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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1970

Research on variable threshold transistor storage systems

A fully integrated, electrically alterable, nonvolatile, nondestructive readout control memory was developed, using as storage elements metal-nitride-silicon variable threshold transistors. An optimum approach to such a memory was developed in which a three dimensional selection technique was used, both for read and write operations. Electrical isolation of writing and memory circuits was obtained by means of separate memory and write circuit chips. This method provided protection from voltage breakdowns, increased circuit flexibility, and greater ease of testing of interim and final circuit elements.

Wegener, H. A. R.↗
NASA NTRS1972

Elemental abundances in stone meteorites.

Measurement of abundances of Na, Al, Sc, Cr, Mn, Fe, Co, and Cu by instrumental neutron activation analyses of 103 chondrites and 17 achondrites. Various sources of error in the method, including sampling errors, are discussed in detail. Examination of the patterns of coherence of the elements determined suggests the presence of effects of fractionation during condensation from the solar nebula of matter parental to chondrites. Such effects seem to be exhibited both in the abundances of lithophilic elements, perhaps being related to varied temperatures of accretion and in the abundances of those elements which would be affected by metal-silicate fractionation in the solar nebula. Atomic abundances relative to Si vary little in carbonaceous chondrites, suggesting that efficient mixing processes operated on these meteorites prior to or during their formation. It is suggested that, at present, no single class of carbonaceous chondrites is clearly more primitive than another. Carbonaceous and unequilibrated ordinary chondrites may represent aggregates of material accreted from the solar nebula at relatively low temperatures. The present data support a model of equilibration and minor mobilization of nonvolatile elements within small domains of chondrites after accretion. Such a model would be consistent with the petrologic types of Van Schmus and Wood (1967).

Schmitt, R. A.↗
NASA NTRS1972

Gas-liquid chromatography in lunar organic analysis.

Gas-liquid chromatography (GLC) is a powerful and sensitive method for the separation and detection of organic compounds at nanogram levels. The primary requirement for successful analyses is that the compounds of interest must be volatile under the chromatographic conditions employed. Nonvolatile organic compounds must be converted to volatile derivatives prior to analysis. The derivatives of choice must be both amenable to chromatographic separation and be relatively stable. The condition of volatility necessitates the development of efficient derivatization reactions for important groups of compounds as amino acids, carbohydrates, nucleosides, etc. Trimethylsilylation and trifluoroacetylation represent specific areas of recent prominence. Some relevant practical aspects of GLC are discussed.

Gehrke, C. W.↗
NASA NTRS1974

Chemical and petrographic correlations among carbonaceous chondrites

Detailed study of the petrographic and chemical properties of carbonaceous chondrites shows that the four distinct petrographic subtypes may be related to one of two distinct chemical subdivisions. These subdivisions are recognized primarily by the relative abundances of the nonvolatile elements Si, Ca, Al, Ti, Cu and Fe. C1, C2 and C3(O) chondrites form one subdivision. Vigarano subtype chondrites form the other subdivision and include chondrites previously referred to as C2, C3 and C4. Normalized to silicon, the abundances of Ca, Al and Ti are relatively enriched in Vigarano subtype chondrites, whereas Fe and Cu are relatively more abundant in C1, C2 and C3(O) chondrites. Volatile elements tend to correlate with petrographic subtypes rather than with chemical subdivisions.

Van Schmus, W. R.↗
NASA NTRS1974

Labile and nonlabile element relationships among Apollo 17 samples

Volatile and nonvolatile trace element contents in a suite of Apollo 17 soils and rocks are studied. It is found that the halogens exhibit a remarkable degree of coherence because of their apparent diverse geochemistry, that the F-Cl-P2O5 coherence previously noted persists among Apollo 17 samples, that both U and Ru-Os support lateral mixing of regolith on a local scale, and that the meteoritic Ru/Os ratios found in a few samples are attributed to primitive lunar material that has not been extensively recycled.

