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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

CORRELATED STRONTIUM AND BARIUM ISOTOPIC COMPOSITIONS OF ACID-CLEANED SINGLE MAINSTREAM SILICON CARBIDES FROM MURCHISON

We present strontium, barium, carbon, and silicon isotopic compositions of 61 acid-cleaned presolar SiC grains from Murchison. Comparison with previous data shows that acid washing is highly effective in removing both strontium and barium contamination. For the first time, by using correlated {sup 88}Sr/{sup 86}Sr and {sup 138}Ba/{sup 136}Ba ratios in mainstream SiC grains, we are able to resolve the effect of {sup 13}C concentration from that of {sup 13}C-pocket mass on s-process nucleosynthesis, which points toward the existence of large {sup 13}C pockets with low {sup 13}C concentrations in asymptotic giant branch stars. The presence of such large {sup 13}C pockets with a variety of relatively low {sup 13}C concentrations seems to require multiple mixing processes in parent asymptotic giant branch stars of mainstream SiC grains.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Quantum compositeness of gravity: black holes, AdS and inflation

Gravitational backgrounds, such as black holes, AdS, de Sitter and inflationary universes, should be viewed as composite of N soft constituent gravitons. It then follows that such systems are close to quantum criticality of graviton Bose-gas to Bose-liquid transition. Generic properties of the ordinary metric description, including geodesic motion or particle-creation in the background metric, emerge as the large-N limit of quantum scattering of constituent longitudinal gravitons. We show that this picture correctly accounts for physics of large and small black holes in AdS, as well as reproduces well-known inflationary predictions for cosmological parameters. However, it anticipates new effects not captured by the standard semi-classical treatment. In particular, we predict observable corrections that are sensitive to the inflationary history way beyond last 60 e-foldings. We derive an absolute upper bound on the number of e-foldings, beyond which neither de Sitter nor inflationary Universe can be approximated by a semi-classical metric. However, they could in principle persist in a new type of quantum eternity state. We discuss implications of this phenomenon for the cosmological constant problem.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Fractional quantum Hall systems near nematicity: Bimetric theory, composite fermions, and Dirac brackets

Here, we perform a detailed comparison of the Dirac composite fermion and the recently proposed bimetric theory for a quantum Hall Jain states near half filling. By tuning the composite Fermi liquid to the vicinity of a nematic phase transition, we discover that the two theories are equivalent to each other. We verify that the single mode approximation for the response functions and the static structure factor becomes reliable near the phase transition. We show that the dispersion relation of the nematic mode near the phase transition can be obtained from the Dirac brackets between the components of the nematic order parameter. The dispersion is quadratic at low momenta and has a magnetoroton minimum at a finite momentum, which is not related to any nearby inhomogeneous phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Evidence of nanoscale Anderson localization induced by intrinsic compositional disorder in InGaN/GaN quantum wells by scanning tunneling luminescence spectroscopy

We present direct experimental evidence of Anderson localization induced by the intrinsic alloy compositional disorder of InGaN/GaN quantum wells. Our approach relies on the measurement of the luminescence spectrum under local injection of electrons from a scanning tunneling microscope tip into a near-surface single quantum well. Fluctuations in the emission line shape are observed on a few-nanometer scale. Narrow emission peaks characteristic of single localized states are resolved. Calculations in the framework of the localization landscape theory provide the effective confining potential map stemming from composition fluctuations. This theory explains well the observed nanometer scale carrier localization and the energies of these Anderson-type localized states. In conclusion, the energy spreading of the emission from localized states is consistent with the usually observed very broad photo- or electroluminescence spectra of InGaN/GaN quantum well structures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Compositional control of radionuclide retention in hollandite-based ceramic waste forms for Cs-immobilization

Hollandite materials, as a class of crystalline nuclear waste forms, are promising candidates for the immobilization of radioactive elements, such as Cs, Ba, as well as a variety of lanthanide and transition-metal fission products. In this study, three Ga-doped titanate hollandite-type phases, Ba 1.33 Ga 2.67 Ti 5.33 O 16 , Ba 0.667 Cs 0.667 Ga 2 Ti 6 O 16 , and Cs 1.33 Ga 1.33 Ti 6.67 O 16 , were synthesized using a solid-state reaction route. All synthesized phases adopted a single phase tetragonal structure, as determined by powder X-ray diffraction (XRD), and elemental analysis confirmed the measured stoichiometries were close to targeted compositions. Extended X-ray absorption fine structure spectroscopy (EXAFS) was used to determine the local structural features for the framework of octahedrally coordinated cations. EXAFS data indicated that Cs 1.33 Ga 1.33 Ti 6.67 O 16 possessed the most disordered local structure centered around the Ga dopant. The enthalpies of formation of all three hollandite phases measured using high-temperature oxide melt solution calorimetry were found to be negative, indicating enthalpies of formation of these hollandites from oxides are thermodynamically stable with respect to their constituent oxides. Furthermore, the formation enthalpies were more negative and hence more favorable with increased Cs content. Finally, aqueous leaching tests revealed that high Cs content hollandite phases exhibited greater Cs retention as compared to low Cs content hollandite. While preliminary in nature, this work draws attention to the links between the capacity for radionuclide retention, atomistic level structural features and bulk thermodynamic properties of materials.

