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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Remote sensing of soil moisture content over bare fields at 1.4 GHz frequency

A simple method of estimating moisture content (W) of a bare soil from the observed brightness temperature (T sub B) at 1.4 GHz is discussed. The method is based on a radiative transfer model calculation, which has been successfully used in the past to account for many observational results, with some modifications to take into account the effect of surface roughness. Besides the measured T sub B's, the three additional inputs required by the method are the effective soil thermodynamic temperature, the precise relation between W and the smooth field brightness temperature T sub B and a parameter specifying the surface roughness characteristics. The soil effective temperature can be readily measured and the procedures of estimating surface roughness parameter and obtaining the relation between W and smooth field brightness temperature are discussed in detail. Dual polarized radiometric measurements at an off-nadir incident angle are sufficient to estimate both surface roughness parameter and W, provided that the relation between W and smooth field brightness temperature at the same angle is known. The method of W estimate is demonstrated with two sets of experimental data, one from a controlled field experiment by a mobile tower and the other, from aircraft overflight. The results from both data sets are encouraging when the estimated W's are compared with the acquired ground truth of W's in the top 2 cm layer. An offset between the estimated and the measured W's exists in the results of the analyses, but that can be accounted for by the presently poor knowledge of the relationship between W and smooth field brightness temperature for various types of soils. An approach to quantify this relationship for different soils and thus improve the method of W estimate is suggested.

Wang, J. R.↗
NASA NTRS1979

Scanning Auger Microprobe and atomic absorption studies of lunar volcanic volatiles

Results on lunar volatile transport processes have been obtained by studying green and brown glass droplets, orange and black core tube samples and the surface sample 74241 with the Scanning Auger Microprobe (SAM) and by Flameless Atomic Absorption Analysis (FLAA). SAM analyses show that the most dominant volatiles in the top few atomic layers of droplets are Zn and S, confirming that the surface Zn and S are good indicators of pyroclastic origin, and they are not entirely present as ZnS. In addition, FLAA thermal release profiles show that almost all the Zn and Cd are on grain surfaces, indicating that Zn and Cd were completely outgassed from lava fountain products during the volcanic eruption, were recondensed during or after the eruptions, and are thus present as surface coating.

Cirlin, E. H.↗
NASA NTRS1981

Remote sensing of soil moisture content over bare field at 1.4 GHz frequency

An algorithm for estimating moisture content of a bare soil from the observed brightness temperature at 1.4 GHz is discussed and applied to a limited data base. The method is based on a radiative transfer model calculation, which has been successfully used in the past to account for many observational results, with some modifications to take into account the effect of surface roughness. Besides the measured brightness temperatures, the three additional inputs required by the method are the effective soil thermodynamic temperature, the precise relation between moisture content and the smooth field brightness temperatures and a pair of parameters related to surface roughness. The procedures of estimating surface roughness parameters and of obtaining moisture content from observed brightness temperature are discussed. The algorithm is applied to observations from truck mounted and airborne radiometers. The estimated moisture contents compare favorably with the observations in the top 2 cm layer.

Wang, J. R.↗
NASA NTRS1983

Spatially resolved methane band photometry of Saturn. II - Cloud structure models at four latitudes

Saturn's cloud vertical structures in the Equatorial Zone, South Equatorial Belt, and North and South Temperate Regions near + or - 30 deg latitudes are determined by means of an analysis of spatially resolved reflectivity measurements in the 6190, 7250, and 8996 A methane bands. Radiative transfer models are computed for a structure whose parameters are the methane column abundance in an aerosol-free layer at the top of the atmosphere, and the specific abundance of methane in a semiinfinite homogeneous gas-and-cloud mixture deep in the atmosphere. The structure for the South Equatorial Belt resembles that for the North Temperate Region. The level where unit cloud optical depth occurs in the South Temperate Region is deeper than the corresponding level at other latitudes. The differences between model parameters derived by means of different absorption bands are discussed.

