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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 1,729 records · Page 96
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Dynamic behavior of reversible oxygen migration in irradiated-annealed high temperature superconducting wires

Large-scale extrusion-based additive manufacturing of high-performance thermoplastic composites like fiber reinforced polyphenylene sulfide (PPS) is well-suited for tooling applications to lower manufacturing costs and lead times. Autoclave tooling requires good mechanical performance at temperatures even above the glass transition temperature (T g ). In this work, the authors have investigated a post-process isothermal annealing technique to improve the mechanical properties of various grades of carbon fiber reinforced PPS components printed on the Big Area Additive Manufacturing (BAAM) system. Since PPS is a semi-crystalline polymer, crystallinity can change during annealing and affect the mechanical properties of the part. In addition, isothermal annealing can also lead to solid-state structural changes in the form of thermal and oxidative branching and/or crosslinking reactions in some grades of PPS which can alter the crystallization process. This work reports the effect of annealing on dynamic mechanical properties of BAAM printed components, along with studies to determine the effect of annealing on crystallinity and the occurrence of oxidative reactions. Results showed that isothermal annealing at 250 °C for 18 h improved the storage modulus of all selected grades (neat and reinforced) of PPS at temperatures above T g . Annealing led to an overall increase in the degree of crystallinity, with secondary crystallization taking place. Although oxidative structural changes were observed to occur more on the surface of the PPS parts, they primarily influenced the size of crystals formed and did not significantly alter the degree of crystallinity at various regions within the sample.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Coaxial wires coax energy from water

Inexpensive, earth-abundant photoabsorbers for solar water splitting have, so far, not demonstrated notable performance. Now, voltage gained from a coaxial heterojunction coupled with nanostructure-enhanced photocurrent results in Cu 2 O photocathodes demonstrating benchmark water-splitting performance.

08 HYDROGEN↗
DOE OSTI2016

Upward shift of the vortex solid phase in high-temperature-superconducting wires through high density nanoparticle addition

Here, we show a simple and effective way to improve the vortex irreversibility line up to very high magnetic fields (60T) by increasing the density of second phase BaZrO 3 nanoparticles. (Y 0.77 ,Gd 0.23 )Ba 2 Cu 3 O y films were grown on metal substrates with different concentration of BaZrO 3 nanoparticles by the metal organic deposition method. We find that upon increase of the BaZrO 3 concentration, the nanoparticle size remains constant but the twin-boundary density increases. Up to the highest nanoparticle concentration (n ~ 1.3 × 10 22 /m 3 ), the irreversibility field (H irr ) continues to increase with no sign of saturation up to 60 T, although the vortices vastly outnumber pinning centers. We find extremely high H irr , namely H irr = 30 T (H||45°) and 24 T (H||c) at 65 K and 58 T (H||45°) and 45 T (H||c) at 50K. The difference in pinning landscape shifts the vortex solid-liquid transition upwards, increasing the vortex region useful for power applications, while keeping the upper critical field, critical temperature and electronic mass anisotropy unchanged.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Live wires: direct extracellular electron exchange for bioenergy and the bioremediation of energy-related contamination

Microorganisms that can form direct electrical connections with insoluble minerals, electrodes, or other microorganisms can play an important role in some traditional as well as novel bioenergy strategies and can be helpful in the remediation of environmental contamination resulting from the use of more traditional energy sources. The surprising discovery that microorganisms in the genus Geobacter are capable of forming highly conductive networks of filaments that transfer electrons along their length with organic metallic-like conductivity, rather than traditional molecule to molecule electron exchange, provides an explanation for the ability of Geobacter species to grow in subsurface environments with insoluble Fe(III) oxides as the electron acceptor, and effectively remediate groundwater contaminated with hydrocarbon fuels or uranium and similar contaminants associated with the mining and processing of nuclear fuel. A similar organic metallic-like conductivity may be an important mechanism for microorganisms to exchange electrons in syntrophic associations, such as those responsible for the conversion of organic wastes to methane in anaerobic digesters, a proven bioenergy technology. Biofilms with conductivities rivaling those of synthetic polymers help Geobacter species generate the high current densities in microbial fuel cells producing electric current from organic compounds. Electron transfer in the reverse direction, i.e. from electrodes to microbes, is the basis for microbial electrosynthesis, in which microorganisms reduce carbon dioxide to fuels and other useful organic compounds with solar energy in a form of artificial photosynthesis that is more efficient and avoids many of the environmental sustainability concerns associated with biomass-based bioenergy strategies. The ability of Geobacter species to produce highly conductive electronic networks that function in water opens new possibilities in the emerging field of bioelectronics.

