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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 1,261 records · Page 70
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Secondary electron emission from a charged dielectric in the presence of normal and oblique electric fields

The secondary electron emission coefficient was obtained for a FEP-Teflon dielectric charged with monoenergetic electrons normally incident upon the surface of the specimen. Measurements of secondary emission coefficient were done for normal and oblique incidence with different primary beam energies in the presence of normal and oblique electric fields. A collimated probing beam was directed to different points on the surface of the specimen and the released or accumulated charge was monitored using an electrometer. The measured data for different probing beam energies, different impact points and different angles of incidence were plotted vs. impact energy and impact point. Data analyzed by computer simulations to find the potential distribution on the surface of the specimen and the electric field around it, is presented and discussed.

Javidi, B.↗
NASA NTRS1981

Methods of editing cloud and atmospheric layer affected pixels from satellite data

The location and migration of cloud, land and water features were examined in spectral space (reflective VIS vs. emissive IR). Daytime HCMM data showed two distinct types of cloud affected pixels in the south Texas test area. High altitude cirrus and/or cirrostratus and "subvisible cirrus" (SCi) reflected the same or only slightly more than land features. In the emissive band, the digital counts ranged from 1 to over 75 and overlapped land features. Pixels consisting of cumulus clouds, or of mixed cumulus and landscape, clustered in a different area of spectral space than the high altitude cloud pixels. Cumulus affected pixels were more reflective than land and water pixels. In August the high altitude clouds and SCi were more emissive than similar clouds were in July. Four-channel TIROS-N data were examined with the objective of developing a multispectral screening technique for removing SCi contaminated data.

Nixon, P. R.↗
NASA NTRS1981

Methods of editing cloud and atmospheric layer affected pixels from satellite data

Plotted transects made from south Texas daytime HCMM data show the effect of subvisible cirrus (SCI) clouds in the emissive (IR) band but the effect is unnoticable in the reflective (VIS) band. The depression of satellite indicated temperatures ws greatest in the center of SCi streamers and tapered off at the edges. Pixels of uncontaminated land and water features in the HCMM test area shared identical VIS and IR digital count combinations with other pixels representing similar features. A minimum of 0.015 percent repeats of identical VIS-IR combinations are characteristic of land and water features in a scene of 30 percent cloud cover. This increases to 0.021 percent of more when the scene is clear. Pixels having shared VIS-IR combinations less than these amounts are considered to be cloud contaminated in the cluster screening method. About twenty percent of SCi was machine indistinguishable from land features in two dimensional spectral space (VIS vs IR).

Nixon, P. R.↗
NASA NTRS1982

Design, production, and testing of field effect transistors

Cryogenic MOSFETS (CRYOFETS), specifically designed for low temperature preamplifier application with infrared extrinsic detectors were produced and comparatively tested with p-channel MOSFETs under matched conditions. The CRYOFETs exhibit lower voltage thresholds, high source-follower gains at lower bias voltage, and lower dc offset source voltage. The noise of the CRYOFET is found to be 2 to 4 times greater than the MOSFET with a correspondingly lower figure of merit (which is established for source-follower amplifiers). The device power dissipation at a gain of 0.98 is some two orders of magnitude lower than for the MOSFET. Further, CRYOFETs are free of low temperature I vs V character hysteresis and balky conduction turn-on effects and operate effectively in the 2.4 to 20 K range. These devices have promise for use on long term duration sensor missions and for on-focal-plane signal processing at low temperatures.

Sclar, N.↗
NASA NTRS1982

Acoustically induced oscillation and rotation of a large drop in space

A 2.5 cm diameter water drop was successfully deployed and manipulated in a triaxial acoustic resonance chamber during a 240 sec low-gravity SPAR rocket flight. Oscillation and rotation were induced by modulating and phase shifting the signals to the speakers. Portions of the film record were digitized and analyzed. Spectral analysis brought out the n = 2, 3, 4 free oscillation modes of the drop, its very low-frequency center-of-mass motion in the acoustic potential well, and the forced oscillation frequency. The drop boundaries were least-square fitted to general ellipses, providing eccentricities of the distorted drop. The normalized equatorial area of the rotating drop was plotted vs a rotational parameter, and was in excellent agreement with values derived from the theory of equilibrium shapes of rotating liquid drops.

Jacobi, N.↗
NASA NTRS1981

Software models: A Bayesian approach to parameter estimation in the Jelenski-Moranda software reliability model

Maximum likelihood estimation procedures for the Jelinski-Moranda software reliability model often give misleading answers. A reparameterization and a Bayesian analysis eliminate some of the problems incurred by MLE methods and often give better predictions on sets of real and simulated data. Practical difficulties in estimating the initial number of errors N and the failure rate of each error phi by the method of maximum likelihood are: N, the MLE of N, is occasionally infinite (i.e., the routines for calculating N and phi do not converge). It is shown that N is finite sub i only if the regression line of the interevent times t sub i vs. i has positive slope. A serious problem is that often N approximates n, the sample size, and sometimes N = n. Thus the MLE predicts that the program is perfect even when it is far from being so. Only when almost all failures have been removed can N and phi be trusted near the end of debugging.

