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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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Studies of Spinons, Majoranas, and Monopoles in Spin Liquid and Quantum Critical Magnets with Neutrons

Quantum and frustrated materials have eminent potential for the future with the promise of transformative properties in energy storage, conversion, and transmission as well as for new types of computing. Many of the new materials being explored are introduced to have highly unusual ground states that show quantum critical behavior or exotic disorder such as spin liquids. Intense interest is focused on the unusual types of fractionalized quasiparticles that these phases can support such as spin-1/2 spinons, Majorana fermions, and magnetic monopoles. Neutron scattering provides a remarkable tool for probing quantum and frustrated states of real magnetic system by measuring the structure and dynamics of atomic spins on the important energy scales involved. Here I review the signatures of these unusual quasiparticles and the evidence for them starting with quasi-1D magnets covering fractionalization of magnons into spinons, confinement effects, and three classes of quantum critical behavior. In 2D I report on the status of quantum spin liquids in triangular and Kagome magnets before considering the current evidence for exotic Majorana fermions in materials that approximate the Kitaev model. Following this I outline the current status of research into magnetic monopoles in 3D spin ice and the potential for emergent electrodynamics in quantum spin ice. Finally, I consider where new developments in materials, experiment, and theory and modeling could lead to new discoveries.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1983

Hue-saturation-intensity split-spectrum processing of Seasat radar imagery

Characteristics of terrain features in orbital radar imagery are investigated on the basis of radar physics and the human visual system. Signal scattering, the dominant factor in radar imagery, is caused by look angle and relief displacement. Power spectra characteristics are explored, noting that surface scattering dominates the low frequencies and slope significantly affects the high frequency tone variations. The maximum human visual response has been identified for achromatic scenes as 7 cycles per degree, whereas in radar imagery the low frequency half-power point occurs near 2.5 cycles/deg. Image feature size at a scale of 1:500,000 has been calculated for the maximum human response at 1.25 km. A hue-saturation-intensity transformation is presented for displaying two or three data sets on the same image and is demonstrated for Seasat SAR imagery. The transformation is shown to restore low spatial frequencies to the SAR imagery in order to identify terrain features which would otherwise not be visually discernible.

Daily, M.↗
DOE OSTI2021

Instrument for in situ hard x-ray nanobeam characterization during epitaxial crystallization and materials transformations

Solid-phase epitaxy (SPE) and other three-dimensional epitaxial crystallization processes pose challenging structural and chemical characterization problems. The concentration of defects, the spatial distribution of elastic strain, and the chemical state of ions each vary with nanoscale characteristic length scales and depend sensitively on the gas environment and elastic boundary conditions during growth. The lateral or three-dimensional propagation of crystalline interfaces in SPE has nanoscale or submicrometer characteristic distances during typical crystallization times. Here, an in situ synchrotron hard x-ray instrument allows these features to be studied during deposition and crystallization using diffraction, resonant scattering, nanobeam and coherent diffraction imaging, and reflectivity. The instrument incorporates a compact deposition system allowing the use of short-working-distance x-ray focusing optics. Layers are deposited using radio-frequency magnetron sputtering and evaporation sources. The deposition system provides control of the gas atmosphere and sample temperature. The sample is positioned using a stable mechanical design to minimize vibration and drift and employs precise translation stages to enable nanobeam experiments. Results of in situ x-ray characterization of the amorphous thin film deposition process for a SrTiO 3 /BaTiO 3 multilayer illustrate implementation of this instrument.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Sodium tungstate-promoted CaMnO 3 as an effective, phase-transition redox catalyst for redox oxidative cracking of cyclohexane

