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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Mg II profile variations of Zeta Aurigae

Variations in the Mg II 2800-A doublet of Zeta Aurigae have been observed. The Mg II profiles deviate from simple P-Cygni profiles in that they exhibit an absorption feature consistent with Chapman's (1981) interpretation of C IV absorption as evidence of a column of accretion onto the B-star component of the binary. The opening angle of the shock cone containing the accretion column is found to exceed 16 deg, implying a stellar wind velocity of approximately 67 km/s, unless the H II region temperature is unusually high. The turbulence velocity of the wind then appears to be about 33 km/s, compared to values of order 10 km/s previously determined closer to the K-star surface.

Ahmad, I. A.↗
NASA NTRS1984

Minor elements in relict olivine grains of deep-sea spheres: Match with Mg-rich olivines from C2 meteorites

The bulk composition and relict minerals of meteoroid ablation spheres from deep sea sediments can be related to the parental material, and bulk compositions and elemental ratios favor a CI/CM affinity for most spheres. Although largely melted, some deep sea spheres (DSS) have retained rare grains apparently unmodified chemically by ablation heating or seawater alteration. Minor elements in relict olivines for comparison with compositions of olivines in known meteorites were analyzed. All relict olivines are very Mg rich. No terrestrial olivines match the chemical features which reinforces other evidence for an extraterrestrial origin. There is no match with achondritic olivines. Mg rich olivines occur in all types of carbonaceous meteorites, but the minor elements of most DSS olivines do not match with those for Allende (C3) olivines, and fit poorly with those of Murchison (C2) olivines. There is a good fit for Fe and Cr with those of the olivines in the unusual Belgica 7904 (C2) meteorite (3). It seems likely that the relict olivines of at least many deep sea spheres are chemically related to olivines in at least one C2 meteorite.

Smith, J. V.↗
NASA NTRS1984

The origin of low-velocity absorption components in the Mg II resonance lines of hybrid-chromosphere stars

It is argued that the low-velocity absorption features seen in the Mg II resonance lines of seven confirmed and three probable hybrid-chromosphere stars are interstellar rather than circumstellar in origin. From a comparison of radial velocities based on all available spectra in the International Ultraviolet Explorer (IUE) archives with estimates of the interstellar velocity along each line of sight, a good correlation between the observed position of the low-velocity component and the predicted interstellar feature is found. It is also shown that previous arguments in favor of the circumstellar origin of the low-velocity absorption features are either incorrect or implausible. The conclusion of the present study may modify previously proposed models of hybrid star winds which have assumed a priori that both Mg II absorption components are circumstellar.

Drake, S. A.↗
NASA NTRS1984

Ionic charge states of N, Ne, Mg, Si and S in solar energetic particle events

The mean ionic charges and source-region temperatures of flare-accelerated N, Ne, Mg, Si and S in three large solar-energetic-particle events during 1978-1979 are determined from ISEE-3 observations, extending the findings of Hovestadt et al. (1981) and Gloeckler et al. (1981) for C, He, O, and Fe. The results are presented in tables and graphs, and the charge states are shown to correspond to different source temperatures even in the same flare, assuming equilibration in the hot plasma. The electron temperatures range from 2 x 10 to the 6th K for C, N, O, Si, and S, 4 x 10 to the 6th K for Ne and Fe, and 7 x 10 to the 6th K for Mg. The possibility that these temperature inconsistencies reflect different stages in the approach to equilibrium is considered.

Luhn, A.↗
NASA NTRS1985

Study on effects of powder and flake chemistry and morphology on the properties of Al-Cu-Mg-X-X-X powder metallurgy advanced aluminum alloys

The effects of alloy chemistry and particulate morphology on consolidation behavior and consolidated product properties in rapid solidification processed, powder-metallurgical Al-3Li-1.5Cu-1Mg-0.5Co-0.2Zr and Al-4.4Cu-1.5Mg-Fe-Ni-0.2Zr extrusions and forgings were studied. Microstructures and mechanical properties of both alloys are largely unaffected by particulate production method (vacuum atomization, ultrasonic atomization, or twin-roller quenching) and by particulate solidification rates between 1000 and 100,000 K/s. Consolidation processing by canning, cold compaction, degassing, and hot extrusion is sufficient to yield mechanical properties in the non-Li-containing alloy extrusions which are similar to those of 7075-Al, but ductilities and fracture toughnesses are inferior owing to poor interparticle bonding caused by lack of a vacuum-hot-pressing step during consolidation. Mechanical properties of extrusions are superior to those of forgings owing to the stronger textures produced by the more severe hot working during extrusion. The effects on mechanical properties of dispersoid size and volume fraction, substructural refinement, solid solution strengthening by Mg, and precipitate size and distribution are elucidated for both alloy types.

