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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

On th meridional surface profile of the Gulf Stream at 55 deg W

Nine-month records from nine inverted echo sounders (IESs) are analyzed to describe the mean baroclinic Gulf Stream at 55 deg W. IES acoustic travel times are converted to thermocline depth which is optimally interpolated. Kinematic and dynamic parameters (Gulf Stream meridional position, velocity, and vorticity) are calculated. Primary Gulf Stream variabiltiy is attributed to meandering and and changes in direction. A mean, stream-coordinate (relative to Gulf Stream instantaneous position and direction) meridional profile is derived and compared with results presented by other investigators. The mean velocity is estimated at 0.84 m/s directed 14 deg to the right eastward, and the thermocline (12 c) drops 657 m (north to south), corresponding to a baroclinic rise of the surface of 0.87 m. The effect of Gulf Stream curvature on temporal mean profiles is found to be unimportant and of minimal importance overall. The derived, downstream current profile is well represented by a Gaussian function and is about 190 km wide where it crosses zero. Surface baroclinic transport is estimated to be 8.5 x 10(exp 4) sq m/s, and maximum shear (flanking the maximum) is 1.2 x 10(exp -5). Results compare well with other in situ observational results from the same time period. On the other hand, analyses (by others) of concurrent satellite altimetry (Geosat) suggest a considerable narrower, more intense mean Gulf Stream.

Hallock, Zachariah R.↗
NASA NTRS2009

Chemical Mixing Model and K-Th-Ti Systematics and HED Meteorites for the Dawn Mission

The Dawn mission will explore 4 Vesta, a large differentiated asteroid believed to be the parent body of the howardite, eucrite and diogenite (HED) meteorite suite. The Dawn spacecraft carries a gamma-ray and neutron detector (GRaND), which will measure the abundances of selected elements on the surface of Vesta. This study provides ways to leverage the large geochemical database on HED meteorites as a tool for interpreting chemical analyses by GRaND of mapped units on the surface of Vesta.

Usui, T.↗
NASA NTRS2016

VNIR Multispectral Observations of Rocks at Spirit of St. Louis Crater and Marathon Valley on Th Rim of Endeavour Crater Made by the Opportunity Rover Pancam

The Mars Exploration Rover Opportunity has been exploring the western rim of the 22 km diameter Endeavour crater since August, 2011. Recently, Opportunity has reached a break in the Endeavour rim that the rover team has named Mara-thon Valley. This is the site where orbital observations from the MRO CRISM imaging spectrometer indicated the presence of iron smectites. On the outer western portion of Marathon Valley, Opportunity explored the crater-form feature dubbed Spirit of St. Louis (SoSL) crater. This presentation describes the 430 to 1009 nm (VNIR) reflectance, measured by the rover's Pancam, of rock units present both at Spirit of St. Louis and within Marathon Valley.

Farrand, W. H.↗
NASA NTRS2016

Apatite/Melt Partitioning Experiments Reveal Redox Sensitivity to Cr, V, Mn, Ni, Eu, W, Th, and U

Apatite is a common mineral in terrestrial, planetary, and asteroidal materials. It is commonly used for geochronology (U-Pb), sensing volatiles (H, F, Cl, S), and can concentrate rare earth elements (REE) during magmatic fractionation and in general. Some recent studies have shown that some kinds of phosphate may fractionate Hf and W and that Mn may be redox sensitive. Experimental studies have focused on REE and other lithophile elements and at simplified or not specified oxygen fugacities. There is a dearth of partitioning data for chalcophile, siderophile and other elements between apatite and melt. Here we carry out several experiments at variable fO2 to study the partitioning of a broad range of trace elements. We compare to existing data and then focus on several elements that exhibit redox dependent partitioning behavior.