Oxidative cracking, which combines catalytic oxidation and cracking reactions, represents a promising approach to reduce the energy and carbon intensities for light olefin production from naphtha. The need to co-feed gaseous oxygen with hydrocarbons, however, leads to significant CO x formation and safety concerns. The cost and energy consumption associated with air separation also affects its economic attractiveness. In this study, we investigated a redox oxidative cracking (ROC) scheme and evaluated perovskites (La 0.8 Sr 0.2 FeO 3 and CaMnO 3 ) and Na 2 WO 4 -promoted perovskite (La 0.8 Sr 0.2 FeO 3 @Na 2 WO 4 and CaMnO 3 @Na 2 WO 4 ) as the redox catalysts for ROC. CaMnO 3 @Na 2 WO 4 redox catalyst shows high activity, selectivity, and stability for light olefin production from cyclohexane. Operated under a redox oxidative cracking (ROC) scheme, CaMnO 3 @Na 2 WO 4 enhances the catalytic cracking of cyclohexane, while showing high selectivity towards hydrogen combustion with its built-in, active lattice oxygen. Over three-fold increase in olefin yield compared to thermal cracking and 35% yield increase compared to conventional O 2 -cofeed oxidative cracking were achieved. Low energy ion scattering (LEIS), X-ray photoelectric spectroscopy (XPS), and differential scanning calorimetry (DSC) indicated a core-shell structure, where a molten Na 2 WO 4 layer covers the CaMnO 3 core. Na 2 WO 4 modifies the oxygen donation behavior of CaMnO 3 and provides a catalytically active surface for cyclohexane activation. In-situ XRD revealed that CaMnO 3 @Na 2 WO 4 exhibited excellent structural stability and regenerability. The transformation of Mn 4+ ↔ Mn 3+ ↔ Mn 2+ in CaMnO 3 , facilitated by reversible phase transition to (Ca/Mn)O solid solution, is responsible for the lattice oxygen donation and uptake during redox cycles. Electrochemical impedance spectroscopy (EIS) measurements further confirmed that the oxygen species were transported through the molten Na 2 WO 4 layer to participate in ROC. These findings offer mechanistic insights to design effective redox catalysts for hydrocarbon valorization using the chemical looping strategy.

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

In-situ EBSD study of deformation behavior of retained austenite in a low-carbon quenching and partitioning steel via uniaxial tensile tests

Through using in-situ electron back-scattered diffraction and uniaxial tensile tests, this work mainly focuses on the deformation behavior of retained austenite (RA) in a low-carbon quenching and partitioning (Q&P) steel. In this paper, three different types of RA can be distinguished from different locations, respectively, RA grains at the triple edges, twinned austenite and RA grains positioned between martensite. The results have shown that grains at the triple edges and twinned austenite could transform easily with increasing strain, i.e. are less stable when compared with RA grains distributed between martensite that could resist a larger plastic deformation. Meanwhile, the strain leads to rotations of RA grains distributed at the triple edges and between martensite. Moreover, RA grains with a similar orientation undergone similar rotations with the same true strain. These RA grains rotated along a specific slip plane and slip direction and the grain rotation is taken as a significant factor to improve the ductility of steel. In addition, grain sizes of RA decreased gradually with an increase of true strain and smaller (0–0.2 μm) grains were more capable of resisting the deformation. According to kernel average misorientation (KAM) analysis, it can be found that strain distribution is preferentially localized near martensite–austenite phase boundaries and in the interior of martensite. The average KAM values increased continuously with increasing true strain. - Highlights: •The in-situ and ex-situ tensile specimens differ to some extent in mechanical properties. •Retained austenite grains at the triple edges and twinned austenite transformed easily at the early stage of true strain. •Film-like retained austenite grains only rotated prior to the transformation during straining. •Retained austenite grains having with a similar orientation experienced similar rotations during the same true strain.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Laponite-Incorporated UiO-66-NH2-Polyethylene Oxide Composite Membranes for Protection against Chemical Warfare Agent Simulants

