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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Space Shuttle laminar heating with finite-rate catalytic recombination

Temperature-dependent catalytic recombination coefficients are used to calculate the heat flux to the Space Shuttle Orbiter. With variable entropy boundary-layer edge properties obtained from a reacting inviscid flow-field calculation, the reacting boundary-layer equations are solved along the forward 50 percent of the windward centerline using the boundary-layer integral matrix procedure. The results are compared with fully catalytic and noncatalytic reacting solutions, with equilibrium solutions, and with the Orbiter-design heating rates. The fully catalytic heat fluxes are about equal to the equilibrium predictions; whereas, the finite catalytic results are about 12 to 27 percent lower than the fully catalytic results (approaching the noncatalytic results downstream) and as much as 30 to 50 percent lower than design predictions away from the nose area.

Scott, C. D.↗
NASA NTRS1981

Exact random walk definition of the collisional-radiative ionization and recombination coefficients

The collisional-radiative ionization and recombination coefficients are shown to be expressible in terms of the 'total probability', from initial level i to final level j, which excludes intermediate returns to the initial level. Applications are made to three-level and four-level systems to illustrate the method of calculation and compare with an approximation currently used.

Kastner, S. O.↗
NASA NTRS1981

A spectroscopic experimental and computer-assisted empirical model for the production and energetics of excited oxygen molecules formed by atom recombination on shuttle tile surfaces

A visible emission spectroscopic method was developed. The amounts of excited singlet and triplet oxygen molecules produced by recombination on the Space Shuttle Orbiter thermal protective tiles at elevated temperatures are determined. Rate constants and energetics of the extremely exothermic reaction are evaluated in terms of a chemical and mathematical model. Implications for potential contribution to Shuttle surface reentry heating fluxes are outlined.

Owan, D. A.↗
NASA NTRS1981

The dissociative recombination of O2/+/ in the ionosphere

Aeronomical determinations of the dissociative recombination reaction rate coefficient for O2(+) and alpha depend directly on a knowledge of the rate coefficient for the charge exchange of O(+) with O2 and k. The aeronomical determination of alpha is reevaluated using Atmosphere Explorer satellite data in light of a subsequent laboratory measurement of k (Chen et al., 1978). The results are found to be in good agreement with laboratory determinations of the coefficient for night-time conditions. For data obtained under sunlit conditions, however, the results differed significantly with those of the laboratory measurements. These results imply that the state of the O2(+) molecule major thermospheric processes needs to be examined in greater detail.

Torr, M. R.↗
NASA NTRS1983

Measuring Diffusion and Recombination in Polycrystalline Silicon

Light-beam-induced currents yield information about solar cell material. Apparatus measures short-circuit current generated when spot of concentrated light is scanned across grains and grain boundaries in material under test. Technique used to evaluate SOC samples for diffusion and recombination effects of cell processing and chemical and structural defects.

Zook, J. D.↗
NASA NTRS1983

Electron Beam Could Probe Recombination Centers

Electron beam probe technique estimate electron/hole capture cross sections in semiconductors with wide band gaps. Amplitude-modulated electron beam induces short-circuit current collected by ohmic contacts. Phase shift between this current and electron-beam current measured as function of frequency. Results of measurements used to ascertain recombination rates and energy levels.

Vonroos, O.↗
NASA NTRS1983

Dissociative recombination of O2(+), NO(+) and N2(+)

A new L(2) approach for the calculation of the threshold molecular capture width needed for the determination of DR cross sections was developed. The widths are calculated with Fermi's golden rule by substituting Rydberg orbitals for the free electron continuum coulomb orbital. It is shown that the calculated width converges exponentially as the effective principal quantum number of the Rydberg orbital increases. The threshold capture width is then easily obtained. Since atmospheric recombination involves very low energy electrons, the threshold capture widths are essential to the calculation of DR cross sections for the atmospheric species studied here. The approach described makes use of bound state computer codes already in use. A program that collects width matrix elements over CI wavefunctions for the initial and final states is described.