West, R. A.↗
NASA NTRS1985

Sidewall boundary-layer effects in two-dimensional airfoil testing

Theoretical studies required to evaluate and validate the streamlined wall test section of the 0.3 m transonic Cryogenic Tunnel were initiated. The various aspects that are being considered presently are deviations of the real wall shape from the true streamline shape, wall adjustment strategy, and the influence of the sidewall boundary layers. Since the top and bottom walls are supported at a finite number of jack points, the true wall shape will be different from the ideal streamline shape. This is determined by calculating the structural shape for cases for which the exact streamline shape can be calculated. For the structural shape calculations, the MSCNASTRAN code is being used. To start with, comparisons are made using simple singularities for model representation and also for a flat plate at angle of attack.

Murthy, A. V.↗
NASA NTRS1986

Convective diffusion in protein crystal growth

A protein crystal modeled as a flat plate suspended in the parent solution, with the normal to the largest face perpendicular to gravity and the protein concentration in the solution adjacent to the plate taken to be the equilibrium solubility, is studied. The Navier-Stokes equation and the equation for convective diffusion in the boundary layer next to the plate are solved to calculate the flow velocity and the protein mass flux. The local rate of growth of the plate is shown to vary significantly with depth due to the convection. For an aqueous solution of lysozyme at a concentration of 40 mg/ml, the boundary layer at the top of a 1-mm-high crystal has a thickness of 80 microns at 1 g, and 2570 microns at 10 to the -6th g.

Baird, J. K.↗
NASA NTRS1990

On the use of IR lidar and K(sub a)-band radar for observing cirrus clouds

Advances in lidar and radar technology have potential for providing new and better information on climate significant parameters of cirrus. Consequently, the NOAA Wave Propagation Lab. is commencing CLARET (Cloud Lidar And Radar Exploratory Test) to evaluate the promise of these new capabilities. Parameters under study include cloud particle size distribution, height of cloud bases, tops, and multiple layers, and cloud dynamics revealed through measurement of vertical motions. The first phase of CLARET is planned for Sept. 1989. The CO2 coherent Doppler lidar and the sensitive K sub a band radar hold promise for providing valuable information on cirrus that is beyond the grasp of current visible lidars.

Eberhard, Wynn L.↗
NASA NTRS1990

The 27-28 October 1986 FIRE IFO cirrus case study - In situ observations of radiation and dynamic properties of a cirrus cloud layer

Observations are presented of cirrus cloud radiative, microphysical, and dynamic properties, their variability, and apparent scale sizes, as observed from NCAR Sabreliner on October 28, 1986. Broadband mass-absorption coefficients were deduced as a function of depth into the cirrus cloud and found to vary with particle dimension. Broadband volume absorption coefficients were deduced. By employing a diffusivity factor of 1.49 this agreement was maximized. Calculated infrared heating rates were typical of thin cirrus layers. The cloud top cooling and cloud base warming were observed to become more accentuated for the denser portions of cloud. The broadband emittances due to the cloud aerosol were found to approach 0.5 to 0.6. The cirrus clouds were observed to exhibit significant horizontal variability and a significant amount of scatter was evident when attempting to relate the broadband infrared and shortwave radiative properties. It is suggested that these radiative properties, which are modulated by the cloud elements, have their scales determined by the eddies detected in the analysis of wind components.

Smith, William L., Jr.↗
NASA NTRS1991

Lidar In-Space Technology Experiment (LITE) - NASA's first in-space lidar system for atmospheric research

Engineering aspects are presented of the design, fabrication, integration, and operation of the Lidar In-Space Technology Experiment (LITE) for flight aboard the Space Shuttle in mid-1993. The LITE system is being developed by NASA/Langley Research Center and will be used to detect stratospheric and tropospheric aerosols, probe the planetary boundary layer, measure cloud top heights, and measure atmospheric temperature and density in the 10- to 40-km range. The system consists of a nominal telescope receiver 1 meter in diameter, a three-color Nd:YAG laser transmitter, and the system electronics. The system makes extensive use of Space Shuttle resources for electrical power, thermal control, and command and data handling.

