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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Navier-Stokes analyses of the redistribution of inlet temperature distortions in a turbine

The flow exiting the combustor and entering the turbine of a gas turbine engine is known to contain both spatial and temporal variations in total temperature. Although historically it has been presumed that the turbine rotor responded to the average temperature, recent experimental evidence has demonstrated that the rotor actually separated the hotter and cooler streams of fluid so that the hotter fluid migrated toward the pressure surface and the cooler fluid migrated toward the suction surface. In the present study a time-accurate, two-dimensional, thin-layer, Navier-Stokes analysis of a turbine stage was used to analyze this phenomenon. The rough qualitative agreement between the measured and the computed results indicated that the analysis had successfully captured many of the important features of the flow.

Rai, Man Mohan↗
NASA NTRS1987

Seasonal air and water mass redistribution effects on LAGEOS and Starlette

Zonal geopotential coefficients have been computed from average seasonal variations in global air and water mass distribution. These coefficients are used to predict the seasonal variations of LAGEOS' and Starlette's orbital node, the node residual, and the seasonal variation in the 3rd degree zonal coefficient for Starlette. A comparison of these predictions with the observed values indicates that air pressure and, to a lesser extent, water storage may be responsible for a large portion of the currently unmodeled variation in the earth's gravity field.

Gutierrez, Roberto↗
NASA NTRS1988

On the redistribution of OB star luminosity and the warming of nearby molecular clouds

IRAS observations of the neighborhoods of six H II regions in the outer Galaxy are correlated with CO maps of the same regions. It is found that more than half of the far-IR luminosity from within about 25 to 75 pc of the ionizing stars is contributed by dust associated with molecular clouds. It is shown that a major and increasing fraction of the OB cluster starlight is not absorbed locally. The observations suggest that the H II regions are not radiation-bounded and have ion densities of about 1/cu cm. A model describing the interstellar environment of OB star clusters as a function of time is presented.

Leisawitz, D.↗
NASA NTRS1989

Turbulence energy redistributive model

A study is made to improve the predictions of turbulent flows through modifications of the pressure-strain correlation of the Reynolds stress equations. The mean-strain term of the pressure-strain correlation is formulated by incorporating the tensor with the Reynolds stresses that account for a non-isotropic turbulence effect in the flows which are accompanied by a turbulent separating flow. This model is compared with other existing models and results are verified with existing experimental results for turbulent shear flows.

Amano, R. S.↗
NASA NTRS1992

Redistribution of subsurface neutrons caused by ground ice on Mars

The purpose of this study is to build on that of Squyres and Evans to approach the specific problem of the buried ice deposits explored by Mellon and Jakosky. Therefore, we calculated the depth dependence of equilibrium neutron energy spectra and related neutron-capture gamma ray production rates for a semi-infinite layer of regolith having a Chryse-fines composition containing 5, 10, and 18 wt percent of water. This high water-content layer was buried beneath the same regolith containing 1 percent water at depths of 20, 40, and 80 g/ sq. cm. A 16-g/sq. cm atmosphere having the abundances measured by Owen et al. was included throughout. We also calculated the effects of a 30-g/sq. cm-thick layer containing 18 percent water embedded within a semi-finite regolith containing 1 percent water, at depths of 20, 40, and 80 g/sq. cm below the atmosphere-surface interface.

Feldman, W. C.↗
NASA NTRS1993

Configuration-shape-size optimization of space structures by material redistribution

This project investigates the configuration-shape-size optimization (CSSO) of orbiting and planetary space structures. The project embodies three phases. In the first one the material-removal CSSO method introduced by Kikuchi and Bendsoe (KB) is further developed to gain understanding of finite element homogenization techniques as well as associated constrained optimization algorithms that must carry along a very large number (thousands) of design variables. In the CSSO-KB method an optimal structure is 'carved out' of a design domain initially filled with finite elements, by allowing perforations (microholes) to develop, grow and merge. The second phase involves 'materialization' of space structures from the void, thus reversing the carving process. The third phase involves analysis of these structures for construction and operational constraints, with emphasis in packaging and deployment. The present paper describes progress in selected areas of the first project phase and the start of the second one.

