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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 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Climate change adaptation and EIA in Austria and Germany – Current consideration and potential future entry points

Highlights: • Direct references to climate change resulted in a very low number of hits. • Several thematic entry points for CC impacts into EIA were identified. • Environmental issues most addressed so far in combination with CC stressors are soil, water and forest habitats. • Mitigation and compensation measures could serve as important methodological entry points. • Primarily statements of environmental authorities and the public introduced climate change related topics so far.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Atmospheric plume progression as a function of time and distance from the release point for radioactive isotopes

The International Monitoring System contains up to 80 stations around the world that have aerosol and xenon monitoring systems designed to detect releases of radioactive materials to the atmosphere from nuclear tests. A rule of thumb description of plume concentration and duration versus time and distance from the release point is useful when designing and deploying new sample collection systems. This paper uses plume development from atmospheric transport modeling to provide a power-law rule describing atmospheric dilution factors as a function of distance from the release point.

atmospheric plume progression↗
DOE OSTI2017

A novel in-situ, lift-out, three-point bend technique to quantify the mechanical properties of an ex-service neutron irradiated inconel X-750 component

A first of its kind small scale mechanical testing technique involving micro-three-point bending was invented, developed, and implemented on reactor irradiated, active Inconel X-750 components removed from service after approximately 53 and 67 dpa. These tests were performed at ambient room temperature in-situ using a scanning electron microscope in order to obtain live recordings of sample deformation and loading curves. Sample and testing apparatus preparation required novel lift-out and fabrication processes. Materials from two irradiation temperature regimes, low temperature (120-280 °C) and high temperature (300 ± 15 °C) were examined. Manufacturing and finishing (grinding) of this component create differences between its edge and center, so micro-specimens from both areas were extracted in order to study these differences. According to three-point beam bending theory, a 0.2% offset yield stress parameter is introduced and calculated for all specimens. Differences in mechanical properties due to irradiation temperature and dose effects were observed. Material irradiated at the higher temperature exhibited yield strength increases of ~540 MPa after 53 dpa and ~1000 MPa after 67 dpa. There was little difference (≤310 MPa) in yield strength between materials irradiated at the lower temperature at 53 dpa and 67 dpa compared with non-irradiated material. Differences in yield strengths between the edge and center of the component are retained after irradiation. The difference in yield strengths for the edge and center regions was ~740 MPa for non-irradiated material. After irradiation to a dose of 67 dpa these differences were ~570 MPa for the lower irradiation temperature and ~710 MPa for higher irradiation temperature. There were no indications of grain boundary failures via cracking except for material irradiated to 67 dpa at low temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Phonon modal analysis of thermal transport in ThO 2 with point defects using equilibrium molecular dynamics

Defects can significantly degrade the thermal conductivity of ThO 2 , an advanced nuclear fuel material as well as a surrogate for other fluorite-structured materials. Here, we investigate how point defects in ThO 2 impact phonon mode-resolved thermal transport. By incorporating phonon modes from lattice dynamics, we decompose the trajectory and heat flux to phonon normal mode space and extract key phonon properties, including phonon relaxation times and their contributions to thermal conductivity. We implement two methods. The first method is based on the Green Kubo formalism to resolve the contribution of each phonon mode to thermal conductivity. The second resolves the lifetime of individual phonon modes and the thermal conductivity is calculated using the Boltzmann transport equation within relaxation time approximation. Notably, a lower contribution of acoustic modes is revealed compared to perturbative approaches considering only three-phonon scattering processes. The effects of four types of point defects are evaluated. The strongest impact on a reduction in thermal conductivity is from Th interstitials, followed by Th vacancies. O interstitials/vacancies have a similar impact, albeit smaller than defects on the thorium sublattice. These observations are consistent with previous studies.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2024

Grain boundary self-diffusion and point defect interactions in α -U via molecular dynamics

