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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

74001 drive tube - Siderophile elements match II B iron meteorite pattern

Eight siderophile elements, seven volatile elements, and U were determined in three samples from 74001 by radiochemical neutron activation analysis. The siderophile pattern closely corresponds to the addition of approximately 0.1% of II B iron meteorites, and the enrichment of nonsiderophile volatile elements seems to be derived from lunar sources with variation generally following Se content. In addition, in 74001 (predominantly black glass), moderately volatile elements (Ag, Zn) are more abundant than In, Cd, and particularly Bi, while in 74220 (mainly orange glass), Ag, Zn, In, and Cd are almost equally abundant, but Bi is as low as in 74001.

Morgan, J. W.↗
NASA NTRS1981

Chemical studies of L-chondrites. I - A study of possible chemical sub-groups

Radiochemical neutron activation analysis of Ag, As, Au, Bi, Co, Cs, Ga, In, Rb, Sb, Te, Tl and Zn and major element data in 14 L4-6 and 3 LL5 chondrites indicates that the L-group is unusually variable and may represent at least 2 sub-groups differing in formation history. Chemical trends in the S/Fe-rich sub-group support textural evidence indicating late loss of a shock-formed Fe-Ni-S melt; the S/Fe-poor sub-group seemingly reflects nebular fractionation only. Highly mobile In and Zn apparently reflect shock-induced loss from L-chondrites. Data for L5 chondrites suggest higher formation temperatures and/or degrees of shock than for LL5 chondrites.

Neal, C. W.↗
NASA NTRS1981

Condensation of activated diguanylates on a Poly/C/ template

The metal-ion catalysis of the oligomerization of activated diguanylate isomers on a polycytidylic acid template is studied in an investigation of possible early prebiotic polynucleotide replication mechanisms. The 5'-imidazolides of diguanylates linked 2' to 5' or 3' to 5' were reacted with polyC in a 1-methylimidazole or a 2,6-lutidine buffer in the presence of a Zn(+2) or a Pb(+2) catalyst, and reaction products were determined by paper chromatography, paper electrophoresis and liquid chromatography. In the lutidine buffer, the presence of both the Zn(+2) catalyst and the polyC template is found to result in the production of 3'-5' linked oligomers with up to 10 diguanylate units, and from diguanylates in the presence of the monomer. In the reactions conducted in the 1-methylimidazole buffer, the addition of Pb(+2) is found to lead to less marked increases in oligomerization in the presence of template, with approximately equal proportions of 2'-5' and 3'-5' oligomers formed from the 2'-5' substrate and mainly 3'-5' bonds from the 3'-5' linked dimer.

Lohrmann, R.↗
NASA NTRS1982

An electrochemical study of Ni/2+/, Co/2+/, and Zn/2+/ ions in melts of composition CaMgSi2O6

Results are reported for a study of the behavior of Ni(2+), Co(2+), and Zn(2+) in molten diopside, determined by cyclic voltametry, as a first step in adapting electrochemical methods for use in experimental geochemistry. The techniques used are described, the theory is briefly discussed, and it is demonstrated that Ni(2+), Co(2+), and Zn(2+) can be reduced, then reoxidized in an uncomplicated case of reversible charge transfer at the Pt electrode. This implies that the neutral metal atoms remain undissolved in the melt. The kinetics of the reduction process, the effects of concentration, the standard reduction potentials, and the diffusion coefficients are discussed in detail. The observations are consistent with the mechanism of Ni(2+) diffusion by transport from site to site. As the proportion of SiO2 in the melt increases, a higher activation energy is required for Ni(2+) to move, and the rate of diffusion is lowered.