Jovanovic, S.↗
NASA NTRS1976

Mariner mission to Encke 1980

Experimental design for the Mariner mission to Comet Encke is considered, examining the following experiments: volatile and nonvolatile chemical analysis, an imaging system for the comet nucleus, the ultraviolet spectrometer, and magnetic field and plasma experiments. Mission design is discussed, emphasizing the mission profile, trajectory and targeting and the spacecraft design.

Yeates, C. M.↗
NASA NTRS1976

Volatile element depletion and K-39/K-41 fractionation in lunar soils

Evidence for selective loss and isotopic fractionation (in the case of K) of volatile elements during formation of agglutinates by micrometeoritic bombardment of lunar soils is presented. Concentrations and isotopic compositions of volatile elements (K, Rb, Pb) and nonvolatile elements (U, Th, Ba, Sr, rare earths) in separates taken from soils 14163, 14259, 15041, 68501, and 71500 are examined. Rayleigh fractionation calculations applied to K-39/K-41 isotopic data indicate ten-fold recycling of bulk soil, to account for observed isotopic anomalies. The lunar soil fines fraction seems to be a site of deposition for volatile or labile Pb produced during agglutination. Local fines (below 75 microns) are viewed as representative of the parent material for agglutinates formed in situ by micrometeoritic impact. Magnetic separation of agglutinates from soil 68501 revealed a bimodal population, with one class comprising welded blocky magnetic glasses.

Church, S. E.↗
NASA NTRS1977

Low-work-function surfaces produced by cesium carbonate decomposition

Cesium carbonate (Cs2CO3) was heated to the decomposition temperature of approximately 600 C. The nonvolatile decomposition products were condensed on a nickel substrate while the carbon dioxide was removed by pumping. The deposited material is characterized by an effective work function of between 1.05 and 1.15 eV at 450 K and by photoemission in the visible and near-infrared region of the spectrum. It is suggested that the deposited material consists of Cs2O, possibly Cs2O2, and adsorbed cesium. Silver, evaporated from a heated silver bead, produced the typical photoemissive and thermionic properties of a silver-oxygen-cesium (S-1) photocathode. The material may be of interest for thermionic energy converters and for the formation of silver-oxygen-cesium photocathodes.

Briere, T. R.↗
NASA NTRS1977

Volatile/mobile trace elements in Karoonda /C4/ chondrite

Concentrations of ten volatile/mobile trace elements and of nonvolatile Co in the Karoonda (C4) meteorite were determined, and the atomic abundances relative to C1 are compared with values for the Murchison (C2) and Allende (C3) meteorites. Empirical Bi, In, and Tl data for Karoonda and heated Allende and Murchison are compared with theoretical curves for condensation from a gas of cosmic composition at low pressures. It is suggested that Karoonda might derive from low-temperature open-system metamorphism of pristine C3-like material.

Matza, S. D.↗
NASA NTRS1978

Meteor ablation spheres from deep-sea sediments

Spheres from mid-Pacific abyssal clays (0 to 500,000 yrs old), formed from particles that completely melted and subsequently recrystallized as they separated from their meteoroid bodies, or containing relict grains of parent meteoroids that did not experience any melting were analyzed. The spheres were readily divided into three groups using their dominant mineralogy. The Fe-rich spheres were produced during ablation of Fe and metal-rich silicate meteoroids. The glassy spheres are considerably more Fe-rich than the silicate spheres. They consist of magnetite and an Fe glass which is relatively low in Si. Bulk compositions and relict grains are useful for determining the parent meteoroid types for the silicate spheres. Bulk analyses of recrystallized spheres show that nonvolatile elemental abundances are similar to chondrite abundances. Analysis of relict grains identified high temperature minerals associated with a fine-grained, low temperature, volatile-rich matrix. The obvious candidates for parent meteoroids of this type of silicate sphere is a carbonaceous chondrite.

