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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Chondrite chronology by initial Sr-87/Sr-86 in phosphates?

New data are presented on Rb-Sr isotope analyses of phosphates from nine ordinary chondrites, including accurate identification of initial Sr-87/Sr-86. The initial Sr-87/Sr-86 ratios found in this study were generally significantly higher than the more primitive initial Sr-87/Sr-86 ratios inferred for carbonaceous chondrite refractory inclusions, basaltic achondrites, or bulk ordinary chondrites. Such elevation of initial Sr-87/Sr-86 is generally considered to reflect isotopic redistribution during metamorphism. However, in this study, no evident correlation was found between the phosphate initial Sr-87/Sr-86 compositions and the metamorphic grade. Two possible alternative hypotheses for high initial Sr-87/Sr-86 ratios are considered.

Podosek, Frank A.↗
NASA NTRS1993

Elevated initial Sr-87/Sr-86 in ordinary chondrite metal

The metal phase of ordinary chondrites has been found to contain a complex assemblage of non-metal phases, evidently formed when elements such as Si, Cr and P, originally dissolved in the metal, were subsequently oxidized and exsolved. We have investigated the Rb-Sr isotopic system in samples of H-chondrite metal, finding small but nontrivial amounts of Sr, apparently concentrated toward the surface of metal grains, and characterized by pronounced excesses of Sr-87/Sr-86 in chondritic metal can plausibly account for the characteristically elevated initial Sr-87/Sr-86 found in ordinary chondrite phosphates, but it remains unclear when and where the metal experienced the high Rb/Sr environment needed to account for such high Sr-87/Sr-86. We have previously reported Rb-Sr data for separated metal from Dhajala (H3), Forest Vale (H4) and Estacado (H6). Here we report data for two size fractions (80-160 and 280-450 microns) of separated metal from the H4 chondrite Ste. Marguerite. These samples were etched twice (.5N HCl for one hour) before dissolution (6N HCl). Aliquots of the solutions were spiked for Fe, Ca and Rb + Sr. The results for Ste. Marguerite metal are presented; errors are two-sigma and elemental concentrations are stated in terms of total sample weight.

Podosek, F. A.↗
NASA NTRS1995

Preliminary airborne measurements for the SR-71 sonic boom propagation experiment

SR-71 sonic boom signatures were measured to validate sonic boom propagation prediction codes. An SR-71 aircraft generated sonic booms from Mach 1.25 to Mach 1.6, at altitudes of 31,000 to 48,000 ft, and at various gross weights. An F-16XL aircraft measured the SR-71 near-field shock waves from close to the aircraft to more than 8,000 ft below, gathering 105 signatures. A YO-3A aircraft measured the SR-71 sonic booms from 21,000 to 38,000 feet below, recording 17 passes. The sonic booms at ground level and atmospheric data were recorded for each flight. Data analysis is underway. Preliminary results show that shock wave patterns and coalescence vary with SR-71 gross weight, Mach number, and altitude. For example, noncoalesced shock wave signatures were measured by the YO-3A at 21,000 ft below the SR-71 aircraft while at a low gross weight, Mach 1.25, and 31,000-ft altitude. This paper describes the design and execution of the flight research experiment. Instrumentation and flight maneuvers of the SR-71, F-16XL, and YO-3A aircraft and sample sonic boom signatures are included.

Haering, Edward A., Jr.↗
NASA NTRS2009

Sm-Nd and Rb-Sr Ages for Northwest Africa 2977, A Young Lunar Gabbro from the PKT

