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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 OSTI2019

Hydrothermal synthesis of lanthanide rhenium oxides: Structures and magnetism of Ln 2 Re 2 O 7 (OH) (Ln = Pr, Nd) and Ln 4 Re 2 O 11 (Ln = Eu, Tb)

The reactions of Ln 2 O 3 (Ln =LaLu) with ReO 2 were examined in high temperature hydrothermal water (650 °C). In all cases the rhenium oxide was added in a three-fold excess. No external mineralizer was needed and the rhenate itself acted as a sufficient mineralizer to form high quality single crystals of several crystalline products. These form in good yield with compositions varying as a function of the size of the rare earth ion. The largest sesquioxide, La 2 O 3 , forms the well-known La 4 Re 6 O 19 phase, but when Ln = Nd or Pr, a new product, Ln 2 Re 2 O 7 (OH), is isolated. Reactions with Ln = SmTb form Ln 4 Re 2 O 11 , and those with DyLu form Ln 2 ReO 5 . The new Ln 2 Re 2 O 7 (OH) series was characterized as a new structure type by single crystal X-ray diffraction. This structure features a tetrameric Re 4 O 16 cluster embedded in a lanthanide oxide framework. Additional detailed structural data is also provided for Tb 4 Re 2 O 11 and Eu 4 Re 2 O 11 , which were not previously reported for the Ln 4 Re 2 O 11 family. In Ln 2 Re 2 O 7 (OH), no direct ReRe bond (ReRe = 2.60 Å) is observed while Ln 4 Re 2 O 11 appears to possess a rhenium-rhenium double bond with a ReRe distance of 2.42 Å. Single crystal Raman data supports both of these characterizations. Magnetic data is reported for Ln 2 Re 2 O 7 (OH) and Tb 4 Re 2 O 11 , and their behavior appears to be dominated by the f-element magnetic moments. At low temperatures Tb 4 Re 2 O 11 displays possible canted antiferromagnetic coupling.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Automated phase segmentation and quantification of high-resolution TEM image for alloy design

In the alloy design and development process, a wealth of atomically resolved structural high-resolution transmission electron microscopy (HRTEM) images are produced. Identifying the different nano-precipitate phases and tracking their evolution under various compositions and during manufacturing or post-processing requires hundreds of HRTEM images and thousands of precipitates. The nanoscopic phase information labeling and analysis purely relies on humans are prohibitively costly and time-consuming, sometimes not reliable because of the lack of authoritative knowledge. Here, in this work, we develop a novel unsupervised machine learning approach coupled with adaptive computer vision techniques with features in the Fourier space to automatically determine the number of phases and segment/quantify the phases with nanoscale resolution, allowing for quantitative correlation between nanostructure formation, processing and functional properties. To automate the phase extraction/quantification and ascertain its applicability, we have applied the developed framework to the HRTEM images from several alloy systems, processing conditions, image magnifications, and phase types and morphologies (precipitates, nano-twins, stacking faults, crystalline matrix, and amorphous structures) for verification. This study paves the road for compression, visualization, and translation of raw image structural data into physically relevant information in real-time with minimal human supervision. It shows the promise of enabling high-throughput materials characterization for the acceleration of alloy manufacturing and design.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Nuclear Structure and Decay Data for A=31 Isobars

Here, experimental nuclear spectroscopic data are evaluated for 11 known nuclides of mass 31 (F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K). Detailed evaluated information is presented for each reaction and decay experiment. Combining all the available data, recommended values are provided for energies, spins and parities, and half-lives of levels, with energies, branching ratios and multipolarities of γ radiations, and characteristics of β and α radiations in radioactive decays. 31 P is the most extensively studied one among all nuclides via various reactions and decays, followed by 31 S, 31 Si, 31 Mg and 31 Al. Information for excited states in 31 Ne, 31 Na, 31 Cl, 31 Ar and 31 K are limited; no excited states have yet been identified in 31 F, even its ground-state half-life is unknown. Significant new data have become available for the structure of 31 S, with its relevance to astrophysical applications. This work supersedes the earlier evaluation of A=31 by 2013Ou01, with literature cutoff date of Feb 15, 2013.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Multiphysics for nuclear energy applications using a cohesive computational framework

