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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Observation of organized structure in turbulent flow within and above a forest canopy

Data obtained with seven triaxial sonic anemometer/thermometers and three Lyman-alpha hygrometers at an experimental site in Ontario, Canada reveal the coherent occurrence of ramp patterns of temperature and humidity at several levels within and above the deciduous forest considered. The ramps appear most clearly in the middle and upper portion of the forest, and near the top of the forest they are composed of a weak ejecting motion transporting warm and/or moist air out of the forest, followed by strong sweeps of cool and/or dry air penetrating into the canopy. In the middle and upper parts of the canopy, the sweeps are found to conduct a large proportion of the overall transfer between the forest and the lower atmosphere, with a lesser contribution from ejections.

Gao, W.↗
NASA NTRS1989

Measurements of CH4, N2O, CO, H2O and O3 in the middle atmosphere by the ATMOS experiment on Spacelab 3

The volume mixing ratios of five minor gases (CH4, N2O, CO, H2O, and O3) were retrieved through the middle atmosphere from the analysis of 0.01/cm resolution infrared solar occultation spectra recorded near 28 N and 48 S latitudes with the ATMOS (Atmospheric Trace Molecule Spectroscopy) instrument, flown on board Spacelab 3. The results, which constitute the first simultaneous observations of continuous profiles through the middle atmosphere for these gases, are in general agreement with reported measurements from ground, balloon and satellite-based instruments for the same seasons. In detail, the vertical profiles of these gases show the effects of the upper and middle atmospheric transport patterns dominant during the season of these observations. The profiles inferred at different longitudes around 28 N suggest a near-uniform zonal distribution of these gases. Although based on fewer observations, the sunrise occultation measurements point to a larger variability in the vertical distribution of these gases at 48 S.

Gunson, M. R.↗
NASA NTRS1990

HF Doppler and VHF radar observations of upper atmospheric disturbances caused by weak cold front during winter time

The simultaneous use of the Taiwan VHF radar and the HF Doppler sounder for remote measurement of three-dimensional winds, gravity waves, and density perturbations at mesospheric and thermospheric heights is demonstrated. A special event of atmospheric disturbances caused by propagating gravity waves excited by weak convective motions in winter time were investigated. The three-dimensional wind velocities at different heights were determined, and the frequency, horizontal wavelength, vertical wavelength, and phase velocity of the gravity waves were measured. The subtropical, low-latitude site makes the VHF radar and HF Doppler array systems unique, and the observations especially valuable for space projects dealing with low-latitude atmosphere.

Hung, R. J.↗
NASA NTRS1990

The equivalence between dislocation pile-ups and cracks

Cracks and dislocation pile-ups are equivalent to each other. In this paper, the physical equivalence between cracks and pile-ups is delineated, and the relationshps between crack-extension force, force on the leading dislocation, stress-intensity factor, and dislocation density are reviewed and summarized. These relations make it possible to extend quantitatively the recent advances in the concepts and practices of fracture mechanics to the studies of microfractures and microplastic deformations.

Liu, H. W.↗
NASA NTRS1990

Manufacture of bulk superconducting YBa2Cu3O(7-delta) by a continuous process

The development of a continuous process for fabricating large bulk superconductors with a predetermined grain orientation is reported. A bar of the 123 compound with dimensions 5 x 0.5 x about 0.3 cm with excellent grain alignment has been fabricated continuously. The bulk 123 thus obtained has magnetically determined J(c)s of about 30,000 and 12,000 A/sq cm at 0 and 1 T, respectively, and transport J(c)s of 20,000, 11,000, and 7500 A-sq cm at 0, 0.54, and 0.83 T.

Meng, R. L.↗
NASA NTRS1990

The cosmological evolution models of active galaxies and the extragalactic gamma-ray background

The source spectra and angular fluctuations produced by various possible models of AGN evolution derived from observations in other wavelength bands are investigated. It is found that the sizes of the angular fluctuations are roughly constant between 10 and 100 MeV, independent of the models chosen. None of the models produce the spectral 'shelf' observed at a few MeV, and from the simulation, the AGN mechanism is only a minor contributor to the extragalactic gamma-ray background (EGB), with its flux only about 10 percent of what is observed. These evolution-independent effects imply that the EGB is not solely produced by the AGN mechanism.

