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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Gd3Lu by Materials Project

LuGd3 is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Lu is bonded to twelve equivalent Gd atoms to form LuGd12 cuboctahedra that share corners with six equivalent LuGd12 cuboctahedra, corners with twelve equivalent GdGd8Lu4 cuboctahedra, edges with eighteen equivalent GdGd8Lu4 cuboctahedra, faces with eight equivalent LuGd12 cuboctahedra, and faces with twelve equivalent GdGd8Lu4 cuboctahedra. There are six shorter (3.52 Å) and six longer (3.58 Å) Lu–Gd bond lengths. Gd is bonded to four equivalent Lu and eight equivalent Gd atoms to form GdGd8Lu4 cuboctahedra that share corners with four equivalent LuGd12 cuboctahedra, corners with fourteen equivalent GdGd8Lu4 cuboctahedra, edges with six equivalent LuGd12 cuboctahedra, edges with twelve equivalent GdGd8Lu4 cuboctahedra, faces with four equivalent LuGd12 cuboctahedra, and faces with sixteen equivalent GdGd8Lu4 cuboctahedra. There are a spread of Gd–Gd bond distances ranging from 3.53–3.60 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na3Gd(PO4)2 by Materials Project

Na3Gd(PO4)2 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are eighteen inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Na–O bond distances ranging from 2.27–2.96 Å. In the second Na1+ site, Na1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Na–O bond distances ranging from 2.39–2.58 Å. In the third Na1+ site, Na1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Na–O bond distances ranging from 2.35–2.92 Å. In the fourth Na1+ site, Na1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Na–O bond distances ranging from 2.36–2.93 Å. In the fifth Na1+ site, Na1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Na–O bond distances ranging from 2.39–2.61 Å. In the sixth Na1+ site, Na1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Na–O bond distances ranging from 2.33–2.93 Å. In the seventh Na1+ site, Na1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Na–O bond distances ranging from 2.39–2.58 Å. In the eighth Na1+ site, Na1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Na–O bond distances ranging from 2.34–2.82 Å. In the ninth Na1+ site, Na1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Na–O bond distances ranging from 2.27–3.01 Å. In the tenth Na1+ site, Na1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Na–O bond distances ranging from 2.36–2.85 Å. In the eleventh Na1+ site, Na1+ is bonded in a 2-coordinate geometry to eight O2- atoms. There are a spread of Na–O bond distances ranging from 2.35–2.95 Å. In the twelfth Na1+ site, Na1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Na–O bond distances ranging from 2.27–3.01 Å. In the thirteenth Na1+ site, Na1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Na–O bond distances ranging from 2.35–2.80 Å. In the fourteenth Na1+ site, Na1+ is bonded to six O2- atoms to form distorted NaO6 octahedra that share corners with six PO4 tetrahedra. There are a spread of Na–O bond distances ranging from 2.38–2.57 Å. In the fifteenth Na1+ site, Na1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Na–O bond distances ranging from 2.28–3.01 Å. In the sixteenth Na1+ site, Na1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Na–O bond distances ranging from 2.41–2.61 Å. In the seventeenth Na1+ site, Na1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Na–O bond distances ranging from 2.35–2.83 Å. In the eighteenth Na1+ site, Na1+ is bonded to six O2- atoms to form distorted NaO6 octahedra that share corners with six PO4 tetrahedra. There are a spread of Na–O bond distances ranging from 2.37–2.58 Å. There are six inequivalent Gd3+ sites. In the first Gd3+ site, Gd3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Gd–O bond distances ranging from 2.30–2.63 Å. In the second Gd3+ site, Gd3+ is bonded in a 7-coordinate geometry to eight O2- atoms. There are a spread of Gd–O bond distances ranging from 2.29–2.92 Å. In the third Gd3+ site, Gd3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Gd–O bond distances ranging from 2.29–2.64 Å. In the fourth Gd3+ site, Gd3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Gd–O bond distances ranging from 2.37–2.79 Å. In the fifth Gd3+ site, Gd3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Gd–O bond distances ranging from 2.38–2.82 Å. In the sixth Gd3+ site, Gd3+ is bonded in a 7-coordinate geometry to eight O2- atoms. There are a spread of Gd–O bond distances ranging from 2.30–2.89 Å. There are twelve inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one NaO6 octahedra. The corner-sharing octahedral tilt angles are 55°. There are a spread of P–O bond distances ranging from 1.54–1.57 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one NaO6 octahedra. The corner-sharing octahedral tilt angles are 56°. There are a spread of P–O bond distances ranging from 1.54–1.57 Å. In the third P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two equivalent NaO6 octahedra. The corner-sharing octahedra tilt angles range from 21–58°. All P–O bond lengths are 1.56 Å. In the fourth P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two equivalent NaO6 octahedra. The corner-sharing octahedra tilt angles range from 22–58°. There is one shorter (1.55 Å) and three longer (1.56 Å) P–O bond length. In the fifth P5+ site, P5+ is bonded in a tetrahedral geometry to four O2- atoms. There is two shorter (1.55 Å) and two longer (1.56 Å) P–O bond length. In the sixth P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one NaO6 octahedra. The corner-sharing octahedral tilt angles are 55°. There is one shorter (1.54 Å) and three longer (1.56 Å) P–O bond length. In the seventh P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one NaO6 octahedra. The corner-sharing octahedral tilt angles are 56°. There are a spread of P–O bond distances ranging from 1.54–1.57 Å. In the eighth P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two