Meschter, P. J.↗
NASA NTRS1985

Abundances of O, Mg, S, Cr, Mn, Ti, Ni and Zn from absorption lines of neutral gas in the Large Magellanic Cloud in front of R136

Weak absorption lines of C I, O I, Mg I, Mg II, Si I, Si II, P I, Cl I, Cr II, Mn II, Fe I, Ni II, Zn II, CO and C2 are detected in neutral gas in front of the 30 Doradus H II region by IUE spectra of R 136. The Large Magellanic Cloud abundances from the absorption lines are a factor of 2 or 3 below those of the Milky Way, in agreement with emission line study results. Neutral gas density and temperature are estimated from the observed excitation and ionization to be about 300/cu cm and 100 K, respectively; this implies a gas pressure of 30,000/cu cm K.

De Boer, K. S.↗
NASA NTRS1985

Electron microprobe analyses of Ca, S, Mg and P distribution in incisors of Spacelab-3 rats

The distribution of Ca, S, Mg and P was mapped within the incisors of Spacelab-3 rats using an electron microprobe. The data indicate that Flight rats maintained in orbit for 7 days have significantly higher Ca/Mg ratios in dentin due to both higher Ca and lower Mg content than in dentin of ground-based Controls. There is no statistical difference in distribution of either P or S within Fligth animals and Controls, but there is clear indication that, for P at least, the reason is the greater variability of the Control data. These results are consistent with those obtained on a previous NASA/COSMOS flight of 18.5 days duration, although they are not pronounced. The results further suggest that continuously growing rat incisors provide useful records of the effects of weightlessness on Ca metabolism.

Rosenberg, G. D.↗
NASA NTRS1986

Differential electron scattering cross sections for the first optically forbidden and resonance transitions in Mg II, Zn II and Cd II

Differential electron scattering cross sections have been measured for dipole-forbidden and resonance transitions in Mg II, Zn II and Cd II in the angular range theta = 4-17 deg at 50 eV. These provide the first recorded angular distributions for an optically forbidden transition. It is found that while the cross section for excitation of the 4s (2)S-3d(9)4s(2) (2)D transition in Zn II is small, those for the 3s (2)S-3d (2)D, 4s (2)S (unresolved lines) in Mg II, and the 5s (2)S-4d(9)5s(2) D in Cd II are comparable in magnitude with the cross sections for resonance excitation. In addition, for Cd II it is found that the allowed and forbidden transitions have very similar angular distributions, and it is proposed that excitation to the 2D state may be dominated by a virtual 'double-dipole' transition via the 2P state. Also, the total excitation cross section of the resonance 2P state in Cd II is a factor of four higher than that predicted by the Gaunt factor approximation, suggesting that the accepted value for the oscillator strength may be too low.

Williams, I. D.↗
NASA NTRS1988

Glasses in ancient and young Apollo 16 regolith breccias - Populations and ultra Mg-prime glass

Electron microprobe analysis was used to determine the major element compositions of glass spheres and fragments in seven possibly ancient (about 4 Gyr) and three young (less than 4 Gyr) Apollo 16 regolith breccias. It is found that mare glasses are extremely rare in the ancient regolith breccias, and silica-poor gabbroic anorthosite and high-alumina silica-poor glasses are not present in ancient breccias. Ultra Mg-prime glasses are unique to the Apollo 16 regolith breccias and are most common in the ancient breccias. It is suggested that the presence of ultra Mg-prime glasses could indicate the presence of previously unsampled crustal or volcanic rock types on the moon.

