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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

23 Na nuclear magnetic resonance study of yNa 2 S +(1-y)[xSiS 2 + (1-x)PS 5/2 ] glassy solid electrolytes

23 Na NMR spin lattice relaxation times, T 1 , and central linewidths were obtained for y Na 2 S +(1-y)[xSiS 2 + (1-x)PS 5/2 ] glassy solid electrolytes for two series of glasses, y=0.5 and 0.67, and x=0.1, 0.3, 0.5, 0.7, and 0.9. No pronounced mixed glass former effect in the activation energy was recorded within experimental uncertainty for either series of glasses. Energy barriers to sodium motion were calculated using the Anderson-Stuart model for the y=0.67 sample, and the results suggested that the energy barriers as a function of composition are strongly influenced by the dielectric constant of these glasses. DC Na + ion conductivity values calculated using NMR-derived correlation times, an available Na + ion site coordination number in the range z=3–4, and an energy cutoff determined from the critical percolation threshold, were in agreement with the increasing trend in the experimental values for the y=0.67 glasses. Using the same model, the conductivity values were calculated for the y=0.50 glasses, which have as yet to be measured, and these revealed a decreasing conductivity as x increased. Sodium NMR second moment studies showed that the cation spatial arrangement followed a homogeneous distribution for y=0.50 and 0.67 samples over most of the composition range, but deviated significantly away from this above a sodium concentration of 1.85 ×10 28 m -3 , implying a tendency for sodium to cluster under these conditions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Understanding the Reactions Between Fe and Se Binary Diffusion Couples

Spurred by recent discoveries of high-temperature superconductivity in Fe-Se based materials, the magnetic, electronic, and catalytic properties of iron-chalcogenides have drawn significant attention. Furthermore, much remains to be understood about the sequence of phase formation in these systems. In this work, we shed light on this issue by preparing a series of binary Fe-Se ultrathin diffusion couples via designed thin film precursors and investigating their structural evolution as a function of composition and annealing temperature. Two previously unreported Fe-Se phases crystallized during the deposition process on a nominally room-temperature Si substrate in the 27-33% and 37-47% Fe (atomic percent) composition regimes. Both phases completely decompose after annealing to 200°C in a nitrogen glovebox. At higher temperatures, the sequence of phase formation is governed by Se loss in the annealing process, consistent with what would be expected from the phase diagram. Films rich in Fe (53-59% Fe) crystalized during deposition as β-FeSe (P4/nmm) with preferred c-axis orientation to the amorphous SiO 2 substrate surface, providing a means to non-epitaxial self-assembly of crystallographically aligned, iron-rich β-FeSe for future research. Our findings suggest the crystallization of binary Fe-Se compounds at room temperature via near diffusionless transformations should be a significant consideration in future attempts to prepare metastable ternary and higher order compounds containing Fe and Se.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Thin-Film Stabilization and Magnetism of η -Carbide-Type Iron Nitrides

Transition-metal nitrides in ..eta..-carbide-type structures exhibit unusual bonding motifs and proximity to magnetic instabilities. Yet they remain unexplored in thin-film form due to the difficulty of stabilizing nitrogen-poor ternaries among competing phases. Here, we report the thin-film synthesis and phase-stability mapping of the ..eta..-nitride systems Fe-W-N and Fe-Mo-N. Amorphous Fe-M-N (M = W, Mo) combinatorial libraries deposited by reactive cosputtering crystallize upon rapid thermal annealing, enabling systematic identification of synthesis windows as a function of composition and annealing temperature. Using laboratory powder X-ray diffraction and synchrotron grazing incidence wide-angle X-ray scattering, we establish that Fe 3 Mo 3 N-based ..eta..-carbide phases form over a substantially broader compositional and thermal range than W-based compositions, where ..eta.. structures are stabilized only when the films are Fe-rich. These trends are rationalized using mixed chemical-potential vs composition phase diagrams that capture the narrow nitrogen chemical-potential stability of ..eta..-nitrides. Magnetic measurements reveal that ferromagnetism is induced in Fe-rich Fe 3.54 Mo 2.46 N with a small exchange-bias-like response that is absent in Fe 3 W 3 N-based compositions, highlighting the sensitivity of magnetic behavior to modest deviations from stoichiometry. This work establishes practical thin-film synthesis routes for ..eta..-nitride materials and demonstrates how composition can be tuned to access emergent magnetic phenomena in these complex nitrides.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Computational Modeling of Realistic Cell Membranes