equivalent NaO6 octahedra. The corner-sharing octahedra tilt angles range from 21–59°. All P–O bond lengths are 1.56 Å. In the ninth P5+ site, P5+ is bonded in a tetrahedral geometry to four O2- atoms. There is two shorter (1.55 Å) and two longer (1.56 Å) P–O bond length. In the tenth P5+ site, P5+ is bonded in a tetrahedral geometry to four O2- atoms. There is two shorter (1.55 Å) and two longer (1.56 Å) P–O bond length. In the eleventh P5+ site, P5+ is bonded in a tetrahedral geometry to four O2- atoms. There is two shorter (1.55 Å) and two longer (1.56 Å) P–O bond length. In the twelfth P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two equivalent NaO6 octahedra. The corner-sharing octahedra tilt angles range from 23–59°. All P–O bond lengths are 1.56 Å. There are forty-eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two Na1+, one Gd3+, and one P5+ atom. In the second O2- site, O2- is bonded in a 1-coordinate geometry to three Na1+, one Gd3+, and one P5+ atom. In the third O2- site, O2- is bonded in a 4-coordinate geometry to two Na1+, one Gd3+, and one P5+ atom. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to two Na1+, one Gd3+, and one P5+ atom. In the fifth O2- site, O2- is bonded in a 1-coordinate geometry to three Na1+, one Gd3+, and one P5+ atom. In the sixth O2- site, O2- is bonded in a 1-coordinate geometry to three Na1+, one Gd3+, and one P5+ atom. In the seventh O2- site, O2- is bonded in a 1-coordinate geometry to one Na1+, one Gd3+, and one P5+ atom. In the eighth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Na1+, one Gd3+, and one P5+ atom. In the ninth O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+, one Gd3+, and one P5+ atom. In the tenth O2- site, O2- is bonded in a 1-coordinate geometry to three Na1+, one Gd3+, and one P5+ atom. In the eleventh O2- site, O2- is bonded in a 1-coordinate geometry to four Na1+, one Gd3+, and one P5+ atom. In the twelfth O2- site, O2- is bonded in a 1-coordinate geometry to three Na1+, one Gd3+, and one P5+ atom. In the thirteenth O2- site, O2- is bonded in a 1-coordinate geometry to one Na1+, two Gd3+, and one P5+ atom. In the fourteenth O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+, one Gd3+, and one P5+ atom. In the fifteenth O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+, one Gd3+, and one P5+ atom. In the sixteenth O2- site, O2- is bonded in a 1-coordinate geometry to four Na1+ and one P5+ atom. In the seventeenth O2- site, O2- is bonded in a 1-coordinate geometry to three Na1+, one Gd3+, and one P5+ atom. In the eighteenth O2- site, O2- is bonded in a 1-coordinate geometry to four Na1+, one Gd3+, and one P5+ atom. In the nineteenth O2- site, O2- is bonded in a 4-coordinate geometry to two Na1+, one Gd3+, and one P5+ atom. In the twentieth O2- site, O2- is bonded in a 1-coordinate geometry to four Na1+, one Gd3+, and one P5+ atom. In the twenty-first O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+, one Gd3+, and one P5+ atom. In the twenty-second O2- site, O2- is bonded in a distorted single-bond geometry to four Na1+, one Gd3+, and one P5+ atom. In the twenty-third O2- site, O2- is bonded in a 1-coordinate geometry to three Na1+, one Gd3+, and one P5+ atom. In the twenty-fourth O2- site, O2- is bonded in a 1-coordinate geometry to one Na1+, one Gd3+, and one P5+ atom. In the twenty-fifth O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+, one Gd3+, and one P5+ atom. In the twenty-sixth O2- site, O2- is bonded in a 1-coordinate geometry to four Na1+, one Gd3+, and one P5+ atom. In the twenty-seventh O2- site, O2- is bonded in a 1-coordinate geometry to four Na1+, one Gd3+, and one P5+ atom. In the twenty-eighth O2- site, O2- is bonded in a 4-coordinate geometry to four Na1+ and one P5+ atom. In the twenty-ninth O2- site, O2- is bonded in a 1-coordinate geometry to four Na1+, one Gd3+, and one P5+ atom. In the thirtieth O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+, one Gd3+, and one P5+ atom. In the thirty-first O2- site, O2- is bonded in a 1-coordinate geometry to four Na1+, one Gd3+, and one P5+ atom. In the thirty-second O2- site, O2- is bonded in a 1-coordinate geometry to three Na1+, one Gd3+, and one P5+ atom. In the thirty-third O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+, one Gd3+, and one P5+ atom. In the thirty-fourth O2- site, O2- is bonded in a 1-coordinate geometry to one Na1+, two Gd3+, and one P5+ atom. In the thirty-fifth O2- site, O2- is bonded in a 1-coordinate geometry to three Na1+, one Gd3+, and one P5+ atom. In the thirty-sixth O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+, one Gd3+, and one P5+ atom. In the thirty-seventh O2- site, O2- is bonded in a 1-coordinate geometry to three Na1+, one Gd3+, and one P5+ atom. In the thirty-eighth O2- site, O2- is bonded in a 1-coordinate geometry to three Na1+, one Gd3+, and one P5+ atom. In the thirty-ninth O2- site, O2- is bonded in a 1-coordinate geometry to three Na1+, one Gd3+, and one P5+ atom. In the fortieth O2- site, O2- is bonded in a 4-coordinate geometry to four Na1+ and one P5+ atom. In the forty-first O2- site, O2- is bonded in a 4-coordinate geometry to two Na1+, one Gd3+, and one P5+ atom. In the forty-second O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+, one Gd3+, and one P5+ atom. In the forty-third O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+, one Gd3+, and one P5+ atom. In the forty-fourth O2- site, O2- is bonded in a 4-coordinate geometry to four Na1+ and one P5+ atom. In the forty-fifth O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+, one Gd3+, and one P5+ atom. In the forty-sixth O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+, one Gd3+, and one P5+ atom. In the forty-seventh O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+, one Gd3+, and one P5+ atom. In the forty-eighth O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+, one Gd3+, and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Gd3SbO3 by Materials Project

