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At least 739 records · Page 41

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NASA NTRS1984

Homogeneous condensation of gaseous mixtures of Si, Fe, O, N, and C in relative cosmic abundance and implications for astronomical condensation

The pressure versus temperature curves for homogeneous nucleation and condensation of two gaseous mixtures with nearly relative solar abundance of Si, Fe, O, N, and C in an excess of H were determined experimentally. Mixtures of CO, Fe(CO)5, H2, SiH4, and N2O in Ar were heated behind reflected shocks in a shock tube. The nucleation and condensation, which took place in the subsequent gas-dynamic expansion (cooling phase), was monitored by light scattering and turbidity. Grain morphologies and crystalline phases present in the condensates were determined by electron microscopy. These data cast doubt on the validity of both equilibrium and classical nucleation theoretical approaches to predict homogeneous condensation in a solar nebula or stellar atmosphere.

Stephens, J. R.↗

NASA NTRS1984

Shutdown characteristics of the Mod-O wind turbine with aileron controls

Horizontal-axis wind turbines utilize partial or full variable blade pitch to regulate rotor speed. The weight and costs of these systems indicated a need for alternate methods of rotor control. Aileron control is an alternative which has potential to meet this need. The NASA Lewis Research Center has been experimentally testing aileron control rotors on the Mod-U wind turbine to determine their power regulation and shutdown characteristics. Experimental and analytical shutdown test results are presented for a 38 percent chord aileron-control rotor. These results indicated that the 38 percent chord ailerons provided overspeed protection over the entire Mod-O operational windspeed range, and had a no-load equilibrium tip speed ratio of 1.9. Thus, the 38 percent chord ailerons had much improved aerodynamic braking capability when compared with the first aileron-control rotor having 20 percent chord ailerons.

Miller, D. R.↗

NASA NTRS1985

Ultraviolet Spectral Morphology of O-type Stellar Winds

The highly systematic behavior of the stellar wind features among the majority of O-type spectra, and their strong correlations with the well-calibrated optical spectral types, are consistent with those wind models which incorporate a structural dependence on the fundamental stellar parameters. On the contrary, wind models which postulate a predominance of random rotational or magnetic effects, unrelated to the fundamental stellar parameters, are not supported by the ultraviolet spectral morphology; rather, such effects may contribute to the observed properties of some of the exceptionally peculiar objects.

Walborn, N. R.↗

NASA NTRS1984

Far Infrared Spectroscopy of (O III) in M82

Emission lines at 52 and 88 micron from O III in the galaxy M82 were observed with the cooled grating spectrometer aboard the Kuiper Airborne Observatory. Raw spectra were corrected for telluric water vapor absorption, instrument response function, and relative detector response by ratioing to a spectrum of Saturn or Mars taken on the same flight. An average electron density Pn regions where oxygen is doubly ionized was derived. The electron density calculated for M 82 is significantly lower than those found in the galaxy using the same method. Results suggest that observations of the galaxy made from a great distance would yield a higher electron density than observed in M82.

Duffy, P.↗

NASA NTRS1984

Fluorescent excitation of Fe 2, Mn 2, Ti 2, N 1 lines by V 4, N 5, O 6: Emission lines in the spectra of symbiotic stars and Seyfert galaxies

Analysis of the published IUE and ground based high resolution spectra of symbiotic stars, particularly RR Tel, shows that the dominant excitation mechanism of Fe II, Mn II, Ti II, and N I lines is the selective fluorescent excitation of some levels by the strong C IV, N V, and O VI emission lines. The same mechanism should work for the excitation of Fe II lines in the spectra of Seyfert galaxies and Q60's whose emission spectra are quite similar to those of symbiotic stars. The similarities and differences between the fluroescent excitation mechanism reported herein and the Bowen's mechanism is analyzed.

Gilra, D. P.↗

NASA NTRS1985

Ideal gas thermodynamic properties for the phenyl, phenoxy, and o-biphenyl radicals

Ideal gas thermodynamic properties of the phenyl and o-biphenyl radicals, their deuterated analogs and the phenoxy radical were calculated to 5000 K using estimated vibrational frequencies and structures. The ideal gas thermodynamic properties of benzene, biphenyl, their deuterated analogs and phenyl were also calculated.

