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At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on LaNb2CuBrO7 by Materials Project

LaNb2CuO7Br is Pb(Zr_(1-x)Ti_x)O3-derived structured and crystallizes in the monoclinic C2 space group. The structure is three-dimensional. La3+ is bonded in a 12-coordinate geometry to ten O2- atoms. There are a spread of La–O bond distances ranging from 2.51–2.77 Å. There are two inequivalent Nb5+ sites. In the first Nb5+ site, Nb5+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Nb–O bond distances ranging from 1.81–2.27 Å. In the second Nb5+ site, Nb5+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Nb–O bond distances ranging from 1.80–2.27 Å. There are two inequivalent Cu2+ sites. In the first Cu2+ site, Cu2+ is bonded in a distorted linear geometry to two equivalent O2- and four equivalent Br1- atoms. Both Cu–O bond lengths are 1.85 Å. There are two shorter (2.72 Å) and two longer (2.86 Å) Cu–Br bond lengths. In the second Cu2+ site, Cu2+ is bonded in a distorted linear geometry to two equivalent O2- and four equivalent Br1- atoms. Both Cu–O bond lengths are 1.85 Å. There are two shorter (2.60 Å) and two longer (3.02 Å) Cu–Br bond lengths. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent La3+ and two Nb5+ atoms. In the second O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent La3+ and two Nb5+ atoms. In the third O2- site, O2- is bonded in a distorted trigonal pyramidal geometry to two equivalent La3+ and two equivalent Nb5+ atoms. In the fourth O2- site, O2- is bonded in a distorted see-saw-like geometry to two equivalent La3+ and two equivalent Nb5+ atoms. In the fifth O2- site, O2- is bonded in a distorted linear geometry to two equivalent La3+ and two Nb5+ atoms. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent La3+ and two Nb5+ atoms. In the seventh O2- site, O2- is bonded in a linear geometry to one Nb5+ and one Cu2+ atom. In the eighth O2- site, O2- is bonded in a linear geometry to one Nb5+ and one Cu2+ atom. Br1- is bonded in a 4-coordinate geometry to four Cu2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on VO2 by Materials Project

VO2 is Pb(Zr_(1-x)Ti_x)O3-derived structured and crystallizes in the tetragonal P4/ncc space group. The structure is three-dimensional. V4+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of V–O bond distances ranging from 1.70–2.29 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to four equivalent V4+ atoms. In the second O2- site, O2- is bonded in a linear geometry to two equivalent V4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Materials Data on Ca2Nb3CuBrO10 by Materials Project

Ca2Nb3CuO10Br is Pb(Zr_(1-x)Ti_x)O3-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Ca2+ is bonded in a 12-coordinate geometry to twelve O2- atoms. There are a spread of Ca–O bond distances ranging from 2.51–3.02 Å. There are two inequivalent Nb5+ sites. In the first Nb5+ site, Nb5+ is bonded to six O2- atoms to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There is two shorter (1.97 Å) and four longer (1.98 Å) Nb–O bond length. In the second Nb5+ site, Nb5+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Nb–O bond distances ranging from 1.81–2.27 Å. Cu2+ is bonded in a distorted linear geometry to two equivalent O2- and four equivalent Br1- atoms. Both Cu–O bond lengths are 1.86 Å. All Cu–Br bond lengths are 2.81 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to four equivalent Ca2+ and two equivalent Nb5+ atoms. In the second O2- site, O2- is bonded in a 2-coordinate geometry to four equivalent Ca2+ and two Nb5+ atoms. In the third O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ca2+ and two equivalent Nb5+ atoms. In the fourth O2- site, O2- is bonded in a linear geometry to one Nb5+ and one Cu2+ atom. Br1- is bonded in a square co-planar geometry to four equivalent Cu2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnPb2WO6 by Materials Project