Cell membranes contain a large variety of lipid types and are crowded with proteins, endowing them with the plasticity needed to fulfill their key roles in cell functioning. The compositional complexity of cellular membranes gives rise to a heterogeneous lateral organization, which is still poorly understood. Computational models, in particular molecular dynamics simulations and related techniques, have provided important insight into the organizational principles of cell membranes over the past decades. Now, we are witnessing a transition from simulations of simpler membrane models to multicomponent systems, culminating in realistic models of an increasing variety of cell types and organelles. Here, we review the state of the art in the field of realistic membrane simulations and discuss the current limitations and challenges ahead.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Extracting Natural Biosurfactants from Humus Deposits for Subsurface Engineering Applications

Environmentally benign, economical, and effective surfactants and additives are needed in engineering subsurface energy recovery processes. Biosurfactants have some advantages over chemically synthesized surfactants, but the high costs of microbial-biosynthesis limit their applications in subsurface engineering. In this work, we propose to use naturally occurring biosurfactants contained within Earth's readily available and inexpensive humus deposits for subsurface engineering applications. We collected humus samples of different types from four different regions, and developed a simple method for extracting natural biosurfactant (NBS) using only four common chemicals. The average NBS extraction yields are 16 ± 3% of the raw humus. No significant differences in elemental composition and functional group chemistry were found among the NBS extracted from humus of different origins, suggesting that any humus deposit can be used for NBS extraction. Measurements of interfacial tensions between air-water and supercritical (sc) CO 2 -water interfaces indicate that the NBS is a highly effective surfactant. NBS has good foaming ability. Preliminary tests with only 0.5 mass % NBS in the aqueous phase (no other additives) yielded scCO 2 -in-water foams of 83% foam quality. The apparent viscosity of 13 cP measured at a shear rate of 2320 s -1 indicates that much higher viscosities are achievable at lower shear rates. Finally, these results suggest that NBS merits further research and development for potential applications in subsurface energy production.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2020

Photogenerated Charge Separation in a CdSe Nanocluster Encapsulated in a Metal–Organic Framework for Improved Photocatalysis

Nanoclusters encapsulated in a metal–organic framework (MOF) are the subject of intense interest because of their high promise for photocatalysis. We show computationally that a CdSe nanocluster incorporated into NU-1000 (Cd 6 Se 6 @NU-1000) allows electron transfer from a visible-light photo-excited organic linker to the lowest unoccupied crystal orbital of the inorganic cluster, which can lead to charge separation. Substituents on the linker can be used to tune the band position and the band gap of the whole composite (Cd 6 Se 6 @NU-1000), and this makes it possible to perform the water splitting reaction under visible light. Here, the achievement of charge separation within the MOF leads to longer life of the excited states, and as a result, it can enhance the photocatalytic activity of the system.

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

Zinc-Stabilized Manganese Telluride with Wurtzite Crystal Structure

Alloying of semiconductors with similar crystal structures is often used to fine-tune materials properties for optoelectronic applications. However, examples of semiconductor alloys between compounds with two different crystal structures, where properties are changing dramatically as a function of composition, are much rarer. Even more unusual are such heterostructural alloys where the structure and properties can be changed with only a small amount of substitution (<10%). One exception is yttria-stabilized zirconia (YSZ) with cubic fluorite crystal structure, used for a wide range of applications. Here, we report on experimental observation of such unusual behavior in zinc-stabilized manganese telluride (ZSMT), and on theoretical explanation of its compositional stabilization in the wurtzite crystal structure. Thin films of Mn 1-x Zn x Te alloys synthesized at 400 degrees C change from the nickeline (NC) to the wurtzite (WZ) crystal structure at x as low as 0.08. Theoretical calculations indicate that this structural transition occurs due to small MnTe polymorph energy differences, and strong preference of Zn atoms to adopt tetrahedral vs octahedral coordination environment. The calculated 1 eV increase of the band gap from NC to WZ structure is consistent with the experimental measurements on ZSMT films. These measurements also indicate 1000-10,000 times lower conductivity than the nickeline MnTe, due to low ZSMT hole concentration. Overall, the wide band gap and low hole density make ZSMT a promising candidate for p-type transparent transistors and other optoelectronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Binder Architecture on the Performance of Silicon/Graphite Composite Anodes for Lithium Ion Batteries

