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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Machine learning etudes in astrophysics: selection functions for mock cluster catalogs

Making mock simulated catalogs is an important component of astrophysical data analysis. Selection criteria for observed astronomical objects are often too complicated to be derived from first principles. However the existence of an observed group of objects is a well-suited problem for machine learning classification. In this paper we use one-class classifiers to learn the properties of an observed catalog of clusters of galaxies from ROSAT and to pick clusters from mock simulations that resemble the observed ROSAT catalog. We show how this method can be used to study the cross-correlations of thermal Sunya'ev-Zeldovich signals with number density maps of X-ray selected cluster catalogs. The method reduces the bias due to hand-tuning the selection function and is readily scalable to large catalogs with a high-dimensional space of astrophysical features.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Multielectrode electrochemical cell for in situ structural characterization of amorphous thin-film catalysts using high-energy X-ray scattering

A multielectrode-based electrochemical cell allows the structural characterization of an amorphous thin-film water oxidation catalyst under various electrochemical potentials using high-energy X-ray scattering and atomic pair distribution function (PDF) techniques. A multielectrode with five electrodes provides a sufficiently low background signal to enable high-energy X-ray scattering (HEXS) measurements and amplifies the extremely low HEXS signals from samples for high-resolution PDF analysis of in situ data from thin-film catalysts. Glassy carbon (GC) creates a relatively low intensity HEXS pattern and is used as a working electrode. Instead of a three-dimensional (3D) porous electrode architecture, the flat geometry of the electrode enables various deposition techniques to be used for the preparation of a highly conductive metal oxide layer. PDF analysis demonstrates high spatial resolution for a 230 nm thick amorphous iridium oxide film deposited on two roughened 60 µm thick GC electrodes. The PDF analysis resolves the domain size and distinguishes changes in fine structure which are directly correlated with the structure and function of the catalysts. In conclusion, the results bring the opportunity to analyze the structure of nanometre-scale amorphous thin-film catalysts in an electrolyte-compatible and compact 3D-printed electrochemical cell in a three-electrode configuration.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Reliable Measures of Spread in High Dimensional Latent Spaces

Understanding geometric properties of the latent spaces of natural language processing models allows the manipulation of these properties for improved performance on downstream tasks. One such property is the amount of data spread in a model’s latent space, or how fully the available latent space is being used. We demonstrate that the commonly used measures of data spread, average cosine similarity and a partition function min/max ratio I (V), do not provide reliable metrics to compare the use of latent space across data distributions. We propose and examine six alternative measures of data spread, all of which improve over these current metrics when applied to seven synthetic data distributions. Of our proposed measures, we recommend one principal component-based measure and one entropy-based measure that provide reliable, relative measures of spread and can be used to compare models of different sizes and dimensionalities.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Unorthodox parallelization for Bayesian quantum state estimation

Quantum state tomography (QST) allows for the reconstruction of quantum states through measurements and some inference technique under the assumption of repeated state preparations. Bayesian inference provides a promising platform to achieve both efficient QST and accurate uncertainty quantification, yet is generally plagued by the computational limitations associated with long Markov chains. In this work, we present a novel Bayesian QST approach that leverages modern distributed parallel computer architectures to efficiently sample a D-dimensional Hilbert space. Using a parallelized preconditioned Crank–Nicholson Metropolis–Hastings algorithm, we demonstrate our approach on simulated data and experimental results from IBM Quantum systems up to four qubits, showing significant speedups through parallelization. Although highly unorthodox in pooling independent Markov chains, our method proves remarkably practical, with validation ex post facto via diagnostics like the intrachain autocorrelation time. We conclude by discussing scalability to higher-dimensional systems, offering a path toward efficient and accurate Bayesian characterization of large quantum systems.

Bayesian inference↗
DOE OSTI2022

Physics-Informed Sparse Gaussian Process for Probabilistic Stability Analysis of Large-Scale Power System with Dynamic PVs and Loads

This work proposes a physics-informed sparse Gaussian process (SGP) for probabilistic stability assessment of large-scale power systems in the presence of uncertain dynamic PVs and loads. The differential and algebraic equations considering uncertainties from dynamic PVs and loads are reformulated to a nonlinear mapping relationship that allows the application of SGP. Thanks to the nonparametric characteristic of Gaussian process, the proposed framework does not require distributions of uncertain inputs and this distinguishes it from existing approaches. As the original Gaussian process is not scalable to large-scale systems with high dimensional uncertain inputs, this paper develops the SGP with a stochastic variational inference technique. It leads to approximately two orders of complex reduction. A data pre-processing step is also introduced to tackle the coexistence of stable and unstable cases by sample clustering and constructing separate SGPs. The probabilistic transient stability index is analyzed to assess system stability under different uncertain dynamics loads and PVs. Comparisons are performed with the sampling-based, the polynomial chaos expansion-based, and traditional Gaussian process-based methods on the modified IEEE 118-bus and Texas 2000-bus systems under various scenarios, including different levels of uncertainties and the existence of nonlinear correlations among dynamic PVs. The impacts of data quality and quantity issues are also investigated. It is shown that the proposed SGP achieves significantly improved computational efficiency while maintaining high accuracy with a limited number of data.

