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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Far-ultraviolet studies. VI - Further limits on diffuse galactic light scattered at large angles by dust

The Apollo 17 wide-field far-ultraviolet spectrometer was used to scan six large bands of the sky during trans-earth coast. After accounting for internal scattered light and the light expected from stars in the field of view, no significant residual flux remains. This imposes important constraints on the scattering properties of the interstellar dust grains: either the grains are extremely strongly forward scattering, or the albedo of the grains is low. The absence of a scattered light signal from dusty, moderate galactic latitude regions of the sky indicates that the high galactic latitude flux reported by Henry et al. (1977) and by Anderson et al. (1979) does not represent starlight backscattered by dust.

Anderson, R. C.↗
NASA NTRS1982

High-resolution X-ray spectra of solar flares. VI - Impulsive soft X-ray flares

Doschek et al. (1980) and Feldman et al. (1980) have discussed high-resolution soft X-ray spectra of solar flares. The present investigation is concerned with the characteristics of the impulsive events as observed in soft X rays and the cooling of the flare plasma in terms of energy loss processes. A class of intense, short-lived solar flares which appear to be characterized by very high densities at high temperatures is found. For the 1979 November 6 event, the cooling time is so rapid that the density obtained may be a lower limit. The main cooling mechanism for the flares is found to be radiative. Two of the events are associated with strong gamma-ray emission and both of these events are very unusual in their soft X-ray emission. The 1979 November 9 flare shows extremely broad X-ray emission lines during the rise phase, indicative of nonthermal velocities of the order of 300 km/s.

Feldman, U.↗
NASA NTRS1983

Aromatic Polyimides With Group VI Linkages

New polymer system combines thermal and solvent resistant properties of aromatic polyimides with processability of PPX polymers. PPX polymers include polyphenylene oxide, polyphenylene sulfide, and polyphenylene sulfone classes. Generally more processable by hot melt or thermoplastic techniques than aromatic polyimides. PPX systems more susceptible to attack by solvents and have lower glass transition temperatures than PI group.

St. Clair, T. L.↗
NASA NTRS1983

Effects of drift on the transport of cosmic rays. VI - A three-dimensional model including diffusion

The first results are presented from a series of computer simulations of the solar modulation of galactic cosmic rays using a full three-dimensional model which incorporates all known important effects on particle transport, particle drifts, convection with the solar wind, energy loss, and anisotropic diffusion. The model is time-independent in the coordinate frame rotating with the sun, so corotating effects can be studied. Modulation in an interplanetary magnetic field model is considered in which the current sheet separating the northern and southern solar hemispheres is warped and corotating with the sun. The amplitude of the warp is varied to simulate possible solar cycle variation of the magnetic field. Substantial effects due to the warp of the current sheet are found. Comparison of the model results with various data is presented. Among other things, it is shown that the intensity may decrease away from the current sheet for both signs of the magnetic field, as suggested by recent observations, and in contrast with inferences from earlier, more approximate calculations.

Kota, J.↗
NASA NTRS1983

The 0.9-2.5 micron spectrum of Comet West 1976 VI

Analyses of IR data of Comet West in the region 0.9-2.5 microns are presented. The spectra were observed with a resolution of 4.6/cm, and the solar-type star Eta Boo was also observed for comparison purposes. The cometary continuum was found to increase slightly from 10,000-5500/cm, and display thermal emission above 5500/cm due to dust particles in the coma. The cometary emissions were identified with CN and C2, with the C2 transitions displaying unblended singlet and triplet systems. It is noted that no emissions or absorptions due to ice of any form were detected.

Johnson, J. R.↗
NASA NTRS1984

Magnetic field line reconnection experiments. VI - Magnetic turbulence

Extensive statistical analysis of the vector components of fluctuating magnetic fields have been performed in a time dependent neutral magnetic sheet. Cross spectral analysis indicates a variety of wave numbers present for each frequency investigated. Comparison of Fourier components of the cross spectral function with dispersion surfaces in k space demonstrates the waves are large amplitude whistlers; this is verified by polarization analysis, which shows the random waves' magnetic fields to be right-hand circular. Ion acoustic and Langmuir turbulence are also observed along with bursts of microwave radiation. Measurements of the electron distribution function f(v, r, t) and its fluctuations in velocity space relate wave and particle activity.

