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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

SharP Data Constructs: Data Constructs to Enable Data-Centric Computing

Extreme-scale applications (i.e., Big-Compute) are becoming increasingly data-intensive, i.e., producing and consuming increasingly large amounts of data. The HPC systems traditionally used for these applications are now used for Big-Data applications such as data analytics, social network analysis, machine learning, and genomics. As a consequence of these trends, the system architecture should be flexible and data-centric. This can already be witnessed in the pre-exascale systems with TBs of on-node hierarchical and heterogeneous memories, PBs of system memory, low-latency, high-throughput networks, and many threaded cores. As such, the pre-exascale systems suit the needs of both Big-Compute and Big-Data applications. Though the system architecture is flexible enough to support both Big-Compute and Big-Data, we argue there is a software gap. Particularly, we need data-centric abstractions to leverage the full potential of the system, i.e., there is a need for native support for data resilience, the ability to express data locality and affinity, mechanisms to reduce data movement, the ability to share data, and abstractions to express User's data usage and data access patterns. In this paper, we (i) show the need for taking a holistic approach towards data-centric abstractions, (ii) show how these approaches were realized in the SHARed data-structure centric Programming abstraction (SharP) library, a data-structure centric programming abstraction, and (iii) apply these approaches to a variety of applications that demonstrate its usefulness. Particularly, we apply these approaches to QMCPack and the Graph500 benchmark and demonstrate the advantages of this approach on extreme-scale systems.

Aderholdt, William Ferrol↗
DOE OSTI2023

ROSE LCOM Tools

This project provides a tool to compute LCOM metrics for important Ada abstraction mechanisms (e.g., packages, protected objects). It analyzes data accesses and routine calls to compute an abstract representation of an Ada package (or some other abstraction). Different LCOM metrics (1-5) are computed from the abstract representation. The project also provides support for representing the abstraction graphically (via graphviz). The LCOM tool requires an existing ROSE installation configured with the GNAT 2019 compiler.

Lamar, KennethM↗
DOE OSTI2021

An Algebra of Machine Learners with Applications

Machine learning (ML) methods are increasingly being applied to solve complex, data-driven problems in diverse areas, by exploiting the physical laws derived from first principles such as thermal hydraulics and the abstract laws developed recently for data and computing infrastructures. These physical and abstract laws encapsulate, typically in compact algebraic forms, the critical knowledge that complements data-driven ML models. We present a unified perspective of these laws and ML methods using an abstract algebra (A;⊕,Ⓧ), wherein the performance estimation and classification tasks are characterized by the additive ⊕ operations, and the diagnosis, reconstruction, and optimization tasks are characterized by the difference Ⓧ operations. This abstraction provides ML codes and their performance characterizations that are transferable across different areas. We describe practical applications of these abstract operations using examples of throughput profile estimation tasks in data transport infrastructures, and power-level and sensor error estimation tasks in nuclear reactor systems.

Rao, Nageswara↗
DOE OSTI2014

Information processing systems, reasoning modules, and reasoning system design methods

Information processing systems, reasoning modules, and reasoning system design methods are described. According to one aspect, an information processing system includes working memory comprising a semantic graph which comprises a plurality of abstractions, wherein the abstractions individually include an individual which is defined according to an ontology and a reasoning system comprising a plurality of reasoning modules which are configured to process different abstractions of the semantic graph, wherein a first of the reasoning modules is configured to process a plurality of abstractions which include individuals of a first classification type of the ontology and a second of the reasoning modules is configured to process a plurality of abstractions which include individuals of a second classification type of the ontology, wherein the first and second classification types are different.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

Information processing systems, reasoning modules, and reasoning system design methods

Information processing systems, reasoning modules, and reasoning system design methods are described. According to one aspect, an information processing system includes working memory comprising a semantic graph which comprises a plurality of abstractions, wherein the abstractions individually include an individual which is defined according to an ontology and a reasoning system comprising a plurality of reasoning modules which are configured to process different abstractions of the semantic graph, wherein a first of the reasoning modules is configured to process a plurality of abstractions which include individuals of a first classification type of the ontology and a second of the reasoning modules is configured to process a plurality of abstractions which include individuals of a second classification type of the ontology, wherein the first and second classification types are different.

