The relationship between fault zone structure and frictional heterogeneity, insight from faults in the High Zagros
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Yassaghi, A. (ORCID:0000000209847721)↗
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Results for “INSIGHTS”
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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Structures of minute virus of mice replication initiator protein N-terminal domain: Insights into DNA nicking and origin binding
Members of the Parvoviridae family all encode a non-structural protein 1 (NS1) that directs replication of single-stranded viral DNA, packages viral DNA into capsid, and serves as a potent transcriptional activator. Here we report the X-ray structure of the minute virus of mice (MVM) NS1 N-terminal domain at 1.45 Å resolution, showing that sites for dsDNA binding, ssDNA binding and cleavage, nuclear localization, and other functions are integrated on a canonical fold of the histidine-hydrophobic-histidine superfamily of nucleases, including elements specific for this Protoparvovirus but distinct from its Bocaparvovirus or Dependoparvovirus orthologs. High resolution structural analysis reveals a nickase active site with an architecture that allows highly versatile metal ligand binding. The structures support a unified mechanism of replication origin recognition for homotelomeric and heterotelomeric parvoviruses, mediated by a basic-residue-rich hairpin and an adjacent helix in the initiator proteins and by tandem tetranucleotide motifs in the replication origins. - Highlights: • The structure of a parvovirus replication initiator protein has been determined; • The structure sheds light on mechanisms of ssDNA binding and cleavage; • The nickase active site is preconfigured for versatile metal ligand binding; • The binding site for the double-stranded replication origin DNA is identified; • A single domain integrates multiple functions in virus replication.
60 APPLIED LIFE SCIENCES↗
Thermally Activated Delayed Fluorescence (TADF) Path toward Efficient Electroluminescence in Purely Organic Materials: Molecular Level Insight
Since the seminal work of Tang and Vanslyke in 1987 on small-molecule emitters and that of Friend and co-workers in 1990 on conjugated-polymer emitters, organic light-emitting diodes (OLEDs) have attracted much attention from academia as well as industry, as the OLED market is estimated to reach the $30B mark by the end of 2018. In these first-generation organic emitters, on the basis of simple spin statistics, electrical excitation resulted in the formation of ~25% singlet excitons and ~75% triplet excitons. Radiative decay of the singlet excitons to the singlet ground state leads to a prompt fluorescence emission, while the triplet excitons only lead to weak phosphorescence due to the very small spin-orbit couplings present in purely organic molecules. The consequence is a ca. 75% energy loss, which triggered wide-ranging efforts to try and harvest as many of the triplet excitons as possible. In 1998, Thompson, Forrest, and their co-workers reported second-generation OLED emitters based on coordination complexes with heavy transition metals (e.g., iridium or platinum). Here, the triplet excitons stimulate efficient and fast phosphorescence due to the strong spin-orbit couplings enabled by the heavy-metal atoms. Internal quantum efficiencies (IQE) up to 100% have been reported, which means that for every electron injected into the device, a photon is emitted. Here, while these second-generation emitters are those mainly exploited in current OLED applications, there is strong impetus from both cost and environmental standpoints to find new ways of exploiting purely organic emitters, which in addition can offer greater flexibility to fine tune the electronic and optical properties by exploiting the synthetic organic chemistry toolbox.
