Laser shock peening of electron beam welded, elastically averaged, split-cell accelerator fabricated from hard Cu alloy
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High gradient, RF accelerator, advanced manufactur↗
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Results for “Splitting”
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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An implicit-explicit time splitting strategy for the far SOL plasma fluid model with DG-FEM discretization
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Mathematics and Computing↗
Robust Split Laser Spectroscopic Sensor for In-situ Characterization of Rare Earth Elements and Critical Minerals in Mining Deposits
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36 MATERIALS SCIENCE↗
Efficient hybrid explicit-implicit learning for multiscale problems
Splitting method is a powerful method to handle application problems by splitting physics, scales, domain, and so on. Many splitting algorithms have been designed for efficient temporal discretization. Here, in this paper, our goal is to use temporal splitting concepts in designing machine learning algorithms and, at the same time, help splitting algorithms by incorporating data and speeding them up. We propose a machine learning assisted splitting scheme which improves the efficiency of the scheme meanwhile preserves the accuracy. We consider a recently introduced multiscale splitting algorithms, where the multiscale problem is solved on a coarse grid. To approximate the dynamics, only a few degrees of freedom are solved implicitly, while others explicitly. This splitting concept allows identifying degrees of freedom that need implicit treatment. In this paper, we use this splitting concept in machine learning and propose several strategies. First, the implicit part of the solution can be learned as it is more difficult to solve, while the explicit part can be computed. This provides a speed-up and data incorporation for splitting approaches. Secondly, one can design a hybrid neural network architecture because handling explicit parts requires much fewer communications among neurons and can be done efficiently. Thirdly, one can solve the coarse grid component via PDEs or other approximation methods and construct simpler neural networks for the explicit part of the solutions. We discuss these options and implement one of them by interpreting it as a machine translation task. This interpretation of the splitting scheme successfully enables us using the Transformer since it can perform model reduction for multiple time series and learn the connection between them. We also find that the splitting scheme is a great platform to predict the coarse solution with insufficient information of the target model: the target problem is partially given and we need to solve it through a known problem which approximates the target. Our machine learning model can incorporate and encode the given information from two different problems and then solve the target problems. We conduct four numerical examples and the results show that our method is stable and accurate.
97 MATHEMATICS AND COMPUTING↗
Spin–Orbit Coupling via Four-Component Multireference Methods: Benchmarking on p-Block Elements and Tentative Recommendations
Within current electronic structure theory methods, fully relativistic four-component (4c) approaches based on the Dirac Hamiltonian treat spin–orbit coupling with the most rigor. The spin treatment arises naturally from the formulation and does not need to be included ad hoc. Spin–orbit splittings can provide insightful benchmark criteria for the assessment of 4c methods; however, there have not been extensive studies in this respect. Spin–orbit splittings of the p-block elements B–I were computed using the 4c-CASSCF, 4c-CASPT2, and 4c-MR-CISD+Q methods, as recently implemented in BAGEL, with uncontracted Dunning basis sets. Comparison with experiment reveals that the four-component methods yield good results, with most of the computed splittings falling within 15% of the experimental values. A large basis set is needed to obtain accurate splittings of the light elements B–F, while splittings of heavier elements show little basis dependence. The 4c-MR-CISD+Q method gave the best splittings for light elements, while 4c-CASSCF showed the best splittings for elements beyond fluorine. In conclusion, the 4c-CASPT2 method gave the best splittings for group 13 atoms.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Spectroscopic Characterization, Computational Investigation, and Comparisons of ECX – (E = As, P, and N; X = S and O) Anions
Three newly-synthesized [Na+(221-kryptofix)] salts containing AsCO–, PCO–, and PCS– anions were successfully electrosprayed into the vacuum, and the ECX– (E = As, P; X = O, S) anions were investigated by negative ion photoelectron spectroscopy (NIPES) and high resolution photoelectron imaging spectroscopy. For each ECX– anion, a well-resolved NIPE spectrum was obtained, in which every major peak is split into a doublet. The splittings are attributed to spin-orbit coupling (SOC) in the ECX• radicals. Vibrational progressions in the NIPE spectra of ECX– were assigned to the symmetric and antisymmetric stretching modes in ECX• radicals. The electron affinities (EAs) and SOC splittings of ECX• are determined from the NIPE spectra to be: AsCO•: EA = 2.414 ± 0.002 eV, SOC splitting = 988 cm-1; PCO•: EA = 2.670 ± 0.005 eV, SOC splitting = 175 cm-1; PCS•: EA = 2.850 ± 0.005 eV, SOC splitting = 300 cm-1. Calculations using the B3LYP, CASPT2, and CCSD(T) methods all predict linear geometries for both the anions and neutral radicals. The calculated EAs and SOC splittings for ECX• are in excellent agreement with the experimentally-measured values. The simulated NIPE spectra, based on the calculated Franck-Condon factors, and SOC splittings nicely reproduce all of the observed spectral peaks, thus allowing unambiguous spectral assignments. The finding that PCS has the greatest EA of the three triatomic molecules considered here is counterintuitive based upon electronegativity considerations, but understandable in terms of the HOMO of PCS– having the greatest degree of delocalization onto both terminal atoms.