With the recent development of advanced numerical algorithms, software design, and low-cost high-performance computer hardware, reliance on coupled multiphysics to predict the behavior of complex physical systems is beginning to become standard practice. This is especially true in nuclear energy applications where strong nonlinear interdependencies exist between reactor physics, radiation transport, multi-scale nuclear fuels performance, thermal fluids, etc. Resolving these nonlinear dependencies requires choices in multiphysics software approaches. Two main multiphysics modeling and simulation approaches have emerged. The first is based upon "code coupling" where disparate physics codes of different software design, code languages, and spatial and temporal integration schemes are coupled together with relatively complex data passing interfaces. The second multiphysics software approach is to employ a "cohesive" framework where all physics applications are developed with a common software design, i.e., data structures, syntax, input format, integrated spatial and temporal discretization schemes, etc. In this paper we present the Multiphysics Object-Oriented Simulation Environment (MOOSE) development and runtime framework and describe the framework's cohesive modeling and simulation multiphysics approach. Then, a "cohesive-like" extension of the MOOSE framework is presented where MOOSE-based physics software applications are efficiently coupled to non-MOOSE (external) physics codes to form multiphysics applications using MOOSE's unique interface capabilities. Finally, several examples of MOOSE's cohesive and cohesive-like multiphysics applications will be demonstrated. These multiphysics demonstrations will incorporate both MOOSE-based applications and external codes, including Nek5000, RELAP-7, TRACE, BISON, and Pronghorn.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2022

Systematic trends of 0 2 + , 1 1 - , 3 1 - and 2 1 + excited states in even-even nuclei

Here, the spin and parity ( J π ) assignments in even-even nuclei were reviewed across the nuclear chart using the Evaluated Nuclear Structure Data File (ENSDF). The prevalence of 2$+\atop{1}$ first or lowest excited states is confirmed. The properties of 0$+\atop{2}$, 1$-\atop{1}$, and 3$-\atop{1}$ lowest excited states were reexamined using the ENSDF data evaluation procedures. The J π systematic trends and correlations between level quantum numbers and nuclear physics phenomena are discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Program optimizations: The interplay between power, performance, and energy

Practical considerations for future supercomputer designs will impose limits on both instantaneous power consumption and total energy consumption. Working within these constraints while providing the maximum possible performance, application developers will need to optimize their code for speed alongside power and energy concerns. This paper analyzes the effectiveness of several code optimizations including loop fusion, data structure transformations, and global allocations. A per component measurement and analysis of different architectures is performed, enabling the examination of code optimizations on different compute subsystems. Using an explicit hydrodynamics proxy application from the U.S. Department of Energy, LULESH, we show how code optimizations impact different computational phases of the simulation. This provides insight for simulation developers into the best optimizations to use during particular simulation compute phases when optimizing code for future supercomputing platforms. Here, we examine and contrast both x86 and Blue Gene architectures with respect to these optimizations.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

The OpenACC data model: Preliminary study on its major challenges and implementations

This paper describes how the OpenACC data model is implemented in current OpenACC compilers, ranging from research compilers (OpenUH and OpenARC) to a commercial compiler (the PGI OpenACC compiler). First, we summarize various memory architectures in today’s accelerator systems. We then describe details and issues in implementing the OpenACC data model in three different OpenACC compilers. This includes managing page tables, asynchronous data transfers, asynchronous memory allocate and free, host data construct, aliasing on a data directive, reusing device memory, partially present data, and adjacent data. We also discusses ongoing work to manage large, complex dynamic data structures. We measured the present table lookups, device memory allocation, pinned memory allocation, and managed memory in the three OpenACC compilers using eight OpenACC applications (seven from the SPEC ACCEL benchmark suite and a shock-hydrodynamics mini-application called LULESH).

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2021

Measurement and analysis of GPU-accelerated applications with HPCToolkit

To address the challenge of performance analysis on the US DOE’s forthcoming exascale supercomputers, Rice University has been extending its HPCToolkit performance tools to support measurement and analysis of GPU-accelerated applications. To help developers understand the performance of accelerated applications as a whole, HPCToolkit’s measurement and analysis tools attribute metrics to calling contexts that span both CPUs and GPUs. To measure GPU-accelerated applications efficiently, HPCToolkit employs a novel wait-free data structure to coordinate monitoring and attribution of GPU performance. To help developers understand the performance of complex GPU code generated from high-level programming models, HPCToolkit constructs sophisticated approximations of call path profiles for GPU computations. To support fine-grained analysis and tuning, HPCToolkit uses PC sampling and instrumentation to measure and attribute GPU performance metrics to source lines, loops, and inlined code. To supplement fine-grained measurements, HPCToolkit can measure GPU kernel executions using hardware performance counters. To provide a view of how an execution evolves over time, HPCToolkit can collect, analyze, and visualize call path traces within and across nodes. Finally, on NVIDIA GPUs, HPCToolkit can derive and attribute a collection of useful performance metrics based on measurements using GPU PC samples. Here, we illustrate HPCToolkit’s new capabilities for analyzing GPU-accelerated applications with several codes developed as part of the Exascale Computing Project.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

