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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Realization of semiconducting layered multiferroic heterojunctions via asymmetrical magnetoelectric coupling

Two-dimensional (2D) semiconducting multiferroics that can effectively couple magnetic and polarization (P) orders have great interest for both fundamental research and technological applications in nanoscale, which are, however, rare in nature. In this work, we propose a general mechanism to realize semiconducting 2D multiferroics via van der Waals (vdW) heterojunction engineering, as demonstrated in a typical heterostructure consisting of magnetic bilayer CrI 3 (bi-CrI 3 ) and ferroelectric monolayer In 2 Se 3 . Interestingly, the novel indirect orbital coupling between Se 4p and Cr 3d orbitals, intermediated by the interfacial I 5p orbitals, is switchable in the opposite P configurations, resulting in an unexpected mechanism of strong asymmetrical magnetoelectric coupling. Therefore, along with the noticeable ferroelectric energy barrier induced by In 2 Se 3 , the realization of opposite magnetic orders in opposite P configurations can eventually result in the novel multiferroicity in bi– CrI 3 /In 2 Se 3 . Finally, we demonstrate that our mechanism can generally be applied to design other vdW multiferroics even with tunable layer thickness.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Celestial Topology, Symmetry Theories, and Evidence for a NonSUSY D3‐Brane CFT

Symmetry Theories (SymThs) provide a flexible framework for analyzing the global categorical symmetries of a D -dimensional QFT D in terms of a (D + 1)-dimensional bulk system SymTh D+1 . In QFTs realized via local string backgrounds, these SymThs naturally arise from dimensional reduction of the linking boundary geometry. To track possible time dependent effects we introduce a celestial generalization of the standard “boundary at infinity” of a SymTh. As an application of these considerations we revisit large N quiver gauge theories realized by spacetime filling D3-branes probing a non-supersymmetric orbifold $\mathbb{R}$ 6 /Γ. Comparing the imprint of symmetry breaking on the celestial geometry at small and large ‘t Hooft coupling we find evidence for an intermediate symmetry preserving conformal fixed point.

conformal field theory↗
DOE OSTI2021

Exploiting the Liquid Phase to Enhance the Cross-Coupling of Alcohols over Nanoporous Gold Catalysts

Controlling selectivity in the cross-coupling of two similar compounds is a classic challenge in heterogeneous catalysis. Here it is shown that the phase in which the catalysis is performed has a dramatic impact on the selectivity of the oxidative coupling of alcohols to esters over unsupported nanoporous gold catalysts, affording nearly optimal cross-coupling to a single ester at equimolar concentrations in the liquid. Operation in the liquid vs the gas phase affects 1) the relative C-H activation rates of methoxy and 1-propoxy, 2) the fraction of C-H activation which leads to esters vs aldehydes, and 3) the fraction of esters which result from cross-coupling vs self-coupling. While activation of the critical adsorbed reactive alkoxy intermediate is faster for 1-propoxy than methoxy in both phases, the liquid phase is more effective in coupling the resulting aldehyde with adsorbed methoxy or 1-propoxy to yield an ester. Additionally, operation in the liquid phase promotes cross-coupling to methyl propionate, whereas in the gas-phase self-coupling of 1-propanol to propyl propionate is favored. The promotion of self-coupling in the gas phase results from the stabilization of larger alkoxides on the surface by Au-alkyl van der Waals forces. However, such forces do not appear dominant in the liquid phase, as evidenced by similar cross-coupling selectivities of methanol with ethanol, 1-propanol, and 1-butanol. Introducing steric hindrance into the higher alcohol (i.e., 2-methyl-1-propanol) further promotes cross-coupling. Here, this promotion is attributed to a kinetic preference for an aldehyde to couple with less-hindered alkoxides. Altogether, these findings demonstrate that alcohol cross-coupling selectivities are strongly impacted by the phase in which the catalysis is conducted, thus altering the phase provides opportunities for selective and efficient chemical syntheses.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Radical Coupling Reactions in Lignin Synthesis: A Density Functional Theory Study