Environmental Molecular Sciences Laboratory↗
Degeneracy Removal of Spin Bands in Collinear Antiferromagnets with Non–Interconvertible Spin–Structure Motif Pair
Energy bands in antiferromagnets are supposed to be spin degenerate in the absence of spin–orbit coupling (SOC). Recent studies have identified formal symmetry conditions for antiferromagnetic crystals in which this degeneracy can be lifted, spin splitting, even in the vanishing SOC (i.e., non-relativistic) limit. Materials having such symmetries could enable spin-split antiferromagnetic spintronics without the burden of using heavy-atom compounds. However, the symmetry conditions that involve spin and magnetic symmetry are not always effective as practical material selection filters. Furthermore, these symmetry conditions do not readily disclose trends in the magnitude and momentum dependence of the spin-splitting energy. Here, it is shown that the formal symmetry conditions enabling spin-split antiferromagnets can be interpreted in terms of local motif pairs, such as octahedra or tetrahedra, each carrying opposite magnetic moments. Here, collinear antiferromagnets with such a spin-structure motif pair, whose components interconvert by neither translation nor spatial inversion, will show spin splitting. Such a real-space motif-based approach enables an easy way to identify and design materials (illustrated in real example materials) having spin splitting without the need for SOC, and offers insights into the momentum dependence and magnitude of the spin splitting.
36 MATERIALS SCIENCE↗
Surface chemistry and photoelectrochemistry—Case study on tantalum nitride
Solar water splitting promises a solution to challenges associated with the intermittent nature of solar energy. Of different implementations, photoelectrochemical water splitting, where one or more photoelectrodes harvest light and catalyze water splitting, represents a convenient platform to understand the governing principles of charge behaviors, especially at the light absorber|H 2 O interface. This Perspective recognizes and discusses the importance of the photoelectrode surface to solar water splitting performance. It presents discussions within the context of a prototypical water splitting material, Ta 3 N 5 , which has gained growing attention lately for its outstanding initial performance. Insights into the mechanisms by which Ta 3 N 5 functions are presented, followed by examples of recent efforts to circumvent the issues that Ta 3 N 5 decays rapidly under solar water splitting conditions. Our visions on the future directions of semiconductor-based solar water splitting will be presented at the end.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Comparing Exciton-Polariton Couplings in Two-Dimensional MoS2 Cavities
Exciton-polaritons (EPs) are an emerging approach to achieve strong light-matter coupling and robust quantum phenomena, with application to areas such as photonic neuromorphic computing for instance reservoir computing. 2D transition metal dichalcogenides (TMDs) are promising candidates to host EPs due to their potential for strong coupling as evidenced by large Rabi splitting energies, which in the case of few-layer MoS2 has been demonstrated to reach 293 meV when coupled to the C exciton, placing it in the ultrastrong coupling regime, at room temperature. Here we examine how the Rabi splitting of CVD-grown monolayer MoS2 in a cavity can be optimized by tuning two variables: cavity geometry (thickness of silver and dielectric spacers) and the targeted exciton for coupling (A at about 1.9 eV, B at about 2.06 eV, or C at about 2.9 eV). With the cavity geometry, there is a tradeoff between optical field confinement and transmission. With the targeted exciton, there may be a tradeoff between Rabi splitting and lifetime. Transfer matrix simulations are used to inform how thick the cavity layers need to be, and at what angle measurements should be performed, to achieve Rabi splitting at a certain exciton energy. Experimentally, the Rabi splitting is measured by placing the cavity at a specified angle and measuring the optical reflectance and transmittance. By fitting the data, we find Rabi splittings of 124 meV, 194 meV, and 288 meV for the A, B, and C excitons, respectively, which places them in the strong, and on the edge of the ultrastrong, coupling regime.