Although significant progress has been made in improving cycling performance of silicon-based electrodes, few studies have been performed on the architecture effect on polymer binder performance for lithium-ion batteries. A systematic study on the relationship between polymer architectures and binder performance is especially useful in designing synthetic polymer binders. In this paper, a graft block copolymer with readily tunable architecture parameters is synthesized and tested as the polymer binder for the high-mass loading silicon (15 wt %)/graphite (73 wt %) composite electrode (active materials >2.5 mg/cm 2 ). With the same chemical composition and functional group ratio, the graft block copolymer reveals improved cycling performance in both capacity retention (495 mAh/g vs 356 mAh/g at 100th cycle) and Coulombic efficiency (90.3% vs 88.1% at first cycle) than the physical mixing of glycol chitosan (GC) and lithium polyacrylate (LiPAA). Galvanostatic results also demonstrate the significant impacts of different architecture parameters of graft copolymers, including grafting density and side chain length, on their ultimate binder performance. Finally, by simply changing the side chain length of GC-g-LiPAA, the retaining delithiation capacity after 100 cycles varies from 347 mAh/g to 495 mAh/g.

25 ENERGY STORAGE↗
DOE OSTI2018

Structure and Magnetism Evolution from FeCo Nanoparticles to Hollow Nanostructure Conversion for Magnetic Applications

Hollow nanostructures have witnessed an increasing interest in emerging fields, including energy storage electrodes, nanocatalysis, photonics, and biomedical carriers, etc. The fundamental mechanisms for hollowing conversion chemistry of complex nanoalloys is indispensable to grow such nanostructures with controlled compositions and functionalities. In this contribution, the Kirkendall effect on magnetic Fe-Co bimetallic alloys with the formation of hollow nanostructures for exchange interactions was studied. The rich diffusion kinetics of binary Fe-Co alloys accompanied with its conversion from solid, core-shell to hollow nanostructures were been captured through X-ray spectroscopy and electron microscopy. We further report the cation exchange improved magnetic performance of hollow nanostructures with increasing the crystallinity.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Interstitial Nature of Mn 2+ Doping in 2D Perovskites

Halide perovskites doped with magnetic impurities (such as the transition metals Mn 2+ , Co 2+ , Ni 2+ ) are being explored for a wide range of applications beyond photovoltaics, such as spintronic devices, stable light-emitting diodes, single-photon emitters, and magneto-optical devices. However, despite several recent studies, there is no consensus on whether the doped magnetic ions will predominantly replace the octahedral B-site metal via substitution or reside at interstitial defect sites. Here, by performing correlated nanoscale X-ray microscopy, spatially and temporally resolved photoluminescence measurements, and magnetic force microscopy on the inorganic 2D perovskite Cs 2 PbI 2 Cl 2 , we show that doping Mn 2+ into the structure results in a lattice expansion. The observed lattice expansion contrasts with the predicted contraction expected to arise from the B-site metal substitution, thus implying that Mn 2+ does not replace the Pb 2+ sites. Photoluminescence and electron paramagnetic resonance measurements confirm the presence of Mn 2+ in the lattice, while correlated nano-XRD and X-ray fluorescence track the local strain and chemical composition. Density functional theory calculations predict that Mn 2+ atoms reside at the interstitial sites between two octahedra in the triangle formed by one Cl – and two I – atoms, which results in a locally expanded structure. These measurements show the fate of the transition metal dopants, the local structure, and optical emission when they are doped at dilute concentrations into a wide band gap semiconductor.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

