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  • Chemistry  (9,463)
  • Polymer and Materials Science  (2,009)
  • Inorganic Chemistry  (1,632)
  • Seismology
  • 2015-2019  (827)
  • 1950-1954  (9,272)
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  • 101
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    A silver cleaver splits cyclic amines (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-07-13
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 102
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    Deconstructive fluorination of cyclic amines by carbon-carbon cleavage (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-07-13
    Description: Deconstructive functionalizations involving scission of carbon-carbon double bonds are well established. In contrast, unstrained C(sp 3 )–C(sp 3 ) bond cleavage and functionalization have less precedent. Here we report the use of deconstructive fluorination to access mono- and difluorinated amine derivatives by C(sp 3 )–C(sp 3 ) bond cleavage in saturated nitrogen heterocycles such as piperidines and pyrrolidines. Silver-mediated ring-opening fluorination using Selectfluor highlights a strategy for cyclic amine functionalization and late-stage skeletal diversification, establishing cyclic amines as synthons for amino alkyl radicals and providing synthetic routes to valuable building blocks.
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 103
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    Regulate to reduce chemical mixture risk (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-07-20
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 104
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    Molecular movies filmed at conical intersections (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-07-06
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 105
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    Tandem catalysis for asymmetric coupling of ethylene and enynes to functionalized cyclobutanes (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-07-06
    Description: Transformation of simple precursors into structurally complex cyclobutanes, present in many biologically important natural products and pharmaceuticals, is of considerable interest in medicinal chemistry. Starting from 1,3-enynes and ethylene, both exceptionally inexpensive starting materials, we report a cobalt-catalyzed route to vinylcyclobutenes, as well as the further enantioselective addition of ethylene to these products to form complex cyclobutanes with all-carbon quaternary centers. These reactions can proceed in discrete stages or in a tandem fashion to achieve three highly selective carbon-carbon bond formations in one pot using a single chiral cobalt catalyst.
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 106
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    Hydrocarbon synthesis with vinyl cations (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-07-27
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 107
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    Nitrogen fixation and reduction at boron (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-02-23
    Description: Currently, the only compounds known to support fixation and functionalization of dinitrogen (N 2 ) under nonmatrix conditions are based on metals. Here we present the observation of N 2 binding and reduction by a nonmetal, specifically a dicoordinate borylene. Depending on the reaction conditions under which potassium graphite is introduced as a reductant, N 2 binding to two borylene units results in either neutral (B 2 N 2 ) or dianionic ([B 2 N 2 ] 2– ) products that can be interconverted by respective exposure to further reductant or to air. The 15 N isotopologues of the neutral and dianionic molecules were prepared with 15 N-labeled dinitrogen, allowing observation of the nitrogen nuclei by 15 N nuclear magnetic resonance spectroscopy. Protonation of the dianionic compound with distilled water furnishes a diradical product with a central hydrazido B 2 N 2 H 2 unit. All three products were characterized spectroscopically and crystallographically.
    Keywords: Chemistry
    Print ISSN: 0036-8075
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 108
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    Unnaturally aglow with a bright inner light (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-02-23
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 109
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    A plastic plan for organic synthesis (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-01-19
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 110
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    Digitization of multistep organic synthesis in reactionware for on-demand pharmaceuticals (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-01-19
    Description: Chemical manufacturing is often done at large facilities that require a sizable capital investment and then produce key compounds for a finite period. We present an approach to the manufacturing of fine chemicals and pharmaceuticals in a self-contained plastic reactionware device. The device was designed and constructed by using a chemical to computer-automated design (ChemCAD) approach that enables the translation of traditional bench-scale synthesis into a platform-independent digital code. This in turn guides production of a three-dimensional printed device that encloses the entire synthetic route internally via simple operations. We demonstrate the approach for the -aminobutyric acid receptor agonist, (±)-baclofen, establishing a concept that paves the way for the local manufacture of drugs outside of specialist facilities.
