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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 1,729 records · Page 96
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Lifetime predictions for dimmable two-channel drivers for color tuning luminaires

Two-channel tunable white lighting (TWL) systems represent the next wave of solid-state lighting (SSL) systems and promise flexibility in light environment while maintaining the high reliability and luminous efficacy expected with SSL devices. TWL systems utilize LED assemblies consisting of two different LED spectra (i.e., often a warm white assembly and a cool white assembly) that are integrated into modules. While these systems provide the ability to adjust the lighting spectrum to match the physiology needs of the task at hand, they also are a potentially more complex lighting system from a performance and reliability perspective. We report an initial study on the reliability performance of such lighting systems including an examination of the lumen maintenance and chromaticity stability of warm white and cool white LED assemblies and the multi-channel driver that provides power to the assemblies. Accelerated stress tests including operational bake tests conducted at 75°C and 95°C were used to age the LED modules, while more aggressive temperature and humidity tests were used for the drivers in this study. Small differences in the performance between the two LED assemblies were found and can be attributed to the different phosphor chemistries. The lumen maintenances of both LED assemblies were excellent. The warm white LED assemblies were found to shift slightly in the green color direction over time while the cool white LED assemblies shifted slightly in the yellow color direction. The net result of these chromaticity shifts is a small, barely perceptible reduction in the tuning range after 6,000 hours of exposure to an accelerating elevated temperature of 75°C.

Chromaticity↗
DOE OSTI2021

Band Edge Control of Quasi–2D Metal Halide Perovskites for Blue Light–Emitting Diodes with Enhanced Performance

Perovskite light–emitting diodes (PeLEDs) have received great attention for their potential as next–generation display technology. While remarkable progress has been achieved in green, red, and near–infrared PeLEDs with external quantum efficiencies (EQEs) exceeding 20%, obtaining high performance blue PeLEDs remains a challenge. Poor charge balance due to large charge injection barriers in blue PeLEDs has been identified as one of the major roadblocks to achieve high efficiency. Here band edge control of perovskite emitting layers for blue PeLEDs with enhanced charge balance and device performance is reported. By using organic spacer cations with different dipole moments, that is, phenethyl ammonium (PEA), methoxy phenethyl ammonium (MePEA), and 4–fluoro phenethyl ammonium (4FPEA), the band edges of quasi–2D perovskites are tuned without affecting their band gaps. Furthermore, detailed characterization and computational studies have confirmed the effect of dipole moment modification to be mostly electrostatic, resulting in changes in the ionization energies of ≈0.45 eV for MePEA and ≈ –0.65 eV for 4FPEA based thin films relative to PEA–based thin films. With improved charge balance, blue PeLEDs based on MePEA quasi–2D perovskites show twofold increase of the EQE as compared to the control PEA based devices.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Lithium Electrochemical Tuning for Electrocatalysis

Abstract Electrocatalysis is of great importance to a variety of energy conversion processes, where developing highly efficient catalysts is critical. While common strategies involve screening a wide range of materials with new chemical compositions or structures, a different approach to continuously, controllably, and effectively tune the electronic properties of existing catalytic materials for optimized activities has been demonstrated recently. Inspired by studies in lithium‐ion batteries, systematical lithium electrochemical tuning (LiET) methods such as Li intercalation, extraction, cycling, and strain engineering, are employed to effectively tune the electronic structures of different existing catalysts and thus improve their catalytic activities dramatically. Herein, the advantages of the LiET method in electrocatalysis are introduced, and then some recent representative examples in improving the performances of important electrochemical reactions are reviewed briefly. Lastly, a few promising directions on extending the applications of the LiET method in electrocatalysis are proposed.

Lu, Zhiyi↗
DOE OSTI2022

Deconvoluting the benefits of porosity distribution in layered electrodes on the electrochemical performance of Li-ion batteries

