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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Population inversion calculations using near resonant charge exchange as a pumping mechanism

Near resonance charge exchange between ions of a large ionization potential gas such as helium or neon and vapors of metals such as zinc, cadmium, selenium, or tellurium has produced laser action in the metal ion gas. The possibility of obtaining population inversions in near resonant charge exchange systems (Xe-Ca, Xe-Mg, Xe-Sr, Xe-Ba, Ar-Mg, N-Ca) was investigated. The analysis is an initial value problem that utilizes rate equations for the densities of relevant levels of the laser gas (Ca, Ba, Mg, or Sr) and an electron energy equation. Electron excitation rates are calculated using the Bohr-Thomson approximation for the cross section. Approximations to experimental values of the electron ionization cross section and the ion-atom charge exchange cross section are used. Preliminary results have been obtained for the Ca-Xe system and show that it is possible to obtain gains greater than 10 to the 14th power/m with inversion times up to 8x10 to the minus 7th power second. A possible charge exchange laser system using a MPD arc plasma accelerator is also described.

Chubb, D. L.↗
NASA NTRS1973

Spectra of normal and nutrient-deficient maize leaves

Reflectance, transmittance and absorptance spectra of normal and six types of nutrient-deficient (N, P, K, S, Mg, and Ca) maize (Zea mays L.) leaves were analyzed at 30 selected wavelengths from 500 to 2600 nm. The analysis of variance showed significant differences in reflectance, transmittance and absorptance in the visible wavelengths among leaf numbers 3, 4, and 5, among the seven treatments, and among the interactions of leaf number and treatments. In the infrared wavelengths only treatments produced significant differences. The chlorophyll content of leaves was reduced in all nutrient-deficient treatments. Percent moisture was increased in S-, Mg-, and N-deficiencies. Polynomial regression analysis of leaf thickness and leaf moisture content showed that these two variables were significantly and directly related. Leaves from the P- and Ca-deficient plants absorbed less energy in the near infrared than the normal plants; S-, Mg-, K-, and N-deficient leaves absorbed more than the normal. Both S- and N-deficient leaves had higher temperatues than normal maize leaves.

Al-Abbas, A. H.↗
NASA NTRS1973

Artificial meteor ablation studies: Olivine

Artificial meteor ablation was performed on a Mg-rich olivine sample using an arc-heated plasma of ionized air. Experimental conditions simulated a meteor traveling about 12 km/sec at an altitude of 70 km. The mineral content of the original olivine sample was 98% olivine (including traces of olivine alteration products) and 2% chromite. Forsterite content of the original olivine was Fo-89. After ablation, the forsterite content had increased to Fo-94 in the recrystallized olivine. In addition, lamella-like intergrowths of magnetite were prevalent constituents. Wherever magnetite occurred, there was an increase in Mg and a corresponding decrease in Fe for the recrystallized olivine. The Allende fusion crust consisted of a recrystallized olivine, which was more Mg-rich and Fe-deficient than the original meteorite's olivine, and abundant magnetite grains. Although troilite and pentlandite were the common opaque mineral constituents in this meteorite, magnetite was the principal opaque mineral found in the fusion crust.

Blanchard, M. B.↗
NASA NTRS1973

Laboratory determination of the luminous efficiency of meteor constituents

A crossed beam apparatus has been used to measure the emission and ionization cross sections for the prominent spectral features of Na, Ca, Mg, and Fe in collisions with N2 and O2 over the velocity range of 30 to 120 km/s. From the emission and ionization cross sections, the absolute luminous efficiencies in air were determined over the range of meteor velocities. The maximum luminous efficiencies for the brightest features were: greater than 1 percent for the Na D-lines, 0.2 percent for the Ca I(2) singlet, 0.06 percent for the Mg I(2) and Mg I(3) triplets, and 0.4 percent for Fe over the visible spectral range. These luminous efficiencies are valid for free molecular flow conditions for velocities above about 30 km/s and are directly applicable to spectroscopic observations of faint meteors. In contrast to previous work, the luminous efficiency found for stone in the present investigation decreased with velocity above about 50 km/s.