Northwest Africa (NWA) 2977 is an olivine gabbro cumulate equivalent to one of the lithologies in lunar mare breccia NWA 773 [1,2,3]. The Ar-39-Ar-40 age is 2.77+/-0.04 Ga based on the last approx.57% of the gas release [4], similar to results for NWA 773 [5]. A Sm-Nd age (T) of 2.865+/-0.031 Ga and Epsilon(sub Nd) = -7.84+/-0.22 for the NWA 773 gabbro reported by [6] has been revised to T = 2.993+/-=0.032 Ga, Epsilon(sub Nd) -4.5+/-0.3 [7]. Sm-147-Nd-143 isochron for NWA 2977: Whole rock, pyroxene, olivine, plagioclase, whole rock leachate (approx.phosphate) and the combined leachates from the mineral separates yield a well defined Sm-Nd isochron for an age T = 3.10+/-0.05 Ga and Epsilon(sub Nd-CHUR) = -3.74+/-0.26 [8], or Epsilon(sub Nd-HEDR) = -4.61+/-0.26 [9]. Rb-87-Sr-87 isochron: NWA 2977 contains only a modest amount of Rb and/or Sr contamination. The Sr-isotopic composition of the contaminant closely resembles that of seawater. The whole rock residue after leaching combined with leach residues for plagioclase and pyroxene define an isochron age of 3.29+/-0.11 Ga for initial Sr-87/Sr-86 = 0.70287+/-18. The olivine residue, with lower Sr abundance of approx 1.5 ppm, is only slightly displaced from the isochron. The relatively small uncertainties of the Rb-Sr isochron parameters and near-concordancy with the Sm-Nd age indicate that both the Rb-Sr and the Sm-Nd ages are reliable.

Nyquist, L. E.↗
NASA NTRS2020

Structural evolution, electrochemical kinetic properties, and stability of A-site doped perovskite Sr(1-x)Yb(x)CoO(3-δ)

Mixed ionic and electronic conducting (MIEC) perovskite SrCoO(3-δ) is a widely studied (electro)catalyst for the oxygen reduction reaction (ORR) and possesses different crystal structures at different temperatures. These temperature dependent phase transitions significantly impact the ordering of oxygen vacancies and electrochemical kinetic properties as well as the reliability of the related devices. Some of the crystal structures formed, e.g. hexagonal phases, turn out to be almost impermeable to oxygen gas. Therefore, it is important to stabilize the crystal structure of SrCoO(3-δ) that favors the ORR over a wide temperature range. Herein, the partial substitution of the A-site Sr with Yb is systematically studied, including synthesis, characterization and analysis of structural evolution, electrochemical kinetic properties, thermal stability, and stability in a CO2-containing atmosphere. The results indicate that Sr(0.90)Yb(0.10)CoO(3-δ) is able to stabilize the tetragonal crystal structure with less ordered oxygen vacancies, leading to polarization resistances of 0.051, 0.115 and 0.272 U sq.cm at 750, 700 and 650 °C, respectively, on symmetrical cells. Sr(0.90)Yb(0.10)CoO(3-δ) demonstrates a very stable surface oxygen vacancy distribution and electronic structure near oxygen vacancies but dissociation of adsorbed oxygen molecules into atomic oxygen is affected by surface Sr segregation, and polarization resistance degradation is mainly induced by surface Sr segregation. Furthermore, Sr(0.90)Yb(0.10)CoO(3-δ) exhibits excellent thermal stability as well as excellent recovery stability and improved polarization performance after a few pure air/CO2-containing air treatment cycles at 700 °C. However, a hysteresis behavior of polarization performance is observed at 650 °C during gas cycling treatment, which may cause long-term degradation of the Sr(0.90)Yb(0.10)CoO(3-δ) electrode. The different polarization behaviors during gas cycling treatment are induced by different sensitivities of the formed surface strontium carbonate and chemisorbed surface oxo-carbonaceous species to different operating temperatures.

electrochemical kinetic↗
NASA NTRSDate not supplied

Direct Simulation Monte Carlo Studies of the Gas Sampling for the VATMOS-SR Mission Concept