A metagenomic assessment of winter and summer bacterioplankton from Antarctica Peninsula coastal surface waters

Antarctic surface oceans are well-studied during summer when irradiance levels are high, sea ice is melting and primary productivity is at a maximum. Coincident with this timing, the bacterioplankton respond with significant increases in secondary productivity. Little is known about bacterioplankton in winter when darkness and sea-ice cover inhibit photoautotrophic primary production. We report here an environmental genomic and small subunit ribosomal RNA (SSU rRNA) analysis of winter and summer Antarctic Peninsula coastal seawater bacterioplankton. Intense inter-seasonal differences were reflected through shifts in community composition and functional capacities encoded in winter and summer environmental genomes with significantly higher phylogenetic and functional diversity in winter. In general, inferred metabolisms of summer bacterioplankton were characterized by chemoheterotrophy, photoheterotrophy and aerobic anoxygenic photosynthesis while the winter community included the capacity for bacterial and archaeal chemolithoautotrophy. Chemolithoautotrophic pathways were dominant in winter and were similar to those recently reported in global ‘dark ocean’ mesopelagic waters. If chemolithoautotrophy is widespread in the Southern Ocean in winter, this process may be a previously unaccounted carbon sink and may help account for the unexplained anomalies in surface inorganic nitrogen content.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Microbial legacies alter decomposition in response to simulated global change

Terrestrial ecosystem models assume that microbial communities respond instantaneously, or are immediately resilient, to environmental change. Here we tested this assumption by quantifying the resilience of a leaf litter community to changes in precipitation or nitrogen availability. By manipulating composition within a global change experiment, we decoupled the legacies of abiotic parameters versus that of the microbial community itself. After one rainy season, more variation in fungal composition could be explained by the original microbial inoculum than the litterbag environment (18% versus 5.5% of total variation). This compositional legacy persisted for 3 years, when 6% of the variability in fungal composition was still explained by the microbial origin. In contrast, bacterial composition was generally more resilient than fungal composition. Microbial functioning (measured as decomposition rate) was not immediately resilient to the global change manipulations; decomposition depended on both the contemporary environment and rainfall the year prior. Finally, using metagenomic sequencing, we showed that changes in precipitation, but not nitrogen availability, altered the potential for bacterial carbohydrate degradation, suggesting why the functional consequences of the two experiments may have differed. Predictions of how terrestrial ecosystem processes respond to environmental change may thus be improved by considering the legacies of microbial communities.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

An ultra-tunable platform for molecular engineering of high-performance crystalline porous materials

Metal-organic frameworks are a class of crystalline porous materials with potential applications in catalysis, gas separation and storage, and so on. Of great importance is the development of innovative synthetic strategies to optimize porosity, composition and functionality to target specific applications. Here we show a platform for the development of metal-organic materials and control of their gas sorption properties. This platform can accommodate a large variety of organic ligands and homo- or hetero-metallic clusters, which allows for extraordinary tunability in gas sorption properties. Even without any strong binding sites, most members of this platform exhibit high gas uptake capacity. As a result, the high capacity is accomplished with an isosteric heat of adsorption as low as 20 kJ mol –1 for carbon dioxide, which could bring a distinct economic advantage because of the significantly reduced energy consumption for activation and regeneration of adsorbents.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Segregation of liquid crystal mixtures in topological defects

The structure and physical properties of liquid crystal (LC) mixtures are a function of composition, and small changes can have pronounced effects on observables, such as phase-transition temperatures. Traditionally, LC mixtures have been assumed to be compositionally homogenous. The results of chemically detailed simulations presented here show that this is not the case; pronounced deviations of the local order from that observed in the bulk at defects and interfaces lead to significant compositional segregation effects. More specifically, two disclination lines are stabilized in this work by introducing into a nematic liquid crystal mixture a cylindrical body that exhibits perpendicular anchoring. Here, it is found that the local composition deviates considerably from that of the bulk at the interface with the cylinder and in the defects, thereby suggesting new assembly and synthetic strategies that may capitalize on the unusual molecular environment provided by liquid crystal mixtures.

