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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Three-Dimensional Full-Core BEAVRS Using OpenMOC with Transport Equivalence

Using an optimized implementation of the three-dimensional (3D) method of characteristics for neutron transport, along with a novel equivalence method for transport calculations that was designed to correct self-shielding errors from neglecting the angular dependence of resonant group absorption, a 3D full-core light water reactor hybrid stochastic-deterministic eigenvalue calculation was achieved. This paper presents the optimizations developed and compares the transport solutions obtained. For the statepoint, run times near 10 000 CPU hours are achieved—improving on previous works by an order of magnitude—with near 1% error on pin fission to 238 U capture ratios and a few dozen pcms on the eigenvalue.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2023

Dyson maps and unitary evolution for Maxwell equations in tensor dielectric media

The propagation and scattering of electromagnetic waves in dielectric media is of theoretical and experimental interest in a wide variety of fields. An understanding of observational results generally requires a numerical solution of Maxwell equations—usually implemented on conventional computers using sophisticated numerical algorithms. In recent years, advances in quantum information science and in the development of quantum computers have piqued curiosity about taking advantage of these resources for an alternate numerical approach to Maxwell equations. This requires a reformulation of the classical Maxwell equations into a form suitable for quantum computers which, unlike conventional computers, are limited to unitary operations. In this paper, a unitary framework is developed for the propagation of electromagnetic waves in a spatially inhomogeneous, passive, nondispersive, and anisotropic dielectric medium. For such a medium, generally, the evolution operator in the combined Faraday-Ampere equations is not unitary. There are two steps needed to convert this equation into a unitary evolution equation. In the first step, a weighted Hilbert space is formulated in which the generator of dynamics is a pseudo-Hermitian operator. In the second step, a Dyson map is constructed which maps the weighted-physical-Hilbert space to the original Hilbert space. Furthermore, the resulting evolution equation for the electromagnetic wave fields is unitary. Utilizing the framework developed in these steps, a unitary evolution equation is derived for electromagnetic wave propagation in a uniaxial dielectric medium. The resulting form is suitable for quantum computing.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Precise Compositional Characterization of Plutonium Alloys by Electron Probe Microanalysis

Key Takeaway Points: • Unlike most other materials, the precise compositional analysis of plutonium, including compounds and alloys, is riddled by numerous difficulties that are unique to the element, including the high atomic number and radioactive nature. There’s work to be done! • Radioactive materials require special handling to ensure precise compositions can be measured by EPMA. • Mean Atomic Number background corrections are limited due to high average atomic number. • Mass Absorption Coefficients are unknown for most light elements. Quantification relies upon calibration curves. • Principal Component Analysis could be a useful tool to improve interpretation of complicated, multiple element X-ray maps.

Maner, IV, James L.↗
DOE OSTI2021

Bladed solar thermal receivers for concentrating solar power

A bladed solar thermal receiver for absorbing concentrated sunlight is disclosed. The receiver includes a plurality of panels arranged in a bladed configuration for absorbing sunlight. The bladed configurations can be radial or planar. The receiver design increases the effective solar absorptance and efficiency by providing a light trap for the incident solar radiation while reducing heat losses from radiation and convection.

Ho, Clifford K.↗
DOE OSTI2022

Method of evaluating pH using a metallic nanoparticle incorporated nanocomposite-based optical pH sensor

A method for evaluating the pH of an aqueous solution by utilizing the optical properties of a pH sensing material comprised of plurality of optically active nanoparticles dispersed in matrix material. The optically active nanoparticles have an electronic conductivity greater than about 10−1 S/cm and generally have an average nanoparticle diameter of less that about 500 nanometers, and the matrix material is a material which experiences a change in surface charge density over a pH range from 2.0 to 12.0 of at least 1%. The method comprises contacting the pH sensing material and the aqueous solution, illuminating the pH sensing material, and monitoring an optical signal generated through comparison of incident light and exiting light to determine the optical transmission, absorption, reflection, and/or scattering of the pH sensitive material. The optical signal of the pH sensitive material varies in response to the pH of the aqueous solution.

