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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 1,243 records · Page 69
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Hybrid Composite Coatings for Durable and Efficient Solar Hydrogen Generation under Diverse Operating Conditions

Safe and practical solar-driven hydrogen generators must be capable of efficient and stable operation under diurnal cycling with full separation of gaseous H 2 and O 2 products. In this paper, a novel architecture that fulfills all of these requirements is presented. The approach is inherently scalable and provides versatility for operation under diverse electrolyte and lighting conditions. The concept is validated using a 1 cm 2 triple-junction photovoltaic cell with its illuminated photocathode protected by a composite coating comprising an organic encapsulant with an embedded catalytic support. The device is compatible with operation under conditions ranging from 1 M H 2 SO 4 to 1 M KOH, enabling flexibility in selection of semiconductor, electrolyte, membrane, and catalyst. Stable operation at a solar-to-hydrogen conversion efficiency of >10% is demonstrated under continuous operation, as well as under diurnal light cycling for at least 4 d, with simulated sunlight. Operational characteristics are validated by extended time outdoor testing. A membrane ensures products are separated, with nonexplosive gas streams generated for both alkaline and acidic systems. Finally, analysis of operational characteristics under different lighting conditions is enabled by comparison of a device model to experimental data.

14 SOLAR ENERGY↗
DOE OSTI2024

Condition-dependent NO x adsorption/desorption over Pd/BEA: A combined microreactor and in situ DRIFTS study

Pd/BEA is chosen as a model passive NO x adsorber (PNA) to elucidate the effect of the feed gas composition on the NO x adsorption/desorption behavior. The Brønsted acid and the partially hydrolyzed framework Al (P-HAl(OH)) sites in HBEA adsorb NO and NO 2 under dry conditions. Moreover, the performance of HBEA is not affected by CO, while CO inhibits nitrate formation and promotes NO adsorption via the Pd(NO)(CO) complexes formation over Pd/BEA. H 2 O inhibits NO adsorption over the Brønsted acid and P-HAl(OH) sites, and ionic Pd is the only active site for NO x adsorption under wet conditions. Furthermore, NO adsorption over hydrated Pd (Pd 2+ (OH)(NO)(H 2 O) 3 ) is weaker than NO adsorption over bare ionic Pd (Z 2 [Pd 2+ (NO)], Z[Pd 2+ (OH)(NO)]). Dehydration of Pd 2+ (OH)(NO)(H 2 O) 3 forms more stable Z[Pd 2+ (OH)(NO)] during desorption. Here, the NO adsorption capacity of Pd/BEA improves in the presence of CO under both dry and wet conditions by forming a stable carbonyl–nitrosyl complex.

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

Sulfonate Group Improves the Solubility and Electrocatalytic Performance of Ru‐Based bda‐ and pda‐Type Water Oxidation Catalysts under Neutral Conditions

Four ruthenium water oxidation catalysts that bear carboxylate and sulfonate groups in the active site have been synthesized and analyzed for their catalytic activity. Here, the sulfonate‐containing catalysts show higher electrochemical activity in pH 7 phosphate buffer with 4 times larger catalytic current, improved durability with sacrificial oxidant, and increased solubility compared to similar species containing two carboxylate groups. Density functional theory calculations suggest that the sulfonate group provides a more favorable geometry for water nucleophilic attack, which is both the energetically most favorable mechanism calculated and the experimentally predicted mechanism under electrochemical conditions. Further experimental studies have been performed to show that under certain conditions catalysts can perform well electrochemically under pH conditions as low as 1.6 and that various structural components can greatly change solubility and catalytic operation.

