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At least 757 records · Page 42

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NASA NTRS1980

Novel duplex vapor-electrochemical method for silicon solar cells

A process was developed for the economic production of high purity Si from inexpensive reactants, based on the Na reduction of SiF4 gas. The products of reaction (NaF, Si) are separated by either aqueous leaching or by direct melting of the NaF-Si product mixture. Impurities known to degrade solar cell performance are all present at sufficiently low concentrations so that melt solidification (e.g., Czochralski) will provide a silicon material suitable for solar cells.

Nanis, L.↗

NASA NTRS1981

Analysis of high excitation planetary nebulae

Combination of extensive ground-based spectroscopic observation of high excitation planetary with IUE data permit determination not only of improved diagnostics but also better abundances for elements such as C and N that are well represented in the ultraviolet spectra and also C, Ar and metals Na, Ca and K whose lines appear in the wavelength 3200-8100 A region.

Aller, L. H.↗

NASA NTRS1980

A survey of solar cosmic ray composition 1974-1978

Data on solar particle composition from the Goddard experiment on IMP 8 now spans a period of five years. During this time, detailed abundances and spectra have been obtained for elements through the Fe group and isotopic abundances have been obtained for H and He from a number of the largest flare-associated solar particle events. In the energy range 6.7-15 MeV/nucleon, a systematic enhancement of solar cosmic ray over solar photospheric Na, Mg, Al and Si abundances relative to oxygen is shown to exist in all these large flare events. An additional enhancement of abundances in the elements beyond carbon relative to oxygen that is correlated with atomic charge (or mass) occurs in certain events and produces a variability in Fe/O greater than a factor of 10. Summed over these eight large flares, the Be/O and B/O ratios are shown to be less than 0.0002 and Li/O to be less than 0.001 between 4.2 and 15 MeV/nucleon.

Mcguire, R. E.↗

NASA NTRS1980

Thermal barrier coatings - Burner rig hot corrosion test results

A Mach 0.3 burner rig test program was conducted to examine the sensitivity of thermal barrier coatings to Na- and V-contaminated combustion gases simulating potential utility gas turbine environments. Coating life of the standard ZrO2-12Y2O3/Ni-16.2Cr-5.6Al-0.6Y (composition in wt %) NASA thermal barrier coating system which was developed for aircraft gas turbines was significantly reduced in such environments. Two thermal barrier coating systems, Ca2SiO4/Ni-16.2Cr-5.6Al-0.6Y and ZrO2-8Y2O3/Ni-16.4Cr-5.1Al-0.15Y and a less insulative cermet coating system, 50 vol % MgO-50 vol % Ni-19.6Cr-17.1Al-0.97Y/Ni-16.2Cr-5.6Al-0.6Y, were identified as having much improved corrosion resistance compared to the standard coating.

Hodge, P. E.↗

NASA NTRS1980

Cosmic ray exposure ages of chondrites, pre-irradiation and constancy of cosmic ray flux in the past

Calibration of the production rate of the Ne-21 nuclide was accomplished by 4 methods based on (Al-26)-age, (Mn-53)-age, Kr-81/Kr-83, and Na-22/Ne-22. These production rates are normalized to a shielding parameter ratio Ne-22/Ne-21 = 1.11 and to the chemical composition of L chondrites; a value of P(21)(1.11) = 0.31 is suggested, and a production rate equation derived in terms of the 'F' parameters for L, LL, and H chondrites. The Al-26 half-life measurements are considered to evaluate the effects resulting from preirradiation of meteorites and to examine the data on the constancy of the cosmic ray flux in the light of current astronomical observations.

Nishizumi, K.↗

NASA NTRS1980

Elemental abundances in chondrules from unequilibrated chondrites Evidence for chondrule origin by melting of pre-existing materials

Bulk abundances of Na, Mg, Al, Ca, Sc, V, Cr, Ir, and Au were analyzed by neutron activation of chondrules separated from unequilibrated H, L, and LL chondrites and correlated with petrographic properties. The geometric mean composition of the whole-rock chondrule suites are almost indistinguishable from each other for many elements; chondrules are enriched in lithophile and depleted in siderophile elements in a pattern consistent with chondrule formation by melting of preexistent materials. The porphyritic chondrules are more enriched in refractory and siderophile elements as compared with the nonporphyrytic chondrules, indicating that these two chondrule groups may have formed from different precursors.

Gooding, J. L.↗

NASA NTRS1980

Infrared photometry of the semistellar nucleus of M31

New broad-band infrared JHK data and narrow-band CO and H2O indices for the semistellar nucleus of M31 are presented. The data were obtained specifically to test a prediction of a recent synthesis model by Faber and French in which the ratio of dwarf-to-giant light increases strongly in going from the bulge to the nucleus of M31. The new infrared data do not support such a model. Some alternative explanations for the behavior of the various indices are given, but the apparent conflict between the Faber-French interpretation of the strength of the Na I 8190 A feature and our data is not satisfactorily resolved.