Pb2MnWO6 is Pb(Zr_(1-x)Ti_x)O3-derived structured and crystallizes in the orthorhombic Pmc2_1 space group. The structure is three-dimensional. there are two inequivalent W6+ sites. In the first W6+ site, W6+ is bonded to six O2- atoms to form WO6 octahedra that share corners with six MnO6 octahedra. The corner-sharing octahedra tilt angles range from 4–19°. There are a spread of W–O bond distances ranging from 1.86–2.15 Å. In the second W6+ site, W6+ is bonded to six O2- atoms to form WO6 octahedra that share corners with six MnO6 octahedra. The corner-sharing octahedra tilt angles range from 5–19°. There are a spread of W–O bond distances ranging from 1.86–2.15 Å. There are two inequivalent Mn2+ sites. In the first Mn2+ site, Mn2+ is bonded to six O2- atoms to form distorted MnO6 octahedra that share corners with six WO6 octahedra. The corner-sharing octahedra tilt angles range from 5–19°. There are a spread of Mn–O bond distances ranging from 2.16–2.44 Å. In the second Mn2+ site, Mn2+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with six WO6 octahedra. The corner-sharing octahedra tilt angles range from 4–18°. There are a spread of Mn–O bond distances ranging from 2.17–2.41 Å. There are two inequivalent Pb2+ sites. In the first Pb2+ site, Pb2+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of Pb–O bond distances ranging from 2.44–2.58 Å. In the second Pb2+ site, Pb2+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of Pb–O bond distances ranging from 2.44–2.59 Å. There are ten inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted see-saw-like geometry to one W6+, one Mn2+, and two equivalent Pb2+ atoms. In the second O2- site, O2- is bonded in a 4-coordinate geometry to one W6+, one Mn2+, and two Pb2+ atoms. In the third O2- site, O2- is bonded in a 4-coordinate geometry to one W6+, one Mn2+, and two equivalent Pb2+ atoms. In the fourth O2- site, O2- is bonded in a distorted linear geometry to one W6+ and one Mn2+ atom. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to one W6+, one Mn2+, and two equivalent Pb2+ atoms. In the sixth O2- site, O2- is bonded in a distorted linear geometry to one W6+ and one Mn2+ atom. In the seventh O2- site, O2- is bonded in a distorted linear geometry to one W6+ and one Mn2+ atom. In the eighth O2- site, O2- is bonded in a linear geometry to one W6+ and one Mn2+ atom. In the ninth O2- site, O2- is bonded in a 4-coordinate geometry to one W6+, one Mn2+, and two equivalent Pb2+ atoms. In the tenth O2- site, O2- is bonded in a 4-coordinate geometry to one W6+, one Mn2+, and two Pb2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NaLaScNbO6 by Materials Project

NaLaScNbO6 is Pb(Zr_(1-x)Ti_x)O3-derived structured and crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Na1+ is bonded in a 10-coordinate geometry to four O2- atoms. There are two shorter (2.53 Å) and two longer (2.66 Å) Na–O bond lengths. La3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of La–O bond distances ranging from 2.46–2.71 Å. Sc3+ is bonded to six O2- atoms to form ScO6 octahedra that share corners with six equivalent NbO6 octahedra. The corner-sharing octahedra tilt angles range from 17–35°. There are a spread of Sc–O bond distances ranging from 2.09–2.13 Å. Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with six equivalent ScO6 octahedra. The corner-sharing octahedra tilt angles range from 17–35°. There are a spread of Nb–O bond distances ranging from 1.91–2.20 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent La3+, one Sc3+, and one Nb5+ atom. In the second O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Na1+, one Sc3+, and one Nb5+ atom. In the third O2- site, O2- is bonded to two equivalent La3+, one Sc3+, and one Nb5+ atom to form a mixture of distorted edge and corner-sharing OLa2ScNb tetrahedra. In the fourth O2- site, O2- is bonded to two equivalent La3+, one Sc3+, and one Nb5+ atom to form a mixture of distorted edge and corner-sharing OLa2ScNb tetrahedra. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Na1+, one Sc3+, and one Nb5+ atom.

36 MATERIALS SCIENCE↗
NASA NTRS1986

A method for linearizing a nonlinear system with six state variables and three control variables

A nonlinear system governed by x = f(x,u) with six state variables and three control variables is considered in this project. A set of transformations from (x,u) - space to (z,v) - space is defined such that the linear tangent model is independent of the operating point in the z-space. Therefore, it is possible to design a control law satisfying all operating points in the transformed space. An algorithm to construct the above transformations and to obtain the associated linearized system is described in this report. This method is applied to a rigid body using pole placement for the control law. Results are verified by numerical simulation. Closed loop poles in x-space using traditional local linearization are compared with those pole placements in the z-space.

Hsia, W. S.↗
NASA NTRS1987

Isotropic probability measures in infinite dimensional spaces: Inverse problems/prior information/stochastic inversion

Let R be the real numbers, R(n) the linear space of all real n-tuples, and R(infinity) the linear space of all infinite real sequences x = (x sub 1, x sub 2,...). Let P sub n :R(infinity) approaches R(n) be the projection operator with P sub n (x) = (x sub 1,...,x sub n). Let p(infinity) be a probability measure on the smallest sigma-ring of subsets of R(infinity) which includes all of the cylinder sets P sub n(-1) (B sub n), where B sub n is an arbitrary Borel subset of R(n). Let p sub n be the marginal distribution of p(infinity) on R(n), so p sub n(B sub n) = p(infinity)(P sub n to the -1(B sub n)) for each B sub n. A measure on R(n) is isotropic if it is invariant under all orthogonal transformations of R(n). All members of the set of all isotropic probability distributions on R(n) are described. The result calls into question both stochastic inversion and Bayesian inference, as currently used in many geophysical inverse problems.