96 KNOWLEDGE MANAGEMENT AND PRESERVATION↗
DOE OSTI2016

Information processing systems, reasoning modules, and reasoning system design methods

Information processing systems, reasoning modules, and reasoning system design methods are described. According to one aspect, an information processing system includes working memory comprising a semantic graph which comprises a plurality of abstractions, wherein the abstractions individually include an individual which is defined according to an ontology and a reasoning system comprising a plurality of reasoning modules which are configured to process different abstractions of the semantic graph, wherein a first of the reasoning modules is configured to process a plurality of abstractions which include individuals of a first classification type of the ontology and a second of the reasoning modules is configured to process a plurality of abstractions which include individuals of a second classification type of the ontology, wherein the first and second classification types are different.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2023

Insight into the Radiolytic Degradation Mechanism of TODGA

Partitioning and transmutation schemes, where americium is separated from other components of used nuclear fuel and burned in a fast neutron reactor, offer a path to dramatically decrease the space requirements for storage of nuclear fuel cycle wastes, allowing more efficient usage of potentially scarce storage resources.[1] Improvements in the efficiency of processes for separating americium from used nuclear fuels can thus have a significant impact on the costs of future nuclear fuel cycles. Understanding separation ligand radiation chemistry is important for development of new ligands and processes, as the ligand degradation products can have a deleterious effect on a separation process. Tetraoctyl diglycolamide (TODGA) has been studied as a ligand for lanthanide/minor actinide extraction for partitioning and transmutation schemes. However, the mechanism of initial energy transfer from products of solvent radiolysis to TODGA is still under debate. One proposed mechanism is attack by a n-dodecane radical cation resulting in electron abstraction and formation of a TODGA radical cation,[2] while later work has proposed hydrogen abstraction from sites adjacent to the central ether oxygen by other radical species.[3] The latter mechanism is proposed to result in degradation products from rupture of the ether bond. However, radiolytic degradation of TODGA in n-dodecane shows products that would result from rupture of all the backbone bonds. There is little information on what degradation products would be expected to form from the TODGA radical cation. In this work, we have begun to investigate this by examining the electron impact (EI) ionization mass spectrum of TODGA, which initially produces a TODGA radical cation in the gas phase. The EI spectrum shows fragments that would result from most backbone bond cleavages, similar to what is observed in the radiolysis of TODGA in n-dodecane. As the lifetime of the solvent radical cation decreases from n-dodecane to n-hexane,[4] irradiation of TODGA in n-hexane should have less solvent radical cations available for reaction with TODGA, and instead should favor reactions with longer-lived radicals. In contrast to n-dodecane, radiolytic degradation of TODGA in n-hexane produces only N,N-dioctylacetamide, which would result from rupture of the ether bond. The n-dodecane radical cation lifetime is long enough to produce TODGA radical cations but the n-hexane radical cation is mostly consumed before reaction with TODGA, so other radical processes that abstract hydrogen from TODGA dominate. This suggests that electron abstraction by the n-dodecane radical cation is an important component of TODGA radiolysis, although it does not rule out the presence of mechanisms involving hydrogen abstraction adjacent to the ether oxygen. References [1] J. Serp et al., Energies 2017, 10 (9), DOI: 10.3390/en10091445. [2] C. Zarzana et al., Solvent Extr. Ion Exch. 2015, 33 (5), 431–447, DOI: 10.1080/07366299.2015.1012885. [3] T. Koubský et al., Prog. Nucl. Energy 2017, 94, 208–215, DOI: 10.1016/j.pnucene.2016.07.010. [4] F. Sviridenko et al., Chem. Phys. Lett. 1998, 297 (3), 343–349, DOI: 10.1016/S0009-2614(98)01099-9.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2024

Syntheses of Tungsten Imido Cyclohexylidene Complexes Using Perfluoro‐ t ‐Butanol or Hexafluoro‐ t ‐Butanol as Acids

