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At least 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Calcium isotopic anomalies in the Allende meteorite

Isotopic anomalies in Ca are reported which were found in two Ca-Al-rich inclusions of the Allende meteorite. The corrected Ca data show nonlinear isotopic effects in Ca-48 of +13.5 per mil and in Ca-42 of +1.7 per mil for one sample. The second sample shows a Ca-48 depletion of -2.9 per mil, but all other isotopes are normal. Samples with large excesses in Mg-26 show no Ca anomalies. The effects demonstrate that isotopic anomalies exist for higher-atomic-number refractory elements in solar-system materials and do not appear to be readily explainable by a simple model. Observed anomalous Mg and Ca compositions for coexisting mineral phases are uniform within each inclusion and require initial isotopic homogeneity within an inclusion but the preservation of wide variations between inclusions. Assuming formation of these inclusions by condensation from a gaseous part of the solar nebula, this implies isotopic heterogeneity on a scale of 10 to 100 km within the nebula.

Lee, T.↗
NASA NTRS1979

Calcium isotopic anomalies and the lack of aluminum-26 in an unusual Allende inclusion

This letter reports the discovery of an unusual Allende inclusion that is rich in hibonite, Ca(Al, Ti, Mg)12O19, the most refractory and possibly the most primitive major oxide mineral from the solar nebula. The Mg and Ca isotopic compositions of this hibonite-rich inclusion are studied in order to investigate the distribution of Al-26 in the solar system and to extend the search for isotopic anomalies. The Mg results indicate that no Mg isotopic anomalies are present, that the initial Al-26/Al-27 ratio for the inclusion when it crystallized was less than 200 billionths, and that the Mg mass-fractionation effect in the inclusion must be less than about 20 per mil/amu for the hibonite and 10 per mil/amu for other phases. The Ca studies reveal that large Ca mass-fractionation effects of about 7.5 per mil/amu are present and that additional small 'nonlinear' effects of presumably nuclear origin at a level of about 1 to 2 per mil are present in at least Ca-42. A plausible model for the evolution of the hibonite-rich inclusion is outlined.

Lee, T.↗
NASA NTRS1980

Effect of sodium, potassium, magnesium, calcium, and chlorine on the high temperature corrosion of IN-100, U-700, IN-792, and Mar M-509

The effects of potential impurities such as Na, K, Mg, Ca, and Cl, in coal-derived liquid fuels on accelerated corrosion of IN-100, U-700, IN-792, and Mar M-509 were investigated using a Mach 0.3 burner rig for times to 200 hours in one hour cycles. These impurities were injected in combination as aqueous solutions into the combustor. Other variables were time, temperature, and fuel-to-air ratio. The experimental matrix was a central composite fractional fractorial design divided into blocks to allow modification of the design as data was gathered. The extent of corrosion was determined by metal consumption. The time exponent was near 1.0 for the least corrosion resistant alloys, U-700 and IN-100; near 0.8 for the moderately resistant IN-792; and close to Mar M-509, the most corrosion resistant alloy. As anticipated, corrosion rapidly increased with increasing temperature as well as Na and K concentrations, while corrosion decreased somewhat as the Ca concentration increased for all alloys. Mg was beneficial for the Ni-base alloys but had little effect on the Co-base alloy. Surprisingly, the effect of increasing Cl was to decrease the corrosion of all alloys. Little interaction among the dopants was noted.

Lowell, C. E.↗
NASA NTRS1980

Effectiveness of using thyrocalcitonin for the prevention of a calcium metabolic disorder in the mineralized tissues of rabbits with 30 days hypokinesia

A 30 day hypokinesia in rabbits led to a considerable lag in weight gain for the skeletal bones, reduction in Ca45 uptake, and an increase in isotope resorption rate in the rapidly metabolized fraction of extremity bones. On the other hand, Ca45 content in the teeth and maxillae increased, which may be explained by redistribution of isotope among the various mineralized tissues. Injection of thyrocalcitonin (50 IU/day) produced a distinct normalizing effect on Ca45 uptake and resorption in the mineralized tissues of rabbits kept hypokinetic.

Volozhin, A. I.↗
NASA NTRS1980

Dielectronic recombination rates, ionization equilibrium, and radiative emission rates for calcium and nickel ions in low-density high-temperature plasmas

The total dielectronic recombination rates for Ca and Ni ions were calculated taking into account autoionization to excited states of the recombining ion and stabilizing radiative transitions of the recombining electron. Radiative transitions of the recombining ion are found to be the dominant stabilizing processes, and the relative importance of Delta n = 0 and Delta n not equal to 0 transitions in the relevant temperature region is determined for each ion. The relative importance of the Delta n = 0 and Delta n not equal to 0 contributions is significantly altered for some ions by the inclusion of autoionization to excited levels. The relative abundance of the various ionization stages has been determined by using a corona equilibrium model in which collisional ionization and inner-shell excitation followed by autoionization are balanced by direct radiative and dielectronic recombination.

Jacobs, V. L.↗
NASA NTRS1981

New ionization fractions for the lithium- and helium-like ionization stages of calcium and iron

A reinterpretation of the high resolution X-ray spectra of Ca XIX and Fe XXV, observed during a solar flare on March 25, 1979, is presented. New ionization fractions for Ca XVIII, Ca XIX, Fe XXIV, and Fe XXV are used, and it is shown that the new calculations substantially change the interpretation of the spectra. It is implied that the flare plasma was ionizing during the early phases of the flare, and recombining during the decay phase.

Doyle, J. G.↗
NASA NTRS1981

Quiescent prominence spectrophotometry - Sodium D1,2, helium D3, and calcium /plus/ lambda 8498

The reported observations were carried out by means of a 25 cm coronagraph/coude spectrograph with a Si vidicon Optical Multichannel Analyzer (OMA) detector. The results of the investigation are presented in a number of tables, and the main conclusions concerning the studies are discussed. The relative behavior of prominence Na D line emission shows that the employed observing techniques yield reliable measures of prominence line strengths, not degraded to any substantial extent, in particular, by possible slit-filling effects. This conclusion is limited principally by the assumption that systematic vertical velocity fields in the prominences are not greater than 1.5 km/s. The Na D line profiles are well fitted by a one-component (i.e., homogeneous) line-forming region, thus reinforcing previous conclusions regarding the source of the enhanced wing emission.

Landman, D. A.↗