Thick Lithium Ion Battery (LIB) electrodes suffer from poor rate capability and high ionic impedance due to their thickness and mesostructure. Therefore, optimizing thick electrode architectures becomes crucial. In this work, we report a systematic assessment of the ionic resistance in heterogeneous porous electrodes through the combination of computational simulations using a 4D-resolved model and experimental measurements. The first part of the study is devoted to a general assessment of Electrochemical Impedance Spectroscopy (EIS) spectra, mapping the impact of ionic and electronic resistances on the overall impedances of uncalendered and calendered LiNi 1/3 Mn 1/3 Co 1/3 O 2 , LiFePO 4 and graphite electrodes. In the second part, in silico-generated electrodes with different porosities are used in computational EIS simulations to analyze the impact of the electrode porosity on the ionic impedance. As expected, the results show that a lower porosity leads to a higher ionic impedance because of a higher electrode tortuosity factor. Furthermore, in silico-generated electrodes with different porosities were stacked and assembled to create heterogeneities of porosity along the thickness, and used in computational EIS and galvanostatic discharge simulations. The computational results show that the porosity heterogeneity along the electrode thickness has a significant effect on the ionic impedance and capacity of the electrode. The electrode architecture with progressively decreasing porosity from separator to current collector shows the highest performance, a trend validated by our in house experimental EIS and galvanostatic discharge also reported in this manuscript. Overall, we conclude that the ionic resistance in a thick electrode can be effectively reduced through proper tuning of the porosity heterogeneity. The proposed heterogeneous electrode architectures presented here could enormously help building efficient thick electrodes for LIBs.

25 ENERGY STORAGE↗
DOE OSTI2020

Gradient microstructure induced shear band constraint, delocalization, and delayed failure in CuZr nanoglasses

The mechanical properties of metallic glasses (MGs) can be significantly tuned by introducing a nanoscale glass-glass interface microstructure. Here, we design three types of Cu 64 Zr 36 MG seamless gradient microstructures by combining glassy grain sizes from 3 to 15 nm. We perform tensile loading molecular dynamics simulations on the named gradient nanoglasses to characterize their mechanical behavior. In all cases, results indicate the generation of gradient plasticity following the gradient in grain size, i.e. local plasticity increases from large to small grain size regions. Loading parallel to the gradient direction results in initial broad necking followed by catastrophic failure. In contrast, loading perpendicular to the gradient direction results in diffused shear band propagation from large to small grain size regions, delaying the generation of a dominant shear band and further delocalizing plastic deformation. In conclusion, the results demonstrate the synergistic effects generated by heterogeneous gradient designs in the mechanical behavior of metallic glasses.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Understanding the effect of refractory metal chemistry on the stacking fault energy and mechanical property of Cantor-based multi-principal element alloys

Multi-principal-element alloys (MPEAs) based on 3d-transition metals show remarkable mechanical properties. In this study, the stacking fault energy (SFE) in face-centered cubic (fcc) alloys is a critical property that controls underlying deformation mechanisms and mechanical response. Here, we present an exhaustive density-functional theory study on refractory- and copper-reinforced Cantor-based systems to ascertain the effects of refractory metal chemistry on SFE. We find that even a small percent change in refractory metal composition significantly changes SFEs, which correlates favorably with features like electronegativity variance, size effect, and heat of fusion. For fcc MPEAs, we also detail the changes in mechanical properties, such as bulk, Young's, and shear moduli, as well as yield strength. A Labusch-type solute-solution-strengthening model was used to evaluate the temperature-dependent yield strength, which, combined with SFE, provides a design guide for high-performance alloys. We also analyzed the electronic structures of two down-selected alloys to reveal the underlying origin of optimal SFE and strength range in refractory-reinforced fcc MPEAs. These new insights on tuning SFEs and modifying composition-structure-property correlation in refractory- and copper-reinforced MPEAs by chemical disorder, provide a chemical route to tune twinning- and transformation-induced plasticity behavior in fcc MPEAs.

36 MATERIALS SCIENCE↗
DOE OSTI2015

High-precision three-dimensional field mapping of a high resolution magnetic spectrometer for hypernuclear spectroscopy at JLab

The High Resolution Kaon Spectrometer (HKS), which consists of two quadrupole magnets and one dipole magnet, was designed and constructed for high-resolution spectroscopy of hypernuclei using the (e,e'K+) reaction in Hall C, Jefferson Lab (JLab). It was used to analyze momenta of around 1.2 GeV/c K^+ s with a resolution of 2 ×10^-4 (FWHM). To achieve the target resolution, a full three-dimensional magnetic field measurement of each magnet was successfully performed, and a full three-dimensional magnetic field map of the HKS magnets was reconstructed. Using the measured field map, the initial reconstruction function was generated. The target resolution would be achieved via careful tuning of the reconstruction function of HKS with the p(e,e'K+)Lambda,Sigma^0 and C-12 (e,e'K+)12_Lambda B_g.s. reactions. After tuning of the initial reconstruction function generated from the measured map, the estimated HKS momentum resolution was 2.2×10^-4 (FWHM).

