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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Common origin of warm dark matter and dark radiation

We consider a cosmological scenario where a relativistic particle and a stable massive particle are simultaneously produced from the decay of a late-decaying particle after Big-Bang Nucleosynthesis but before matter-radiation equality. The relativistic and massive particles behave as dark radiation and warm dark matter, respectively. Due to a common origin, the warmness and abundances are closely related. We refer to the models that lead to such a scenario as Common Origin of Warm and Relativistic Decay Products (COWaRD). We show that COWaRD predicts a correlation between the amount of dark radiation and suppression of the large scale structure, which can be tested in future precision cosmology observations. Furthermore, we demonstrate that COWaRD is realized, as an example, in a class of supersymmetric axion models and that future observations by the next generation Cosmic Microwave Background, Large Scale Structure, and 21-cm surveys can reveal the structure of the theory.

cosmology of theories beyond the SM↗
NASA NTRS2001

Comparison of 250 MHz R10K Origin 2000 and 400 MHz Origin 2000 Using NAS Parallel Benchmarks

This report describes results of benchmark tests on Steger, a 250 MHz Origin 2000 system with R10K processors, currently installed at the NASA Ames National Advanced Supercomputing (NAS) facility. For comparison purposes, the tests were also run on Lomax, a 400 MHz Origin 2000 with R12K processors. The BT, LU, and SP application benchmarks in the NAS Parallel Benchmark Suite and the kernel benchmark FT were chosen to measure system performance. Having been written to measure performance on Computational Fluid Dynamics applications, these benchmarks are assumed appropriate to represent the NAS workload. Since the NAS runs both message passing (MPI) and shared-memory, compiler directive type codes, both MPI and OpenMP versions of the benchmarks were used. The MPI versions used were the latest official release of the NAS Parallel Benchmarks, version 2.3. The OpenMP versions used were PBN3b2, a beta version that is in the process of being released. NPB 2.3 and PBN3b2 are technically different benchmarks, and NPB results are not directly comparable to PBN results.

Turney, Raymond D.↗
DOE OSTI2021

Origin, nature, and the dynamic behavior of nanoscale vacancy clusters in Ni-rich layered oxide cathodes

Oxygen and transition metal (TM) vacancies in transition metal oxides (TMOs) play an important role in materials functionalities. For TMO cathodes of Li-ion batteries, vacancies can be introduced, either deliberately or inevitably, during materials synthesis or upon electrochemical cycling. Effects of vacancies on the electrochemical properties of cathodes critically depend on the dynamic characteristics of vacancies during the battery cycling. However, a fundamental understanding of such characteristics in the layer structured cathode remains elusive. Here, using scanning transmission electron microscopy (STEM), we reveal a cycling-induced aggregation behavior of oxygen and TM vacancies in a Ni-rich layer structured cathode of secondary particles. We discover that during the initial charging, vacancies aggregate to form visible vacancy-rich nanoregions (vacancy clusters) firstly at the outer layer of the secondary particle, and then the vacancy-cluster populated region extends to the inner part of particle upon fully charged. The spatial distinction of preferential nucleation of vacancy clusters at the outer layer indicates that the vacancy migration and clustering is associated with Li migration flux, which is larger at the outer layer, as all the Li from the inner part has to go through the outer layer. With extended cycling (> 50), these vacancy clusters become immobilized. We further reveal that the generation of these vacancy clusters is correlated to the material-synthesis conditions. Our findings solve a long-standing puzzle on the origin, nature, and behavior of the commonly visible vacancy clusters in the NMC cathode, providing insights on correlation between properties and dynamic behaviors of atomic-scale defects in layered oxide cathodes.

Li-ion batteries, layered oxide cathodes, NMC, cat↗
DOE OSTI2021

Origin of Selective Production of Hydrogen Peroxide by Electrochemical Oxygen Reduction

Oxygen reduction reaction (ORR) is one of the most important electrochemical reactions. Starting from a common reaction intermediate *–O–OH, the ORR splits into two pathways, either producing hydrogen peroxide (H 2 O 2 ) by breaking the *–O bond or leading to water formation by breaking the O–OH bond. However, it is puzzling why many catalysts, despite the strong thermodynamic preference for the O–OH breaking, exhibit high selectivity for hydrogen peroxide. Moreover, the selectivity is dependent on the potential and pH, which remain not understood. Here, for this work, we develop an advanced first-principles model for effective calculation of the electrochemical reaction kinetics at the solid–water interface, which were not accessible by conventional models. Using this model to study representative catalysts for H 2 O 2 production, we find that breaking the O–OH bond can have a higher energy barrier than breaking *–O, due to the rigidity of the O–OH bond. Importantly, we reveal that the selectivity dependence on potential and pH is rooted into the proton affinity to the former/later O in *–O–OH. For single cobalt atom catalyst, decreasing potential promotes proton adsorption to the former O, thereby increasing the H 2 O 2 selectivity. In contrast, for the carbon catalyst, the proton prefers the latter O, resulting in a lower H 2 O 2 selectivity in acid condition. These findings explain the experiments and highlight the kinetic origins of the selectivity. Our work improves the understanding of ORR by uncovering the proton affinity as a new factor and provides a new model to effectively simulate the atomic-level kinetics of heterogeneous electrochemistry.