Guberman, S. L.↗
NASA NTRS1983

Concerning sources of O/1D/ in Aurora - Electron impact and dissociative recombination

The present investigation is concerned with two questions. One is related to the possibility that the O(1D) level is produced by an as yet unidentified process in aurora. The second question is concerned with the need for an additional source and the altitude over which it is required. The data base of the AE satellite (AE-D in particular) was examined for this study. It is found that dissociative recombination and electron impact are inadequate sources of O(1D) in aurora. Nearly 90% of the source function is unidentified below 200 km and about 55% is missing above 250 km. The possibility that thermal electron impact could provide the missing source above 250 km was examined. Calculations showed that the missing source above 250 km could be explained by thermal electron impact if the electron temperatures were approximately 2900 K.

Sharp, W. E.↗
NASA NTRS1983

Chlorine nitrate - The sole product of the ClO + NO2 + M recombination

A laser operating at 266 nm is used to photolyze the product of the ClO + NO2 + M reaction, and the yield of Cl atoms, measured by resonance fluorescence, is found to be identical with that from equivalent concentrations of ClONO2. This is interpreted as a strong indication that no other isomers are formed in the recombination reaction. Evidence for isomers is surveyed, and the apparent forward-and-reverse-rate constant discrepancy is explained as a probable uncertainty in the thermochemistry.

Margitan, J. J.↗
NASA NTRS1983

O(1S) from dissociative recombination of O2(+) - Nonthermal line profile measurements from Dynamics Explorer

The measurements reported were made of the O(1S) emission line profile at 5577 A at high spectral resolution with the Fabry-Perot interferometer on the Dynamics Explorer spacecraft. It is found that the line profile has marked nonthermal characteristics in the nightglow. A simple collisional relaxation model is used to analyze the nighttime emission line profiles, measured in the equatorial region. The branching ratio is inferred for the dissociative recombination of O2(+) leading to O(1S). The result reveals that the O(1S) + O(1D) channel is favored over the O(1S). The result reveals that the O(1S) + O(1D) channel is favored over the O(1S) + O(3P) channel by a factor of 4; this does not agree with the ratio reported by Hernandez (1971). It is noted, however, that the result is consistent with the active channel for O(1S) production being via the 1Sigma u + repulsive state of O2, as suggested by the theoretical calculations of Guberman (1983). In addition, a value is obtained for the excitation exchange cross section for O(1S).

Killeen, T. L.↗
NASA NTRS1984

Observations of infrared hydrogen recombination line emission from external galaxies

Observations of infrared hydrogen recombination line emission are presented for several positions within the galaxies NGC 1068, NGC 1097, NGC 2903, and NGC 4151. Emission is seen from the arms and nuclei of these spiral galaxies. The luminosity from the most recent burst of star formation is deduced and compared to the infrared luminosity which accounts for the bulk of the total energy. Young stars (primarily O and B stars) provide most of the luminosity in the arms and nuclei of the normal galaxies NGC 1097 and NGC 2903. The infrared luminosities of the nuclei in the Seyfert galaxies NGC 1068 and NGC 4151 exceed those provided by young stars by factors of approximately 10.

Gatley, I.↗
NASA NTRS1984

Generation-recombination noise in extrinsic photoconductive detectors

A theory of generation-recombination noise is presented and applied to the analysis of the performance limitations of extrinsic photoconductive detectors. The theory takes account both of the photoinduced generation of carriers and of thermal generation that is due to the finite temperature of the detector. Explicit formulas are derived that relate the detector response time, responsivity, and noise equivalent power to the material properties of the photoconductor (such as the presence of compensating impurities) and to the detector's operating conditions, such as its temperature and the presence of background radiation. The detector's performance is shown to degrade at high background levels because of saturation effects.

