Search NASA⌕ Search

SEARCH · Search NASA

Results for “Sun: evolution”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Modeling discontinuous dynamic recrystallization containing second phase particles in magnesium alloys utilizing phase field method

Pre-existing second phase particles can induce particle stimulated nucleation (PSN) and pinning effect on grain boundaries during DRX process of magnesium alloys. The interaction among pinning effect, PSN mechanism and strain-induced grain boundary migration (SIBM) nucleation mechanism imposes challenge in quantitative study of microstructure evolution. A phase field model that describes discontinuous dynamic recrystallization process considering second phase particles (PF-DDRX-SP) which mainly distribute along grain boundaries is developed. The second phase order parameter with diffusion interface is introduced to the free energy function. With considering the pinning effect of second phase particles on grain boundaries, the grain boundary energy couples the interaction between second phase and grains. The effect of second phase on dislocation density evolution is considered in the model, and the PSN and SIBM mechanism are both executed by limiting the nucleation position to the grain boundary and the second phase interface. For the validation, the initial topology consistent with initial microstructure is applied to the simulation of DRX kinetics and flow behavior of AZ80 magnesium alloy, and great reliability and accuracy of developed model is indicated. Furthermore, through the model, the microstructure evolution with different particle size and with different volume fraction of round particle during DRX process were simulated. Finally, the results show that particles with higher dispersion reduce the number of DRX nuclei, which indicate that second phase particles suppress the nucleation at grain boundaries because of the pinning effect. More importantly, the proposed model could also quantitatively predict the relationships between the parameters of second phase particles and DRX behaviors, and enable to optimize the initial second phase structure in a uniform grain structure during thermomechanical process.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Boosting electrochemical reaction and suppressing phase transition with a high-entropy O3-type layered oxide for sodium-ion batteries

Complex phase transitions induced by interlayer slides in layered cathode materials lead to poor cycling stability and rate capability for sodium-ion batteries. Herein, we design and prepare a new six-component high-entropy oxide (HEO) layered cathode O3–Na(Fe 0.2 Co 0.2 Ni 0.2 Ti 0.2 Sn 0.1 Li 0.1 )O 2 to enable highly reversible electrochemical reaction and phase-transition behavior. The HEO cathode exhibits good cycling performance (capacity retention of ~81% after 100 cycles at 0.5C) and outstanding rate capability (capacity of ~81 mA h g –1 at 2.0C) due to the higher sodium diffusion coefficient (above 5.75 × 10 –11 cm 2 s –1 ) than most reported O3-type cathodes. Moreover, the high-entropy cathode has superior compatibility with the hard carbon anode and delivers a specific capacity of 90.4 mA h g –1 (energy density of ~267.5 W h kg –1 ). Ex situ X-ray diffraction proves that the high-entropy designing effectively suppresses the intermediate phase change to achieve reversible O3–P3 phase evolution, and in turn stabilizes the layered structure. X-ray absorption spectroscopy and Mössbauer spectrum of 57 Fe suggest that Ni 2+ /Ni 3.5+ , Co 3+ /Co 3.5+ , and part of Fe 3+ /Fe 3.5+ redox reaction contribute the charge compensation. Finally, the enhanced performance can be attributed to the disordered distribution of multi-component transition metals in HEO suppressing the ordering of electric charges and sodium vacancies, thereby inhibiting the interlayer slide and phase transition.

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

Simulation of Li-pellet triggered ELMs in EAST with an impurity model implemented under BOUT++ framework

A simple impurity model has been developed under the BOUT++ framework to investigate the Li-pellet triggered edge localized mode (ELM) in EAST configuration. The present impurity model decouples the ion pressure enhancement effect (IPEE) (which affects radial E X B flow shear and gyro-viscosity of deuterium ions and is implicitly included in our previous work) to make the simulation of Li pellet injection more physically reasonable. In addition, the present impurity model also includes the impurity equilibrium effect (IEE) (which induces modifications on vorticity and gyro-viscosity). The simulation results show that without IPEE a turbulent ELM induced by Li pellet is triggered by multiple peeling-ballooning modes (PBMs) rather than by a single dominant mode, and the simultaneous growth of multiple modes is conducive to reducing the time for pedestal entering the energy loss state. When a turbulent ELM occurs, the nonlinearly dominant modes undergo a secondary fast growth during fast crash phase. The finding explains the secondary increase of D α emission observed in the DIII-D Li injection experiments. During the evolution of a turbulent ELM, the continuous pedestal collapse dominates the pedestal energy loss in turbulent transport phase; however, in saturation phase, the stabilizing effects on PBMs (n ≠ 0) by n = 0 mode and radial E X B flow shear within the steepest gradient region are more prominent. It is also found that with IEE and without IPEE, the size threshold of ELM triggering and the magnitude of ELM sizes both show a good agreement with EAST and DIII-D experimental observations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Electrode strain dynamics in layered intercalation battery cathodes

