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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Examination of nucleon distribution with Bayesian imaging for isobar collisions

Relativistic collision of isobaric systems is found to be valuable in differentiating the nucleon distributions for nuclei with the same mass number. In recent contrast experiment of $^{96}_{44}$Ru + $^{96}_{44}$Ru versus $^{96}_{40}$Zr + $^{96}_{40}$Zr collisions at $\sqrt{s_{NN}}$ = 200 GeV, the ratios of multiplicity distribution, elliptic flow, triangular flow, and radial flow are precisely measured and found to be significantly different from unity, indicating the difference in the shapes of the isobar pair. Here, in this work, we investigate the feasibility of nuclear structure reconstruction from heavy-ion collision observables. We perform Bayesian Inference with employing the Monte-Carlo Glauber model as an estimator of the mapping from nuclear structure to the final state observables and to provide the mock data for reconstruction. By varying combination of observables included in the mock data, we find it plausible to infer Woods–Saxon parameters from the observables. We also observe that single-system multiplicity distribution for the isobar system, rather than their ratio, is crucial to simultaneously determine the nuclear structure for the isobar system.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Examination of decay heat measurements and their relevance for understanding the origin of the reactor antineutrino anomaly

Measurements of the decay energy released as a function of time following the thermal neutron induced fission of 235 U and 239,241 Pu were performed in the 1970s at Oak Ridge National Laboratory with the purpose of quantifying possible loss of coolant accident scenarios. The derivative of this decay energy with respect to time, known in technical parlance as decay heat, is mainly composed of two terms, that of the electrons produced together with antineutrinos in the $β$-minus decay of the neutron-rich fission products, and that of the $γ$ rays produced in the subsequent decay of excited nuclear levels. In this work we study if this extensive set of decay energy measurements can be used to assess the reactor antineutrino anomaly, that is, the approximately 5% deficit of electron antineutrinos produced by nuclear reactors, first deduced by Mention and collaborators in 2011, and observed by the major reactor antineutrino experiments since. Furthermore, with the assistance of nuclear databases, we are able to obtain the ratio of electron spectra under equilibrium conditions for 235 U to 239 Pu, in better agreement with the lower trend recently reported by Kopeikin and collaborators, as well as those for 235 U to 241 Pu and 241 Pu to 239 Pu, which do not agree well with those measured at the Institut Laue-Langevin in the 1980s. We conclude that a new experimental campaign is needed to measure the electron spectra utilizing a high resolution and signal-to-noise-ratio electron spectrometer and a highly precise fission normalization procedure.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Examining the justification for the introduction of a fermion localization function

Becke and Edgecombe suggested in 1990 a theoretical tool to describe electron localization in atoms and molecules, an idea which was borrowed by a large number of nuclear theorists since 2011 to describe nucleon localization in nuclear systems. I argue here that these arguments are highly questionable and cannot be used in interacting systems where effects beyond the naive mean field or the simple Hartree-Fock framework are important and the inclusion of correlations induced by particle interactions is necessary in order to introduce such a localization function. Furthermore, I also describe several aspects of the exchange and irreducible two-body density matrices, which depend on the character and strength of the two-particle interaction and which can be useful in justifying the derivation of an appropriate energy density functional.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Examining the possibility that normal nuclear matter is quarkyonic

The possibility that nuclear matter might be quarkyonic is considered. Quarkyonic matter is high baryon density matter that is confined but can be approximately thought of as a filled Fermi sea of quarks surrounded by a shell of nucleons. Here, nuclear matter is described by the IdylliQ sigma model for quarkyonic matter, generalizing the noninteracting IdylliQ model [Y. Fujimoto et al., Phys. Rev. Lett. 132, 112701 (2024)] to include interactions with a σ meson and a pion. When such interactions are included, we find that isospin-symmetric nuclear matter binds with acceptable values of the compressibility and other parameters for nuclear matter at saturation. The energy per nucleon and sound velocity of such matter is computed, and the isospin dependence is determined. Nuclear matter is formed at a density close to but slightly above the density at which quarkyonic matter forms. Quarkyonic matter predicts a strong depletion of nucleons in normal nuclear matter at low momentum. Finally, such a depletion for nucleon momenta k ≲ 120 MeV is shown to be consistent with electron scattering data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Complex Structure of Molten FLiBe (2 Li F – Be F 2 ) Examined by Experimental Neutron Scattering, X-Ray Scattering, and Deep-Neural-Network Based Molecular Dynamics

