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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Spatial variability of soil hydraulics and remotely sensed soil parameters

The development of methods to correctly interpret remotely sensed information about soil moisture and soil temperature requires an understanding of water and energy flow in soil, because the signals originate from the surface, or from a shallow surface layer, but reflect processes in the entire profile. One formidable difficulty in this application of soil physics is the spatial heterogeneity of natural soils. Earlier work has suggested that the heterogeneity of soil hydraulic properties may be described by the frequency distribution of a single scale factor. The sensitivity of hydraulic and energetic processes to the variation of this scale factor is explored with a suitable numerical model. It is believed that such an analysis can help in deciding how accurately and extensively basic physical properties of field soils need to be known in order to interpret thermal or radar waveband signals. It appears that the saturated hydraulic conductivity needs to be known only to its order of magnitude, and that the required accuracy of the soil water retention function is about 0.02 volume fraction. Furthermore, the results may be helpful in deciding how the total scene or view field, as perceived through a sensor, is composed from the actual mosaic of transient soil properties, such as surface temperature or surface soil moisture. However, the latter proposition presupposes a random distribution of permanent properties, a condition that may not be met in many instances, and no solution of the problem is apparent.

Lascano, R. J.↗
NASA NTRS1985

Proceedings of the Workshop on Identification and Control of Flexible Space Structures, volume 1

Identification and control of flexible space structures were studied. Exploration of the most advanced modeling estimation, identification and control methodologies to flexible space structures was discussed. The following general areas were discussed: space platforms, antennas, and flight experiments; control/structure interactions - modeling, integrated design and optimization, control and stabilization, and shape control; control technology; control of space stations; large antenna control, dynamics and control experiments, and control/structure interaction experiments.

Rodriguez, G.↗
NASA NTRS1985

Dynamics explorer guest investigator

The use of Dynamics Explorer (DE) data sets to model the auroral inputs for the time dependent ionospheric model (TDIM) is reported. The modelling requires DE-1 SAI images and simultaneous DE-2 LAPI particle data. The data sets allow the large scale relative auroral variations and local absolute energy flexes and characteristics energies to be defined. The images enabled global scale auroral modelling with 12 min. time resolution and the LAPI data presented a detailed energy flux and characteristic energy calibration of the image model. The auroral model is used as an input to the TDIM and studies ionospheric storms.

Sojka, J. J.↗
NASA NTRS1986

Constraints on the NH3 and PH3 distributions in the Great Red Spot

Medium resolution (10 A) UV spectra were obtained for the Great Red Spot (GRS) and South Tropical Zone (STZ) of Jupiter using the low dispersion mode of the IUE spectrometers at wavelengths from 1900-2200 A. The scans were carried out to determine the coloring agent for the GRS to improve the database for developing photochemical models of the feature. The wavelengths were selected to cover the absorption features of NH3 and PH3. The resulting data were interpreted using a vertically inhomogeneous Rayleigh scattering radiative transfer model. Various NH3 concentrations were explored in an effort to fit the data, taking into account changes which would occur at different atmospheric pressure levels and due to the projected temperature fields. A forbidden NH3/forbidden H2 mixing ratio that was calculated at the 80-125 mbar pressure level in the GRS was enhanced by 3-10 percent relative to the STZ. An upper limit was obtained for the mixing ratio of PH3 in the GRS that is significantly lower than previously predicted concentrations, implying that vertical transport in the GRS is not much greater than in adjacent regions.

Wagener, R.↗
NASA NTRS1987

Innovative methods for the measurement of I* quantum yields and kinetics by diode laser gain-versus-absorption

The quantum yields of a variety of candidate molecules for solar lasant materials to produce I* were tested. The absorption spectrum was measured for each compound and the I* yield determined by the diode laser or by infrared emission, using C3F7I as a standard. The results of these measurements are summarized. A GaAsInP diode laser system was developed to probe I and I* atoms to obtain yields and kinetics. A technique of gain-versus-absorption spectroscopy was investigated to measure quantum yields with high accuracy. The errors in the yield data were reduced to +/- 2% or less. In addition, experiments were set up to measure the rates of F-sublevel changing collisions in both the I ground state and the I* excited state. Finally, experiments and modelling were carried out to explore the possibility of measuring the recombination rates of I* with C3F7 radicals.

Leone, Stephen R.↗
NASA NTRS1987

Automated problem scheduling and reduction of synchronization delay effects

It is anticipated that in order to make effective use of many future high performance architectures, programs will have to exhibit at least a medium grained parallelism. A framework is presented for partitioning very sparse triangular systems of linear equations that is designed to produce favorable preformance results in a wide variety of parallel architectures. Efficient methods for solving these systems are of interest because: (1) they provide a useful model problem for use in exploring heuristics for the aggregation, mapping and scheduling of relatively fine grained computations whose data dependencies are specified by directed acrylic graphs, and (2) because such efficient methods can find direct application in the development of parallel algorithms for scientific computation. Simple expressions are derived that describe how to schedule computational work with varying degrees of granularity. The Encore Multimax was used as a hardware simulator to investigate the performance effects of using the partitioning techniques presented in shared memory architectures with varying relative synchronization costs.