Though metallic U-Zr fuel has been used in nuclear reactors since the 1960s, many of its fundamental and thermodynamic properties are still unknown. The a-U phase, which has a highly anisotropic crystal structure and physical properties, is present in U-Zr fuel. The character and behavior of a-U grain boundaries will strongly impact fuel thermophysical performance under irradiation. Here, we study the interaction of point defects with grain boundaries, diffusion along grain boundaries, and the predicted diffusional creep behavior of a-U via molecular dynamics. We calculate the segregation energy of vacancies and interstitials to grain boundaries and quantify the biased sink strength of the grain boundaries, and observe that this sink strength is not strongly dependent on the grain boundary orientation. We also find that grain boundary diffusivity is strongly dependent on the grain boundary energy and grain boundary orientation. The presence of point defects within the grain boundary can induce diffusion in grain boundaries with low formation energies and can enhance diffusion in high-energy grain boundaries. We also find that diffusional creep of a-U at prototypical metallic fuel operation conditions is extremely high and could help explain observed metallic fuel swelling behaviors.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Effect of stereotactic dosimetric end points on overall survival for Stage I non–small cell lung cancer: A critical review

Stereotactic body radiation therapy (SBRT) delivers a high biologically effective dose while minimizing toxicities to surrounding tissues. Within the scope of clinical trials and local practice, there are inconsistencies in dosimetrics used to evaluate plan quality. The purpose of this critical review was to determine if dosimetric parameters used in SBRT plans have an effect on local control (LC), overall survival (OS), and toxicities. A database of relevant trials investigating SBRT for patients with early-stage non–small cell lung cancer was compiled, and a table of dosimetric variables used was created. These parameters were compared and contrasted for LC, OS, and toxicities. Dosimetric end points appear to have no effect on OS or LC. Incidences of rib fractures correlate with a lack of dose-volume constraints (DVCs) reported. This review highlights the great disparity present in clinical trials reporting dosimetrics, DVCs, and toxicities for lung SBRT. Further evidence is required before standard DVCs guidelines can be introduced. Dosimetric end points specific to stereotactic treatment planning have been proposed but require further investigation before clinical implementation.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2019

Baryon Clustering at the critical line and near the hypothetical critical point

We study clustering of baryons at the freeze-out point of relativistic heavy-ion collisions, see [E. Shuryak and J.M. Torres-Rincon, arXiv:1805.04444 [hep-ph]]. Using a Walecka-Serot model for the nucleon-nucleon (NN) interaction we analyze how the modified/critical σ mode—responsible for the NN attraction—allows for clustering of nucleons when the system is close to a possible critical point of QCD. We investigate clusters of few nucleons, and also large cluster configurations when the system is long lived. For realistic heavy-ion collisions we study to how extend such clusters can be formed in a finite time, and perform the statistical analysis of cumulants and higher-order moments (skewness and kurtosis) for collisions at the Beam Energy Scan of RHIC. We finally suggest usage of out-of-equilibrium production of light nuclei d, t, He3, He4 and provide estimates for their formation in such collisions due to clustering.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

On extreme points of the diffusion polytope

Here, we consider a class of diffusion problems defined on simple graphs in which the populations at any two vertices may be averaged if they are connected by an edge. The diffusion polytope is the convex hull of the set of population vectors attainable using finite sequences of these operations. A number of physical problems have linear programming solutions taking the diffusion polytope as the feasible region, e.g. the free energy that can be removed from plasma using waves, so there is a need to describe and enumerate its extreme points. We also review known results for the case of the complete graph Kn, and study a variety of problems for the path graph Pn and the cyclic graph Cn. Finall, we describe the different kinds of extreme points that arise, and identify the diffusion polytope in a number of simple cases. In the case of increasing initial populations on Pn the diffusion polytope is topologically an n-dimensional hypercube.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Point cloud-based diffusion models for the Electron-Ion Collider