VATMOS-SR (Venus ATMOSpheric - Sample Return) is a small spacecraft mission concept which would return a gas sample from the upper atmosphere of Venus to Earth for scientific analysis. This could be the first sample return mission for an extra-terrestrial atmosphere, and potentially the first sample return from an Earth-sized planet. The VATMOS-SR mission concept consists of a SmallSat atmospheric sampling probe (45 deg. sphere/cone geometry, <1 m diameter) that is designed to skim through the Venus upper atmosphere and acquire gas samples below the homopause altitude (around ~110 km altitude), where the different atmospheric gases are mixed. The velocity of the spacecraft where sampling would occur is expected to be between ~10.5 km/s and ~13.1 km/s, depending on the trajectory chosen. This presentation will discuss hypervelocity sampling in the upper atmosphere of Venus, with respect to the VATMOS-SR mission concept. VATMOS-SR would enable critical atmospheric measurements to form a full picture of how, why, and when Venus evolved to be so different from Earth and Mars. The abundances and isotopic compositions of volatile elements (such as N, C, S, O and the noble gases) in planetary atmospheres record volatile delivery during accretion, outgassing from planetary interiors, and atmospheric loss to space. Precise and accurate determinations of atmospheric volatile signatures are the key to understanding the origins and geodynamical evolution of Venus compared to the other terrestrial planets. Hypersonic sampling poses unique technical and scientific challenges. To ensure it is possible to relate the composition of the sampled gases to the free stream atmospheric composition, large-scale numerical simulations are employed to model the flow through the VATMOS-SR sampling system. In particular, an emphasis is placed on quantifying noble gas isotopic fractionation that occurs during the sample acquisition and transfer process in order to determine how measured isotopic ratios of noble gases in the sample compare to actual isotopic ratios in the Venusian atmosphere. The Direct Simulation Monte Carlo (DSMC) code SPARTA, an open source software package developed by Sandia National Laboratories, is used in this work. SPARTA, based on Bird’s DSMC method, is a molecular-level gas-kinetic technique. As SPARTA is able to model hypervelocity reacting flows in strong chemical and thermal non-equilibrium, this software package is well suited to determine relevant flow properties for the VATMOS-SR mission concept, and to numerically quantify the expected level of elemental and/or isotopic fractionation in the sample acquired by VATMOS-SR. This presentation will show results from 3D simulations correlating the noble gas isotopic fractionation in the gas acquired at hypervelocity speeds to its ambient atmosphere value. In particular, emphasis will be placed at Xenon isotopes of masses 128 and 130, as precise measurements of that ratio would yield a comparison to Earth’s atmosphere. Additionally, sensitivity studies that quantify the uncertainties due to the freestream parameters as well as the modeling parameters will be performed.

direct simulation Monte Carlo↗
NASA NTRSDate not supplied

The VATMOS-SR Mission Concept: DSMC Studies of the Gas Sampling

VATMOS-SR (Venus ATMOSpheric - Sample Return) is a small spacecraft mission concept that would return a gas sample from the upper atmosphere of Venus to Earth for scientific analysis. This could be the first sample return mission for an extra-terrestrial atmosphere and potentially the first sample return from an Earth-sized planet. The VATMOS-SR mission concept consists of a SmallSat atmospheric sampling probe (45 deg. sphere/cone geometry, <1 m diameter) that is designed to skim through the Venus upper atmosphere and acquire gas samples below the homopause altitude (around ~110 km altitude), where the different atmospheric gases are mixed. The velocity of the spacecraft where sampling would occur is expected to be between ~10.5 km/s and ~13.1 km/s, depending on the trajectory chosen. This presentation will discuss hypervelocity sampling in the upper atmosphere of Venus with respect to the VATMOS-SR mission concept. VATMOS-SR would enable critical atmospheric measurements to form a complete picture of how, why, and when Venus evolved to be so different from Earth and Mars. The abundances and isotopic compositions of volatile elements (such as N, C, S, O, and the noble gases) in planetary atmospheres record volatile delivery during accretion, outgassing from planetary interiors, and atmospheric loss to space. Precise and accurate determinations of volatile atmospheric signatures are the key to understanding the origins and geodynamical evolution of Venus compared to the other terrestrial planets. Hypersonic sampling poses unique technical and scientific challenges. To ensure it is possible to relate the composition of the sampled gases to the free stream atmospheric composition, large-scale numerical simulations are employed to model the flow through the VATMOS-SR sampling system. In particular, an emphasis is placed on quantifying noble gas isotopic fractionation that occurs during the sample acquisition and transfer process to determine how measured isotopic ratios of noble gases in the sample compared to actual isotopic ratios in the Venusian atmosphere. The Direct Simulation Monte Carlo (DSMC) code SPARTA, an open-source software package developed by Sandia National Laboratories, is used in this work. SPARTA, based on Bird’s DSMC method, is a molecular-level gas-kinetic technique. As SPARTA is able to model hypervelocity reacting flows in strong chemical and thermal non-equilibrium, this software package is well suited to determine relevant flow properties for the VATMOS-SR mission concept and to numerically quantify the expected level of elemental and/or isotopic fractionation in the sample acquired by VATMOS-SR. This presentation will show results from 3D simulations correlating the noble gas isotopic fractionation in the gas acquired at hypervelocity speeds to its ambient atmosphere value. In particular, emphasis will be placed on Xenon isotopes of masses 128 and 130, as precise measurements of that ratio would yield comparison to Earth’s atmosphere. Additionally, sensitivity studies that quantify the uncertainties due to the freestream parameters, as well as the modeling parameters, will be performed.