Semkow, K. W.↗
NASA NTRS1982

Comparison of advanced thermal and electrical storage for parabolic dish solar thermal power systems

Parabolic dish solar concentrator cluster concepts are explored, with attention given to thermal storage systems coupled to Stirling and Brayton cycle power conversion devices. Sensible heat storage involving molten salt (NaOH), liquid sodium, and solid cordierite bricks are considered for 1500 F thermal storage systems. Latent heat storage with NaF-MgF2 phase change materials are explored in terms of passive, active, and direct contact designs. Comparisons are made of the effectiveness of thermal storage relative to redox, Na-S, Zn-Cl, and Zn-Br battery storage systems. Molten lead trickling down through a phase change eutectic, the NaF-MgF2, formed the direct contact system. Heat transport in all systems is effected through Inconel pipes. Using a cost goal of 120-150 mills/kWh as the controlling parameter, sensible heat systems with molten salts transport with either Stirling or Brayton engines, or latent heat systems with Stirling engines, and latent heat-Brayton engine with direct contact were favored in the analyses. Battery storage systems, however, offered the most flexibility of applications.

Fujita, T.↗
NASA NTRS1983

Water and acid soluble trace metals in atmospheric particles

Continental aerosols are collected above a deciduous forest in eastern Tennessee and subjected to selective extractions to determine the water-soluble and acid-leachable concentrations of Cd, Mn, Pb, and Zn. The combined contributions of these metals to the total aerosol mass is 0.5 percent, with approximately 70 percent of this attributable to Pb alone. A substantial fraction (approximately 50 percent or more) of the acid-leachable metals is soluble in distilled water. In general, this water-soluble fraction increases with decreasing particle size and with increasing frequency of atmospheric water vapor saturation during the sampling period. The pattern of relative solubilities (Zn being greater than Mn, which is approximately equal to Cd, which is greater than Pb) is found to be similar to the general order of the thermodynamic solubilities of the most probable salts of these elements in continental aerosols with mixed fossil fuel and soil sources.

Lindberg, S. E.↗
NASA NTRS1984

Effects of water-vapor on friction and deformation of polymeric magnetic media in contact with a ceramic oxide

The effects of humidity (water-vapor) in nitrogen on the friction and deformation behavior of magnetic tape in contact with a Ni-Zn ferrite spherical pin were studied. The coefficient of friction is markedly dependent on the ambient relative humidity. In elastic contacts the coefficient of friction increased linearly with increasing humidity; it decreased linearly when humidity was lowered. This effect is the result of changes in the chemistry and interaction of tape materials such as degradation of the lubricant. In plastic contacts there was no effect of humidity on friction below 40 percent relative humidity. There is no effect on friction associated with the breakthrough of the adsorbed water-vapor film at the interface of the tape and Ni-Zn ferrite. The coefficient of friction, however, increased rapidly with increasing relative humidity above 40 percent in plastic contacts.

Miyoshi, K.↗
NASA NTRS1985

Humidity effects on adhesion of nickel-zinc ferrite in elastic contact with magnetic tape and itself

The effects of humidity on the adhesion of Ni-Zn ferrite and magnetic tape in elastic contact with a Ni-Zn ferrite hemispherical pin in moist nitrogen were studied. Adhesion was independent of normal load in dry, humid, and saturated nitrogen. Ferrites adhere to ferrites in a saturated atmosphere primarily from the surface tension effects of a thin film of water adsorbed on the ferrite surfaces. The surface tension of the water film calculated from the adhesion results was 48 times 0.00001 to 56 times 0.00001 N/cm; the accepted value for water is 72.7 x 0.00001 N/cm. The adhesion of ferrite-ferrite contacts increased gradually with increases in relative humidity to 80 percent, but rose rapidly above 80 percent. The adhesion at saturation was 30 times or more greater than that below 80 percent relative humidity. Although the adhesion of magnetic tape - ferrite contacts remained low below 40 percent relative humidity and the effect of humidity was small, the adhesion increased considerably with increasing relative humidity above 40 percent. The changes in adhesion of elastic contacts were reversible on humidifying and dehumidifying.