A High-Performance Discrete-Element Framework for Simulating Flow and Jamming of Moisture Bearing Biomass Feedstocks

We developed and verified a high-performance open-source discrete element method (DEM) solver with simultaneously-supported feedstock-specific interaction models, including bonded-sphere, liquid bridge, cohesion, and non-linear contact models. Our solver uses parallel data structures on hybrid central and graphics processing unit (CPU/GPU) architectures, with favorable strong scaling performance observed for large problem sizes comprised of (100 M particles), and 4X single-node GPU speedup. The particles for corn stover feedstock were conceptualized and calibrated based on experimental measurements and results. Sensitivity analyses demonstrate that the mass flow rate from a wedge hopper is governed primarily by moisture content, friction coefficient, and cohesion energy density. The model is used to reproduce experimentally observed hopper jamming results, highlighting that the experimental no-flow trends can only be achieved by using non-spherical particles, liquid bridge and cohesion models, highlighting the importance of using concurrent feedstock specialized models for the effective representation of biomass material handling problems.

bioenergy↗
DOE OSTI2015

Array-based Hierarchical Mesh Generation in Parallel

In this paper, we describe an array-based hierarchical mesh generation capability through uniform refinement of unstructured meshes for efficient solution of PDE's using finite element methods and multigrid solvers. A multi-degree, multi-dimensional and multi-level framework is designed to generate the nested hierarchies from an initial mesh that can be used for a number of purposes such as multi-level methods to generating large meshes. The capability is developed under the parallel mesh framework “Mesh Oriented dAtaBase” a.k.a MOAB. We describe the underlying data structures and algorithms to generate such hierarchies and present numerical results for computational efficiency and mesh quality. In conclusion, we also present results to demonstrate the applicability of the developed capability to a multigrid finite-element solver.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

X-ray Emission Spectroscopy as an in Situ Diagnostic Tool for X-ray Crystallography of Metalloproteins Using an X-ray Free-Electron Laser

Serial femtosecond crystallography (SFX) using the ultrashort X-ray pulses from a X-ray free-electron laser (XFEL) provides a new way of collecting structural data at room temperature that allows for following the reaction in real time after initiation. XFEL experiments are conducted in a shot-by-shot mode as the sample is destroyed and replenished after each X-ray pulse, and therefore, monitoring and controlling the data quality by using in situ diagnostic tools is critical. To study metalloenzymes, we developed the use of simultaneous collection of X-ray diffraction of crystals along with X-ray emission spectroscopy (XES) data that is used as a diagnostic tool for crystallography, by monitoring the chemical state of the metal catalytic center. We have optimized data analysis methods and sample delivery techniques for fast and active feedback to ensure the quality of each batch of samples and the turnover of the catalytic reaction caused by reaction triggering methods. Here, we describe this active in situ feedback system using Photosystem II as an example that catalyzes the oxidation of H2O to O2at the Mn4CaO5active site. We used the first moments of the Mn Kβ1,3emission spectra, which are sensitive to the oxidation state of Mn, as the primary diagnostics. This approach is applicable to different metalloproteins to determine the integrity of samples and follow changes in the chemical states of the reaction that can be initiated by light or activated by substrates and offers a metric for determining the diffraction images that are used for the final data sets.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Nanometer-Resolved Spectroscopic Study Reveals the Conversion Mechanism of CaO·Al 2 O 3 ·10H 2 O to 2CaO·Al 2 O 3 ·8H 2 O and 3CaO·Al 2 O 3 ·6H 2 O at an Elevated Temperature

