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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Chemical compositions of refractory inclusions in the Murchison C2 chondrite

Neutron activation has been used to analyze samples from ten refractory inclusions in Murchison for 36 elements. Two inclusions, BB-5 and MUCH-1, have large negative Yb anomalies unaccompanied by correspondingly large and negative Eu anomalies; six inclusions have group II or III patterns, or variants of such patterns. The frequency of highly fractionated REE patterns, and the absence of group I patterns, suggest that refractory inclusions in Murchison stopped equilibrating with the nebular gas at higher temperatures than most Allende coarse grained inclusions. Murchison inclusions tend to be lower in nonrefractory elements than Allende coarse grained inclusions, further suggesting that, on average, the former underwent less severe secondary alteration than the latter.

Ekambaram, V.↗
NASA NTRS1985

Chemical compositional study of 35 iron meteorites and its application in taxonomy

Structural and compositional data are reported as a guide to the classification of 35 iron meteorites. The Xinjiang iron meteorite, previously classified as III AB, is reclassified as III E on the basis of its lower Ga/Ni and Ge/Ni ratios, its wider, swollen kamacite bands, and the ubiquitous presence of haxonite, (Fe,Ni)22C. The Dongling (III CD) appears not to be a new meteorite, but to be paired with the Nantan. Four Antarctic iron meteorites, IAB Allan Hills A77250, A77263, A77289, and A77290, are classified as a paired meteorite because of their similarities in structure and in concentrations of various elements. It is shown that Cu shares certain properties with Ga and Ge, which makes them excellent taxonomic parameters.

Wang, D.↗
NASA NTRS1986

The chemical composition of the cool white dwarf LP 701-29

New observations and a new synthetic spectrum of the cool white dwarf LP 701-29 are presented. The analysis suggests that the atmosphere of this star is helium dominated, with enhanced metal abundances compared to the usual abundances of white dwarfs. The best fit is achieved with an effective temperature of 4500 K and an abundance of heavy elements (especially Ca) of the order 0.01 of the solar ratio of metals to helium.

Kapranidis, S.↗
NASA NTRS1987

Chemical composition and origin of Apollo 15 impact melts

Fourteen Apollo 15 impact melt rocks were analyzed for major (fused bead microprobe) and trace element (INAA) abundances, and the compositions of these Apennine Front rocks were compared with samples from other landing sites. The rocks show a wide range in trace element abundances, although all but one have a typical KREEP incompatible element pattern and have low-K Fra Mauro basaltic or medium-K Fra Mauro basaltic compositions. The melt chemistries appear to form five groups (labeled A to E in order of decreasing incompatible elements), with the compositions unlike nearly all other impact melts and regoliths from highland sites. All groups except Group A may represent single impact events (either Imbrian or post-Imbrian). One unique sample has a non-KREEP incompatible element pattern, with low abundances and a positive Eu anomaly. Its target is believed to be either a pre-Imbrian melt or exotic.

Ryder, Graham↗
NASA NTRS1986

The chemical composition of comets and possible contribution to planet composition and evolution

The theory of cold aggregation of interstellar dust into comets is shown to support the ideas that comets provided not only a substantial part of the earth's water but also of its complex organic surface material. Comparison of the density of interstellar dust with meteor densities leads to the conclusion that comets are very fluffy bodies whose solid matter occupies no more than 2/5 of the total volume and possibly substantially less. This implies an extremely low comet albedo of about 0.05 in the visual even for slightly absorbing individual components.

Greenberg, J. Mayo↗
NASA NTRS1988

The spectrophotometry and chemical composition of the oxygen-poor bipolar nebula NGC 6164-5

The paper presents new ground-based and IUE spectrophotometry of several positions in NGC 6164-5 surrounding the Population I Of star HD 148937. Electron temperatures, densities, and abundances are derived for the various positions in the nebula using spectral line information. For all of the regions observed, Ne/H is depleted by an amount comparable to O/H, while S/H and Ar/H have normal values. The results suggest that the nebula consists partly of material ejected from inner shell-burning regions of the Of star. In effect, HD 148937 is older and more advanced than what was previously thought.

Dufour, Reginald J.↗
NASA NTRS1988

The chemical composition of the Lambda Bootis stars

Measurements of the equivalent widths of 24 ultraviolet lines from IUE spectra of 10 Lambda Bootis or suspected Lambda Bootis stars and 19 normal standard stars of spectral types B8-A7 have been compared with line strengths determined using model atmospheres. Abundance differences are estimated via a differential analysis technique. It is found that the ratio of C, N, and O to the heavier elements Mg to Ni is significantly larger than that for solar composition stars.

Baschek, B.↗
NASA NTRS1990

Fabrication and chemical composition of RF magnetron sputtered Tl-Ca-Ba-Cu-O high Tc superconducting thin films

The preparation of TlCaBaCuO superconducting thin films on (100) SrTiO3 substrates is described, and the results of their characterization are presented. Sintering and annealing the thin films in a Tl-rich ambient yielded superconductivity with a Tc of 107 K. The results of an XPS study support two possible mechanisms for the creation of holes in the TlCaBaCuO compound: (1) partial substitution of Ca(2+) for Tl(3+), resulting in hole creation, and (2) charge transfer from Tl(3+) to the CuO layers, resulting in a Tl valence between +3 and +1.