Persson, S. E.↗

NASA NTRS1980

Interstellar gas in the Gum Nebula

A survey of the interstellar gas near the Gum Nebula by optical observation of 67 stars at Ca II, 42 stars at Na I, and 14 stars in the UV with the Copernicus satellite provided radial velocities and column densities for all resolved absorption components. Velocity dispersions for gas in the Gum Nebula are not significantly larger than in the general interstellar medium; the ionization structure is predominantly that of an H II region with moderately high ionization. Denser, more highly ionized clouds are concentrated toward the Gum Nebula; these clouds do not show the anomalously high ionization observed in the Vela remnant clouds.

Wallerstein, G.↗

NASA NTRS1980

The morphology of metallic ions in the upper atmosphere

Analysis of metallic ion data from a day-night pair of rockets, OGO 6, and the elliptic phases of AE-C and AE-D shows the presence of Fe(+) ions at altitudes above 400 km only at low magnetic latitudes. The detection probability of this ion decreases with altitude, with a maximum over the Atlantic and a minimum over India; the rocket data indicate ions in the E region during the day and on the bottom of the F layer at night. Mg(+) and Fe(+) are the dominant ions below 250 km at all latitudes, but Al(+), Na(+), Si(+), and Ca(+) are also detectable; a correlation was found between solar activity and metallic ion detection probability at low latitudes and high altitudes at night

Kumar, S.↗

NASA NTRS1981

Silicon by sodium reduction of silicon tetrafluoride

High purity silicon can be prepared from the reaction of Na with SiF4 to form Si and NaF. The SiF4 is obtained from inexpensive H2SiF6 by precipitation and decomposition of Na2SiF6. Concentrations of B and P are each in the 0.1 ppm wt range in the product Si, separated from NaF by aqueous leaching.

Sanjurjo, A.↗

NASA NTRS1981

Design and performance of the solar maximum mission Hard X-ray Burst Spectrometer

The Hard X-ray Burst Spectrometer acquires data on the temporal and energy distribution of solar X-rays in the energy region from 25 to 385 keV. The detector system is a CsI(Na) central detector, and an anti-coincidence shield with photomultiplier tubes optically coupled to the central and shield crystals. Additional detectors are included for calibration and South Atlantic Anomaly monitoring. A 15 channel pulse height analysis is performed over the energy range every 128 milliseconds. This instrument is capable of handling event rates up to 500 kHz and provides high rate data up to 100 kHz with low spectral distortion. Nine accumulated rates are telemetered every 8.192 seconds. A unique feature of the instrument is the ability to sample rates from the central detector or shield with a one millisecond minimum time resolution. Such samples are stored in a 32768 sample memory with a 40 percent pretrigger event history and a 60 percent posttrigger history.

Workman, L. G.↗

NASA NTRS1981

Plasma volume, osmolality, vasopressin, and renin activity during graded exercise in man

The influence of work intensity on plasma volume, osmolality, vasopressin and renin activity and the interrelationships between these responses are investigated. Plasma volume, renin activity and osmotic, sodium and arginine vasopressin concentrations were measured in venous blood samples taken from 15 healthy male subjects before and after six minutes of bicycle ergometer exercise at 100, 175 and 225 W. Plasma volume is found to decrease significantly with increasing work intensity, while increases in Na(+) concentration, osmolality and vasopressin are only observed to be significant when the work intensity exceeds 40% maximal aerobic capacity and plasma resin activity increased linearly at all work levels. In addition, significant correlations are observed between plasma volume and osmolality and sodium changes, and between vasopressin and osmolality and sodium content changes. Data thus support the hypotheses that (1) vasopressin may be the primary controlling endocrine for fluid and electrolyte levels following exercise; (2) an exercise intensity greater than 40% maximal aerobic capacity is required to stimulate vasopressin release through changes in plasma osmolality; and (3) the stimulation of the renin-angiotensin system is a more general stress response.

Convertino, V. A.↗

NASA NTRS1980

An explanation for the alternating north-south asymmetry of Io's sodium cloud

The hot Jovian plasma torus discovered by Voyager 1 is responsible for the periodic intensity variations of Io's sodium cloud, which are correlated with Io's magnetic latitude. The plasma torus must be a long-lived phenomenon in spite of its apparent absence at the time of the Pioneer flybys. The hot electrons (100,000 K) must be concentrated about one Jupiter radius from the magnetic equator in order to produce the observed variations. Electron impact ionization in the hot plasma torus is strong enough to form and to maintain Io's ionosphere; the hot plasma torus may be the dominant agent forming the ionosphere. Io's bound atmosphere is dense enough that the plasma torus electrons cannot cause a noticeable variation in its Na emission intensity.