direct simulation Monte Carlo↗
DOE OSTI2020

Materials Data on Sr(GeRh)2 by Materials Project

Sr(RhGe)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Sr is bonded in a 8-coordinate geometry to eight equivalent Rh and eight equivalent Ge atoms. All Sr–Rh bond lengths are 3.46 Å. All Sr–Ge bond lengths are 3.32 Å. Rh is bonded to four equivalent Sr and four equivalent Ge atoms to form a mixture of distorted corner, edge, and face-sharing RhSr4Ge4 tetrahedra. All Rh–Ge bond lengths are 2.48 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Sr, four equivalent Rh, and one Ge atom. The Ge–Ge bond length is 2.90 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(CdGa)2 by Materials Project

Sr(CdGa)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Sr is bonded in a 8-coordinate geometry to eight equivalent Cd and eight equivalent Ga atoms. All Sr–Cd bond lengths are 3.68 Å. All Sr–Ga bond lengths are 3.49 Å. Cd is bonded to four equivalent Sr and four equivalent Ga atoms to form a mixture of distorted face, edge, and corner-sharing CdSr4Ga4 tetrahedra. All Cd–Ga bond lengths are 2.81 Å. Ga is bonded in a 9-coordinate geometry to four equivalent Sr, four equivalent Cd, and one Ga atom. The Ga–Ga bond length is 2.52 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(GeAu)2 by Materials Project

Sr(AuGe)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Sr is bonded in a 8-coordinate geometry to eight equivalent Au and eight equivalent Ge atoms. All Sr–Au bond lengths are 3.49 Å. All Sr–Ge bond lengths are 3.50 Å. Au is bonded in a 4-coordinate geometry to four equivalent Sr and four equivalent Ge atoms. All Au–Ge bond lengths are 2.67 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Sr, four equivalent Au, and one Ge atom. The Ge–Ge bond length is 2.56 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(As2Rh3)2 by Materials Project

Sr(Rh3As2)2 crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Sr is bonded to six equivalent Rh and six equivalent As atoms to form face-sharing SrAs6Rh6 cuboctahedra. All Sr–Rh bond lengths are 3.21 Å. All Sr–As bond lengths are 3.10 Å. There are two inequivalent Rh sites. In the first Rh site, Rh is bonded in a 6-coordinate geometry to two equivalent Sr and four As atoms. There are two shorter (2.49 Å) and two longer (2.56 Å) Rh–As bond lengths. In the second Rh site, Rh is bonded in a 5-coordinate geometry to five As atoms. There are one shorter (2.55 Å) and four longer (2.60 Å) Rh–As bond lengths. There are two inequivalent As sites. In the first As site, As is bonded in a 8-coordinate geometry to two equivalent Sr and six Rh atoms. In the second As site, As is bonded in a 9-coordinate geometry to nine Rh atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(Ni2Sn)2 by Materials Project

Sr(Ni2Sn)2 crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. Sr is bonded in a 8-coordinate geometry to eight equivalent Ni and eight equivalent Sn atoms. All Sr–Ni bond lengths are 3.14 Å. All Sr–Sn bond lengths are 3.55 Å. Ni is bonded in a 9-coordinate geometry to two equivalent Sr, three equivalent Ni, and four equivalent Sn atoms. There are one shorter (2.53 Å) and two longer (2.55 Å) Ni–Ni bond lengths. There are a spread of Ni–Sn bond distances ranging from 2.60–2.66 Å. Sn is bonded in a 12-coordinate geometry to four equivalent Sr and eight equivalent Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(GeRu)2 by Materials Project

Sr(RuGe)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Sr is bonded in a 8-coordinate geometry to eight equivalent Ru and eight equivalent Ge atoms. All Sr–Ru bond lengths are 3.39 Å. All Sr–Ge bond lengths are 3.40 Å. Ru is bonded in a 4-coordinate geometry to four equivalent Sr and four equivalent Ge atoms. All Ru–Ge bond lengths are 2.45 Å. Ge is bonded in a 4-coordinate geometry to four equivalent Sr and four equivalent Ru atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(ClO3)2 by Materials Project

