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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

β-Functionalized push–pull opp-dibenzoporphyrins as sensitizers for dye-sensitized solar cells: the role of the phenylethynyl bridge

A novel class of β-functionalized push–pull zinc opp-dibenzoporphyrins was designed and synthesized as sensitizers for dye-sensitized solar cells. Dibenzoporphyrin YH7 displayed strong push–pull characteristics, which included clearly segregated HOMO/LUMO and fast charge injection from the singlet excited state of zinc porphyrin to the conduction band of TiO 2 . The incorporation of both the phenylethynyl bridge and amino group was critical to achieve the enhanced push–pull effect. The highest PCE value in this series obtained with the YH6 cell was 6.7%, which is comparable to that of the best ruthenium dye, N719 (η = 7.4%), under similar conditions. The high PCE of the YH6 cell is ascribed to its high light harvesting ability and favorable cell kinetics, which is supported by electrochemical impedance spectroscopy studies and femtosecond transient absorption studies. An unusual illumination-induced photodegradation was observed for YH7, which was attributed as the major reason for the unexpected lower PCE of the YH7 cell (η = 5.7%). Furthermore, this work demonstrates the applicability of π-extended porphyrins as a new generation of sensitizers for high performance dye-sensitized solar cells.

Hu, Yi↗
DOE OSTI2014

K{sub α} and bremsstrahlung x-ray radiation backlighter sources from short pulse laser driven silver targets as a function of laser pre-pulse energy

Measurements of silver K-shell and bremsstrahlung emission from thin-foil laser targets as a function of laser prepulse energy are presented. The silver targets were chosen as a potential 22 keV backlighter source for the National Ignition Facility Experiments. The targets were irradiated by the Titan laser with an intensity of 8 × 10{sup 17} W/cm{sup 2} with 40 ps pulse length. A secondary nanosecond timescale laser pulse with controlled, variable energy was used to emulate the laser prepulse. Results show a decrease in both K{sub α} and bremsstrahlung yield with increasing artificial prepulse. Radiation hydrodynamic modeling of the prepulse interaction determined that the preplasma and intact target fraction were different in the three prepulse energies investigated. Interaction of the short pulse laser with the resulting preplasma and target was then modeled using a particle-in-cell code PSC which explained the experimental results. The relevance of this work to future Advanced Radiographic Capability laser x-ray backlighter sources is discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Redox-active on-surface polymerization of single-site divalent cations from pure metals by a ketone-functionalized phenanthroline

Metallic iron, chromium, or platinum mixing with a ketone-functionalized phenanthroline ligand on a single crystal gold surface demonstrates redox activity to a well-defined oxidation state and assembly into thermally stable, one dimensional, polymeric chains. The diverging ligand geometry incorporates redox-active sub-units and bi-dentate binding sites. The gold surface provides a stable adsorption environment and directs growth of the polymeric chains, but is inert with regard to the redox chemistry. These systems are characterized by scanning tunnelling microscopy, non-contact atomic force microscopy, and X-ray photoelectron spectroscopy under ultra-high vacuum conditions. The relative propensity of the metals to interact with the ketone group is examined, and it is found that Fe and Cr more readily complex the ligand than Pt. The formation and stabilization of well-defined transition metal single-sites at surfaces may open new routes to achieve higher selectivity in heterogeneous catalysts.

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

Research Update: Towards designed functionalities in oxide-based electronic materials

One of the grand challenges facing materials-by-design approaches for complex oxide deployment in electronic devices is how to balance transformative first-principles based predictions with experimental feasibility. Here, we briefly review the functionality-driven approach (inverse design) for materials discovery, encapsulated in three modalities for materials discovery (m{sup 3}D) that integrate experimental feedback. We compare it to both traditional theoretical and high-throughput database-directed approaches aimed at advancing oxide-based materials into technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Average neutron time-of-flight instrument response function inferred from single D-T neutron events within a plastic scintillator

The apparent ion temperature and neutron-reaction history are important characteristics of a fusion plasma. Extracting these quantities from a measured neutron-time-of-flight signal requires accurate knowledge of the instrument response function (IRF). This paper describes a novel method for obtaining the IRF directly for single DT neutron interactions by utilizing n-alpha coincidence. The t(d,α)n nuclear reaction was produced at Sandia National Laboratories’ Ion Beam Laboratory using a 300 keV Cockcroft-Walton generator to accelerate a 2.5 μA beam of 175 keV D + ions into a stationary ErT 2 target. The average neutron IRF was calculated by taking a time-corrected average of individual neutron events within an EJ-228 plastic scintillator. The scintillator was coupled to two independent photo-multiplier tubes operated in the current mode: a Hamamatsu 5946 mod-5 and a Photek PMT240. Finally, the experimental setup and results will be discussed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Structure and Function of REP34 Implicates Carboxypeptidase Activity in Francisella tularensis Host Cell Invasion