Righter, K.↗
NASA NTRS2019

Orbit determination sensitivity analysis for th Europa Clipper Mission tour

This paper will assess the sensitivity of OD delivery and knowledge performance for the current Europa Mission trajectory through parametric variation of a baseline tour navigation strategy.2 Variations of several parameters are run, one at a time, to determine the impact on spacecraft ephemeris uncertainties at OD knowledge, delivery, and encounter reconstruction times. There are two basic categories of sensitivity runs considered: variations of tracking data type and amount, and variations to dynamic parameters. The results of these parameter and data variations are compared against the values necessary to achieve accurate instrument pointing and observation planning.

Young, Brian↗
DOE OSTI2020

Materials Data on Th2Co7 by Materials Project

Th2Co7 crystallizes in the trigonal P3m1 space group. The structure is three-dimensional. there are eight inequivalent Th sites. In the first Th site, Th is bonded in a 6-coordinate geometry to eighteen Co atoms. There are a spread of Th–Co bond distances ranging from 2.87–3.30 Å. In the second Th site, Th is bonded in a 6-coordinate geometry to eighteen Co atoms. There are a spread of Th–Co bond distances ranging from 2.87–3.30 Å. In the third Th site, Th is bonded in a 9-coordinate geometry to twelve Co atoms. There are a spread of Th–Co bond distances ranging from 2.86–3.31 Å. In the fourth Th site, Th is bonded in a 9-coordinate geometry to twelve Co atoms. There are a spread of Th–Co bond distances ranging from 2.86–3.31 Å. In the fifth Th site, Th is bonded in a 9-coordinate geometry to twelve Co atoms. There are a spread of Th–Co bond distances ranging from 2.87–3.30 Å. In the sixth Th site, Th is bonded in a 6-coordinate geometry to eighteen Co atoms. There are a spread of Th–Co bond distances ranging from 2.87–3.30 Å. In the seventh Th site, Th is bonded in a 9-coordinate geometry to twelve Co atoms. There are a spread of Th–Co bond distances ranging from 2.86–3.32 Å. In the eighth Th site, Th is bonded in a 6-coordinate geometry to eighteen Co atoms. There are a spread of Th–Co bond distances ranging from 2.87–3.30 Å. There are sixteen inequivalent Co sites. In the first Co site, Co is bonded in a 12-coordinate geometry to three equivalent Th and nine Co atoms. There are a spread of Co–Co bond distances ranging from 2.45–2.87 Å. In the second Co site, Co is bonded to five Th and seven Co atoms to form a mixture of distorted corner, edge, and face-sharing CoTh5Co7 cuboctahedra. There are a spread of Co–Co bond distances ranging from 2.45–2.62 Å. In the third Co site, Co is bonded to five Th and seven Co atoms to form distorted CoTh5Co7 cuboctahedra that share corners with seventeen CoTh6Co6 cuboctahedra, edges with eight CoTh5Co7 cuboctahedra, and faces with fourteen CoTh6Co6 cuboctahedra. There are a spread of Co–Co bond distances ranging from 2.45–2.63 Å. In the fourth Co site, Co is bonded to four Th and eight Co atoms to form a mixture of corner, edge, and face-sharing CoTh4Co8 cuboctahedra. There are a spread of Co–Co bond distances ranging from 2.48–2.50 Å. In the fifth Co site, Co is bonded to five Th and seven Co atoms to form a mixture of distorted corner, edge, and face-sharing CoTh5Co7 cuboctahedra. There are a spread of Co–Co bond distances ranging from 2.45–2.62 Å. In the sixth Co site, Co is bonded in a 12-coordinate geometry to three equivalent Th and nine Co atoms. There are three shorter (2.45 Å) and three longer (2.49 Å) Co–Co bond lengths. In the seventh Co site, Co is bonded in a 12-coordinate geometry to three equivalent Th and nine Co atoms. There are three shorter (2.50 Å) and three longer (2.87 Å) Co–Co bond lengths. In the eighth Co site, Co is bonded in a 12-coordinate geometry to three equivalent Th and nine Co atoms. All Co–Co bond lengths are 2.87 Å. In the ninth Co site, Co is bonded to four Th and eight Co atoms to form a mixture of corner, edge, and face-sharing CoTh4Co8 cuboctahedra. There are three shorter (2.48 Å) and two longer (2.49 Å) Co–Co bond lengths. In the tenth Co site, Co is bonded to six Th and six Co atoms to form CoTh6Co6 cuboctahedra that share corners with twelve CoTh5Co7 cuboctahedra, edges with six equivalent CoTh6Co6 cuboctahedra, and faces with eighteen CoTh5Co7 cuboctahedra. In the eleventh Co site, Co is bonded to five Th and seven Co atoms to form distorted CoTh5Co7 cuboctahedra that share corners with seventeen CoTh6Co6 cuboctahedra, edges with eight CoTh5Co7 cuboctahedra, and faces with fourteen CoTh6Co6 cuboctahedra. There are a spread of Co–Co bond distances ranging from 2.47–2.62 Å. In the twelfth Co site, Co is bonded in a 12-coordinate geometry to three equivalent Th and nine Co atoms. All Co–Co bond lengths are 2.87 Å. In the thirteenth Co site, Co is bonded in a 12-coordinate geometry to three equivalent Th and nine Co atoms. In the fourteenth Co site, Co is bonded in a 12-coordinate geometry to three equivalent Th and nine Co atoms. In the fifteenth Co site, Co is bonded to six Th and six Co atoms to form CoTh6Co6 cuboctahedra that share corners with twelve CoTh5Co7 cuboctahedra, edges with six equivalent CoTh6Co6 cuboctahedra, and faces with eighteen CoTh5Co7 cuboctahedra. In the sixteenth Co site, Co is bonded in a 12-coordinate geometry to three equivalent Th and nine Co atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Th8Al4H11 by Materials Project