08 HYDROGEN↗
DOE OSTI2019

Origin of Intrinsically Low Thermal Conductivity in Talnakhite Cu 17.6 Fe 17.6 S 32 Thermoelectric Material: Correlations between Lattice Dynamics and Thermal Transport

Understanding the nature of phonon transport in solids and the underlying mechanism linking lattice dynamics and thermal conductivity is important in many fields, including the development of efficient thermoelectric materials where a low lattice thermal conductivity is required. Herein, we choose the pair of synthetic chalcopyrite CuFeS 2 and talnakhite Cu 17.6 Fe 17.6 S 32 compounds, which possess the same elements and very similar crystal structures but very different phonon transport, as contrasting examples to study the influence of lattice dynamics and chemical bonding on the thermal transport properties. Chemically, talnakhite derives from chalcopyrite by inserting extra Cu and Fe atoms in the chalcopyrite lattice. The CuFeS 2 compound has a lattice thermal conductivity of 2.37 W m -1 K -1 at 625 K, while Cu 17.6 Fe 17.6 S 32 features Cu/Fe disorder and possesses an extremely low lattice thermal conductivity of merely 0.6 W m -1 K -1 at 625 K, approaching the amorphous limit κmin. Low-temperature heat capacity measurements and phonon calculations point to a large anharmonicity and low Debye temperature in Cu 17.6 Fe 17.6 S 32 , originating from weaker chemical bonds. Moreover, Mössbauer spectroscopy suggests that the state of Fe atoms in Cu 17.6 Fe 17.6 S 32 is partially disordered, which induces the enhanced alloy scattering. All of the above peculiar features, absent in CuFeS 2 , contribute to the extremely low lattice thermal conductivity of the Cu 17.6 Fe 17.6 S 32 compound.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Structural origins of the electronic properties of materials via time-resolved infrared spectroscopy

Time-resolved mid-infrared (TRIR) spectroscopy offers new opportunities to investigate how the molecular and structural properties of optoelectronic materials influence their electronic and transport states. This capability emerges from the ability to measure low energy electronic transitions in the mid-infrared that are related to delocalized states in materials and to simultaneously detect the vibrational properties of the materials that influence those states. Furthermore, the ability to simultaneously measure electronic and vibrational transitions in materials offers unprecedented opportunities to correlate structural dynamics of materials with their electronic and transport properties. Here, these capabilities are introduced by first describing the basic principles of TRIR spectroscopy used to examine electronic processes in materials. Then, several applications of TRIR spectroscopy are described in which measurements of the vibrational spectra of electronic excited states are probed as a means to correlate the structural properties of materials with the delocalization of their electronic states. In one example, exciton localization mechanisms in organic semiconductors are probed through vibrational spectra of the molecules in their excited states and correlated with their crystalline packing arrangements. Another example highlights the use of TRIR spectroscopy to examine singlet fission reaction dynamics through a combination of low energy electronic transitions and the vibrational spectra that are unique to the electronic states involved in the reaction. Finally, the use of TRIR spectroscopy to investigate charge carrier localization mechanisms in lead-halide perovskites is described, followed by an outlook of future applications of the technique in optoelectronic materials research.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Detection of hot electrons originating from an upper valley at ∼1.7eV above the Γ valley in wurtzite GaN using electron emission spectroscopy

Using electron emission spectroscopy, measurement and analysis were conducted on the energy distribution of vacuum emitted electrons from electrically driven InGaN/GaN green (peak wavelengths 𝜆 ≈ 515nm) light-emitting diodes (LEDs) with and without a prewell superlattice (SL). Here, we report on the detection of a high-energy upper valley at ∼ 1.7eV above the Γ valley from samples with no prewell SL. We propose that these upper valley electrons originate predominantly from trap-assisted Auger recombination (TAAR) in green LEDs, as the intensity of these peaks is found to have quadratic dependence on the carrier density 𝑛 [see Espenlaub et al., J. Appl. Phys. 126, 184502 (2019)]. The high-energy upper valley peak was not observed in the sample with a prewell SL which is attributed to gettering by the prewell SL of still unidentified impurities that act as TAAR centers.

carrier generation & recombination↗
NASA NTRS1982

The intercrater plains of Mercury and the Moon: Their nature, origin and role in terrestrial planet evolution. Discussion of the nature, origin and role of the intercrater plains of Mercury and the Moon

The nature and origin of the intercrater plains of Mercury and the Moon as determined through geologic mapping, crater statistics, and remotely sensed data are summarized. Implications of these results regarding scarp formation, absolute ages, and terrestrial planet surfaces are included. The role of the intercrater plains is defined and future work which might lead to a better understanding of these units and terrestrial planet evolution is outlined.