Blanchard, M. B.↗
NASA NTRS1978

Trace elements in ocean ridge basalts

A study is made of the trace elements found in ocean ridge basalts. General assumptions regarding melting behavior, trace element fractionation, and alteration effects are presented. Data on the trace elements are grouped according to refractory lithophile elements, refractory siderophile elements, and volatile metals. Variations in ocean ridge basalt chemistry are noted both for regional and temporal characteristics. Ocean ridge basalts are compared to other terrestrial basalts, such as those having La/Yb ratios greater than those of chondrites, and those having La/Yb ratios less than those of chondrites. It is found that (1) as compared to solar or chondrite ratios, ocean ridge basalts have low ratios of large, highly-charged elements to smaller less highly-charged elements, (2) ocean ridge basalts exhibit low ratios of volatile to nonvolatile elements, and (3) the transition metals Cr through Zn in ocean ridge basalts are not fractionated more than a factor of 2 or 3 from the chondritic abundance ratios.

Kay, R. W.↗
NASA NTRS1977

Monochromatic brightness variations of comets. II - Core-mantle model

A class of comets, of which Comet Kohoutek (1973f) is typical, show total as well as monochromatic brightness asymmetries about perihelion. They are fainter after perihelion than before at the same heliocentric distance. A model of the cometary nucleus consisting of a growing nonvolatile dust mantle surrounding a volatile icy core is used to discuss this phenomenon. Numerical results are obtained for Comet Kohoutek (1973f). It is found that dust mantles of thickness in the range of 10-75 cm can be grown by perihelion passage for various values of the thermal conductivity of the dust if there is no substantial dust blow-off by the sublimating volatiles. The thermal conductivity of the dust mantle is quite small and is dominated by 'radiative conductivity' for heliocentric distances less than about 2 AU. Since the radiative conductivity is larger for larger grain size, the thickest mantle corresponds to coarsest matrix. The production rate of the 'parent-molecules' as well as the monochromatic brightness of their 'daughter' products increases less steeply than in the mantleless case, as the comet approaches perihelion.

Mendis, D. A.↗
NASA NTRS1975

Ancient meteoritic component in Apollo 17 boulders

The reported investigation is concerned with the resolution of a number of questions related to the ancient meteoritic component in Apollo 17 boulders. Numerical taxonomic methods have been adopted to objectively group the components. Only the nonvolatile siderophile elements have been used for the classification. Efforts were made to obtain data on the metal composition of breccias analyzed for trace elements, to determine if metal homogeneity was reflected in siderophile ratios. Thirty-one samples were analyzed of which twenty-eight have significant siderophile contents. It is concluded that highland breccias are largely the product of large basin-forming impacts. Highland soils are then produced by comminution of the breccias by small local impacts and micrometeorite bombardment. The long-lived component of bulk soils considered by Baedecker et al. (1974) is thought to contain a substantial micrometeorite contribution, plus assorted debris.

Higuchi, H.↗
NASA NTRS1978

New High Temperature Cross Linking Monomers

This report describes the results of a one-year program designed to synthesize new, nonvolatile crosslinking monomers and to prove their feasibility in the development of lower temperature curing PMR-polyimide resins with high temperature capability. The objective of this program is to develop PMR-polyimide resins capable of being processed at a maximum temperature of 232C to 288C (450F to 500F) without sacrifice of the high temperature 316C (600F) capability of the state-of-the-art PMR-15 polyimide resin. Four monomethyl esters were synthesized and characterized for use in the crosslinking studies. It was found that all four crosslinkers were capable of entering into a crosslinking reaction to produce polymer specimens which were strong, dense and free of voids. The infrared and DSC studies of each crosslinker with monomers 4,4'-methylenedianiline (MDA) and the dimethyl ester of 3,3',4,4'-benzophenonetetracarboxylic acid (BTDE) comprising the resin systems, crosslinker/MDA/BTDE suggested that curing could be accomplished at 288C (550F). However, fabrication of dense, void free polymer specimens required a temperature of 316C (600F) and a pressure of 0.69 MPa (100 psi). The crosslinkers, monomethyl ester of 2,5-bicyclo[2.2.1]heptadiene-2,3-dicarboxylic acid (NDE) and monomethyl ester of maleic acid (MAE) were selected for evaluation in Celion 6000/PMR polyimide composites. These composites were characterized at RT, 288C (550F) and 316C (600F) initially and after isothermal aging at 288C (550F) and 316C (600F) for several hundred hours. The results of the isothermal aging studies suggested that both PMR systems NDE-MDA-BTDE and MAE-MDA-BTDE are promising candidates as matrices for addition type polyimide composites. These studies demonstrated that alternate crosslinkers to NE/MDA/BTDE are feasible, but mechanisms to lower the crosslinking temperature must be developed to provide lower temperature processing PMR-type polyimides.

