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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Proton-mediated energy storage in intermediate-temperature solid-oxide metal–air batteries

Proton-containing ceramics have been investigated for the first time as the supporting phase for the energy storage medium in intermediate-temperature (IT) solid-oxide metal–air redox batteries. The strong interaction between H 2 O and oxygen vacancies creates ample protons on the surface of the proton-containing perovskites, which significantly enhanced the reversibility and cycle performance.

25 ENERGY STORAGE↗
DOE OSTI2019

Gastrointestinal stromal tumor risk classification: spectral CT quantitative parameters

Purpose: To examine the value of spectral CT quantitative parameters in gastrointestinal stromal tumor (GIST) risk classification. Materials and methods: This retrospective study was approved by the institutional review board. The requirement for informed consent was signed. The authors evaluated 86 patients (30 high risk, 22 medium risk, 28 low risk, and 6 very low risk; mean age: 59 years [range 19–83 years]) with pathologically confirmed GIST who underwent plain and triple-phase contrast-enhanced CT with spectral CT imaging mode from March 2015 through September 2017, with manual follow-up. Quantitative parameters including the CT value of 70 keV monochromatic images, the slope of spectral curves, and the normalized iodine concentration (NIC) and water (iodine) concentrations were measured and calculated, and conducted a power analysis of the above data. Results: (1) The CT values at 70 keV of the high-risk group were higher than the intermediate and low groups in each of the enhanced phases (P ≤ 0.001), no significant differences in the intermediate-risk and low-risk groups were noted (P = 0.874, 0.871, 0.831, respectively). (2) The slope of the spectral curve of the high-risk group was higher than those of the intermediate and low groups in each of the enhanced phases (P ≤ 0.001), and there were no significant differences between the intermediate- and low-risk groups (P = 0.069, 0.466, 0.840, respectively). (3) The NIC of the high-risk group significantly differed from the lower risk groups (P ≤ 0.001). There was also no significant difference observed between the intermediate- and low-risk groups (P = 0.671, 0.457, 0.833, respectively). (4) The power analysis results show that only the low-risk group with delay period is 0.530, the rest groups are all greater than 0.999. Conclusion: Dual-energy spectral CT with quantitative analysis may help to increase the accuracy in differentiating the pathological risk classification of GIST between high risk and non-high risk, preoperatively. There were limitations for distinguishing the intermediate- and low-risk groups.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Direct evidence of an incommensurate phase in NaNbO{sub 3} and its implication in NaNbO{sub 3}-based lead-free antiferroelectrics

Hot-stage in situ transmission electron microscopy was employed to investigate the temperature-induced complex sequence of phase transitions in NaNbO{sub 3} polycrystalline. In addition to the commonly recognized P (Pbma) → R (Pmnm) → S (Pnmm) phase transitions, incommensurate phases were observed to exist in P and R phase regions. The former (in the P → R transition region) is coincident with a diffused dielectric peak appearing at ∼170 °C, and the latter (in the R → S transition region) serves as an intermediate structure to bridge the two sub-phases in the R phase region. The incommensurate phase in the P phase region can be inferred from the polarization current density and differential dielectric permittivity anomalies, and it provides the bridge structure during the electric field-induced polarization reversal and antiferroelectric-to-ferroelectric transition in NaNbO{sub 3} solid solutions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Microstructure Development in Electron Beam-Melted Inconel 718 and Associated Tensile Properties

During the electron beam melting (EBM) process, builds occur at temperatures in excess of 800°C for nickel-base superalloys such as Inconel 718. When coupled with the temporal differences between the start and end of a build, a top-to-bottom microstructure gradient forms. Characterized in this study is the microstructure gradient and associated tensile property gradient that are common to all EBM Inconel 718 builds. From the characteristic microstructure elements observed in EBM Inconel 718 material, the microstructure gradient can be classified into three distinct regions. Region 1 (top of a build) and is comprised of a cored dendritic structure that includes carbides and Laves phase within the interdendritic regions. Region 2 is an intermediate transition zone characterized by a diffuse dendritic structure, dissolution of the Laves phase, and precipitation of δ needle networks within the interdendritic regions. The bulk structure (Region 3) is comprised of a columnar grain structure lacking dendritic characteristics with δ networks having precipitated within the grain interiors. Mechanically at both 20°C and 650° C, the yield strength, ultimate tensile strength, and elongation at failure exhibit the general trend of increasing with increasing build height.