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 111
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    A reaction screen in flowing solvent (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-01-26
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 112
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    How to get two bonds for the price of one (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-01-26
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 113
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    A platform for automated nanomole-scale reaction screening and micromole-scale synthesis in flow (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-01-26
    Description: The scarcity of complex intermediates in pharmaceutical research motivates the pursuit of reaction optimization protocols on submilligram scales. We report here the development of an automated flow-based synthesis platform, designed from commercially available components, that integrates both rapid nanomole-scale reaction screening and micromole-scale synthesis into a single modular unit. This system was validated by exploring a diverse range of reaction variables in a Suzuki-Miyaura coupling on nanomole scale at elevated temperatures, generating liquid chromatography–mass spectrometry data points for 5760 reactions at a rate of 〉1500 reactions per 24 hours. Through multiple injections of the same segment, the system directly produced micromole quantities of desired material. The optimal conditions were also replicated in traditional flow and batch mode at 50- to 200-milligram scale to provide good to excellent yields.
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 114
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    Synthesis of partially and fully fused polyaromatics by annulative chlorophenylene dimerization (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-01-26
    Description: Since the discovery by Ullmann and Bielecki in 1901, reductive dimerization (or homocoupling) of aryl halides has been extensively exploited for the generation of a range of biaryl-based functional molecules. In contrast to the single-point connection in these products, edge-sharing fused aromatic systems have not generally been accessible from simple aryl halides via annulation cascades. Here we report a single-step synthesis of fused aromatics with a triphenylene core by the palladium-catalyzed annulative dimerization of structurally and functionally diverse chlorophenylenes through double carbon-hydrogen bond activation. The partially fused polyaromatics can be transformed into fully fused, small graphene nanoribbons, which are otherwise difficult to synthesize. This simple, yet powerful, method allows access to functional -systems of interest in optoelectronics research.
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 115
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    An elevated lithium battery (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-08-24
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 116
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    A high-energy-density lithium-oxygen battery based on a reversible four-electron conversion to lithium oxide (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-08-24
    Description: Lithium-oxygen (Li-O 2 ) batteries have attracted much attention owing to the high theoretical energy density afforded by the two-electron reduction of O 2 to lithium peroxide (Li 2 O 2 ). We report an inorganic-electrolyte Li-O 2 cell that cycles at an elevated temperature via highly reversible four-electron redox to form crystalline lithium oxide (Li 2 O). It relies on a bifunctional metal oxide host that catalyzes O–O bond cleavage on discharge, yielding a high capacity of 11 milliampere-hours per square centimeter, and O 2 evolution on charge with very low overpotential. Online mass spectrometry and chemical quantification confirm that oxidation of Li 2 O involves transfer of exactly 4 e – /O 2 . This work shows that Li-O 2 electrochemistry is not intrinsically limited once problems of electrolyte, superoxide, and cathode host are overcome and that coulombic efficiency close to 100% can be achieved.
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 117
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    Steering together all four Ugi pieces (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-09-14
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 118
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    A swift citrusy path to chiral phosphorus (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-09-21
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 119
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    Robust assembly of aromatic molecules (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-09-21
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 120
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    Easy access to elusive radical reactions (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-10-12
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 121
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    Selective formation of {gamma}-lactams via C-H amidation enabled by tailored iridium catalysts (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-03-06
    Description: Intramolecular insertion of metal nitrenes into carbon-hydrogen bonds to form -lactam rings has traditionally been hindered by competing isocyanate formation. We report the application of theory and mechanism studies to optimize a class of pentamethylcyclopentadienyl iridium(III) catalysts for suppression of this competing pathway. Modulation of the stereoelectronic properties of the auxiliary bidentate ligands to be more electron-donating was suggested by density functional theory calculations to lower the C–H insertion barrier favoring the desired reaction. These catalysts transform a wide range of 1,4,2-dioxazol-5-ones, carbonylnitrene precursors easily accessible from carboxylic acids, into the corresponding -lactams via sp 3 and sp 2 C–H amidation with exceptional selectivity. The power of this method was further demonstrated by the successful late-stage functionalization of amino acid derivatives and other bioactive molecules.
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 122
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    Guiding nitrenes away from a migration (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-03-06
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 123
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    Real-time imaging of adatom-promoted graphene growth on nickel (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-03-16
    Description: Single adatoms are expected to participate in many processes occurring at solid surfaces, such as the growth of graphene on metals. We demonstrate, both experimentally and theoretically, the catalytic role played by single metal adatoms during the technologically relevant process of graphene growth on nickel (Ni). The catalytic action of individual Ni atoms at the edges of a growing graphene flake was directly captured by scanning tunneling microscopy imaging at the millisecond time scale, while force field molecular dynamics and density functional theory calculations rationalize the experimental observations. Our results unveil the mechanism governing the activity of a single-atom catalyst at work.