Ohodnicki, Jr., Paul R.↗
DOE OSTI2022

Selective Thermal Emission with Radiation and Adsorption in Annuli (STERADIAN): An Advanced Heat Exchanger Concept for Supercritical CO 2 Power Cycles

One of the key limitations affecting ability to achieve the efficiency and cost saving advantages of a supercritical CO 2 (scCO 2 ) power cycle resides with the primary heat exchanger where costs can exceed 50% of the plant capital budget depending on design. This project established the foundational groundwork for a new type of heat exchanger optimized to take advantage of radiative heat transfer to scCO 2 . Selective thermal emission coatings were designed and tested that radiated more light tuned to the 4.2 µm infrared absorption band of CO 2 . Coating design utilized principles of nanophotonic bandgap theory to design a selective emitter that has: 1) low emissivity in the visible band, 2) near 100% effective emissivity in the mid-IR wavelength between 4 and 4.5 µm wavelength, and 3) strong suppression of far-IR light emission that will maximize radiative heat transfer efficiency to scCO 2 . Computational fluid dynamics simulations show that an advanced heat exchanger implementing this selective thermal emitter coating is 25 to as much as 40% smaller than conventional heat exchanger designs.

14 SOLAR ENERGY↗
DOE OSTI2020

Hot Electron Driven Photocatalysis on Plasmon-Resonant Grating Nanostructures

Here, we demonstrate the hot electron injection of photoexcited carriers in an Ag-based plasmon resonant grating structure. By varying the incident angle of irradiation, sharp dips are observed in the reflectance with p-polarized light (electric field perpendicular to grating lines) when there is wavevector matching between the incident light and the plasmon resonant modes of the grating and no angle dependence is observed with s-polarized light. This configuration enables us to compare photoelectrochemical current produced by plasmon resonant excitation with that of bulk metal interband absorption simply by rotating the polarization of the incident light while keeping all other parameters of the measurement fixed. With 633 nm light, we observed a 12-fold enhancement in the photocurrent (i.e., reaction rate) between resonant and nonresonant polarizations at incident angles of ±7.6° from normal. At 785 nm irradiation, we observed similar resonant profiles to those obtained with 633 nm wavelength light but with a 44-fold enhancement factor. Using 532 nm light, we observed two resonant peaks (with approximately 10× enhancement) in the photocurrent at 19.4° and 28.0° incident angles, each corresponding to higher order modes in the grating with more nodes per period. The lower enhancement factors observed at shorter wavelengths are attributed to interband transitions, which provide a damping mechanism for the plasmon resonance. Finite difference time domain (FDTD) simulations of these grating structures confirm the resonant profiles observed in the angle-dependent spectra of these gratings and provide a detailed picture of the electric field profiles on and off resonance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Si Microwire-Array Photocathodes Decorated with Cu Allow CO 2 Reduction with Minimal Parasitic Absorption of Sunlight

High loadings of Cu were integrated on the light-facing side of Si microwire arrays used under simulated sunlight for the photoelectrochemical reduction of CO 2 (aq) to hydrocarbons in 0.10 M KHCO 3 (aq). Radial-junction n + p-Si microwire arrays decorated with Cu exhibited absolute photocurrent densities comparable to an uncovered Si surface. Moreover, with respect to a Cu foil electrode, the positive shift in the onset potential for hydrocarbon formation at n + p-Si/Cu microwire arrays was equal to or greater than the photovoltage of the semiconductor alone. Selective electrodeposition of Cu on the tips and sidewalls of Si microwires was responsible for the minimal parasitic reflection and absorption exhibited by the catalyst, such that light-limited, absolute current densities >25 mA·cm –2 were sustained for 48 h under simulated sunlight. Photoelectrodes prepared from semiconductors with low diode quality factors and electrocatalysts with large Tafel slopes are shown to benefit from increased microstructured surface area. Si microwire arrays are thus suitable for photoelectrochemical reactions requiring high loadings of metallic and reflective electrocatalysts.