Abstract The fluorinated alcohols, (CF 3 ) 3 COH (R F9 OH) and (CF 3 ) 2 MeCOH (R F6 OH), react with W(NR) 2 Cy 2 (Cy=Cyclohexyl; R=2,6‐diisopropylphenyl or 1‐adamantyl) in C 6 D 6 at 55 °C to give cyclohexylidene complexes. Traditional routes to terminal alkylidene complexes (neopentylidene or neophylidene) have used either triflic acid or HCl (rarely), but relatively weak fluorinated acids are sufficient and active bisalkoxide catalysts are therefore prepared directly. An α hydrogen abstraction reaction to give a cyclohexylidene complex from a biscyclohexyl complex appears to be as facile as α hydrogen abstraction to give a neopentylidene or neophylidene ligand, but isomerization of a cyclohexene formed through β hydrogen abstraction is also a possibility. The OR F9 ligands can be replaced readily with dimethylpyrrolide (Me 2 Pyr) or other more basic alkoxides. Single crystal X‐ray studies were carried out on W(NAr) 2 Cy 2 , W(NAr)(OR F9 ) 2 (C 6 H 10 )(ArNH 2 ), W(NAr)(OR F6 ) 2 (C 6 H 10 )(ArNH 2 ), W(NAd)(OR F9 ) 2 (C 6 H 10 )(AdNH 2 ), W(NAr)(O‐ i ‐Pr F6 ) 3 Cy, and W(NAd)(η 1 ‐Me 2 Pyr) 2 (C 6 H 10 ) (C 6 H 10 =cyclohexylidene).

Maji, Milan↗
DOE OSTI2017

Assessing anthropogenic impacts on limited water resources under semi-arid conditions: three-dimensional transient regional modelling in Jordan

Both increasing aridity and population growth strongly stress freshwater resources in semi-arid areas such as Jordan. The country’s second largest governorate, Irbid, with over 1 million inhabitants, is already suffering from an annual water deficit of 25 million cubic meters (MCM). The population is expected to double within the next 20 years. Even without the large number of refugees from Syria, the deficit will likely increase to more then 50 MCM per year by 2035 The Governorate’s exclusive resource is groundwater, abstracted by the extensive Al Arab and Kufr Asad well fields. This study presents the first three-dimensional transient regional groundwater flow model of the entire Wadi al Arab to answer important questions regarding the dynamic quality and availability of water within the catchment. Emphasis is given to the calculation and validation of the dynamic groundwater recharge, derived from a multi-proxy approach, including (1) a hydrological model covering a 30-years dataset, (2) groundwater level measurements and (3) information about springs. The model enables evaluation of the impact of abstraction on the flow regime and the groundwater budget of the resource. Sensitivity analyses of controlling parameters indicate that intense abstraction in the southern part of the Wadi al Arab system can result in critical water-level drops of 10 m at a distance of 16 km from the production wells. Moreover, modelling results suggest that observed head fluctuations are strongly controlled by anthropogenic abstraction rather than variable recharge rates due to climate changes.

58 GEOSCIENCES↗
DOE OSTI2019

Approximating Two-Stage Chance-Constrained Programs with Classical Probability Bounds

We consider a joint-chance constraint (JCC) as a union of sets, and approximate this union using bounds from classical probability theory. When these bounds are used in an optimization model constrained by the JCC, we obtain corresponding upper and lower bounds on the optimal objective function value. We compare the strength of these bounds against each other under two different sampling schemes, and observe that a larger correlation between the uncertainties tends to result in more computationally challenging optimization models. We also observe the same set of inequalities to provide the tightest upper and lower bounds in our computational experiments.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