Wentworth, Susan J.↗
NASA NTRS1988

Mg I absorption features in the solar spectrum near 9 and 12 microns

High-resolution FTS observations from the Kitt Peak National Solar Observatory and the Spacelab 3 ATMOS experiment have revealed additional infrared transitions due to Mg I in the spectra of both quiet sun and sunspot penumbra. In contrast to previous observations, these transitions are seen in absorption, not emission. Absorption intensities range from 1 to 7 percent of the continuum in the quiet sun. In the penumbra, the same features appear to show Zeeman splitting. Modeling of the line profiles in the photospheric spectrum shows evidence for a factor of three overabundance in the n = 5 or more levels of Mg I in the upper photosphere, but with no deviations from a Planck source function. It is concluded that whatever the process that produces the emission (including the Lemke and Holweger mechanism), it must occur well above the tau(5000) = 0.01 level.

Glenar, David A.↗
NASA NTRS1989

Observations of the 12 micron Mg I lines in various solar features

Measurements of the solar Mg I line at 812/cm are presented, confirming the ubiquitous narrow emission from the quiet sun with secant limb brightening observed by Brault and Noyes (1983). It is found that the central intensity of 12-micron emission lines is greater in plages than in the quiet sun, with an equivalent width up to 3 times greater than for the quiet sun. The magnetic fields measured in plages range from 300 to 800 Gauss. The secant-like limb brightening, and line ratios suggest that the lines are optically thin and are formed in collisional equilibrium with Mg II in a thin layer just above the temperature minimum.

Zirin, Harold↗
NASA NTRS1989

Theoretical investigations of the structures and binding energies of Be(sub n) and Mg(sub n) (n = 3-5) clusters

Researchers determined the equilibrium geometries and binding energies of Be and Mg trimers, tetramers and pentamers using single and double excitation coupled cluster (CCSD) and complete active space self-consistent-field (CASSCF) multireference configuration interaction (MRCI) wave functions in conjunction with extended atomic basis sets. Best estimates of the cluster binding energies are 24, 83 and 110 kcal/mole for Be3, Be4 and Be5; and 9, 31 and 41 kcal/mole for Mg3, Mg4 and Mg5, respectively. A comparison of the MRCI and CCSD results shows that even the best single-reference approach (limited to single and double excitations) is not capable of quantitative accuracy in determining the binding energies of Be and Mg clusters.

Lee, Timothy J.↗
NASA NTRS1990

Line broadening of Mg X 609 and 625 A coronal emission lines observed above the solar limb

A University of Colorado sounding rocket experiment on March 17, 1988, provided high-resolution EUV spectra along a solar diameter and out to 1.2 solar radius with spatial resolution of 20 x 60 arcsec. Each spectrum contains transition region and coronal emission lines in the wavelength range 605-635 A and 1210-1270 A, including the emission lines Mg X 609 and 625 A, Fe XII 1242 A, O V 629 A, N V 1238 and 1242 A, corresponding to a wide range of temperatures of formation. Increased line broadening is observed above the limb for all lines, and this effect is illustrated by presenting observed line widths as a function of height above the limb for the higher temperature lines Mg X 609 and 625 A. On the basis of calculations, the most likely cause of the increased broadening above the limb appears to be the presence of hydromagnetic waves in the corona.

Hassler, Donald M.↗
NASA NTRS1990

Theoretical investigations of the structures and binding energies of Be(n) and Mg(n) (n = 3-5) clusters

The equilibrium geometries and binding energies of Be and Mg trimers, tetramers and pentamers have been determined using single and double excitation coupled cluster (CCSD) and complete active space self-consistent-field (CASSCF) multireference configuration interaction (MRCI) wave functions in conjunction with extended atomic basis sets. The best estimates of the cluster binding energies are 24, 83, and 110 kcal/mol for Be3, Be4, and Be5; and 9, 31, and 41 kcal/mol for Mg3, Mg4, and Mg5, respectively. A comparison of the MRCI and CCSD results shows that even the best single-reference approach (limited to single and double excitations) is not capable of quantitative accuracy in determining the binding energies of Be and Mg clusters.