Th8Al4H11 crystallizes in the tetragonal P-42m space group. The structure is three-dimensional. there are six inequivalent Th sites. In the first Th site, Th is bonded in a 5-coordinate geometry to four Al and five H atoms. There are two shorter (3.27 Å) and two longer (3.29 Å) Th–Al bond lengths. There are a spread of Th–H bond distances ranging from 2.28–2.43 Å. In the second Th site, Th is bonded in a 5-coordinate geometry to four Al and five H atoms. There are two shorter (3.26 Å) and two longer (3.31 Å) Th–Al bond lengths. There are a spread of Th–H bond distances ranging from 2.27–2.43 Å. In the third Th site, Th is bonded in a 7-coordinate geometry to four Al and seven H atoms. There are two shorter (3.30 Å) and two longer (3.31 Å) Th–Al bond lengths. There are a spread of Th–H bond distances ranging from 2.28–2.46 Å. In the fourth Th site, Th is bonded in a 7-coordinate geometry to four Al and seven H atoms. There are two shorter (3.29 Å) and two longer (3.30 Å) Th–Al bond lengths. There are a spread of Th–H bond distances ranging from 2.27–2.44 Å. In the fifth Th site, Th is bonded in a 5-coordinate geometry to four Al and five H atoms. All Th–Al bond lengths are 3.28 Å. There are two shorter (2.39 Å) and three longer (2.42 Å) Th–H bond lengths. In the sixth Th site, Th is bonded in a 4-coordinate geometry to four Al and four H atoms. There are two shorter (3.27 Å) and two longer (3.28 Å) Th–Al bond lengths. There are three shorter (2.40 Å) and one longer (2.41 Å) Th–H bond lengths. There are four inequivalent Al sites. In the first Al site, Al is bonded in a 10-coordinate geometry to eight Th and two equivalent Al atoms. Both Al–Al bond lengths are 3.19 Å. In the second Al site, Al is bonded in a 10-coordinate geometry to eight Th and two equivalent Al atoms. Both Al–Al bond lengths are 3.17 Å. In the third Al site, Al is bonded in a 10-coordinate geometry to eight Th and two Al atoms. The Al–Al bond length is 3.15 Å. In the fourth Al site, Al is bonded in a 10-coordinate geometry to eight Th and two Al atoms. There are nine inequivalent H sites. In the first H site, H is bonded to four Th atoms to form a mixture of corner, edge, and face-sharing HTh4 tetrahedra. In the second H site, H is bonded to four Th atoms to form a mixture of corner, edge, and face-sharing HTh4 tetrahedra. In the third H site, H is bonded to four equivalent Th atoms to form a mixture of corner and edge-sharing HTh4 tetrahedra. In the fourth H site, H is bonded to four Th atoms to form a mixture of corner and edge-sharing HTh4 tetrahedra. In the fifth H site, H is bonded to four Th atoms to form a mixture of corner and edge-sharing HTh4 tetrahedra. In the sixth H site, H is bonded to four Th atoms to form a mixture of corner and edge-sharing HTh4 tetrahedra. In the seventh H site, H is bonded to four Th atoms to form a mixture of corner, edge, and face-sharing HTh4 tetrahedra. In the eighth H site, H is bonded to four Th atoms to form a mixture of corner, edge, and face-sharing HTh4 tetrahedra. In the ninth H site, H is bonded to four Th atoms to form a mixture of corner and edge-sharing HTh4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ThMg2 by Materials Project