Savage, H. F.↗
NASA NTRS1974

Artificial meteor ablation studies - Olivine

Artificial meteor ablation has been performed on a Mg-rich olivine sample by means of an arc-heated plasma of ionized air. Experimental conditions simulated a meteor traveling about 12 km/sec at an altitude of 70 km. The mineral content of the original olivine was 98% olivine (including traces of olivine alteration products) and 2% chromite. The forsterite content of the original olivine was Fo 89 and increased to Fo 94 in the recrystallized olivine after ablation. In addition, lamella-like intergrowths of magnetite were prevalent. Wherever magnetite occurred, Mg increased and Fe decreased in the recrystallized olivine. The Fe for the magnetite exsolved from the original olivine crystals. Individual particles (i.e., spherules) were also characterized by magnetite intergrowths. Fusion crusts on the Allende and Murchison meteorites were compared with the fusion crust on the olivine sample. The Allende fusion crust consisted of a recrystallized olivine, richer in Mg and deficient in Fe in comparison with the original meteorite's olivine, and abundant magnetite grains.

Blanchard, M. B.↗
NASA NTRS1975

High temperature condensates among meteors

It is noted that two meteors which exhibited no lines of iron or sodium in their spectra have been tentatively attributed to aubrites in order to explain their lack of iron. It is shown, however, that no meteorites, including aubrites, have simultaneously low abundances of iron and sodium and that possible parent materials other than aubrites must be considered for the observed meteors. Other possible parent materials considered in this letter include melilite and diopside, two minerals containing both Ca and Mg but neither Fe nor Na. It is suggested that meteoroids rich in Ca and Mg but lacking Fe and Na might form a reservoir for the so-called 'lost' elements (Ca, Mg, Al, Ti, the lanthanides, and other refractory elements) which are depleted in ordinary and enstatite chondrites relative to cosmic abundances.

Wilkening, L. L.↗
NASA NTRS1976

Satellite measurements of high-altitude twilight Mg/plus/ emission

Observations made by the ultraviolet spectrometer on board the orbiting geophysical observatory OGO 4 confirmed the presence of resonance scattering at 2800 A of Mg(plus) ions in the twilight subtropical ionosphere. The column density reached 4 billion ions/sq cm above 160 km. Photometric measurements by the ESRO TD 1 satellite revealed a maximum of the Mg(plus) abundance at equinoxes in the top side F region. The interhemisphere asymmetries observed in the intensity distribution are essentially attributed to the effect of eastward thermospheric winds. The 2800-A doublet was also detected by OGO 4 at middle and high latitudes from 110 to 250 km. The brightness of the emission and other evidence indicate that evaporation of meteoritic matter cannot explain the abundance of ions at 200 km. Therefore Mg(plus) ions are probably transported upward from the 100-km permanent source layer.

Gerard, J.-C.↗
NASA NTRS1976

Mineralogy and petrology of complex breccia 14063,14

Breccia 14063,14 is a complex, probably pre-Imbrian, unmetamorphosed breccia dominated almost entirely by mineral clasts. Electron-probe and microscope examination showed at least four distinct lithologies in a centimeter-sized thin-section. Examination of each lithology showed or suggested the following contributing rock types or mineralogies: (1) dunite with minor chromite, very high-Mg ilmenite and bronzite; (2) spinel troctolite with olivine and Mg-Al spinel; (3) high-Ti mare-like basalt with high-Mg ilmenite and coarse pyroxene; (4) low-KREEP noritic breccia; (5) anorthosite; (6) very Ni-rich Fe metal.

Steele, I. M.↗
NASA NTRS1977

Cortisol-mediated synchronization of circadian rhythm in urinary potassium excretion

Conscious chair-acclimatized squirrel monkeys (Saimiri sciureus) studied with lights on (600 lx) from 0800 to 2000 hr daily (LD 12:12) display a prominent circadian rhythm in renal potassium excretion. The characteristics of this rhythm were reproduced in adrenalectomized monkeys by infusing 5 mg cortisol and 0.001 mg aldosterone, or 5 mg cortisol alone, between 0800 and 0900 kr daily. When the timing of cortisol administration (with or without aldosterone) was phase-delayed by 8 hr, the urinary potassium rhythm resynchronized by 80% of the cortisol phase shift, but only after a transient response lasting 3-4 days. With the same daily dose of adrenal steroids given as a continuous infusion throughout each 24 hr, urinary potassium excretion showed free-running oscillations no longer synchronized to the light-dark cycle. These results indicate that the circadian rhythm of plasma cortisol concentration acts as an internal mediator in the circadian timing system, synchronizing a potentially autonomous oscillation in renal potassium excretion to environmental time cues and to other circadian rhythms within the animal.