36 MATERIALS SCIENCE↗
NASA NTRS1989

DMSK Receiver For Mobile/Satellite Service

Receiver for 2.4-kbit/s differential minimum-shift keying (DMSK) and Gaussian minimum-shift keying(GMSK) suitable for communication between land-mobile stations via geostationary satellites. Operating on phase-shifted signal in 800-MHz band, in presence of fading and Doppler frequency shifts, receiver compact, makes efficient use of frequency spectrum, and wastes little power. Receiver design implemented in very-large-scale-integrated circuits. Basic DMSK receiver design relies on baseband rather than intermediate-frequency processing of in-phase and quadrature signal components because phase errors due to differential delays smaller at baseband.

Davarian, Faramaz↗
DOE OSTI2023

Decoding Li + /Na + Exchange Route Toward High-Performance Mn-Based Layered Cathodes for Li-Ion Batteries

Li + /Na + exchange has been extensively explored as an effective method to prepare high-performance Mn-based layered cathodes for Li-ion batteries, since the first report in 1996 by P. G. Bruce (Nature, 1996. 381, 499–500). Understanding the detailed structural changes during the ion-exchange process is crucial to implement the synthetic control of high-performance layered Mn-based cathodes, but less studied. Herein, in situ synchrotron X-ray diffraction, density functional theory calculations, and electrochemical tests are combined to conduct the systemic studies into the structural changes during the ion-exchange process of an Mn-only layered cathode O3-type Li 0.67 [Li 0.22 Mn 0.78 ]O 2 (LLMO) from the corresponding counterpart P3-type Na 0.67 [Li 0.22 Mn 0.78 ]O 2 (NLMO). The temperature-resolved observations combined with theoretical calculations reveal that the Li + /Na + exchange is favorable thermodynamically and composited with two tandem topotactic phase transitions: 1) from NLMO to a layered intermediate through ≈60% of Li + /Na + exchange. 2) then to the final layered product LLMO through further Li insertion. Moreover, the intermediate-dominate composite is obtained by slowing down the exchange kinetics below room temperature, showing better electrochemical performance than LLMO obtained by the traditional molten-salt method. Finally, the findings provide guides for the synthetic control of high-performance Mn-based cathodes under mild conditions.

25 ENERGY STORAGE↗
DOE OSTI2022

Electron Counting and High-Pressure Phase Transformations in Metal Hexaborides

Pressure-induced structural transitions of the alkaline earth hexaborides, CaB 6 , SrB 6 , and BaB 6 , are studied theoretically using electron counting rules and density functional theory calculations. Here, we demonstrate the applicability of gas-phase borane electron counting methods to solid-state metal borides under pressure and validate the assumptions of the rules by density functional theory (DFT) calculations. All three compounds share ambient-pressure and high-pressure structures, but BaB 6 differs from CaB 6 and SrB 6 at intermediate pressures. The unique BaB 6 phase is shown to break electron counting rules, while all other phases obey them. This anomaly is resolved by DFT, which reveals B–Ba covalency and unusual B–B π bonding under pressure. The relationships between structure and bonding can help us to understand the exotic behavior of lanthanide hexaborides and design new borides with desirable properties. Developing electron counting procedures for solids will enhance materials discovery efforts with chemical intuition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Atomistic Mechanisms of the Crystallographic Orientation‐Dependent Cu 1.8 S Conductive Channel Formation in Cu 2 S‐Based Memristors