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

Metabolic interactions underpinning high methane fluxes across terrestrial freshwater wetlands

Current estimates of wetland contributions to the global methane budget carry high uncertainty, particularly in accurately predicting emissions from high methane-emitting wetlands. Microorganisms drive methane cycling, but little is known about their conservation across wetlands. To address this, we integrate 16S rRNA amplicon datasets, metagenomes, metatranscriptomes, and annual methane flux data across 9 wetlands, creating the Multi-Omics for Understanding Climate Change (MUCC) v2.0.0 database. This resource is used to link microbiome composition to function and methane emissions, focusing on methane-cycling microbes and the networks driving carbon decomposition. We identify eight methane-cycling genera shared across wetlands and show wetland-specific metabolic interactions in marshes, revealing low connections between methanogens and methanotrophs in high-emitting wetlands. Methanoregula emerged as a hub methanogen across networks and is a strong predictor of methane flux. In these wetlands it also displays the functional potential for methylotrophic methanogenesis, highlighting the importance of this pathway in these ecosystems. Collectively, our findings illuminate trends between microbial decomposition networks and methane flux while providing an extensive publicly available database to advance future wetland research.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Data analytics approach to predict high-temperature cyclic oxidation kinetics of NiCr-based Alloys

Abstract Although of practical importance, there is no established modeling framework to accurately predict high-temperature cyclic oxidation kinetics of multi-component alloys due to the inherent complexity. We present a data analytics approach to predict the oxidation rate constant of NiCr-based alloys as a function of composition and temperature with a highly consistent and well-curated experimental dataset. Two characteristic oxidation models, i.e., a simple parabolic law and a statistical cyclic oxidation model, have been chosen to numerically represent the high-temperature oxidation kinetics of commercial and model NiCr-based alloys. We have successfully trained machine learning (ML) models using highly ranked key input features identified by correlation analysis to accurately predict experimental parabolic rate constants ( k p ). This study demonstrates the potential of ML approaches to predict oxidation kinetics of alloys over wide composition and temperature ranges. This approach can also serve as a basis for introducing more physically meaningful ML input features to predict the comprehensive cyclic oxidation behavior of multi-component high-temperature alloys with proper constraints based on the known underlying mechanisms.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Qiita: rapid, web-enabled microbiome meta-analysis

Multi-omic insights into microbiome function and composition typically advance one study at a time. However, in order for relationships across studies to be fully understood, data must be aggregated into meta-analyses. This makes it possible to generate new hypotheses by finding features that are reproducible across biospecimens and data layers. Qiita dramatically accelerates such integration tasks in a web-based microbiome-comparison platform, which we demonstrate with Human Microbiome Project and Integrative Human Microbiome Project (iHMP) data.

microbiome, bioinformatics software, open source s↗
DOE OSTI2022

Improvement of eukaryotic protein predictions from soil metagenomes

During the last decades, metagenomics has highlighted the diversity of microorganisms from environmental or host-associated samples. Most metagenomics public repositories use annotation pipelines tailored for prokaryotes regardless of the taxonomic origin of contigs. Consequently, eukaryotic contigs with intrinsically different gene features, are not optimally annotated. Using a bioinformatics pipeline, we have filtered 7.9 billion contigs from 6,872 soil metagenomes in the JGI’s IMG/M database to identify eukaryotic contigs. We have re-annotated genes using eukaryote-tailored methods, yielding 8 million eukaryotic proteins and over 300,000 orphan proteins lacking homology in public databases. Comparing the gene predictions we made with initial JGI ones on the same contigs, we confirmed our pipeline improves eukaryotic proteins completeness and contiguity in soil metagenomes. The improved quality of eukaryotic proteins combined with a more comprehensive assignment method yielded more reliable taxonomic annotation. This dataset of eukaryotic soil proteins with improved completeness, quality and taxonomic annotation reliability is of interest for any scientist aiming at studying the composition, biological functions and gene flux in soil communities involving eukaryotes.

54 ENVIRONMENTAL SCIENCES↗