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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Temperature response of Rubisco kinetics in Arabidopsis thaliana : thermal breakpoints and implications for reaction mechanisms

Enhancement of Rubisco kinetics could improve photosynthetic efficiency, ultimately resulting in increased crop yield. However, imprecise knowledge of the reaction mechanism and the individual rate constants limits our ability to optimize the enzyme. Membrane inlet mass spectrometry (MIMS) may offer benefits over traditional methods for determining individual rate constants of the Rubisco reaction mechanism, as it can directly monitor concentration changes in CO 2 , O 2 , and their isotopologs during assays. However, a direct comparison of MIMS with the traditional radiolabel method of determining Rubisco kinetic parameters has not been made. Here, the temperature responses of Rubisco kinetic parameters from Arabidopsis thaliana were measured using radiolabel and MIMS methods. The two methods provided comparable parameters above 25 °C, but temperature responses deviated at low temperature as MIMS-derived catalytic rates of carboxylation, oxygenation, and CO 2 /O 2 specificity showed thermal breakpoints. Here, we discuss the variability and uncertainty surrounding breakpoints in the Rubisco temperature response and the relevance of individual rate constants of the reaction mechanisms to potential breakpoints.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Bhatnagar-Gross-Krook subgrid model for neutrino quantum kinetics

Here, we present a new subgrid model for neutrino quantum kinetics, which is primarily designed to incorporate effects of collective neutrino oscillations into neutrino-radiation-hydrodynamic simulations for core-collapse supernovae and mergers of compact objects. We approximate the neutrino oscillation term in a quantum kinetic equation using the Bhatnagar-Gross-Krook (BGK) relaxation-time prescription, and the transport equation is directly applicable for classical neutrino transport schemes. The BGK model is motivated by recent theoretical indications that nonlinear phases of collective neutrino oscillations settle into quasisteady structures. We explicitly provide basic equations of the BGK subgrid model for both multiangle and moment-based neutrino transport to facilitate the implementation of the subgrid model in the existing neutrino transport schemes. We also show the capability of our BGK subgrid model by comparing it to fully quantum kinetic simulations for fast neutrino-flavor conversion. We find that the overall properties can be well reproduced in the subgrid model; the error of angular-averaged survival probability of neutrinos is within ~20%. By identifying the source of error, we also discuss perspectives to improve the accuracy of the subgrid model.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Kinetic theory for classical and quantum many-body chaos

For perturbative scalar field theories, the late-time-limit of the out-of-time-ordered correlation function that measures (quantum) chaos is shown to be equal to a Boltzmann-type kinetic equation that measures the total gross (instead of net) particle exchange between phase-space cells, weighted by a function of energy. This derivation gives a concrete form to numerous attempts to derive chaotic many-body dynamics from ad hoc kinetic equations. A period of exponential growth in the total gross exchange determines the Lyapunov exponent of the chaotic system. Physically, the exponential growth is a front propagating into an unstable state in phase space. As in conventional Boltzmann transport, which follows from the dynamics of the net particle number density exchange, the kernel of this kinetic integral equation for chaos is also set by the 2-to-2 scattering rate. This provides a mathematically precise statement of the known fact that in dilute weakly coupled gases, transport and scrambling (or ergodicity) are controlled by the same physics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Kinetics of Enzymatic Mercury Methylation at Nanomolar Concentrations Catalyzed by HgcAB