Gao, Yi-Tian↗
NASA NTRS1990

Characterization of the tip field of a discrete dislocation pileup for the development of physically based micromechanics

It is shown, on the basis of calculations by Eshelby et al. (1951), Armstrong et al. (1966), and Chou and Li (1969), that a single parameter, such as the force on the leading dislocation (F), the crack extension force, or the stress intensity factor, is capable of characterizing uniquely the entire tip field of a discrete dislocation pileup, including the positions of mobile dislocations behind the locked leading dislocation at the tip. Conversely, the position of the i-th mobile dislocation X(i) is related to the value of F and is capable of characterizing the entire stress, strain, and displacement fields at the tip of a discrete dislocation pileup. If the interactions between dislocations are linear elastic, the measured positions of the mobile dislocations can be used to determine the value of F, which can then be used as a quantitative measure of the strength of a dislocation barrier resisting the propagation of a microslip or the nucleation of a microfracture.

Gao, Q.↗
NASA NTRS1990

Low-frequency oscillations in total ozone measurements

Low frequency oscillations with periods of approximately one to two months are found in eight years of global grids of total ozone data from the Total Ozone Mapping Spectrometer (TOMS) satellite instrument. The low frequency oscillations corroborate earlier analyses based on four years of data. In addition, both annual and seasonal one-point correlation maps based on the 8-year TOMS data are presented. The results clearly show a standing dipole in ozone perturbations, oscillating with 35 to 50 day periods over the equatorial Indian Ocean-west Pacific region. This contrasts with the eastward moving dipole reported in other data sets. The standing ozone dipole appears to be a dynamical feature associated with vertical atmospheric motions. Consistent with prior analyses based on lower stratospheric temperature fields, large-scale standing patterns are also found in the extratropics of both hemispheres, correlated with ozone fluctuations over the equatorial west Pacific. In the Northern Hemisphere, a standing pattern is observed extending from the tropical Indian Ocean to the north Pacific, across North America, and down to the equatorial Atlantic Ocean region. This feature is most pronounced in the NH summer.

Gao, X. H.↗
NASA NTRS1990

Large-scale anisotropy in the extragalactic gamma-ray background as a probe for cosmological antimatter

Intrinsic anisotropies in the extragalactic gamma-ray background (EGB), which should be detectable with the forthcoming Gamma Ray Observatory, can be used to examine some of the mechanisms proposed to explain its origin, one of which, the baryon-symmetric big bang (BSBB) model, is investigated here. In this simulation, large domains containing matter and antimatter galaxies produce gamma rays by annihilation at the domain boundaries. This mechanism can produce mountain-chain-shaped angular fluctuations in the EGB flux.

Gao, Yi-Tian↗
NASA NTRS1991

An iterative method for obtaining the optimum lightning location on a spherical surface

A brief introduction to the basic principles of an eigen method used to obtain the optimum source location of lightning is presented. The location of the optimum source is obtained by using multiple direction finders (DF's) on a spherical surface. An improvement of this method, which takes the distance of source-DF's as a constant, is presented. It is pointed out that using a weight factor of signal strength is not the most ideal method because of the inexact inverse signal strength-distance relation and the inaccurate signal amplitude. An iterative calculation method is presented using the distance from the source to the DF as a weight factor. This improved method has higher accuracy and needs only a little more calculation time. Some computer simulations for a 4DF system are presented to show the improvement of location through use of the iterative method.

Chao, Gao↗
NASA NTRS1989

Column atmospheric water vapor retrievals from airborne imaging spectrometer data

High-spatial-resolution column atmospheric water vapor amounts were derived from spectral data collected by the Airborne Visible Infrared Imaging Spectrometer (AVIRIS). The quantitative derivation is made by curve fitting observed spectra with calculated spectra in the 1.14- and 0.94-micron water-vapor band absorption regions with a nonlinear least-squares technique. The precision of the retrieved column water vapor is approximately 5 percent. The derived column water vapor amounts are independent of the absolute surface reflectance. Curve fitting of spectra near 1 micron from areas covered with vegetation indicates that both the amount of atmospheric water vapor and the moisture content of vegetation can be retrieved simultaneously. It should be possible to measure column water vapor over land areas from satellite altitude with the proposed high-resolution imaging spectrometer or even the moderate-resolution imaging spectrometer.

Gao, Bo-Cai↗
NASA NTRS1991

Comparison between the magnetic and transport critical current densities in high critical current density melt-textured yttrium barium copper-oxide

Using a recently developed pulsed critical current density (Jc) measuring system, the Jc of the high-Jc melt-textured YBa2Cu3O(7-delta) (Y123) bulk samples has been determined. I-V curves with a voltage resolution of 0.5 microV were obtained, and transport Jc's along the a-b plane as high as 7.2 x 10 to the 4th A/sq cm were extracted. These results are comparable to the values obtained magnetically. On the other hand, transport Jc along the c axis were found to be two orders of magnitude smaller, even though the magnetic Jc along the c axis is only about five times smaller than Jc along the a-b plane. It is suggested that for the high-temperature superconducting materials which are highly anisotropic, caution should be taken when using the nontransport magnetic methods to determine Jc.

