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

Importance of the Lu-Hf isotopic system in studies of planetary chronology and chemical evolution

The Lu-176-Hf-176 isotope method and its applications in earth sciences are discussed with regard to planetary-evolution studies. From new data on basalts from oceanic islands, Hf-176/Hf-177 and Nd-143/Nd-144 are found to display a single linear isotopic variation in the suboceanic mantle, whereas considerable divergences occur in Hf-176/Hf-177-Sr-87/Sr-86 and Nd-143/Nd-144-Sr87/Sr-86 diagrams. With the acquisition of further Hf-Sr-Nd isotopic data, these discordant Sr-87/Sr-86 relationships may allow a distinction between processes such as mantle metasomatism, influence of sea-water altered material in the magma source, or recycling of sediments into the mantle. The best quality Hf isotope data are obtained from granitoid or zircons, and are most suitable for studying ancient terrestrial Hf isotopic variations. Lu-Hf is shown to be a viable method for dating ancient terrestrial and extraterrestrial samples, but is unlikely to find wide application in pure chronological studies because it offers little advantage over existing methods.

Patchett, P. J.↗
NASA NTRS1984

An implict LU scheme for the Euler equations applied to arbitrary cascades

An implicit scheme for solving the Euler equations is derived and demonstrated. The alternating-direction implicit (ADI) technique is modified, using two implicit-operator factors corresponding to lower-block-diagonal (L) or upper-block-diagonal (U) algebraic systems which can be easily inverted. The resulting LU scheme is implemented in finite-volume mode and applied to 2D subsonic and transonic cascade flows with differing degrees of geometric complexity. The results are presented graphically and found to be in good agreement with those of other numerical and analytical approaches. The LU method is also 2.0-3.4 times faster than ADI, suggesting its value in calculating 3D problems.

Buratynski, E. K.↗
NASA NTRS1986

Zircon Lu-Hf systematics: Evidence for the episodic development of Archaean greenstone belts

A combined U-Th-Pb and Lu-Hf isotopic study of zircons was undertaken in order to determine the provenance and age of an Archean granite-greenstone terrain and to test the detailed application of the Lu-Hf system in various Archean zircons. The eastern Wawa subprovince of the Superior province consists of the low grade Michipicoten and Gamitagama greenstone belts and the granitic terrain. The Hf isotopic data indicate that the typical lithological features of a greenstone belt cycle could be accommodated in a crustal growth model that involved decreasing depth of melting in three isotopically distinct reservoirs: mantle, lower crust and upper crust. The model age of the sources given by the intersection of the lower crustal curve with the bulk earth evolution curve is about 2900 My, in good agreement with the zircon U-Pb basement age. This linear array also has a similar intersection age to that of Proterozoic carbonatite complexes. The general convergence of the other reservoir vectors around this age suggests that mantle depletion, crustal extraction and intracrustal differentiation were all part of the same episodic event. It is also apparent that recycling of older basement was important in the formation of many of the later greenstone belt rocks.

Smith, P. E.↗
NASA NTRS1986

An LU-SSOR scheme for the Euler and Navier-Stokes equations

A new multigrid relaxation scheme, lower-upper symmetric successive overrelaxation (LU-SSOR) is developed for the steady-state solution of the Euler and Navier-Stokes equations. The scheme, which is based on central differences, does not require flux splitting for approximate Newton iteration. Application to transonic flow shows that the new method is efficient and robust. The vectorizable LU-SSOR scheme needs only scalar diagonal inversions.

Yoon, Seokkwan↗
NASA NTRS1987

Composite grid and finite-volume LU implicit scheme for turbine flow analysis

A composite grid was generated in an attempt to improve grid quality for a typical turbine blade with large camber in terms of mesh control, smoothness, and orthogonality. This composite grid consists of the C grid (or O grid) in the immediate vicinity of the blade and the H grid in the upstream region and in the middle of the blade passage between the C grids. It provides a good boundary layer resolution around the leading edge region for viscous calculation, has orthogonality at the blade surface and slope continuity at the C-H (or O-H) interface, and has flexibility in controlling the mesh distribution in the upstream region without using excessive grid points. This composite grid eliminates the undesirable qualities of a single grid when generated for a typical turbine geometry. A finite-volume lower-upper (LU) implicit scheme can be used in solving for the turbine flows on the composite grid. This grid has a special grid node that is connected to more than four neighboring nodes in two dimensions and to more than six nodes in three dimensions. But the finite-volume approach poses no problem at the special point because each interior cell has only four neighboring cells in two dimensions and only six cells in three dimensions. The finite-volume LU implicit scheme was demonstrated to be robust and efficient for both external and internal flows in a broad flow regime.