Gd3SbO3 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are three inequivalent Gd3+ sites. In the first Gd3+ site, Gd3+ is bonded in a 4-coordinate geometry to four equivalent Sb3- and four O2- atoms. There are two shorter (3.42 Å) and two longer (3.47 Å) Gd–Sb bond lengths. There are a spread of Gd–O bond distances ranging from 2.29–2.66 Å. In the second Gd3+ site, Gd3+ is bonded in a distorted see-saw-like geometry to two equivalent Sb3- and four O2- atoms. Both Gd–Sb bond lengths are 3.29 Å. There are a spread of Gd–O bond distances ranging from 2.24–2.35 Å. In the third Gd3+ site, Gd3+ is bonded in a distorted see-saw-like geometry to two equivalent Sb3- and four O2- atoms. Both Gd–Sb bond lengths are 3.24 Å. There are a spread of Gd–O bond distances ranging from 2.26–2.46 Å. Sb3- is bonded in a body-centered cubic geometry to eight Gd3+ atoms. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded to four Gd3+ atoms to form a mixture of edge and corner-sharing OGd4 tetrahedra. In the second O2- site, O2- is bonded to four Gd3+ atoms to form a mixture of edge and corner-sharing OGd4 trigonal pyramids. In the third O2- site, O2- is bonded to four Gd3+ atoms to form a mixture of distorted edge and corner-sharing OGd4 trigonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on GdClO2 by Materials Project

