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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 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

The role of proton coupled electron transfer in water oxidation

Water oxidation is a key half reaction in energy conversion schemes based on solar fuels and targets such as light driven water splitting or carbon dioxide reduction into CO, other oxygenates, or hydrocarbons. Carrying out these reactions at rates that exceed the rate of solar insolation for the extended periods of time required for useful applications presents a major challenge. Water oxidation is the key “other” half reaction in these schemes and it is dominated by PCET given its multi-electron, multi-proton character, 2H2O → O2 + 4e- + 4H+. Identification of PCET was an offshoot of experiments designed to investigate energy conversion by electron transfer quenching of molecular excited states. The concepts “redox potential leveling” and concerted electron–proton transfer came from measurements on stepwise oxidation of cis-RuII(bpy)2(py)(OH2)2+ to RuIV(bpy)2(py)(O)2+. The Ru “blue dimer”, cis,cis-(bpy)2(H2O)RuORu(OH2)(bpy)24+, was the first designed catalyst for water oxidation. It undergoes oxidative activation by PCET to give the transient (bpy)2(O)RuVORuV(O)(bpy)24+, O-atom attack on water to give a peroxidic intermediate, and further oxidation and O2 release. More recently, a class of single site water oxidation catalysts has been identified, e.g., Ru(tpy)(bpm)(OH2)2+ (tpy is 2,2':6',2''-terpyridine; bpm is 2,2'-bipyrimidine). They undergo stepwise PCET oxidation to RuIV=O2+ or RuV(O)3+ followed by O-atom transfer with formation of peroxidic intermediates which undergo further oxidation and O2 release. PCET plays a key role in the three zones of water oxidation reactivity: oxidative activation, O•••O bond formation, oxidation and O2 release from peroxidic intermediates. Similar schemes have been identified for electrocatalytic water oxidation on oxide electrode surfaces based on phosphonated derivatives such as [Ru(Mebimpy)(4,4'-(PO3H2CH2)2bpy)(OH2)]2+. A PCET barrier to RuIII–OH2+ → RuIV=O2+ oxidation arises from the large difference in pKa values between RuIII–OH2+ and RuIV(OH)3+. On oxide surfaces this oxidation occurs by multiple pathways. Kinetic, mechanistic, and DFT results on single site catalysts reveal a new pathway for the O•••O bond forming step (Atom-Proton Transfer, APT), significant rate enhancements by added proton acceptor bases, and accelerated water oxidation in propylene carbonate as solvent with water added as a stoichiometric reagent. Lessons learned about water oxidation and the role of PCET and concerted pathways appear to have direct relevance for water oxidation in Photosystem II (PSII) with PSII a spectacular example of PCET in action. This includes a key role for Multiple Site-Electron Proton Transfer in oxidative activation of the Oxygen Evolving Complex (OEC) in the S0 → S1 transition in the Kok cycle.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Neutron production using a pyroelectric driven target coupled with a gated field ionization source

A palm sized, portable neutron source would be useful for widespread implementation of detection systems for shielded, special nuclear material. We present progress towards the development of the components for an ultracompact neutron generator using a pulsed, meso-scale field ionization source, a deuterated (or tritiated) titanium target driven by a negative high voltage lithium tantalate crystal. Neutron production from integrated tests using an ion source with a single, biased tungsten tip and a 3 Multiplication-Sign 1 cm, vacuum insulated crystal with a plastic deuterated target are presented. Component testing of the ion source with a single tip produces up to 3 nA of current. Dielectric insulation of the lithium tantalate crystals appears to reduce flashover, which should improve the robustness. The field emission losses from a 3 cm diameter crystal with a plastic target and 6 cm diameter crystal with a metal target are compared.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Quantifying charge resonance and multiexciton character in coupled chromophores by charge and spin cumulant analysis

We extend excited-state structural analysis to quantify the charge-resonance and multi-exciton character in wave functions of weakly interacting chromophores such as molecular dimers. The approach employs charge and spin cumulants which describe inter-fragment electronic correlations in molecular complexes. We introduce indexes corresponding to the weights of local, charge resonance, and biexciton (with different spin structure) configurations that can be computed for general wave functions thus allowing one to quantify the character of doubly excited states. The utility of the approach is illustrated by applications to several small dimers, e.g., He-H{sub 2}, (H{sub 2}){sub 2}, and (C{sub 2}H{sub 4}){sub 2}, using full and restricted configuration interaction schemes. In addition, we present calculations for several systems relevant to singlet fission, such as tetracene, 1,6-diphenyl-1,3,5-hexatriene, and 1,3-diphenylisobenzofuran dimers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Study of ablation and implosion stages in wire arrays using coupled ultraviolet and X-ray probing diagnostics