Vandenbelt, D. N.↗
NASA NTRS1993

Post-igneous redistribution of components in eucrites

In our analyses, we utilize a microdrilling technique that removes 40 to 100 micron diameter cores from mineral grains in thin sections analyzed by microprobe. The cores are then analyzed by INAA using the technique of Lindstrom. Three eucrites were selected for application of this analytical technique: monomict breccias Pasamonte and Stannern and unbrecciated EET90020. Pasamonte is among the most unequilibrated of the eucrites on the basis of zoning in pyroxenes and is considered to be an igneous rock not significantly affected by metamorphism. Stannern has igneous texture but its pyroxenes indicate some re-equilibration, although little, if any, recrystallization. EET90020 has a granulite texture and has been substantially recrystallized. Our sample of Pasamonte contains several clasts of different grain sizes ranging from glass to fine grained with diabasic texture containing lathy plagioclase, unexsolved pigeonite, and mesostasis. Cores were taken of the glass and from minerals and mesostases in six lithic clasts which normally allowed sampling of more than one phase per clast. Our sample of Stannern is also a breccia but with little difference in grain size between clasts and matrix. The plagioclase and pigeonite are blocky, twinned, and exsolved and coexist with a bit of mesostasis. Cores were taken of plagioclase and pigeonite with no attempt to distinguish separate clasts. EET90020 is a granular mixture of twinned plagioclase and pigeonite having rather uniform size and many triple junctions. Several cores were taken of both phases. Both clear and cloudy grains of plagioclase and pyroxene were sampled in all three eucrites.

Phinney, W. C.↗
NASA NTRS1993

Diffusive redistribution of water vapor in the solar nebula revisited

Stevenson and Lunine presented a model for enhancing the abundance of solid material in the region of the solar nebula at the water condensation point. This was used to provide a means to produce a much more rapid formation of Jupiter than the standard solar nebula models. However, they underestimated the drag induced sun-ward radial drift of the planetesimals of interest. Reanalysis reveals that these particles would spread over the inner solar system and might influence the formation of the asteroids.

Sears, William D.↗
NASA NTRS1994

Quasi-periodic atmosphere-regolith-cap CO2 redistribution in the martian past

Our earlier Mars regolith-atmosphere-cap CO2 distribution model (Fanale et al., 1982, Icarus 50, 381-407) has been improved, revised, and extended back over Mars' mid to late history. The present model takes into account four new factors: (1) a more realistic long-term obliquity cycle, (2) thermal conduction as it affects the surface energy balance, (3) the changing solar constant, and (4) atmospheric erosion 3.5 byr ago to the present. Solar insolation and temperatures are computed for the full range of obliquities, latitudes, and epochs, and a CO2 adsorption relation is used, together with a conservation of mass constraint, to calculate atmospheric pressures and exchangeable CO2 mass as functions of obliquity and epoch for the regolith, atmosphere, and polar caps for two assumed thicknesses of a basalt regolith. It is found that the heat conduction term in the surface boundary condition has an important effect in reducing the range of atmospheric pressures over the obliquity cycle at all epochs.

Fanale, Fraser P.↗
NASA NTRS1997

Zonal and Meridional Mass Redistribution in the Tropical Pacific During El Nino Southern Oscillation Events

This note aims at documenting the ENSO-related sea level changes for the whole tropical Pacific, and for the 1979-1996 period which covers numerous El Nino and La Nina events. For this purpose, we rely on (a) 0/450 dbar surface dynamic height anomaly (an alias for sea level) derived from XBT and TOGA-TAO measurements during 1979-1996, (b) TOPEX/Poseidon derived sea level anomaly during 1993-1996, and (c) Murtugudde et al. [1996] model sea level output during 1979-1995.

Delcroix, Thierry↗
NASA NTRS2001

Gravitational Signal of Mass Redistribution Due to Interannual Meteorological Oscillations in Atmosphere and Ocean

Interannual meteorological oscillations (ENSO, QBO, NAO, etc.) have demonstrable influences on Earth's rotation. Here we study their effects on global gravitational field, whose temporal variations are being studied using SLR (satellite laser ranging) data and in anticipation of the new space mission GRACE. The meteorological oscillation modes are identified using the EOF (empirical orthogonal function)/PC (principal component) decomposition of surface fields (in which we take care of issues associated with the area-weighting and non-zero mean). We examine two fields, one for the global surface pressure field for the atmosphere obtained from the NCEP reanalysis (for the past 40 years), one for the surface topography field for the ocean from the Topex/Poseidon (T/P) data (for the past 8 years). We use monthly maps, and remove the mean-monthly ("climatology") values from each grid point, hence focusing only on non-seasonal signals. The T/P data were first subject to a steric correction where the steric contribution to the ocean surface topography was removed according to output of the numerical POCM model. The respective atmospheric and oceanic contributions to the gravitational variation, in terms of harmonic Stokes coefficients, are then combined mode-by-mode. Since the T/P data already contain the oceanic response to overlying atmospheric pressure, no regards to the inverted-barometer behavior for the ocean need be considered. Results for the lowest-degree Stokes coefficients can then be compared with space geodetic observations including the Earth's rotation and the SLR data mentioned above, to identify the importance of each meteorological oscillations in gravitational variation signals.