Lignin is a complex, heterogeneous polymer in plant cell walls that provides mechanical strength to the plant stem and confers resistance to degrading microbes, enzymes, and chemicals. Lignin synthesis initiates through oxidative radical-radical coupling of monolignols, the most common of which are p-coumaryl, coniferyl, and sinapyl alcohols. Here, we use density functional theory to characterize radical-radical coupling reactions involved in monolignol dimerization. We compute reaction enthalpies for the initial self- and cross-coupling reactions of these monolignol radicals to form dimeric intermediates via six major linkages observed in natural lignin. The 8-O-4, 8-8, and 8-5 coupling are computed to be the most favorable, whereas the 5-O-4, 5-5, and 8-1 linkages are less favorable. Overall, p-coumaryl self- and cross-coupling reactions are calculated to be the most favorable. For cross-coupling reactions, in which each radical can couple via either of the two sites involved in dimer formation, the more reactive of the two radicals is found to undergo coupling at its site with the highest spin density.

09 BIOMASS FUELS↗
DOE OSTI2019

Specific energy cost for nitrogen fixation as NO x using DC glow discharge in air

Abstract We report on factors influencing the specific energy costs of producing NO x from pin-to-pin DC glow discharges in air at atmospheric pressure. Discharge current, gap distance, gas flowrate, exterior tube wall temperature and the presence and position of activated Al 2 O 3 catalyst powder were examined. The presence of heated catalyst adjacent to the plasma zone improved energy efficiency by as much as 20% at low flows, but the most energy efficient conditions were found at the highest flowrates that allowed a stable discharge (about 10–15 l min −1 ). Under these conditions, the catalyst had no effect on efficiency in the present study. The lowest specific energy cost was observed to be between about 200–250 GJ/tN. The transport of active chemical species and energy are likely key factors controlling the specific energy costs of NO x production in the presence of a catalyst. Air plasma device design and operating conditions must ensure that plasma-generated active intermediate chemical species transport is optimally coupled with catalytically active surfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Structure of amorphous materials in the NASICON system Na 1+x Ti 2 Si x P 3−x O 12

Abstract The structure of glasses in the sodium (Na) super-ionic conductor (NASICON) system Na 1 + x Ti 2 Si x P 3 − x O 12 with x = 0.8 and x = 1.0 was explored by combining neutron and high-energy x-ray diffraction with 29 Si, 31 P and 23 Na solid-state nuclear magnetic resonance (NMR) spectroscopy. The 29 Si magic angle spinning (MAS) NMR spectra reveal that the silica component remains fully polymerized in the form of Si 4 units, i.e. the silicon atoms are bound to four bridging oxygen atoms. The 31 P{ 23 Na} rotational echo adiabatic passage double resonance (REAPDOR) NMR data suggest that the 31 P MAS NMR line shape originates from four-coordinated P n units, where n = 1, 2 or 3 is the number of bridging oxygen atoms per phosphorus atom. These sites differ in their 31 P- 23 Na dipolar coupling strengths. The results support an intermediate range order scenario of a phosphosilicate mixed network-former glass in which the phosphate groups selectively attract the Na + modifier ions. Titanium takes a sub-octahedral coordination environment with a mean Ti–O coordination number of 5.17(4) for x = 0.8 and 4.86(4) for x = 1.0. A mismatch between the P–O and Si–O bond lengths of 8% is likely to inhibit the incorporation of silicon into the phosphorus sites of the NASICON crystal structure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Enhanced pairing of quantum critical metals near d = 3 + 1

We study the dynamics of a quantum critical boson coupled to a Fermi surface in intermediate energy regimes where the Landau damping of the boson can be parametrically controlled, either via large Fermi velocity or by large- N techniques. We develop a systematic approach to the BCS instability of such systems, including careful treatment of the enhanced log 2 and log 3 singularities which appear already at 1-loop. These singularities arise due to the exchange of a critical boson in the Cooper channel and are absent in Fermi liquid theory. We also treat possible instabilities to charge density wave (CDW) formation, and compare the scales Λ BCS and Λ CDW of the onset of the instabilities in different parametric regimes. We address the question of whether the dressing of the fermions into a non-Fermi liquid via interactions with the order parameter field can happen at energies > Λ BCS , Λ CDW .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Electron-Phonon Systems on a Universal Quantum Computer