exciton-polaritons↗
A Thermogravimetric Temperature-Programmed Thermal Redox Protocol for Rapid Screening of Metal Oxides for Solar Thermochemical Hydrogen Production
As combinatorial and computational methods accelerate the identification of potentially suitable thermochemically-active oxides for use in solar thermochemical hydrogen production (STCH), the onus shifts to quickly evaluating predicted performance. Traditionally, this has required an experimental setup capable of directly carrying out a two-stage thermochemical water-splitting process. But this can be a difficult endeavor, as most off-the-shelf equipment cannot adequately deal simultaneously with the high temperatures, varying oxygen partial pressures, and high H 2 O partial pressures required; achieving sufficient temporal sensitivity to accurately quantify the kinetics is also a major challenge. However, as proposed here, a less complicated experiment can be used as a first screening for thermochemical water splitting potential. Temperature-Programmed Thermal Redox (TPTR) using thermogravimetry evaluates the thermal reduction behavior of materials. This technique does not require water splitting or CO 2 -splitting analogs but can nonetheless predict water-splitting performance. Three figures of merit are obtained from the TPTR experiment: reduction onset temperature, extent of reduction, and extent of recovery upon reoxidation. These metrics can collectively be used to determine if a material is capable of thermochemical water-splitting, and, to good approximation, predict whether the thermodynamics are favorable for use under more challenging high-conversion conditions. This paper discusses the pros and cons of using TPTR and proposes a protocol for use within the STCH community.
08 HYDROGEN↗
Hydrogen and its Vital Role in a Clean Energy Future
Large-scale, low -cost hydrogen production can enable an economically competitive, secure, and environmentally beneficial future energy system across multiple sectors. Furthermore, clean hydrogen can address specific sectors that are hard to decarbonize (e.g., heavy-duty trucking, load-following electricity, iron, steel, and cement) and can help the U.S. meet the net zero carbon goal by 2050. To achieve this goal, tens of millions of metric tons of clean, reliable, and affordable hydrogen will be needed annually1. In 2021, the Hydrogen Energy Earthshot was launched, and its goal is to reduce the cost of clean hydrogen to $1 per $1 kilogram in 1 decade (1 1 1) 2. One very promising pathway for large-scale hydrogen production is water splitting. Water splitting technologies range from commercial technologies such as electrolyzers to approaches that are at a much earlier stage of development, such as photoelectrochemical (PEC) and thermochemical (TCH) processes. All these water splitting pathways offer diverse benefits in energy storage, grid services, and cross-sector emissions reductions while taking advantage of the diverse domestic resources. However, critical materials-, component- and system-level challenges must be addressed to improve efficiency and durability and reduce cost. To address these barriers and move these promising and high impact technologies forward, the HydroGEN Advanced Water Splitting Materials (AWSM) and the H2 from the Next-generation of Electrolyzers of Water (H2NEW) consortia were formed and supported by the Department of Energy (DOE) EERE Hydrogen and Fuel Cell Technologies Office (HFTO). HydroGEN (https://www.energy.gov/eere/h2awsm/) consortium, established in 2016, is an Energy Materials Network (EMN) that aims to accelerate the materials R&D of low technology readiness level (TRL) advanced water splitting (AWS) technologies. The consortium comprises five core national laboratories and focuses on four early-stage AWS pathways: alkaline exchange membrane (AEM) electrolysis, proton conducting solid oxide electrolysis (p-SOEC), photoelectrochemical, and thermochemical water splitting. Liquid alkaline and PEM electrolyzers are already commercial and significant advancements in oxygen conducting solid oxide electrolysis cells (o-SOECs) have been realized. Yet, these systems are still too expensive and not sufficiently durable for wide-scale commercialization. To enable high-volume manufacturing of affordable, durable, efficient electrolyzers, H2NEW (https://h2new.energy.gov/), another multi-lab consortium, was established in 2020. This comprehensive, concerted effort is focused on overcoming barriers related to components and materials integration and scale-up to achieve performance, durability, with an initial focus to achieve $2/kg H2 by 2026.