Subramanyam, G.↗
NASA NTRS1992

Huygens/ACP: An instrument for aerosols chemical composition measurements

The Aerosol Collector Pyrolyzer (ACP) which will be used aboard the Huygens probe is introduced. The scientific objectives, scientific rationale, and a technical description of the ACP are given. The ACP will sample the aerosols of the Titan's atmosphere in two regions, 160 to 60 and 60 to 25 km, respectively. In the first region, it will collect aerosol particles absorbed by a complex core (organic polymers) coated with absorbed or condensed molecules. The second collect will sample larger aerosols and the N2-CH4 droplets. In each sampling, the particles are collected on a metallic filter through which the atmospheric gas is pumped. The filter is then inserted into an oven connected to the Gas Chromatograph Mass Spectrometer (GCMS) Experiment which analyzes the gases produced during the heating of the samples. For each sample it will be possible to bring information on the nature and abundance of the volatile components contained in the particles and/or the composition of the photochemical core.

Israel, Guy↗
NASA NTRS1992

Refractory inclusions with unusual chemical compositions from the Vigarano carbonaceous chondrite

Neutron activation was used to test ten inclusions, nine Vigarano and one from Leoville, for major and trace elements. Six Vigarano refractory inclusions have refractory element fractionations that are rare or absent in Allende inclusions. Vig 1623-11 has Th/La and Ir/Mo ratios that are lower than those of any Allende Group I or modified Group I inclusions, and Os/La, Ir/La, and Zr/Hf ratios that are among the lowest in those inclusions. The low Os/La, Ir/La, and Ir/Mo ratios seem to require nonrepresentative sampling of condensate phase in the nebula to a degree that is usual for Allende Group I and modified group I inclusions. The nature and origins of the different inclusions are discussed.

Sylvester, Paul J.↗
NASA NTRS1992

North Massif lithologies and chemical compositions viewed from 2-4 mm particles of soil sample 76503

We identify the lithologic and compositional components of soil 76503 based on INAA of 243 2-4-mm particles and 72 thin sections from these and associated 1-2-mm particles (76502). We present a statistical distribution of the major compositional types as the first step of a detailed comparative study of the North and South Massifs. The soil sample was collected well away from any boulder and is more representative of typical North Massif material than any single large rock or boulder sample. So far, our examination of the 76503 particles has provided a better definition of precursor igneous lithologies and their petrogenetic relationships. It has enabled us to refine the nature of mixing components for the North Massif less than 1-mm fines. It has confirmed the differences in lithologies and their proportions between materials of the North and South Massifs; e.g., the North Massif is distinguished by the absence of a 72275-type KREEP component, the abundance of a highly magnesian igneous component, and the absence of certain types of melt compositions found in the South Massif samples.

Bishop, Kaylynn M.↗
NASA NTRS1940

The lead susceptibility of fuels and its dependence on the chemical composition

The fact that by the use of tetraethyl lead a number of otherwise unsuitable fuels could be made to meet engine requirements was not sufficiently appreciated. While use of tetraethyl lead is limited, the addition of special leaded fuels that increase the octane number is a requirement for many fuels. In this connection, the extent to which the action of tetraethyl lead through the addition of knock-resistant hydrocarbons to the base gasoline is influenced, is quite important. To the elucidation of this problem and of the storage stability of leaded fuels, the present report is dedicated.

Widmaier, O↗
NASA NTRS2001

New Evidence for Impact-induced Hydrothermal Alteration at the Lunar Crater, India: Implications for the Effect of Small Craters on the Mineralogical and Chemical Composition of the Martian Regolith

The Lunar crater has several unique characteristics that make it a valid analogue for similar craters on Mars. We have characterized the secondary alteration assemblage at Lunar in order to make implications for martian alteration materials. Additional information is contained in the original extended abstract.

Hagerty, J.↗
NASA NTRS2002

Chemical Compositions and Abundance Anomalies in Stellar Coronae ADP99

We have been investigating different statistical methods for analysing the metal abundances of sources with low S/N. A Bayesian technique has been developed that determines the most probable line-to-continuum ratio in the source, thereby leading to the metallicity. This method is a promising approach with which to mine the ASCA archive. Some of this work has now been published in conference proceedings. The flavour of the project has changed very slightly in the last year owing to the increasing availability of several good quality Chandra HETG and LETG spectra for stars for which we had reduced and analysed ASCA data. The Chandra grating spectra in principle provide a means of calibrating the results from the low resolution ASCA spectra and we have started some work toward that goal. One paper concerning abundance ratios in active stars is appearing shortly in conference proceedings and is being readied for publication in a main-stream astrophysical journal. This paper demonstrates for the first time that abundance anomalies cannot be categorized simply in terms of First Ionization Potential (FIP) or inverse-FIP based effects. Different Ne enhancements are found in different star types but a link between enhancement factors and stellar properties is not obvious. The publication noted as in preparation in an earlier report, finding strong Ne enhancements in active stars, is now published. These results will again be used to "calibrate" low resolution results for which line ratio techniques cannot be employed.

Drake, Jeremy↗