Burcat, A.↗

NASA NTRS1985

Implications of new measurements of O-16 + p + C-12,13, N-14,15 for the abundances of C, N isotopes at the cosmic ray source

The fragmentation of a 225 MeV/n O-16 beam was investigated at the Bevalac. Preliminary cross sections for mass = 13, 14, 15 fragments are used to constrain the nuclear excitation functions employed in galactic propagation calculations. Comparison to cosmic ray isotonic data at low energies shows that in the cosmic ray source C-13/C approximately 2% and N-14/0=3-6%. No source abundance of N-15 is required with the current experimental results.

Guzik, T. G.↗

NASA NTRS1984

Mass loss in O-type stars - Parameters which affect it

Newly determined mass loss rates are presented for sixteen O-type stars in three open clusters. Combining the data with that already in the literature, no evidence is found that the rates are different in clusters with differing galactocentric distances and compositions, at least near the sun. There is still appreciable dispersion in the relationship between the mass loss rate and the stellar luminosity. It may be that the mass loss depends additionally on the stellar mass and/or radius, but these data cannot unequivocally indicate which physical dependence is correct. Evidence is found that a stellar wind increases as a massive star evolves from the zero-age main sequence.

Garmany, C. D.↗

NASA NTRS1984

Search for plasma shifts of C VI, N VII, and O VIII resonance lines

The resonance lines of the hydrogenlike ions C VI, N VII, and O VIII were observed in laser-produced plasmas with electron densities in the range 10 to the 21st - 10 to the 22nd per cu cm and electron temperatures between about 70 and 100 eV. The lines of the hydrogenlike ions were recorded photographically with a 3-m grazing-incidence spectrograph. No significant plasma line shift was observed.

Goldsmith, S.↗

NASA NTRS1983

Fragmentation of approximately 500 MeV/nuc Ne and O nuclei in CH2, C and H targets - Charge and isotopic cross sections

Fragmentation of Ne-20 and O-16 nuclei in CH2 and C targets at several energies between 400 and 1000 MeV/nuc is carried out in order to obtain cross sections in hydrogen for use in the galactic cosmic ray propagation problem. Charge changing and isotopic cross sections for the fragments with Z greater than or equal to 4 are obtained. The hydrogen cross sections are obtained by a subtraction procedure. The predictions of the semi-empirical model of Tsao and Silberberg (1979) are given and in general there is good agreement between the measurements and the predictions.

Webber, W. R.↗

NASA NTRS1985

Suprathermal O(+) and H(+) ion behavior during the March 22, 1979 (CDAW 6), substorms

The present investigation has the objective to report on the behavior of energetic (approximately 130 keV) O(+) ions in the earth's plasma sheet, taking into account observations by the ISEE 1 spacecraft during a magnetically active time interval encompassing two major substorms on March 22, 1979. Attention is also given to suprathermal H(+) and He(++) ions. ISEE 1 plasma sheet observations of the proton and alpha particle phase space densities as a function of energy per charge during the time interval 0933-1000 UT on March 22, 1979 are considered along with the proton phase space density versus energy in the energy interval approximately 10 to 70 keV for the selected time periods 0933-1000 UT (presubstorm) and 1230-1243 UT (recovery phase) during the 1055 substorm on March 22, 1979. A table listing the proton energy density for presubstorm and recovery periods is also provided.

Ipavich, F. M.↗

NASA NTRS1985

Detailed course of the O + HO2 reaction

The elementary radical-radical reactions that are of such importance in laser, astrophysical, atmospheric, and combustion processes are increasingly open to direct rate measurement. Attention is presently given to the O + HO2 reaction, which has only one exothermic product channel: OH + O2. Isotopic product analysis was conducted spectroscopically using laser-induced fluorescence of OH. It is found that the simple atom-radical reaction takes place by way of the rapid formation and breakup of an unexpected radical intermediate, thereby raising questions as to the formation, thermochemistry, and decomposition of poorly known products in many other radical-radical reaction systems.