At high-energy collider experiments, generative models can be used for a wide range of tasks, including fast detector simulations, unfolding, searches of physics beyond the Standard Model, and inference tasks. In particular, it has been demonstrated that score-based diffusion models can generate high-fidelity and accurate samples of jets or collider events. This work expands on previous generative models in three distinct ways. First, our model is trained to generate entire collider events, including all particle species with complete kinematic information. We quantify how well the model learns event-wide constraints such as the conservation of momentum and discrete quantum numbers. We focus on the events at the future Electron-Ion Collider, but we expect that our results can be extended to proton-proton and heavy-ion collisions. Second, previous generative models often relied on image-based techniques. The sparsity of the data can negatively affect the fidelity and sampling time of the model. We address these issues using point clouds and a novel architecture combining edge creation with transformer modules called Point Edge Transformers. Third, we adapt the foundation model OmniLearn, to generate full collider events. This approach may indicate a transition toward adapting and fine-tuning foundation models for downstream tasks instead of training new models from scratch.

Araz, Jack Y. [Stony Brook Univ., NY (United State↗
DOE OSTI2021

POINT: Partially Observable Imitation Network for Traffic Signal Control

Smart traffic signals bring together transportation infrastructure and advance technologies to improve the mobility and efficiency of urban transportation network. Adaptive traffic signal control studies can be categorized into modeling-based approaches and learning-based approaches. In order to take advantages of these two systems, this study developed an offline-online combined Partial Observable Imitation Network for Traffic signal control (POINT). In the offline system, the traffic signal timing optimization problem was formulated as a Mixed Integer Nonlinear Programming (MINLP) given complete traffic information, i.e., second-by-second speeds and locations of all vehicles. Furthermore, the objective of MINLP is to minimize total travel delays considering individual vehicle trajectories under Connected Vehicle (CV) environment. The calculated optimal solutions under various traffic conditions were considered as the ”expert” decisions. In the online system, an imitation neural network model was developed to learn the ”expert” signal plans generated from offline system. Given partial observable traffic conditions in real time, e.g., the aggregate-level of traffic volume, the POINT model can compute the signal timing parameters in the online system. The numerical results demonstrated that the proposed method outperformed other state-of-the-art signal control method under high and unbalanced traffic demand levels in terms of reducing travel delays and queue length.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2025

Pointing stabilization of a 1 Hz high-power laser via machine learning

Abstract High-power lasers are vital for particle acceleration, imaging, fusion and materials processing, requiring precise control and high-energy delivery. Laser plasma accelerators (LPAs) demand laser positional stability at focus to ensure consistent electron beams in applications such as X-ray free-electron lasers and high-energy colliders. Achieving this stability is especially challenging for the low-repetition-rate lasers in current LPAs. We present a machine learning method that predicts and corrects laser pointing instabilities in real-time using a high-frequency pilot beam. By preemptively adjusting a correction mirror, this approach overcomes traditional feedback limits. Demonstrated on the BELLA petawatt laser operating at the terawatt level (30 mJ amplification), our method achieved root mean square pointing stabilization of 0.34 and 0.59 $\unicode{x3bc} \mathrm{rad}$ in the x and y directions, reducing jitter by 65% and 47%, respectively. This is the first successful application of predictive control for shot-to-shot stabilization in low-repetition-rate laser systems, paving the way for full-energy petawatt lasers and transformative advances across science, industry and security.

Amodio, Alessio↗
DOE OSTI2022

Power-transfer and fixed-point analysis of sawtooth simulations of a current-carrying stellarator

Power-transfer and fixed-point analysis of previous NIMROD simulations (Roberds et al. , Phys. Plasmas , vol. 23, issue 9, 2016, 092513) improved the understanding of the effect of 3D (non-axisymmetric equilibrium) magnetic fields on sawtooth oscillations in the Compact Toroidal Hybrid (CTH) experiment. Computing the locations of order-1 fixed points, their Greene's residues, and local values for the rotational transform results in a description of CTH sawteeth consistent with Kadomtsev's model. A power-transfer analysis quantifies the distribution of energy among toroidal Fourier modes and their nonlinear interactions. The Lorentz power transfer drives sawtooth growth, and it is unambiguously interpreted as the flow of energy from toroidal mode $n'$ to mode $n$ , catalysed by $\boldsymbol {B}_{n-n'}$ . It has been reported previously that the CTH sawtooth frequency increases with the 3D field strength. This is attributed to an increased growth rate of the internal kink that drives sawtooth oscillations. Here, 3D fields remove energy from the kink, eliminating the possibility that these fields are an additional energy source that drives growth. Instead, 3D fields catalyse energy transfer from large-to-small scales, where magnetic reconnection is stronger. It is proposed that this energy transfer increases the reconnection rate at small scales, which is consistent with the increased growth rate observed at higher 3D field strengths.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Role of Point Defects in Spinel Mg Chalcogenide Conductors