ThMg2 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are three inequivalent Mg sites. In the first Mg site, Mg is bonded to six Mg and six Th atoms to form a mixture of edge, face, and corner-sharing MgTh6Mg6 cuboctahedra. There are two shorter (3.03 Å) and four longer (3.04 Å) Mg–Mg bond lengths. All Mg–Th bond lengths are 3.53 Å. In the second Mg site, Mg is bonded to six Mg and six Th atoms to form a mixture of edge, face, and corner-sharing MgTh6Mg6 cuboctahedra. There are a spread of Mg–Mg bond distances ranging from 2.94–3.13 Å. There are two shorter (3.53 Å) and four longer (3.55 Å) Mg–Th bond lengths. In the third Mg site, Mg is bonded to six Mg and six Th atoms to form a mixture of edge, face, and corner-sharing MgTh6Mg6 cuboctahedra. There are three shorter (3.56 Å) and three longer (3.57 Å) Mg–Th bond lengths. There are five inequivalent Th sites. In the first Th site, Th is bonded in a 12-coordinate geometry to twelve Mg and four Th atoms. There are one shorter (3.66 Å) and three longer (3.73 Å) Th–Th bond lengths. In the second Th site, Th is bonded in a 12-coordinate geometry to twelve Mg and four Th atoms. There are three shorter (3.53 Å) and three longer (3.57 Å) Th–Mg bond lengths. There are one shorter (3.60 Å) and three longer (3.73 Å) Th–Th bond lengths. In the third Th site, Th is bonded in a 12-coordinate geometry to twelve Mg and four Th atoms. All Th–Mg bond lengths are 3.53 Å. In the fourth Th site, Th is bonded in a 12-coordinate geometry to twelve Mg and four Th atoms. All Th–Mg bond lengths are 3.56 Å. In the fifth Th site, Th is bonded in a 12-coordinate geometry to twelve Mg and four Th atoms. All Th–Mg bond lengths are 3.57 Å. There are one shorter (3.60 Å) and three longer (3.73 Å) Th–Th bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on La2Th11O26 by Materials Project