We present an algorithm that extends existing quantum algorithms for simulating fermion systems in quantum chemistry and condensed matter physics to include bosons in general and phonons in particular. We introduce a qubit representation for the low-energy subspace of phonons which allows an efficient simulation of the evolution operator of the electron-phonon systems. As a consequence of the Nyquist-Shannon sampling theorem, the phonons are represented with exponential accuracy on a discretized Hilbert space with a size that increases linearly with the cutoff of the maximum phonon number. The additional number of qubits required by the presence of phonons scales linearly with the size of the system. The additional circuit depth is constant for systems with finite-range electron-phonon and phonon-phonon interactions and linear for long-range electron-phonon interactions. Our algorithm for a Holstein polaron problem was implemented on an Atos quantum learning machine quantum simulator employing the quantum phase estimation method. The energy and the phonon number distribution of the polaron state agree with exact diagonalization results for weak, intermediate, and strong electron-phonon coupling regimes.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

Changes in an enzyme ensemble during catalysis observed by high-resolution XFEL crystallography

Enzymes populate ensembles of structures necessary for catalysis that are difficult to experimentally characterize. We use time-resolved mix-and-inject serial crystallography at an x-ray free electron laser to observe catalysis in a designed mutant isocyanide hydratase (ICH) enzyme that enhances sampling of important minor conformations. The active site exists in a mixture of conformations, and formation of the thioimidate intermediate selects for catalytically competent substates. The influence of cysteine ionization on the ICH ensemble is validated by determining structures of the enzyme at multiple pH values. Large molecular dynamics simulations in crystallo and time-resolved electron density maps show that Asp 17 ionizes during catalysis and causes conformational changes that propagate across the dimer, permitting water to enter the active site for intermediate hydrolysis. ICH exhibits a tight coupling between ionization of active site residues and catalysis-activated protein motions, exemplifying a mechanism of electrostatic control of enzyme dynamics.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Beam Echoes in the Presence of Coupling

Transverse beam echoes could provide a new technique of measuring diusion characteristics orders of magnitude faster than the current methods; however, their interaction with many accelerator parameters is poorly understood. Using a program written in C, we explored the relationship between coupling and echo strength. We found that echoes could be generated in both dimensions, even with a dipole kick in only one dimension. We found that the echo eects are not destroyed even when there is strong coupling, falling o only at extremely high coupling values. We found that at intermediate values of skew quadrupole strength, the decoherence time of the beam is greatly increased, causing a destruction of the echo eects. We found that this is caused by a narrowing of the tune width of the particles. Results from this study will help to provide recommendations to IOTA (Integrable Optics Test Accelerator) for their upcoming echo experiment.

43 PARTICLE ACCELERATORS↗
DOE OSTI2017

Beam echoes in the presence of coupling

Transverse beam echoes could provide a new technique of measuring diusion characteristics orders of magnitude faster than the current methods; however, their interaction with many accelerator parameters is poorly understood. Using a program written in C, we explored the relationship between coupling and echo strength. We found that echoes could be generated in both dimensions, even with a dipole kick in only one dimension. We found that the echo eects are not destroyed even when there is strong coupling, falling o only at extremely high coupling values. We found that at intermediate values of skew quadrupole strength, the decoherence time of the beam is greatly increased, causing a destruction of the echo eects. We found that this is caused by a narrowing of the tune width of the particles. Results from this study will help to provide recommendations to IOTA (Integrable Optics Test Accelerator) for their upcoming echo experiment.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Hydroxyacetone production from C 3 Criegee intermediates