Littlewood, B.↗
NASA NTRS1980

Measurement of hydroxyl temperatures in the upper atmosphere with a high sensitivity spectrometer

The hydroxyl temperatures in the upper atmosphere were measured over a five-week period in January and February of 1975 and 1976 in order to determine the variation of the rotational temperatures of OH with stratospheric warming events occurring over the New England area. The OH temperatures were also recorded during the summer of 1975 in the Fairfield, Connecticut area. Data show a wide fluctuation in temperatures amounting to as much as a couple of hundred degrees in the course of an evening. A modified Ebert-Fastie spectrometer with a focal length of 1 meter was used to examined the vibration-rotation bands of atmospheric OH in the 7000 to 9000 range. This wavelength was searched and the strongest signal was obtained from the 6-2 band (band head at 8280 A). Graphs show the 6-2 band of the Meinel OH spectrum, the real time and average spectra for the 6-2 band of OH, and rotational temperature of OH vs time for two evenings.

Mcelaney, J. H.↗
NASA NTRS1982

Space environmental effects: Construction and utilization of a system to measure low thermal strain in one meter graphite epoxy tubes

A system for measuring the expansion of low coefficient of thermal expansion (CTE) materials was constructed around a H.P. 5526-A laser measuring system. The vacuum CTE measurements in the -150 F to +120 F range were made over a 6 month period on a graphite epoxy tube yielding CTE values of 2.5 to one fifty-millionth/F above ambient and 2 + or - one ten-millionth F below ambient temperature. To assure that the below ambient, approximately 10 microns high open loop nature of the delta L/L vs. T curves was not apparatus related, similar size quartz tubes (A and B) were checked and found to have only a 2 micron (negligable for quartz) open loop component. These two quartz tubes, A and B, had ambient CTE values 20% and 45% respectively higher than the average handbook value. The overnight microcreep diminished an order of magnitude during the first several cycles after the system had been reopened.

Davis, J. H.↗
NASA NTRS1981

Temperature dependence of the self-reaction of CH3O2 radicals

The rate constants for the reaction CH3O2 + CH3O2 yields products (1) were measured in the temperature range from 248 to 417 K, taking into consideration pressures in the range from 60 to 700 torr of N2. The experimental investigation was carried out in a Pyrex flash photolysis system employing ultraviolet absorption detection. Methylperoxy radicals (CH3O2) were produced by the photolysis of Cl2-CH4-O2 mixtures. Rate constants were measured by observing the second-order disappearance of CH3O2 radicals. Plots of 1/(CH3O2 optical density) vs. time were observed to be linear over a concentration change of a factor of 10-50. Results of the kinetic runs at each temperature are summarized in a table, and an Arrhenius plot of the data is shown in a graph.

Sander, S. P.↗
NASA NTRS1981

A classification system for O-B2 stars based on the Si IV and C IV resonance lines

Low-dispersion ultraviolet spectra from Skylab Experiment S-019 are used to explore the variations of Si IV and C IV line strengths with temperature and luminosity. These considerations lead to a classification system in which the Si/C ratio is used to discriminate luminosity among the O stars and temperature among the O9-B2 stars of lower luminosity. Stars falling in these two regimes may be distinguished either by the presence of C IV emission or on the basis of C IV absorption strength. The log(Si IV/C IV) vs C IV diagram is proposed as a primary tool in such a classification system. The rapid variation in the Si IV/C IV ratio from less than 1/10 at O9 to greater than 10 at B1.5 for luminosity class III-V stars appears to be an especially useful criterion for the temperature classification of stars in this spectral range.

Henize, K. G.↗
NASA NTRS1982

Limits on the lunar temperature profile

Limits on the selenotherm are estimated using (1) a preferred set of bounds on the lunar electrical conductivity profile; (2) published laboratory conductivity vs. temperature data for an olivine and several aluminous orthopyroxenes; and (3) estimates for the Al2O3 content of the deep interior suggested by bulk composition models. The inferred limits are narrowest in the depth range 450 to 1350 km and are in accord with independent geophysical constraints. Thermal history models which yield present-day selenotherms that are in best agreement with these limits are those which permit subsolidus convection at depths greater than 800 km in the moon.