Methylmercury (MeHg) is a potent bioaccumulative neurotoxin that is produced by certain anaerobic bacteria and archaea. Mercury (Hg) methylation has been linked to the gene pair hgcAB , which encodes a membrane-associated corrinoid protein and a ferredoxin. Although microbial Hg methylation has been characterized in vivo , the cellular biochemistry and the specific roles of the gene products HgcA and HgcB in Hg methylation are not well understood. Here, we report the kinetics of Hg methylation in cell lysates of Desulfovibrio desulfuricans ND132 at nanomolar Hg concentrations. The enzymatic Hg methylation mediated by HgcAB is highly oxygen sensitive, irreversible, and follows Michaelis-Menten kinetics, with an apparent K m of 3.2 nM and V max of 19.7 mol · min -1 · mg -1 total protein for the substrate Hg(II). Although the abundance of HgcAB in the cell lysates is extremely low, Hg(II) was quantitatively converted to MeHg at subnanomolar substrate concentrations. Interestingly, increasing thiol/Hg(II) ratios did not impact Hg methylation rates, which suggests that HgcAB-mediated Hg methylation effectively competes with cellular thiols for Hg(II), consistent with the low apparent K m . Supplementation of 5-methyltetrahydrofolate or pyruvate did not enhance MeHg production, while both ATP and a nonhydrolyzable ATP analog decreased Hg methylation rates in cell lysates under the experimental conditions. These studies provide insights into the biomolecular processes associated with Hg methylation in anaerobic bacteria. The concentration of Hg in the biosphere has increased dramatically over the last century as a result of industrial activities. The microbial conversion of inorganic Hg to MeHg is a global public health concern due to bioaccumulation and biomagnification of MeHg in food webs. Exposure to neurotoxic MeHg through the consumption of fish represents a significant risk to human health and can result in neuropathies and developmental disorders. Anaerobic microbial communities in sediments and periphyton biofilms have been identified as sources of MeHg in aquatic systems, but the associated biomolecular mechanisms are not fully understood. In the present study, we investigate the biochemical mechanisms and kinetics of MeHg formation by HgcAB in sulfate-reducing bacteria. These findings advance our understanding of microbial MeHg production and may help inform strategies to limit the formation of MeHg in the environment.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Chemical Kinetics in Microdroplets

Micrometer-sized compartments play significant roles in driving heterogeneous transformations within atmospheric and biochemical systems as well as providing vehicles for drug delivery and novel reaction environments for the synthesis of industrial chemicals. Many reports now indicate that reaction kinetics are accelerated under microconfinement, for example, in sprays, thin films, droplets, aerosols, and emulsions. These observations are dramatic, posing a challenge to our understanding of chemical reaction mechanisms with potentially significant practical consequences for predicting the complex chemistry in natural systems. Here we introduce the idea of kinetic confinement, which is intended to provide a conceptual backdrop for understanding when and why microdroplet reaction kinetics differ from their macroscale analogs.

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

High-Pressure Turbulent Flame Speeds and Chemical Kinetics of Syngas Blends with and without Impurities

This Final Report documents the entire four years of the project, from October 1, 2013 through September 30, 2017. This project was concerned with the chemical kinetics of fuel blends with high-hydrogen content in the presence of impurities. Emphasis was also on the design and construction of a new, high-pressure turbulent flame speed facility and the use of ignition delay times and flame speeds to elucidate the diluent and impurity effects on the fuel chemistry at gas turbine engine conditions and to also validate the chemical kinetics models. The project was divided into five primary tasks: 1) Project Management and Program Planning; 2) Turbulent Flame Speed Measurements at Atmospheric Pressure; 3) Experiments and Kinetics of Syngas Blends with Impurities; 4) Design and Construction of a High-Pressure Turbulent Flame Speed Facility; and 5) High-Pressure Turbulent Flame Speed Measurements. Details on the execution and results of each of these tasks are provided in the main report.

08 HYDROGEN↗
DOE OSTI2023

Collaborative Research: Effects of the magnetic field shear and flow shear on the kinetic physics and particle acceleration in relativistic magnetic reconnection (Final Report)

Magnetic reconnection is a fundamental plasma process that allows rapid changes of magnetic field topology and the conversion of magnetic energy into plasma kinetic energy. There has been a strong surge of interest in relativistic reconnection over the past few years in plasma astrophysics, but the rich physics of collisionless reconnection and its associated particle acceleration in the relativistic regime remain less studied compared to the non-relativistic counterparts. Magnetic reconnection in a realistic system is often accompanied with the magnetic field shear and shear flows. This setting is more general and likely the more common situation where most reconnection takes place. Within the past few decades, researchers had made significant progress in understanding how magnetic reconnection works under these conditions in the non-relativistic regime. However, how the effect of special relativity, among other effects, influences the dynamics of reconnection in the strongly magnetized astrophysical plasmas under these conditions is largely unknown. Our proposed research is to use fully kinetic simulations to understand kinetic physics and particle acceleration in relativistic magnetic reconnection in more realistic configurations and physical conditions. The primary goal of this project is to identify the fundamental effects caused by special relativity under the presence of field shear and flow shear.

