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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 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Visible-light-driven ZnFe{sub 2}O{sub 4}/Ag/Ag{sub 3}VO{sub 4} photocatalysts with enhanced photocatalytic activity under visible light irradiation

Highlights: • The ZnFe2O4/Ag/Ag3VO4 composites were successfully synthesized by a hydrothermal method. • ZnFe2O4/Ag/Ag3VO4 composites showed better photocatalytic activity for MO and TC degradation under visible light. • The ZnFe2O4/Ag/Ag3VO4 photocatalyst is promising for designing an environmental purification material. - Abstract: A novel visible-light driven ZnFe{sub 2}O{sub 4}/Ag/Ag{sub 3}VO{sub 4} photocatalyst was successfully fabricated through a two-step hydrothermal method. The structure, morphology and composition of the samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray photo-electron spectroscopy (XPS). The as-prepared ZnFe{sub 2}O{sub 4}/Ag/Ag{sub 3}VO{sub 4} composites possessed an excellent performance in the photocatalytic degradation of methyl orange and tetracycline under visible-light irradiation. The results of electrochemical impedance spectroscopy (EIS) indicated that the ZnFe{sub 2}O{sub 4}/Ag/Ag{sub 3}VO{sub 4} composite could facilitate the separation of photo-generated carriers, as well as accelerated charge transfer. The 5% ZnFe{sub 2}O{sub 4}/Ag/Ag{sub 3}VO{sub 4} composite exhibited the upmost photocatalytic activity, the degradation constant of 5% ZnFe{sub 2}O{sub 4}/Ag/Ag{sub 3}VO{sub 4} is as high as 1.49 times to that of Ag/Ag{sub 3}VO{sub 4}. Also, according to the trapping experiments, it’s found that the superoxide radicals (·O{sub 2}{sup −}) and hole (h{sup +}) were the predominant reactive species in this system. The ZnFe{sub 2}O{sub 4}/Ag/Ag{sub 3}VO{sub 4} photocatalyst is promising for designing as an environmental purification material in treatment of antibiotic pollutant.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Ti3+-TiO2/Ce3+-CeO2 Nanosheet heterojunctions as efficient visible-light-driven photocatalysts

Highlights: • A novel Ti{sup 3+}-TiO{sub 2}/Ce{sup 3+}-CeO{sub 2} nanosheet heterojunction is fabricated. • It owns the bandgap of 2.6 eV and extends the photoresponse to visible light region. • It exhibits excellent visible-light-driven photocatalytic performance. • It is due to synergy of Ti{sup 3+}, Ce{sup 3+} co-doping and nanosheet heterojunction. - Abstract: Novel Ti{sup 3+}-TiO{sub 2}/Ce{sup 3+}-CeO{sub 2} nanosheet heterojunctions are successfully prepared via a facile hydrothermal approach combined with a wet-chemical deposition precipitation and an in situ solid-state chemical reduction strategy. The structures of the as-prepared samples are characterized in detail by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and UV–vis diffuse reflectance spectroscopy. The results show that Ti{sup 3+} and Ce{sup 3+} are both doped into the lattice of TiO{sub 2} and CeO{sub 2}, respectively, which narrow the band gap to 2.7 eV and extend the photoresponse to visible light region. The photocatalytic degradation rate of methyl orange and methylene blue are as high as 93.3% and 97.1% under visible-light illumination, respectively. The high degradation rate is attributed to the efficient doping of Ti{sup 3+} and Ce{sup 3+}, formation of surface oxygen vacancy and heterojunction, which favors the absorption of visible light and separation of photogenerated charge carriers.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

An in situ annealing route to [Bi6O6(OH)2](NO3)4·2H2O/g-C3N4 heterojunction and its visible-light-driven photocatalytic performance