25 ENERGY STORAGE↗
DOE OSTI2022

Beta Radiation Hardness of GYGAG(Ce) Transparent Ceramic Scintillators

GYGAG(Ce) transparent ceramic garnet scintillators were irradiated with electrons from 0.5 to 2 MeV with fluences from 10 16 e – /cm 2 to 10 19 e – /cm 2 , corresponding to doses from 0.3 to 310 Gigarad. Absorption spectra were measured before and after irradiations. Light yields from alpha, beta, and gamma excitations were measured before and after irradiation and compared to preirradiation values to gain a deeper understanding of how electron irradiations can affect light yield, as well as defects generated in both the surface and bulk. Within experimental error, no degradation in light yield was observed for the electron-irradiated samples, as measured via beta or gamma excitation, with minimal degradation observed via alpha excitation. A small increase in optical absorption near the wavelength of emission was observed following the largest dose irradiation. These results suggest that GYGAG(Ce) is radiation hard to electron irradiation up to 10 19 e – /cm 2 and doses up to 310 Gigarad. Furthermore, this robustness to irradiation indicates that transparent ceramic garnets may prove useful for applications such as scintillation-based nuclear batteries by allowing for higher energy beta emitters, increased power densities, and enabling long service lifetimes.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Robust chain aggregation of low-entropy rigid ladder polymers in solution

Conjugated polymers have been widely investigated where ladder-type conjugated polymers receive more attention due to their rigid backbones and extraordinary properties. However, the understanding of how the rigid conformation of ladder polymers translates to material properties is still limited. Here, we systematically investigated the solution aggregation properties of a carbazole-derived conjugated ladder polymer (LP) and its analogous non-ladder control polymer (CP) via light scattering, neutron scattering, and UV-vis absorption spectroscopy characterization techniques, revealing a highly robust, temperature-insensitive aggregation behavior of the LP. The experimental findings were further validated by computational molecular dynamics simulations. Here we found that the peak positions and intensities of the UV spectra of the LP remained constant between 20 °C and 120 °C in chlorobenzene solution. The polymer also showed a stable hydrodynamic radius measured by dynamic light scattering from 20 °C to 70 °C in the chlorobenzene solution. Using small-angle neutron scattering, no Guinier region was reached in the measured q range down to 0.008 Å –1 , even at elevated temperature. In contrast, the non-ladder control polymer CP was fully soluble in the chlorobenzene solvent without the observation of any notable aggregates. The Brownian dynamics simulation showed that during polymer aggregation, the entropy change of the LP was significantly less negative than that of the non-ladder control polymer. These findings revealed the low entropy nature of rigid conjugated ladder polymers and the low entropy penalty for their aggregation, which is promising for highly robust intermolecular interactions at high temperatures. Such a unique thermodynamic feature of rigid ladder polymers can be leveraged in the design and application of next-generation electronic and optoelectronic devices that function under unconventional high temperature conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Building a Framework to Understand Transition Metals' Behavior in Euxinic Conditions (Final Technical Report)

This project focuses first and foremost on metal sulfide geochemistry and mineralogy as controlled by a complex matrix of environmental factors. The principal investigator’s group aim to illuminate the metal-sulfide reaction mechanisms, rates, and pathways through systematic experimentation and data collection and analyzing the relationships between the characteristics of the produced metal sulfide solid-phase/aqueous complexes and the environmental factors. This understanding is essential for obtaining a full picture of the complex cycling patterns of single or multi metal species in sulfidic environments ranging from deep-see basins, hydrothermal vents, inland seas, terrestrial water bodies, to engineered remediation systems. The specific goal of this past project was to illuminate the reaction mechanisms and kinetics of metal anions and sulfide in mixed metal cation-metal anion-sulfide systems under various aqueous conditions (which resembled a range of naturally occurring euxinic settings). For the period of this contract, we investigated the molybdenum-iron-sulfide system, with an emphasis on the conditions that caused solid phase formation. We focused on quantifying the mobility/sequestration of molybdenum under each experimental condition and identified the changes of valence states for each involved element (i.e., Mo, Fe, and S) in the precipitate. We also proposed pathways for the electron transfer that occurred in aqueous chemistry. The major analytical tools used for this study include UV-visible light spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and synchrotron-based X-ray absorption spectroscopy (access gained through facility proposals to the Canadian Light Source). The biggest finding of this project was that besides pH, the iron-sulfur chemistry has a dominant control of the thiolation kinetics and subsequent reduction of Mo(VI), which are likely prerequisites of molybdenum sequestration in anoxic conditions. The results have been written up as manuscript by the end of this project (see Phillips et al.). The experimental results of this project may be critical for advancing our understanding of (1) basic chemistry involving transition metals and reduced sulfur species, (2) the validity of certain geochemical proxies, and (3) the stability and evolution of euxinic geochemical environments. It is noted that the basic results obtained through this project also have implications for Mo-S cluster-based catalyst development in inorganic chemistry and materials sciences.