14 SOLAR ENERGY↗
DOE OSTI2015

Isotopic exchange on solid-phase micro extraction fiber in sediment under stagnant conditions: Implications for field application of performance reference compound calibration

An overlooked issue for field application of in situ performance reference compound (PRC) calibration methods is the validity of the assumption that both the sorption of a target compound and desorption of its corresponding PRC follow the first-order kinetics with the same rate constants under stagnant conditions. In the present study, disposable polydimethylsiloxane fibers of 2 sizes (7 and 35 µm) impregnated with 8 13 C-labeled or deuterated PRCs were statically deployed into different marine sediments, from which the kinetics for sorption of the target compounds and desorption of the PRCs were characterized. Nonsymmetrical profiles were observed for exchange of the target analytes and their corresponding PRCs in sediment under stagnant conditions. Further, the hysteretic desorption of PRCs in the kinetic regime may be ascribed to the low chemical potential between the fiber and sediment porewater, which reflects the inability of water molecules to rapidly diffuse through sediment to solvate the PRCs in the aqueous layer around the fiber surface. A moderate correlation (r = 0.77 and r = 0.57, p < 0.05 for both regressions) between the PRC-calibrated equilibrium concentrations of 1,1-dichloro-2,2-bis-(chlorophenyl) ethylene (p,p'-DDE) and polychlorinated biphenyl (PCB)-153 and the lipid normalized levels in worms (Neanthes arenaceodentata) was obtained in co-exposure tests under simulating field conditions, probably resulting from slightly overestimated bioavailability because of the hysteretic desorption of PRCs and toxic effects. Environ Toxicol Chem 2016;35:1978–1985. © 2015 SETAC

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

Characterization of ambient polychlorinated biphenyl background conditions in surface waters of the Pajarito Plateau, New Mexico

Abstract This study presents the development of polychlorinated biphenyl (PCB) background threshold values (BTVs) that statistically characterize ambient background conditions for surface waters in undeveloped and developed landscapes of the Pajarito Plateau in the Rio Grande Basin of New Mexico. Between 2009 and 2018, surface water data were collected at 45 locations under a variety of flow conditions and regimes. A total of 163 samples were collected, with roughly 1/3 of samples and locations being in undeveloped areas (n = 53 from 17 locations), and the remainder being in developed areas (n = 110 from 28 locations). While there are areas on the Pajarito Plateau where PCB point sources are known or likely to have contributed to PCBs in soils, PCB BTVs calculated for undeveloped portions of watersheds (upstream of areas where PCB point sources are known or likely to have contributed to PCBs in soils, and therefore not affected by PCB sources within the watershed) are well above New Mexico's human health organism-only (HH-OO) water quality criterion (0.64 ng/L). Background threshold values are even higher in developed areas upstream of managed soil sites, suggesting that in developed areas, both diffuse ambient PCB sources (e.g., atmospheric deposition) and localized urban sources (e.g., building materials, paints, and electrical equipment) contribute to PCBs in those watersheds. These findings indicate that New Mexico's current HH-OO water quality criterion for PCBs cannot practicably be met due to ambient conditions. It is also impracticable to meet the US Environmental Protection Agency (EPA) criterion continuous concentration (CCC) of 14 ng/L in developed background areas, where the BTV is approximately 1.5 times the CCC. Integr Environ Assess Manag 2023;19:1307–1319. © 2022 SETAC

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

The denatured state of HIV ‐1 protease under native conditions

Abstract The denatured state of several proteins has been shown to display transient structures that are relevant for folding, stability, and aggregation. To detect them by nuclear magnetic resonance (NMR) spectroscopy, the denatured state must be stabilized by chemical agents or changes in temperature. This makes the environment different from that experienced in biologically relevant processes. Using high‐resolution heteronuclear NMR spectroscopy, we have characterized several denatured states of a monomeric variant of HIV‐1 protease, which is natively structured in water, induced by different concentrations of urea, guanidinium chloride, and acetic acid. We have extrapolated the chemical shifts and the relaxation parameters to the denaturant‐free denatured state at native conditions, showing that they converge to the same values. Subsequently, we characterized the conformational properties of this biologically relevant denatured state under native conditions by advanced molecular dynamics simulations and validated the results by comparison to experimental data. We show that the denatured state of HIV‐1 protease under native conditions displays rich patterns of transient native and non‐native structures, which could be of relevance to its guidance through a complex folding process.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