GdO2Cl crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. Gd is bonded in a 9-coordinate geometry to six O and three equivalent Cl atoms. There are a spread of Gd–O bond distances ranging from 2.30–2.46 Å. There are two shorter (2.84 Å) and one longer (2.94 Å) Gd–Cl bond lengths. There are two inequivalent O sites. In the first O site, O is bonded in a distorted trigonal planar geometry to three equivalent Gd atoms. In the second O site, O is bonded in a trigonal non-coplanar geometry to three equivalent Gd atoms. Cl is bonded in a distorted trigonal non-coplanar geometry to three equivalent Gd atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Gd2(Al3Rh)3 by Materials Project

Gd2(RhAl3)3 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Gd is bonded in a 11-coordinate geometry to eleven Al atoms. There are a spread of Gd–Al bond distances ranging from 3.06–3.14 Å. There are two inequivalent Rh sites. In the first Rh site, Rh is bonded in a 8-coordinate geometry to eight Al atoms. There are four shorter (2.57 Å) and four longer (2.62 Å) Rh–Al bond lengths. In the second Rh site, Rh is bonded in a 8-coordinate geometry to eight Al atoms. There are a spread of Rh–Al bond distances ranging from 2.56–2.62 Å. There are four inequivalent Al sites. In the first Al site, Al is bonded in a 2-coordinate geometry to two equivalent Gd and two equivalent Rh atoms. In the second Al site, Al is bonded in a 3-coordinate geometry to three equivalent Gd and three Rh atoms. In the third Al site, Al is bonded in a 3-coordinate geometry to two equivalent Gd and three Rh atoms. In the fourth Al site, Al is bonded in a 2-coordinate geometry to two equivalent Gd and two equivalent Rh atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Distance‐based reconstruction of protein quaternary structures from inter‐chain contacts

Abstract Predicting the quaternary structure of protein complex is an important problem. Inter‐chain residue‐residue contact prediction can provide useful information to guide the ab initio reconstruction of quaternary structures. However, few methods have been developed to build quaternary structures from predicted inter‐chain contacts. Here, we develop the first method based on gradient descent optimization (GD) to build quaternary structures of protein dimers utilizing inter‐chain contacts as distance restraints. We evaluate GD on several datasets of homodimers and heterodimers using true/predicted contacts and monomer structures as input. GD consistently performs better than both simulated annealing and Markov Chain Monte Carlo simulation. Starting from an arbitrarily quaternary structure randomly initialized from the tertiary structures of protein chains and using true inter‐chain contacts as input, GD can reconstruct high‐quality structural models for homodimers and heterodimers with average TM‐score ranging from 0.92 to 0.99 and average interface root mean square distance from 0.72 Å to 1.64 Å. On a dataset of 115 homodimers, using predicted inter‐chain contacts as restraints, the average TM‐score of the structural models built by GD is 0.76. For 46% of the homodimers, high‐quality structural models with TM‐score ≥ 0.9 are reconstructed from predicted contacts. There is a strong correlation between the quality of the reconstructed models and the precision and recall of predicted contacts. Only a moderate precision or recall of inter‐chain contact prediction is needed to build good structural models for most homodimers. Moreover, GD improves the quality of quaternary structures predicted by AlphaFold2 on a Critical Assessment of Techniques for Protein Structure Prediction–Critical Assessments of Predictions of Interactions dataset.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Production and Purification of Terbium-155 Using Natural Gadolinium Targets

Terbium-155 (t 1/2 = 5.32 days) is one of four medically relevant radioisotopes of terbium. It is of interest to the field as a suitable diagnostic counterpart for therapeutic radiolanthanides, as its decay scheme includes γ-rays that are suitable for single photon emission computed tomography (SPECT) imaging. Additionally, 155 Tb has an Auger electron (AE) yield that is viable for AE therapy. There are several direct and indirect production routes that can produce 155 Tb. Two possible direct routes include proton irradiation on gadolinium targets via 155 Gd(p,n) 155 Tb and 156 Gd(p,2n) 155 Tb. The 155 Gd(p,n) 155 Tb reaction is accessible at incident proton beam energies of ∼10 MeV, whereas the 156 Gd(p,2n) 155 Tb nuclear reaction requires ∼18 MeV. This study aims to investigate the production of 155 Tb from natGd through the nat Gd(p,x) nuclear reaction, wherein both (p,n) and (p,2n) reactions were leveraged, and the purification using a three-column ion chromatography method. Using this system, recoveries of radioterbium of up to 97% were achieved in addition to high recoveries of the Gd target material, illustrating the suitability of this technique for enriched targets.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Eu speciation in apatite at 1 bar: An experimental study of valence-state partitioning by XANES, lattice strain, and Eu/Eu* in basaltic systems