Highlights: • The heterojunction (BBN-g-C{sub 3}N{sub 4}) was synthesized by in situ calcination route. • The baked Bi(NO{sub 3}){sub 3}·5H{sub 2}O as raw material is crucial to obtain highly crystalline BBN-g-C{sub 3}N{sub 4}. • BBN-g-C{sub 3}N{sub 4} exhibited better visible-light-driven photocatalytic activity than Bi{sub 2}O{sub 3}-g-C{sub 3}N{sub 4}. • BBN-g-C{sub 3}N{sub 4} prepared by calcining route possessed better photocatalytic activity than by mechanical mixing method. - Abstract: Known as incomplete hydrolysis products of Bi(NO{sub 3}){sub 3}·5H{sub 2}O, basic bismuth nitrates (BBN), were commonly obtained via a solution route. Herein, BBN-CN ([Bi{sub 6}O{sub 6}(OH){sub 2}](NO{sub 3}){sub 4}·2H{sub 2}O/g-C{sub 3}N{sub 4}) and Bi{sub 2}O{sub 3}-g-C{sub 3}N{sub 4} heterojunctions were prepared in situ by mixing g-C{sub 3}N{sub 4} with baked Bi(NO{sub 3}){sub 3}·5H{sub 2}O and subsequent calcining at 250 °C and 550 °C, respectively. The baked Bi(NO{sub 3}){sub 3}·5H{sub 2}O as a bismuth source was crucial to the formation of highly crystalline BBN, and otherwise, the product was poor-crystalline and low photoactive. The as-prepared BBN-CN exhibited better photocatalytic activity for rhodamine B (RhB) degradation under visible light irradiation than BBN, g-C{sub 3}N{sub 4}, and Bi{sub 2}O{sub 3}-g-C{sub 3}N{sub 4}, although Bi{sub 2}O{sub 3} is more visible-light-active. These could be attributed to higher surface areas and more negative conduction band potentials of BBN, which benefits for capturing the photogenerated electrons to form active O{sub 2}{sup −} radicals. Furthermore, the presence of g-C{sub 3}N{sub 4} plays a crucial role in enlarging visible light response.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Plasmonic Ag/Ag2O nanoparticles anchored needle-like Bi2O3 as an efficient visible-light-driven nanocomposite photocatalyst

Highlights: • Deposition of plasmonic Ag/Ag{sub 2}O NPs on the surface of Bi{sub 2}O{sub 3}. • Synthesis of Ag/Ag{sub 2}O@Bi{sub 2}O{sub 3} by thermal-assisted precipitation. • SPR of Ag enhances use of solar energy and transfer of carriers. • Degradation of Reactive Black 5 by CCD model. - Abstract: In this study, a thermal-assisted precipitation method was applied for the uniform deposition of plasmonic Ag/Ag{sub 2}O nanoparticles on the surface of needle-like Bi{sub 2}O{sub 3} to synthesis Ag/Ag{sub 2}O@Bi{sub 2}O{sub 3} nanocomposite. The synthesized nanocomposite was characterized by different techniques including UV–vis spectrophotometry, X-ray diffraction (XRD), scanning electronic microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray mapping, and photoluminescence (PL). The visible-light-driven photocatalytic activities of Ag{sub 2}O@Bi{sub 2}O{sub 3} and Ag/Ag{sub 2}O@Bi{sub 2}O{sub 3} were evaluated on photo-degradation of Reactive Black 5 (RB 5) dye as model pollutant. The effect of process variables including the initial dye concentration, reaction time, and pH on the photo-degradation of RB 5 was studied by Central Composite Design (CCD) methodology. It was found that the photo-degradation rate of Ag/Ag{sub 2}O@Bi{sub 2}O{sub 3} was higher than that of the Ag{sub 2}O@Bi{sub 2}O{sub 3} and Bi{sub 2}O{sub 3}. The highly efficient photocatalytic activity of Ag/Ag{sub 2}O@Bi{sub 2}O{sub 3} nanocomposite is mainly ascribed to enhancing photogenerated electron-hole separation and the surface plasmon resonance (SPR) influence of silver-based nanoparticles.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

CdS quantum dots/Ti3+-TiO2 nanobelts heterojunctions as efficient visible-light-driven photocatalysts