Backus, George↗
NASA NTRS1987

Isotropic probability measures in infinite-dimensional spaces

Let R be the real numbers, R(n) the linear space of all real n-tuples, and R(infinity) the linear space of all infinite real sequences x = (x sub 1, x sub 2,...). Let P sub in :R(infinity) approaches R(n) be the projection operator with P sub n (x) = (x sub 1,...,x sub n). Let p(infinity) be a probability measure on the smallest sigma-ring of subsets of R(infinity) which includes all of the cylinder sets P sub n(-1) (B sub n), where B sub n is an arbitrary Borel subset of R(n). Let p sub n be the marginal distribution of p(infinity) on R(n), so p sub n(B sub n) = p(infinity) (P sub n to the -1 (B sub n)) for each B sub n. A measure on R(n) is isotropic if it is invariant under all orthogonal transformations of R(n). All members of the set of all isotropic probability distributions on R(n) are described. The result calls into question both stochastic inversion and Bayesian inference, as currently used in many geophysical inverse problems.

Backus, George↗
NASA NTRS2002

RXTE Observations of Selected Blazars

The work completed includes the analysis of observations obtained during Cycles 4 and 5 of the Rossi X-ray Timing Explorer (RXTE). The project is part of a longer-term, continuing program to study the X-ray emission process in blazars in collaboration with Dr. Ian McHardy (U. of Southampton, UK).

Marscher, Alan P.↗
NASA NTRS2002

RXTE Observations of Selected Blazars

The work completed includes the analysis of observations obtained during Cycles 4 and 5 of the Rossi X-ray Timing Explorer (RXTE). The project is part of a longer-term, continuing program to study the X-ray emission process in blazars in cooperation with Dr. Ian McHardy (U. of Southampton, UK). The goals of the program are to study the X-ray emission mechanism in blazars and the relation of the X-ray emission to changes in the relativistic jet. The program includes contemporaneous brightness and linear polarization monitoring at radio and optical wavelengths, total and polarized intensity imaging at 43 GHz with a resolution of 0.1 milliarcseconds with the Very Long Baseline Array (VLBA), and well-sampled X-ray light curves obtained from a series of approved RXTE programs.

Aller, Margo F.↗
NASA NTRS2012

Influence of Containment on the Growth of Silicon-Germanium: A Materials Science Flight Project

A series of Ge(1-x)Si(x) crystal growth experiments are planned to be conducted in the Low Gradient Furnace (LGF) onboard the International Space Station. The primary objective of the research is to determine the influence of containment on the processing-induced defects and impurity incorporation in germanium-silicon alloy crystals. A comparison will be made between crystals grown by the normal and "detached" Bridgman methods and the ground-based float zone technique. Crystals grown without being in contact with a container have superior quality to otherwise similar crystals grown in direct contact with a container, especially with respect to impurity incorporation, formation of dislocations, and residual stress in crystals. "Detached" or "dewetted" Bridgman growth is similar to regular Bridgman growth in that most of the melt is in contact with the crucible wall, but the crystal is separated from the wall by a small gap, typically of the order of 10-100 microns. Long duration reduced gravity is essential to test the proposed theory of detached growth. Detached growth requires the establishment of a meniscus between the crystal and the ampoule wall. The existence of this meniscus depends on the ratio of the strength of gravity to capillary forces. On Earth, this ratio is large and stable detached growth can only be obtained over limited conditions. Crystals grown detached on the ground exhibited superior structural quality as evidenced by measurements of etch pit density, synchrotron white beam X-ray topography and double axis X-ray diffraction. The plans for the flight experiments will be described.

Volz, M. P.↗
NASA NTRS2001

From the Cluster Temperature Function to the Mass Function at Low Z

The project consists of three X-ray Multimirror Mission (XMM) observations of the hot, nearby galaxy cluster Triangulum Australis (one pointing to the cluster center and two offsets). The major goal of the project is to obtain an accurate radial gas temperature profile out to large radii and derive the total gravitating mass within the radius of over density 500. A secondary goal is to obtain a detailed two-dimensional gas temperature map of the central region. We have recently received the central pointing (of the two CDROMs received, one contains the central pointing and the other, a zero-exposure dummy observation). The analysis of the data at hand is underway with the aim of deriving the two-dimensional temperature map. At present, we have to limit quantitative analysis to the EPIC-MOS data because of the absence of the necessary calibration products for the Extended Full Frame mode used for EPIC-pn in these observations. We anticipate the arrival of the data from the remaining two offset pointings in the near future, after which we will be able to undertake the total mass derivation. Money from this year's installment of the grant was partially spent on an upgrade of the computer used for the above data analysis, and on travel to a conference that extensively discussed the XMM calibration issues.