Abstract Partition coefficients for rare earth elements (REEs) between apatite and basaltic melt were determined as a function of oxygen fugacity (fO2; iron-wüstite to hematite-magnetite buffers) at 1 bar and between 1110 and 1175 °C. Apatite-melt partitioning data for REE3+ (La, Sm, Gd, Lu) show near constant values at all experimental conditions, while bulk Eu becomes more incompatible (with an increasing negative anomaly) with decreasing fO2. Experiments define three apatite calibrations that can theoretically be used as redox sensors. The first, a XANES calibration that directly measures Eu valence in apatite, requires saturation at similar temperature-composition conditions to experiments and is defined by: ( E u 3 + ∑ E u ) Apatite = 1 1 + 10 - 0.10 ± 0.01 × l o g ⁡ ( f o 2 ) - 1.63 ± 0.16 . The second technique involves analysis of Sm, Eu, and Gd in both apatite and coexisting basaltic melt (glass), and is defined by: ( Eu E u * ) D Sm × Gd = 1 1 + 10 - 0.15 ± 0.03 × l o g ⁡ ( f o 2 ) - 2.46 ± 0.41 . The third technique is based on the lattice strain model and also requires analysis of REE in both apatite and basalt. This calibration is defined by ( Eu E u * ) D lattice strain = 1 1 + 10 - 0.20 ± 0.03 × l o g ⁡ ( f o 2 ) - 3.03 ± 0.42 . The Eu valence-state partitioning techniques based on (Sm×Gd) and lattice strain are virtually indistinguishable, such that either methodology is valid. Application of any of these calibrations is best carried out in systems where both apatite and coexisting glass are present and in direct contact with one another. In holocrystalline rocks, whole rock analyses can be used as a guide to melt composition, but considerations and corrections must be made to either the lattice strain or Sm×Gd techniques to ensure that the effect of plagioclase crystallization either prior to or during apatite growth can be removed. Similarly, if the melt source has an inherited either a positive or negative Eu anomaly, appropriate corrections must also be made to lattice strain or Sm×Gd techniques that are based on whole rock analyses. This being the case, if apatite is primary and saturates from the parent melt early during the crystallization sequence, these corrections may be minimal. The partition coefficients for the REE between apatite and melt range from a maximum DEu3+ = 1.67 ± 0.25 (as determined by lattice strain) to DLu3+ = 0.69 ± 0.10. The REE partition coefficient pattern, as observed in the Onuma diagram, is in a fortuitous situation where the most compatible REE (Eu3+) is also the polyvalent element used to monitor fO2. These experiments provide a quantitative means of assessing Eu anomalies in apatite and how they be used to constrain the oxygen fugacity of silicate melts.

Geochemistry & Geophysics↗
NASA NTRS1995

MHD Simulations of Earth's Bow Shock at low Mach Numbers: Standoff Distances

Global, three-dimensional, ideal MHD simulations of Earth's bow shock are reported for low Alfven Mach numbers M(sub A) and quasi-perpendicular magnetic field orientations. The simulations use a hard, infinitely conducting magnetopauause obstacle, with axisymmetric three-dimensional location given by scaled standard model, to directly address previous gasdynamic (GD) and field-aligned MHD (FA-MHD) work. Tests of the simulated shocks' density jumps X for 1.4 approx. less than MA approx. less than 10 and the high M(sub A) shock location, and reproduction of the GD relation between magnetosheath thickness and X for quasi-gasdynamic MHD runs with M(sub A) much greater than M(sub s), confirm that the MHD code is working correctly. The MHD simulations show the standoff distance a(sub s), increasing monotonically with decreasing M(sub A). Significantly larger a(sub s), are found at low M(sub A) than predicted by GD and phenomenological MHD models and FA-MHD simulations, as required qualitatively by observations. The GD and FA-MHD predictions err qualitatively, predicting either constant or decreasing a(sub s), with decreasing M(sub A). This qualitative difference between quasi- perpendicular MHD and FA-MHD simulations is direct evidence for a(sub s), depending on the magnetic field orientation Theta. The enhancement factor over the phenomenological MHD predictions at MA approx. 2.4 agrees quantitatively with one observatiorial estimate. A linear relationship is found between the magnetosheath thickness and X, modified both quantitatively and intrinsically by MHD effects from the GD result. The MHD and GD results agree in the high M(sub A) limit. An MHD theory is developed for a(sub s), restricted to sufficiently perpendicular Theta and high sonic Mach numbers M(sub s). It explains the simulation results with excellent accuracy. Observational and further simulation testing of this MHD theory, and of its predicted M(sub A), Theta, and M(sub s) effects, is desirable.