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

Excited-State Dynamics of All the Mono-cis and the Major Di-cis Isomers of β-Apo-8′-Carotenal as Revealed by Femtosecond Time-Resolved Transient Absorption Spectroscopy

Cis isomers of carotenoids play important roles in light harvesting and photoprotection in photosynthetic bacteria, such as the reaction center in purple bacteria and the photosynthetic apparatus in cyanobacteria. Carotenoids containing carbonyl groups are involved in efficient energy transfer to chlorophyll in light-harvesting complexes, and their intramolecular charge–transfer (ICT) excited states are known to be important for this process. Previous studies, using ultrafast laser spectroscopy, have focused on the central-cis isomer of carbonyl-containing carotenoids, revealing that the ICT excited state is stabilized in polar environments. However, the relationship between the cis isomer structure and the ICT excited state has remained unresolved. In this study, we performed steady-state absorption and femtosecond time-resolved absorption spectroscopy on nine geometric isomers (7-cis, 9-cis, 13-cis, 15-cis, 13′-cis, 9,13′-cis, 9,13-cis, 13,13′-cis, and all-trans) of β-apo-8′-carotenal, whose structures are well-defined, and discovered correlations between the decay rate constant of the S1 excited state and the S0−S1 energy gap, as well as between the position of the cis-bend and the degree of stabilization of the ICT excited state. Our results demonstrate that the ICT excited state is stabilized in polar environments in cis isomers of carbonyl-containing carotenoids and suggest that the position of the cis-bend plays an important role in the stabilization of the excited state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Impact of Classical and Quantum Light on Donor–Acceptor–Donor Molecules

Investigations of entangled and classical two-photon absorption have been carried out for six donor (D)–acceptor (A)–donor (D) compounds containing the dithieno pyrrole (DTP) unit as donor and acceptors with systematically varied electronic properties. Comparing ETPA (quantum) and TPA (classical) results reveals that the ETPA cross section decreases with increasing TPA cross section for molecules with highly off-resonant excited states for single-photon excitation. Theory (TDDFT) results are in semiquantitative agreement with this anticorrelated behavior due to the dependence of the ETPA cross section but not TPA on the two-photon excited state lifetime. Furthermore, the largest cross section is found for a DTP derivative that has a single photon excitation energy closest to resonance with half the two-photon excitation energy. These results are important for the possible use of quantum light for low-intensity energy-conversion applications.

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

Enabling robust, stable, and accurate nonlinear optical measurements from squeezed light generated in hot rubidium vapor

The feasibility of nonlinear optical (NLO) imaging and spectroscopy using low intensity quantum states of light including entangled photon and squeezed light sources, such as those driven by two-photon absorption (TPA), has been a topic of ongoing debate. An unambiguous identification of the appreciable quantum advantage in such quantum light applications could enable NLO imaging of biological samples without photodegradation and phototoxicity. Recently, we have constructed a two-mode squeezed light source based on four-wave mixing in 85Rb vapor, which is capable of 7.9 dB of intensity-difference squeezing (IDS), corresponding to 8.7 dB upon electronic noise correction. In this talk, we discuss the stability of our system, including implementation details on achieving and maintaining 8.7 dB of IDS for several hours, and ensuring the two spatially multimode beams are properly overlapped in a sample with minimal optical loss.