Chao, B. F.↗
NASA NTRS2003

Blowing in the Wind: II. Creation and Redistribution of Refractory Inclusions in a Turbulent Protoplanetary Nebula

Ca-Al rich refractory mineral inclusions (CAIs) found at 1-6% mass fraction in primitive chondrites appear to be 1-3 million years older than the dominant (chondrule) components which were accreted into the same parent bodies. A prevalent concern is that it is difficult to retain CAIs for this long against gas-drag-induced radial drift into the sun. We reassess the situation in terms of a hot inner (turbulent) nebula context for CAI formation, using analytical models of nebula evolution and particle diffusion. We show that outward radial diffusion in a weakly turbulent nebula can overwhelm inward drift, and prevent significant numbers of CAI-size particles from being lost into the sun for times on the order of 10(exp 6) years. CAIs can form early, when the inner nebula was hot, and persist in sufficient abundance to be incorporated into primitive planetesimals at a much later time. Small (less than or approx. equal to 0.1 mm diameter) CAIs persist for longer times than large (greater than or approx. equal to 5mm diameter ones). To obtain a quantitative match t o the observed volume fractions of CAIs in chondrites, another process must be allowed for: a substantial enhancement of the inner hot nebula in silicate-forming material, which we suggest was caused by rapid inward drift of meter-sized objects. This early in nebula history, the drifting rubble would have a carbon content probably an order of magnitude larger than even the most primitive (CI) carbonaceous chondrites. Abundant carbon in the evaporating material would help keep the nebula oxygen fugacity low, plausably solar, as inferred for the formation environment of CAIs. The associated production of a larger than canonical amount of CO2 might also play a role in mass-independent fractionation of oxygen isotopes, leaving the gas rich in l60 as inferred from CAIs and other high temperature condensates.

Cuzzi, Jeffrey N.↗
NASA NTRS2003

Blowing in the Wind: II. Creation and Redistribution of Refractory Inclusions in a Turbulent Protoplanetary Nebula

Ca-A1 rich refractory mineral inclusions (CAIs) found at 1-6% mass fraction in primitive chondrites appear to be 1-3 million years older than the dominant (chondrule) components which were accreted into the same parent bodies. A prevalent concern is that it is difficult to retain CAIs for this long against gas-drag-induced radial drift into the sun. We reassess the situation in terms of a hot inner (turbulent) nebula context for CAI formation, using analytical models of nebula evolution and particle diffusion. We show that outward radial diffusion in a weakly turbulent nebula can overwhelm inward drift, and prevent significant numbers of CAI-size particles from being lost into the sun for times on the order of 10(exp 6) years. CAIs can form early, when the inner nebula was hot, and persist in sufficient abundance to be incorporated into primitive planetesimals at a much later time. Small (less than or approximately 0.1 mm diameter) CAIs persist for longer times than large (greater than or approximately 5mm diameter ones. To obtain a quantitative match to the observed volume fractions of CAIs in chondrites, another process must be allowed for: a substantial enhancement of the inner hot nebula in silicate-forming material, which we suggest was caused by rapid inward drift of meter-sized objects. This early in nebula history, the drifting rubble would have a carbon content probably an order of magnitude larger than even the most primitive (CI) carbonaceous chondrites. Abundant carbon in the evaporating material would help keep the nebula oxygen fugacity low, plausibly solar; as inferred for the formation environment of CAIs. The associated production of a larger than canonical amount of CO2 might also play a role in mass-independent fractionation of oxygen isotopes, leaving the gas rich in O-16 as inferred from CAIs and other high temperature condensates.

Cuzzi, Jeffrey N.↗
NASA NTRS2003

Compositions of Partly Altered Olivine and Replacement Serpentine in the CM2 Chondrites QUE93005 and Nogoya: Implications for Scales of Elemental Redistribution During Aqueous Alteration

Some phyllosilicates in CM carbonaceous chondrites formed by aqueous alteration of anhydrous precursor phases. Although broad trends in the compositions of hydrous phyllosilicates are recognized and believed to be related to trends in degree of aqueous alteration, details of the reactions that formed specific secondary minerals remain obscure. This paper reports compositional relationships between remnants of partially pseudomorphically replaced silicates and their alteration products (serpentine) in the CM2 chondrites QUE93005 and Nogoya and compares both with previously published results for Allan Hills 81002. By focusing on serpentine formed from known reactants (olivines), and on only those instances in which some of the reactant silicate remains, direct compositional relationships between reactants and products, and the elemental mobility required by the reactions, can be established.