Choo, Yung K.↗
NASA NTRS1987

An LU-SSOR scheme for the Euler and Navier-Stokes equations

A new multigrid relaxation scheme, lower-upper symmetric successive overrelaxation (LU-SSOR) is developed for the steady-state solution of the Euler and Navier-Stokes equations. The scheme, which is based on central differences, does not require flux splitting for approximate Newton iteration. Application to transonic flow shows that the new method is efficient and robust. The vectorizable LU-SSOR scheme needs only scalar diagonal inversions.

Yoon, Seokkwan↗
NASA NTRS1987

Composite grid and finite-volume LU implicit scheme for turbine flow analysis

A composite grid was generated in an attempt to improve grid quality for a typical turbine blade with large camber in terms of mesh control, smoothness, and orthogonality. This composite grid consists of the C grid (or O grid) in the immediate vicinity of the blade and the H grid in the upstream region and in the middle of the blade passage between the C grids. It provides a good boundary layer resolution around the leading edge region for viscous calculation, has orthogonality at the blade surface and slope continuity at the C-H (or O-H) interface, and has flexibility in controlling the mesh distribution in the upstream region without using excessive grid points. This composite grid eliminates the undesirable qualities of a single grid when generated for a typical turbine geometry. A finite-volume lower-upper (LU) implicit schemes can be used in solving for the turbine flows on the composite grid. This grid has a special grid node that is connected to more than four neighboring nodes in two dimensions and to more than six nodes in three dimensions. But the finite-volume approach poses no problem at the special point because each interior cell has only four neighboring cells in two dimensions and only six cells in three dimensions. The finite-volume LU implicit scheme was demonstrated to be robust and efficient for both external and internal flows in a broad flow regime.

Choo, Yung K.↗
NASA NTRS1997

Communication Improvement for the LU NAS Parallel Benchmark: A Model for Efficient Parallel Relaxation Schemes

The first release of the MPI version of the LU NAS Parallel Benchmark (NPB2.0) performed poorly compared to its companion NPB2.0 codes. The later LU release (NPB2.1 & 2.2) runs up to two and a half times faster, thanks to a revised point access scheme and related communications scheme. The new scheme sends substantially fewer messages. is cache "friendly", and has a better load balance. We detail the, observations and modifications that resulted in this efficiency improvement, and show that the poor behavior of the original code resulted from deriving a message passing scheme from an algorithm originally devised for a vector architecture.

Yarrow, Maurice↗
DOE OSTI2020

Materials Data on Lu(SiRu)2 by Materials Project

LuRu2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Lu3+ is bonded in a 8-coordinate geometry to eight equivalent Si4- atoms. All Lu–Si bond lengths are 3.19 Å. Ru+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing RuSi4 tetrahedra. All Ru–Si bond lengths are 2.37 Å. Si4- is bonded in a 4-coordinate geometry to four equivalent Lu3+ and four equivalent Ru+2.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Lu(FeO2)2 by Materials Project

LuFe2O4 is Aluminum carbonitride-like structured and crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Lu3+ is bonded to six equivalent O2- atoms to form distorted LuO6 octahedra that share corners with six equivalent FeO5 trigonal bipyramids and edges with six equivalent LuO6 octahedra. There are four shorter (2.24 Å) and two longer (2.26 Å) Lu–O bond lengths. Fe+2.50+ is bonded to five O2- atoms to form FeO5 trigonal bipyramids that share corners with three equivalent LuO6 octahedra, corners with six equivalent FeO5 trigonal bipyramids, and edges with three equivalent FeO5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 63°. There are a spread of Fe–O bond distances ranging from 2.00–2.18 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to four equivalent Fe+2.50+ atoms to form OFe4 trigonal pyramids that share corners with four equivalent OLu3Fe tetrahedra, corners with six equivalent OFe4 trigonal pyramids, and edges with three equivalent OFe4 trigonal pyramids. In the second O2- site, O2- is bonded to three equivalent Lu3+ and one Fe+2.50+ atom to form OLu3Fe tetrahedra that share corners with nine equivalent OLu3Fe tetrahedra, corners with four equivalent OFe4 trigonal pyramids, and edges with three equivalent OLu3Fe tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Lu(NbCl3)6 by Materials Project