36 MATERIALS SCIENCE↗
Insights into Supported Subnanometer Catalysts Exposed to CO via Machine-Learning-Enabled Multiscale Modeling
Subnanometer catalysts offer high noble metal utilization and superior performance for several reactions. However, understanding their structures and properties on an atomic scale under working conditions is challenging due to the large configurational space. Here, we introduce an efficient multiscale framework to predict their stability exposed to an adsorbate. The framework integrates a comprehensive toolset including density functional theory (DFT) calculations, cluster expansion, machine learning, and structure optimization. The end-to-end machine-learning workflow guides DFT data generation and enables significant computational acceleration. We demonstrate the approach for CO-adsorbed Pdn (n = 1–55) clusters on CeO 2 (111). Simulation results reveal that CO can facilitate restructuring by stabilizing smaller planar structures and bilayer structures of specific intermediate sizes, consistent with experimental reports. Metal–support interactions, preferential CO adsorption, and metal nuclearity and structure control catalyst stability. As a result, the framework allows automatic discovery of stable catalyst structures and a systematic strategy to exploit properties in the subnanometer scale.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Insights into Boron-Based Polyanion-Tuned High-Nickel Cathodes for High-Energy-Density Lithium-Ion Batteries
Ultrahigh-Ni layered oxide cathodes (Ni content > 90%) are at the forefront for potentially enabling higher-energy density lithium-ion batteries. Unfortunately, they suffer from rapid capacity fade, poor thermal stability, and increased air sensitivity. Introduction of boron-based polyanion into layered cathodes has been found to be effective in stabilizing high-Ni cathodes, but the mechanism behind it is not yet fully understood. To develop a better understanding, we present here an extensive characterization of the ultrahigh-Ni cathode LiNi 0.94 Co 0.06 O 2 (NC) and B 2 O 3 -LiNi 0.94 Co 0.06 O 2 (B-NC). The B-NC delivers a capacity of 223 mA h g -1 with 80% capacity retention after 400 cycles in full cells with graphite anodes, superior to 61% retention for NC. In-depth interphase investigations reveal that the improved cyclability is attributed to the development of a well-passivated boron/phosphorus-rich cathode-electrolyte interphase in B-NC. Moreover, B-NC demonstrates a considerably enhanced air-exposure and thermal stability. A 30-day air-stored B-NC delivers a discharge capacity of 125 mA h g -1 at 10C rate, in sharp contrast to 65 mA h g -1 for the stored NC. Finally, this work advances the understanding of the effect boron-based polyanion insertion into layered oxides has on battery performance and offers a viable strategy for developing practically viable ultra-high-Ni cathodes with high-energy density.
25 ENERGY STORAGE↗
Regional Influence of Aerosol Emissions from Wildfires Driven by Combustion Efficiency: Insights from the BBOP Campaign
Abstract Wildfires are important contributors to atmospheric aerosols and a large source of emissions that impact regional air quality and global climate. In this study, wildfire emissions in the Pacific Northwest region of the United States were characterized using real-time measurements near their sources using an aircraft, and farther downwind from a fixed ground site located at the Mt. Bachelor Observatory (~ 2700 m a.s.l.). The characteristics of aerosol emissions were found to depend strongly on the modified combustion efficiency (MCE), a qualitative index of the combustion processes of a fire. Organic aerosol emissions had negative correlations with MCE, whereas the carbon oxidation state of organic aerosol increased with MCE. The relationships between the aerosol properties and MCE were consistent between fresher emissions (~1 hour old) and emissions sampled after atmospheric transport (6 - 45 hours), suggesting that organic aerosol mass loading and chemical properties were strongly influenced by combustion processes at the source and conserved to a significant extent during regional transport. These results suggest that MCE can be a useful metric for describing aerosol properties of regionally transported wildfire emissions and their impacts on regional air quality and global climate.
54 ENVIRONMENTAL SCIENCES↗
Molecular Insights into Arctic Soil Organic Matter Degradation under Warming
Molecular composition of the Arctic soil organic carbon (SOC) and its susceptibility to microbial degradation are uncertain due to heterogeneity and unknown SOC compositions. Using ultrahigh resolution mass spectrometry, we determined the susceptibility and compositional changes of extractable dissolved organic matter (EDOM) in an anoxic warming incubation experiment (up to 122 days) with a tundra soil from Alaska, United States. EDOM was extracted with 10 mM NH4HCO3 from both the organic and mineral-layer soils during incubation at either –2 or 8°C. Based on their O:C and H:C ratios, EDOM molecular formulas were qualitatively grouped into nine biochemical classes of compounds, among which lignin-like compounds dominated both the organic and mineral soils and were the most stable, whereas amino sugars, peptides and carbohydrate-like compounds were the most biologically labile. These results corresponded with shifts in EDOM elemental composition, in which the ratios of O:C and N:C decreased, while average C content in EDOM, molecular mass, and aromaticity increased after 122 days of incubation. This research demonstrates that certain EDOM molecules, such as amino sugars, peptides, and carbohydrate-like compounds, are disproportionately more susceptible to microbial degradation than others in the soil, and these results should be considered in SOC degradation models to improve predictions of Arctic climate feedbacks.