AEM↗
Experimental Assessment of Mammalian Lipidome Complexity Using Multimodal 21 T FTICR Mass Spectrometry Imaging
Herein, we assess the complementarity and complexity of data that can be detected within mammalian lipidome mass spectrometry imaging (MSI) via matrix-assisted laser desorption ionization (MALDI) and nanospray desorption electrospray ionization (nano-DESI). We do so by employing 21 T Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) with absorption mode FT processing in both cases, allowing unmatched mass resolving power per unit time (≥613k at m/z 760, 1.536 s transients). While our results demonstrated that molecular coverage and dynamic range capabilities were greater in MALDI analysis, nano-DESI provided superior mass error, and all annotations for both modes had sub-ppm error. Taken together, these experiments highlight the coverage of 1676 lipids and serve as a functional guide for expected lipidome complexity within nano-DESI-MSI and MALDI-MSI. To further assess the lipidome complexity, mass splits (i.e., the difference in mass between neighboring peaks) within single pixels were collated across all pixels from each respective MSI experiment. The spatial localization of these mass splits was powerful in informing whether the observed mass splits were biological or artificial (e.g., matrix related). Mass splits down to 2.4 mDa were observed (i.e., sodium adduct ambiguity) in each experiment, and both modalities highlighted comparable degrees of lipidome complexity. Further, we highlight the persistence of certain mass splits (e.g., 8.9 mDa; double bond ambiguity) independent of ionization biases. Here, we also evaluate the need for ultrahigh mass resolving power for mass splits ≤4.6 mDa (potassium adduct ambiguity) at m/z > 1000, which may only be resolved by advanced FTICR-MS instrumentation.
21T-FTICR-MS↗
BaCe 0.25 Mn 0.75 O 3–δ —a promising perovskite-type oxide for solar thermochemical hydrogen production
Solar-thermal based hydrogen production technologies employing two-step metal oxide water-splitting cycles are emerging as a viable approach to renewable and sustainable solar fuels. However, materials innovations that overcome thermodynamic constraints native to the current class of solar-thermal water splitting oxides are required to increase solar utilization and process efficiency. Lowering oxide thermal reduction temperature while maintaining high water-splitting favorability are important ways to enhance such performance metrics. Recent attention to perovskite-type oxides as an alternative to ceria, which is widely viewed as the state-of-the art redox material, is driven by demonstrated thermodynamic and structural tuning derived through engineered composition. Here we discuss the unique properties of BaCe 0.25 Mn 0.75 O 3 (BCM) within the context of thermochemical water splitting materials. Firstly, BCM is a novel example of a line compound with B-site substitution of Mn by Ce. It also exhibits a polymorph phase transition during thermal reduction and yields nearly 3× more H 2 than ceria when reduced at lower temperature (1350 °C). More importantly, BCM exhibits faster oxidation kinetics and higher water-splitting favorability than Sr x La 1–x Mn y Al 1–y O 3 (x, y = 0.4, 0.6), which is a well-studied and popular Mn-based perovskite formulation. Furthermore, the unique properties manifested by BCM through engineered composition offer new pathways towards unlocking higher performing materials for solar thermochemical water splitting.
14 SOLAR ENERGY↗
Control of hybrid boosting in highly diluted internal combustion engines
A novel hybrid system enabling both flexible supercharging and limited torque assist is studied to mitigate transient response challenges of a turbocharged spark ignition engine equipped with low pressure exhaust gas recirculation. The hybrid system, called a power split supercharger (SC), is configured with a planetary gear set that splits the supercharging power between a small low-voltage electric motor and the engine crankshaft. The air path controller relies on the coordination of four actuators on the engine side and three low-level actuators on the hybrid boosting device. A decentralized control scheme is used in this work, in which the master–slave structure of the boost pressure controller decreases the turbo-lag associated with exhaust gas recirculation, while minimizing the SC operation for fuel economy. A vector reference governor is used to prevent compressor surge during engine tip-outs. In addition, the desired intake manifold pressure is modified to provide time for evacuating the exhaust gas recirculation and avoiding misfires when transitioning to low load, while the hybrid capability of the power split SC is used to recuperate the unwanted generated power. All controllers are validated on both a mean value engine model and a high-fidelity engine model. Practical challenges of implementing the vector reference governor to the highly nonlinear engine air path with pressure pulsations originating from the engine reciprocation are discussed and some solutions are proposed.