Achieving multiple types of resistive switching in a single material with controlled ionic motion is a key challenge in neuromorphic computing, traditionally addressed by combining materials with distinct switching behaviors. Here, Cu 2-x S is identified as a promising candidate to overcome this limitation due to its hierarchical phase transitions. Using in situ biasing experiments, reversible and non-reversible phase transitions (and resistive switching) are demonstrated in γ-Cu 2 S by controlling the compliance current. The formation of parallel high-digenite Cu 1.8 S channels, orientated along the γ-Cu 2 S [201] crystallographic direction, drives the nonvolatile resistive switching. These channels emerge via an intermediate δ-Cu 2 S phase and are stabilized at room temperature by residual strains, alongside β-Cu 2 S phase. In conclusion, the work clarifies the complex, electrically triggered phase transformations in γ-Cu 2 S, and highlights the potential of Cu 2-x S as a versatile material for neuromorphic computing.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Low-temperature microstructural studies on superconducting CaFe2As2

Abstract Undoped CaFe 2 As 2 (Ca122) can be stabilized in two slightly different non-superconducting tetragonal phases, PI and PII, through thermal treatments. Upon proper annealing, superconductivity with a T c up to 25 K emerges in the samples with an admixture of PI and PII phases. Systematic low-temperature X-ray diffraction studies were conducted on undoped Ca122 samples annealed at 350 °C over different time periods. In addition to the diffraction peaks associated with the single-phase aggregation of PI and PII, a broad intermediate peak that shifts with annealing time was observed in the superconducting samples only. Our simulation of phase distribution suggests that the extra peak is associated with the admixture of PI and PII on the nanometer scale. High-resolution transmission electron microscopy confirms the existence of these nano-scale phase admixtures in the superconducting samples. These experimental results and simulation analyses lend further support for our conclusion that interfacial inducement is the most reasonable explanation for the emergence of superconductivity in undoped Ca122 single crystals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1991

A calibration of solar envelope models using the frequencies of intermediate-degree solar acoustic oscillations

The frequency dependence of the phase shift, which arises from the reflection of internal acoustic waves (p-modes) at the outer solar layers, can be determined from the accurately measured frequencies of intermediate-degree p-modes. This dependence is sensitive to the complicated structure of the outer solar layers, down to the depth of the second ionization zone of helium. It can be used to calibrate solar envelope models. The results of the direct tests of a variety of solar envelope models using the phase shift inferred from the solar oscillation frequencies are reported.

Pamiatnykh, A. A.↗
DOE OSTI2019

Anisotropy effects on the kinetics of colloidal crystallization and melting: comparison of spheres and ellipsoids

We use alternating current (AC) electric field assisted self-assembly to produce two-dimensional, millimeter scale arrays of ellipsoidal colloids and study the kinetics of their phase reconfiguration by means of confocal microscopy, light scattering, and computer simulation. We find that the kinetics of orientational and positional ordering can be manipulated by changing the shape of the colloids: ellipsoids with aspect ratio 2.0 melt into disordered structures 5.7 times faster compared to spheres. On the other hand, ellipsoids self-assemble into ordered crystals at a similar rate to spheres. Confocal microscopy is used to directly visualize defects in the self-assembled structures. Small-angle light scattering (SALS) quantifies the light diffraction response, which is sensitive to the kinetics of positional and orientational ordering in the self-assembled anisotropic structures. We find three different light diffraction patterns: a phase with high orientational order (with chain-like structure in real space), a phase with high positional and orientational order (characteristic of a close-packed structure), and a phase that is disordered in position but with intermediate orientational order. The large influence of aspect ratio on the kinetics of the positionally and orientationally ordered phase is explored through simulation; it is found that the number of particle degrees of freedom controls the difference between the melting rates of the ellipsoids and spheres. This research contributes to the understanding of reconfiguration kinetics and optical properties of colloidal crystals produced from anisotropic colloids.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Analysis and prediction of reaction kinetics using the degree of rate control