Hydroxyacetone (CH 3 C(O)CH 2 OH) is observed as a stable end product from reactions of the (CH 3 ) 2 COO Criegee intermediate, acetone oxide, in a flow tube coupled with multiplexed photoionization mass spectrometer detection. In the experiment, the isomers at m/z = 74 are distinguished by their different photoionization spectra and reaction times. Hydroxyacetone is observed as a persistent signal at longer reaction times at a higher photoionization threshold of ca. 9.7 eV than Criegee intermediate and definitively identified by comparison with the known photoionization spectrum. Complementary electronic structure calculations reveal multiple possible reaction pathways for hydroxyacetone formation, including unimolecular isomerization via hydrogen atom transfer and –OH group migration as well as self-reaction of Criegee intermediates. Varying the concentration of Criegee intermediates suggests contributions from both unimolecular and self-reaction pathways to hydroxyacetone. As a result, the hydroxyacetone end product can provide an effective, stable marker for the production of transient Criegee intermediates in future studies of alkene ozonolysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Importance of proton-coupled electron transfer in cathodic regeneration of organic hydrides

Electrochemical regeneration of organic hydrides is often hindered by the rapid dimerization of organic radicals produced as the first intermediates of these electrochemical transformations. Here, we utilize proton-coupled electron transfer to outcompete the undesired dimerization and achieve successful hydride regenerations of two groups of organic hydrides – acridines and benzimidazoles. An analysis of the critical factors that control the regeneration pathways of organic hydrides is demonstrated in this report.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Flame dynamics and kinetic coupling of ammonia and dimethyl-ether in non-premixed cool and warm flames at elevated pressure

Developing advanced low-temperature combustion engines with ammonia-biofuel blends requires a comprehensive understanding of low-temperature flame dynamics and kinetic interactions between ammonia and oxygenated fuels at elevated pressures. This work aims to study the dynamics and kinetics of non-premixed Dimethyl Ether (DME)/Ammonia (NH 3 ) cool and warm flames, and their reignition to hot flames. A counterflow burner is employed to establish DME/NH 3 cool/warm flames at pressures up to 5 atm. The extinction limits of cool flame and the reignition limits of warm flame to hot flame are measured by varying NH 3 concentrations and compared to simulations to quantitatively examine the effects on DME/NH 3 flames. It is found that NH 3 inhibits low-temperature DME oxidation and results in lower cool flame extinction limits. Warm flames in the presence of NH 3 are observed for the first time, revealing a non-monotonic effect of NH 3 addition: a small amount of NH 3 presence enhances warm flame chemistry and promotes reignition to hot flames, while a high NH 3 concentration weakens the warm flame. This trend is further explained by 0-D PSR kinetic simulations and 1-D S-curve flame dynamic calculations. Three flame transition regimes between cool flames (CF), warm flames (WF), and hot flames (HF) by different levels of NH 3 additions at a specific strain rate are identified, namely WFHF reignition, WF-CF transition, and WF extinction. Reaction sensitivity analyses of OH at low temperatures show that NH3 inhibits DME oxidation through OH consumption via H-abstraction and the kinetic couplings of RO 2 /NH 2 , RO 2 /NO x , R/NO x , and O 2 QOOH/NO x further suppress the low-temperature branching. At intermediate-temperatures, NH 2 /NO x /HO 2 coupling promotes warm flames via the pathway NH 2 → H 2 NO → HNO → NO by converting O 2 → HO 2 → OH. At even higher NH₃ concentrations, radical termination reactions of NH 2 + NO/NO 2 and excessive OH consumption via H-abstraction inhibit the flame. The insights into the kinetic coupling between NH 3 and low-temperature chemistry at elevated pressure and its impact on the dynamics of cool-warm-hot flame transitions will contribute to advancing combustion technologies with reduced emissions and improved energy-efficiency.

42 ENGINEERING↗
DOE OSTI2020

Disparate Exciton-Phonon Couplings for Zone-Center and Boundary Phonons in Solid-State Graphite

The exciton-phonon coupling in highly oriented pyrolytic graphite is studied using resonant inelastic x-ray scattering (RIXS) spectroscopy. With ~70 meV energy resolution, multiple low energy excitations associated with coupling to phonons can be clearly resolved in the RIXS spectra. Here, using resonance dependence and the closed form for RIXS cross section without considering the intermediate state mixing of phonon modes, the dimensionless coupling constant g is determined to be 5 and 0.35, corresponding to the coupling strength of 0.42 eV+/-20 meV and 0.20 eV+/-20 meV, for zone center and boundary phonons, respectively. The reduced g value for the zone-boundary phonon may be related to its double resonance nature.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Optimized Substrate Positioning Enables Switches in the C–H Cleavage Site and Reaction Outcome in the Hydroxylation–Epoxidation Sequence Catalyzed by Hyoscyamine 6β-Hydroxylase