A strategy is developed to enhance the barrier protection of polyethylene oxide (PEO)-metal–organic framework (MOF) composite films against chemical warfare agent simulants. To achieve enhanced protection, an impermeable high-aspect-ratio filler in the form of Laponite RD (LRD) clay platelets was incorporated into a composite PEO film containing MOF UiO-66-NH 2 . The inclusion of the platelets aids in mitigating permeation of inert hydrocarbons (octane) and toxic chemicals (2-chloroethyl ethyl sulfide, 2-CEES) of dimensions/chemistry similar to prominent vesicant threats while still maintaining high water vapor transport rates (WVTR). By utilizing small-angle neutron scattering, small-angle X-ray scattering, and wide-angle X-ray scattering, the LRD platelet alignment of the films was determined, and the structure of the films was correlated with performance as a barrier material. Performance of the membranes against toxic chemical threats was assessed using permeation testing of octane and 2-CEES, a common simulant for the vesicant mustard gas, and breathability of the membranes was assessed using WVTR measurements. To assess their robustness, chemical exposure (in situ diffuse reflectance infrared Fourier transform spectroscopy) and mechanical (tensile strength) measurements were also performed. It was demonstrated that the barrier performance of the film upon inclusion of the LRD platelets exceeds that of other MOF-polymer composites found in the literature and that this approach establishes a new path for improving permselective materials for chemical protection applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Effect of the grain arrangements on the thermal stability of polycrystalline nickel-rich lithium-based battery cathodes

One of the most challenging aspects of developing high-energy lithium-based batteries is the structural and (electro)chemical stability of Ni-rich active cathode materials at thermally-abused and prolonged cell cycling conditions. Here, we report in situ physicochemical characterizations to improve the fundamental understanding of the degradation mechanism of charged polycrystalline Ni-rich cathodes at elevated temperatures (e.g., ≥ 40 °C). Using multiple microscopy, scattering, thermal, and electrochemical probes, we decouple the major contributors for the thermal instability from intertwined factors. Our research work demonstrates that the grain microstructures play an essential role in the thermal stability of polycrystalline lithium-based positive battery electrodes. We also show that the oxygen release, a crucial process during battery thermal runaway, can be regulated by engineering grain arrangements. Furthermore, the grain arrangements can also modulate the macroscopic crystallographic transformation pattern and oxygen diffusion length in layered oxide cathode materials.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Topology-imprinting in nonlinear metasurfaces

Flat optical components, or metasurfaces, have transformed optical imaging, data storage, information processing, and biomedical applications by providing unprecedented control over light-matter interactions. These nano-engineered structures enable compact, multidimensional manipulation of light’s amplitude, phase, polarization, and wavefront, producing scalar and vector beams with unique properties such as orbital angular momentum and knotted topologies. This flexibility has potential applications in optical communication and imaging, particularly in complex environments such as atmospheric turbulence and undersea scattering. However, designing metasurfaces for shorter wavelengths, such as visible and ultraviolet light, remains challenging due to fabrication limitations and material absorption. Here, we introduce an innovative concept called topology imprinting using judiciously designed all-dielectric nonlinear optical metasurfaces to replicate desired waveforms at fundamental and harmonic frequencies, opening promising avenues for advanced photonic applications.

42 ENGINEERING↗
NASA NTRS1983

Spectral consequences of photoreceptor sampling in the rhesus retina

Optical transforms were used to compute the power spectra of rhesus cones treated as arrays of image sampling points. Spectra were obtained for the central fovea, parafovea, periphery, and far periphery. All were consistent with a novel spatial sampling principle that introduces minimal noise for spatial frequencies below the Nyquist limits implied by local receptor densities, while frequencies above the nominal Nyquist limits are not converted into conspicuous moiree patterns, but instead are scattered into broadband noise. This sampling scheme allows the visual system to escape aliasing distortion despite a large mismatch between retinal image bandwidth and the Nyquist limits implied by extrafoveal cone densities.