Francisella tularensis is the etiological agent of tularemia, or rabbit fever. Although F. tularensis is a recognized biothreat agent with broad and expanding geographical range, its mechanism of infection and environmental persistence remain poorly understood. Previously, we identified seven F. tularensis proteins that induce a rapid encystment phenotype (REP) in the free-living amoeba, Acanthamoeba castellanii. Encystment is essential to the pathogen's long term intracellular survival in the amoeba. Here, we characterize the cellular and molecular function of REP34, a REP protein with a mass of 34 kDa. A REP34 knock-out strain of F. tularensis has a reduced ability to both induce encystment in A. castellanii and invade human macrophages. We determined the crystal structure of REP34 to 2.05-Å resolution and demonstrate robust carboxypeptidase B-like activity for the enzyme. REP34 is a zinc-containing monomeric protein with close structural homology to the metallocarboxypeptidase family of peptidases. REP34 possesses a novel topology and substrate binding pocket that deviates from the canonical funnelin structure of carboxypeptidases, putatively resulting in a catalytic role for a conserved tyrosine and distinct S1' recognition site. Taken together, these results identify REP34 as an active carboxypeptidase, implicate the enzyme as a potential key F. tularensis effector protein, and may help elucidate a mechanistic understanding of F. tularensis infection of phagocytic cells.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Isospin effects in N ≈ Z nuclei in extended density functional theory

This paper overviews various phenomena related to the concept of isospin symmetry. The focus is on N ≈ Z nuclei, which are excellent laboratories of isospin physics. The theoretical framework applied is nuclear density functional theory and its isospin- and angular-momentum projected extensions, as well as symmetry-projected multi-reference models. The topics covered include: isospin impurities, superallowed beta decays, beta-transitions in mirror nuclei, isospin breaking hadronic interactions, mirror and triplet binding energy differences, and isoscalar pairing.

Physics↗
DOE OSTI2015

Electronic Structure, Phonon Dynamical Properties, and CO 2 Capture Capability of Na 2 - x M x Zr O 3 ( M = Li ,K): Density-Functional Calculations and Experimental Validations

The electronic structural and phonon properties of Na 2-α M α ZrO 3 (M ¼ Li,K, α = ¼ 0.0,0.5,1.0,1.5,2.0) are investigated by first-principles density-functional theory and phonon dynamics. The thermodynamic properties of CO 2 absorption and desorption in these materials are also analyzed. With increasing doping level α, the binding energies of Na 2-α Li α ZrO 3 are increased while the binding energies of Na 2-α K α ZrO 3 are decreased to destabilize the structures. The calculated band structures and density of states also show that, at the same doping level, the doping sites play a significant role in the electronic properties. The phonon dispersion results show that few soft modes are found in several doped configurations, which indicates that these structures are less stable than other configurations with different doping levels. From the calculated relationships among the chemical-potential change, the CO 2 pressure, and the temperature of the CO 2 capture reactions by Na 2-α M α ZrO 3 , and from thermogravimetric-analysis experimental measurements, the Li- and K-doped mixtures Na 2-α M α ZrO 3 have lower turnover temperatures (T t ) and higher CO 2 capture capacities, compared to pure Na 2 ZrO 3 . The Li-doped systems have a larger T t decrease than the K-doped systems. When increasing the Li-doping level α, the T t of the corresponding mixture Na 2-α Li α ZrO 3 decreases further to a low-temperature range. However, in the case of K-doped systems Na 2-α K α ZrO 3 , although doping K into Na 2 ZrO 3 initially shifts its T t to lower temperatures, further increases of the K-doping level α causes T t to increase. Therefore, doping Li into Na 2 ZrO 3 has a larger influence on its CO 2 capture performance than the K-doped Na 2 ZrO 3 . Compared with pure solidsM 2 ZrO 3 , after doping with other elements, these doped systems’ CO 2 capture performances are improved.

Duan, Yuhua↗
DOE OSTI2024

First simultaneous global QCD analysis of dihadron fragmentation functions and transversity parton distribution functions

We perform a comprehensive study within quantum chromodynamics (QCD) of dihadron observables in electron-positron annihilation, semi-inclusive deep-inelastic scattering, and proton-proton collisions, including recent cross section data from Belle and azimuthal asymmetries from STAR. We extract simultaneously for the first time π + π − dihadron fragmentation functions (DiFFs) and the nucleon transversity distributions for up and down quarks as well as antiquarks. For the transversity distributions we impose their small- x asymptotic behavior and the Soffer bound. In addition, we utilize a new definition of DiFFs that has a number density interpretation to then calculate expectation values for the dihadron invariant mass and momentum fraction. Furthermore, we investigate the compatibility of our transversity results with those from single-hadron fragmentation (from a transverse momentum dependent/collinear twist-3 framework) and the nucleon tensor charges computed in lattice QCD. We find a universal nature to all of this available information. Future measurements of dihadron production can significantly further this research, especially, as we show, those that are sensitive to the region of large parton momentum fractions. Published by the American Physical Society 2024

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