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 124
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    Comment on "Synthesis and characterization of the pentazolate anion cyclo-N5- in (N5)6(H3O)3(NH4)4Cl" (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-03-16
    Description: Zhang et al . (Reports, 27 January 2017, p. 374) reported synthesis of a cyclo -N 5 – ion putatively stabilized in a solid-state salt by hydrogen bonding from surrounding counterions. We performed theoretical calculations suggesting that HN 5 would be favored over the anion in the reported pentazolate salt via proton transfer.
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 125
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    Response to Comment on "Synthesis and characterization of the pentazolate anion cyclo-N5- in (N5)6(H3O)3(NH4)4Cl" (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-03-16
    Description: Huang and Xu argue that the cyclo -N 5 – ion in (N 5 ) 6 (H 3 O) 3 (NH 4 ) 4 Cl we described in our report is theoretically unfavorable and is instead protonated. Their conclusion is invalid, as they use an improper method to assess the proton transfer in a solid crystal structure. We present an in-depth experimental and theoretical analysis of (N 5 ) 6 (H 3 O) 3 (NH 4 ) 4 Cl that supports the results in the original paper.
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 126
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    Boron compounds tackle dinitrogen (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-02-23
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 127
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    Boron learns to give back to nitrogen (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-02-23
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 128
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    Non-Double-Couple Component Analysis of Induced Microearthquakes in the Val d’Agri Basin (Italy) (2018)
    Details
    Publication Date: 2018-03-23
    Description: In recent years it has become accepted that earthquake source can attain significant Non-Double-Couple (NDC) components. Among the driving factors of deviation from normal double-couple (DC) mechanisms there is the opening/closing of fracture networks and the activation of pre-existing faults by pore fluid pressure perturbations. This observation makes the thorough analysis of source mechanism of key importance for the understanding of withdrawal/injection induced seismicity from geothermal and hydrocarbon reservoirs, as well as of water reservoir induced seismicity. In addition to the DC component, seismic moment tensor can be decomposed into isotropic (ISO) and compensated linear vector dipole (CLVD) components. In this study we performed a careful analysis of the seismic moment tensor of induced microseismicity recorded in the Val d'Agri (Southern Apennines, Italy) focusing our attention on the NDC component. The Val d'Agri is a Quaternary extensional basin that hosts the largest onshore European oil field and a water reservoir (Pertusillo Lake impoundment) characterized by severe seasonal level oscillations. Our input data-set includes swarm-type induced micro-seismicity recorded between 2005-2006 by a high-performance network and accurately localized by a reservoir-scale local earthquake tomography. We analyze two different seismicity clusters: (i) a swarm of 69 earthquakes with 0.3 ML 1.8 induced by a wastewater disposal well of the oilfield during the initial daily injection tests (10 days); (ii) 526 earthquakes with -0.2 ML 2.7 induced by seasonal volume changes of the artificial lake. We perform the seismic moment tensor inversion by using HybridMT code. After a very accurate signal-to-noise selection and hand-made picking of P-pulses, we obtain %DC, %ISO, %CLVD for each event. DC and NDC components are analyzed and compared with the spatio-temporal distribution of seismicity, the local stress field, the injection parameters and the water level in the impoundment. We find significant NDC components and abrupt temporal variations in the DC and ISO components that appear linked to the extremely variable parameters of the injection tests into the disposal well.
