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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

An integrated user-oriented laboratory for verification of digital flight control systems: Features and capabilities

A Digital Flight Control Systems Verification Laboratory (DFCSVL) has been established at NASA Ames Research Center. This report describes the major elements of the laboratory, the research activities that can be supported in the area of verification and validation of digital flight control systems (DFCS), and the operating scenarios within which these activities can be carried out. The DFCSVL consists of a palletized dual-dual flight-control system linked to a dedicated PDP-11/60 processor. Major software support programs are hosted in a remotely located UNIVAC 1100 accessible from the PDP-11/60 through a modem link. Important features of the DFCSVL include extensive hardware and software fault insertion capabilities, a real-time closed loop environment to exercise the DFCS, an integrated set of software verification tools, and a user-oriented interface to all the resources and capabilities.

Defeo, P.↗
NASA NTRS1982

An absorption feature in the spectrum of a gamma ray burst on 25 March 1978

The High Energy X-ray and Low Energy Gamma Ray Experiment on HEAO-1 detected a gamma ray burst on March 25, 1978. The main peak of the event lasted 10 seconds, while less intense emission was observed for approximately 100 seconds. The burst spectrum shows an apparent absorption feature at 55 +/- 5 keV with an equivalent width of 13 +/- 3 keV, values commensurate with those reported for bursts recorded by the KONUS experiment. The integrated fluence between 30 keV and 6.1 Mev was 0.000015 ergs/sq cm. The detection syste has localized the burst source to within a degree of RA = 237.2 deg and Dec. = 76.4 deg.

Hueter, G. J.↗
NASA NTRS1983

Evidence for variability of the hard X-ray feature in the Hercules X-1 energy spectrum

The hard X-ray spectrum of HER X-1 was measured for the first time with a high resolution (1.4 keV FWHM) germanium spectrometer. The observation was performed near the peak of the on-state in the 35 day cycle and the 1.24 pulsations were observed between the energies of 20 keV and 70 keV. The feature corresponds to an excess of 7.5 sigma over the low energy continuum. Smooth continuum models are poor fits to the entire energy range (chance probabilities of 2 percent or less). The best fit energies are 35 keV for an absorption line and 39 keV for an emission line. These are significantly lower energies than those derived from previous experiments. A direct comparison of our data with the results of the MPI/AIT group shows statistically significant variations which strongly suggest variability in the source.

Tueller, J.↗
NASA NTRS1981

Imaging radar observations of volcanic features in Medicine Lake Highland, California

Synthetic aperture L-band radar images of Medicine Lake Highland, California, as obtained from the JPL-NASA aircraft and Seasat orbital systems, are presented. Image interpretation is based on two types of information: slope and topographic effects for geomorphic information, and reflectivity or backscatter in flat terrain which is related to surface roughness and to the surface dielectric constant. Cinder cones and lava tubes are visible (geomorphic features), and three types of lava surfaces are: aa, pahoehoe, and block. In addition, to infer lava flow relative ages, overlapping flow fronts and roughness attenuation observations may be used. It is hoped that this research will improve the understanding of the radar signature of volcanic areas, and will be helpful in interpreting data obtained from spaceborne sensors over the earth and, in particular, Venus.

Farr, T. G.↗
NASA NTRS1982

Structural features of conducting quasi-one-dimensional organic halides and pseudohalides

The physical properties of quasi-one-dimensional conductors are profoundly influenced by slight changes in structure. The unusual structural features of this class of materials include only short range order of the anions and structure modulation. The nature of disorder and structure modulation can affect the character of the metal-to-insulator transition at low temperature, and may allow us to make some predictions of low temperature behavior based on room temperature structural properties.

Williams, R.↗
NASA NTRS1982

Feature Identification and Location Experiment

The Feature Identification and Location Experiment (FILE), which was flown on the second Space Shuttle flight to test a technique for real-time, autonomous classification of water, vegetation and bare land as well as clouds, snow and ice, senses earth radiation in spectral bands centered at 0.65 and 0.85 microns. The radiance ratio classification algorithm has successfully made automatic data selection decisions. A classification image obtained on the mission is providing data needed to evaluate the FILE algorithm and overall system performance.