Rechargeable batteries using electrodes based on intercalation chemistry exhibit notable cyclability, yet their performance still suffers from chemomechanical degradation. In this study, by combining a suite of operando microscopy methods, we explored electrode strain evolution and observed intricate particle cluster rearrangement under electrochemical stimuli. We show that early-stage strain accumulation in intercalation cathodes occurs during the period of interparticle charge transfer and redox reactions stemming from asynchronous coupling and decoupling between chemical (de)intercalation and physical grain motion. This interplay drives heterogeneous redox activity, localized charge equilibration, and multiscale strain cascades that propagate through an asynchronous network of chemical-mechanical interactions. Together, these findings reveal how collective particle dynamics and hierarchical strain transmission dictate electrode deformation and degradation in intercalation cathodes.

25 ENERGY STORAGE↗
DOE OSTI2024

Sub-volt conversion of activated biochar and water for H 2 production near equilibrium via biochar-assisted water electrolysis

Sluggish water oxidation reactions limit water electrolysis for H 2 production, which can be alleviated by the use of carbon-based ma- terials like agricultural wastes as reducing agents. Biochar from such biomass can reduce equilibrium cell potentials at standard condi- tions from 1.23 V to 0.21 V by avoiding direct water splitting at the anode. However, some challenges hinder biochar oxidation, including poor biochar binding, electrode caking, and surface passivation. We find that enhanced C/O ratio, crystallinity, and negative zeta potential improve biochar oxidation kinetics at mod- erate temperatures. Smaller particle sizes and better mixing pre- vent electrode caking, enhancing biochar stability. Here, we report sub-volt biochar-coupled H 2 production, often referred to as a bio- char-assisted water electrolysis (BAWE), yielding 250 mA/g cat H 2 current at 100% Faradaic efficiency. Over 1 mA current was observed at a near-equilibrium cell potential of 0.2 V cell potential. Using a single-junction solar cell-powered BAWE, 15 mA H 2 is generated at 1 Sun, resulting in 4.8% solar-to-hydrogen efficiency, equivalent to 35% when the energy of H 2 relative to H 2 O (without biochar) is assumed.

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

Constraining the charge-, time-, and rigidity-dependence of cosmic-ray solar modulation with AMS-02 observations during Solar Cycle 24

Our basic theoretical understanding of the sources of cosmic rays and their propagation through the interstellar medium is hindered by the Sun, that through the solar wind affects the observed cosmic-ray spectra. This effect is known as solar modulation. Recently released cosmic-ray observations from the Alpha Magnetic Spectrometer (AMS-02) and publicly available measurements of the solar wind properties from the Advanced Composition Explorer and the Wilcox observatory allow us to test the analytical modeling of the time-, charge- and rigidity-dependence of solar modulation. We rely on associating measurements on the local heliospheric magnetic field and the heliospheric current sheet’s tilt angle, to model the time-dependence and amplitude of cosmic-ray solar modulation. We find evidence for the solar modulation’s charge- and rigidity-dependence during the era of solar cycle 24. Our analytic prescription to model solar modulation can explain well the large-scale time evolution of positively charged cosmic-ray fluxes in the range of rigidities from 1 GV to 10 GV. Here, we also find that cosmic-ray electron fluxes measured during the first years of cycle 24 are less trivial to explain, due to the complex and rapidly evolving structure of the heliosphere’s magnetic field that they experienced as they propagated inwards.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Regulatory Coordination of Photophysical, Photochemical, and Biochemical Reactions in the Photosynthesis of Land Plants