Fujii, Yuu (ORCID:0000000166252241)↗
DOE OSTI2013

Kinetic particle simulation of discharge and wall erosion of a Hall thruster

The primary lifetime limiting factor of Hall thrusters is the wall erosion caused by the ion induced sputtering, which is predominated by dielectric wall sheath and pre-sheath. However, so far only fluid or hybrid simulation models were applied to wall erosion and lifetime studies in which this non-quasi-neutral and non-equilibrium area cannot be treated directly. Thus, in this study, a 2D fully kinetic particle-in-cell model was presented for Hall thruster discharge and lifetime simulation. Because the fully kinetic lifetime simulation was yet to be achieved so far due to the high computational cost, the semi-implicit field solver and the technique of mass ratio manipulation was employed to accelerate the computation. However, other artificial manipulations like permittivity or geometry scaling were not used in order to avoid unrecoverable change of physics. Additionally, a new physics recovering model for the mass ratio was presented for better preservation of electron mobility at the weakly magnetically confined plasma region. The validity of the presented model was examined by various parametric studies, and the thrust performance and wall erosion rate of a laboratory model magnetic layer type Hall thruster was modeled for different operation conditions. The simulation results successfully reproduced the measurement results with typically less than 10% discrepancy without tuning any numerical parameters. It is also shown that the computational cost was reduced to the level that the Hall thruster fully kinetic lifetime simulation is feasible.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

A hybrid double-dot in silicon

We report electrical measurements of a single arsenic dopant atom in the tunnel barrier of a silicon single-electron transistor (SET). In addition to performing the electrical characterisation of the individual dopants, we study the series electrical transport through the dopant and SET. We measure the bias triangles of this hybrid double-dot and show that we can tune the electrostatic coupling between the two sub-systems. Additionally, we measured SET in which an additional plunger gate allows the reduction of the electron number in the SET down to the few-electron regime where the dot presents well-defined spin configurations. Finally, we discuss the challenges of operating a dopant-dot hybrid system in the few-electron regime.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Machine learning surrogate models for Landau fluid closure

The first result of applying the machine/deep learning technique to the fluid closure problem is presented in this letter. As a start, three different types of neural networks (multilayer perceptron (MLP), convolutional neural network (CNN) and two-layer discrete Fourier transform (DFT) network) were constructed and trained to learn the well-known Hammett-Perkins Landau fluid closure in configuration space. We found that in order to train a well-preformed network, a minimum size of training data set is needed; MLP also requires a minimum number of neurons in the hidden layers equals to the degrees of freedom in Fourier space despite training data is fed in configuration space. Out of three models DFT performs the best for the clean data most likely due to the existence of nice Fourier expression for Hammett-Perkins closure but it is least robust with respect to input noise. Overall, with appropriate tuning and optimization, all three neural networks are able to accurately predict Hammett-Perkins closure and reproduce the inherit nonlocal feature, suggesting a promising path to calculate more sophisticated closures with the machine/deep learning technique.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Machine learning-accelerated path integral molecular dynamics simulations of reactive organic electrolytes

Hydrogen bonded electrolytes that exhibit accelerated proton transport via sequential reactive hops have drawn interest for their promise in clean energy applications. Molecular dynamics simulations of these electrolytes offer the opportunity to uncover microscopic mechanistic details that could be used to design and tune the properties of candidate electrolyte technologies. However, accurately modeling the proton transfer reactions and transport properties that give rise to high charge conductivites in these electrolytes proves computationally challenging because of the need to perform lengthy condensed phase simulations, treating both the electronic and nuclear degrees of freedom quantum mechanically. In this paper, we demonstrate that such a modeling task can be efficiently achieved with the use of density functional theory (DFT)-trained machine learning potentials (MLP) to accelerate path integral molecular dynamics (PIMD) simulations. We highlight the practical utility of this approach by using it to benchmark how closely PIMD simulations employing different DFT exchange–correlation functionals reproduce the composition-dependent densities, diffusion coefficients, and electrical conductivities of mixtures consisting of imidazole and levulinic acid. Even with the speedup afforded by our MLPs, PIMD simulations remain quite expensive. Furthermore, in order to render PIMD more computationally tractable, we introduce and benchmark the accuracy of a ring polymer contraction approach that leverages a computationally efficient short-range MLP to accelerate our PIMD simulations by an additional factor of four.