Markevitch, Maxim↗
NASA NTRS2012

Gravity and Extreme Magnetism SMEX

The Gravity and Extreme Magnetism SMEX mission will be the first mission to catalogue the X-ray polarisation of many astrophysical objects including black-holes and pulsars. This first of its kind mission is enabled by the novel use of a time projection chamber as an X-ray polarimeter. The detector has been developed over the last 5 years, with the current effort charged toward a demonstration of it's technical readiness to be at level 6 prior to the preliminary design review. This talk will describe the design GEMS polarimeter and the results to date from the engineering test unit.

Source record↗
NASA NTRS1999

X-33, X-34, X-37 Press Conference (Tape 2)

Live footage shows Project Managers Susan Turner, MSFC and David Manley, Boeing Co. participating in the X-37 Briefing. NASA's Public Affairs June Malone introduced these panelists who went on to discuss the vehicle and its secondary payload. Manley mentions the X-37 capabilities, main propulsion system, its lithium iron batteries, hot control surfaces, and its fly by wire system. Turner mentions the on-board operations, the deployment of the solar arrays, and the autonomous navigation and landing system. Also included is an animation of the X-37 vehicle during flight and the secondary payload release into orbit.

Source record↗
DOE OSTI2025

Distributed Stochastic Optimization of a Neural Representation Network for Time-Space Tomography Reconstruction

4D time-space reconstruction of dynamic events or deforming objects using X-ray computed tomography (CT) is an important inverse problem in non-destructive evaluation. Conventional back-projection based reconstruction methods assume that the object remains static for the duration of several tens or hundreds of X-ray projection measurement images (reconstruction of consecutive limited-angle CT scans). However, this is an unrealistic assumption for many in-situ experiments that causes spurious artifacts and inaccurate morphological reconstructions of the object. To solve this problem, we propose to perform a 4D time-space reconstruction using a distributed implicit neural representation (DINR) network that is trained using a novel distributed stochastic training algorithm. Our DINR network learns to reconstruct the object at its output by iterative optimization of its network parameters such that the measured projection images best match the output of the CT forward measurement model. Here, we use a forward measurement model that is a function of the DINR outputs at a sparsely sampled set of continuous valued 4D object coordinates. Unlike previous neural representation architectures that forward and back propagate through dense voxel grids that sample the object's entire time-space coordinates, we only propagate through the DINR at a small subset of object coordinates in each iteration resulting in an order-of-magnitude reduction in memory and compute for training. DINR leverages distributed computation across several compute nodes and GPUs to produce high-fidelity 4D time-space reconstructions. We use both simulated parallel-beam and experimental cone-beam X-ray CT datasets to demonstrate the superior performance of our approach.

36 MATERIALS SCIENCE↗
DOE OSTI2021

SPIDERS: an overview of the largest catalogue of spectroscopically confirmed x-ray galaxy clusters

SPIDERS is the spectroscopic follow-up effort of the Sloan Digital Sky Survey IV (SDSS-IV) project for the identification of X-ray selected galaxy clusters. We present our catalogue of 2740 visually inspected galaxy clusters as part of the SDSS Data Release 16 (DR16). Here we detail the target selection, our methods for validation of the candidate clusters, performance of the survey, the construction of the final sample, and a full description of what is found in the catalogue. Of the sample, the median number of members per cluster is approximately 10, with 818 having 15 or greater. We find that we are capable of validating over 99 per cent of clusters when five redshifts are obtained below z < 0.3 and when nine redshifts are obtained above z > 0.3. We discuss the improvements in this catalogue’s identification of cluster using 33 340 redshifts, with Δz phot /Δz spec ~100, over other photometric and spectroscopic surveys, as well as presenting an update to previous (σ–L X ) and (σ– λ ) relations. Finally, we present our cosmological constraints derived using the velocity dispersion function.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1993

Ultra-high resolution water window x ray microscope optics design and analysis

This project has been focused on the design and analysis of an ultra-high resolution water window soft-x-ray microscope. These activities have been accomplished by completing two tasks contained in the statement of work of this contract. The new results from this work confirm: (1) that in order to achieve resolutions greater than three times the wavelength of the incident radiation, it will be necessary to use spherical mirror surfaces and to use graded multilayer coatings on the secondary in order to accommodate the large variations of the angle of incidence over the secondary when operating the microscope at numerical apertures of 0.35 or greater; (2) that surface contour errors will have a significant effect on the optical performance of the microscope and must be controlled to a peak-to-valley variation of 50-100 A and a frequency of 8 periods over the surface of a mirror; and (3) that tolerance analysis of the spherical Schwarzschild microscope has been shown that the water window operations will require 2-3 times tighter tolerances to achieve a similar performance of operations with 130 A radiation. These results have been included in a manuscript included in the appendix.

Shealy, David L.↗