Highlights: • A novel CdS QDs/Ti{sup 3+}-TiO{sub 2} nanobelts heterojunction photocatalyst is prepared. • It narrows the bandgap and extends the photoresponse to visible light region. • It exhibits excellent visible-light-driven photocatalytic performance. • It is due to synergistic effect of CdS QDs, Ti{sup 3+} self-doping and heterojunction. - Abstract: CdS quantum dots (QDs)/Ti{sup 3+}-TiO{sub 2} nanobelts heterojunctions as 0D/1D architectures are fabricated through hydrothermal-chemical bath deposition combine with in-situ solid-state chemical reduction approach. The CdS QDs of ∼7 nm are loaded on TiO{sub 2} nanobelts with width of 50–300 nm and several micrometers long, and the heterojunctions are formed efficiently. The prepared heterojunctions exhibit excellent photocatalytic performance for complete removal of methylene blue (∼99%) and hydrogen production efficiency (∼480.6 μmol h{sup −1}) under visible light irradiation, which are as high as 2 and 23 times than that of pristine TiO{sub 2} nanobelts. The enhancement is attributed to the Ti{sup 3+} self-doping and CdS QDs extend the photoresponse to visible light region and the formation of heterojunctions favor the spatial separation of photogenerated charge carriers. Therefore, the high-efficient 0D/1D heterojunction composites have potential applications in the field of environment and energy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Te-doped perovskite NaTaO3 as a promising photocatalytic material for hydrogen production from water splitting driven by visible light

Highlights: • S, Se and Te-doped NaTaO{sub 3} is a promising material for photocatalytic water splitting. • Enhanced absorption coefficient in the visible light range is identified for Te-doped NaTaO{sub 3}. • Te-doped NaTaO{sub 3} exhibits higher electron and hole mobility than pristine NaTaO{sub 3}. - Abstract: The photocatalytic hydrogen production from water splitting can be achieved by using the pristine NaTaO{sub 3} experimentally, but the reaction cannot be driven by the visible light because of the wide band gap of NaTaO{sub 3}. The present work focuses on tuning the photocatalytic performance of NaTaO{sub 3} into the visible light range by doping S, Se, and Te elements. The obvious decrease in band energy gaps (E{sub g}s) and noticeable red-shift of the absorption edges are observed for the doped structures. The valence band maximum and conduction band minimum of the doped structures satisfy the requirement of the water splitting. Moreover, a significant enhancement of absorption coefficient in the visible light range is observed for the doped structure of Te@O. The calculated carrier mobility is used to evaluate the charge spatial separation of Te@O and the unusual increases and the obvious differences of the mobility of the electrons and holes are observed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Electrolyte-driven interphase stabilization in high-voltage sodium-ion full cells

Sodium-ion batteries with a high-voltage O3-type layered oxide cathode paired with a hard carbon anode can offer high energy density; however, significant interfacial instabilities driven by electrode/electrolyte reactions limit a broader industrial adoption. Localized high concentration electrolytes (LHCEs) are a rational choice as they promote salt decomposition over solvent, forming stable, inorganic-rich electrode-electrolyte interphases (EEIs). We present here a comparison of high-voltage (4.2 V) hard carbon | NaNi 1/3 Fe 1/3 Mn 1/3 O 2 pouch cells in LHCEs and in a standard carbonate-based electrolyte by (i) examining the influence of diluent choice on the electrochemical performance of LHCEs and (ii) investigating how the electrolyte chemistry affects the composition and structure of EEIs formed. Importantly, LHCEs demonstrate superior electrochemical performance, achieving 37% higher capacity after 200 cycles (119 vs. 87 mA h g -1 ) compared to the carbonate-based electrolyte. The enhanced stabilization provided by LHCEs at the interface with high-voltage sodium layered oxide cathode is revealed by gas evolution measurements obtained through online electrochemical mass spectrometry (OEMS). Time-of-flight secondary ion mass spectrometry paired with focused ion beam and advanced statistical analyses reveal that the superior performance of LHCE stems from a robust, thin cathode electrolyte interphase formed on the sodium layered oxide cathode and a homogeneous solid electrolyte interphase formation on the hard carbon anode. Furthermore, this study highlights the critical importance of electrolyte design in interphase stabilization, which plays a key role in advancing sodium-ion batteries toward commercial viability.