Leake, M. A.↗
NASA NTRS2018

The Origins Survey Spectrometer (OSS): A Far-IR Discovery Machine for the Origins Space Telescope

The OSS on the Origins Space Telescope is designed to decode the cosmic history of nucleosynthesis, star formation, and supermassive black hole growth with wide-area spatial-spectral 3-D surveys across the full 25 to 590 micron band. Six wideband grating modules combine to cover the full band at R=300, each couples a long slit with 60–190 beams on the sky. OSS will have a total of 120,000 background-limited detector pixels in the six 2-D arrays which provide spatial and spectral coverage. The suite of grating modules can be used for pointed observations of targets of interest, and are particularly powerful for 3-D spectral spectral surveys. To chart the transition from interstellar material, particularly water, to planetary systems, two high-spectral-resolution modes are included. The first incorporates a Fourier-transform spectrometer (FTS) in front of the gratings providing resolving power of 25,000 (δv = 12 km/s) at 179µm to resolve water emission in protoplanetary disk spectra. The second boosts the FTS capability with an additional etalon (Fabry-Perot interferometer) to provide 2 km/s resolution in this line to enable detailed structural studies of disks in the various water and HD lines. Optical, thermal, and mechanical designs are presented, and the system approach to the detector readout enabling the large formats is described.

Pontoppidan, Klaus↗
DOE OSTI2019

Revealing the Atomic Origin of Heterogeneous Li-Ion Diffusion by Probing Na

Tracing the dynamic process of Li-ion transport at the atomic scale is a long-cherished wish in solid state ionics and essential for battery material engineering. Approaches via phase change, strain, and valence states of redox species are developed to circumvent the technical challenge of direct imaging Li, however, all are limited by poor spatial resolution and weak correlation with state-of-charge (SOC). Here, we adopt an ion-exchange approach by sodiating the de-lithiated cathode and probing Na distribution to trace the Li de-intercalation, which enables us to visualize the heterogeneous Li-ion diffusion down to atomic level. In the model LiNi1/3Mn1/3Co1/3O2 cathode, dislocation-mediated ion diffusion is kinetically favorable at low SOC and planar diffusion along (003) layers dominates at high SOC, which work synergistically to determine the ion diffusion dynamics. Our work unveils the heterogeneous nature of ion diffusion in battery material and stresses the role of defect engineering in tailoring ion transport kinetics.

Xiao, Biwei↗
DOE OSTI2017

Hierarchical calibration and validation framework of bench-scale computational fluid dynamics simulations for solvent-based carbon capture. Part 2: Chemical absorption across a wetted wall column: Original Research Article: Hierarchical calibration and validation framework of bench-scale computational fluid dynamics simulations

Part 1 of this paper presents a numerical model for non-reactive physical mass transfer across a wetted wall column (WWC). In Part 2, we improved the existing computational fluid dynamics (CFD) model to simulate chemical absorption occurring in a WWC as a bench-scale study of solvent-based carbon dioxide (CO 2 ) capture. In this study, to generate data for WWC model validation, CO 2 mass transfer across a monoethanolamine (MEA) solvent was first measured on a WWC experimental apparatus. The numerical model developed in this work can account for both chemical absorption and desorption of CO 2 in MEA. In addition, the overall mass transfer coefficient predicted using traditional/empirical correlations is conducted and compared with CFD prediction results for both steady and wavy falling films. A Bayesian statistical calibration algorithm is adopted to calibrate the reaction rate constants in chemical absorption/desorption of CO 2 across a falling film of MEA. The posterior distributions of the two transport properties, i.e., Henry's constant and gas diffusivity in the non-reacting nitrous oxide (N 2 O)/MEA system obtained from Part 1 of this study, serves as priors for the calibration of CO 2 reaction rate constants after using the N 2 O/CO 2 analogy method. Finally, the calibrated model can be used to predict the CO 2 mass transfer in a WWC for a wider range of operating conditions.

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

Device-scale CFD modeling of gas-liquid multiphase flow and amine absorption for CO2 capture

In this paper we aim to develop a validated device-scale CFD model that can predict quantitatively both hydrodynamics and CO2 capture efficiency for an amine-based solvent absorber column with random Pall ring packing. A Eulerian porous-media approach and a two-fluid model were employed, in which the momentum and mass transfer equations were closed by literature-based empirical closure models. We proposed a hierarchical approach for calibrating the parameters in the closure models to make them accurate for the packed column. Specifically, a parameter for momentum transfer in the closure was first calibrated based on data from a single experiment. With this calibrated parameter, a parameter in the closure for mass transfer was next calibrated under a single operating condition. Last, the closure of the wetting area was calibrated for each gas velocity at three different liquid flow rates. For each calibration, cross validations were pursued using the experimental data under operating conditions different from those used for calibrations. This hierarchical approach can be generally applied to develop validated device-scale CFD models for different absorption columns.

Pan, Wenxiao↗