Star and cylindrical wire arrays were studied using laser probing and X-ray radiography at the 1-MA Zebra pulse power generator at the University of Nevada, Reno. The Leopard laser provided backlighting, producing a laser plasma from a Si target which emitted an X-ray probing pulse at the wavelength of 6.65 Å. A spherically bent quartz crystal imaged the backlit wires onto X-ray film. Laser probing diagnostics at the wavelength of 266 nm included a 3-channel polarimeter for Faraday rotation diagnostic and two-frame laser interferometry with two shearing interferometers to study the evolution of the plasma electron density at the ablation and implosion stages. Dynamics of the plasma density profile in Al wire arrays at the ablation stage were directly studied with interferometry, and expansion of wire cores was measured with X-ray radiography. The magnetic field in the imploding plasma was measured with the Faraday rotation diagnostic, and current was reconstructed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Excitons in coupled type-II double quantum wells under electric and magnetic fields: InAs/AlSb/GaSb

We calculate the wave functions and the energy levels of an exciton in double quantum wells under electric (F) and magnetic (B) fields along the growth axis. The result is employed to study the energy levels, the binding energy, and the boundary on the F–B plane of the phase between the indirect exciton ground state and the semiconductor ground state for several typical structures of the type-II quasi-two-dimensional quantum wells such as InAs/AlSb/GaSb. The inter-well inter-band radiative transition rates are calculated for exciton creation and recombination. We find that the rates are modulated over several orders of magnitude by the electric and magnetic fields.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Using coupled micropillar compression and micro-Laue diffraction to investigate deformation mechanisms in a complex metallic alloy Al{sub 13}Co{sub 4}

In this study, we have used in-situ micro-Laue diffraction combined with micropillar compression of focused ion beam milled Al{sub 13}Co{sub 4} complex metallic alloy to investigate the evolution of deformation in Al{sub 13}Co{sub 4}. Streaking of the Laue spots shows that the onset of plastic flow occurs at stresses as low as 0.8 GPa, although macroscopic yield only becomes apparent at 2 GPa. The measured misorientations, obtained from peak splitting, enable the geometrically necessary dislocation density to be estimated as 1.1 × 10{sup 13 }m{sup −2}.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Coupled laboratory and field investigations resolve microbial interactions that underpin persistence in hydraulically fractured shales

Hydraulic fracturing is one of the industrial processes behind the surging natural gas output in the United States. This technology inadvertently creates an engineered microbial ecosystem thousands of meters below Earth’s surface. Here, we used laboratory reactors to perform manipulations of persisting shale microbial communities that are currently not feasible in field scenarios. Metaproteomic and metabolite findings from the laboratory were then corroborated using regression based modeling performed on metagenomic and metabolite data from more than 40 produced fluids from five hydraulically fractured shale wells. Collectively, our findings show that Halanaerobium, Geotoga, and Methanohalophilius strain abundances predict a significant fraction of nitrogen and carbon metabolites in the field. Our laboratory findings also exposed cryptic predatory, cooperative, and competitive interactions that impact microorganisms across fractured shales. Scaling these results from the laboratory to the field identified mechanisms underpinning biogeochemical reactions, yielding knowledge that can be harnessed to potentially increase energy yields and inform management practices in hydraulically fractured shales.

hydraulic fracturing, metaproteomics, methanogenes↗
DOE OSTI2015

A Micromegas-based low-background x-ray detector coupled to a slumped-glass telescope for axion research

Here, we report on the design, construction and operation of a low background x-ray detection line composed of a shielded Micromegas detector of the microbulk technology. The detector is made from radiopure materials and is placed at the focal point of a ~ 5 cm diameter, 1.5 m focal-length, cone-approximation Wolter I x-ray telescope (XRT) assembled from thermally-formed (or "slumped") glass substrates deposited with multilayer coatings. The system has been conceived as a technological pathfinder for the future International Axion Observatory (IAXO), as it combines two of the techniques (optic and detector) proposed in the conceptual design of the project. It is innovative for two reasons: it is the first time an x-ray optic has been designed and fabricated specifically for axion research, and the first time a Micromegas detector has been operated with an x-ray optic. The line has been installed at one end of the CERN Axion Solar Telescope (CAST) magnet and is currently looking for solar axions. Furthermore, the combination of the XRT and Micromegas detector provides the best signal-to-noise ratio obtained so far by any detection system of the CAST experiment with a background rate of 5.4×10 –3 counts per hour in the energy region-of-interest and signal spot area.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Tau flavored dark matter and its impact on tau Yukawa coupling

In this paper we perform a systematic study of the tau flavored dark matter (DM) model by introducing two kinds of mediators (a scalar doublet and a charged scalar singlet). The electromagnetic properties of the DM, as well as their implications in DM direct detections, are analyzed in detail. The model turns out contributing a significant radiative correction to the tau lepton mass, in addition to loosing the tension between the measured DM relic density and constraints of DM direct detections. The loop corrections can be O(10%) of the total tau mass. Signal rates of the Higgs measurements from the LHC in the h →τ τ and h → γ γ channels, relative to the Standard Model expectations, can be explained in this model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