“Degree of rate control” (DRC) analysis provides a quantitative approach for analysing the kinetics of multi-step reaction mechanisms that has been widely applied to both heterogeneous and homogeneous catalysis research, as well as electrocatalysis. The DRC of any given transition state or intermediate is defined as a partial derivative such that it approximately equals the fractional increase in net rate to the product of interest per differential decrease in its standard-state free energy for that species (÷RT), holding constant the standard-state free energies of all other transition states and intermediates. Even very complex mechanisms usually have only a few species with non-zero DRCs and are thus the species whose interactions with the catalyst most strongly affect the net rate. These key DRC values thus offer a simple and intuitive route to optimize catalyst materials, especially with the assistance of computational methods like density functional theory (DFT). These high-DRC species are also the species whose energetics must be most accurately measured or calculated to achieve an accurate kinetic model for any reaction mechanism. In simple cases with a single “rate-determining step”, the DRC for its transition state (TS) is + 1. Catalyst-bound intermediates, on the other hand, often have negative DRCs equal to a small integer times their fractional occupancy of catalyst sites. The apparent activation energy equals a weighted average of the standard-state enthalpies (relative to reactants) of all the species (intermediates, transition states and products) in the reaction mechanism, each weighted by its DRC (+RT). It has been shown that the apparent transfer coefficient in electrocatalysis, an inverted form of the Tafel slope, is a weighted average of the number of electrons transferred to generate each intermediate or product species in the mechanism, weighted again by the DRC. Quantitative analysis of kinetic isotope effects (KIEs, or the ratio of net rates for different reactant isotopes) in complex mechanisms has shown that the logarithm of the KIE equals the weighted average over all species in the mechanism of the difference between the two isotopes in their standard-state free energies (÷RT), again weighted by the DRC. The reaction orders with respect to fluid-phase concentrations of reactants, products and intermediates have also been proven to be directly related to DRCs. Thus, there are numerous experimental observables which equate to short linear combinations of DRCs, so that combinations of experimental measurements might provide access to DRC values. Since its invention for transition states in 1994 and its generalization to include intermediates in 2009, the DRC has thus far mainly been calculated for microkinetic models based either entirely on DFT or on DFT with the key energies (i.e., those for high-DRC species) being fine-tuned to match experiments. The relationships summarized in this work provide new opportunities for using experiments earlier in the development and optimization of microkinetic models that require input from computational catalysis.

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

The Electrochemical Sodiation of Sb Investigated by Operando X-ray Absorption and 121 Sb Mössbauer Spectroscopy: What Does One Really Learn?

In this study, we want to highlight the assets and restrictions of X-ray absorption spectroscopy (XAS) and Mössbauer spectroscopy for investigating the mechanism of the electrochemical reaction of antimony electrode materials vs. Na. For this, operando XAS was carried out during the first one and a half cycles, and the whole set of measured data was analysed using a statistical-chemometric approach, while low temperature Mössbauer spectroscopy measurements were carried out ex situ on selected samples stopped at different points of the electrochemical reaction. Complementary ab initio calculations were performed to support the experimental findings. Both techniques show that, upon the first sodiation, most Sb reacts with Na to form disordered Na 3 Sb. This step is accompanied by the formation of amorphous Sb as an intermediate. Upon inversion of the current Na 3 Sb is desodiated and an amorphous Sb phase, distinct from the pristine bulk Sb state, is gradually formed. However, both XAS and Mössbauer spectroscopy were unable to spot the formation of intermediate Na x Sb phases, which were evinced in previous works by operando Pair Distribution Function analyses. The results shown here clearly assign such failure to the intrinsic inability of both techniques to identify these intermediates.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Cross Entropy Benchmark for Measurement-Induced Phase Transitions

Here, we investigate prospects of employing the linear cross entropy to experimentally access measurement-induced phase transitions without requiring any postselection of quantum trajectories. For two random circuits that are identical in the bulk but with different initial states, the linear cross entropy χ between the bulk measurement outcome distributions in the two circuits acts as an order parameter, and can be used to distinguish the volume law from area law phases. In the volume law phase (and in the thermodynamic limit) the bulk measurements cannot distinguish between the two different initial states, and χ = 1. In the area law phase χ < 1. For circuits with Clifford gates, we provide numerical evidence that χ can be sampled to accuracy ϵ from O⁢(1/ϵ 2 ) trajectories, by running the first circuit on a quantum simulator without postselection, aided by a classical simulation of the second. We also find that for weak depolarizing noise the signature of the measurement-induced phase transitions is still present for intermediate system sizes. In our protocol we have the freedom of choosing initial states such that the “classical” side can be simulated efficiently, while simulating the “quantum” side is still classically hard.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1985