25 ENERGY STORAGE↗
DOE OSTI2025

Pressure-driven density match nucleates metastable r8 phases from amorphous Si and Ge

The pressure–temperature phase behavior of covalent disordered solids such as amorphous silicon and germanium is complex. Questions remain on possible glass transitions, on polyamorphism via amorphous–amorphous transitions, on connections with liquid–liquid transitions, on structure-behavior relationships, and on their potential as precursor for novel methods for material discovery. Here we demonstrate experimentally the nucleation of a metastable, four-fold coordinated rhombohedral r8 phase from pure amorphous silicon and germanium upon room temperature compression at pressures below 10 GPa. Accompanying theory reveals a strong pressure-driven distortion of the bond angle transforming the starting tetrahedral low-density amorphous network to a distorted four-fold coordinated medium-density state. This state is of lower density than metallic high-density networks, resembles the crystalline r8 phase and initiates its nucleation. Our finding shows that polyamorphism is not the only possible transformation mode for these amorphous solids and that instead nucleation of interesting functional phases at potentially useful pressures is possible. Such novel access modes to metastable structures are critical for future exploitability and could be useful for other tetrahedral materials including carbon, where the related (bc8) post-diamond phase remains elusive. Our observed density match between an amorphous and a metastable crystalline phase clearly allows for a new phase transition pathway, while corresponding theory demonstrates how carefully validated atomistic simulations can guide prediction, discovery and synthesis of novel material structures.

Materials discovery↗
DOE OSTI2017

A tabletop, ultrashort pulse photoneutron source driven by electrons from laser wakefield acceleration

Relativistic electron beams driven by laser wakefield acceleration were utilized to produce ultrashort neutron sources. The experiment was carried out on the 38 fs, ∼0.5 J, 800 nm Ti:Sapphire laser in the 10 TW UT3 laser lab at University of Texas at Austin. The target gas was a high density pulsed gas jet composed of 90% He and 10% N2. The laser pulse with a peak intensity of 1.5 × 1018 W/cm2 interacted with the target to create a cylindrical plasma channel of 60 μm radius (FWHM) and 1.5 mm length (FWHM). Electron beams of ∼80 pC with the Gaussian energy distribution centered at 37 MeV and a width of 30 MeV (FWHM) were produced via laser wakefield acceleration. Neutron fluences of ∼2.4 × 106 per shot with hundreds of ps temporal length were generated through bremsstrahlung and subsequent photoneutron reactions in a 26.6 mm thick tungsten converter. Results were compared with those of simulations using EPOCH and GEANT4, showing agreement in electron spectrum, neutron fluence, neutron angular distribution and conversion rate.

Jiao, X. J.↗
DOE OSTI2026

Comprehensive structural characterization of charged polymers involved in moisture-driven direct air capture

This study provides a comprehensive structural characterization of commercially available alkaline anion-exchange polymers (Fumasep FAA-3 and IRA 900) used in moisture-driven direct air capture (DAC) of carbon dioxide. Using X-ray diffraction, SAXS/WAXS, atomic force microscopy, FIB-SEM, and transmission electron microscopy, the authors identify nanoscale clustering, porosity, swelling behavior, and humidity-dependent structural changes that influence CO₂ adsorption and release. These findings establish structure–function relationships critical for designing more durable and energy-efficient DAC polymer materials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

General features of experiments on the dynamics of laser-driven electron–positron beams

The experimental study of the dynamics of neutral electron–positron beams is an emerging area of research, enabled by the recent results on the generation of this exotic state of matter in the laboratory. Electron–positron beams and plasmas are believed to play a major role in the dynamics of extreme astrophysical objects such as supermassive black holes and pulsars. For instance, they are believed to be the main constituents of a large number of astrophysical jets, and they have been proposed to significantly contribute to the emission of gamma-ray bursts and their afterglow. However, despite extensive numerical modelling and indirect astrophysical observations, a detailed experimental characterisation of the dynamics of these objects is still at its infancy. Here in this paper, we will report on some of the general features of experiments studying the dynamics of electron–positron beams in a fully laser-driven setup.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

An expert-driven literature review of “negative” chemicals for developmental neurotoxicity (DNT) in vitro assay evaluation