Trafton, L.↗

NASA NTRS1981

Acid rain at Kennedy Space Center, Florida - Recent observations

During the period July, 1977 to September, 1979, rainfall was collected in the vicinity of the Kennedy Space Center and subjected to appropriate chemical analysis for purposes of characterization of general composition and acidity. Results obtained form the basis for future comparisons, should significant alteration of the chemical composition of rain occur during the space shuttle era. Acidity extremes calculated on a monthly basis from event samples collected from five sites within a 200 sq km area varied from pH 5.1 in November, 1977, and April, 1978 to pH 4.3 in July, 1978 and July, 1979. Weighted average pH for the entire period was 4.55. Acidity was due to the presence of sulfuric and nitric acids. The mole ratio of excess SO4(-2):NO3(-) was typically greater than one. Monthly weighted average Cl(-) concentrations ranged from 20-240 micromoles/liter. The Cl(-):Na(+) ratio was slightly lower than that present in sea water.

Madsen, B. C.↗

NASA NTRS1981

The salts of Mars

Salt compounds are apparently an important component of the fine-grained regolith on Mars. Salt enrichment may be explained either as a secondary concentration of chemical weathering products or as direct incorporation of planetary released volatiles. Geochemical measurements and chemical relationships constrain the salt species and resultant physicochemical consequences. A likely assemblage is dominated by (Mg,Na)SO4, NaCl, and (Mg,Ca)CO3. Formation of brine in equilibrium with such a salt mixture is unlikely under the temperature and water-vapor restrictions prevalent over most, if not all, of the Martian surface. Acidic conditions, accompanying salt formation, favor the preferential destruction of susceptible igneous minerals.

Clark, B. C.↗

NASA NTRS1981

Galactic disk absorption lines in the spectrum of the quasar 3C 273

It is pointed out that the line of sight to 3C 273 is unique because of the possibility of obtaining both radio and optical absorption line measurements. This information may make it possible to understand in detail the structure of the interstellar medium along the line of sight. To take advantage of this possibility, high-resolution optical spectra were obtained of 3C 273. The observations were made using the echelle spectrograph at the Cassegrain focus of the 4 m telescope at the Cerro Tololo Inter-American Observatory in 1980 January. Both Na D and Ca K lines were obtained on the same plate. In the visual lines, the galactic disk absorption shows a main component at 20 km/sec with a trailing wing in the negative velocities.

Cowie, L. L.↗

NASA NTRS1980

Nonbonded interactions in membrane active cyclic biopolymers. IV - Cation dependence

Interactions of valinomycin and form of its analogs in several conformations with the central ions Li(+), Na(+), K(+), Rb(+) and Cs(+) are investigated as part of a study of the specific preference of valinomycin for potassium and the mechanisms of carrier-mediated ion transport across membranes. Ion binding energies and conformational potential energies are calculated taking into account polarization energy formulas and repulsive energy between the central ion and the ligand atoms for conformations representing various stages in ion capture and release for each of the two ring chiralities of valinomycin and its analogs. Results allow the prediction of the chirality and conformation most likely to be observed for a given analog, and may be used to synthesize analogs with a desired rigidity or flexibility. The binding energies with the alkali metal cations are found to decrease with increasing ion size, and to be smaller than the corresponding ion hydration energies. It is pointed out that the observed potassium preference may be explainable in terms of differences between binding and hydration energies. Binding energies are also noted to depend on ligand conformation.

Radhakrishnan, R.↗

NASA NTRS1981

Studies of Jupiter's lower ionospheric layers

Fluxes of heavy ions necessary to form layers of enhanced ionization observed in the lower ionosphere of Jupiter are theoretically calculated, and possible formation mechanisms of the layers are investigated. Estimates of ion drift velocities and neutral wind speeds are made from the shape of the ionization layers, and are found to range from a few centimeters per second to meters per second. Zonal wind shear ranges from 50 m/s westward to 200 m/s eastward over a 70 km altitude range, while small meridional winds are sufficient to form the layer. Results indicate that if the layers are formed from sodium or sulfur ions from the Galilean satellite which are injected into the Jovian atmosphere, then the Na(+) flux must be 30,000 sq cm/s, and the S(+) flux must be 4000 sq cm/s in order to correlate with Pioneer 10 observations of the L(6) layer. At low altitudes of the L(6) and L(7) layers, the denser atmosphere makes diffusion very slow, and the vertical drift velocity of 1 cm/s requires a zonal wind of only several centimeters per second to drive it.

Chen, R. H.↗