nuclear (including radiation effects), materials a↗
DOE OSTI2024

Using Median Point in Keeling Plot to Reduce the Uncertainty of the Isotopic Composition of Evapotranspiration

Abstract The isotopic composition of evapotranspirationδ ET is a crucial parameter in isotope-based evapotranspiration (ET) partitioning and moisture recycling studies. The Keeling plot method is the most prevalent method to calculateδ ET , though it contains large extrapolated uncertainties from the least squares regression. Traditional Keeling regression uses the mean point of individual measurements. Here, a modified Keeling plot framework was proposed using the median point of individual measurements. We tested theδ ET uncertainty using the mean point [σ ET (mean)] and median point [σ ET (median)]. Multiple resolutions of input and output data from six independent sites were used to test the performance of the two methods. Theσ ET (mean) would be greater thanσ ET (median) when the mean value of inverse vapor concentration () is greater than the median value of inverse vapor concentration []. When applying the filter ofr 2 > 0.8, around 70% ofσ ET (mean) was greater thanσ ET (median). This phenomenon might be due to the normality of the vapor concentrationC υ producing the asymmetric distribution of 1/C υ . The median method could perform significantly better than the mean method when inputting high-resolution measurements (e.g., 1 Hz) and when the water vapor concentrationC υ is relatively low. Compared to the mean method, applying the median method could on average reduce 6.88% of ET partitioning uncertainties and could on average reduce 9.00% of moisture recycling uncertainties. This study provided a new insight of the Keeling plot method and emphasized handling model output uncertainty from multiple perspectives instead of only from input parameters.

Meteorology & Atmospheric Sciences↗
DOE OSTI2017

Uncertainty quantification of fiber orientation distribution measurements for long-fiber-reinforced thermoplastic composites

We present a detailed methodology for experimental measurement of fiber orientation distribution (FOD) in injection-molded discontinuous fiber composites using the method of ellipses on 2D cross sections. Best practices to avoid biases occurring during surface preparation and optical imaging of carbon-fiber-reinforced thermoplastics are discussed. A marker-based watershed transform routine for efficient image segmentation and the separation of touching fiber ellipses is developed. The sensitivity of the averaged orientation tensor to the image sample size is studied for the case of long-fiber thermoplastics. A Mori-Tanaka implementation of the Eshelby model is then employed to quantify the sensitivity of elastic stiffness predictions to biases in the FOD measurements.

fiber orientation distribution measurement↗
DOE OSTI2022

A novel post-processing method for progressive failure analysis of brittle composite compression

Finite element analysis of brittle materials in axial compression typically uses element deletion to allow continued global deformation post-element-failure. However, element deletion produces cyclic load-displacement curves that underestimate energy absorption and are not representative of a continuum system. Two key observations support the conclusion that results from an appropriately discretized model can be an adequate representation of a continuum system. Specifically, the frequency of the oscillations in the load-displacement curve is directly dependent upon element length in the loading direction, and the peak amplitudes of oscillations are mesh size independent. A method of post-processing the analysis results, by connecting the peak amplitudes of oscillations, is proposed and applied to a series of continuous carbon fiber composite crush tubes. The load-displacement curve, stable crushing load, and specific energy absorption of the post-processed results compare well to an experimental study of crush tubes with similar layups.