The use of molten salts as coolants, fuels, and tritium breeding blankets in the next generation of fission and fusion nuclear reactors benefits from furthering the characterization of the molecular structure of molten halide salts, paving the way to predictive capability of the chemical and thermophysical properties of molten salts. Due to its neutronic, chemical, and thermochemical properties, 2 Li F - Be F 2 is a candidate molten salt for several fusion- and fission-reactor designs. We performed neutron and x-ray total-scattering measurements to determine the atomic structure of liquid 2 Li F - Be F 2 . We also performed and neural-network molecular-dynamics simulations to predict the structure obtained by neutron- and x-ray-diffraction experiments. The use of machine learning provides improvements to the efficiency in predicting the structure at a longer length scales than is achievable with simulations at significantly lower computational expense while retaining near accuracy. We found that the NNMD simulations accurately predicted the Be F 4 2 − oligomer formations seen in the experimental first-structure-factor peak. Our combination of high-resolution measurements with large-scale molecular dynamics provided an avenue to explore and experimentally verify the intermediate-range ordering beyond the first-nearest neighbor that has posed too many experimental and computational challenges in previous works. With a deeper understanding of the salt structure and ion ordering, the evolution of salt chemistry over the lifetime of a reactor can be better predicted, which is crucial to the licensing and operation of advanced fission and fusion reactors that employ molten salts. To this end, this work will serve as a reference for future studies of salt structure and macroscopic properties with and without the addition of solutes. Published by the American Physical Society 2024

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Examining the Performance of Walsh-DSSS Against FBMC-SS in HF Channels

Abstract—Filter bank multicarrier spread spectrum (FBMCSS) has proven to be a robust and reliable waveform choice for communication over high frequency (HF) skywave links. However, the performance of this waveform has yet to be contextualized against typical robust HF waveforms, such as the Walsh-encoded waveform detailed in the MIL-STD-188-110D, Appendix D document. In this paper, we first outline the advantages of both the Walsh and FBMC-SS waveforms as well as present their developments. Simulation results are then presented for ideal, simulated HF, and HF with interference channel conditions. Lastly, skywave-HF results are presented for these two waveforms both with and without interference.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2023

Examining the Feasibility of Modeling the Inner Current Loop of a Grid-Following Inverter in the Phasor-Based Solver

Historically, when modeling a grid-following (GFL) inverter in the phasor domain, the fast inner current loop is typically ignored. To achieve a more accurate modeling, the authors have attempted to model the inner current loop in the phasor domain, but experienced significant numerical stability issues. This paper conducts a detailed analysis and provides insight into the feasibility of modeling the inner current loop of a GFL inverter in the phasor domain. It points out that: a) because of the neglection of the inverter filter dynamic, the bandwidth of the inner current loop becomes infinite with typical parameters in the phasor domain, resulting in an inaccurate representation of the actual inner current loop, whose bandwidth is typically between 600 Hz to 2 kHz, and b) the relatively large simulation time step in the phasor simulation causes numerical stability issues when simulating such an inner current loop with an infinite bandwidth. Detailed electromagnetic (EMT) and phasor modeling, and frequency response analysis are performed to explain this phenomenon. The findings of this paper explain why it is inappropriate to model the fast current loop of a GFL inverter in the phasor domain.

Mohiuddin, Sheik Mohammad↗
DOE OSTI2021

Examination of Humidity and Ice Supersaturation Profiles Over West Antarctica Using Ground-Based G-Band Radiometer Retrievals