Gekelman, W.↗
NASA NTRS1984

Statistical mechanics of light elements at high pressure. VI - Liquid-state calculations with Thomas-Fermi-Dirac theory

A model free energy is developed for hydrogen-helium mixtures based on solid-state Thomas-Fermi-Dirac calculations at pressures relevant to the interiors of giant planets. Using a model potential similar to that for a two-component plasma, effective charges for the nuclei (which are in general smaller than the actual charges because of screening effects) are parameterized, being constrained by calculations at a number of densities, compositions, and lattice structures. These model potentials are then used to compute the equilibrium properties of H-He fluids using a charged hard-sphere model. The results find critical temperatures of about 0 K, 500 K, and 1500 K, for pressures of 10, 100, and 1000 Mbar, respectively. These phase separation temperatures are considerably lower (approximately 6,000-10,000 K) than those found from calculations using free electron perturbation theory, and suggest that H-He solutions should be stable against phase separation in the metallic zones of Jupiter and Saturn.

Macfarlane, J. J.↗
NASA NTRS1984

Combined distillation and normal freezing to purify elements of groups II and VI

A practical system and its application to the purification of Te and Cd is described. Single crystals are grown directly in vitreous silica ampoules subsequently used for sealed Bridgman growth of (Hg-Cd)Te. The system also prepares the ampoules by heating in high vacuum. Purification of the elements is by the combined effect of distillation and normal freezing. Transport and segregation are discussed.

Holland, L. R.↗
NASA NTRS1985

Occultations of stars by solar system objects. VI - Occultations of catalog stars by asteroids in 1986 and 1987

Results are presented of a search for upcoming asteroid occultations involving stars in six major astrometric catalogs containing a total of approximately 326,000 individual stars. Within stated constraints on solar elongation, asteroid angular diameter, orbit quality, and occultation duration, the search is complete for all numbered asteroids. Circumstances of 74 occultations occurring in 1986 and 59 in 1987 are described.

Wasserman, L. H.↗
NASA NTRS1986

The ionization structure of planetary nebulae. VI - NGC 7662

Spectrophotometric observations of NGC 7662, obtained in the UV using the IUE in May 1983 and at 340-720 nm using the 90-cm and 2.1-m telescopes at KPNO during 1982-1984, are reported and analyzed. The line intensities and the temperatures, densities, and ionic abundances determined from them are presented in tables and characterized in detail. Generally good agreement is found among these UV/optical abundances, abundances derived from optical data alone, and the model predictions of Harrington et al. (1982).

Barker, T.↗
NASA NTRS1986

Dynamics of solar filaments. VI - Center-to-limb study of H-alpha and C IV velocities in a quiescent filament

The rotation of a stable quiescent filament from near disk center to the limb has been observed. Observations of intensity and velocity were made in H-alpha and C IV, and compared with magnetic field measurements. From the H-alpha observations, it is concluded that the filament is made up of many small scale magnetic features that are not coherently aligned along the neutral line. They are especially convoluted at the apparent 'footpoints'. The measured velocities are of the order of a few kilometers per second in both lines. However, the comparison of the standard deviations of the C IV velocities in and out of the filament as it rotates toward the limb shows that the vertical velocities in the filament are greater than the horizontal velocities. Measurements of velocity do not make it possible to distinguish between the Raadu-Kuperus (1973) or Kippenhahn-Schluter (1957) models for prominences because neither theory is adequately developed for this comparison. However, the observation of the many fine loops brings into question the correctness of either model.