Materials Science↗
DOE OSTI2016

Unit cell determination of coexisting post-perovskite and H-phase in (Mg,Fe)SiO3 using multigrain XRD: compositional variation across a laser heating spot at 119 GPa

Multigrain X-ray diffraction (XRD) can be used to accurately calculate the unit cell parameters of individual mineral phases in a mineral assemblage contained in a diamond anvil cell (DAC). Coexisting post-perovskite (ppv) and H-phase were synthesized at 119 GPa and 2500 K from (Mg 0.85 Fe 0.15 )SiO 3 in a laser-heated DAC. The unit cell parameters of the ppv and coexisting H-phase were determined using multigrain XRD with a 5 μm spatial resolution, close to the size of the X-ray beam, to understand compositional variations across the center area (20–30 μm) in a laser-heated sample. The ppv phase was Fe-depleted and the unit cell volume of ppv decreased by only 0.16 % (corresponding to ~3 % variation of FeSiO 3 ) from the heating center to 10 μm off the center, while the sample pressure remained at 119 GPa in a Ne quasi-hydrostatic environment. The unit cell volume of the H-phase decreased by 0.54 % (~10 % variation of FeSiO 3 content) over the same 10 μm distance. Both phases were more Fe-enriched in the slightly hotter center. This observation suggests that thermal diffusion may not be the major driver for the compositional variations of ppv and H-phase in the center portion of a laser-heated sample. Instead, these variations could be caused by a temperature effect on the partitioning between the ppv and H-phase over the small gradient.

58 GEOSCIENCES↗
DOE OSTI2024

Statistical mechanics and pressure of composite multimoded weakly nonlinear optical systems

Statistical mechanics can provide a versatile theoretical framework for investigating the collective dynamics of weakly nonlinear-wave settings that can be utterly complex to describe otherwise. In optics, composite systems arise due to interactions between different frequencies and polarizations. The purpose of this work is to develop a thermodynamic theory that takes into account the synergistic action of multiple components. We find that the type of the nonlinearity involved can have important implications in the thermalization process and, hence, can lead to different thermal equilibrium conditions. Importantly, we derive closed-form expressions for the actual optomechanical pressure that is exerted on the system. In particular, the total optomechanical pressure is the sum of the partial pressures due to each component. Our results can be applied to a variety of weakly nonlinear optical settings such as multimode fibers, bulk waveguides, photonic lattices, and coupled microresonators. We present two specific examples, where two colors interact in a one-waveguide array with either a cubic or quadratic nonlinearity.

Efremidis, Nikolaos K. (ORCID:0000000298300268)↗
DOE OSTI2022

Hanford Site Composite Analysis Special Analysis: Inventory and Solid Waste Release Modeling for the LLBG Sensitivity Case - UCAQ-22-01 Inventory Discrepancies for 218-E-12B, 218-W-3A, and 218-W-3AE in the Hanford Site Composite Analysis

This environmental calculation file (ECF) documents the methodologies, assumptions, and results of four sensitivity analyses that reevaluate the representativeness of solid-waste radionuclide inventory and release rate from three solid waste sites included in the recently completed Hanford Site Composite Analysis (CA) (DOE-RL-2019-52, Composite Analysis for Low-Level Waste Disposal in the Hanford Site Central Plateau (FY 2020), Rev. 1) (hereinafter called the CA Update). Specifically, this ECF reevaluates the representativeness of the base case inventory and radionuclide waste release rates from three solid waste sites (i.e., 218-E-12B, 218-W-3A, and 218-W-3AE) and two radionuclides (i.e., carbon-14 [C-14] and technetium-99 [Tc-99]). These three waste sites and two radionuclides were identified as being the most significant contributors to groundwater contamination and dose in the CA Update for the Inner Area boundary at times periods after the compliance period. This ECF first evaluates the representativeness of the C-14 and Tc-99 inventory and second, radionuclide release rates for the three waste sites1. If the inventory and release rates assumed in the CA Update are determined to be not representative, as hypothesized in the CA Update, then this ECF evaluates the impact of more representative inventories and release rates on the transfer of radionuclides to the vadose zone. The four analyses described in this ECF are as follows: 1) 218-E-12B C-14 Inventory and Release Rate Sensitivity Case – Determine the representativeness of the C-14 inventory and associated waste release rate from the 218-E-12B waste site assumed in the CA Update. If the inventory and associated waste release are more appropriately characterized as being different from the assumptions in the CA Update, then update the predicted C-14 release rate and compare the results to the results presented in the CA Update (DOE/RL-2019-52); 2) 218-W-3A C-14 Inventory and Release Rate Sensitivity Case – Determine the representativeness of the C-14 inventory and associated waste release rate from the 218-W-3A waste site assumed in the CA Update. If the inventory and associated waste release are more appropriately characterized as being different from the assumptions in the CA Update, then update the predicted C-14 release rate and compare the results to the results presented in the CA Update (DOE/RL-2019-52); 3) 218-W-3AE Tc-99 Release Rate Sensitivity Case – Determine the representativeness of the Tc-99 inventory and associated waste release rate from the 218-W-3AE waste site assumed in the CA Update. If the inventory and associated waste release are more appropriately characterized as being different from the assumptions in the CA Update, then update the predicted Tc-99 release rate and compare the results to the results presented in the CA Update (DOE/RL-2019-52); 4) 218-W-3AE Tc-99 Release Footprint Sensitivity Case – Determine the representativeness of the Tc-99 waste area footprint for the 218-W-3AE waste site assumed in the CA Update. If the footprint of the waste is more appropriately characterized as being different from the assumptions in the CA Update, then update the predicted Tc-99 release rate and compare the results to the result presented in the CA Update (DOE/RL-2019-52).