Saltz, Joel H.↗
NASA NTRS1987

Vertical constituent transport in the mesosphere

Ground-based microwave spectroscopy measurements of mesospheric CO and H2O vertical mixing ratio profiles are used to infer vertical mixing rates in the upper mesosphere. The CO and H2O data consistently imply vertical eddy diffusion coefficients in the 70- to 85-km region of 100,000-200,000 sq cm/s during spring through summer at midlatidues. Although chemical acceleration of vertical transport is substantial for O and O3, below the mesopause, the divergences of their associated fluxes are modest, with at most a factor of 2 effect on the concentrations of O and O3 for measured variability in gravity wave activity. Comparison of Solar Mesosphere Explorer (SME) O3 data with model results reinforces the conclusions of slow vertical mixing in the upper mesosphere as a consequence of the reduced HO(x) catalytic loss of odd oxygen. The changes in chemical rate constants recommended by Rusch and Eckman (1985), in conjunction with slow vertical mixing, yield good agreement with SME O3 data. The slow vertical mixing deduced in this study is consistent with upper limits obtained from studies of the mesospheric heat budget and could be construed as evidence for an advectively controlled mesosphere. A comparison of the vertical eddy diffusion coefficients for momentum stresses, constituent transport, and heat transport suggests that the eddy Prandtl number must be of order 10.

Strobel, Darrell F.↗
NASA NTRS1988

Energy branching in the Io plasma torus - The failure of neutral cloud theory

Model calculations are used to explore the energy source characteristics of the energy branching of the hot Io plasma torus. It is assumed that the energy is derived from the kinetic energy acquired by ions created in the rotating planetary magnetic field, and that Coulomb collisions with the electron gas control the flow of energy to the ionizing and radiative processes. The results show that neutral cloud theory is qualitatively inadequate. It is shown that neutral cloud theory can only support a dominantly singly ionized system (at the measured electron densities in the plasma torus) and that it fails to predict observed plasma properties relative to variations in number density.

Shemansky, D. E.↗
NASA NTRS1988

Broad-line variability in NGC 5548

The possible explanations for the variability behavior of the He II 4686A and H-beta lines in the Seyfert galaxy NGC 5548 as observed by Peterson and Ferland (1986) are discussed. The range of variability expected from these lines is explored according to the standard models for broad-line clouds, assuming changes in the values of various of the clouds' defining parameters. When compared with model predictions, the observed line variability suggests the existence of a strong, variable EUV component of the ionizing spectrum and of two populations of clouds which differ in their velocity distributions and in their response to continuum variations.

Kallman, T.↗
NASA NTRS1989

The cosmic microwave background

Recent observational and theoretical investigations of the cosmic microwave background radiation (CMBR) are reviewed. Particular attention is given to spectral distortions and CMBR temperature anisotropies at large, intermediate, and small angular scales. The implications of the observations for inflationary cosmological models with curvature fluctuation are explored, and it is shown that the limits determined for intermediate-scale CMBR anisotropy almost rule out a baryon-dominated cosmology.

Silk, Joseph↗
NASA NTRS1990

The permanent electric dipole moment of CaOH

The X 2 Sigma(+), A 2Pi, and B 2Sigma(+) states of CaOH are characterized theoretically and experimentally, with a focus on the value of the permanent electric dipole moment (mu). Calculations based on SCF and SDCI studies of CaOH (Bauschlicher et al., 1984 and 1986) give mu values of 0.98, 0.49, and 0.11 D for the X, A, and B states, respectively, in good agreement with experiments in which the pure rotational spectra of these states were not detected. Modified Rittner (1951) and ligand-field models of these states are explored in detail, and the applicability of these results to observational searches for CaOH in circumstellar envelopes is indicated.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1991

Diskoseismology: Probing accretion disks. I - Trapped adiabatic oscillations

The normal modes of acoustic oscillations within thin accretion disks which are terminated by an innermost stable orbit around a slowly rotating black hole or weakly magnetized compact neutron star are analyzed. The dominant relativistic effects which allow modes to be trapped within the inner region of the disk are approximated via a modified Newtonian potential. A general formalism is developed for investigating the adiabatic oscillations of arbitrary unperturbed disk models. The generic behavior is explored by way of an expansion of the Lagrangian displacement about the plane of symmetry and by assuming separable solutions with the same radial wavelength for the horizontal and vertical perturbations. The lowest eigenfrequencies and eigenfunctions of a particular set of radial and quadrupole modes which have minimum motion normal for the plane are obtained. These modes correspond to the standard dispersion relation of disk theory.

Nowak, Michael A.↗
NASA NTRS1992

Onsite analysis of data from the Dynamics Explorer (DE) spacecraft

The tasks performed by ARC Professional Services Group, Inc. fell into five parts: (1) dynamics explorer (DE) data analysis and modeling; (2) DE project support; (3) chemical release observations support; (4) VLF emissions and plasma instability studies; and (5) modeling of planetary radio emissions. Some recommendations for future considerations are also addressed.