Chemical bonding↗
DOE OSTI2013

Power/energy use cases for high performance computing

Power and Energy have been identified as a first order challenge for future extreme scale high performance computing (HPC) systems. In practice the breakthroughs will need to be provided by the hardware vendors. But to make the best use of the solutions in an HPC environment, it will likely require periodic tuning by facility operators and software components. This document describes the actions and interactions needed to maximize power resources. It strives to cover the entire operational space in which an HPC system occupies. The descriptions are presented as formal use cases, as documented in the Unified Modeling Language Specification [1]. The document is intended to provide a common understanding to the HPC community of the necessary management and control capabilities. Assuming a common understanding can be achieved, the next step will be to develop a set of Application Programing Interfaces (APIs) to which hardware vendors and software developers could utilize to steer power consumption.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2026

FOCAL Campaign IV: Integrated System Control: Turbine + Hull

Campaign IV of the Floating Offshore-wind Controls Advanced Laboratory Experimental Program (FOCAL) aimed to generate a dataset enabling the validation of a floating offshore wind turbine with turbine and hull controls. The turbine considered in this campaign is the scaled IEA 15MW Reference Wind Turbine similar to the setup considered in FOCAL Campaign I. This turbine is mounted on the VolturnUS platform with integrated hull controls similar to the hull considered in FOCAL Campaign II/III. This system is deployed for a fully-coupled wind and wave testing campaign at the University of Maine's Harold Alfond Wind and Wave (W2) facility. System dynamics and turbine characteristics are measured to determine global performance and assess the effect of the control strategies employed. NREL's reference open-source controller (ROSCO) is used for active blade pitch control and hull structural control is examined through the use of tuned mass dampers (TMD's) tuned to the systems pitch and tower-bending natural frequency. The naming convention of the load cases considered are described in the data details section. Detailed properties on the modeled system are found in the following reference: Lenfest E., Floating Offshore-wind Controls Advanced Laboratory (FOCAL) Experimental Program - Campaign IV: 1:70 Model-scale Testing of the IEA-Wind 15MW Reference Turbine and the VolturnUS-S Platform. UMaine ASCC Report Number 23-57-1183.

17 WIND ENERGY↗
DOE OSTI2020

Ionic/electronic conductivity regulation of n-type polyoxadiazole lithium sulfonate conductive polymer binders for high-performance silicon microparticle anodes

Low-cost silicon microparticles (SiMP), as a substitute for nanostructured silicon, easily suffer from cracks and fractured during the electrochemical cycle. A novel n-type conductive polymer binder with excellent electronic and ionic conductivities as well as good adhesion, has been successfully designed and applied for high-performance SiMP anodes in lithium-ion batteries to address this problem. Its unique features are attributed to the strong electron-withdrawing oxadiazole ring structure with sulfonate polar groups. The combination of rigid and flexible components in the polymer ensures its good mechanical strength and ductility, which is beneficial to suppress the expansion and contraction of SiMP s during the charge/discharge process. By fine-tuning the monomer ratio, the conjugation and sulfonation degrees of the polymer can be precisely controlled to regulate its ionic and electronic conductivities, which has been systematically analyzed with the help of an electrochemical test method, filling in the gap on the conductivity measurement of the polymer in the doping state. The experimental results indicate that the cell with the developed n-type polymer binder and SiMP (~0.5 μm) anodes achieves much better cycling performance than traditional non-conductive binders. It has been considered that the initial capacity of the SiMP anode is controlled by the synergetic effect of ionic and electronic conductivity of the binder, and the capacity retention mainly depends on its electronic conductivity when the ionic conductivity is sufficient. Here, it is worth noting that the fundamental research of this work is also applicable to other battery systems using conductive polymers in order to achieve high energy density, broadening their practical applications.

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

Electrical tuning of mechanical characteristics in qPlus sensor: Active Q and resonance frequency control

We present an electrical feedback method for independent and simultaneous tuning of both the resonance frequency and the quality factor of a harmonic oscillator, the so called “qPlus” configuration of quartz tuning forks. We incorporate a feedback circuit with two electronic gain parameters into the original actuation-detection system, and systematically demonstrate the control of the original resonance frequency of 32 592 Hz from 32 572 Hz to 32 610 Hz and the original quality factor 952 from 408 up to 20 000. This tunable module can be used for enhancing and optimizing the oscillator performance in compliance with specifics of applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Designing ultrastable Pt/CeO 2 -Al 2 O 3 nanosheet catalysts for three-way catalysts applications