Phthalate exposure and childrens neurodevelopment: A systematic review

Background: Emerging evidence from observational studies suggests that prenatal exposure to phthalates affects neurodevelopment in children. Objective: To conduct a systematic review of the existing literature on the association between urinary phthalate concentrations and children's neurodevelopment. Methods: We searched electronic bibliographic databases (MEDLINE, PubMed, EMBASE, PsycINFO, CINAHL, Global Health, CAB abstracts, and ERIC) (1910 to February 21st, 2014); reference lists of included articles, and conference abstracts (American Psychiatric Association, American Academy of Neurology, and Pediatric Academic Societies). Two independent reviewers screened abstracts and extracted data. We included original studies reporting on the association between prenatal or childhood urinary phthalate metabolites, and cognitive and behavioral outcomes (e.g., IQ scores, BASC-2 scores or equivalent) in children 0–12 years of age. Results: Of 2804 abstracts screened, 11 original articles met our criteria for inclusion. Conclusions: A systematic review of the literature supports the contention that prenatal exposure phthalates is associated with adverse cognitive and behavioral outcomes in children, including lower IQ, and problems with attention, hyperactivity, and poorer social communication. Further research characterizing the associations between specific phthalate metabolites and children's neurodevelopmental outcomes is needed to support the development of mitigation strategies and enhance the development of appropriate health policy. - Highlights: • Prenatal maternal urinary concentrations of phthalate metabolites appear to be associated with adverse cognitive and behavioral outcomes in children. • Both low molecular weight (e.g., monobutyl phthalate, MBP) and high molecular weight (e.g., di(2-ethylhexyl) phthalate, DEHP) phthalate metabolites are associated with adverse cognitive and behavioral outcomes. • Sex-specific effects from phthalate exposure were noted between low (e.g., mono-n-butyl phthalate, MnBP) and high (e.g., DEHP) molecular weight phthalate metabolites, and cognitive and behavioral outcomes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Region templates: Data representation and management for high-throughput image analysis

Compartment fires exhibit unique features associated with smoke accumulation and restricted air ventilation. The objective of the present study is to evaluate the ability of CFD-based fire models to simulate these features and in particular the effects of flame extinction that results from under-ventilated fire conditions. The study is performed using FireFOAM; FireFOAM is an advanced fire modeling software developed by FM Global and is based on a general-purpose open-source software called OpenFOAM. A new flame extinction model based on the concept of a critical value of the flame Damköhler number is incorporated into FireFOAM. The performance of the extinction model is evaluated via comparisons with a previously developed experimental database corresponding to a reduced-scale, heptane-fueled, compartment fire configuration. The numerical simulations also include a description of fuel evaporation driven by the computed gas-to-liquid heat feedback. Comparisons between experimental data and numerical results provide a suitable test bed to evaluate the ability of CFD-based fire models to describe the transition from over- to under-ventilated fire conditions, as well as the transition from extinction-free conditions to conditions in which the flame experiences partial or total quenching.

Energy & Fuels↗
DOE OSTI2020

Effects of isoalcohol blending with gasoline on autoignition behavior in a rapid compression machine: Isopropanol and isobutanol

Alcohols, and particularly isoalcohols, are potentially advantageous blendstocks towards achieving efficient, low-carbon intensity internal combustion engines. Their use in advanced configurations, such as boosted spark-ignition or spark-assisted compression ignition, requires a comprehensive understanding of their blending effects on the low- and intermediate-temperature autoignition behavior of petroleum-derived gasoline. This work reports an experimental and modeling study of such autoignition characteristics quantified in a twin-piston rapid compression machine. Isopropanol and isobutanol are blended into a research-grade gasoline (FACE-F) at oxygenate blend levels of 0 to 30% vol/vol, with tests conducted at pressures of 20 and 40 bar, temperatures from 700 to 1000 K, and dilute stoichiometric fuel loadings. Changes to overall reactivity, including first-stage and main ignition times, and preliminary exothermicity are established, with comparisons made to previous measurements with ethanol-blended FACE-F gasoline. Furthermore, it is found that at low-temperature/NTC conditions (700–860 K) the isoalcohols suppress first-stage reactivity and associated heat release while main ignition times are extended. At NTC/intermediate-temperature (860–1000 K) conditions changes to fuel reactivity are less significant with isopropanol slightly suppressing reactivity and isobutanol promoting ignition. Detailed chemical kinetic modeling is used to interpret the experimental measurements. Overall trends of suppression or promotion in the blending behavior are reasonably captured by the model. Sensitivity and rate of production analyses indicate that at lower temperatures H-atom abstraction reactions from the surrogate fuel molecules (e.g., cyclopentane, isooctane) and the isoalcohols via OH are important leading to TC 3 H 6 OH and IC 4 H 8 OH–C radicals, for isopropanol and isobutanol respectively, which act as scavengers in the system. At higher temperatures, similar chemistries are dominant, but there is an increasing importance of abstraction by HO 2 . The kinetic modeling also indicates that the promoting effect of isobutanol at higher temperatures is due to the increased abstractions at the γ-sites, while at lower temperatures abstraction at the α-site leads to greater reactivity suppression.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Pre-vaporized ignition behavior of ethyl- and propyl-terminated oxymethylene ethers