43 PARTICLE ACCELERATORS↗
DOE OSTI2026

Flow Reactor Study and Kinetic Model Development of HEFA-SPK and its Surrogate

In this work, we formulate a two-component surrogate for HEFA-SPK, incorporating aromatic or cycloalkane components, and develop reduced kinetic models for the surrogates to be used in high-performance computing simulations. The HEFA-SPK surrogate was selected and optimized based on the fuel's physical and combustion properties, including ignition delay times and flame speeds. The resulting surrogate consists of 40% n-undecane and 60% 2-methylnonane. The surrogate was confirmed by flow reactor experiments for both the HEFA-SPK fuel and the suggested two-component surrogates, where excellent agreement was observed. To meet aromatic requirements, 1,2,4-trimethylbenzene (8%) was selected, and we determined that incorporating 30% propylcyclohexane into the HEFA-SPK will achieve a volume swell equivalent to 8% aromatics. The properties of the surrogates were measured, and a new reduced kinetic model was developed based on the semi-decoupling methodology, using a reduced CH4 chemistry from NUIG 1.0 as base chemistry. Kinetic models will be employed in combustor simulations to enable a comprehensive understanding of the effect of SAF fuel properties on aviation combustor performance.

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

Influence of Heterointerfaces on the Kinetics of Oxygen Surface Exchange on Epitaxial La 1.85 Sr 0.15 CuO 4 Thin Films

Considerable attention has been directed to understanding the influence of heterointerfaces between Ruddlesden–Popper (RP) phases and ABO 3 perovskites on the kinetics of oxygen electrocatalysis at elevated temperatures. Here, we report the effect of heterointerfaces on the oxygen surface exchange kinetics by employing heteroepitaxial oxide thin films formed by decorating LaNiO 3 (LNO) on La 1.85 Sr 0.15 CuO 4 (LSCO) thin films. Regardless of LNO decoration, tensile in-plane strain on LSCO films does not change. The oxygen surface exchange coefficients (kchem) of LSCO films extracted from electrical conductivity relaxation curves significantly increase with partial decorations of LNO, whereas full LNO coverage leads to the reduction in the kchem of LSCO films. The activation energy for oxygen exchange in LSCO films significantly decreases with partial LNO decorations in contrast with the full coverage of LNO. Optical spectroscopy reveals the increased oxygen vacancies in the partially covered LSCO films relative to the undecorated LSCO film. We attribute the enhanced oxygen surface exchange kinetics of LSCO to the increased oxygen vacancies by creating the heterointerface between LSCO and LNO.

25 ENERGY STORAGE↗
DOE OSTI2024

Mechanistic and Kinetic Analysis of Complete Methane Oxidation on a Practical PtPd/Al 2 O 3 Catalyst

A PtPd/Al 2 O 3 catalyst developed for the complete oxidation of methane from the ventilation air of underground coal mines is compared against a model PdO/Al 2 O 3 catalyst. Although the PtPd/Al 2 O 3 catalyst is substantially more active and stable than the model catalyst, the nature of active sites between the two catalysts is deemed to be fundamentally the same based on their response to different feed gas compositions and the evolution of surface CO adsorption complexes during time-resolved CO adsorption DRIFTS experiment. For both catalysts, coordinatively unsaturated Pd sites are considered the active centers for methane activation and the subsequent oxidation reaction. H 2 O competes with CH 4 for the same active sites, resulting in severe inhibition. Additionally, the CH 4 oxidation reaction also causes self-inhibition. Taking both inhibition effects into consideration, a relatively simple kinetic model is developed. The model provides a good fit of the 72 sets of kinetic data collected on the PtPd/Al 2 O 3 catalyst under practically relevant reaction conditions with CH 4 concentration in the range of 0.05–0.4%, H 2 O concentration of 1.0–5.0%, and reaction temperatures of 450–700 °C. Kinetic parameters based on the model suggest that the CH 4 activation energy on the PtPd/Al 2 O 3 catalyst is 96.7 kJ/mol, and the H 2 O adsorption energy is –31.0 kJ/mol. Both values are consistent with the parameters reported in the literature. The model can be used to develop catalyst sizing guidelines and be incorporated into the control algorithm of the catalytic system.

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

Effects of Impact and Target Parameters on the Results of a Kinetic Impactor: Predictions for the Double Asteroid Redirection Test (DART) Mission