Close-packed chalcogenide spinels, such as MgSc2Se 4 , MgIn2S 4 , and MgSc2S 4 , show potential as solid electrolytes in Mg batteries, but are affected by non-negligible electronic conductivity, which contributes to self-discharge when used in an electrochemical storage device. Using first-principles calculations, we evaluate the energy of point defects as a function of synthesis conditions and Fermi level to identify the origins of the undesired electronic conductivity. Our results suggest that Mg-vacancies and Mg-metal antisites (where Mg is exchanged with Sc or In) are the dominant point defects that can occur in the systems under consideration. While we find anion-excess conditions and slow cooling to likely create conditions for low electronic conductivity, the spinels are likely to exhibit significant n-type conductivity under anion-poor environments, which are often present during high-temperature synthesis. Finally, we explore extrinsic aliovalent doping to potentially mitigate the electronic conductivity in these chalcogenide spinels. Furthermore, the computational strategy is general and can be easily extended to other solid electrolytes (and electrodes) to aid the optimization of the electronic properties of the corresponding frameworks.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Point Defects and Grain Boundaries in Rotationally Commensurate MoS 2 on Epitaxial Graphene

With reduced degrees of freedom, structural defects are expected to play a greater role in two-dimensional materials in comparison to their bulk counterparts. In particular, mechanical strength, electronic properties, and chemical reactivity are strongly affected by crystal imperfections in the atomically thin limit. Here, ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) and spectroscopy (STS) are employed to interrogate point and line defects in monolayer MoS 2 grown on epitaxial graphene (EG) at the atomic scale. Five types of point defects are observed with the majority species showing apparent structures that are consistent with vacancy and interstitial models. The total defect density is observed to be lower than MoS 2 grown on other substrates and is likely attributed to the van der Waals epitaxy of MoS 2 on EG. Grain boundaries (GBs) with 30° and 60° tilt angles resulting from the rotational commensurability of MoS 2 on EG are more easily resolved by STM than atomic force microscopy at similar scales due to the enhanced contrast from their distinct electronic states. For example, band gap reduction to ~0.8 and ~0.5 eV is observed with STS for 30° and 60° GBs, respectively. In addition, atomic resolution STM images of these GBs are found to agree well with proposed structure models. In conclusion, this work offers quantitative insight into the structure and properties of common defects in MoS 2 and suggests pathways for tailoring the performance of MoS 2 /graphene heterostructures via defect engineering.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Oxygen Point Defect Chemistry in Ruddlesden–Popper Oxides (La 1- x Sr x ) 2 MO 4±δ (M = Co, Ni, Cu)

Here, stability of oxygen point defects in Ruddlesden–Popper oxides (La 1- x Sr x ) 2 MO 4±δ (M = Co, Ni, Cu) is studied with density functional theory calculations to determine their stable sites, charge states, and energetics as functions of Sr content ( x ), transition metal (M), and defect concentration (δ). We demonstrate that the dominant O point defects can change between oxide interstitials, peroxide interstitials, and vacancies. In general, increasing x and atomic number of M stabilizes peroxide over oxide interstitials as well as vacancies over both peroxide and oxide interstitials; increasing δ destabilizes both oxide interstitials and vacancies but barely affects peroxide interstitials. We also demonstrate that the O 2p-band center is a powerful descriptor for these materials and correlates linearly with the formation energy of all defects. The trends of formation energy versus x , M, and δ and the correlation with O 2p-band center are explained in terms of oxidation chemistry and electronic structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Effects of Side Chain Branch Point on Self Assembly, Structure, and Electronic Properties of High Mobility Semiconducting Polymers