Cairns, Iver H.↗
NASA NTRS2003

The Chemical Composition and Gas-to-Dust Mass Ratio of Nearby Interstellar Matter

We use recent results on interstellar gas toward nearby stars and interstellar by-products within the solar system to select among the equilibrium radiative transfer models of the nearest interstellar material presented in Slavin & Frisch. For the assumption that O/H - 400 parts per million, models 2 and 8 are found to yield good fits to available data on interstellar material inside and outside of the heliosphere, with the exception of the Ne abundance in the pickup ion and anomalous cosmic-ray populations. For these models, the interstellar medium (ISM) at the entry point to the heliosphere has n(H(sup 0)) = 0.202-0.208/cu cm, n(He(sup 0) = 0.0137-0.0152/cu cm, and ionizations X(H) = 0.29-0.30, X(He) = 0.47-0.51. These best models suggest that the chemical composition of the nearby ISM is approx.60%-70% subsolar if S is undepleted. Both H(0) and H(+) need to be included when evaluating abundances of ions found in warm diffuse clouds. Models 2 and 8 yield an H filtration factor of approx.0.46. Gas-to-dust mass ratios for the ISM toward epsilon CMa are R(sub gd) = 178-183 for solar abundances of Holweger or R(sub gd) = 611-657 for an interstellar abundance standard 70% solar. Direct observations of dust grains in the solar system by Ulysses and Galileo yield R(sub gd) appr0x. 115 for models 2 and 8, supporting earlier results (Frisch and coworkers). If the local ISM abundances are subsolar, then gas and dust are decoupled over small spatial scales. The inferred variation in R(sub gd) over parsec length scales is consistent with the fact that the ISM near the Sun is part of a dynamically active cluster of cloudlets flowing away from the Sco-Cen association. Observations toward stars within approx.500 pc show that R(sub gd) correlates with the percentage of the dust mass that is carried by iron, suggesting that an Fe-rich grain core (by mass) remains after grain destruction. Evidently large dust grains (>10(exp -13) g) and small dust grains (<10(exp -13) g) are not well mixed over parsec length spatial scales in the ISM. It also appears that very small C-dominated dust grains have been destroyed in the ISM within several parsecs of the Sun, since C appears to be essentially undepleted. However, if gas-dust coupling breaks down over the cloud lifetime, the missing mass arguments applied here to determine R(sub gd) and dust grain mineralogy are not appropriate.

Frisch, Priscilla C.↗
NASA NTRS2023

Influence of Cation Species on Thermal Expansion of Y2Si2O7–Gd2Si2O7 Solid Solutions

Mixtures of Y 2 Si 2 O 7 and Gd 2 Si 2 O 7 were synthesized by solid-state reaction at 1600°C and characterized via in situ x-ray diffraction (XRD) to determine their coefficients of thermal expansion (CTE). All solid solutions within the system exhibited the orthorhombic δ-RE 2 Si 2 O 7 (Pna2 1 ) structure. Thermal expansion measurements of Y 2 Si 2 O 7 and Gd 2 Si 2 O 7 correlated well with reported values in literature, and all synthesized solid solutions exhibited CTEs between Y 2 Si 2 O 7 and Gd 2 Si 2 O 7 . Generally, there was a slight decrease in CTE exhibited by the materials with increasing Gd 2 Si 2 O 7 content, with Gd 2 Si 2 O 7 having the lowest CTEs and Y 2 Si 2 O 7 the highest CTEs. The decrease in CTE was attributed to stronger bonds of Gd-O over Y-O, as determined by calculated crystal orbital Hamilton populations using density functional theory. However, such differences were very small and crystal structure was the dominating factor in CTE trends.