Gao, L.↗
NASA NTRS1990

The development of physically based micro-mechanics - Based on the characteristic tip field of dislocation pileup

Based on the analytical solution by Eshelby et al. (1951) and the numerical calculations by Chou and Li (1969) and Armstrong et al. (1962), it is shown that the force, F, on the locked leading dislocation of a discrete dislocation pileup is capable of characterizing uniquely the stress, strain, and displacement field at the tip of the pileup, including the positions of the discrete mobile dislocations next to the leading dislocation. Conversely, the positions of the mobile dislocations can be used to measure F. The F thus measured can be used to study micro-plastic deformation and micro-fractures at grain boundaries or any other dislocation barriers.

Gao, Q.↗
NASA NTRS1991

Cloud area determination from AVIRIS data using water vapor channels near 1 micron

Fractional cloud area is derived from spectral images collected by the Airborne Visible-IR Imaging Spectrometer (AVIRIS). The derivation is made by ratioing radiances near the 0.94- and the 1.14-microns water vapor band centers against those in the intermediate atmospheric window regions. The derivation makes use of the facts that (1) the reflectances of most ground targets vary approximately linearly with wavelength in the 0.94- and the 1.14-micron water vapor band absorption regions, and (2) the peak absorptions of the water vapor band over cloudy areas are smaller than those over nearby clear surface areas because of the rapidly decreasing atmospheric water vapor concentration with height. The band ratioing technique effectively discriminates among clouds and surface areas having similar reflectance values.

Gao, Bo-Gai↗
NASA NTRS1990

Determination of total column water vapor in the atmosphere at high spatial resolution from AVIRIS data using spectral curve fitting and band ratioing techniques

Techniques are developed for quantitative retrievals of high spatial resolution column atmospheric water vapor that is largely contained in the lower portion of the troposphere. One method consists of curve fitting observed spectra with simulated spectra in the 1.14 microns or the 0.94 micron water vapor band absorption region. The other method is a simple band ratioing technique, which requires less computer time than the curve fitting method. The advantage of the technique over humidity sounding by IR emission measurements is that the retrieved column water vapor amounts over land surfaces have significantly higher precision.

Gao, Bo-Cai↗
NASA NTRS1991

A study of the radiative effects of the 9.4- and 10.4-micron bands of carbon dioxide

The potential radiative impact of the relatively weak 9.4- and 10.4-micron bands of CO2 is investigated. A comparison of line-by-line calculations to laboratory data demonstrates that the line-by-line procedure and laboratory data typically yield comparable results; however, there are cases of substantial disagreement between the line-by-line results and the laboratory data. It is observed that the Goody narrow-band model yields band absorptances in good agreement with the reference line-by-line calculations. For application to climate models, new broadband parameterizations, are presented for the 9.4- and 10.4-micron bands of CO2. Clear-sky flux calculations demonstrate that for projected increases of CO2 the impact of the 9.4- and 10.4-micron bands is comparable to that attributed to projected increases of tropospheric ozone.

Kratz, D. P.↗
NASA NTRS1991

Systematic study of sulfur isotopic composition in iron meteorites and the occurrence of excess S-33 and S-36

The paper concentrates on isotopic measurements of sulfur in different sulfur-carrier phases: troilite inclusions, Fe-Ni alloy, and schreibersite (possibly including daubreelite). Variations in S-34 isotope ratio are observed in some troilite inclusions, and no evidence of nucleosynthetic sulfur isotopic anomalies are found in the troilite inclusions. Excesses of S-33 and S-36 are observed in both FeNi alloy and schreibersite of Grant, Santa Clara, Tlacotepec, and Gibeon, with schreibersite possessing the greater magnitude of presumably spallogenic S-33 and S-36. It is concluded that the magnitude of the observed fractionation is consistent with troilite dissociation and/or vaporization following a collisional impact.

Gao, Xia↗
NASA NTRS1991

Research on inverse, hybrid and optimization problems in engineering sciences with emphasis on turbomachine aerodynamics: Review of Chinese advances

Advances in inverse design and optimization theory in engineering fields in China are presented. Two original approaches, the image-space approach and the variational approach, are discussed in terms of turbomachine aerodynamic inverse design. Other areas of research in turbomachine aerodynamic inverse design include the improved mean-streamline (stream surface) method and optimization theory based on optimal control. Among the additional engineering fields discussed are the following: the inverse problem of heat conduction, free-surface flow, variational cogeneration of optimal grid and flow field, and optimal meshing theory of gears.

Liu, Gao-Lian↗