Hood, L. L.↗
NASA NTRS1980

K/Ar dating of lunar soils. IV - Orange glass from 74220 and agglutinates from 14259 and 14163

Total fusion Ar-40 - A-39 analyses of orange glass from lunar soil 74220 combined with the sums of earlier stepwise heating data by other workers have yielded a precise K/Ar isochron with a slope corresponding to an age of 3.66 + or - 0.03 G.y. for the orange glass. The result is in marginal agreement with Huneke's (1978) age of 3.60 + or - 0.04 G.y. for 74220 glass. The Ar systematics in the agglutinates from 14259 and 14163 are dominated by volume correlated argon. Step-wise heating analyses yield data which define experimentally reproducible linear arrays in Ar-40/Ar-36 vs. K-40/Ar-36 diagrams. The slopes of these arrays correspond formally to very old ages, but it is not clear, however, that such ages have any physical significance.

Alexander, E. C., Jr.↗
NASA NTRS1982

Laser reflection from oxide-coated aluminum

The theory of reflection from an oxide-coated metal is combined with experimentally measured parameters of aluminum to produce useful amplitude and phase shift information applicable to the concentration and direction of laser light. Amplitude and phase are plotted vs angle of incidence for several important laser wavelengths in the near UV, visible, and IR spectral regions.

Williams, M. D.↗
NASA NTRS1981

Amino acid codes in mitochondria as possible clues to primitive codes

Differences between mitochondrial codes and the universal code indicate that an evolutionary simplification has taken place, rather than a return to a more primitive code. However, these differences make it evident that the universal code is not the only code possible, and therefore earlier codes may have differed markedly from the previous code. The present universal code is probably a 'frozen accident.' The change in CUN codons from leucine to threonine (Neurospora vs. yeast mitochondria) indicates that neutral or near-neutral changes occurred in the corresponding proteins when this code change took place, caused presumably by a mutation in a tRNA gene.

Jukes, T. H.↗
NASA NTRS1981

Application of scanning microdensitometer data in selected plant science case studies

This paper treats a representative sample of projects aimed at vegetation mapping and assessment via analysis of both digital photographic and Landsat data projects and illustrates the potential for using scanning microdensitometric data extracted from color infrared photographs in the following applications: freshwater wetlands mapping, tree type mapping, and yield vs. reflectance modeling in corn fertilization experiments. These case studies are presented to illustrate the general applicability of scanning microdensitometer data in the contexts of image classification and enhancement as well as quantitative modeling of ground parameters.

Lillesand, T. M.↗
NASA NTRS1982

Einstein observations of BY Draconis variables and RS CVn binaries

Observations of five BY Draconis variables and four RS Canum Venaticorum systems with the Einstein Observatory are presented. All nine stars were detected. Although the BY Draconis stars have an average X-ray luminosity one to two orders of magnitude lower than the RS CVn binaries, at least three of these systems fit the X-ray/bolometric luminosity ratio-vs-period relation first described by Walter and Bowyer (1981) for RS CVn's. Since one of the BY Draconis stars is almost certainly single, this result lends strong support to the suggestion that rapid rotation, and not duplicity, is the determining factor in defining the level of stellar activity in such stars. In addition, the X-ray data are consistent with the suggestion, made by Vogt and Fekel (1979), that the BY Draconis stars are in the final stages of pre-main-sequence evolution.

Caillault, J.-P.↗
NASA NTRS1982

Flow behavior of ten iron-containing silicate compositions

The viscosity of ten iron-containing silicates has been measured over the temperature range 400 to 650 C. The compositions contain trace amounts up to 30 wt. pct. or 20 mole. pct. Fe3O4 from 10 to 20 wt. pct. or 10 to 20 mole. pct. Na2O and the remainder is SiO2. Samples were melted in air to form oxidized samples, in forming gas (95% N2-5% H2) to form mildly reduced samples, and in forming gas with carbon in the batch to form strongly reduced samples. In general, the viscosity decreased with increasing mole. pct. Na2O and decreasing mole. pct. SiO2 for a given temperature. In samples with increasing mole. pct. FeO(x) the difference in the viscosity between the oxidized sample and the reduced sample grew in magnitude at a given temperature. In all of the compositions, the log or viscosity, vs reciprocal-of-temperature relation shows curvature with an apparent activation energy between 90 and 100 kcal/mole.

Klein, L. C.↗
NASA NTRS1982

The alkali metal thermoelectric converter /AMTEC/ - A new direct energy conversion technology for aerospace power

A thermally regenerative electrochemical device for the direct conversion of heat to electrical energy, the alkali metal thermoelectric converter (AMTEC), is characterized by potential efficiencies on the order of 15-40% and possesses no moving parts, making it a candidate for space power system applications. Device conversion efficiency is projected on the basis of experimental voltage vs current curves exhibiting power densities of 0.7 W/sq cm and measured electrode efficiencies of up to 40%. Preliminary radiative heat transfer measurements presented may be used in an investigation of methods for the reduction of AMTEC parasitic radiation losses. AMTEC assumes heat input and rejection temperatures of 900-1300 K and 400-800 K, respectively. The working fluid is liquid sodium, and the porous electrode employed is of molybdenum.

Bankston, C. P.↗