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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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

The photolytic stability of the Martian atmosphere.

Several recent suggestions for stabilizing the Martian atmosphere against photolysis have proved untenable. However, downward convective transport as well as a low altitude (0-35 km) aerosol, which catalyzes two-body molecular recombination reactions, can bring about such stability. The 'effective' convection velocity and 'average' two-body reaction rate coefficients required by observed abundances are evaluated. The computed profiles of CO and O at high altitude are shown to agree well with observations.

Whitten, R. C.↗
NASA NTRS1973

Effect of energetic oxygen atoms on neutral density models.

The dissociative recombination of O2(+) and NO(+) in the F region results in the production of atomic oxygen and atomic nitrogen with substantially greater kinetic energy than the ambient atoms. In the exosphere these energetic atoms have long free paths. They can ascend to altitudes of several thousand kilometers and can travel horizontally to distances of the order of the earth's radius. The distribution of energetic oxygen atoms is derived by means of models of the ion and neutral densities for quiet and disturbed solar conditions. A distribution technique is used to study the motion of the atoms in the collision-dominated region. Ballistic trajectories are calculated in the spherical gravitational field of the earth. The present calculations show that the number densities of energetic oxygen atoms predominate over the ambient atomic oxygen densities above 1000 km under quiet solar conditions and above 1600 km under disturbed solar conditions.

Rohrbaugh, R. P.↗
NASA NTRS1974

Spectrometer

Ultraviolet spectrometer measures pure monochromatic wavelengths in predetermined narrow wave bands. Two stages are incorporated: stationary dispersed beam is intercepted by array of slits cut into plate at discrete wavelength locations; second stage is inverted spectrometer which recombines dispersed spectrum at single exit slit.

Menzel, D. H.↗
NASA NTRS1973

Methods of Measurement for Semiconductor Materials, Process Control, and Devices

The development of methods of measurement for semiconductor materials, process control, and devices is reported. Significant accomplishments include: (1) Completion of an initial identification of the more important problems in process control for integrated circuit fabrication and assembly; (2) preparations for making silicon bulk resistivity wafer standards available to the industry; and (3) establishment of the relationship between carrier mobility and impurity density in silicon. Work is continuing on measurement of resistivity of semiconductor crystals; characterization of generation-recombination-trapping centers, including gold, in silicon; evaluation of wire bonds and die attachment; study of scanning electron microscopy for wafer inspection and test; measurement of thermal properties of semiconductor devices; determination of S-parameters and delay time in junction devices; and characterization of noise and conversion loss of microwave detector diodes.

Bullis, W. M.↗
NASA NTRS1973

Fabrication and properties of gallium phosphide variable colour displays

The unique properties of single-junction gallium phosphide devices incorporating both red and green radiative recombination centers were investigated in application to the fabrication of monolithic 5 x 7 displays capable of displaying symbolic and alphanumeric information in a multicolor format. A number of potentially suitable material preparation techniques were evaluated in terms of both material properties and device performance. Optimum results were obtained for double liquid-phase-epitaxial process in which an open-tube dipping technique was used for n-layer growth and a sealed tipping procedure for subsequent p-layer growth. It was demonstrated that to prepare devices exhibiting a satisfactory range of dominant wavelengths which can be perceived as distinct emission colors extending from the red through green region of the visible spectrum involves a compromise between the material properties necessary for efficient red emission and those considered optimum for efficient green emission.

Effer, D.↗
NASA NTRS1973

Wall boundary equations with slip and catalysis for multicomponent, nonequilibrium gas flows

Boundary equations obtained for a low Reynolds number, high enthalpy gas flow in regions of velocity slip and temperature jump are presented. The formulation treats, through a first-order distribution function used to include multicomponent diffusion, a multicomponent gas mixture that may be in nonequilibrium with finite-rate catalytic recombination occurring on the wall. In the boundary equations, which are obtained for use in flow-field calculations applicable to low-density flow regimes, a simplified gas/wall interaction is assumed wherein individual atoms or molecules either reflect specularly off the wall or stick and are fully accommodated. Fluxes in terms of evaluated integrals over the distribution function and integrals necessary for determining fluxes are given.