24 POWER TRANSMISSION AND DISTRIBUTION↗
NASA NTRS1989

Preliminary results on two-dimensional interferometry of HL Tau

Preliminary two-dimensional speckle interferometry results of HL Tau were found to be qualitatively similar to those found with one-dimensional slit scanning techniques; results consist of a resolved component (approximately 0.7 arcsec in size) and an unresolved component. Researchers are currently reducing the rest of the data (taken on three different telescopes and at three different wavelengths) and are also exploring other high resolution methods like the shift and add technique and selecting only the very best images for processing. The availability of even better two-dimensional arrays within the next couple of years promises to make speckle interferometry and other high resolution techniques very powerful and exiting tools for probing a variety of objects in the subarcsec regime.

Tollestrup, Eric V.↗
DOE OSTI2018

Blazing Signature Filter: a library for fast pairwise similarity comparisons

Identifying similarities between datasets is a fundamental task in data mining and has become an integral part of modern scientific investigation. Whether the task is to identify co-expressed genes in large-scale expression surveys or to predict combinations of gene knockouts which would elicit a similar phenotype, the underlying computational task is often a multi-dimensional similarity test. As datasets continue to grow, improvements to the efficiency, sensitivity or specificity of such computation will have broad impacts as it allows scientists to more completely explore the wealth of scientific data. A significant practical drawback of large-scale data mining is the vast majority of pairwise comparisons are unlikely to be relevant, meaning that they do not share a signature of interest. It is therefore essential to efficiently identify these unproductive comparisons as rapidly as possible and exclude them from more time-intensive similarity calculations. The Blazing Signature Filter (BSF) is a highly efficient pairwise similarity algorithm which enables extensive data mining within a reasonable amount of time. The algorithm transforms datasets into binary metrics, allowing it to utilize the computationally efficient bit operators and provide a coarse measure of similarity. As a result, the BSF can scale to high dimensionality and rapidly filter unproductive pairwise comparison. Furthermore, two bioinformatics applications of the tool are presented to demonstrate the ability to scale to billions of pairwise comparisons and the usefulness of this approach.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Determination of shape anisotropy in embedded low contrast submonolayer quantum dot structures

We describe a procedure for the morphological characterization of hard-to-image submonolayer quantum dot structures. This procedure employs high resolution x-ray diffraction based reciprocal space mapping, accompanied by rigorous diffraction modeling for precise determination of the morphology of submonolayer quantum dots. Our modelling results and experimental data clearly show that the investigated quantum dots are anisotropically elongated along the [110] orientation. Complementary polarization dependent photoluminescence measurements, combined with our previously reported magneto-photoluminescence data, confirm this conclusion. Our formalism enables direct extraction of structural information of complex embedded three-dimensional structures, which, due to their low electron density contrast with respect to the surrounding host matrix, cannot be readily investigated by traditional electron diffraction techniques.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Materials Data on SiO2 by Materials Project

SiO2 is high (beta) Cristobalite structured and crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Si4+ is bonded to four equivalent O2- atoms to form corner-sharing SiO4 tetrahedra. All Si–O bond lengths are 1.63 Å. O2- is bonded in a bent 150 degrees geometry to two equivalent Si4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Materials Data on SiO2 by Materials Project

SiO2 is High (Orthorhombic) Tridymite-like structured and crystallizes in the orthorhombic Fddd space group. The structure is three-dimensional. Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. There is two shorter (1.62 Å) and two longer (1.63 Å) Si–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent Si4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SiO2 by Materials Project

SiO2 is High (Orthorhombic) Tridymite-like structured and crystallizes in the orthorhombic Pccn space group. The structure is three-dimensional. Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.62–1.64 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent Si4+ atoms. In the second O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms. In the third O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AlPO4 by Materials Project

AlPO4 is High (Orthorhombic) Tridymite-derived structured and crystallizes in the orthorhombic Ima2 space group. The structure is three-dimensional. there are three inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with four PO4 tetrahedra. There are a spread of Al–O bond distances ranging from 1.73–1.76 Å. In the second Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with four PO4 tetrahedra. There is one shorter (1.74 Å) and three longer (1.75 Å) Al–O bond length. In the third Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with four PO4 tetrahedra. All Al–O bond lengths are 1.74 Å. There are three inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with four AlO4 tetrahedra. There is three shorter (1.53 Å) and one longer (1.54 Å) P–O bond length. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with four AlO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.52–1.54 Å. In the third P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with four AlO4 tetrahedra. All P–O bond lengths are 1.53 Å. There are eleven inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to one Al3+ and one P5+ atom. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to one Al3+ and one P5+ atom. In the third O2- site, O2- is bonded in a linear geometry to one Al3+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a linear geometry to one Al3+ and one P5+ atom. In the fifth O2- site, O2- is bonded in a bent 150 degrees geometry to one Al3+ and one P5+ atom. In the sixth O2- site, O2- is bonded in a bent 150 degrees geometry to one Al3+ and one P5+ atom. In the seventh O2- site, O2- is bonded in a linear geometry to one Al3+ and one P5+ atom. In the eighth O2- site, O2- is bonded in a linear geometry to one Al3+ and one P5+ atom. In the ninth O2- site, O2- is bonded in a bent 150 degrees geometry to one Al3+ and one P5+ atom. In the tenth O2- site, O2- is bonded in a linear geometry to one Al3+ and one P5+ atom. In the eleventh O2- site, O2- is bonded in a linear geometry to one Al3+ and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SiO2 by Materials Project