Lee, Timothy J.↗
NASA NTRS1991

Effect of a prior stretch on the aging response of an Al-Cu-Li-Ag-Mg-Zr alloy

Recently, a family of Al-Cu-Li alloys containing minor amounts of Ag, Mg, and Zr and having desirable combinations of strength and toughness were developed. The Weldalite (trademark) alloys exhibit a unique characteristic in that with or without a prior stretch, they obtain significant strength-ductility combinations upon natural and artificial aging. The ultra-high strength (approximately 690 MPa yield strength) in the peak-aged tempers (T6 and T8) were primarily attributed to the extremely fine T(sub 1) (Al2CuLi) or T(sub 1)-type precipitates that occur in these alloys during artificial aging, whereas the significant natural aging response observed is attributed to strengthening from delta prime (Al3Li) and GP zones. In recent work, the aging behavior of an Al-Cu-Li-Ag-Mg alloy without a prior stretch was followed microstructurally from the T4 to the T6 condition. Commercial extrusions, rolled plates, and sheets of Al-Cu-Li alloys are typically subjected to a stretching operation before artificial aging to straighten the extrusions and, more importantly, introduce dislocations to simulate precipitation of strengthening phases such as T(sub 1) by providing relatively low-energy nucleation sites. The goals of this study are to examine the microstructure that evolves during aging of an alloy that was stretch after solution treatment and to compare the observations with those for the unstretched alloy.

Kumar, K. S.↗
NASA NTRS1991

The influence of Ag+Mg additions on the nucleation of strengthening precipitates in a non-cold-worked Al-Cu-Li alloy

Aluminum-copper-lithium alloys generally require cold work to attain their highest strengths in artificially aged tempers. These alloys are usually strengthened by a combination of the metastable delta prime (Al3Li) and theta prime (Al2Cu) phases and the equilibrium T sub 1 (Al2CuLi) phase, and where the T sub 1 phase is a more potent strengthener than the delta prime. Various investigators have shown that the high strengths obtained after artificial aging associated with cold work result from the heterogeneous precipitation of T sub 1 on matrix dislocations. The objective here is to elucidate the mechanism by which the Ag+Mg additions stimulate the precipitation of T sub 1 type precipitates without cold work. To accomplish this, the microstructure of an Al-6.3Cu-1.3Li-0.14Zr model alloy was evaluated in a T6 type temper with and without the Ag+Mg addition.

Source record↗
NASA NTRS1990

Observations of the 12.3 micron Mg I emission line during a major solar flare

The extremely Zeeman-sensitive 12.32 micron Mg I solar emission line was observed during a 3B/X5.7 solar flare on October 24, 1989. When compared to postflare values, Mg I emission-line intensity in the penumbral flare ribbon was 20 percent greater at the peak of the flare in soft X-rays, and the 12 micron continuum intensity was 7 percent greater. The flare also excited the emission line in the umbra where it is normally absent. The umbral flare emission exhibits a Zeeman splitting 200 G less than the adjacent penumbra, suggesting that it is excited at higher altitude. The absolute penumbral magnetic field strength did not change by more than 100 G between the flare peak and postflare period. However, a change in the inclination of the field lines, probably related to the formation and development of the flare loop system, was seen.

Deming, Drake↗
NASA NTRS1991

The shock wave equation of state of brucite Mg(OH)2

New shock equation of state (EOS) data on magnesium hydroxide between 12 and 60 GPa is presented. It is found that the brucite EOS data between 12 and 97 GPa can be fit with a single linear U(s) - u(p) relationship: U(s) = 4.76(0.11) + 1.35(0.05)u(p). The third order Birch-Murnaghan equation parameters are K(os) = 51 + or - 4 GPa and K(os)prime = 5.0 + or - 0.4. The first partial release states measured for brucite Mg(OH)2 are reported. Calculated phase boundaries using the EOS data are found to be consistent with the experimental data and indicate that brucite is unlikely to be stable under lower mantle conditions. At high pressure, bulk sound velocities calculated for MgO and Mg(OH)2 are very similar, indicating that the presence of hydrous assemblages in the lower mantle may not produce anomalous bulk seismic velocities. A comparison of densities in brucite and other high-pressure phases under mantle conditions shows that the water content of the lower mantle is between 0 and 3 wt pct.

Duffy, Thomas S.↗