Miyoshi, K.↗
NASA NTRS1984

Magnesium doping of efficient GaAs and Ga(0.75)In(0.25)As solar cells grown by metalorganic chemical vapor deposition

Magnesium has been substituted for zinc in GaAs and Ga(0.75)In(0.25)As solar cells grown by metalorganic chemical vapor deposition (MOCVD). Bis(cyclopentadienyl)magnesium (Cp2Mg) is used as the MOCVD transport agent for Mg. Full retention of excellent material quality and efficient cell performance results. The substitution of Mg for Zn would enhance the abruptness and reproducibility of doping profiles, and facilitate high temperature processing and operation, due to the much lower diffusion coefficient of Mg, relative to Zn, in these materials.

Lewis, C. R.↗
NASA NTRS1985

Diffusion in Immiscible Melts

The objective of this program is to measure the diffusion coefficients for molten Pb in Zn in the immiscible liquid-phase region. Diffusion couples of pure Pb and Zn were prepared using a shear cell. These have been placed in graphite crucibles and encapsulated in stainless steel cartridges and are awaiting the next Materials Experiment Assembly (MEA) flight opportunity. In flight, one couple will be soaked for 40 minutes at 440 deg C (just above the monotectic temperature) and the second couple will be soaked for 40 minutes 820 deg C (just above the consolute temperature). After the soak both samples will be rapidly quenched by flowing He to minimize redistribution of the immiscible phases. Post flight compositional analysis will be accomplished using X-ray fluorescence in the scanning electron microscopy.

Pond, R. B.↗
NASA NTRS1986

Abrasion and deformed layer formation of manganese-zinc ferrite in sliding contact with lapping tapes

Wear experiments were conducted using replication electron microscopy and reflection electron diffraction to study abrasion and the deformed layers produced in single-crystal Mn-Zn ferrite simulated heads during contact with lapping tapes. The crystaline state of the head is changed drastically during the abrasion process. Crystalline states ranging from nearly amorphous to highly textured polycrystalline can be produced on the wear surface of a single-crystal Mn-Zn ferrite head. The total thickness of the deformed layer was approximately 0.8 microns. This thickness increased as the load and abrasive grit size increased. The anisotropic wear of the ferrite was found to be inversely proportional to the hardness of the wear surface. The wear was lower in the order 211 111 10 0110. The wear of the ferrite increased markedly with an increase in sliding velocity and abrasive grit size.

Miyoshi, K.↗
NASA NTRS1986

Effect of crystallographical and geometrical changes of a ferrite head on magnetic signals during the sliding process with magnetic tape

This paper reviews changes in the crystalline structure and geometry of lapped Mn-Zn ferrite heads in sliding contact with magnetic tape and the effects of these changes on magnetic signals. A highly textured, polycrystalline structure was produced on the surface of a single-crystal Mn-Zn ferrite head when it was finished with an aluminum oxide lapping tape. Sliding this lapped surface against a magnetic tape produced a nearly amorphous structure. The sliding process led to a degradation in readback signal of 1 to 2 dB (short-wavelength recording). Furthermore, wear of the magnetic head caused geometrical changes in the head surface. The signal read back with the worn magnetic head was sensitive to operating parameters such as head displacement and tape tension. A change in operating parameters created head-to-tape spacings and, consequently, excessive gains or losses in the readback signal.

Miyoshi, K.↗
NASA NTRS1986

The adsorption and reaction of adenine nucleotides on montmorillonite

The binding of AMP to Zn(2+)-montmorillonite is investigated in the presence of salts and Good's zwitterion buffers, PIPES and MES. The initial concentrations of nucleotide and the percent adsorbtion are used to calculate the adsorption isotherms, and the Langmuir adsorption equation is used for the analysis of data. The adsorption coefficient was found to be three times greater in the presence of 0.2 M PIPES than in its absence. In addition, basal spacings measured by X-ray diffraction were increased by the buffer. These results are interpreted in terms of a model in which the adsorption of AMP is mediated by a Zn(2+) complex of PIPES in different orientations in the interlamellar region of the montmorillonite. Mixed ligand complexes of this type are reminiscent of the complexes observed between metal ions and biological molecules in living systems.