LuNb6Cl18 crystallizes in the trigonal R-3 space group. The structure is three-dimensional. Lu3+ is bonded to six equivalent Cl1- atoms to form LuCl6 octahedra that share corners with six equivalent NbCl5 square pyramids. All Lu–Cl bond lengths are 2.61 Å. Nb+2.50+ is bonded to five Cl1- atoms to form NbCl5 square pyramids that share a cornercorner with one LuCl6 octahedra and corners with four equivalent NbCl5 square pyramids. The corner-sharing octahedral tilt angles are 42°. There are a spread of Nb–Cl bond distances ranging from 2.45–2.67 Å. There are three inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a 2-coordinate geometry to two equivalent Nb+2.50+ atoms. In the second Cl1- site, Cl1- is bonded in a 2-coordinate geometry to two equivalent Nb+2.50+ atoms. In the third Cl1- site, Cl1- is bonded in a distorted bent 150 degrees geometry to one Lu3+ and one Nb+2.50+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Lu(CuSi)2 by Materials Project

LuCu2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Lu3+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All Lu–Si bond lengths are 3.00 Å. Cu+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of corner and edge-sharing CuSi4 tetrahedra. All Cu–Si bond lengths are 2.37 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Lu3+, four equivalent Cu+2.50+, and one Si4- atom. The Si–Si bond length is 2.31 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Lu(BRu)4 by Materials Project

LuRu4B4 crystallizes in the tetragonal I4_1/acd space group. The structure is three-dimensional. Lu3+ is bonded in a 12-coordinate geometry to twelve equivalent B3- atoms. There are a spread of Lu–B bond distances ranging from 2.93–3.22 Å. Ru+2.25+ is bonded to five equivalent B3- atoms to form a mixture of distorted edge and corner-sharing RuB5 trigonal bipyramids. There are a spread of Ru–B bond distances ranging from 2.14–2.29 Å. B3- is bonded in a 6-coordinate geometry to three equivalent Lu3+, five equivalent Ru+2.25+, and one B3- atom. The B–B bond length is 1.78 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Lu(FeSi)2 by Materials Project

LuFe2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Lu3+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All Lu–Si bond lengths are 3.04 Å. Fe+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing FeSi4 tetrahedra. All Fe–Si bond lengths are 2.26 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Lu3+, four equivalent Fe+2.50+, and one Si4- atom. The Si–Si bond length is 2.49 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Lu(Mo3S4)2 by Materials Project

LuMo6S8 crystallizes in the trigonal R-3 space group. The structure is three-dimensional. Lu3+ is bonded in a body-centered cubic geometry to eight S2- atoms. There are two shorter (2.64 Å) and six longer (2.98 Å) Lu–S bond lengths. Mo+2.17+ is bonded to five S2- atoms to form a mixture of corner and edge-sharing MoS5 square pyramids. There are a spread of Mo–S bond distances ranging from 2.42–2.57 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a 1-coordinate geometry to one Lu3+ and three equivalent Mo+2.17+ atoms. In the second S2- site, S2- is bonded in a 5-coordinate geometry to one Lu3+ and four equivalent Mo+2.17+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Lu(MnSi)2 by Materials Project

LuMn2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Lu3+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All Lu–Si bond lengths are 2.98 Å. Mn+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of corner and edge-sharing MnSi4 tetrahedra. All Mn–Si bond lengths are 2.35 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Lu3+, four equivalent Mn+2.50+, and one Si4- atom. The Si–Si bond length is 2.43 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Structural and Optical Properties of High Entropy (La,Lu,Y,Gd,Ce)AlO 3 Perovskite Thin Films

Mixtures of Ce-doped rare-earth aluminum perovskites are drawing a significant amount of attention as potential scintillating devices. However, the synthesis of complex perovskite systems leads to many challenges. Designing the A-site cations with an equiatomic ratio allows for the stabilization of a single-crystal phase driven by an entropic regime. This work describes the synthesis of a highly epitaxial thin film of configurationally disordered rare-earth aluminum perovskite oxide (La 0.2 Lu 0.2 Y 0.2 Gd 0.2 Ce 0.2 )AlO 3 and characterizes the structural and optical properties. The thin films exhibit three equivalent epitaxial domains having an orthorhombic structure resulting from monoclinic distortion of the perovskite cubic cell. An excitation of 286.5 nm from Gd 3+ and energy transfer to Ce 3+ with 405 nm emission are observed, which represents the potential for high-energy conversion. These experimental results also offer the pathway to tunable optical properties of high-entropy rare-earth epitaxial perovskite films for a range of applications.

36 MATERIALS SCIENCE↗