Hyoscyamine 6β-hydroxylase (H6H) is an Fe(II)- and 2-oxoglutarate-dependent (Fe/2OG) oxygenase that catalyzes the last two steps in the biosynthesis of scopolamine, a prolifically administered anti-nausea drug. After its namesake first reaction, H6H couples the newly installed C6-bonded oxygen to C7 to form the epoxide of scopolamine. Oxoiron(IV) (ferryl) intermediates initiate both reactions by cleaving C–H bonds, but it remains unclear how the enzyme switches target site and promotes (C6)O–C7 coupling in preference to C7 hydroxylation in the second step. In one possible epoxidation mechanism, the C6 oxygen would – analogously to mechanisms proposed for the Fe/2OG halogenases and, in the preceding paper, N-acetylnorloline synthase (LolO) – coordinate as alkoxide to the C7–H-cleaving ferryl intermediate to enable alkoxyl coupling to the ensuing C7 radical. Here we provide structural and kinetic evidence that H6H instead exploits the distinct spatial dependencies of competitive C–H-cleavage (C6 vs C7) and C–O-coupling (oxygen rebound vs cyclization) steps to promote the two-step sequence without substrate coordination or repositioning for the epoxidation step. Structural comparisons of ferryl-mimicking vanadyl complexes of wild-type H6H and a variant that preferentially hydroxylates C7 of 6-hydroxyhyoscyamine suggest that only a modest (~ 10°) shift in the Fe–O–H(C7) approach angle is sufficient to change the outcome. Finally, the observation that, in wild-type H6H, 2 H 2 O solvent also increases the C7-hydroxylation:epoxidation ratio by ~ 8-fold implies that the latter outcome requires cleavage of the alcohol O-H bond, which, unlike in the LolO oxacyclization, is not accomplished in advance of C–H cleavage.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Design principles of tandem cascade photoelectrochemical devices

Cascade photoelectrocatalysis (PEC) is a possible method to improve the selectivity of solar-driven CO 2 reduction (CO 2 R). This concept can be realized by coupling different CO 2 R catalysts to different subcells in a multijunction photovoltaic (PV) stack. Efficient implementation will require careful tuning of the photocurrents and design of the photovoltages provided by the subcells to the CO 2 R catalysts in such a way as to facilitate the target reaction. Here, we outline the design principles of the tandem PEC approach using two-step conversion of CO 2 to ethylene in aqueous electrolyte, via a CO intermediate, as a model system. To perform this reaction, the first coupled PV-catalyst component should provide 4 electrons to reduce 2 molecules of CO 2 to CO; the second component should provide 8 electrons to reduce 2 CO molecules to C 2 H 4 . Based on known CO 2 R catalysts, the overpotential required to produce CO can be less than that required to reduce it to ethylene, creating the opportunity for improved efficiency. Cascade PEC can be realized in a three-terminal tandem (3TT) configuration using III–V-semiconductor based subcells coupled to Au (produces CO intermediate) and Cu (converts CO to ethylene). The current to each catalyst can be controlled by the area of the subcell exposed to the electrolyte, and the photovoltage is determined by the materials selected and device configuration. Operating conditions are found by simulating the coupled system using the open-source circuit simulator SPICE (Simulation Program with Integrated Circuits Emphasis). We identify conditions under which a 3TT configuration can have a higher solar to chemical conversion efficiency compared to a two-terminal two-junction tandem (2T 2J) with the same absorbers and a Cu catalyst only. We also show that 3TT PEC devices can be less sensitive to variations in catalyst activity compared to 2T devices. Lastly, we discuss the applications of cascade PEC to CO 2 reduction, using different intermediates, and to other chemical networks.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