Lovley, DR↗
DOE OSTI2016

Self-generated concentration and modulus gradient coating design to protect Si nano-wire electrodes during lithiation

Surface coatings as artificial solid electrolyte interphases have been actively pursued as an effective way to improve the cycle efficiency of nanostructured Si electrodes for high energy density lithium ion batteries, where the mechanical stability of the surface coatings on Si is as critical as Si itself. However, the chemical composition and mechanical property change of coating materials during the lithiation and delithiation process imposed a grand challenge to design coating/Si nanostructure as an integrated electrode system. In our work, we first developed reactive force field (ReaxFF) parameters for Li–Si–Al–O materials to simulate the lithiation process of Si-core/Al 2 O 3 -shell and Si-core/SiO 2 -shell nanostructures. With reactive dynamics simulations, we were able to simultaneously track and correlate the lithiation rate, compositional change, mechanical property evolution, stress distributions, and fracture. A new mechanics model based on these varying properties was developed to determine how to stabilize the coating with a critical size ratio. Furthermore, we discovered that the self-accelerating Li diffusion in Al 2 O 3 coating forms a well-defined Li concentration gradient, leading to an elastic modulus gradient, which effectively avoids local stress concentration and mitigates crack propagation. Finally, based on these results, we propose a modulus gradient coating, softer outside, harder inside, as the most efficient coating to protect the Si electrode surface and improve its current efficiency.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Diferrocenyl oligothiophene wires: Raman and quantum chemical study of valence-trapped cations

A combination of Raman spectroscopy and density functional theory calculations is used to describe the structural and spectroscopic properties of the different isomeric cations of diferrocenyl quaterthiophenes. Isomerisation of the thienyl {beta}-positions provides site selective oxidation, which gives rise to species that can interconvert by moving the charge over the bridge. The spectroscopic study allows us to describe a sequence of stationary trapped cationic, either ferrocenyl or thienyl, states which constitutes an energy cascade of accessible sites through which the charge transfer can proceed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Diagnosis of a two wire X-pinch by X-ray absorption spectroscopy utilizing a doubly curved ellipsoidal crystal

X-ray absorption spectroscopy is a powerful tool for the diagnosis of plasmas over a wide range of both temperature and density. However, such a measurement is often limited to probing plasmas with temperatures well below that of the x-ray source in order to avoid object plasma emission lines from obscuring important features of the absorption spectrum. This has excluded many plasmas from being investigated by this technique. We have developed an x-ray spectrometer that provides the ability to record absorption spectra from higher temperature plasmas than the usual approach allows without the risk of data contamination by line radiation emitted by the plasma under study. This is accomplished using a doubly curved mica crystal which is bent both elliptically and cylindrically. We present here initial absorption spectra obtained from an aluminum x-pinch plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Effect of magnetic field on the donor impurity in CdTe/Cd{sub 1-x}Mn{sub x}Te quantum well wire

The donor impurity binding energy in CdTe / Cd{sub 1-x}Mn{sub x}Te QWW with square well confinement along x – direction and parabolic confinement along y – direction under the influence of externally applied magnetic field has been computed using variational principle in the effective mass approximation. The spin polaronic shift has also been computed. The results are presented and discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Computational modeling of charge hopping dynamics along a disordered one-dimensional wire with energy gradients in quantum environments

This computational study investigates the effects of energy gradients on charge hopping dynamics along a one-dimensional chain of discrete sites coupled to quantum bath, which is modeled at the level of Pauli master equation (PME). This study also assesses the performance of different approximations for the hopping rates. Three different methods for solving the PME, a fourth order Runge–Kutta method, numerical diagonalization of the rate matrix followed by analytic propagation, and kinetic Monte Carlo simulation method, are tested and confirmed to produce virtually identical values of time dependent mean square displacement, diffusion constant, and mobility. Five different rate expressions, exact numerical evaluation of Fermi’s Golden Rule (FGR) rate, stationary phase interpolation (SPI) approximation, semiclassical approximation, classical Marcus rate, and Miller–Abrahams rate, are tested to help understand the effects of approximations in representing quantum environments in the presence of energy gradients. The results based on direct numerical evaluation of FGR rate exhibit transition from diffusive to non-diffusive behavior with the increase in the gradient and show that the charge transport in the quantum bath is more sensitive to the magnitude of the gradient and the disorder than in the classical bath. Among all the four approximations for the hopping rates, the SPI approximation is confirmed to work best overall. A comparison of two different methods to calculate the mobility identifies drift motion of the population distribution as the major source of non-diffusive behavior and provides more reliable information on the contribution of quantum bath.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Grasses use an alternatively wired bHLH transcription factor network to establish stomatal identity

Significance Plants both control and are controlled by the global climate. Grasses in natural and agricultural systems participate in the exchange of atmospheric CO 2 for biosphere-derived oxygen and water vapor via microscopic epidermal valves (stomata), but how these stomata are made in grasses is unknown. Using genetic screens and targeted genome editing, we identify and characterize master transcriptional regulators of stomatal initiation in the wheat relative Brachypodium . Surprisingly, the unique stomatal form and pattern of grasses is regulated by orthologs of Arabidopsis stomatal basic helix–loop–helix (bHLH) transcription factors, although the function of individual genes and regulation of their protein products have diverged. This finding suggests that the stomatal core bHLH transcription factors are excellent breeding targets to enhance performance in grasses.

Raissig, Michael T.↗