Balance among the sequential photophysical, photochemical, and biochemical reactions of photosynthesis is needed for converting fleeting energy in light to stable energy in chemical bonds. Any imbalance acts as either a bottleneck for limiting photosynthetic efficiency or an agent for inducing structural and functional damage to photosynthetic apparatus. Not only must each reaction be carefully regulated, but regulatory processes must also be coordinated across the reactions. However, regulations of different stages of photosynthesis have rarely been studied jointly. Non-photochemical quenching (NPQ) and stomatal conductance (g s ) are key regulators of photophysical and biochemical reactions, respectively. Existing evidence suggests that the redox state of plastoquinone regulates g s and that the photochemical reactions are partially regulated by the ultrastructural dynamics of thylakoids induced by osmotic water fluxes in chloroplasts of land plants. To examine how these regulations are coordinated and feedback to each other, we simultaneously measured NPQ and gs and inferred the redox state of plastoquinone and the light-induced thylakoid swelling/shrinking on numerous C 3 and C 4 species. For all species measured, NPQ and gs covary with the redox states of the electron transport chain, particularly plastoquinone, and increase as thylakoid swelling is inferred. NPQ has the maximal sensitivity at the light intensity at which thylakoid is inferred to be fully swollen. Our findings suggest that plant energy and water use strategies are intimately linked by evolution, and studying the regulations of different photosynthetic stages as a whole can lead to new insights of the functioning of photosynthetic machinery in dynamic environments.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Multitime Landau–Zener model: classification of solvable Hamiltonians

We discuss a class of models that generalize the two-state Landau–Zener Hamiltonian to both the multistate and multitime evolution. It is already known that the corresponding quantum mechanical evolution can be understood in great detail. Here, we present an approach to classify such solvable models, namely, to identify all their independent families for a given number N of interacting states and prove the absence of such families for some types of interactions. We also discuss how, within a solvable family, one can classify the scattering matrices, i.e., the system's dynamics. Furthermore, due to the possibility of such a detailed classification, the multitime Landau–Zener model defines a useful special function of theoretical physics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Disentangling long and short distances in momentum-space TMDs

The extraction of nonperturbative TMD physics is made challenging by prescriptions that shield the Landau pole, which entangle long- and short-distance contributions in momentum space. The use of different prescriptions then makes the comparison of fit results for underlying nonperturbative contributions not meaningful on their own. We propose a model-independent method to restrict momentum-space observables to the perturbative domain. This method is based on a set of integral functionals that act linearly on terms in the conventional position-space operator product expansion (OPE). Artifacts from the truncation of the integral can be systematically pushed to higher powers in Λ QCD /k T . We demonstrate that this method can be used to compute the cumulative integral of TMD PDFs over k T ≤ k$^{cut}_{T}$ in terms of collinear PDFs, accounting for both radiative corrections and evolution effects. This yields a systematic way of correcting the naive picture where the TMD PDF integrates to a collinear PDF, and for unpolarized quark distributions we find that when renormalization scales are chosen near k$^{cut}_{T}$, such corrections are a percent-level effect. We also show that, when supplemented with experimental data and improved perturbative inputs, our integral functionals will enable model-independent limits to be put on the non-perturbative OPE contributions to the Collins-Soper kernel and intrinsic TMD distributions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Interfacial Connections between Organic Perovskite/n + Silicon/Catalyst that Allow Integration of Solar Cell and Catalyst for Hydrogen Evolution from Water

Abstract The rapidly increasing solar conversion efficiency (PCE) of hybrid organic–inorganic perovskite (HOIP) thin‐film semiconductors has triggered interest in their use for direct solar‐driven water splitting to produce hydrogen. However, application of these low‐cost, electronic‐structure‐tunable HOIP tandem photoabsorbers has been hindered by the instability of the photovoltaic‐catalyst‐electrolyte (PV+E) interfaces. Here, photolytic water splitting is demonstrated using an integrated configuration consisting of an HOIP/n + silicon single junction photoabsorber and a platinum (Pt) thin film catalyst. An extended electrochemical (EC) lifetime in alkaline media is achieved using titanium nitride on both sides of the Si support to eliminate formation of insulating silicon oxide, and as an effective diffusion barrier to allow high‐temperature annealing of the catalyst/TiO 2 ‐protected‐n + silicon interface necessary to retard electrolytic corrosion. Halide composition is examined in the (FA 1‐x Cs x )PbI 3 system with a bandgap suitable for tandem operation. A fill factor of 72.5% is achieved using a Spiro‐OMeTAD‐hole‐transport‐layer (HTL)‐based HOIP/n + Si solar cell, and a high photocurrent density of −15.9 mA cm −2 (at 0 V vs reversible hydrogen electrode) is attained for the HOIP/n + Si/Pt photocathode in 1 m NaOH under simulated 1‐sun illumination. While this thin‐film design creates stable interfaces, the intrinsic photo‐ and electro‐degradation of the HOIP photoabsorber remains the main obstacle for future HOIP/Si tandem PEC devices.