To date, approximately 200 chemicals have been tested in US Environmental Protection Agency (EPA) or Organization for Economic Co-operation and Development (OECD) developmental neurotoxicity (DNT) guideline studies, leaving thousands of chemicals without traditional animal information on DNT hazard potential. To address this data gap, a battery of in vitro DNT new approach methodologies (NAMs) has been proposed. Evaluation of the performance of this battery will increase the confidence in its use to determine DNT chemical hazards. One approach to evaluate DNT NAM performance is to use a set of chemicals to evaluate sensitivity and specificity. Since a list of chemicals with potential evidence of in vivo DNT has been established, this study aims to develop a curated list of “negative” chemicals for inclusion in a “DNT NAM evaluation set”. A workflow, including a literature search followed by an expert-driven literature review, was used to systematically screen 39 chemicals for lack of DNT effect. Expert panel members evaluated the scientific robustness of relevant studies to inform chemical categorizations. Following review, the panel discussed each chemical and made categorical determinations of “Favorable”, “Not Favorable”, or “Indeterminate” reflecting acceptance, lack of suitability, or uncertainty given specific limitations and considerations, respectively. Further, the panel determined that 10, 22, and 7 chemicals met the criteria for “Favorable”, “Not Favorable”, and “Indeterminate”, for use as negatives in a DNT NAM evaluation set. Ultimately, this approach not only supports DNT NAM performance evaluation but also highlights challenges in identifying large numbers of negative DNT chemicals.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

A data-driven framework for error estimation and mesh-model optimization in system-level thermal-hydraulic simulation

We report over the past decades, several computer codes have been developed for simulation and analysis of thermal-hydraulics and system response in nuclear reactors under operating, abnormal transient, and accident conditions. However, simulation errors and uncertainties still inevitably exist even while these codes have been extensively assessed and used. In this work, a data-driven framework (Optimal Mesh/Model Information System, OMIS) is formulated and demonstrated to estimate simulation error and suggest optimal selection of computational mesh size (i.e., nodalization) and constitutive correlations (e.g., wall functions and turbulence models) for low-fidelity, coarse-mesh thermal-hydraulic simulation, in order to achieve accuracy comparable to that of high-fidelity simulation. Using results from high-fidelity simulations and experimental data with many fast-running low-fidelity simulations, an error database is built and used to train a machine learning model that can determine the relationship between local simulation error and local physical features. This machine learning model is then used to generate insight and help correct low-fidelity simulations for similar physical conditions. The OMIS framework is designed as a modularized six-step procedure and accomplished with state-of-the-art methods and algorithms. A mixed-convection case study was performed to illustrate the entire framework.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2017

Computing eddy-driven effective diffusivity using Lagrangian particles

A novel method to derive effective diffusivity from Lagrangian particle trajectory data sets is developed and then analyzed relative to particle-derived meridional diffusivity for eddy-driven mixing in an idealized circumpolar current. Quantitative standard dispersion- and transport-based mixing diagnostics are defined, compared and contrasted to motivate the computation and use of effective diffusivity derived from Lagrangian particles. We compute the effective diffusivity by first performing scalar transport on Lagrangian control areas using stored trajectories computed from online Lagrangian In-situ Global High-performance particle Tracking (LIGHT) using the Model for Prediction Across Scales Ocean (MPAS-O). Furthermore, the Lagrangian scalar transport scheme is compared against an Eulerian scalar transport scheme. Spatially-variable effective diffusivities are computed from resulting time-varying cumulative concentrations that vary as a function of cumulative area. The transport-based Eulerian and Lagrangian effective diffusivity diagnostics are found to be qualitatively consistent with the dispersion-based diffusivity. All diffusivity estimates show a region of increased subsurface diffusivity within the core of an idealized circumpolar current and results are within a factor of two of each other. The Eulerian and Lagrangian effective diffusivities are most similar; smaller and more spatially diffused values are obtained with the dispersion-based diffusivity computed with particle clusters.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Predicting material microstructure evolution via data-driven machine learning

The recent rapid rise in data-driven practices in the materials science domain has led to the development of efficient, generalizable, and accurate approaches for several applications, including: material property prediction, mining (micro)structure- property and (micro)structure-processing relationships, and characterization of material microstructures. Central to the materials science domain is linking microstructure to properties and performance, and critical to building such linkages is understanding how microstructures evolve as a function of environmental exposure or processing conditions (e.g., time, temperature, applied stress or strain, irradiation). This preview article summarizes recent work on the development of recurrent neural networks for predicting spatio-temporal microstructure evolution detailed by Yang et al in their manuscript entitled 'Self-supervised Learning and Prediction of Microstructure Evolution with Recurrent Neural Networks'.