Fung, Shing F.↗
NASA NTRS1992

Studies of the kinetics and mechanisms of perfluoroether reactions on iron and oxidized iron surfaces

Polymeric perfluoroalkylethers are being considered for use as lubricants in high temperature applications, but have been observed to catalytically decompose in the presence of metals. X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) were used to explore the decomposition of three model fluorinated ethers on clean polycrystalline iron surfaces and iron surfaces chemically modified with oxygen. Low temperature adsorption of the model fluorinated ethers on the clean, oxygen modified and oxidized iron surfaces was molecular. Thermally activated defluorination of the three model compounds was observed on the clean iron surface at remarkably low temperatures, 155 K and below, with formation of iron fluoride. Preferential C-F bond scission occurred at the terminal fluoromethoxy, CF3O, of perfluoro-1-methoxy-2-ethoxy ethane and perfluoro-1-methoxy-2-ethoxy propane and at CF3/CF2O of perfluoro-1,3-diethoxy propane. The reactivity of the clean iron toward perfluoroalkylether decomposition when compared to other metals is due to the strength of the iron fluoride bond and the strong electron donating ability of the metallic iron. Chemisorption of an oxygen overlayer lowered the reactivity of the iron surface to the adsorption and decomposition of the three model fluorinated ethers by blocking active sites on the metal surface. Incomplete coverage of the iron surface with chemisorbed oxygen results in a reaction which resembles the defluorination reaction observed on the clean iron surface. Perfluoro-1-methoxy-2-ethoxy ethane reacts on the oxidized iron surface at 138 K, through a Lewis acid assisted cleavage of the carbon oxygen bond, with preferential attack at the terminal fluoromethoxy, CF3O. The oxidized iron surface did not passivate, but became more reactive with time. Perfluoro-1-methoxy-2-ethoxy propane and perfluoro-1,3-diethoxy propane desorbed prior to the observation of decomposition on the oxidized iron surface.

Napier, Mary E.↗
NASA NTRS1992

The search for crustal resources - MAGSAT and beyond

In the decade since global satellite magnetic field data have been available from MAGSAT, notable progress has been made in processing these data for purposes of mapping crustal anomalies. Several regional magnetic anomaly maps compiled using these new techniques (e.g. Kursk region, U.S.S.R.; central Africa; Kiruna, Sweden; and the U.S.A. midcontinent) provide insight into the nature and tectonic evolution of the crust that contribute to conceptual crustal models useful in regional resource exploration. A recent mail survey of geopotential-field specialists involved in resource exploration indicates interest in MAGSAT data and future satellite missions with improved resolution. It is apparent that magnetic anomalies derived from satellite observations can aid in the search for crustal resources.

Taylor, P. T.↗
NASA NTRS1993

Dense clouds near the central engine of active galactic nuclei

A model is presented which assumes the existence of cold dense clouds near the central engine of active galactic nuclei (AGNs). The effects of such clouds on the observed spectrum are explored. It is shown that this model is consistent with the complicated observed spectra and variability behavior of most extensively studied Seyfert nuclei. The results are compared with other proposed models. The existing observational evidence appears to support the 'cloud-model'.

Sivron, R.↗
NASA NTRS1993

Estimating modal abundances from the spectra of natural and laboratory pyroxene mixtures using the modified Gaussian model

The modified Gaussian model (MGM) is used to explore spectra of samples containing multiple pyroxene components as a function of modal abundance. The MGM allows spectra to be analyzed directly, without the use of actual or assumed end-member spectra and therefore holds great promise for remote applications. A series of mass fraction mixtures created from several different particle size fractions are analyzed with the MGM to quantify the properties of pyroxene mixtures as a function of both modal abundance and grain size. Band centers, band widths, and relative band strengths of absorptions from individual pyroxenes in mixture spectra are found to be largely independent of particle size. Spectral properties of both zoned and exsolved pyroxene components are resolved in exsolved samples using the MGM, and modal abundances are accurately estimated to within 5-10 percent without predetermined knowledge of the end-member spectra.

Sunshine, Jessica M.↗
NASA NTRS1992

A feasibility study regarding the addition of a fifth control to a rotorcraft in-flight simulator

The addition of a large movable horizontal tail surface to the control system of a rotorcraft in-flight simulator being developed from a Sikorsky UH-60A Black Hawk Helicopter is evaluated. The capabilities of the control surface as a trim control and as an active control are explored. The helicopter dynamics are modeled using the Generic Helicopter simulation program developed by Sikorsky Aircraft. The effect of the horizontal tail on the helicopter trim envelope is examined by plotting trim maps of the aircraft attitude and controls as a function of the flight speed and horizontal tail incidence. The control power of the tail surface relative to that of the other controls is examined by comparing control derivatives extracted from the simulation program over the flight speed envelope. The horizontal tail's contribution as an active control is evaluated using an explicit model following control synthesis involving a linear model of the helicopter in steady, level flight at a flight speed of eighty knots. The horizontal tail is found to provide additional control flexibility in the longitudinal axis. As a trim control, it provides effective control of the trim pitch attitude at mid to high forward speeds. As an active control, the horizontal tail provides useful pitching moment generating capabilities at mid to high forward speeds.

Turner, Simon↗