Yellott, J. I., Jr.↗
NASA NTRS1989

Structural comparison of nickel electrodes and precursor phases

A summary of previous Raman spectroscopic results and a discussion of important structural differences in the various phases of active mass and active mass precurors are presented. Raman spectra provide unique signatures for these phases, and allow one to distinguish each phase, even when the compound is amorphous to X-rays (i.e., does not scatter X-rays because of a lack of order and/or small particle size). The structural changes incurred during formation, charge and discharge, cobalt addition, and aging will be discussed and related to electrode properties. Important structural differences include NiO2 layer stacking, nonstoichiometry (especially cation-deficit nonstoichiometry), disorder, dopant content, and water content. The results indicate that optimal nickel active mass is non-close packed and nonstoichiometric. The formation process transforms precursor phases into this structure. Therefore, the precursor disorder, or lack thereof, influences this final active mass structure and the rate of formation. Aging processes induce structural change which is believed to be detrimental. The role of cobalt addition can be appreciated in terms of structures favored or stabilized by the dopant. In recent work, the in situ Raman technique to characterize the critical structural parameters was developed. An in situ method relates structure, electrochemistry, and preparation. In situ Raman spectra of cells during charge and discharge, either during cyclic voltammetry or under constant current conditions were collected. With the structure-preparation knowledge and the in situ Raman tool, it will be possible to define the structure-property-preparation relations in more detail. This instrumentation has application to a variety of electrode systems.

Cornilsen, Bahne C.↗
DOE OSTI2024

Reversible hydrogen storage in multilayer graphane: Lattice dynamics, compressibility, and heat capacity studies

Multilayer graphane (hydride of graphite) is a crystalline hydrocarbon of composition CH, which can be synthesized from graphite and molecular hydrogen at pressures above 2GPa [V.E. Antonov et al. Carbon 100 (2016) 465]. Using X-ray diffraction, this compound was tentatively identified as the “graphane II” phase of 3D-graphane predicted by ab initio calculations [X.-D. Wen et al. PNAS 108 (2011) 6833] and consisting of layers of 2D-graphane in the “chair” conformation. When heated in a vacuum, the compound does not form any intermediate hydrocarbons and reversibly decomposes back into graphite and hydrogen at 770–920 K. In the present work, almost single-phase samples of graphite hydride and deuteride were synthesized at 7.4 GPa and 870 K. Their investigation by inelastic neutron scattering supplemented by ab initio calculations gave spectra g(E) of the phonon density of states with a gap of about 15 meV at approx. 100 meV, which is a unique identifier for the chair form of graphane. The equation of state V(P) of the hydride was studied at room temperature and hydrogen pressures up to 53 GPa by synchrotron X-ray diffraction in a diamond anvil cell. Further, the graphane II phase did not react with the surrounding hydrogen and did not undergo any phase transformations upon the compression and after heating to 1500 K at 53GPa. The high thermal and pressure stability of this exotic phase makes it an important part of the C–H system. The obtained g(E) spectra of graphite hydride and deuteride were used to calculate temperature dependences of their heat capacity. Measurements of the heat capacity at temperatures 120–673 K confirmed the good accuracy of these calculations.

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

Functional determinants of radial operators in AdS 2

We study the zeta-function regularization of functional determinants of Laplace and Dirac-type operators in two-dimensional Euclidean AdS 2 space. More specifically, we consider the ratio of determinants between an operator in the presence of background fields with circular symmetry and the free operator in which the background fields are absent. By Fourier-transforming the angular dependence, one obtains an infinite number of one-dimensional radial operators, the determinants of which are easy to compute. The summation over modes is then treated with care so as to guarantee that the result coincides with the two-dimensional zeta-function formalism. The method relies on some well-known techniques to compute functional determinants using contour integrals and the construction of the Jost function from scattering theory. Here, our work generalizes some known results in flat space. The extension to conformal AdS 2 geometries is also considered. We provide two examples, one bosonic and one fermionic, borrowed from the spectrum of fluctuations of the holographic 1/4-BPS latitude Wilson loop.