Sr(O3Cl)2 crystallizes in the orthorhombic Fdd2 space group. The structure is three-dimensional. Sr is bonded in a 8-coordinate geometry to eight O atoms. There are a spread of Sr–O bond distances ranging from 2.63–2.71 Å. There are three inequivalent O sites. In the first O site, O is bonded in a bent 150 degrees geometry to one Sr and one Cl atom. The O–Cl bond length is 1.49 Å. In the second O site, O is bonded in a 2-coordinate geometry to one Sr and one Cl atom. The O–Cl bond length is 1.51 Å. In the third O site, O is bonded in a trigonal planar geometry to two equivalent Sr and one Cl atom. The O–Cl bond length is 1.53 Å. Cl is bonded in a trigonal non-coplanar geometry to three O atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(CuGe)2 by Materials Project

Sr(CuGe)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Sr is bonded in a 8-coordinate geometry to eight equivalent Cu and eight equivalent Ge atoms. All Sr–Cu bond lengths are 3.35 Å. All Sr–Ge bond lengths are 3.30 Å. Cu is bonded in a 4-coordinate geometry to four equivalent Sr and four equivalent Ge atoms. All Cu–Ge bond lengths are 2.49 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Sr, four equivalent Cu, and one Ge atom. The Ge–Ge bond length is 2.61 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(InAu)3 by Materials Project

SrAu3In3 crystallizes in the orthorhombic Pmmn space group. The structure is three-dimensional. Sr is bonded in a 12-coordinate geometry to eight Au and six equivalent In atoms. There are a spread of Sr–Au bond distances ranging from 3.43–3.73 Å. There are four shorter (3.65 Å) and two longer (3.90 Å) Sr–In bond lengths. There are two inequivalent Au sites. In the first Au site, Au is bonded in a 1-coordinate geometry to three equivalent Sr, two equivalent Au, and four In atoms. Both Au–Au bond lengths are 2.86 Å. There are a spread of Au–In bond distances ranging from 2.76–2.99 Å. In the second Au site, Au is bonded in a 9-coordinate geometry to two equivalent Sr and seven In atoms. There are a spread of Au–In bond distances ranging from 2.83–2.98 Å. There are two inequivalent In sites. In the first In site, In is bonded to three equivalent Sr and four Au atoms to form distorted InSr3Au4 tetrahedra that share corners with two equivalent InAu7 hexagonal pyramids, corners with four equivalent InSr3Au4 tetrahedra, edges with two equivalent InAu7 hexagonal pyramids, edges with six equivalent InSr3Au4 tetrahedra, and faces with four equivalent InSr3Au4 tetrahedra. In the second In site, In is bonded to seven Au atoms to form distorted InAu7 hexagonal pyramids that share corners with four equivalent InSr3Au4 tetrahedra, edges with six equivalent InAu7 hexagonal pyramids, and edges with four equivalent InSr3Au4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(BIr)2 by Materials Project

Sr(IrB)2 is alpha Pu-derived structured and crystallizes in the orthorhombic Fddd space group. The structure is three-dimensional. Sr is bonded in a 10-coordinate geometry to eight equivalent Ir and six equivalent B atoms. There are four shorter (3.10 Å) and four longer (3.36 Å) Sr–Ir bond lengths. There are two shorter (3.09 Å) and four longer (3.18 Å) Sr–B bond lengths. Ir is bonded in a 4-coordinate geometry to four equivalent Sr and four equivalent B atoms. There are two shorter (2.12 Å) and two longer (2.17 Å) Ir–B bond lengths. B is bonded in a 4-coordinate geometry to three equivalent Sr and four equivalent Ir atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(BRh)2 by Materials Project

Sr(RhB)2 is alpha Pu-derived structured and crystallizes in the orthorhombic Fddd space group. The structure is three-dimensional. Sr is bonded in a 10-coordinate geometry to eight equivalent Rh and six equivalent B atoms. There are four shorter (3.09 Å) and four longer (3.34 Å) Sr–Rh bond lengths. There are two shorter (3.11 Å) and four longer (3.17 Å) Sr–B bond lengths. Rh is bonded in a 4-coordinate geometry to four equivalent Sr and four equivalent B atoms. There are two shorter (2.12 Å) and two longer (2.15 Å) Rh–B bond lengths. B is bonded in a 4-coordinate geometry to three equivalent Sr and four equivalent Rh atoms.

36 MATERIALS SCIENCE↗