Allen, Harry [ORNL] (ORCID:0000000190253914)↗
DOE OSTI2020

Variable optical properties of light-harvesting complex II revisited

Understanding photosynthetic light harvesting requires knowledge of the molecular mechanisms that dissipate excess energy in thylakoids. However, it remains unclear how the physical environment of light-harvesting complex II (LHCII) influences the process of chlorophyll de-excitation. Here, we demonstrate that protein-protein interactions between LHCIIs affect the optical properties of LHCII and thus influence the total energy budget. Aggregation of LHCII in the dark altered its absorption properties, independent of the amount of prior light exposure. We also revisited the triplet excited state involved in light-induced fluorescence quenching and found another relaxation pathway involving emission in the green region, which might be related to triplet excited energy transfer to neighboring carotenoids and annihilation processes that result in photoluminescence. LHCII- containing liposomes with different protein densities exhibited altered fluorescence and scattering properties. Our results suggest that macromolecular reorganization affects overall optical properties, which need to be addressed to compare the level of energy dissipation.

Iwai, Masakazu↗
DOE OSTI2021

Slow Auger Recombination of Trapped Excitons Enables Efficient Multiple Electron Transfer in CdS–Pt Nanorod Heterostructures

We report solar-to-fuel conversion reaction often requires multiple proton-coupled electron transfer (PCET) processes powered by the energetic electrons and/or holes generated by the absorption of multiple photons. The effective coupling of multiple electron transfer from the light absorber with the multiple PCET reactions at the catalytic center is one of the key challenges in efficient and selective conversion of solar energy to chemical fuels. In this paper, we examine the dynamics of multiple electron transfer in quantum confined CdS nanorods with a Pt tip, in which the CdS rod functions as the light absorber and the Pt tip the catalytic center. By excitation-fluence-dependent transient absorption spectroscopic measurements, we show that the multiexciton Auger recombination rate in CdS rods follows a carrier-collision model, k n A = n 2 (n – 1)/4k 2 A , with a biexciton lifetime (1/k 2 A ) of 2.0 ± 0.2 ns. In CdS–Pt nanorods, electron transfer kinetics from the CdS conduction band edge to the Pt show negligible dependence on the excitation fluence, occurring with a half-life time of 5.6 ± 0.6 ps. The efficiency of multiple exciton dissociation by multiple electron transfer to Pt decreases from 100% in biexciton states to ~41% at 22 exciton state due to the competition with Auger recombination. The half-lifetime of the n-charge separated state recombination (with n electrons in the Pt and n holes in the CdS) decreases from 10 μs in the single charge separated state to 42 ns in nine charge separated states. Our findings suggest the possibility of driving multielectron photocatalytic reactions under intense illumination and controlling product selectivity through multielectron transfer.

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

Giant Magnetic and Optical Anisotropy in Cerium-Substituted M-Type Strontium Hexaferrite Driven by $4f$ Electrons

By performing density-functional calculations, we find a giant magnetocrystalline anisotropy (MCA) constant in abundant element cerium $\mathrm{Ce}$ substituted M-type hexaferrite, in the energetically favorable strontium site, assisted by a quantum confined electron transfer from $\mathrm{Ce}$ to a specific iron $\mathrm{2a}$ site. Remarkably, the calculated electronic structure shows that the electron transfer leads to the formation of $\mathrm{Ce}^{3+}$ and $\mathrm{Fe}^{2+}$ at the $\mathrm{2a}$ site producing an occupied $\mathrm{Ce}$$(4f^1)$ state below the Fermi level that adds a significant contribution to MCA and magnetic moment. A half $\mathrm{Ce}$ substitution forms a metallic state, while a full substitution retains the semiconducting state of the strontium hexaferrite (host). In the latter, the band gap is reduced due to the formation of charge-transferred states in the gap region of the host. The optical absorption coefficient shows an enhanced anisotropy between light polarization in parallel and perpendicular directions. Calculated formation energies, including the analysis of probable competing phases, and elastic constants confirm that both compositions are chemically and mechanically stable. With successful synthesis, the $\mathrm{Ce}$ hexaferrite can be an alternative high-performing critical-element-free permanent magnet material adapted for use in devices such as automotive traction drive motors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