Wilson↗
DOE OSTI2018

Event-based processing of neutron scattering data at the Spallation Neutron Source

Here, the Spallation Neutron Source at Oak Ridge National Laboratory, USA, ushered in a new era of neutron scattering experiments through the use of event-based data. Tagging each neutron event allows pump–probe experiments, measurements with a parameter asynchronous to the source, measurements with continuously varying parameters and novel ways of testing instrument components. This contribution will focus on a few examples. A pulsed magnet has been used to study diffraction under extreme fields. Continuous ramping of temperature is becoming standard on the POWGEN diffractometer. Battery degradation and phase transformations under heat and stress are often studied on the VULCAN diffractometer. Supercooled Al 2 O 3 was studied on NOMAD. A study of a metallic glass through its glass transition was performed on the ARCS spectrometer, and the effect of source variation on chopper stability was studied for the SEQUOIA spectrometer. Besides a summary of these examples, an overview is provided of the hardware and software advances to enable these and many other event-based measurements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1992

Transient scattering from dielectric cylinders - E-field, H-field, and combined field solutions

In this work, the problem of transient scattering by arbitrarily shaped two-dimensional dielectric cylinders is solved using the marching-on-in-time technique. The dielectric problem is approached via the equivalence principle. Three different formulations, namely, the electric field integral equation formulation, the magnetic field integral equation formulation, and the combined field integral equation formulation are considered. Numerical results are presented for two cross sections, namely, a circle and a square, and compared with inverse discrete Fourier transform (IDFT) techniques. In each case, good agreement is obtained with the IDFT solution.

Vechinski, Douglas A.↗
NASA NTRS1994

Radiation and scattering from printed antennas on cylindrically conformal platforms

The goal was to develop suitable methods and software for the analysis of antennas on cylindrical coated and uncoated platforms. Specifically, the finite element boundary integral and finite element ABC methods were employed successfully and associated software were developed for the analysis and design of wraparound and discrete cavity-backed arrays situated on cylindrical platforms. This work led to the successful implementation of analysis software for such antennas. Developments which played a role in this respect are the efficient implementation of the 3D Green's function for a metallic cylinder, the incorporation of the fast Fourier transform in computing the matrix-vector products executed in the solver of the finite element-boundary integral system, and the development of a new absorbing boundary condition for terminating the finite element mesh on cylindrical surfaces.

Kempel, Leo C.↗
DOE OSTI2026

Laser-Induced Enhancement of Acoustic Mode Quality Factor Revealed by Correlated Single-Particle Optical and Electron Microscopy

Acoustic modes in plasmonic nanostructures provide fundamental insights into their optomechanical behavior at the nanoscale, enabling emerging applications in plasmon-enhanced optomechanics, ultrasensitive sensing, and nanoscale energy transduction. Here we explore the modulation of acoustic phonon dynamics in lithographically fabricated gold nanodisks via laser-induced photothermal annealing. Using a correlated approach that utilizes both single-particle transient extinction spectroscopy and advanced electron microscopy, we directly link nanoscale structural transformations to changes in mechanical properties as probed through the coherence of the excited acoustic modes. Specifically, ultrafast pump–probe microscopy reveals an enhancement in the acoustic mode quality factor of annealed gold nanodisks, indicative of reduced damping and improved vibrational coherence. Structural characterization via scanning electron microscopy and electron backscatter diffraction confirms that photoinduced annealing results in smoother surface morphology and overall enhanced crystallinity. The improved crystalline order reduces defect and crystal boundary scattering, which we suggest as the reason underlying the lower quality factor before annealing. Furthermore, these findings demonstrate that targeted structural engineering at the nanoscale offers a powerful strategy for optimizing the optomechanical performance of plasmonic nanostructures, with broad implications for the design of next-generation nanophotonic and optomechanical systems.

Annealing (metallurgy)↗
DOE OSTI2020

Exact and fast calculation of the X-ray pair distribution function

A fast and exact algorithm to calculate the powder pair distribution function (PDF) for the case of periodic structures is presented. The new algorithm calculates the PDF by a detour via reciprocal space. The calculated normalized total powder diffraction pattern is transferred into the PDF via the sine Fourier transform. The calculation of the PDF via the powder pattern avoids the conventional simplification of X-ray and electron atomic form factors. It is thus exact for these types of radiation, as is the conventional calculation for the case of neutron diffraction. The new algorithm further improves the calculation speed. Additional advantages are the improved detection of errors in the primary data, the handling of preferred orientation, the ease of treatment of magnetic scattering and a large improvement to accommodate more complex instrumental resolution functions.

36 MATERIALS SCIENCE↗