Sivertson, W. E., Jr.↗
NASA NTRS1983

Aerodynamic features of turbulent flames

The paper provides an interpretation for a variety of turbulent flame phenomena relating them to the aerodynamic properties of the flow field. This includes the classical notion of the breakdown of laminar flames propagation in ducts, the characteristic features of turbulent flame-fronts recorded by schlieren photography, as well as flame instabilities leading to flashback occurring in a combustion chamber behind a bluff-body flame holder. The rudimentary nature of turbulent flame propagation is shown to be associated with (1) vortex motion of a large-scale turbulent eddy, combined with (2) self-advancement of the flame at the appropriate normal burning speed and (3) the concomitant action of distributed sources of specific volume. The results furnish an insight into the macroscopic properties of the mechanism of turbulent flame propagation, rationalizing in particular its capability to sustain high flow velocities at relatively low normal burning speeds.

Oppenheim, A. K.↗
NASA NTRS1983

A feature in the X-ray spectrum of Cygnus X-1 - A possible positron annihilation line

The paper presents a 10 keV to 1 MeV X-ray spectrum of Cyg X-1 in its low state, accumulated over 3 months in 1977 and 1978. The spectrum is smooth up to 300 keV. The excess at higher energy may be interpreted as a broad 511 keV emission line from the annihilation of positrons. The width and centroid of the line indicate that the temperature of the line-emitting region is 20-200 keV. The feature could also be caused by Comptonized emission from a 165 keV region.

Nolan, P. L.↗
NASA NTRS1982

The evolution of tectonic features on Ganymede

The bands of bright resurfaced terrain on Ganymede are probably broad grabens formed by global expansion and filled with deposits of ice. Grooves within the bands are thought to be extensional features formed during the same episode of expansion. The crust of Ganymede is modeled as a viscoelastic material subjected to extensional strain. With sufficiently high strain rates and stresses, deep normal faulting will occur, creating broad grabens that may then be filled. Continuing deformation at high strain rates and stresses will cause propagation of deep faults up into the flood deposits and normal faulting at the surface, while lower strain rates and stresses will cause formation of open extension fractures or, if the crustal strength is very low, grabens at the surface. The spacing between adjacent fractures may reflect the geothermal gradient at the time of deformation. Surface topography resulting from fracturing and normal faulting will decay with time as a result of viscous relaxation and mass-wasting.

Squyres, S. W.↗
NASA NTRS1983

The diffuse interstellar feature at 4430 A and interstellar extinction in the far-ultraviolet

IUE measurements have been obtained for the UV extinction characteristics of 20 reddened stars previously reported to have anomalously high or low A(4430)/E(B-V) ratios, in order to conduct a first statistical study of the correlations between these ratios and interstellar extinction features in the UV. A marginally significant positive correlation is noted between A(4430)/E(B-V) and the normalized strength of the 2175 A extinction jump, but no correlation is found with the total extinction at the wavelength and a marginally negative correlation is found with the extinction rise at 1250 A. The hypothesis that 4430 A diffuse absorption is produced by very small interstellar grains is not supported by the present observations.

Witt, A. N.↗
NASA NTRS1981

Some features of unsteady separating turbulent boundary layers

The physical features of steady and unsteady separating turbulent boundary layers are discussed with reference to wind-tunnel data obtained at a Reynolds number of 5.1 x 10 to the 6th and a reduced frequency of 0.55. It is shown that a moderate-amplitude (R less than 0.3) oscillating turbulent boundary layer has a mean flow structure that is close to that of a steady free-stream turbulent boundary layer. Well upstream of the separation, unexpected phase shifts of the velocity and turbulence oscillations occur near the wall between the viscous sublayer and the semilogarithmic region. Significant phase variations between the velocity and turbulence also exist in the detached and back flows downstream. Large amplitude oscillations are shown to have a substantial effect on the flow structure.

Simpson, R. L.↗
NASA NTRS1983

Optical features associated with the extended HI envelope of M83

Deep red Schmidt plates (127-04 + RG630) of the galaxy M83 show the presence of extensive faint optical structure well beyond the Holmberg radius of the galaxy. Digital processing has been used to bring these features out in detail. They consist of arc-like structures and clumps of H II regions, which seem to follow the H I distribution and thus are likely to participate in the warping of the H I disk.