08 HYDROGEN↗
DOE OSTI2022

In situ study on heavy ion irradiation induced microstructure evolution in single crystal Cu with nanovoids at elevated temperature

Understanding the response of nanovoids to irradiation damage advances our capability to design radiation tolerant materials. Recent in situ studies reveal the shrinkage of hexagon-shaped nanovoids in (110) textured Cu. However, the evolution of voids with irregular geometries under irradiation is less well understood. Here, in situ Kr ion irradiation was performed at 100 °C on single-crystal Cu (112) that possesses nanovoids with high aspect ratio. In situ studies show these elongated voids fragment into smaller voids and shrink gradually with increasing dose. Phase field simulations confirm that fragmentation of the void is governed by the competing kinetics between atoms diffusing toward and away from the elongated nanovoid. In conclusion, cost irradiation analysis reveals the formation of high-density defect clusters.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2021

Unveiling the mechanism of phase and morphology selections during the devitrification of Al-Sm amorphous ribbon

The complex interplay between energetic and kinetic factors that governs the phase and morphology selections can originate at the earliest stage of crystallization in the amorphous parent phases. Because of the extreme difficulties in capturing the microscopic nucleation process, a detailed picture of how initial disordered structures affect the transformation pathway remains unclear. Here, we report the experimental observation of widely varying phase selection and grain size evolution during the devitrification of a homogeneous melt-spun glassy ribbon. Two different crystalline phases, θ-Al 5 Sm and ε-Al 60 Sm 11 , are found to form in the different regions of the same metallic glass ribbon during the devitrification. The grain size of ε-Al 60 Sm 11 phase shows a strong spatial heterogeneity. Coarse-grained ε-Al 60 Sm 11 phase coupled with the small volume fraction of θ-Al 5 Sm phase is preferably formed close to wheel side of the melt-spun ribbon. Combining experimental characterization and computational simulations, we show that phase selection and microstructure evolution can be traced back to different types and populations of atomic clusters that serve as precursors for the nucleation of different crystalline phases. Inhomogeneous cooling rates cause different structure orders across the glass sample during the quenching process. Our findings provide direct insight into the effect of structural order on the crystallization pathways during the devitrification of metallic glass. It also opens an avenue to study the detailed nucleation process at the atomic level using the metallic glass as a platform and suggests the opportunity of microstructure and property design via controlling the cooling process.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

The Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) Survey Design, Reductions, and Detections*

In this work, we describe the survey design, calibration, commissioning, and emission-line detection algorithms for the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX). The goal of HETDEX is to measure the redshifts of over a million Lyα emitting galaxies between 1.88 < z < 3.52, in a 540 deg 2 area encompassing a comoving volume of 10.9 Gpc 3 . No preselection of targets is involved; instead the HETDEX measurements are accomplished via a spectroscopic survey using a suite of wide-field integral field units distributed over the focal plane of the telescope. This survey measures the Hubble expansion parameter and angular diameter distance, with a final expected accuracy of better than 1%. Additionally, we detail the project's observational strategy, reduction pipeline, source detection, and catalog generation, and present initial results for science verification in the Cosmological Evolution Survey, Extended Groth Strip, and Great Observatories Origins Deep Survey North fields. We demonstrate that our data reach the required specifications in throughput, astrometric accuracy, flux limit, and object detection, with the end products being a catalog of emission-line sources, their object classifications, and flux-calibrated spectra.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Isotopic Evolution of the Inner Solar System Inferred from Molybdenum Isotopes in Meteorites

The fundamentally different isotopic compositions of non-carbonaceous (NC) and carbonaceous (CC) meteorites reveal the presence of two distinct reservoirs in the solar protoplanetary disk that were likely separated by Jupiter. However, the extent of material exchange between these reservoirs, and how this affected the composition of the inner disk, are not known. Here we show that NC meteorites display broadly correlated isotopic variations for Mo, Ti, Cr, and Ni, indicating the addition of isotopically distinct material to the inner disk. The added material resembles bulk CC meteorites and Ca–Al-rich inclusions in terms of its enrichment in neutron-rich isotopes, but unlike the latter materials is also enriched in s-process nuclides. The comparison of the isotopic composition of NC meteorites with the accretion ages of their parent bodies reveals that the isotopic variations within the inner disk do not reflect a continuous compositional change through the addition of CC dust, indicating an efficient separation of the NC and CC reservoirs and limited exchange of material between the inner and outer disk. Instead, the isotopic variations among NC meteorites more likely record a rapidly changing composition of the disk during infall from the Sun's parental molecular cloud, where each planetesimal locks the instant composition of the disk when it forms. Here, a corollary of this model is that late-formed planetesimals in the inner disk predominantly accreted from secondary dust that was produced by collisions among pre-existing NC planetesimals.