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2013

Silicon Carbide and Silicon Carbide Composites for Fusion Reactor Applications

This paper reviews recent achievements as to "nuclear-grade" SiC composites in particular for materials-system integration. SiC composite component development are reviewed including VHTR control rod scale model and compact intermediate heat exchanger scale mode by current joining and assembly techniques. Joining methods for SiC to metal and results of characterization of joint shear strength by the torsion tests using small specimens were also reviewed. The recent results of neutron irradiation experiments were also reviewed including detailed analysis of mechanical properties, irradiation creep and preliminary results on tritium behavior in SiC.

Hinoki, Tatsuya↗
DOE OSTI2023

Host genetics and gut microbiota composition: Baseline gut microbiota composition as a possible prognostic factor for the severity of COVID-19 in patients with familial Mediterranean fever disease

It is known that the gut microbiome of a healthy person affects the process of COVID-19 after getting infected with SARS-CoV-2 virus. It is also believed that colchicine can alleviate the severity of COVID-19. Current investigations aimed to evaluate the associations between the baseline gut microbiota composition of healthy and Familial Mediterranean fever (FMF) - carrier Armenian men populations, and the severity of the COVID-19 disease after their infection with the SARS-CoV-2. The study has a purpose of answering three core questions: i. Do the characteristics of gut microbiome of Armenians affect the course of COVID-19 severity? ii. How does the COVID-19 disease course on go for FMF patients who have been taking colchicine as a medication over the years after getting infected with SARS-CoV-2? iii. Is there an initial gut micribiota structure pattern for non-FMF and FMF patients in the cases when COVID-19 appears in mild form? The gut microbiota composition in non-FMF and FMF patients before the first infection (mild and moderate course of COVID-19) was considered. COVID-19 was diagnosed by SARS-CoV-2 nucleic acid RT-PCR in nasopharyngeal swab and/or sputum. The number of patients with male FMF with mild COVID-19 was approximately two times higher than that of non-FMF male subjects with COVID-19. In addition, an association of COVID-19 disease severity with the baseline gut Prevotella, Clostridium hiranonis, Eubacterium biforme, Veillonellaceae, Coprococcus, and Blautia diversities in the non-FMF and FMF populations were revealed by us, which can be used as risk/prognostic factor for the severity of COVID-19.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

It takes a village: using a crowdsourced approach to investigate organic matter composition in global rivers through the lens of ecological theory

Though community-based scientific approaches are becoming more common, many scientific efforts are conducted by small groups of researchers that together develop a concept, analyze data, and interpret results that ultimately translate into a publication. Here, we present a community effort that breaks these traditional boundaries of the publication process by engaging the scientific community from initial hypothesis generation to final publication. We leverage community-generated data from the Worldwide Hydrobiogeochemistry Observation Network for Dynamic River Systems (WHONDRS) consortium to study organic matter composition through the lens of ecological theory. This community endeavor will use a suite of paired physical and chemical datasets collected from 97 river corridors across the globe. With our first step aimed at ideation, we engaged a community of scientists from 20 countries and 60 institutions, spanning disciplines and career stages by holding a virtual workshop (April 2021). In the workshop, participants generated content for questions, hypotheses, and proposed analyses based on the WHONDRS dataset. These ideation efforts resulted in several narratives investigating different questions led by different teams, which will be the basis for research articles in a Frontiers in Water collection. Currently, the community is collectively analyzing, interpreting, and synthesizing these data that will result in seven crowdsourced articles using a single, existing WHONDRS dataset. The use of a shared dataset across articles not only lowers barriers for broad participation by not requiring generation of new data, but also provides unique opportunities for emergent learning by connecting outcomes across studies. Here we will explain methods used to enable this community endeavor aimed to promote a greater diversity of thinking on river corridor biogeochemistry through community science.

Borton, Mikayla A.↗