A Rényi quantum null energy condition: proof for free field theories

The Quantum Null Energy Condition (QNEC) is a lower bound on the stress-energy tensor in quantum field theory that has been proved quite generally. It can equivalently be phrased as a positivity condition on the second null shape derivative of the relative entropy S rel (ρ||σ) of an arbitrary state ρ with respect to the vacuum σ. The relative entropy has a natural one-parameter family generalization, the Sandwiched Rényi divergence S n (ρ||σ), which also measures the distinguishability of two states for arbitrary n &isin; [1/2, ∞). A Rényi QNEC, a positivity condition on the second null shape derivative of S n (ρ||σ), was conjectured in previous work. In this work, we study the Rényi QNEC for free and superrenormalizable field theories in spacetime dimension d > 2 using the technique of null quantization. In the above setting, we prove the Rényi QNEC in the case n > 1 for arbitrary states. We also provide counterexamples to the Rényi QNEC for n < 1.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Implementing the three-particle quantization condition including higher partial waves

We present an implementation of the relativistic three-particle quantization condition including both s - and d -wave two-particle channels. For this, we develop a systematic expansion of the three-particle K matrix, \( \mathcal{K} \) df,3 , about threshold, which is the generalization of the effective range expansion of the two-particle K matrix, \( \mathcal{K} \) 2 . Relativistic invariance plays an important role in this expansion. We find that d -wave two-particle channels enter first at quadratic order. We explain how to implement the resulting multichannel quantization condition, and present several examples of its application. We derive the leading dependence of the threshold three-particle state on the two-particle d -wave scattering amplitude, and use this to test our implementation. We show how strong two-particle d -wave interactions can lead to significant effects on the finite-volume three-particle spectrum, including the possibility of a generalized three-particle Efimov-like bound state. We also explore the application to the 3 π + system, which is accessible to lattice QCD simulations, where we study the sensitivity of the spectrum to the components of \( \mathcal{K} \) df,3 . Finally, we investigate the circumstances under which the quantization condition has unphysical solutions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

On exact-WKB analysis, resurgent structure, and quantization conditions

There are two well-known approaches to studying nonperturbative aspects of quantum mechanical systems: saddle point analysis of the partition functions in Euclidean path integral formulation and the exact-WKB analysis based on the wave functions in the Schrödinger equation. In this work, based on the quantization conditions obtained from the exact-WKB method, we determine the relations between the two formalism and in particular show how the two Stokes phenomena are connected to each other: the Stokes phenomenon leading to the ambiguous contribution of different sectors of the path integral formulation corresponds to the change of the “topology” of the Stoke curves in the exact-WKB analysis. We also clarify the equivalence of different quantization conditions including Bohr-Sommerfeld, path integral and Gutzwiller’s ones. In particular, by reorganizing the exact quantization condition, we improve Gutzwiller’s analysis in a crucial way by bion contributions (incorporating complex periodic paths) and turn it into an exact result. Furthermore, we argue the novel meaning of quasi-moduli integral and provide a relation between the Maslov index and the intersection number of Lefschetz thimbles.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Spatiotemporal distribution of chemical signatures exhibited by Myxococcus xanthus in response to metabolic conditions

Myxococcus xanthus is a common soil bacterium with a complex life cycle, which is known for production of secondary metabolites. However, little is known about the effects of nutrient availability on M. xanthus metabolite production. In this study, we utilize confocal Raman microscopy (CRM) to examine the spatiotemporal distribution of chemical signatures secreted by M. xanthus and their response to varied nutrient availability. Here, ten distinct spectral features are observed by CRM from M. xanthus grown on nutrient-rich medium. However, when M. xanthus is constrained to grow under nutrient-limited conditions, by starving it of casitone, it develops fruiting bodies, and the accompanying Raman microspectra are dramatically altered. The reduced metabolic state engendered by the absence of casitone in the medium is associated with reduced, or completely eliminated, features at 1140 cm –1 , 1560 cm –1 , and 1648 cm –1 . In their place, a feature at 1537 cm –1 is observed, this feature being tentatively assigned to a transitional phase important for cellular adaptation to varying environmental conditions. In addition, correlating principal component analysis heat maps with optical images illustrates how fruiting bodies in the center co-exist with motile cells at the colony edge. While the metabolites responsible for these Raman features are not completely identified, three M. xanthus peaks at 1004, 1151, and 1510 cm –1 are consistent with the production of lycopene. Thus, a combination of CRM imaging and PCA enables the spatial mapping of spectral signatures of secreted factors from M. xanthus and their correlation with metabolic conditions.

