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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Biostimulation induces syntrophic interactions that impact C, S and N cycling in a sediment microbial community

Stimulation of subsurface microorganisms to induce reductive immobilization of metals is a promising approach for bioremediation, yet the overall microbial community response is typically poorly understood. Here we used community proteogenomics to test the hypothesis that excess input of acetate activates syntrophic interactions among autotrophs and heterotrophs. A flow-through sediment column was incubated in a groundwater well of an acetate-amended aquifer. Genomic sequences from the community recovered during microbial sulfate reduction were used to econstruct, de novo, near-complete genomes for Desulfobacter (Deltaproteobacteria) and relatives of Sulfurovum and Sulfurimonas (Epsilonproteobacteria), and Bacteroidetes. Partial genomes were obtained for Clostridiales (Firmicutes) and Desulfuromonadales-like Deltaproteobacteria. The majority of proteins identified by mass spectrometry corresponded to Desulfobacter-like species, and demonstrate the role of this organism in sulfate reduction (Dsr and APS), nitrogen-fixation (Nif) and acetate oxidation to CO2 during amendment. Results suggest less abundant Desulfuromonadales and Bacteroidetes also actively contributed to CO2 production via the TCA cycle. Proteomic data indicate that sulfide was partially re-oxidized by Epsilonproteobacteria through nitrate-dependent sulfide oxidation (using Nap, Nir, Nos, SQR and Sox), with CO2 fixed using the reverse TCA cycle. Modeling shows that this reaction was thermodynamically possible, and kinetically favorable relative to acetate-dependent denitrification. We conclude that high-levels of carbon amendment aimed to stimulate anaerobic heterotrophy led to carbon fixation in co-dependent chemoautotrophs. These results have implications for understanding complex ecosystem behavior, and show that high levels of organic carbon supplementation can expand the range of microbial functionalities accessible for ecosystem manipulation.

metagenomics/proteomics/subsurface/sediment/syntro↗
DOE OSTI2021

Quantifying the unknown impact of segmentation uncertainty on image-based simulations

Abstract Image-based simulation, the use of 3D images to calculate physical quantities, relies on image segmentation for geometry creation. However, this process introduces image segmentation uncertainty because different segmentation tools (both manual and machine-learning-based) will each produce a unique and valid segmentation. First, we demonstrate that these variations propagate into the physics simulations, compromising the resulting physics quantities. Second, we propose a general framework for rapidly quantifying segmentation uncertainty. Through the creation and sampling of segmentation uncertainty probability maps, we systematically and objectively create uncertainty distributions of the physics quantities. We show that physics quantity uncertainty distributions can follow a Normal distribution, but, in more complicated physics simulations, the resulting uncertainty distribution can be surprisingly nontrivial. We establish that bounding segmentation uncertainty can fail in these nontrivial situations. While our work does not eliminate segmentation uncertainty, it improves simulation credibility by making visible the previously unrecognized segmentation uncertainty plaguing image-based simulation.

42 ENGINEERING↗
DOE OSTI2013

The impact of crystal symmetry on the electronic structure and functional properties of complex lanthanum chromium oxides

Complex oxides exhibit a wide range of crystal structures, chemical compositions and physical properties. The underlying drivers determining the complicated structure-composition-property phase diagrams are the relative positions and orbital overlaps between the metal cations and the oxygen anions. Here we report a combined experimental and theoretical investigation of the structure and bonding in a series of lanthanum chromium oxides prepared by reactive molecular beam epitaxy. Of particular interest is the charge state and local coordination of the Cr. We have stabilized LaCrO 3 , LaCrO 4 and La 2 CrO 6 films by controlling the three elemental fluxes during deposition, and have carried out x-ray diffraction, x-ray photoemission, and x-ray absorption spectroscopy, as well as first-principles calculations, to determine structure, charge state, chemical bonding, and electronic structure. Significant changes in bonding character and orbital interaction are revealed with decreasing ligand symmetry from octahedral to tetrahedral Cr coordination. Both LaCrO 4 and LaCrO 6 with tetrahedrally coordinated Cr show strong pre-edge features in the Cr K-edge near-edge structure whereas LaCrO 3 with octahedrally coordinated Cr exhibits very weak pre-edge features. The origin of these pre-edge features is discussed based on various selection rules and ligand symmetry. We also demonstrate an increase in cation-anion orbital hybridization and a decrease in long-range ligand coupling induced by this symmetry reduction. These in turn result in dramatic modifications of the macroscopic optical and magnetic properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Mesoscopic analyses of the impact of morphology and operating conditions on the transport resistances in a proton-exchange-membrane fuel-cell catalyst layer

Exploring the origins of local transport resistance and characterizing the oxygen transport resistances in the catalyst layer (RCL) are critical for cost reduction. In this paper, a comprehensive mesoscopic model for simulating coupled transport processes of oxygen and water vapor for different structural parameters under different operating conditions in reconstructed microstructures is proposed. The local transport resistance is calculated after achieving the limiting current density and the effective diffusivity of oxygen. The results demonstrate that RCL increases greatly with decreasing platinum loading (LPt) and the transport resistances in other components of the cell dominate for high-loadings. Both the reduced oxygen permeation coefficient in the ionomer thin-film and the adsorption resistance account for the origins of local transport resistance. The local transport resistance increases with the bare carbon ratio for a constant LPt and Pt/C ratio due to the decreased effective ionomer surface, and increases with the I/C ratio due to the increased ionomer thickness and decreased Knudsen diffusivity. Due to the presence of liquid water, a slight decrease followed by an increase of the local transport resistance versus relative humidity is obtained. The contribution of ionomer thin-films to RCL is more sensitive to liquid saturation compared with that of pores. This journal is

Mu, YT↗