SiO2 is High (Orthorhombic) Tridymite-like structured and crystallizes in the orthorhombic Cmce space group. The structure is three-dimensional. Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. There is one shorter (1.61 Å) and three longer (1.62 Å) Si–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms. In the second O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms. In the third O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent Si4+ atoms. In the fourth O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SiO2 by Materials Project

SiO2 is High (Orthorhombic) Tridymite-like structured and crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. there are four inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. There is one shorter (1.61 Å) and three longer (1.62 Å) Si–O bond length. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. All Si–O bond lengths are 1.62 Å. In the third Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. There is three shorter (1.61 Å) and one longer (1.63 Å) Si–O bond length. In the fourth Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. There is three shorter (1.62 Å) and one longer (1.63 Å) Si–O bond length. There are ten inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms. In the second O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms. In the third O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to two Si4+ atoms. In the fifth O2- site, O2- is bonded in a linear geometry to two Si4+ atoms. In the sixth O2- site, O2- is bonded in a bent 150 degrees geometry to two Si4+ atoms. In the seventh O2- site, O2- is bonded in a bent 150 degrees geometry to two Si4+ atoms. In the eighth O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms. In the ninth O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms. In the tenth O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent Si4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SiO2 by Materials Project

SiO2 is High (Orthorhombic) Tridymite-like structured and crystallizes in the orthorhombic Pmmn space group. The structure is three-dimensional. there are seven inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. All Si–O bond lengths are 1.62 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. There is three shorter (1.62 Å) and one longer (1.63 Å) Si–O bond length. In the third Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. All Si–O bond lengths are 1.62 Å. In the fourth Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. There is three shorter (1.62 Å) and one longer (1.63 Å) Si–O bond length. In the fifth Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. There is three shorter (1.62 Å) and one longer (1.63 Å) Si–O bond length. In the sixth Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. All Si–O bond lengths are 1.62 Å. In the seventh Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. There is two shorter (1.62 Å) and two longer (1.63 Å) Si–O bond length. There are ten inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to two Si4+ atoms. In the second O2- site, O2- is bonded in a linear geometry to two Si4+ atoms. In the third O2- site, O2- is bonded in a bent 150 degrees geometry to two Si4+ atoms. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to two Si4+ atoms. In the fifth O2- site, O2- is bonded in a linear geometry to two Si4+ atoms. In the sixth O2- site, O2- is bonded in a bent 150 degrees geometry to two Si4+ atoms. In the seventh O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms. In the eighth O2- site, O2- is bonded in a bent 150 degrees geometry to two Si4+ atoms. In the ninth O2- site, O2- is bonded in a linear geometry to two Si4+ atoms. In the tenth O2- site, O2- is bonded in a linear geometry to two Si4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SiO2 by Materials Project

SiO2 is High (Orthorhombic) Tridymite-like structured and crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. there are two inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. All Si–O bond lengths are 1.62 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. All Si–O bond lengths are 1.62 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to two Si4+ atoms. In the third O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent Si4+ atoms. In the fourth O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SiO2 by Materials Project

SiO2 is High (Orthorhombic) Tridymite-like structured and crystallizes in the orthorhombic Cmme space group. The structure is three-dimensional. there are two inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.61–1.63 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. There is one shorter (1.61 Å) and three longer (1.62 Å) Si–O bond length. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent Si4+ atoms. In the second O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms. In the third O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms. In the fourth O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms. In the fifth O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent Si4+ atoms. In the sixth O2- site, O2- is bonded in a linear geometry to two Si4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SiO2 by Materials Project

SiO2 is High (Orthorhombic) Tridymite-like structured and crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. there are three inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. All Si–O bond lengths are 1.62 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. All Si–O bond lengths are 1.62 Å. In the third Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. All Si–O bond lengths are 1.62 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to two Si4+ atoms. In the second O2- site, O2- is bonded in a linear geometry to two Si4+ atoms. In the third O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms. In the fourth O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms. In the fifth O2- site, O2- is bonded in a linear geometry to two Si4+ atoms. In the sixth O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms.

36 MATERIALS SCIENCE↗