    Description: Published
    Description: New Orleans, LA
    Description: 2T. Sorgente Sismica
    Keywords: Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 129
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    Structural inheritance controlling active crustal deformation in the Val d’Agri area (southern Apennines, Italy): new insights from finite element modelling (2018)
    Details
    Publication Date: 2019-01-18
    Description: The availability of a large amount of surface geological data and subsurface information gathered by the oil industry, together with seismic and geodetic data, allowed us to define and analyse the active structures in the Val d'Agri area of the southern Apennines. Taking into account that the study of interseismic deformation can be significant to identify locked fault areas that can potentially slip, in this study we present 2D elastoplastic finite-element models to reproduce interseismic characteristics of the study area. This hosts the largest Europe's onshore oil field and is characterised by an active extensional tectonic regime, as inferred from earthquake focal mechanisms and fault slip data from late Quaternary structures. Based on high-quality seismic profiles tied with deep well logs, we constructed a detailed geological section across the study area. Outcropping units are dissected by numerous brittle structures that formed at various stages during the tectonic evolution of the Apennines, while the deep ones are dominated by deeply rooted major faults. The rheological behaviour has been constrained by the reconstruction of the thermal structure of the fold and thrust belt, using available information from the foreland Apulian Platform and from temperature data from a series of wells. Starting from the geological model, we reproduced interseismic deformation by means of finite-element numerical modelling, varying boundary conditions and unlocking different fault segments. Our numerical models provide new insights into the controversial and widely debated active tectonic setting of the Val d'Agri area, confirming the major role played by structural inheritance and reactivation processes. In fact, recent low-magnitude seismicity tends to illuminate fault segments consisting of pre-existing reverse faults reactivated as normal faults in the present-day stress field. These long-lived, mature fault systems occurring in the buried Apulian Platform carbonates (and underlying basement) represent major brittle structures that cumulated displacements of up to a few kilometres over geologic time. As a result of their reactivation within the late Quaternary extensional stress field, these long-lived crustal structures are capable of nucleating also moderate- to large-magnitude earthquakes. The decoupling between deep and shallow structural levels, and the different inherited structures affecting them, explain the apparent contrast between the subdued surface expression of active fault systems and the known occurrence of large magnitude seismic events in the study area, thus reconciling apparently contrasting geological and geophysical constraints.
    Description: Published
    Description: 111-114
    Description: 1T. Deformazione crostale attiva
    Description: N/A or not JCR
    Keywords: Active tectonics ; Fault reactivation ; Stress field ; Seismicity ; Extensional tectonics ; Seismology ; Tectonophysics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 130
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    Journal of Geophysics - Zeitschrift für Geophysik 48 (2018)
    Springer, Berlin
    In:  SUB Göttingen | 8 Z NAT 2148
    Details
    Publication Date: 2021-03-29
    Description: Dieser Band enthält 28 Artikel zu Themengebieten der Geophysik, veröffentlicht durch die Deutsche Geophysikalische Gesellschaft in dem Jahr 1980.
    Description: Inhaltsverzeichnis: Journal of Geophysics 48 〈html〉 〈body〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0012.pdf"〉The Analysis of Simultaneous Observations of Nighttime Pi Pulsations on an East-West Profile〈/a〉〈br〉 (Baranskiy, L. N., Troitskaya, V. A., Sterlikova, I. V., Gokhberg, M. B., Ivanov, N. A., Khartchenko, I. P., Münch, J. W., Wilhelm, K.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0013.pdf"〉Coordinated Magnetic Observations of Morning Sector Auroral Zone Currents With Triad and the Scandinavian Magnetometer Array: A Case Study〈/a〉〈br〉 (Sulzbacher, H., Baumjohann, W., Potemra, T. A.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0014.pdf"〉K – Ar Age Determinations on Tertiary Volcanic Rocks: V. Siebengebirge, Siebengebirge-Graben〈/a〉〈br〉 (Todt, W., Lippolt, H. J.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0015.pdf"〉The Geothermal Anomaly of Landau/Pfalz: An Attempt of Interpretation〈/a〉〈br〉 (Werner, D., Parini, M.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0016.pdf"〉Magnetic and Gravity Investigations of the Dead Sea Rift and Adjacent Areas in Northern Israel〈/a〉〈br〉 (Folkman, Y.