Oxymethylene ethers (OMEs) have been studied in recent years for use as compression ignition fuel blendstocks, but the methyl-terminated OMEs commonly studied exhibit properties that are poorly optimized for engine use and distribution. Recent work has shown that OMEs with larger (ethyl, propyl, or butyl) end groups may have superior properties for fuel usage/storage. In this work, we consider ignition of four OMEs - diethoxymethane (E-1-E), dipropoxymethane (P-1-P), ethoxy-(methoxy) 2 -ethane (E-2-E), and diisopropoxymethane (iP-1-iP) - as representatives of the possible effects of changes to OME structures. To our knowledge, ignition behaviors of the latter three fuels have not been studied prior to this work. Further, we find that all of the tested linear OMEs (E-1-E, P-1-P, and E-2-E) show two-stage ignition at low temperatures and nonlinear ignition behavior, consistent with literature on methyl-terminated OMEs and E-1-E. The nonlinear, branched OME (iP-1-iP) required higher pressure and temperature to ignite than the linear OMEs; further, this fuel experienced only single stage ignition and a linear ignition delay curve. By analogy to existing kinetic mechanisms for ethers and higher alcohols, the chemical basis for the observed trends are hypothesized. Faster ignition of E-2-E results from the additional oxymethylene group providing additional sites for ROO formation and more possible QOOH structures. Slower low temperature ignition of P-1-P is driven by lower H abstraction rates in comparison to E-1-E, however at high temperatures P-1-P ignites faster, driven by increasing abstraction from the additional H site on the propyl group that opens up additional QOOH formation pathways. iP-1-iP ignition is slowed significantly by preferential H abstraction from the central carbon of the isopropyl group, which is crowded and unlikely to bond with O 2 , however at high temperatures, abstraction from H sites on the methyl groups allows for the ROO cascade initiation and subsequent rapid ignition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

The water trimer reaction OH + (H 2 O) 3 → (H 2 O) 2 OH + H 2 O

All important stationary points on the potential energy surface (PES) for the reaction OH + (H 2 O) 3 → (H 2 O) 2 OH + H 2 O have been fully optimized using the “gold standard” CCSD(T) method with the large Dunning correlation-consistent cc-pVQZ basis sets. Three types of pathways were found. For the pathway without hydrogen abstraction, the barrier height of the transition state (TS1) is predicted to lie 5.9 kcal mol -1 below the reactants. The two major complexes (H 2 O) 3 ∙∙∙OH (CP1 and CP2a) are found to lie 6.3 and 11.0 kcal mol -1 , respectively, below the reactants [OH + (H 2 O) 3 ]. For one of the H-abstraction pathways the lowest classical barrier height is predicted to be much higher, 6.1 kcal mol -1 (TS2a) above the reactants. For the other H-abstraction pathway the barrier height is even higher, 15.0 (TS3) kcal mol -1 . Vibrational frequencies and the zero-point vibrational energies connected to the PES are also reported. Fianlly, the energy barriers for the H-abstraction pathways are compared with those for the OH + (H 2 O) 2 and OH + H 2 O reactions, and the effects of the third water on the energetics are usually minor (0.2 kcal mol -1 ).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