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

First and Second Order Necessary Conditions for Stochastic Optimal Control Problems

In this work we consider a stochastic optimal control problem with either convex control constraints or finitely many equality and inequality constraints over the final state. Using the variational approach, we are able to obtain first and second order expansions for the state and cost function, around a local minimum. This fact allows us to prove general first order necessary condition and, under a geometrical assumption over the constraint set, second order necessary conditions are also established. We end by giving second order optimality conditions for problems with constraints on expectations of the final state.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Necessary Conditions of Optimality for Some Stochastic Integrodifferential Equations of Neutral Type on Hilbert Spaces

In this work, we develop the necessary conditions of optimality for partially observed control problems governed by stochastic integrodifferential equations of neutral type on Hilbert spaces driven by relaxed controls. Under suitable conditions, we establish the existence and the uniqueness of mild solution which has a continuous modification. We prove the continuity of the control to the solution map. Then we consider an optimal control problem of Bolza type. Using these results we give necessary conditions of optimality for a class of stochastic integrodifferential equations of neutral type on Hilbert spaces.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Improved subseasonal-to-seasonal precipitation prediction of climate models with nudging approach for better initialization of Tibetan Plateau-Rocky Mountain Circumglobal wave train and land surface conditions

Abstract Reliable subseasonal-to-seasonal (S2S) precipitation prediction is highly desired due to the great socioeconomical implications, yet it remains one of the most challenging topics in the weather/climate prediction research area. As part of the Impact of Initialized Land Temperature and Snowpack on Sub-seasonal to Seasonal Prediction (LS4P) project of the Global Energy and Water Exchanges (GEWEX) program, twenty-one climate models follow the LS4P protocol to quantify the impact of the Tibetan Plateau (TP) land surface temperature/subsurface temperature (LST/SUBT) springtime anomalies on the global summertime precipitation. We find that nudging towards reanalysis winds is crucial for climate models to generate atmosphere and land surface initial conditions close to observations, which is necessary for meaningful S2S applications. Simulations with nudged initial conditions can better capture the summer precipitation responses to the imposed TP LST/SUBT spring anomalies at hotspot regions all over the world. Further analyses show that the enhanced S2S prediction skill is largely attributable to the substantially improved initialization of the Tibetan Plateau-Rocky Mountain Circumglobal (TRC) wave train pattern in the atmosphere. This study highlights the important role that initial condition plays in the S2S prediction and suggests that data assimilation technique (e.g., nudging) should be adopted to initialize climate models to improve their S2S prediction.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Main bearing response in a waked 15-MW floating wind turbine in below-rated conditions

Increased wind turbine size raises unknowns related to structural flexibility. Moreover, moving to deeper waters, component reliability becomes more critical. This work investigates main bearing response dependence on drivetrain flexibility and wake impingement in a two-turbine wind farm. A 15-MW floating direct-drive turbine is considered. Large eddy simulations (LES) are employed to model neutral, stable and unstable atmospheric conditions at below-rated mean wind speed, while the engineering codes OpenFAST and FAST.Farm simulate turbine and wake behavior. Results indicate significant sensitivities in fatigue estimates to lateral distance between the upstream and downstream turbine. The trends are most substantial in stable conditions, where the waked downwind main bearing sees twice the fatigue damage estimates of the upstream turbine for one position and 50% for another. Main bearing fatigue sensitivity to drivetrain flexibility is minor, while properly including generator rotor inertia loads is important for the axial forces of the locating (axially fixed) bearing, especially in stable conditions.