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0017.pdf"〉Changes of Structure, Phase Composition and Electric Conductivity Under High-Temperature Oxidation of Titanomagnetites〈/a〉〈br〉 (Kropáček, V., Laštovičková, M.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0018.pdf"〉Maximum Velocity Amplitudes of 〈i〉P〈/i〉 and 〈i〉S〈/i〉 Waves From Filtered Broadband Records〈/a〉〈br〉 (Sitaram, M. V. D, Plešinger, A., Vaněk, J.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0019.pdf"〉Comment on: On the Sources of the 12-Month Wave in the 〈i〉an〈/i〉 and 〈i〉as〈/i〉 Geomagnetic Activity Indices〈/a〉〈br〉 (Mayaud, P. N.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0020.pdf"〉Book Reviews〈/a〉〈br〉 (Schopper, J., Hartmann, G.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0021.pdf"〉A Late Cretaceous 〈sup〉40〈/sup〉Ar–〈sup〉39〈/sup〉Ar Age for the Lappajärvi Impact Crater, Finland〈/a〉〈br〉 (Jessberger, E. K., Reimold, W. U.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0022.pdf"〉Magnetic Properties of Swiss Flysch〈/a〉〈br〉 (Channell, J., Freeman, R., Heller, F.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0023.pdf"〉Source Parameters of Earthquakes From the Himalayan Region〈/a〉〈br〉 (Upadhyay, S. K., Duda, S. J.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0024.pdf"〉Teleseismic Evidence for Velocity Heterogeneity Beneath the Rhenish Massif〈/a〉〈br〉 (Raikes, S.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0025.pdf"〉The Simulation Problem for Broad-Band Seismograms〈/a〉〈br〉 (Seidl, D.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0026.pdf"〉Load-Induced Stresses and Their Relation to the Initial Stress Field〈/a〉〈br〉 (Bock, G.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0027.pdf"〉Ground-Based Observations of an Onset of Localized Field-Aligned Currents During Auroral Breakup Around Magnetic Midnight〈/a〉〈br〉 (Opgenoorth, H. J., Pellinen, R. J., Maurer, H., Küppers, F., Heikkila, W. J., Kaila, K. U., Tanskanen, P.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0028.pdf"〉Simultaneous Maxima of Geomagnetic Pulsations and Riometer Absorption on the Afternoon Side of the Auroral Zone〈/a〉〈br〉 (Novikov, Y., Kopytenko, Y., Raspopov, O., Bösinger, T., Kangas, J., Ranta, H.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0029.pdf"〉Numerical Investigation of the Spectral Resolving Power of Burg's Maximum Entropy Method〈/a〉〈br〉 (Wenzel, F., Zürn, W.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0030.pdf"〉Errors in Matrix Element Expressions for the Reflectivity Method〈/a〉〈br〉 (Baumgardt, D.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0031.pdf"〉Magnetometer Array Observations of a Giant Pulsation Event〈/a〉〈br〉 (Glaßmeier, K.-H.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0032.pdf"〉Palaeomagnetic Secular Variation Curves Extending Back to 13,400 years B.P. Recorded by Sediments Deposited in Lac de Joux, Switzerland〈/a〉〈br〉 (Creer, K., Hogg, T. E., Readman, P. W., Reynaud, C.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0033.pdf"〉Anhysteretic Remanent Magnetization of Small Multidomain Fe〈sub〉3〈/sub〉O〈sub〉4〈/sub〉 Particles Dispersed in Various Concentrations in a Non Magnetic Matrix〈/a〉〈br〉 (Schmidbauer, E., Veitch, R. J.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0034.pdf"〉Stirred Remanent Magnetization: A Laboratory Analogue of Post-Depositional Realignment〈/a〉〈br〉 (Tucker, P.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0035.pdf"〉High Precision Measurement of the Frequency of Mode 〈sub〉O〈/sub〉S〈sub〉O〈/sub〉〈/a〉〈br〉 (Zürn, W., Knopoff, L., Rydelek, P. A.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0036.pdf"〉The Solution of Dynamic Problems of Elastic Wave Propagation in Inhomogeneous Media by a Combination of Partial Separation of Variables and Finite-Difference Methods〈/a〉〈br〉 (Alekseev, A. S., Mikhailenko, B. G.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0037.pdf"〉A Characteristic Method for Numerical Solution of the Inverse Kinematic Seismic Problems〈/a〉〈br〉 (Romanov, M. E., Alekseev, A. S.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0038.pdf"〉Geomagnetic Induction Studies in Scandinavia〈/a〉〈br〉 (Jones, A. G.)〈/li〉 〈li〉〈a href="https://gdz.sub.uni-goettingen.de/download/pdf/PPN1015067948_0048/LOG_0039.pdf"〉Comments on Polarization and Coherence〈/a〉〈br〉 (Samson, J. C.)〈/li〉 〈/body〉 〈/html〉
    Description: research
    Description: DFG, SUB Göttingen
    Keywords: 550 ; Geophysik ; Auroral Zone Physics ; Broad Band Seismograms ; Earth’s Crust ; Earth’s Mantle ; Electrical Conductivity of Rocks ; Electrical Conductivity of the Earth ; Electromagnetic lnduction in the Earth ; Free Oscillations ; Geochronology ; Geomagnetic Activity ; Geomagnetic Pulsations ; Geomagnetic Time Variations ; Geothermal Anomalies ; Gravity Anomalies ; Himalaya ; Impact Structures ; Induced Seismicity ; Inverse Seismic Problems ; Israel ; Magnetic Anomalies ; Maximum Entropy Method ; Palaeomagnetism ; Polarization Analysis ; Reflectivity Method ; Rheinisches Massiv ; Rock Magnetism ; Rock Physics ; Scandinavia ; Secular Variation ; Seismology ; Siebengebirge ; Stress Field ; Theoretical Seismograms ; FID-GEO-DE-7