Simon, G.↗
NASA NTRS1986

M.I.T./Canadian vestibular experiments on the Spacelab-1 mission. VI - Vestibular reactions to lateral acceleration following ten days of weightlessness

The effects of weightlessness on human orientation and balance are investigated. The responses of the Spacelab-1 crew to linear acceleration are measured using a perception of linear motion test, a closed-loop otolith assessment test (CLOAT), a dynamic ocular torsion test, and a lateral eye deviations test. The perception of linear motion tests measures a subject's ability to detect the presence and direction of small changes in linear acceleration; CLOAT assesses a person's ability to use linear acceleration cues to perform a manual control task; and the dynamic ocular torsion test examines the gravitoinertial contribution to dynamic ocular counterrolling. The threshold accelerations, velocity constants, regression coefficients, scalar performance measures, and torsion measurements for the subjects are analyzed and described. It is noted that the data support the tilt-translation reinterpretation hypothesis of Young et al. (1984, 1986).

Arrott, A. P.↗
NASA NTRS1987

Optical region elemental abundance analyses of B and A stars. VI - The normal stars HR 6559 (A7 IV) and Eta Leporis (F0 IV)

Abundance analyses using optical region data and fully line-blanketed model atmospheres have been performed for the sharp-lined superficially normal stars HR 6559 (A7 IV) and Eta Leporis (F0 IV), consistent with previous studies of middle B through early A type stars. HR 6559 and Eta Lep are slightly metal-weak in general. Their analyses and that of Theta Leo (A2 V) support the suggestion of Smith (1974) that sharp-lined normal A stars do not necessarily have photospheric abundances identical with those of normal middle to late B stars.

Adelman, S. J.↗
NASA NTRS1987

II-VI and I-III-VI2 alloy crystals for photovoltaic applications

The results of the photoreflectance, photoconductivity, and photoluminescence studies on Mn(x)Cd(1-x)Te single crystals are discussed from the viewpoint of the utility of these compounds as gap components in multijunction solar cells. Attention is also given to recent results on CuInSe2 and on quaternary I-III-VI2 alloys based on CuInSe2. Recent Kelvin probe and X-ray photoemission spectroscopy studies of the surface properties of CuInSe2 and Mn(x)Cd(1-x)Te, respectively, are described. In addition, recent results on the radiation damage and annealing kinetics of Mn(x)Cd(1-x)Te are considered in the context of future work on the sputtering and ion beam deposition of thin films of this material.

Bachmann, K. J.↗
NASA NTRS1987

Protostellar formation in rotating interstellar clouds. VI - Nonuniform initial conditions

The collapse and fragmentation of rotating protostellar clouds is explored, starting from nonuniform density and nonuniform rotation initial conditions. Whether binary fragmentation occurs during the first dynamic collapse phase depends strongly on the initial density profile. Exponential clouds are only somewhat more resistant to fragmentation than uniform-density clouds, but power-law clouds do not undergo fragmentation for likely values of a relevant parameter. Because binary fragments start from profiles intermediate between uniform density and exponential clouds, minimum protostellar mass for population I stars should be increased to approximately 0.02 solar mass. The axisymmetric Terey et al. (1984) model should be stable with respect to nonaxisymmetric perturbations. Considering the observed binary frequency, collapse from power-law initial conditions appears to be less common than collapse from more uniform initial conditions.

Boss, Alan P.↗
NASA NTRS1987

Studies of the Virgo cluster. VI - Morphological and kinematical structure of the Virgo cluster

The structure of the Virgo cluster is analyzed on the basis of the positions, Hubble types, and radial velocities of 1277 Virgo cluster galaxies. The surface distribution of galaxies is considered according to type, and is discussed using maps, isopleths, strip counts, and radial-density distributions. It is found that the Virgo cluster shows pronounced double structure. The main concentration has a large velocity dispersion and is made up predominantly of early-type galaxies, while the secondary concentration has a much smaller velocity dispersion and contains late types. There is a strong spatial segregation of the Hubble types, the early-type galaxies being more concentrated toward the cluster center. There is significant substructure in the cluster core. The irregularity of the Virgo cluster in both configuration and velocity space shows that the core and the envelope are still forming, and hence that the cluster is young.

Binggeli, Bruno↗