Velbel, M. A.↗
NASA NTRS2003

Melt Redistribution in Dynamic Systems: Applications to Core Formation

Samples of olivine + Fe-S were fabricated by hot-pressing a mechanical mixture of the two phases. Olivine powders with a starting grain size of approx. 10 microns were prepared by crushing crystals of San Carlos olivine followed by pulverization in a fluid energy mill. Iron sulfide powder with a particle size of approx. 5 microns was prepared from a 2:1 mixture of reagent grade iron sulfide (FeS) plus iron. Rods 20 mm in length by 10 mm in diameter were cold-pressed into iron capsules with a uniaxial stress of approx. 200 MPa. These rods were then hot-pressed at 1523 K and 300 MPa for 4 h to obtain a starting material with <2% porosity. Samples for shear experiments were cut perpendicular to the long axis of these rods. The discs were shaped into ellipses approx. 6 mm by approx. 8 mm with a thickness ranging from 0.6 to 1.0 mm. An iron foil strain marker was inserted into a cut made along the minor axis. The sample was placed between two thoriated tungsten pistons cut at 45 deg to the long axis and then placed into an iron sleeve capped by alumina discs. The sample was then sheared in a gas pressure-medium apparatus at a temperature of 1523 K and a confining pressure of 300 MPa.

Hustoft, J. W.↗
NASA NTRS2000

Redistribution of annexin in gravistimulated pea plumules

We used immunocytochemistry to investigate the effects of gravistimulation on annexin localization in etiolated pea plumule shoots. In longitudinal sections, an asymmetric annexin immunostaining pattern was observed in a defined group of cells located just basipetal to apical meristems at the main shoot apex and at all of the axillary buds, an area classically referred to as the leaf gap. The pattern was observed using both protein-A-purified anti-annexin and affinity-purified anti-annexin antibodies for the immunostaining. A subset of the cells with the annexin staining also showed an unusually high level of periodic acid Schiff (PAS) staining in their cell walls. Prior to gravistimulation, the highest concentration of annexin was oriented toward the direction of gravity along the apical end of these immunostained cells. In contrast, both at 15 and 30 min after gravistimulation, the annexin immunostain became more evenly distributed all around the cell and more distinctly cell peripheral. The asymmetry along the lower wall of these cells was no longer evident. In accord with current models of annexin action, we interpret the results to indicate that annexin-mediated secretion in the leaf gap area is preferentially toward the apical meristem prior to gravistimulation, and that gravistimulation results in a redirection of this secretion. These data are to our knowledge the first to show a correlation between the vector of gravity and the distribution of annexins in the cells of flowering plants. c 2000 Editions scientifiques et medicales Elsevier SAS.

Non-NASA Center↗
NASA NTRS1990

Effects of ethylene on the kinetics of curvature and auxin redistribution in gravistimulated roots of Zea mays

We tested the involvement of ethylene in maize (Zea mays L.) root gravitropism by measuring the kinetics of curvature and lateral auxin movement in roots treated with ethylene, inhibitors of ethylene synthesis, or inhibitors of ethylene action. In the presence of ethylene the latent period of gravitropic curvature appeared to be increased somewhat. However, ethylene-treated roots continued to curve after control roots had reached their final angle of curvature. Consequently, maximum curvature in the presence of ethylene was much greater in ethylene-treated roots than in controls. Inhibitors of ethylene biosynthesis or action had effects on the kinetics of curvature opposite to that of ethylene, i.e. the latent period appeared to be shortened somewhat while total curvature was reduced relative to that of controls. Label from applied 3H-indole-3-acetic acid was preferentially transported toward the lower side of stimulated roots. In parallel with effects on curvature, ethylene treatment delayed the development of gravity-induced asymmetric auxin movement across the root but extended its duration once initiated. The auxin transport inhibitor, 1-N-naphthylphthalamic acid reduced both gravitropic curvature and the effect of ethylene on curvature. Since neither ethylene nor inhibitors of ethylene biosynthesis or action prevented curvature, we conclude that ethylene does not mediate the primary differential growth response causing curvature. Because ethylene affects curvature and auxin transport in parallel, we suggest that ethylene modifies curvature by affecting gravity-induced lateral transport of auxin, perhaps by interfering with adaptation of the auxin transport system to the gravistimulus.

Non-NASA Center↗