Scott, C. D.↗
NASA NTRS1973

Magnetospheric convection and the high latitude F2 ionosphere

Behavior of the polar ionospheric F-layer as it is convected through the cleft, over the polar cap, and through the night side F-layer trough zone was investigated. Passage through the cleft adds of the order of 200,000 ions/cu cm in the vicinity of the F 2 peak and redistributes the ionization above approximately 400 km altitude to conform with an increased electron temperature. The F-layer is also raised of the order of 20 km in altitude by the convection electric field. In the night soft electron precipitation zone, the layer is lowered in altitude by the convection electric field, and then decays, primarily by chemical recombination, as it convects equatorward and around the dawn side of the earth. In the absence of ionization sources, decay by factors of the order of 100 to 1000 occur prior to entry into the sunlit hemisphere, thus forming the F-layer night trough.

Knudsen, W. C.↗
NASA NTRS1974

Cracking and reformation of saturated hydrocarbons by ultrasound in the presence of water

The exposure of saturated hydrocarbons to ultrasound (800 kHz, 6 W/sq cm) in the presence of water results in: (1) cleavage of the carbon chain, producing saturated and unsaturated hydrocarbons with a lower number of carbons than the initial hydrocarbon (cracking); and (2) recombination after cleavage, producing saturated and unsaturated hydrocarbons with a higher number of carbons than the initial hydrocarbon (reformation). The addition of argon facilitates these phenomena. The effects are attributed to a homolytic (radical) mechanism occurring within the cavitation bubbles under the effects of microsparks.

Prudhomme, M. R. O.↗
NASA NTRS1974

Silicon ions below 100 km: A case for SiO2(+)

Silicon ions are normally detected at altitudes above 100 km and within sporadic E layers. Traces have rarely been observed within the more permanent metallic layer near 93 km. This is surprising since silicon is an important constituent of chondritic meteorites, which ablate material in this region to provide a primary source of the metallic species observed there. Evidence is presented that Si(+)ions form SiO2(+) at the lower altitudes, and exist in this ionic state prior to recombination. A rocket launched from El Arenosillo, Spain on 3 July 1972, at 0743 LMT, during the predicted period of the Beta Taurids meteor shower, passed through a continuous belt of metallic ions that began near 85 km, ended near 115 km, and exhibited an order of magnitude increase in the form of a layer near 114 km. Si(+)was measured in and below the ledge down to 103 km. It showed a rapid decrease below this height. Radiative association is offered as a primary mechanism for SiO2(+) production.

Goldberg, R. A.↗
NASA NTRS1973

Recent developments in shock tube research; Proceedings of the Ninth International Symposium, Stanford University, Stanford, Calif., July 16-19, 1973

Recent advances in shock tube research are described in papers dealing with the design and performance features of new devices as well as applications in aerodynamic, chemical, and physics experiments. Topics considered include a cryogenic shock tube for studying liquid helium fluid mechanics, studies of shock focusing and nonlinear resonance in shock tubes, applications in gas laser studies, very-low and very-high temperature chemical kinetic measurements, shock tube studies of ionization and recombination phenomena, applications in bioacoustic research, shock-tube simulation studies of sonic booms, and plasma research. Individual items are announced in this issue.

Bershader, D.↗
NASA NTRS1974

On the nature of the nonthermal radio emission from the galactic center

Some recent observations of the galactic center appear at first sight to have made the character of the radio source Sgr A unclear. The flatness of the usually quoted spectrum, the lack of any measured polarization, the presence of hydrogen recombination lines, and the radio-infrared luminosity ratio are all consistent with Sgr A being a rather hot H II region. It is shown here, however, that when flux measurements between 80 MHz and 91000 MHz are all included and the multiple nature of the source is accounted for, the spectral index exceeds 0.4 - much too steep to be bremsstrahlung. There is, therefore, no question that Sgr A is a nonthermal source. It is further argued on the basis of a comparison of appearance, energetics and the recent results which no longer put Sgr A exactly at the center of the galaxy that Sgr A could be a supernova remnant rather than a miniature of active extragalactic radio sources.

Jones, T. W.↗
NASA NTRS1973

Jovian ionospheric models

This paper reports results obtained on ionosphere formation in the Jovian upper atmosphere with special reference to some of the recently available reaction rates, and to recent models of the Jovian neutral atmosphere based on the possibility of a warmer mesopause. In the older models of the Jovian ionosphere, the major ions were H+ which were lost only by pure radiative recombination. This led to high electron densities and practically no diurnal change. In contrast, recent models have relatively much smaller electron densities, especially in lower regions, and may be susceptible to significant diurnal variation.