Couch, Richard H.↗
NASA NTRS1992

Remote Sensing by Spaceborne Lidar Aided by Surface Returns

Spaceborne lidar offers the possibility of global mapping of clouds and atmospheric aerosols. Mapping of cloud-top heights, multiple layers of thin clouds and the depth of the planetary boundary layer (PBL), given sufficient aerosols, are applications that should be fairly easy to accomplish from space with even a modest lidar system. However, the constraints imposed on spaceborne lidar by large ranging distances, limited available power/weight, and fast moving platforms present significant challenges to achieving more quantitative retrievals such as extracting aerosol extinction profiles, PBL optical depths and cloud optical depths. Ways to take advantage of the strong signals available from ground/sea reflections to improve upon atmospheric aerosol and cloud retrievals as well as to distinguish certain surface types are explored.

Reagan, J. A.↗
NASA NTRS1990

The diurnal variability of marine stratocumulus clouds

Observations of the diurnal variation of marine stratocumulus clouds obtained during July 1987 as part of the First ISCCP Regional Experiment are described. The observations show a clear diurnal signature in the structure of the cloud-topped marine boundary layer, with a large variation in the height of the cloud base, with lower heights observed at night. The observational results are numerically simulated using a 1D second-moment turbulence-closure model of Koracin and Rogers (1990) for a hydrostatically incompressible fluid. The model results indicate that the differential heating of the cloud layer promotes mixing in the upper part of the cloud and stabilizes the lower part of the layer.

Rogers, David P.↗
NASA NTRS1991

Effects of depth-variations in creep laws on the formation of plates in mantle dynamics

The influences of depth-varying rheologies on the structure of mantle convection and the near surface flow fields are studied. Upwelling flows crossing the upper-lower mantle boundary become considerably thinner and faster. Streamlines are concentrated near the surface and other platelike characteristics are enhanced by this type of rheological stratification in which the averaged effective viscosity of the upper mantle is about two orders of magnitude lower than that of the lower mantle. The presence of a lithosphere with a higher nonlinear dependence in the flow law further promotes platelike behavior. Platelike character of the top boundary-layer is encouraged by a decreasing depth-dependent viscosity in the non-Newtonian upper-mantle and by greater convective vigor.

Van Den Berg, Arie P.↗
NASA NTRS1993

Electrically Conductive Polyimide Films

Semiconducting surfaces of SnO2 formed by curing polyamic acids containing tin complexes. Polyimide films made semiconductive via incorporation of semiconductive surface layers of SnO2. If SnO2-surfaced polyimide film used as free-standing film, then semiconductive layer protected by top coat of polyimide, deposited as film from solution directly onto SnO2. Resultant films flexible and resistant to both weather and high temperature. Used on aircraft to provide resistance to lightning strikes, and in microelectronics and flexible circuitry.

St. Clair, Anne K.↗
NASA NTRS1994

Investigation of nucleation and growth processes of diamond films by atomic force microscopy

The nucleation and growth of plasma-enhanced chemical-vapor deposited polycrystalline diamond films were studied using atomic force microscopy (AFM). AFM images were obtained for (1) nucleated diamond films produced from depositions that were terminated during the initial stages of growth, (2) the silicon substrate-diamond film interface side of diamond films (1-4 micrometers thick) removed from the original surface of the substrate, and (3) the cross-sectional fracture surface of the film, including the Si/diamond interface. Pronounced tip effects were observed for early-stage diamond nucleation attributed to tip convolution in the AFM images. AFM images of the film's cross section and interface, however, were not highly affected by tip convolution, and the images indicate that the surface of the silicon substrate is initially covered by a small grained polycrystalline-like film and the formation of this precursor film is followed by nucleation of the diamond film on top of this layer. X-ray photoelectron spectroscopy spectra indicate that some silicon carbide is present in the precursor layer.