rare earth silicates↗
DOE OSTI2020

Materials Data on GdCuGe by Materials Project

GdCuGe is hexagonal omega structure-derived structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Gd is bonded to six equivalent Cu and six equivalent Ge atoms to form a mixture of distorted edge and face-sharing GdCu6Ge6 cuboctahedra. There are three shorter (3.02 Å) and three longer (3.18 Å) Gd–Cu bond lengths. There are three shorter (3.02 Å) and three longer (3.18 Å) Gd–Ge bond lengths. Cu is bonded in a 9-coordinate geometry to six equivalent Gd and three equivalent Ge atoms. All Cu–Ge bond lengths are 2.48 Å. Ge is bonded in a 9-coordinate geometry to six equivalent Gd and three equivalent Cu atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on GdGeRu by Materials Project

GdRuGe crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Gd is bonded in a 9-coordinate geometry to four equivalent Ru and six equivalent Ge atoms. There are a spread of Gd–Ru bond distances ranging from 2.96–3.01 Å. There are a spread of Gd–Ge bond distances ranging from 3.07–3.26 Å. Ru is bonded in a 8-coordinate geometry to four equivalent Gd and four equivalent Ge atoms. There are a spread of Ru–Ge bond distances ranging from 2.54–2.59 Å. Ge is bonded in a 10-coordinate geometry to six equivalent Gd and four equivalent Ru atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on GdSiRu by Materials Project

GdRuSi is Matlockite structured and crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. Gd is bonded in a 9-coordinate geometry to four equivalent Ru and five equivalent Si atoms. All Gd–Ru bond lengths are 3.01 Å. There are four shorter (3.12 Å) and one longer (3.31 Å) Gd–Si bond lengths. Ru is bonded in a 8-coordinate geometry to four equivalent Gd and four equivalent Si atoms. All Ru–Si bond lengths are 2.44 Å. Si is bonded in a 9-coordinate geometry to five equivalent Gd and four equivalent Ru atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on GdMg2Ag by Materials Project

Mg2GdAg is Heusler structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Mg is bonded in a body-centered cubic geometry to four equivalent Gd and four equivalent Ag atoms. All Mg–Gd bond lengths are 3.11 Å. All Mg–Ag bond lengths are 3.11 Å. Gd is bonded in a 8-coordinate geometry to eight equivalent Mg and six equivalent Ag atoms. All Gd–Ag bond lengths are 3.59 Å. Ag is bonded in a distorted body-centered cubic geometry to eight equivalent Mg and six equivalent Gd atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on GdPbAu by Materials Project

GdAuPb is half-Heusler structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Gd is bonded to four equivalent Au and six equivalent Pb atoms to form a mixture of distorted face and corner-sharing GdPb6Au4 tetrahedra. All Gd–Au bond lengths are 2.99 Å. All Gd–Pb bond lengths are 3.46 Å. Au is bonded in a body-centered cubic geometry to four equivalent Gd and four equivalent Pb atoms. All Au–Pb bond lengths are 2.99 Å. Pb is bonded in a distorted q6 geometry to six equivalent Gd and four equivalent Au atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on GdSnAu by Materials Project

GdAuSn crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Gd is bonded in a 12-coordinate geometry to six equivalent Au and six equivalent Sn atoms. There are three shorter (3.06 Å) and three longer (3.64 Å) Gd–Au bond lengths. There are three shorter (3.21 Å) and three longer (3.44 Å) Gd–Sn bond lengths. Au is bonded in a 10-coordinate geometry to six equivalent Gd and four equivalent Sn atoms. There are three shorter (2.83 Å) and one longer (3.04 Å) Au–Sn bond lengths. Sn is bonded in a 10-coordinate geometry to six equivalent Gd and four equivalent Au atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on GdIn2Rh by Materials Project

GdRhIn2 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Gd is bonded in a 1-coordinate geometry to three equivalent Rh and ten equivalent In atoms. There are one shorter (2.88 Å) and two longer (3.11 Å) Gd–Rh bond lengths. There are a spread of Gd–In bond distances ranging from 3.33–3.47 Å. Rh is bonded in a 9-coordinate geometry to three equivalent Gd and six equivalent In atoms. There are two shorter (2.80 Å) and four longer (2.81 Å) Rh–In bond lengths. In is bonded in a 3-coordinate geometry to five equivalent Gd and three equivalent Rh atoms.

36 MATERIALS SCIENCE↗