58 GEOSCIENCES↗
DOE OSTI2023

Proton Relay for the Rate Enhancement of Electrochemical Hydrogen Reactions at Heterogeneous Interfaces

Proton transfer is critically important to many electrocatalytic reactions, and directed proton delivery could open new avenues for the design of electrocatalysts. However, although this approach has been successful in molecular electrocatalysis, proton transfer has not received the same attention in heterogeneous electrocatalyst design. Here, in this work, we report that a metal oxide proton relay can be built within heterogeneous electrocatalyst architectures and improves the kinetics of electrochemical hydrogen evolution and oxidation reactions. The volcano-type relationship between activity enhancement and pK a of amine additives confirms this improvement; we observe maximum rate enhancement when the pK a of a proton relay matches the pH of the electrolyte solution. Density-functional-theory-based reactivity studies reveal a decreased proton transfer energy barrier with a metal oxide proton relay. These findings demonstrate the possibility of controlling the proton delivery and enhancing the reaction kinetics by tuning the chemical properties and structures at heterogeneous interfaces.

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

A general strategy for preparing pyrrolic-N 4 type single-atom catalysts via pre-located isolated atoms

Single-atom catalysts (SACs) have been applied in many fields due to their superior catalytic performance. Because of the unique properties of the single-atom-site, using the single atoms as catalysts to synthesize SACs is promising. In this work, we have successfully achieved Co 1 SAC using Pt 1 atoms as catalysts. More importantly, this synthesis strategy can be extended to achieve Fe and Ni SACs as well. X-ray absorption spectroscopy (XAS) results demonstrate that the achieved Fe, Co, and Ni SACs are in a M1-pyrrolic N 4 (M= Fe, Co, and Ni) structure. Density functional theory (DFT) studies show that the Co(Cp) 2 dissociation is enhanced by Pt 1 atoms, thus leading to the formation of Co 1 atoms instead of nanoparticles. These SACs are also evaluated under hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), and the nature of active sites under HER are unveiled by the operando XAS studies. These new findings extend the application fields of SACs to catalytic fabrication methodology, which is promising for the rational design of advanced SACs.

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

Multimodal Analysis of Reaction Pathways of Cathode Materials for Lithium Ion Batteries

Conversion mechanism in lithium ion batteries provides higher capacity than intercalation mechanism since multiple numbers of electrons and lithium ions are associated. However, poor cycling stability, large voltage hysteresis, and low energy efficiency have been great challenges of conversion reaction. To address those issues, conversion-type electrode materials have been reformed via doping or substituting other elements. For example, iron fluorides (FeF 2 , FeF 3 ) have modified as iron oxyfluorides (FeF 1-x O x ), showing enhanced long-term stability. Furthermore, co-substituted (both anion and cation substituted) Fe 0.9 Co 0.1 OF (FeCoOF) was demonstrated excellent cycling stability. (capacity of 350 mAh g -1 at a current of 500 mA g -1 for 1000 cycles). Substituting anion and cation in iron fluoride has been suggested as an effective method to achieve better reversibility but understanding of lithiation reactions in co-substituted FeCoOF is not clear. This work takes advantage of ex-situ/ in-situ synchrotron X-ray based techniques and transmission electron microscopy to elucidate structural changes with lithium ion, which may provide fundamental insights into modifying conversion-type materials. Figure 1 presents discharge-charge curves and pair distribution function patterns acquired at each potential. As lithium ions were inserted, structural changes were noticed both at short-range and long-range. However, long-range ordering was nearly maintained even at 1 V, indicating absence of conversion reaction. Figure 2 shows lithiation induced structural evolution of a single FeCoOF nanorod observed in real time. As lithiation proceeds, the width of nanorods shows a stepwise increase, particularly A in figure 2d, which may indicate multiple steps of lithiation occur. Considering that conversion reaction takes place around 2 V in FeF 3 , co-substitution Co and O into iron fluoride may change thermodynamic features of lithiation reactions by lowering the initiation potential for conversion reaction. Instead, phase transformations occur at long-range order, which may help maintaining structural integrity during operation, eventually, achieving cycling stability.

25 ENERGY STORAGE↗