Scola, Daniel A.↗
NASA NTRS1978

Postperihelion interference filter photometry of the 'annual' Comet P/Encke

Interference filter photometry was taken of Comet Encke on June 14, 1974 (1.07 AU heliocentric distance, postperihelion) at the CTIO (Cerro Tololo Interamerican Observatory) 150-cm reflector. Production rates were calculated as 4.1 x 10 to the 23nd power mol/sec for CN, 5.3 x 10 to 23nd power mol/sec for C3, and 4.3 x 10 to the 24th power mol/sec for C2. These are about three times smaller than at comparable heliocentric distance preperihelion, assuming a value of 100 for the ratio H2O/(C2 + C3 + CN). An upper limit was placed on the production of nonvolatiles at about one-third that of volatiles in mass by assuming a bulk density of 1 g/cu cm, a particle geometric albedo of 0.1, and a phase function of 0.2.

Newburn, R. L., Jr.↗
NASA NTRS1978

A solid state data recorder for spacecraft telemetry applications

A solid state data recorder (SSDR) has been developed which offers a high-reliability alternative to tape recorders in many spacecraft telemetry applications. The storage medium used in this recorder was ferrimagnetic garnet films supporting nonvolatile magnetic bubble domains. The recorder was designed using modular construction consisting of a digital control unit, power supply, and two memory modules. A prototype SSDR has been fabricated which is designed for 100-million bits of storage but was populated with 128 chips for a 13-million bit capacity. Preliminary tests indicate satisfactory operation.

Stermer, R. L., Jr.↗
NASA NTRS1979

Volatiles in Chainpur chondrules

A study of volatile element concentrations in individual chondrules in the Chainpur LL3 chondrite is presented. Volatile elements differing in geochemical behavior tended to vary randomly and correlated variations were observed only for those elements inferred to occupy similar mineral sites. Variations in Co and Ni in kamacite show that metal in chondrule interiors has not approached equilibrium, and that postformational element distribution has mainly altered siderophile concentrations in surface metal grains, and has probably left ionic species unaltered. Etching to remove 3 to 5% of the chondrule dissolved siderophiles, enhanced Zn and Na volatiles relative to nonvolatile Cr in the etch, and produced a large Cd enhancement. If metamorphic redistribution of nonsiderophile volatiles was neglible, their high concentrations are inconsistent with chondrule formation by direct condensation, and models involving sudden melting of preexisting solids can explain the observations but require rapid cooling to prevent volatile loss.

Grossman, J. N.↗
NASA NTRS1980

Measurement of particulates

The size distributions of particles in the exhaust plumes from the Titan rockets launched in August and September 1977 were determined from in situ measurements made from a small sampling aircraft that flew through the plumes. Two different sampling instruments were employed, a quartz crystal microbalance (QCM) cascade impactor and a forward scattering spectrometer probe (FSSP). The QCM measured the nonvolatile component of the aerosols in the plume covering an aerodynamic size ranging from 0.05 to 25 micrometers diameter. The FSSP, flown outside the aircraft under the nose section, measured both the liquid droplets and the solid particles over a size range from 0.5 to 7.5 micrometers in diameter. The particles were counted and classified into 15 size intervals. The presence of a large number of liquid droplets in the exhaust clouds is discussed and data are plotted for each launch and compared.

Woods, D.↗