Sridharan, U. C.↗

NASA NTRS1984

Ultraviolet studies of O and B stars in the LMC cluster NGC 2100, the SMC cluster NGC 330 and the Galactic cluster NGC 6530

High-resolution and low-resolution IUE spectra of O and B stars in the LMC cluster NGC 2100, the SMC cluster NGC 330, and the young Galactic cluster NGC 6530 are investigated. Temperatures and luminosities are determined. In the LMC and SMC clusters, the most luminous stars are evolved stars on the horizontal supergiant branch, while in NGC 6530 the stars are all still on the main sequence. Extinction laws were determined. They confirm the known differences between LMC and Galactic extinctions. No mass loss was detected for the evolved B stars in the LMC and SMC clusters, while the high-luminosity stars in NGC 6530 show P Cygni profiles.

Boehm-Vitense, E.↗

NASA NTRS1984

Oscillator strengths for O(II) ions

Oscillator strengths between various doublet states of OII ions are calculated in which extensive multi-configuration wave functions are used. The lower levels for the transitions are of the 2p(3) D(2)o and 2p(3) 2po states, and the upper levels are 2p(4), 3s, and 3d states. The results, which are estimated to have errors of less than 10 percent for individual transitions, agree quite well with the beam foil experiments, as well as with the calculations by use of the non-closed shell many-electron theory (NCMET). The agreement with the rocket measurements is also good except for the 538/581 A pair, in which the 538 A line is believed to blend with the other stronger quartet line. However, a comparison with the recent branching ratio measurement indicates that discrepancies between the present calculation and the experiment do exist for certain transitions.

Ho, Y. K.↗

NASA NTRS1985

The changes in small metal cluster size with adsorption Be13Xn, X = H, O, S, Cl and F

The Be-Be and Be-adsorbate distances are optimized for small Be13Xn clusters,s assuming only two independent degrees of freedom. Results for chemisorption into the three-fold hollows are quite similar to those found for small metal clusters on supports. It is predicted that Cl and F will have the same effect on the metal-metal bond lengths, and so will O and S.

Bauschlicher, C. W., Jr.↗

NASA NTRS1985

Narrow-band forbidden O III imaging of the QSO 4C 18.68 - A tidal tail revealed?

The z = 0.313 quasar 4C 18.68 and its surroundings in the light of redshifted forbidden O III were imaged. The QSO appears much more extended than in broad-band images, with a large halo and possibly a faint tidal tail discerned. A broad-band I CCD image taken in 1 - 1.2 arcsec seeing resolves the QSO from a companion galaxy 3.6 arcsec distant, similar to many others seen in the field. It is suggested that the elongated and asymmetric shapes of some QSOs may be due to not-quite-resolved companion galaxies, and that caution be exercised in interpreting luminosity and color profiles as evidence for underlying spiral or elliptical structure.

Shara, M. M.↗

NASA NTRS1985

Abundances of O, Mg, S, Cr, Mn, Ti, Ni and Zn from absorption lines of neutral gas in the Large Magellanic Cloud in front of R136

Weak absorption lines of C I, O I, Mg I, Mg II, Si I, Si II, P I, Cl I, Cr II, Mn II, Fe I, Ni II, Zn II, CO and C2 are detected in neutral gas in front of the 30 Doradus H II region by IUE spectra of R 136. The Large Magellanic Cloud abundances from the absorption lines are a factor of 2 or 3 below those of the Milky Way, in agreement with emission line study results. Neutral gas density and temperature are estimated from the observed excitation and ionization to be about 300/cu cm and 100 K, respectively; this implies a gas pressure of 30,000/cu cm K.

De Boer, K. S.↗

NASA NTRS1986

Coverage dependent effects on metal surfaces - O, S, F, and Cl on Ni

The c(2 x 2) and p(2 x 2) vibrational frequencies for a rigid Ni lattice are computed for O, S, F, and Cl on Ni(100). It is found that only O/Ni(100) shows a large difference in rigid lattice vibrational frequency. A large shift in rigid lattice vibrational frequency is also found for O/Ni(111) between 0.25 and 0.5 monolayer coverages. Also associated with the change in coverage, is a change in the height above the surface R(perpendicular). This varies from a 0.11 A reduction for O/Ni(100), to an expansion of 0.06 A for F/Ni(100).

Bauschlicher, C. W., Jr.↗