Abstract The Double Asteroid Redirection Test (DART) spacecraft will impact into the asteroid Dimorphos on 2022 September 26 as a test of the kinetic impactor technique for planetary defense. The efficiency of the deflection following a kinetic impactor can be represented using the momentum enhancement factor, β , which is dependent on factors such as impact geometry and the specific target material properties. Currently, very little is known about Dimorphos and its material properties, which introduces uncertainty in the results of the deflection efficiency observables, including crater formation, ejecta distribution, and β . The DART Impact Modeling Working Group (IWG) is responsible for using impact simulations to better understand the results of the DART impact. Pre-impact simulation studies also provide considerable insight into how different properties and impact scenarios affect momentum enhancement following a kinetic impact. This insight provides a basis for predicting the effects of the DART impact and the first understanding of how to interpret results following the encounter. Following the DART impact, the knowledge gained from these studies will inform the initial simulations that will recreate the impact conditions, including providing estimates for potential material properties of Dimorphos and β resulting from DART’s impact. This paper summarizes, at a high level, what has been learned from the IWG simulations and experiments in preparation for the DART impact. While unknown, estimates for reasonable potential material properties of Dimorphos provide predictions for β of 1–5, depending on end-member cases in the strength regime.

58 GEOSCIENCES↗
DOE OSTI2021

An out-of-distribution-aware autoencoder model for reduced chemical kinetics

While detailed chemical kinetic models have been successful in representing rates of chemical reactions in continuum scale computational fluid dynamics (CFD) simulations, applying the models in simulations for engineering device conditions is computationally prohibitive. To reduce the cost, data-driven methods, e.g., autoencoders, have been used to construct reduced chemical kinetic models for CFD simulations. Despite their success, data-driven methods rely heavily on training data sets and can be unreliable when used in out-of-distribution (OOD) regions (i.e., when extrapolating outside of the training set). In this paper, we present an enhanced autoencoder model for combustion chemical kinetics with uncertainty quantification to enable the detection of model usage in OOD regions, and thereby creating an OOD-aware autoencoder model that contributes to more robust CFD simulations of reacting flows.Here, we first demonstrate the effectiveness of the method in OOD detection in two well-known datasets, MNIST and Fashion-MNIST, in comparison with the deep ensemble method, and then present the OOD-aware autoencoder for reduced chemistry model in syngas combustion.

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

Data and code from: Selective oxidation of 3-hydroxypropionic acid to malonic acid over Pd/C: Mechanistic and kinetic study

Malonic acid (MA) is a high-value dicarboxylic acid with strong industrial demand, yet its current production heavily relies on petrochemical feedstocks. Here, we report the first systematic study for the sustainable production of MA via oxidation of 3-hydroxypropionic acid (3-HP) with a Pd/Carbon catalyst. The effects of oxidant type (O2 and H2O2), pH, and temperature on the reaction chemistry were comprehensively evaluated. Guided by experimental observation and DFT-calculated thermochemical energetics, reaction networks for 3-HP oxidation with both oxidants are proposed and validated through kinetic modeling. MA was identified as the primary oxidation product, while further oxidation yields acetic acid and oxalic acid. The kinetic model validated the network, displaying excellent agreement (R2 > 0.95). Kinetic observations also enabled a direct comparison between O2 and H2O2 and revealed their distinct behaviors. The model was further developed into a temperature-time map, providing insight into conditions that maximize MA production. Malonic acid selectivity of 56.9 % and yield of 50.5 % were achieved at 3 bar oxygen, equimolar NaOH:3-HP ratio, and 50 °C.

3-Hydroxypropionic Acid↗
NASA NTRS2001

Kinetics of chromatid break repair in G2-human fibroblasts exposed to low- and high-LET radiations

The purpose of this study is to determine the kinetics of chromatid break rejoining following exposure to radiations of different quality. Exponentially growing human fibroblast cells AG1522 were irradiated with gamma-rays, energetic carbon (290 MeV/u), silicon (490 MeV/u) and iron (200 MeV/u, 600 MeV/u). Chromosomes were prematurely condensed using calyculin A. Prematurely condensed chromosomes were collected after several post-irradiation incubation times, ranging from 5 to 600 minutes, and the number of chromatid breaks and exchanges in G2 cells were scored. The relative biological effectiveness (RBE) for initial chromatid breaks per unit dose showed LET dependency having a peak at 55 keV/micrometers silicon (2.4) or 80 keV/micrometers carbon particles (2.4) and then decreased with increasing LET. The kinetics of chromatid break rejoining following low- or high-LET irradiation consisted of two exponential components. Chromatid breaks decreased rapidly after exposure, and then continued to decrease at a slower rate. The rejoining kinetics was similar for exposure to each type of radiation, although the rate of unrejoined breaks was higher for high-LET radiation. Chromatid exchanges were also formed quickly.