The main binding phases of calcium aluminate cement (CAC) concrete, CaO·Al2O3·10H2O (CAH10) and 2CaO·Al 2 O 3 ·8H 2 O (C 2 AH 8 ), slowly convert to 3CaO·Al 2 O 3 ·6H 2 O (C 3 AH 6 ) and Al(OH) 3 (AH 3 ). This reaction increasingly speeds up at a temperature higher than ~30 °C, and over time leads to significant strength loss in CAC concrete. Because of the lack of direct evidence that simultaneously probes morphological and chemical/crystallographic information, intense debate remains whether the conversion is generated by a solid-state or through-solution reaction. The conversion of CAH 10 at an elevated temperature is studied herein using synchrotron-radiation-based X-ray spectromicroscopy capable of acquiring near edge X-ray absorption fine structure data and ptychographic images with a resolution of ~15 nm. We demonstrate that, when stored at 60 °C, CAH 10 first converts to C 2 AH 8 by solid-state decomposition, followed by the through-solution formation of C 3 AH 6 . The C 3 AH 6 crystallizes from both the relics of dissolved C 2 AH 8 and from the surface of existing C 3 AH 6 crystals. The solid-state decomposition of CAH 10 occurs in multiple sites inside the CAH 10 crystals; the spatial range of each decomposition site spans a few tens of nanometers, which overcomes the kinetics barrier of ion transportation in the solid-state. Our work provides the first nanoscale crystal-chemical evidence to explain the microstructure evolution of converted CAC concrete.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A Spectroscopic and Computational Evaluation of Uranyl Oxo Engagement with Transition Metal Cations

Here, we report the synthesis and characterization of five novel Cd 2+ /UO 2 2+ heterometallic complexes that feature Cd-oxo distances ranging from 78 to 171% of the sum of the van der Waals radii for these atoms. This work marks an extension of our previously reported Pb 2+ /UO 2 2+ and Ag + /UO 2 2+ complexes, yet with much more pronounced structural and spectroscopic effects resulting from Cd-oxo interactions. We observe a major shift in the U═O symmetric stretch and significant uranyl bond length asymmetry. The ρbcp values calculated using Quantum Theory of Atoms in Molecules (QTAIM) support the asymmetry displayed in the structural data and indicate a decrease in covalent character in U═O bonds with close Cd-oxo contacts, more so than in related compounds containing Pb 2+ and Ag + . Second-order perturbation theory (SOPT) analysis reveals that O sp x → Cd s is the most significant orbital overlap and U═O bonding and antibonding orbitals also contribute to the interaction (U═O σ/π → Cd d and Cd s → U═O σ/π*). The overall stabilization energies for these interactions were lower than those in previously reported Pb 2+ cations, yet larger than related Ag + compounds. Analysis of the equatorial coordination sphere of the Cd 2+ /UO 2 2+ compounds (along with Pb 2+ /UO 2 2+ complexes) reveals that 7-coordinate uranium favors closer, stronger M n+ -oxo contacts. These results indicate that U═O bond strength tuning is possible with judicious choice of metal cations for oxo interactions and equatorial ligand coordination.

cations↗
DOE OSTI2019

Structural, Chemical, Electrical, and Thermal Properties of n -Type NbFeSb

Here, we report on the structural, chemical, electrical, and thermal properties of n -type polycrystalline NbFeSb synthesized by induction melting of the elements. Although several studies on p -type conduction of this half-Heusler composition have recently been reported, including reports of relatively high thermoelectric properties, very little has been reported on the transport properties of n-type compositions. We combine transport property investigations together with short- and long-range structural data obtained by Mössbauer spectroscopy of iron-57 and antimony-121 and by neutron total scattering, as well as first-principles calculations. In our investigation, we show that n -type conduction can occur from antiphase boundaries in this material. This work is intended to provide a greater understanding of the fundamental properties of NbFeSb as this material continues to be of interest for potential thermoelectric applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Coordination of 2,2'-(Trifluoroazanediyl)bis( N , N '-dimethylacetamide) with U(VI), Nd(III), and Np(V): A Thermodynamic and Structural Study