Engineering↗
Stabilization of Catalytically Active Surface Defects on Ga-doped La–Sr–Mn Perovskites for Improved Solar Thermochemical Generation of Hydrogen
Solar thermochemical hydrogen (STCH) production from water splitting typically requires performing redox cycles at temperatures above 1200 °C to reduce and re-oxidize the bulk of a reversible material. Bulk processes such as oxygen vacancy formation and oxygen diffusion energies dictate the viability of a material for STCH. The surface plays an important role in the formation and destruction of vacancies and interacts with gas phase water and surface adsorbed species. These surface processes can lead to surface reconfigurations and even the formation of surface phases with stoichiometry and oxygen content very different from the bulk composition. Understanding in-situ the surface chemical state and its evolution under water splitting is important to design nonstoichiometric oxides capable of longer-lasting STCH generation at lower temperatures. In this work, we describe the water splitting active defect sites in LSM ((La 0.65 Sr 0.35 ) 0.95 MnO 3–δ ) and Ga-doped LSM ((La 0.6 Sr 0.4 ) 0.95 (Mn 0.8 Ga 0.2 )O 3–δ ) perovskites during Operando thermochemical water splitting conditions using ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) experiments at 800 °C under steam. We show that sub-stoichiometric La +3 in the oxygen-vacancy rich surface at operating conditions can be used to correlate surface water splitting activity and the creation of surface hydroxide intermediates. The addition of Ga in LSM is shown to drastically stabilize the surface chemical composition by preventing Sr segregation and stabilizing catalytically active surface defects that promote the binding of adsorbed hydroxides. Here, we use Operando AP-XPS quantification of metastable surface hydroxide intermediates (La(OH) 3 ) to determine the amount of catalytically active surface sites in LSM (2.9%) and in LSMG (7.8–8.1%, depending on the bulk oxidation state).
08 HYDROGEN↗
From Pure to Seawater Electrolysis: Unveiling the Impact of Ionic Species and Contaminants on Electrocatalysis
Water electrolysis, including seawater splitting to produce hydrogen and oxygen, stands as a promising approach for the efficient storage of intermittent energy. However, the half-reactions of water splitting, the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), are known to be very sensitive toward the quality of water employed and are susceptible to contaminants originating from various sources, including the electrolyte or the electrodes. Those contaminants have a profound impact on the activity of these reactions of water splitting by modifying the electronic and physical structures of electrocatalysts as well as electrode–electrolyte interfaces. For seawater electrolysis, the unintentional presence of impurities, such as anions, cations, and organic compounds, affects the catalyst stability, selectivity, and activity. Despite the existence of numerous comprehensive reviews that delve into various aspects of catalysts and their structure–property relationships for several electrocatalytic reactions, the impact of contaminants has often been ignored. This critical review endeavors to address this issue by providing an overview of the diverse sources of contaminants influencing electrocatalytic water splitting and seawater splitting reactions, delineating the trends in electrochemical parameters and detailing different characterization methods for elucidating the physical and electronic changes of the electrode and electrolyte.
HER↗
SiGe quantum wells with oscillating Ge concentrations for quantum dot qubits
Large-scale arrays of quantum-dot spin qubits in Si/SiGe quantum wells require large or tunable energy splittings of the valley states associated with degenerate conduction band minima. Existing proposals to deterministically enhance the valley splitting rely on sharp interfaces or modifications in the quantum well barriers that can be difficult to grow. Here, we propose and demonstrate a new heterostructure, the “Wiggle Well”, whose key feature is Ge concentration oscillations inside the quantum well. Experimentally, we show that placing Ge in the quantum well does not significantly impact our ability to form and manipulate single-electron quantum dots. We further observe large and widely tunable valley splittings, from 54 to 239 μ eV. Tight-binding calculations, and the tunability of the valley splitting, indicate that these results can mainly be attributed to random concentration fluctuations that are amplified by the presence of Ge alloy in the heterostructure, as opposed to a deterministic enhancement due to the concentration oscillations. Quantitative predictions for several other heterostructures point to the Wiggle Well as a robust method for reliably enhancing the valley splitting in future qubit devices.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Local and global approaches to treat the torsional barriers of 4-methylacetophenone using microwave spectroscopy
The Fourier transform microwave spectrum of 4-methylacetophenone recorded from 8 GHz to 18 GHz under jet-cooled conditions has revealed large tunneling splittings arising from a low barrier to internal rotation of the ring methyl group and small splittings from a high torsional barrier of the acetyl methyl group. The large splittings are especially challenging to model, while the small splittings are difficult to analyze due to the resolution limit of 120 kHz. The combination of two methyl groups undergoing internal rotations caused each rotational transition to split into five torsional species, which were resolved and fitted using a modified version of the XIAM code and the newly devel- oped ntop code to a root-mean-square deviation close to measurement accuracy, providing an estimate of the V 3 potential barriers of about 22 cm -1 and 584–588 cm -1 for the ring and the acetyl methyl groups, respectively. The assignment was aided by separately fitting the five torsional species using odd-power order operators. Only one conformer in which all heavy atoms are located on a symmetry plane could be identified in the spectrum, in agreement with results from conformation analysis using quantum chemical calculations.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