Wamsteker, W.↗
NASA NTRS1983

Transmission electron microscopy characterization of microstructural features of Al-Li-Cu alloys

A transmission electron microscopy (TEM) examination of aluminum-lithium-copper alloys was conducted. The principal purpose is to characterize the nature, size, and distribution of stringer particles which result from the powder metallurgy (P/M) processing of these alloys. Microstructural features associated with the stringer particles are reported that help explain the stress corrosion susceptibility of the powder metallurgy-processed Al-Li-Cu alloys. In addition, matrix precipitation events are documented for a variety of heat treatments and process variations. Hot rolling is observed to significant alter the nature of matrix precipitation, and the observations are correlated with concomitant mechanical property variations.

Avalos-Borja, M.↗
NASA NTRS1982

Morphology and movements of polarization features on Venus

Ground and spacecraft based polarization observations of Venus detected the signature of the so called 1-micron radius cloud particles that constitute the main cloud deck on Venus, as well as that of sub-micron sized particles that form a haze above this main cloud layer. Whether such observations showed any local clustering or organization in the polarimetry data remained uncertain until the relatively high resolution observations from the Pioneer Venus Orbiter Cloud Photopolarimeter (OCPP) became available. The available polarization data from this instrument was studied to see whether local organization was present, to study the morphology of such features or polarization clouds, and finally, to see if they can be followed in a sequence of observations to study their motions.

Limaye, S. S.↗
NASA NTRS1984

Aerodynamic features of flames in premixed gases

A variety of experimentally established flame phenomena in premixed gases are interpreted by relating them to basic aerodynamic properties of the flow field. On this basis the essential mechanism of some well known characteristic features of flames stabilized in the wake of a bluff-body or propagating in ducts are revealed. Elementary components of the flame propagation process are shown to be: rotary motion, self-advancement, and expansion. Their consequences are analyzed under a most strict set of idealizations that permit the flow field to be treated as potential in character, while the flame is modelled as a Stefan-like interface capable of exerting a feed-back effect upon the flow field. The results provide an insight into the fundamental fluid-mechanical reasons for the experimentally observed distortions of the flame front, rationalizing in particular its ability to sustain relatively high flow velocities at amazingly low normal burning speeds.

Oppenheim, A. K.↗
NASA NTRS1984

Rapid extraction of relative topography from Viking orbiter images. 2: Application to irregular topographic features

The ratio and flat field photoclinometric methods for determining crater form topography are described. Both methods compensate for the effects of atmospheric scattering by subtracting a haze value from all brightness values. Algorithms were altered to derive relative topographic data for irregular features such as ejecta blankets, lava flows, graben and ridge scarps, dune forms, and stratified materials. After the elevations along the profiles are obtained by integration of the photometric function, a matrix transformation is applied to the image coordinates of each pixel within each profile, utilizing each pixel's integral height, to produce a projection of each profile line onto the surface. Pixel brightness values are then resampled along the projected track of each profile to determine a more correct height value for each pixel. Precision of the methods is discussed.

Davis, P. A.↗
NASA NTRS1984

Satellite Elevation Magnetic and Gravity Models of Major South American Plate Tectonic Features

Some MAGSAT scalar and vector magnetic anomaly data together with regional gravity anomaly data are being used to investigate the regional tectonic features of the South American Plate. An initial step in this analysis is three dimensional modeling of magnetic and gravity anomalies of major structures such as the Andean subduction zone and the Amazon River Aulacogen at satellite elevations over an appropriate range of physical properties using Gaus-Legendre quadrature integration method. In addition, one degree average free-air gravity anomalies of South America and adjacent marine areas are projected to satellite elevations assuming a spherical Earth and available MAGSAT data are processed to obtain compatible data sets for correlation. Correlation of these data sets is enhanced by reduction of the MAGSAT data to radial polarization because of the profound effect of the variation of the magnetic inclination over South America.

Vonfrese, R. R. B.↗
NASA NTRS1984

A simulation of remote sensor systems and data processing algorithms for spectral feature classification

A computational model of the deterministic and stochastic processes involved in multispectral remote sensing was designed to evaluate the performance of sensor systems and data processing algorithms for spectral feature classification. Accuracy in distinguishing between categories of surfaces or between specific types is developed as a means to compare sensor systems and data processing algorithms. The model allows studies to be made of the effects of variability of the atmosphere and of surface reflectance, as well as the effects of channel selection and sensor noise. Examples of these effects are shown.

Arduini, R. F.↗