Thermodynamic properties of the complexation of 2,2'-(trifluoroazanediyl)bis(N,N'-dimethylacetamide) (CF 3 ABDMA) with U(VI), Nd(III), and Np(V) have been studied in 1.0 M NaNO 3 at 25 °C. Equilibrium constants of the complexation were determined by potentiometry and spectrophotometry. In comparison with a series of structurally related amine-bridged diacetamide ligands, including 2,2'-(benzylazanediyl)bis(N,N'-dimethylacetamide) (BnABDMA), 2,2'-azanediylbis(N,N'-dimethylacetamide) (ABDMA), and 2,2'-(methylazanediyl)bis(N,N'-dimethylacetamide) (MABDMA), CF 3 ABDMA forms weaker complexes with U(VI), Nd(III), and Np(V) due to the lower basicity of the center N atom in CF 3 ABDMA resulting from the attachment of the strong electron-withdrawing CF 3 - moiety. The complexation strength of CF 3 ABDMA with the three metal ions follows the order: UO 2 2+ > Nd 3+ > NpO 2 + , consistent with the order of the “effective” charges of the metal ions. Structural information on the U(VI)/CF 3 ABDMA complexes in solution and in solid was obtained by theoretical computation, single crystal X-ray diffractometry, 19 F NMR, and electrospray ionization mass spectrometry. Finally, the structural data indicate that, similar to the three previously studied amine-bridged diacetamide ligands (BnABDMA, ABDMA, and MABDMA), the CF 3 ABDMA ligand coordinates to UO 2 2+ in a tridentate mode, through the center nitrogen and the two amide oxygen atoms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Functional and Structural Studies on the Esperamicin Thioesterase and Progress toward Understanding Enediyne Core Biosynthesis

Enediynes are among the most potent antitumor and antibacterial natural products. Studies on their biosynthetic pathways have identified a shared, linear polyene precursor generated from an iterative type I polyketide synthase (PKSE) as the source of the enediyne warhead. A key step is the release of this polyene from the PKSE by a discrete thioesterase (TE). Here, in this study, we used X-ray crystallography, site-directed mutagenesis, and heterologous coexpression of PKSEs and TEs to elucidate how enediyne TEs mediate the production of the polyene. We solved the structure of wild-type EspE7 from esperamicin producer Actinomodura verrucosospora. The substrate binding pocket was also defined upon serendipitous cocrystallization of an EspE7 mutant with a fatty acyl-CoA ligand. Structural data and in vitro activity assays with EspE7 mutants provide strong evidence that Glu68 in EspE7 and the analogous Glu residue in other enediyne TEs functions as a key catalytic residue, thus supporting a hydrolysis mechanism for enediyne TEs that aligns with that of Pseudomonas sp. 4-HB-CoA TE. Furthermore, combinations of 9- and 10-membered enediyne PKSEs and TEs produced 1,3,5,7,9,11,13-pentadecaheptaene (1) as the major product. Thus, the data further support previous conclusions that 1 serves as the sole precursor for the biosynthesis of all enediyne cores.

Enediynes↗
DOE OSTI2024

Kinetics and Mechanism of the Singlet Oxygen Atom Reaction with Dimethyl Ether

Here, we combine in situ laser spectroscopy, quantum chemistry, and kinetic calculations to study the reaction of a singlet oxygen atom with dimethyl ether. Infrared laser absorption spectroscopy and Faraday rotation spectroscopy are used for the detection and quantification of the reaction products OH, H 2 O, HO 2 , and CH 2 O on submillisecond time scales. Fitting temporal profiles of products with simulations using an in-house reaction mechanism allows product branching to be quantified at 30, 60, and 150 Torr. The experimentally determined product branching agrees well with master equation calculations based on electronic structure data and transition state theory. The calculations demonstrate that the dimethyl peroxide (CH 3 OOCH 3 ) generated via O-insertion into the C–O bond undergoes subsequent dissociation to CH 3 O + CH 3 O through energetically favored reactions without an intrinsic barrier. This O-insertion mechanism can be important for understanding the fate of biofuels leaking into the atmosphere and for plasma-based biofuel processing technologies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Potential Foldamers Based on an ortho- Terphenyl Amino Acid

We describe the synthesis and characterization of a new class of oligomers built from a terphenyl-based amino acid. Here, these oligomeric amides are of interest because the adoption of specific conformations could potentially be driven by the coordinated formation of inter-residue hydrogen bonds and aromatic interactions. Although high-resolution structural data have proven inaccessible, circular dichroism and nuclear magnetic resonance studies suggest that the new oligomers fold concomitantly with discrete self-association in chloroform. Molecular simulations find no sign of folding as a monomer, and in fact suggest that hydrogen bond patterning is anti-cooperative, inhibiting longer helices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