Th11La2O26 is Fluorite-derived structured and crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are six inequivalent Th sites. In the first Th site, Th is bonded in a body-centered cubic geometry to eight O atoms. There are a spread of Th–O bond distances ranging from 2.41–2.44 Å. In the second Th site, Th is bonded in a body-centered cubic geometry to eight O atoms. There are six shorter (2.43 Å) and two longer (2.45 Å) Th–O bond lengths. In the third Th site, Th is bonded in a body-centered cubic geometry to eight O atoms. There are a spread of Th–O bond distances ranging from 2.42–2.45 Å. In the fourth Th site, Th is bonded in a body-centered cubic geometry to eight O atoms. There are four shorter (2.42 Å) and four longer (2.45 Å) Th–O bond lengths. In the fifth Th site, Th is bonded in a body-centered cubic geometry to eight O atoms. There are a spread of Th–O bond distances ranging from 2.41–2.44 Å. In the sixth Th site, Th is bonded in a body-centered cubic geometry to eight O atoms. There are four shorter (2.42 Å) and four longer (2.45 Å) Th–O bond lengths. La is bonded in a body-centered cubic geometry to eight O atoms. There are six shorter (2.50 Å) and two longer (2.51 Å) La–O bond lengths. There are thirteen inequivalent O sites. In the first O site, O is bonded to four Th atoms to form a mixture of edge and corner-sharing OTh4 tetrahedra. In the second O site, O is bonded to four Th atoms to form a mixture of edge and corner-sharing OTh4 tetrahedra. In the third O site, O is bonded to three Th and one La atom to form a mixture of edge and corner-sharing OLaTh3 tetrahedra. In the fourth O site, O is bonded to three Th and one La atom to form OLaTh3 tetrahedra that share corners with sixteen OTh4 tetrahedra and edges with six OLaTh3 tetrahedra. In the fifth O site, O is bonded to three Th and one La atom to form a mixture of edge and corner-sharing OLaTh3 tetrahedra. In the sixth O site, O is bonded to four Th atoms to form OTh4 tetrahedra that share corners with sixteen OTh4 tetrahedra and edges with six OLaTh3 tetrahedra. In the seventh O site, O is bonded to three Th and one La atom to form OLaTh3 tetrahedra that share corners with sixteen OTh4 tetrahedra and edges with six OLaTh3 tetrahedra. In the eighth O site, O is bonded to three Th and one La atom to form a mixture of edge and corner-sharing OLaTh3 tetrahedra. In the ninth O site, O is bonded to three Th and one La atom to form a mixture of edge and corner-sharing OLaTh3 tetrahedra. In the tenth O site, O is bonded to four Th atoms to form a mixture of edge and corner-sharing OTh4 tetrahedra. In the eleventh O site, O is bonded to three Th and one La atom to form a mixture of edge and corner-sharing OLaTh3 tetrahedra. In the twelfth O site, O is bonded to three Th and one La atom to form a mixture of edge and corner-sharing OLaTh3 tetrahedra. In the thirteenth O site, O is bonded to four Th atoms to form a mixture of edge and corner-sharing OTh4 tetrahedra.

36 MATERIALS SCIENCE↗
NASA NTRS1999

Thorium Enrichment within the Procellarum KREEP Terrane: The Record in Surface Deposits and Significance for Thermal Evolution