Humidity profiles retrieved from a ground-based millimeter-wave radiometer located at McMurdo Station, Antarctica and the West Antarctica Ice Sheet Divide are presented and their suitability to study the humidity of the polar climate is assessed. The dry conditions of the Antarctic winter and spring are ideal for ground-based millimeter-wave measurements and the retrievals appear to realistically reproduce the spatial and temporal variability of humidity at both sites. Furthermore, the radiometer has the ability to capture daily variability of very low humidity (0.5 to 4 g/kg) in the low-to-mid troposphere with an uncertainty of 10-20% during the Antarctic winter, spring, and summer. Despite the coarse vertical resolution (200-600 m in the first 4 km), the retrievals provide additional information with respect to the European Centre for Medium Range Weather Forecasts (ECMWF) profiles used as background information. The radiometer is also able to realistically identify the location and frequency of supersaturated layers with respect to ice in the mid troposphere. The occurrence of supersaturated layers is correlated with the occurrence of ice clouds identified by a cloud mask. Overall, results show that ground-based microwave and millimeter-wave radiometry is a viable complement to satellite observations to provide continuous information on the thermodynamic state of the low-to-mid troposphere at high latitudes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Examining the Economic Optimality of Automatic Generation Control

The automatic generation control (AGC) system is temporally situated between economic dispatch and synchronous generator dynamics, and its primary role is to regulate frequency within and tie-line flows between control areas. Given appropriate choice of participation factors (feed-forward controller gains that govern the disaggregation of the area-level power requirement to individual generators), the AGC can be engineered to nudge system dynamics toward a steady-state operating point corresponding to economic optimality. This paper establishes necessary and sufficient conditions under which a widely accepted choice of participation factors guarantees the alignment of steady-state synchronous generator outputs with a global minimum of a prototypical economic dispatch problem. In so doing, it resolves several ambiguities and formalizes technical assumptions governing the role of the standard AGC architecture in the context of economic dispatch and steady-state operation. Numerical case studies tailored to a modified version of the New England 39-bus 10-machine test system validate the theoretical results.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2022

A re-examination of the mechanism of whiting events: A new role for diatoms in Fayetteville Green Lake (New York, USA)

Whiting events—the episodic precipitation of fine-grained suspended calcium carbonates in the water column—have been documented across a variety of marine and lacustrine environments. Whitings likely are a major source of carbonate muds, a constituent of limestones, and important archives for geochemical proxies of Earth history. While several biological and physical mechanisms have been proposed to explain the onset of these precipitation events, no consensus has been reached thus far. Fayetteville Green Lake (New York, USA) is a meromictic lake that experiences annual whitings. Materials suspended in the water column collected through the whiting season were characterized using scanning electron microscopy and scanning transmission X-ray microscopy. Whitings in Fayetteville Green Lake are initiated in the spring within the top few meters of the water column, by precipitation of fine amorphous calcium carbonate (ACC) phases nucleating on microbial cells, as well as on abundant extracellular polymeric substances (EPS) frequently associated with centric diatoms. Whiting particles found in the summer consist of 5–7 μm calcite grains forming aggregates with diatoms and EPS. Simple calculations demonstrate that calcite particles continuously grow over several days, then sink quickly through the water column. In the late summer, partial calcium carbonate dissolution is observed deeper in the water column. Settling whiting particles, however, reach the bottom of the lake, where they form a major constituent of the sediment, along with diatom frustules. The role of diatoms and associated EPS acting as nucleation surfaces for calcium carbonates is described for the first time here as a potential mechanism participating in whitings at Fayetteville Green Lake. This mechanism may have been largely overlooked in other whiting events in modern and ancient environments.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Microstructural examination of interactions between chromia-based refractory and nuclear glass in a melter

This study shows the effects of nuclear waste glass production on Monofrax K-3 refractory corrosion. A continuously fed research-scale melter containing an Fe- and Ni-rich simulated nuclear waste feed with borosilicate glass-forming chemicals was cyclically melted at 1150°C and idled at 1050°C for a total of 11 weeks. Chemical maps using scanning electron microscopy show the interactions between the quenched melt and the refractory. Nanoscale X-ray-computed tomography was used for a three-dimensional visualization of certain parts of the interface. Unreacted K-3 consists of primarily corundum (Al,Cr) 2 O 3 and spinel (Fe 2+ ,Mg)(Al,Cr) 2 O 4 interlocking crystalline phases. Some of the Cr from the refractory interacts with the Ni and Fe from the melt to form a reaction layer comprising (Ni,Fe 2+ )(Cr,Fe 3+ ) 2 O 4 spinel crystals. Simultaneously, melt components (Na,Si) infiltrate into the refractory. This interaction proceeds at the expense of the integrity of the refractory structure. Intact refractory grains (e.g., (Al,Cr) 2 O 3 ) as well as the reaction layer itself can lose mechanical integrity and spall off into the melt, especially near the top of the melter. As the reaction layer can be a protective boundary for the refractory against further melt infiltration, a reduction in the reaction layer thickness allows an increase in refractory corrosion.