Semiconducting polymers exhibiting lyotropic liquid-crystalline (LC) mesophases allow for precise control over crystallinity and crystallite orientation using scalable equilibrium processing techniques. The ability to control morphologies from molecular to macroscopic scales is desirable for optimizing polymer electronic devices such as field-effect transistors. LC mesophases can form in semiconducting polymers with branched side chains, but steric repulsion from the side chain structure increases π-stacking distances. This change in unit cell negatively impacts electronic transport, negating any improvements gained by achieving more favorable mesostructures. Herein, we show that the π-stacking distance in cyclopentadithiophene-benzothiadiazole donor–acceptor copolymers is successively shortened by moving the branch point further away from the conjugated backbone. These materials retain their favorable LC properties, and the change in unit cell is accompanied by a monotonic increase in charge carrier mobility in field effect transistors. Mobility values span from ~10 –4 to 0.41 cm2 V –1 s –1 , reaching their highest value when the branch point is furthest from the polymer backbone. Additionally, these LC materials can be aligned across large length scales on rubbed polyimide, resulting in an improvement of charge carrier mobility by a factor of 56 when comparing transistors fabricated parallel and perpendicular to the alignment direction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Optimizing Blue Persistent Luminescence in (Sr 1-δ Ba δ ) 2 MgSi 2 O 7: Eu 2+ ,Dy 3+ via Solid Solution for Use in Point-of-Care Diagnostics

Inorganic persistent luminescent phosphors are an excellent class of optical reporters for enabling sensitive point-of-care diagnostics, particularly with smartphone-based biosensing devices in testing formats such as the lateral flow assay (LFA). Here, the development of persistent phosphors for this application is focused on the solid solution (Sr 1-δ Ba δ ) 2 MgSi 2 O 7 :Eu 2 +,Dy 3+ (δ = 0, 0.125, 0.25, 0.375), which is prepared using a high-temperature solid-state reaction as confirmed by synchrotron X-ray powder diffraction. The substitution of barium for strontium enables control over the Eu 2+ 5d-orbital crystal field splitting (CFS) as a tool for tuning the emission wavelength while maintaining luminescence lifetimes >9 min across the composition range. Thermoluminescence measurements of the solid solution provide evidence that trap states contribute to the persistent lifetimes with the trap depths also remaining constant as a function of composition. Time-gated luminescence images of these compounds are captured on a smartphone arranged in a layout to mimic a point-of-care test and demonstrate the viability of using these materials as optical reporters. Moreover, comparing the blue-emitting (Sr 0.625 Ba 0.375 ) 2 MgSi 2 O 7 :Eu 2+ ,Dy 3+ and the green-emitting SrAl 2 O 4: Eu 2+ ,Dy 3+ in a single LFA-type format shows these two compounds can be detected and resolved simultaneously, thereby permitting the development of a multiplexed LFA.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Liquid-Vapor Coexistence and Critical Point of Mg 2 SiO 4 From Ab Initio Simulations

Hypervelocity impact-driven vaporization is characteristic of late-stage planet formation. Yet the behavior and properties of liquid-vapor mixtures of planetary materials of interest are typically unknown. Multiphase equations of state used in hydrodynamic simulations of planet impacts therefore lack reliable data for this important phenomenon. Here, we present the first constraints on the liquid-vapor critical point and coexistence phase boundary of Mg2SiO4 computed from ab initio molecular dynamics simulations. We found that the vapor is depleted in magnesium and enriched in silica and oxygen, while the coexisting liquid is enriched in magnesium and depleted in oxygen, from which we infer vaporization is incongruent. The critical point was estimated from an equation of state fit to the data. The results are in line with recent calculations of MgSiO3 and together confirm that extant multiphase equation of state (EOS) models used in planetary accretion modeling significantly underestimate the amount of supercritical material postimpact.

58 GEOSCIENCES↗