Chen, Hongmei↗
Experimental Insights into the Coupling of Methane Combustion and Steam Reforming in a Catalytic Plate Reactor in Transient Mode
The microstructured reactor concept is very promising technology to develop a compact reformer for distributed hydrogen generation. In this work, a catalytic plate reactor (CPR) is developed and investigated for the coupling of methane combustion (MC) and methane steam reforming (MSR) over Pt/Al 2 O 3 -coated microchannels in cocurrent and counter-current modes in transient experiments during start-up. A three-dimensional (3D) computational fluid dynamics (CFD) simulation shows uniform velocity and pressure distribution profiles in microchannels. For a channel velocity from 5.1 to 57.3 m/s in the combustor, the oxidation of methane is complete and self-sustainable without explosion, blow-off, or extinction; nevertheless, flashbacks are observed in counter-current mode. In the reformer, the maximum methane conversion is 84.9% in cocurrent mode, slightly higher than that of 80.2% in counter-current mode at a residence time of 33 ms, but at the cost of three times higher energy input in the combustor operating at ~1000 °C. Nitric oxide (NO) is not identified in combustion products, but nitrous oxide (N 2 O) is a function of coupling mode and forms significantly in cocurrent mode. Furthermore, this research would be helpful to establish the start-up strategy and environmental impact of compact reformers on a small scale.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
New Insights into Low-Temperature Oxidation of Propane from Synchrotron Photoionization Mass Spectrometry and Multiscale Informatics Modeling
We investigated the low-temperature oxidation of propane at 4 Torr and temperatures of 530, 600, and 670 K. The oxidation is initiated by pulsed laser photolysis of oxalyl chloride, (COCl)2, at 248 nm, which rapidly generates a ~1:1 mixture of 1-propyl (n-propyl) and 2-propyl (i-propyl) radicals via the fast Cl + propane reaction. Reactants, intermediates and products are probed with isomeric selectivity by time-resolved multiplexed photoionization mass spectrometry (MPIMS) with tunable synchrotron vacuum UV radiation as the ionization source. At all three temperatures, the major stable product species is propene, formed in the C3H7 + O2 reactions by direct HO2-elimination from both n- and i-propyl peroxy radicals. The experimentally derived propene yields relative to the initial concentration of Cl atoms are (20 ± 4)% at 530 K, (55 ± 11)% at 600 K, and (86 ± 17)% at 670 K at a reaction time of 20 ms. The lower yield of propene at low temperature reflects substantial formation of propyl peroxy radicals, which do not completely decompose on the experimental time scale. In addition, we detect the C3H6O isomers methyloxirane, oxetane, acetone and propanal as minor products. Our measured yields of oxetane and methyloxirane, which are co-products of OH radicals, suggest a revision of the OH formation pathways in models of low-temperature propane oxidation. The experimental results are modeled and interpreted using a multi-scale informatics approach that is presented in detail in a separate publication (Burke, M. P.; Goldsmith, C. F.; Klippenstein, S. J.; Welz, O.; Huang H.; Antonov I. O.; Savee J. D.; Osborn D. L.; Zádor, J.; Taatjes, C. A.; Sheps, L., Multi-Scale Informatics for Low-Temperature Propane Oxidation: Further Complexities in Studies of Complex Rections, submitted, 2015). The model predicts the time profiles and yields of the experimentally observed primary products well, and shows satisfactory agreement for products formed mostly via secondary radical-radical reactions.
Combustion↗
Comment on “Additional Insights Between Fermi-Löwdin Orbital SIC and the Localization Equation Constraints in SIC-DFT”
In a recent Letter, Aquino and Wong (AW) analyze the connection between the Fermi-Löwdin orbital self-interaction correction (FLO-SIC) and the traditional Perdew– Zunger self-interaction correction (PZ-SIC) methods. In this work, the authors present a derivation of the conditions required to minimize the SIC density functional theory (DFT) total energy in FLO-SIC. These involve the gradient of the energy with respect to parameters known as Fermi-orbital descriptors (FODs) (called orbital “centroids” in ref 1) that are used together with the total charge density to determine the Fermi- Löwdin orbitals (FLOs). AW state that the conditions, the vanishing of the FOD gradient components, “resemble” the localization equations (LE), the minimum energy conditions in traditional PZ-SIC. The LE involve the equality of certain off-diagonal matrix elements of different orbital-dependent Hamiltonians. While AW are careful to say that their equations do not prove the mathematical equivalence of the two methods, the discussion in the text and the graphical table of contents figure suggest that vanishing FOD gradients imply satisfaction of the LE and vice versa, and hence that the methods are equivalent. We believe this ambiguity clouds an important issue, rather than clarifying it.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Synthesis of 1 nm Pd Nanoparticles in a Microfluidic Reactor: Insights from in Situ X ray Absorption Fine Structure Spectroscopy and Small-Angle X ray Scattering
In this paper we show that the temporal separation of nucleation and growth is not a necessary condition for the colloidal synthesis of monodisperse nanoparticles. The synthesis mechanism of Pd nanoparticles was determined by in situ XAFS and SAXS in a microfluidic reactor capable of millisecond up to an hour time resolution. The SAXS results showed two autocatalytic growth phases, a fast growth phase followed by a very slow growth phase. The steady increase in the number of particles throughout the two growth phases indicates the synthesis is limited by slow continuous nucleation. The transition from fast to slow growth was caused by rapid increase in bonding with the capping agent as shown by XAFS. Based on this fundamental understanding of the synthesis mechanism, we show that 1 nm monodisperse Pd nanoparticles can be synthesized at low temperature using a strong binding capping agent such as trioctylphosphine (TOP).