36 MATERIALS SCIENCE↗
DOE OSTI2024

An examination of the performance of molecular dynamics force fields: Silicon and silicon dioxide reactive ion etching

Classical molecular dynamics (MD) simulations of plasma-surface interactions were performed of physical sputtering and reactive ion etching (RIE), with predictions based on several force fields. In this paper, we focus mainly on SiO 2 but include some results for Si substrates as well. Here, we compare predictions from these MD simulations to experimental studies of SiO 2 physical sputtering (by Ar + ions), RIE of Si, and RIE of SiO 2 (both using F atoms and Ar + ions). MD results using different published force fields are compared to reported yields from published vacuum beam experiments. The near-surface depth profiles predicted using different force fields are compared. One motivation for the present study is to document the nature and magnitude of differences in the predictions for selected systems and conditions of practical interest.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Examining metastatic behavior within 3D bioprinted vasculature for the validation of a 3D computational flow model

Understanding the dynamics of circulating tumor cell (CTC) behavior within the vasculature has remained an elusive goal in cancer biology. To elucidate the contribution of hydrodynamics in determining sites of CTC vascular colonization, the physical forces affecting these cells must be evaluated in a highly controlled manner. To this end, we have bioprinted endothelialized vascular beds and perfused these constructs with metastatic mammary gland cells under physiological flow rates. By pairing these in vitro devices with an advanced computational flow model, we found that the bioprinted analog was readily capable of evaluating the accuracy and integrated complexity of a computational flow model, while also highlighting the discrete contribution of hydrodynamics in vascular colonization. This intersection of these two technologies, bioprinting and computational simulation, is a key demonstration in the establishment of an experimentation pipeline for the understanding of complex biophysical events.

42 ENGINEERING↗
DOE OSTI2020

A CRISPRi-dCas9 System for Archaea and Its Use To Examine Gene Function during Nitrogen Fixation by Methanosarcina acetivorans

CRISPR-based systems are emerging as the premier method to manipulate many cellular processes. In this study, a simple and efficient CRISPR interference (CRISPRi) system for targeted gene repression in archaea was developed. The Methanosarcina acetivorans CRISPR-Cas9 system was repurposed by replacing Cas9 with the catalytically dead Cas9 (dCas9) to generate a CRISPRi-dCas9 system for targeted gene repression. To test the utility of the system, genes involved in nitrogen (N2) fixation were targeted for dCas9-mediated repression. First, the nif operon (nifHI 1 I 2 DKEN) that encodes molybdenum nitrogenase was targeted by separate guide RNAs (gRNAs), one targeting the promoter and the other targeting nifD. Remarkably, growth of M. acetivorans with N 2 was abolished by dCas9-mediated repression of the nif operon with each gRNA. The abundance of nif transcripts was >90% reduced in both strains expressing the gRNAs, and NifD was not detected in cell lysate. Next, we targeted NifB, which is required for nitrogenase cofactor biogenesis. Expression of a gRNA targeting the coding sequence of NifB decreased nifB transcript abundance >85% and impaired but did not abolish growth of M. acetivorans with N2. Finally, to ascertain the ability to study gene regulation using CRISPRi-dCas9, nrpR1, encoding a subunit of the repressor of the nif operon, was targeted. The nrpR1 repression strain grew normally with N2 but had increased nif operon transcript abundance, consistent with NrpR1 acting as a repressor. Furthermore, these results highlight the utility of the system, whereby a single gRNA when expressed with dCas9 can block transcription of targeted genes and operons in M. acetivorans.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2026

Transcriptomic data sets examining several stress responses in Zymomonas mobilis strains

We used RNA-seq to compare gene expression from Zymomonas mobilis ZM4 grown under various conditions: aerobic ± paraquat, anaerobic ± hydrogen peroxide, or an iron chelator. We analyzed two mutant strains lacking predicted transcription factors (ZMO_0442 and ZMO_1411) grown under aerobic or anaerobic conditions. We report the RNA-seq data from these experiments.

Bacterial Stress Response↗