17 WIND ENERGY↗
DOE OSTI2021

Differential effects of redox conditions on the decomposition of litter and soil organic matter

Soil redox conditions exert substantial influence on biogeochemical processes in terrestrial ecosystems. Humid tropical forests are often characterized by fluctuating redox dynamics, yet how redox fluctuations affect patterns in soil versus litter decomposition and associated CO2 fluxes are not well understood in these ecosystems. We used a 13C-labeled litter addition to explicitly follow the decomposition of litter-derived vs. native soil-derived organic matter in response to four different soil redox regimes—static oxic or anoxic, and two oscillating treatments—in soil from the Luquillo Experimental Forest, Puerto Rico. We coupled this incubation experiment with high-resolution mass spectrometry analysis to characterize the preferential decomposition of specific classes of organic molecules. CO2 production from litter and soil organic matter (SOM) showed distinctly different responses to redox manipulation. The cumulative production of SOM-derived CO2 was positively correlated with the length of soil exposure to an oxic headspace (r = 0.89, n = 20), whereas cumulative 13C-litter-derived CO2 production was not linked to oxygen availability. The CO2 production rate from litter was highest under static anoxic conditions in the first half of the incubation period, and later dropped to the lowest among all redox treatments. In the consistently anoxic soils, we observed the depletion of more oxidized water-extractable organic matter (especially amino sugars, carbohydrates, and proteins) over time, suggesting that under anaerobic conditions, microbes preferentially used more oxidized litter-derived compounds during the early stages of decomposition. Results from kinetic modeling showed that more frequent anoxic exposure limited the decomposition of a slow-cycling C pool, but not a fast-cycling pool. Overall, our results demonstrate that substrate source—freshly added litter vs. native organic matter—plays an important role in the redox sensitivity of organic matter decomposition. In soil environments that regularly experience redox fluctuations, anaerobic heterotrophs can be surprisingly effective in degrading fresh plant litter.

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

Stability Analysis of Coupled Advection-Diffusion Models with Bulk Interface Condition

Numerical stability is of critical importance in general circulation models because it affects the design of algorithms, time to solution, and computational costs associated with the simulations, which are very expensive in practice. In this paper we extend the stability analysis for ocean-atmosphere coupling proposed in [Zhang et al., J. Sci. Comput. 84, 44(2020)] to a more realistic model that includes horizontal advection. We analyze various time-stepping strategies. We find that advection has a stabilizing effect in scenarios common to climate models when bulk interface condition and explicit flux coupling are used. We also show that our method can be used to study the stability impact of advection for other interface conditions such as Dirichlet-Neumann conditions.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Acoustic Emission-Based Methodology to Evaluate Delamination Crack Growth Under Quasi-static and Fatigue Loading Conditions

The aim of this study was to investigate the applicability of acoustic emission (AE) technique to evaluate delamination crack in glass/epoxy composite laminates under quasi-static and fatigue loading. To this aim, double cantilever beam specimens were subjected to mode I quasi-static and fatigue loading conditions and the generated AE signals were recorded during the tests. By analyzing the mechanical and AE results, an analytical correlation between the AE energy with the released strain energy and the crack growth was established. It was found that there is a 3rd degree polynomial correlation between the crack growth and the cumulative AE energy. Using this correlation the delamination crack growth was predicted under both the static and fatigue loading conditions. The predicted crack growth values was were in a good agreement with the visually recorded data during the tests. The results indicated that the proposed AE-based method has good applicability to evaluate the delamination crack growth under quasi-static and fatigue loading conditions, especially when the crack is embedded within the structure and could not be seen visually.

42 ENGINEERING↗
DOE OSTI2018

Estimates for Functionals of Solutions to Higher-Order Heat-Type Equations with Random Initial Conditions

In the present paper we continue the investigation of solutions to higher-order heat-type equations with random initial conditions, which play the important role in many applied areas. We consider the random initial conditions given by harmonizable φ-sub-Gaussian processes. The main results are the bounds for the distributions of the suprema over bounded and unbounded domains for solutions of such equations. The results obtained in the paper hold, in particular, for the case of Gaussian initial condition.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