Moore-Ede, M. C.↗
NASA NTRS1977

Evidence for Al-26 in the solar system

Evidence is reviewed for the presence of short-lived Al-26 (half-life of 720,000 years) in the early solar system. Large excesses of Mg-26 of up to 5% have been found in Ca-Al-rich inclusions of the Allende meteorite. The Mg excesses correlate well with Al-27/Mg-24 and in two cases they are found in high-purity separates of coarse-grained Al-rich minerals which tend to exclude Mg. The data demonstrate that Al-26 was present in the early solar system. Mechanisms for addition of Al-26 to the solar nebula or for production within an active solar system are required within a few million years of condensation of small (centimeter-sized) objects. The Al-26 abundance in Allende inclusions is high enough to provide for effective melting of kilometer-size bodies or larger, if such bodies accreted early enough (a few million years) to incorporate the Al-26.

Papanastassiou, D. A.↗
NASA NTRS1978

Stellar model chromospheres. VIII - 70 Ophiuchi A /K0 V/ and Epsilon Eridani /K2 V/

Model atmospheres for the late-type active-chromosphere dwarf stars 70 Oph A and Epsilon Eri are computed from high-resolution Ca II K line profiles as well as Mg II h and k line fluxes. A method is used which determines a plane-parallel homogeneous hydrostatic-equilibrium model of the upper photosphere and chromosphere which differs from theoretical models by lacking the constraint of radiative equilibrium (RE). The determinations of surface gravities, metallicities, and effective temperatures are discussed, and the computational methods, model atoms, atomic data, and observations are described. Temperature distributions for the two stars are plotted and compared with RE models for the adopted effective temperatures and gravities. The previously investigated T min/T eff vs. T eff relation is extended to Epsilon Eri and 70 Oph A, observed and computed Ca II K and Mg II h and k integrated emission fluxes are compared, and full tabulations are given for the proposed models. It is suggested that if less than half the observed Mg II flux for the two stars is lost in noise, the difference between an active-chromosphere star and a quiet-chromosphere star lies in the lower-chromospheric temperature gradient.

Kelch, W. L.↗
NASA NTRS1979

Interstellar absorption lines in the spectrum of Gamma Velorum

Copernicus scans of selected interstellar absorption lines in the UV spectrum of Gamma Vel are analyzed, together with ground-based data, to obtain column densities for various ion states of C, N, O, Na, Mg, Al, Si, P, S, Cl, Ar, Ca, Mn, Fe, and CO. N I and O I are fitted to a single empirical curve of growth with a velocity parameter (b) of 8 km/s; Mg II, Si II, P II, S II, Mn II, and Fe II are fitted to another curve with b between 3 and 9 km/s. Abundance determinations relative to H I show that: (1) C, N, P, S, and Ar are probably close to their solar values; (2) O may be depleted by about a factor of 2; (3) Mg, Al, Si, Cl, Mn, and Fe are depleted by a factor of 4 or more: (4) Al is depleted by at least a factor of 10 in the H II region; and (5) both N V and O VI are present, but not C IV. The N V/O VI ratio implies that the electron temperature in the H II region is about 275,000 K.

Morton, D. C.↗
NASA NTRS1979

Magnesium isotopic variations in hibonite from the Murchison meteorite - An ion microprobe study

Ion microprobe measurements show that some hibonite crystals from refractory-rich inclusions in Murchison contain isotopically anomalous Mg. The observed effects include: (1) the largest mass fractionation ever observed in nature for this element, about 10% per mass unit; (2) small Mg-26 excesses; (3) isotopic variability on a scale of microns or less in individual grains. These observations are corroborative evidence for the primitiveness of the Murchison inclusions. More importantly, they indicate that the types of Mg isotopic anomalies previously observed in Allende and Leoville inclusions are not confined to CV meteorites.

Macdougall, J. D.↗
NASA NTRS1978

Chemistry and petrology of Luna 24 lithic fragments and less than 250-micron soils - Constraints on the origin of VLT mare basalts