Environmental Molecular Sciences Laboratory↗
Insight into hydrogen bonding of uranyl hydroxide layers and capsules by use of 1 H magic-angle spinning NMR spectroscopy [Insight into the hydrogen bonding for uranyl hydroxides using 1 H MAS NMR spectroscopy]
Solid-state 1 H magic-angle spinning (MAS) NMR was used to investigate local proton environments in anhydrous [UO 2 (OH) 2 ] (α-UOH) and hydrated uranyl hydroxide [(UO 2 ) 4 O(OH) 6 ·5H 2 O (metaschoepite). For the metaschoepite material, proton resonances of the μ 2 -OH hydroxyl and interlayer waters were resolved, with two-dimensional (2D) double-quantum (DQ) 1 H– 1 H NMR correlation experiments revealing strong dipolar interactions between these different proton species. The experimental NMR results were combined with first-principles CASTEP GIPAW (gauge including projector-augmented wave) chemical shift calculations to develop correlations between hydrogen-bond strength and observed 1 H NMR chemical shifts. Furthermore, these NMR correlations allowed characterization of local hydrogen-bond environments in uranyl U 24 capsules and of changes in hydrogen bonding that occurred during thermal dehydration of metaschoepite.
36 MATERIALS SCIENCE↗
Novel Solar Cell Materials: Insights from First-Principles
Although silicon solar cells currently dominate the market share for photovoltaic (PV) devices, it is important to explore other materials and device configurations that could be cheaper and more environmentally friendly to produce, as well as potentially more efficient at energy conversion. Here, we review some of our recent theoretical work aimed at accurate evaluation of key materials properties associated with optimizing alternative PV materials. These include potential new light absorbers and transparent conductors in devices ranging from traditional PVs to tandem dye-sensitized solar cells and thin-film PVs to intermediate band gap PVs. We specifically focus on two materials families: transition-metal oxides (TMOs), such as NiO, CoO, FeO, and Cu 2 O, and mixed metal sulfides, such as Cu 2 ZnSnS 4 . Furthermore, both families are p-type semiconductors being explored as less expensive solar cell components.
14 SOLAR ENERGY↗
Insight into the Phase Transformation Pathways of Copper Oxidation: from Oxygen Chemisorption on the Clean Surface to Multi-Layer Bulk Oxide Growth
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99 GENERAL AND MISCELLANEOUS↗
Insights into the Composition and Function of a Bismuth-Based Catalyst for Reduction of CO2 to CO
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99 GENERAL AND MISCELLANEOUS↗
Computational Screening of Supported Metal Oxide Nanoclusters for Methane Activation: Insights into Homolytic versus Heterolytic C–H Bond Dissociation
Since its discovery in zeolites, the [CuOCu] 2+ motif has played an important role in our understanding of selective methane activation over supported metal oxide nanoclusters. Although there are two known C-H bond dissoci-ation mechanisms, namely homolytic and heterolytic cleavage, most computational studies on optimizing metal oxide nanoclusters for improved methane activation reactivity have focused only on the homolytic mechanism. In this work, both mechanisms were examined for a set of 21 mixed metal oxide complexes of the form of [M 1 OM 2 ] 2+ (M 1 , M 2 = Mn, Fe, Co, Ni, Cu, Zn). Except for pure copper, heterolytic cleavage was found to be the dominant C-H bond activation pathway for all systems. Furthermore, mixed systems including [CuOMn] 2+ , [CuONi] 2+ , and [CuOZn] 2+ are predicted to possess similar methane activation activity as pure [CuOCu] 2+ . Furthermore, these results suggest that both homolytic and heterolytic mechanisms should be considered in computing methane activation energies on supported metal oxide nanoclusters.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