Recovering Microwave Cross-Polarization Losses

Reception improved by adding normally discarded portion of signal. For signal enhancement, major and minor signals combined in slaved closedloop receiver channels. Both receiver channels served by common local oscillator controlled by phase-locked loop in main channel. 10-MHz intermediate-frequency (IF) signals of channels coherently summed. For polarization tracking, phasemeter added to measure phase difference between points A and B. With new circuit, low-level signal used at receiver to augment main signal.

Seidel, B. L.↗
NASA NTRS1989

A study of several F and G supergiant-like stars with infrared excesses as candidates for proto-planetary nebulae

Ground-based observations have been obtained for eight F and G supergiant-like stars showing large IR excesses. The combination of ground-based and IRAS data shows that these objects have dual-peak energy distributions, with comparable amounts of energy emitted in the visible and the IR. The IR-emitting cool dust shells are likely to represent the remnants of ejecta from an earlier phase of evolution. It is suggested that these eight objects are similar to IRAS 18095 + 2704 and are intermediate-mass stars in a post-AGB phase of evolution. Model fittings to the 0.4-100 micron energy distribution of these objects suggest that they left the AGB within the last 1000 yr.

Hrivnak, Bruce J.↗
DOE OSTI2018

First-principles insights on phase stability of titanium interstitial alloys

Titanium can dissolve unusually high concentrations of interstitial elements such as carbon and nitrogen to form a rich variety of compounds with beneficial structural and functional properties. Here, a first-principles statistical mechanics study was performed to predict phase stability in the Ti-C and Ti-N binaries. Density functional theory calculations were combined with the cluster-expansion approach to determine ground-state carbon-vacancy and nitrogen-vacancy orderings over the octahedral sites of hcp and fcc Ti. A large number of vacancy-ordered rocksalt phases were found to be stable at low temperature. Monte Carlo simulations showed that the ordered rocksalts transform to a disordered rocksalt that can tolerate high vacancy concentrations at intermediate to high temperatures. Clear trends in phase stability, rooted in electronic structure, are revealed upon a comparison of the calculated Ti-C and Ti-N phase diagrams with the Ti-O phase diagrams from a previous study [N. S. H. Gunda et al., Phys. Rev. Mater. 2, 033604 (2018)].

36 MATERIALS SCIENCE↗
DOE OSTI2018

Temperature Dependence of Paramagnetic Critical Magnetic Field in Disordered Attractive Hubbard Model

Within the generalized DMFT+Σ approach, we study disorder effects in the temperature dependence of paramagnetic critical magnetic field H{sub cp}(T) for Hubbard model with attractive interaction. We consider the wide range of attraction potentials U—from the weak coupling limit, when superconductivity is described by BCS model, up to the limit of very strong coupling, when superconducting transition is related to Bose–Einstein condensation (BEC) of compact Cooper pairs. The growth of the coupling strength leads to the rapid growth of H{sub cp}(T) at all temperatures. However, at low temperatures, paramagnetic critical magnetic field H{sub cp} grows with U much more slowly, than the orbital critical field, and in BCS limit, the main contribution to the upper critical magnetic filed is of paramagnetic origin. The growth of the coupling strength also leads to the disappearance of the low temperature region of instability towards type I phase transition and Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase, characteristic of BCS weak coupling limit. Disordering leads to the rapid drop of H{sub cp}(T) in BCS weak coupling limit, while in BCS–BEC crossover region and BEC limit H{sub cp}(T → 0) dependence on disorder is rather weak. Within DMFT+Σ approach, disorder influence on H{sub cp}(T) is of universal nature at any coupling strength and is related only to disorder widening of the conduction band. In particular, this leads to the drop of the effective coupling strength with disorder, so that disordering restores the region of type I transition in the intermediate coupling region.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