Brukilacchio, T. J.↗
NASA NTRS1984

Recombination stellar wind model for the coronae of early-type stars

The wind structures of early-type stars which have base coronal zones are discussed. The calculations give rise to what is called a recombination stellar wind structure because of the transition from a coronally driven wind to a radiatively driven wind. The coronal X-rays are a dominant factor in determining the wind structure because of their effect on the ionization structure, which in turn determines the heating, cooling, and the attenuating properties of the stellar wind. The decreased continuum opacity allows for an increase in the emergent X-ray flux at energies less than 1 keV. The X-ray spectra are compared with those observed with the IPC instrument on the Einstein Observatory and are found to be in excellent agreement. This shows that contrary to earlier analyses, base coronae are not ruled out by the existing IPC X-ray data. The predicted emergent X-ray luminosities are in agreement with the observed values. However, the incident X-ray luminosities from the base coronal zones can be three to four orders of magnitude larger. This suggests that the X-ray IPC spectra reflect the absorption properties of the wind and not the nature of the X-ray source.

Waldron, W. L.↗
NASA NTRS1985

Phenomena Simulation for Heavy Doping and Surface Recombination Velocity

The theoretical models now available that characterize heavily doped (highly conducting) regions in silicon are survyed. Analytical and numerical approaches that determine the influence of such regions on the conversion efficiency of solar cells are examined. Although dilutely doped silicon is well characterized except for some disagreement about optical absorption coefficients, what exists now for heavily doped silicon and its interplay with adjoining regions is an incomplete theory in which not all contributers to transport, recombination, generation, and trapping are defined. Further, the parameters relating to these mechanisms and their values as determined by experiment are subject to various interpretations. The characterization of heavily doped silicon is treated not as a theory but rather as an imperfectly articulated and incompletely formalized body of experience. This view is intended to help point the way toward the attainment of a more complete of heavily doped silicon and thereby toward more informed designs of solar cells. Because computer programs constitute tools both for design and for estimating performance limits, the review includes some remarks pertinent to existing and developing programs.

Lindholm, F. A.↗
NASA NTRS1984

Recombination-active defects in silicon ribbon and polycrystalline solar cells

This paper reports results from a study of recombination-active structural defects in silicon ribbon and polycrystalline solar cells using the electron beam induced current (EBIC) technique in a scanning electron microscope. It is demonstrated that low temperature EBIC measurements can reveal a range of defects that are not observable at room temperature, including slip dislocations in silicon dendritic web ribbons as well as decorated twin boundaries and dislocation complexes in cast polycrystalline silicon solar cell materials.

Cheng, L. J.↗
NASA NTRS1985

Surface-catalyzed recombination into excited electronic, vibrational, rotational, and kinetic energy states: A review

Laboratory experiments in which recombined CO, CO2, D2O, OH, N2, H2, and O2 molecules desorb from surfaces in excited internal and translational states are briefly reviewed. Unequilibrated distributions predominate from the principally catalytic metal substrates so far investigated. Mean kinetic energies have been observed up to approx. 3x, and in some cases less than, wall-thermal; the velocity distributions generally vary with emission angle, with non-Lambertian particle fluxes. The excitation state populations are found to depend on surface impurities, in an as yet unexplained way.

Kofsky, I. L.↗
NASA NTRS1986

Oxygen recombination in individual pressure vessel nickel-hydrogen batteries

A metal-hydrogen cell is described which avoids damage and retards flooding of the hydrogen electrodes by providing for chemical recombination of oxygen and hydrogen in areas or sites remote from the hydrogen electrodes. In the metal-hydrogen cell, a plurality of electrical cell units are place in a back to back relationship. The cells may be lined with a wick, having one or more catalyzed sites on the inner surface of the cell. Separators disposed between the respective metal and hydrogen electrodes of each cell unit are provided with gas directing notches around their peripheries to facilitate the desired movement of gasses within the metal-hydrogen cell. Any two metal electrodes separated by a gas screen are provided with gas tight sealing means between the electrodes at each aperature. The sealing means may be a fing of rubber or elastomeric material which is somewhat compressible but nonreactive with other materials in the cell.

Smithrick, J. J.↗
NASA NTRS1985

Advanced techniques for the measurement of multiple recombination parameters in solar cells

A survey of bulk recombination measurement techniques was presented. Classical methods were reviewed along with their limiting assumptions and simplifications. A modulated light measurement system was built and showed the large effects of junction capacitance. Techniques for extension of classical methods for measurement of multiparameter multiregression measurements were identified and analyzed.

Newhouse, M.↗