Capone, L. A.↗
NASA NTRS1974

Influence of ablation impurities on blunt body re-entry ionization

Electron density profiles which include the effect of an ablated sodium impurity were computed for the boundary layer on a blunt-nosed body re-entering the atmosphere at 7.62 km/sec. Profiles are computed from the nose to a distance of four diameters along the RAM C-payload. A finite-difference, laminar, nonequilibrium chemistry boundary-layer program was used. Comparison of theory with S-band diagnostic antenna results, electron concentration deduced from X- and C-band attenuation data, and Langmuir probe data at several different aft body locations show that agreement is good at high altitude. At the lower altitudes there is disagreement between theory and S-band antenna data where the apparent discrepancy is attributed to the three-body recombination rate constant used for deionization of sodium coupled with the effect of angle of attack.

Schexnayder, C. J., Jr.↗
NASA NTRS1974

Low-high junction theory applied to solar cells

Recent use of alloying techniques for rear contact formation has yielded a new kind of silicon solar cell, the back surface field (BSF) cell, with abnormally high open-circuit voltage and improved radiation resistance. Several analytical models for open-circuit voltage based on the reverse saturation current are formulated to explain these observations. The zero surface recombination velocity (SRV) case of the conventional cell model, the drift field model, and the low-high junction (LHJ) model can predict the experimental trends. The LHJ model applies the theory of the low-high junction and is considered to reflect a more realistic view of cell fabrication. This model can predict the experimental trends observed for BSF cells.

Godlewski, M. P.↗
NASA NTRS1974

Thermally-restorable optical degradation and the mechanism of current transport in Cu2S-CdS photovoltaic cells

The photovoltaic properties of single-crystal Cu2S-CdS heterojunctions have been investigated as a function of heat treatment by detailed measurements of the dependence of short-circuit current on photon energy, temperature, and the state of optical degradation or enhancement. A coherent picture is formulated for the relationship between enhancement and optical degradation, and their effect on the transport of short-circuit photoexcited current and dark, forward-bias current in the cell. Optical degradation in the Cu2S-CdS cell is shown to be closely identical to optical degradation of lifetime in a homogeneous CdS:Cd:Cu crystal, indicating that the CdS:Cu layer near the junction interface controls carrier transport in the cell. It is proposed that both the photoexcited short-circuit current and the dark, forward-bias current are controlled by a tunneling-recombination process through interface states.

Fahrenbruch, A. L.↗
NASA NTRS1974

Non-equilibrium stagnation region aerodynamic heating of hypersonic glide vehicles

A simple method of predicting aerodynamic heating and corresponding radiation equilibrium surface temperature-time histories for critical locations on space shuttle orbiter-type vehicles is presented. The method is based on a generalization of correlation equations developed earlier by Rosner for predicting the energy transfer and radiation equilibrium temperatures of surfaces with arbitrary catalytic activity and total hemispheric emittance. Recently obtained experimental data for O and N atom recombination probabilities on candidate material surfaces above 1000 K are used to assess nonequilibrium effects for a range of nose radii and a specific space shuttle re-entry trajectory. It is concluded that low catalytic activity will be especially important in locations of large effective nose radii by both increasing oxidation-resistant coating lifetime and reducing energy transfer into the vehicle.

Rosner, D. E.↗
NASA NTRS1974

Boltzmann equation for the electron gas of a nondegenerate plasma

The collision terms in the Boltzmann equation associated with various processes are derived. For processes having a Fokker-Planck (F-P) limit, the associated F-P operator is derived by means of physical arguments to determine the form of the operator; its multiplying constant is fixed by calculating the total energy exchange rate and comparing with the rate computed by other means. In this manner, the F-P operator is derived for electron-ion scattering, electron-electron scattering in the high-velocity limit, electron-atom elastic scattering, Compton scattering, and the high-velocity limit for inelastic scattering. Other processes considered are bremsstrahlung, radiative-recombination, photoionization, collisional ionization of atoms, and suprathermal-particle ionization of atoms.

Gould, R. J.↗