Results are reported on a combined INAA-petrologic study of 17 small (0.2-1.5 mg) Luna 24 lithic and mineral fragments and INAA study of 5 bulk soils and mineral separates from gabbro 24170. Lithic and mineral fragments are classified into VLT mare basalts (ferrobasalt and metabasalts), low-Ti, variolitic mare basalt, gabbros, melt rock and soil breccia. Data indicate 5 possible magma types, represented by: (1) VLT ferrobasalt and gabbro fragments, with low-TiO2 (about 1%), slightly bow-shaped REE pattern, and low REE concentrations (5-10X chondritic); (2) a ferrobasalt (Laul et al., 1978) and metabasalt fragments with major and trace element contents similar to (1), but positive Eu anomalies; (3) one gabbro fragment with distinctive pyroxene compositional trend (increasing Ti with nearly constant Fe/Fe + Mg) and highest REE contents of any Luna 24 mare basaltic sample, (4) a gabbro fragment with considerably less V and Cr2O3 than ferrobasalt and metabasalt fragments; and (5) variolitic basalt fragment with higher Ti2(2.3%) than other Luna 24 basalts and pyroxene that has increasing then decreasing Ti with increasing Fe/Fe + Mg. Trace element data place constraints on the nature of the source region and possible parent magmas for the Luna 24 VLT ferrobasalt.

Ma, M.-S.↗
NASA NTRS1978

Chemical and Sr-isotopic characteristics of the Luna 24 samples

The chemical and Sr isotopic characteristics of Luna 24 bulk soil samples are determined and interpreted within the framework of lunar mare basalt evolution. Major and trace element compositions lead to the suggestion of candidate rock types consisting of a basalt/gabbro with very low TiO2 and MgO content (52%), a very low TiO2 basalt with 10% MgO (23%), olivine vitrophyre (20%), low K Fra Mauro basalt (4%) and anorthositic gabbro (1%). The proposed compositions are supported by the agreement of mixing models based on the proposed compositions with observed soil compositions. Sr ratios for plagioclase samples imply a lower Sr-87/Sr-86 value for low Mg soils than for other mare basalts and higher Rb/Sr and a more evolved Sr ratio in high Mg basalts. Rb, Sr and rare earth element compositions for low Mg basalts fit a model of partial remelting of cumulates containing small amounts of plagioclase.

Nyquist, L. E.↗
NASA NTRS1978

Ion microprobe, electron microprobe and cathodoluminescence data for Allende inclusions with emphasis on plagioclase chemistry

Three Type B inclusions from the Allende meteorite have been analyzed. A grain-to-grain characterization of mineral chemistry and isotopic content was made possible by the use of a range of techniques, including luminescence and scanning electron microscopy and electron and ion microprobe analysis. Cathodoluminescence was used in fine-grained, optically opaque regions to distinguish between sub-micrometer phases, such as garnet and Si-rich material, subsequently identified by electron probe and scanning electron microscope analyses. Four types of luminescence patterns, due to twinning, primary sector zoning, alteration of boundaries and fractures, and shock effects, were identified in Allende plagioclase. Luminescence color exhibited a strong correlation with Mg content and provided a guide for an electron probe quantitative map of Mg and Na distributions. Ion microprobe studies of individual grains revealed large excesses of Mg-26.

Hutcheon, I. D.↗
NASA NTRS1980

Temporal variations of loop structures in the solar atmosphere

The temporal characteristics of coronal loops are described using a number of unique time-lapse sequences of Ne VII 465 A, Mg IX 368 A, and Fe XV 284 A spectroheliograms. These sequences were obtained with the NRL Skylab/ATM slitless spectrograph during the final Skylab mission (November 1973-February 1974). In the first sequence, Ne VII and Mg IX images were obtained simultaneously at 1.5-mm intervals for a 27-min duration on Nov. 28, 1973. In the second sequence, simultaneous Ne VII-Mg IX pairs were obtained at approximately 3-hr intervals (on alternate satellite orbits) for a 36-hr duration on Jan. 19-20, 1974. The intervening orbits were used to obtain a third sequence which consisted of Fe XV images at 3-hr intervals for the same 36-hr duration. The results place severe constraints on theoretical models of coronal heating and mass flow.

Sheeley, N. R., Jr.↗
NASA NTRS1980

Analysis of the solar magnesium lines

The observed quiet-sun profiles for a number of Mg I and II lines are compared with theoretical spectra computed for two upper-photosphere lower-chromosphere models published by Ayres and Linsky (1976). Both the Mg I and the Mg II resonance line wings, observed with the University of Hawaii Echelle Rocket Spectrographs, favor a model with a higher temperature in the upper photosphere than required to match the visible region lines 4571 and 5172. Neither model atmosphere reproduces the observed shapes in the cores of the strong lines or the limb darkening of the 4571 A intercombination line. The wings of the ultraviolet lines in plages can be reproduced either with a mean one-component atmosphere or by a two-component model with an ad hoc filling factor.

Heasley, J. N.↗