determine theoretically due to the wide range of intrinsic grain properties such as particle sizes, shapes, packing densities, and emergent properties such as tortuosity. An experiment is being designed which will allow us to more accurately determine diffusivity, permeability, and water desorption isotherms for regolith simulants.

Hudson, T. L.↗

NASA NTRS2013

Water Contents of the Mantle Beneath the Rio Grande Rift: FTIR Analysis of Kilbourne Hole Peridotite Xenoliths

Although nominally anhydrous mantle minerals contain only trace amounts of water, they are the main reservoir of water in the mantle. Added up at the scale of the Earth's mantle, these trace amounts of water represent oceans worth in mass]. Mantle xenoliths from Kilbourne Hole in southern New Mexico are ideal to study mantle water distribution in a rift tectonic setting as they come from a recently‐erupted maar in the middle of the Rio Grande Rift. Eleven lherzolites, one harzburgite, and one dunite are being analyzed for water contents by FTIR. The xenoliths will also be analyzed for major and trace element composition, Fe3+/Summation (Fe) ratios, and characterized petrologically. Olivines exhibit variable water contents with less water at the rims compared to the cores. This is probably due to H loss during decompression and xenolith transport by the host magma. Mantle water contents appear to have been primarily preserved in the core of the olivines, based on diffusion modeling of the typically plateau-shaped water content profiles across these grains. Water concentrations are in equilibrium between clino- and orthopyroxene, but olivine concentrations are typically not in equilibrium with those of either pyroxene. Lherzolites analyzed so far have water contents of 2‐12 ppm H2O in olivines, 125‐165 ppm H2O in orthopyroxenes, and 328‐447 ppm H2O in clinopyroxenes. These water contents are similar to, but with a narrower range, than those for the respective minerals in other continental peridotite xenoliths. The lherzolites have bulk-rock (BR) Al2O3 contents that range between 3.17 and 3.78 wt%, indicating similar degrees of partial melting, which could explain the narrow range of their pyroxene water contents. Primitive mantle normalized rare earth element (REE) profiles of the bulk lherzolites vary from light REE depleted to flat, with no significant differences between, nor relation to, their mineral water contents. Consequently, the metasomatic agents that enriched LREEs in these lherzolites were most likely water-poor. The harzburgite and the dunite have lower weight percent Al2O3 compared to the lherzolites (2.11% and 0.34% respectively) indicating higher degrees of melting. Their olivine water contents, however, are similar to those of the lherzolites. Moreover, no correlations are observed between pyroxene water contents and indices of melting or metasomatism between the lherzolite group, the harzburgite, and the dunite, although the latter has the lowest pyroxene water contents. More samples will be analyzed to determine if the water contents are controlled by melting, metasomatism, or a combination of the two in the Kilbourne Hole mantle.

Schaffer, Lillian A.↗