George, M. A.↗
NASA NTRS1995

Investigation of nucleation and growth processes of diamond films by atomic force microscopy

The nucleation and growth of plasma enhanced chemical vapor deposited (PECVD) polycrystalline diamond films were studied using atomic force microscopy (AFM). AFM images were obtained for: (1) nucleated diamond films produced from depositions that were terminated during the initial stages of growth, (2) the silicon substrate-diamond film interface side of diamond films (1-4 micrometers thick) removed from the original surface of the substrate, and (3) cross-sectional fracture surface of the film, including the Si/diamond interface. Pronounced tip effects were observed for early-stage diamond nucleation attributed to tip convolution in the AFM images. AFM images of the films cross-section and interface however were not affected by tip convolution, and the images indicate that the surface of the silicon substrate is initially covered by small grained polycrystalline-like film and the formation of this precursor film is followed by nucleation of the diamond film on top of this layer. X-ray photoelectron spectroscoy (XPS) spectra indicates that some silicon carbide is present in the precursor layer.

George, M. A.↗
NASA NTRS1998

Developing Information Power Grid Based Algorithms and Software

This exploratory study initiated our effort to understand performance modeling on parallel systems. The basic goal of performance modeling is to understand and predict the performance of a computer program or set of programs on a computer system. Performance modeling has numerous applications, including evaluation of algorithms, optimization of code implementations, parallel library development, comparison of system architectures, parallel system design, and procurement of new systems. Our work lays the basis for the construction of parallel libraries that allow for the reconstruction of application codes on several distinct architectures so as to assure performance portability. Following our strategy, once the requirements of applications are well understood, one can then construct a library in a layered fashion. The top level of this library will consist of architecture-independent geometric, numerical, and symbolic algorithms that are needed by the sample of applications. These routines should be written in a language that is portable across the targeted architectures.

Dongarra, Jack↗
NASA NTRS2000

InGaP/InGaAs-on-Ge Concentrator Solar Cell for Space Power Generation

The passivating front and back window layer of the top cell has been chosen. We have chosen to use InGaAs as the tunnel junction interconnect compound since it is easily degenerately doped. All of the dual junction cell structures were grown on GaAs substrates. Time constraints prevented us from completing the development of the GaAs-on-Ge growth process. Analysis of the I-V and EQE data, and comparison with computer-modeled data, shows that the performance of the dual-junction cell is still being controlled by the bottom cell, in spite of top cell thinning. Further improvement in the dual-junction cell efficiency is possible by thinning the front window.

Sinharoy, Samar↗
NASA NTRS2004

In situ Pulsed Laser Deposition of C-Axis Oriented MgB2 Films and Their Characterization

The recent discovery of an intermetallic superconductor MgB2 has renewed interest in the area of superconductivity not only because of fundamental understanding of superconductivity but also due to its potential applicability in devices such as thermal detectors. Considerable amount of research has been devoted to obtain MgB2 films by an all in situ growth technique. We have grown MgB2 thin films by an all in situ pulsed laser deposition process from pure B and Mg targets. Ultrathin layers of B and Mg were deposited in a multilayer configuration. Hundreds of such Mg-B bilayers with a capping Mg layer on the top were deposited on sapphire substrate. These depositions were done in high vacuum (approx. 10(exp -7) Torr) and at room temperature. After deposition, such a configuration was annealed at high temperature for a short time in a forming gas (4% H2 in Ar). The best films, obtained by this procedure, showed superconducting transition temperature approx. 30 K. These films have been characterized by x-ray diffraction, Rutherford Backscattering Spectrometry, AC susceptibility-, resistivity- (with and without magnetic field) and 1/f noise-measurements. The physical properties of these films will be presented and discussed.

Shinde, Sanjay↗