machine learning (ML), materials characterization↗
DOE OSTI2026

A buoyancy–shear–drag–scalar-based turbulence model for power-law acceleration-driven Rayleigh–Taylor, reshocked Richtmyer–Meshkov, and Kelvin–Helmholtz mixing

A previously developed phenomenological turbulence model for Rayleigh–Taylor, reshocked Richtmyer–Meshkov, and Kelvin–Helmholtz instability-induced mixing based on a general buoyancy–shear–drag model [O. Schilling, “A buoyancy–shear–drag-based turbulence model for Rayleigh–Taylor, reshocked Richtmyer–Meshkov, and Kelvin–Helmholtz mixing,” Physica D 402, 132238 (2020)] is extended to include active or passive scalar mixing and power-law acceleration-driven Rayleigh–Taylor mixing. The buoyancy–shear–drag equations are coupled to a scalar variance equation that is used to define the molecular mixing parameter θ m , and when the scalar is active, modifies the Rayleigh–Taylor and Kelvin–Helmholtz mixing layer growth parameters to depend on the asymptotic value of this parameter, θ mol . Here, the scalar variance equation is closed by algebraically or differentially modeling the scalar variance dissipation rate. Nonlinear analytical solutions of the model are obtained in the total and separate bubble and spike mixing layer width formulations with the algebraic scalar variance dissipation rate for each instability, which are then used to calibrate the mechanical and scalar equation coefficients to predict specific values of physical observables and molecular mixing parameters. Surrogate mechanical and scalar turbulent fields can be constructed by multiplying a presumed self-similar spatial profile by appropriate functions of the width and its time derivative, and of the scalar obtained by solving the ordinary differential model equations. The explicit modeling and solution of turbulent transport equations are not required. The bubble and spike mixing layer width and scalar variance equations are then solved numerically for constant-acceleration Rayleigh–Taylor, impulsively reshocked Richtmyer–Meshkov, and Kelvin–Helmholtz mixing, confirming that the prescribed level of molecular mixing is correctly predicted and illustrating the spatiotemporal evolution of the scalar fields.

Buoyancy–drag↗
DOE OSTI2025

Magnetic field driven emergent phenomena: Insights from magneto-optics and nanoscopy

This review explores magnetic field-driven emergent phenomena across various material systems, emphasizing the pivotal roles of magneto-optical and nanoscopy techniques. We examine fundamental aspects of Landau electrodynamics in both 2D and 3D systems, including quantum Hall and topological magnetoelectric effects in graphene and topological insulators. Particularly attention is given to magnetic excitations and magnetopolaritons, such as surface magnon polaritons, magnetoplasmons, and magnetoexcitons in novel quantum materials, including quantum magnets and hybrid heterostructures. Advanced imaging techniques, such as scattering-type scanning near-field optical microscopy (SNOM) and microwave impedance microscopy, are showcased for their capability to resolve these phenomena with microscopic and nanoscopic resolution. These insights are complemented by discussions of advanced experimental approaches, including cryogenic environments, ultrafast pump-probe techniques, and the integration of magnetic fields into near-field optical methodologies. We further investigate the potential of these imaging techniques for unraveling complex magnetic orders, quantum phases, and correlated electronic behaviors. Finally, we offer perspectives on future research directions and highlight emerging opportunities in the evolving field of optical magneto-nanoscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Multi-level optimization with the koopman operator for data-driven, domain-aware, and dynamic system security

Cyber-Physical Systems (CPSs) like the power grid are critically important but also increasingly vulnerable; ensuring reliable system operation in the face of disruptions is becoming more and more challenging. Multi-Level Optimization (MLO) is a powerful way to model adversarial interactions, which naturally makes it applicable to studying CPS security. However, MLO typically does not address underlying system dynamics, and incorporating nonlinear dynamics is generally infeasible. In this paper, we show how to combine MLO with the Koopman Operator (KO) to remedy this. The KO maps nonlinear dynamics to a lifted space in which those dynamics are linear, thus making it ideal for use with MLO. Moreover, the structure of the KO also provides convenient ways to incorporate domain knowledge into the data-driven process of learning the KO representation of a given system. Here we then demonstrate the use of MLO-KO on a small example problem taken from the power grid domain, discuss the scalability and computational cost of MLO-KO, and identify future research directions for this work.

42 ENGINEERING↗