The nearside-farside structural and compositional asymmetry of the Moon was recognized during the early days of Apollo and the suggestion was made that the migration of mantle melts to the nearside would have been favored by early Earth-Moon orbital dynamics and nonuniform planetesimal bombardment. Recent global geochemical mapping by Lunar Prospector has provided additional data, particularly in the Th distribution, that strongly supports the notion of global, preferential melt migration, which led in part to the development of the Procellarum KREEP Terrane (PKT) [2-5]. The surface distribution of Th was then reshaped by basin-forming impacts into the PKT, especially the Imbrium impact, which was the last and largest to strike in that region. The Imbrium event probably excavated material from a partially molten zone deep in the crust and delivered Th-rich ejecta Moon-wide. A fundamentally important but poorly understood aspect of the global Th distribution is the concentration of Th in the subsurface rocks of the PKT crustal section. For example, depending on what assumptions are made, the PKT crustal section, which is about 12% of the crust and only about 1.2% of the whole Moon, may contain as much as 40% of the Moon's entire Th budget. Such a distribution of Th and related heat-producing elements would have had a profound effect on melting, mixing, and the thermal evolution of the PKT and the underlying mantle. In this abstract, we examine the compositions of terra formations within the PKT and relate them to some of the Th-bearing rock types known from the Apollo samples. It appears that the existence of the PKT may be a unifying concept for a number of petrologic and geochemical observations. From the initial Lunar Prospector gamma-ray spectrometer data(-about 5 deg. resolution) and from the preliminary low-orbit data, there appears to be a number of relatively hotter "spots" within the PKT in terms of Th concentration. Some of the hotter spots correspond to intermediate-sized craters that penetrated volcanic flows and excavated Th-rich, submare material, such as Aristarchus, Aristillus, and Kepler. Other spots, however, correspond to surficial formations that constitute mainly rough topography associated with Imbrium ejecta or circum-Imbrium ring mountains and do not necessarily imply the presence of exposed KREEP basalts. The Fra Mauro Formation south of Copernicus toward the Apollo 14 site and regions of the Alpes Formation southwest of Copernicus in the vicinity of Reinhold lie within the most prominent hotspot; here them concentration is consistent with that found in the Apollo 14 soils (about 12-13 ppm) when the proportions of Fra Mauro Formation and mare basalt are considered. The area between Copernicus and Kepler and northwest of Copernicus in terra extending to the Carpathians is similarly enriched in Th. The Apennines from Eratosthenes toward the Apollo 15 site contain elevated Th concentrations, as does the northwestern quadrant of circum-Imbrium terra, especially between (but not including) La Condamine and Plato, and in the region northwest of the Jura mountains extending southward past Mairan to the Gruithuisen-Domes region. Within the main topographic rim of Imbrium, the Apennine Bench formation south of Archimedes appears to have relatively elevated Th concentration. Comparing the map of Th distribution to a digital-elevation map derived from Clementine altimetry, it appears that most of the areas richest in Th occur where the surface is elevated relative to the majority of PKT volcanic plains. Not all rough topography within the PKT has such elevated Th, however. Based on an analysis of the 5 deg. data, and using the calibration of, the mean Th concentrations for mainly volcanic-resurfaced terrain and rugged terrain are similar (about 5.5 ppm). This occurs in part because craters that penetrated mare basalt excavated Th-rich material. Even so, there appear to be extensive areas of volcanic resurfacing that have no obvious extrinsic source of Th-rich material, suggesting that the basalts, themselves, may contain as much as 5-6 ppm Th. High-FeO concentrations (18 to >20 wt%) indicate that these are not KREEP basalts but mare basalts. If so, this is surprising because most of the Apollo-sampled mare basalts have very low-Th (typically <2 ppm). A variety of Th-rich materials occur in the sample collection, particularly in the samples from the Apollo 12,14, and 15 sites. The most abundant Th-rich rock types are the mafic impact-melt breccias, which although found at all sites, are most abundant at Apollo 14, where they dominate the rock samples and make up some 40% of the rock particles in the soil. These have Th concentrations ranging up to about 30 ppm and averaging about 18 ppm. The Apollo 14 soils contain about 13 ppm Th, reflecting the high abundance of this melt-breccia component. At the nearby Apollo 12 site, the rocks consist mainly of mare basalts, and these have low-Th concentrations, mostly <1 ppm. Among the nonmare rocks, however, a few such as complex breccia 12013 contain a variety of evolved lithologies and represent potential sources of Th-rich components ranging from 17 to 50 ppm. A single fragment of KREEP basalt from the Apollo 12 soil contains about 50 ppm Th. Despite the identification of highly Th-enriched lithologic components at the Apollo 12 site, the soils there vary linearly in composition so as to extrapolate to a moderate Th KREEP-basalt component or a composition like that of the Fra Mauro formation as reflected by Apollo 14 soil (14 ppm Th at 10 wt% FeO). The nearby Lansberg Crater (39-km diameter) is a likely candidate to have delivered submare material such as buried Fra Mauro or Alpes material to the Apollo 12 site. Additional information contained in the original.

Jolliff, B. L.↗