Ferris, James P.↗
NASA NTRS1987

Identification of lines in the satellite ultraviolet - The spectrum of Tau Scorpii

The method of wavelength coincidence statistics (WCS) is applied to the ultraviolet spectra of Tau Sco obtained by the IUE. No identifications of elements heavier than Zn were made. With the exception of Zn IV, all identifications had been previously made in an exhaustive study of Copernicus spectra by Rogerson and Ewell (1985). A comparison of the identifications made in the two studies is in very good agreement for those spectra rich in lines, where the WCS parameters indicate the strong presence of the species. Useful information is added by WCS in cases where species are only weakly, or arguably, present. It is shown that WCS is an important tool in the exploration of any complicated stellar spectrum, and even in the case of a spectrum that has been well studied by traditional methods, it adds important information.

Cowley, Charles R.↗
NASA NTRS1987

Ureilites - Trace element clues to their origin

The question of the origin of ureilites was reexamined using new data obtained by radiochemical NAA for Ag, Au, Bi, Br, Cd, Cs, Ge, In, Ir, Ni, Pd, Os, Rb, Re, Sb, Se, Te, Tl, U, and Zn in two vein separates from Haveroe and Kenna and a bulk sample of Kenna. Vein material was found to be enriched in all elements analyzed, except Zn, and to account for most of the carbon, noble gases, and, presumably, siderophiles in the meteorite. The results support the earlier interpretation of Higuchi et al. (1976) on the composition of ureilite parent body (similar to C3V or H3, but not C3O chondrites).

Janssens, Marie-Josee↗
NASA NTRS1988

Modeling of mechanical properties of II-VI materials

This paper reviews some new developments in the theory of alloy correlations, order-disorder transitions, and solidus phase-transition curves. It is argued that semiconductor alloys are never truly random, and the various phenomena that drive deviations from random arrangements are introduced. Likely consequences of correlations on the ability to fine-tune the lattice match of epitaxial layers to substrates, on vacancy formation, on diffusion, and on vapor-phase crystal growth are discussed. Examples are chosen for the alloys Hg(1-x)Cd(x)Te, Hg(1-x)Zn(x)Te, Cd(1-y)Zn(y)Te, and CdSe(1-y)Te(y).

Sher, A.↗
NASA NTRS1988

Galactic interstellar abundance surveys with IUE. II - The equivalent widths and column densities

This paper continues a survey of interstellar densities, abundances, and cloud structure in the Galaxy, using the International Ultraviolet Explorer (IUE) satellite. Equivalent widths of 18 ultraviolet resonance transitions are presented and column densities for Si II, Mn II, Fe II, S II, and Zn II toward 261 early-type stars are derived. These equivalent widths and column densities agree within the stated errors of earlier Copernicus, BUSS, or IUE surveys of Mn II, Fe II, S II, and Zn II for 45 stars in common. The column densities are derived from single-component curves of growth with a common b-value based on that of Fe II and Si II.

Van Steenberg, Michael E.↗
NASA NTRS1988

Galactic interstellar abundance surveys with IUE. III - Silicon, manganese, iron, sulfur, and zinc

This paper continues a survey of intestellar densities, abundances, and cloud structure in the Galaxy using the IUE satellite. A statistical data set of 223 O3-B2.5 stars is constructed, including 53 stars in the Galactic halo. It is found that S II lines in B stars, of luminosity classes IV and V, have possible contamination from stellar S II, particular for stars with v sin i less than 200 km/s. The mean logarithmic depletions are -1.00, -1.19. -0.63, and -0.23 (Si, Mn,Fe,S, Zn). Depletions of Si, Mn, and Fe correlate with the mean hydrogen density n-bar along the line of sight, with a turnover for n-bar greater than 1/cm. Sulfur depletions correlate with n-bar along the line of sight. The slight Zn depletion correlation also appears to be statistically insignificant. No correlation of depletion is found with the physical density derived from H2 rotational states in 21 lines of sight. Depletion variations in the disk are consistent with a Galactic abundance gradient or with enhanced mean depletions in the anticenter region.

Van Steenberg, Michael E.↗