NASA Center JSC↗
NASA NTRS2004

Kinetics of organic transformations under mild aqueous conditions: implications for the origin of life and its metabolism

The rates of thermal transformation of organic molecules containing carbon, hydrogen, and oxygen were systematically examined in order to identify the kinetic constraints that governed origin-of-life organic chemistry under mild aqueous conditions. Arrhenius plots of the kinetic data were used to estimate the reaction of half-lifes at 50 degrees C. This survey showed that hydrocarbons and organic substances containing a single oxygenated group were kinetically the most stable; whereas organic substances containing two oxygenated groups in which one group was an alpha- or beta-positioned carbonyl group were the most reactive. Compounds with an alpha- or beta-positioned carbonyl group (aldehyde or ketone) had rates of reaction that were up to 10(24)-times faster than rates of similar molecules lacking the carbonyl group. This survey of organic reactivity, together with estimates of the molecular containment properties of lipid vesicles and liquid spherules, indicates that an origins process in a small domain that used C,H,O-intermediates had to be catalytic and use the most reactive organic molecules to prevent escape of its reaction intermediates.

Biogenesis↗
NASA NTRS2012

Optimization of KINETICS Chemical Computation Code

NASA JPL has been creating a code in FORTRAN called KINETICS to model the chemistry of planetary atmospheres. Recently there has been an effort to introduce Message Passing Interface (MPI) into the code so as to cut down the run time of the program. There has been some implementation of MPI into KINETICS; however, the code could still be more efficient than it currently is. One way to increase efficiency is to send only certain variables to all the processes when an MPI subroutine is called and to gather only certain variables when the subroutine is finished. Therefore, all the variables that are used in three of the main subroutines needed to be investigated. Because of the sheer amount of code that there is to comb through this task was given as a ten-week project. I have been able to create flowcharts outlining the subroutines, common blocks, and functions used within the three main subroutines. From these flowcharts I created tables outlining the variables used in each block and important information about each. All this information will be used to determine how to run MPI in KINETICS in the most efficient way possible.

planetary atmospheres↗
NASA NTRS1993

Advances in Studies of Electrode Kinetics and Mass Transport in AMTEC Cells

Previous work reported from JPL has included characterization of electrode kinetics and alkali atom transport from electrodes including Mo, W, WRh x (Mn), in sodium AMTEC cells and vapor exposure cells; and Mo in potassium vapor exposure cells. These studies were generally performed in cells with small area electrodes (about 1 to 5 cm 2 ), and device geometry had little effect on transport. Alkali metal diffusion coefficients through these electrodes have been characterized, and approximate surface diffusion coefficients were derived in cases of activated transport. A basic model of electrode kinetics and transport at the alkali metal vapor/pourous metal electrode/alkali beta"-alumina solid electrolyte (BASE) three phase boundary has been proposed which accounts for electrochemical reaction rates with a collision frequency near the three phase boundary and tunneling from the porous electrode partially covered with adsorbed alkali metal atoms. The small electrode effect in AMTEC cells has been discussed in several papers, but quantitative investigations have described only the overall effect and the important contribution of electrolyte resistance. The quantitative characterization of transport losses in cells with large area electrodes has been limited to simulations of large area electrode effects, or characterization of transport losses from large area electrodes with significant longitudinal temperature gradients. This paper describes new investigations of electrochemical kinetics and transport, with four 14.4 cm 2 WPt 3.5 electrodes, including the influence of electrode size on the mass transport loss in the AMTEC cell. These electrodes exhibit very slow sintering, as well as excellent sodium transport properties, making them attractive candidates for AMTEC power conversion use. However, the facile sodium transport in WPt 3.5 electrodes makes characterization of the transport process difficult.

electrode↗
DOE OSTI2021

Fuel Properties and Kinetics

The Co-Optimization of Fuels and Engines (CoOptima) program is focused on a two-pronged approach to develop new, lower net-carbon fuels and advanced engine technologies in tandem. This effort brings nine national labs and several university and industry partners together to simultaneously identify new fuel candidates and to further engine technology development in the light-, medium-, and heavy-duty vehicle sectors with a focus on fuel economy and emission reduction. The fuel properties and kinetics project is aimed at achieving a better understanding of fuel property kinetics and how they impact engine performance such that more efficient and lower emitting engines can be made a reality. Several promising biofuel candidates were identified through tiered screening approaches and were evaluated utilizing unique bench-scale measurement techniques. Kinetic models were developed to describe autoignition and soot pre-cursor formation mechanisms to identify the most promising candidates that advanced various combustion strategies.

ADVANCED PROPULSION SYSTEMS↗