Designing Rh-free, especially Pt-only, three-way catalysts with improved low-temperature activity/stability is highly desirable. Herein, we demonstrate that ultrastable Pt/CeO 2 -Al 2 O 3 nanosheet catalysts can be obtained based on a Sabatier principle of metal-support interaction. Tuning the surface coverage of penta-site rich γ-Al 2 O 3 nanosheets (AlNS, weak adhesion to Pt) by CeO 2 “nano-islands” (strong adhesion to Pt) can lead to the synthesis of Pt/60 wt.%CeO 2 -AlNS that have lower light-off temperatures for CO, hydrocarbons, and NO compared to conventional Pt/CeO 2 and Pt/Al 2 O 3 catalysts by 100–200°C and a similar performance with the state-of-the-art Rh-based catalyst. Further, incorporating CeO 2 on the surface of AlNS can retard the sintering of CeO 2 during harsh redox hydrothermal aging, associate with the strong interaction between CeO 2 “nano-island” and penta-site rich γ-Al 2 O 3 nanosheets. Moreover, the improved activity/stability of Pt/CeO 2 -AlNS catalysts can be attributed to tuning of the Pt detachment and migration from and back to the CeO 2 “nano-islands”, respectively, that keeps Pt as nanoclusters on CeO 2 , the most active species for three-way catalyst applications.

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

Gold core/ceria shell-based redox active nanozyme mimicking the biological multienzyme complex phenomenon

Catalytically active individual gold (Au) and cerium oxide (CeO2) nanoparticles are well known to exhibit specific enzyme-like activities, such as natural catalase, oxidase, superoxide dismutase, and peroxidase enzymes. These activities have been maneuvered to design several biological applications such as immunoassays, glucose detection, radiation and free radical protection and tissue engineering. A functional nanozyme depicting multienzyme like properties that functions as a synthetic super enzyme has eluded the researchers in the nanoscience community for past decade. In current report, we have designed a functional multienzyme in the form of Gold (core)-CeO2 (shell) nanoparticles (Au@CeO2 CSNPs) exhibiting excellent peroxidase, catalase and superoxide dismutase enzyme-like activities that are controlled simply by tuning the pH. The reaction kinetic parameters reveal that the peroxidase-like activity of this core shell nanozyme is comparable to natural HRP enzyme. Unlike peroxidase-like activity exhibited by other nanomaterials, Au@CeO2 CSNPs showed decrease in hydroxyl radical formation, suggesting that the bio catalytic reactions are performed by efficient electron transfers. A significant enzyme-like activity of this core shell nanoparticle was conserved at extreme pH (2 – 11) and temperatures (up to 90 °C), clearly suggesting the superiority over natural enzymes. Further, the utility of peroxidase-like activity of this core shell nanoparticles was extended for the detection of glucose, which showed a linear range of detection between (100 µM – 1 mM). It is hypothesized that the proximity of the redox potentials of Au+/Au and Ce (III)/Ce (IV) may result in a redox couple promoting the multienzyme activity of core shell nanoparticles. Au@CeO2 CSNPs may open new directions for development of single platform sensors in multiple biosensing applications.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2019

Amphoteric Indium Enables Carrier Engineering to Enhance the Power Factor and Thermoelectric Performance in n -Type Ag n Pb 100 In n Te 100+2 n (LIST)

The Ag and In co-doped PbTe, Ag n Pb 100 In n Te 100+2n (LIST), exhibits n-type behavior and features unique inherent electronic levels that induce self-tuning carrier density. Results show that In is amphoteric in the LIST, forming both In 3+ and In 1+ centers. Through unique interplay of valence fluctuations in the In centers and conduction band filling, the electron carrier density can be increased from ≈3.1 × 10 18 cm -3 at 323 K to ≈2.4 × 10 19 cm -3 at 820 K, leading to large power factors peaking at ≈16.0 μWcm -1 K -2 at 873 K. The lone pair of electrons from In + can be thermally continuously promoted into the conduction band forming In 3+ , consistent with the amphoteric character of In. Moreover, with rising temperature, the Fermi level shifts into the conduction band, which enlarges the optical band gap based on the Moss–Burstein effect, and reduces bipolar diffusion and thermal conductivity. Adding extra Ag in LIST improves the electrical transport properties and meanwhile lowers the lattice thermal conductivity to ≈0.40 Wm -1 K -1 . Here, the addition of Ag creates spindle-shaped Ag 2 Te nanoprecipitates and atomic-scale interstitials that scatter a broader set of phonons. As a result, a maximum ZT value ≈1.5 at 873 K is achieved in Ag 6 Pb 100 InTe 102 (LIST).

36 MATERIALS SCIENCE↗