    Language: English
    Type: anthology_digi
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    Using Bio-Chemistry Genetics Markers to Distinguish Barbus in Khozestan (2018)
    Iranian Fisheries Science Research Institute | Tehran, Iran
    Details
    Publication Date: 2021-05-19
    Description: 0Genetic polymorphism by means of biochemical genetic markers using polyacrylamide gel electrophoresis system in four barbus fish species has been investigated. Species scientific name were Barbus sharpeyi ; Gunther, 1847 , Barbus grypus ; Heckel, 1843, Barbus xanthopterus ; Heckel, 1843 and Barbus esocinus ; Heckel, 1843.Sampling site and location were mainly in the rivers located in Khoozestan province such as Karoon and Karkheh rivers and the Dez dam. Different organs such as blood, muscle, kidney, eye and heart were sampled and analysed for the presence of tf, es, sod and pgm alleles. High polymorphism and presence of different alleles scored, but populations were not in the H-W equilibrium. Considring results, using current and avaiable genetic markers such as microsattelits is recommended for future works.
    Description: Iranian Fisheries Science Research Institute
    Description: Published
    Keywords: Chemistry ; Genetics ; Genetics Markers ; Distinguish ; Barbus ; Species ; Barbus sharpeyi ; Barbus xanthopterus ; Barbus esocinus
    Repository Name: AquaDocs
    Type: Report , Refereed
    Format: 62pp.
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    Trout Farms and Other Human activities Effects on Cheshmehkileh River Ecosystem in Tonekabon (2018)
    Iranian Fisheries Science Research Institute | Tehran, Iran
    Details
    Publication Date: 2021-05-19
    Description: Cheshmehkileh River and adjacent mountainous streams, play a strategic role as a historical axis for anthropogenic civilization, human welfare also habitat and migration pathway of commercial – biologic valuable fishes e.g. Caspian trout, Caspian kuttum, members of Cyprinidae family in south Caspian Sea drainage. Treats such as overfishing of Caspian trout and Red spotted trout stocks in mountainous headwaters, barriers construction and manipulations those are out of river carrying capacity developed by human activities, affected normal function of river as well. Sand mining big factories establishment next to the river, legal and illegal trade of river sediments, direct entry of Tonekabon landfill leakage into the river, development of Rainbow trout farms since 3 decades and huge effluents into the river containing dead fish and types of solids, escapement of cultured Rainbow trouts into the river, … are major minimum factors which needs basic information for integrating inclusively drainage management system. Cheshmehkileh River contains Headwaters of Dohezar (Daryasar & Nusha), Sehezar and Valamroud rivers during 13 monthly sampling phases between September 2009 and October 2010 based on macrozoobenthoses investigations by EPT, EPT/C EPA protocols, measurements of nominated physic-chemical and microbiologic parameters. Probability of Rainbow trouts escapement and invasion, existence, nutrition in Cheshmehkileh environment indeed investigated. Data analysis explained significant differences (P〈0.05) between groups of measured parameters in different sampling stations. Dendogram of clustered analysis based on consolidation of major biologic/ physic-chemical and microbiologic parameters, separated stations No. 1, 3, 2, 4 in one group and remained classified in different groups. Station 8 and 9 similarly separated which expressed general similarities according to Sehezar river environment which were differs in comparison with other stations. Station 11 separated according to its natural quality of water and environment. Similarities between station 10 to Sehezar river stations 8 and 9 expressed general influence of Sehezar River more than Dohezar River in Cheshmehkileh condition especially in station No. 10. High scores of EPT and EPT/C indices in upstream stations 1, 3 and 8 also low score of indices in stations 7, 13 and 6 expressed levels of environment quality between these groups of stations. Maximum average biomass of macroinvertebrates belongs to Trichoptera order in Cheshmehkileh River. Significant decrease of biomass in stations 11, 12 and 13 in comparison with other stations stated environment degradation in mentioned stations relevant to excessive sand mining as well. Pollution resistant groups of invertebrates significantly increased in downstreams against upstream stations. Also disappearing of Plecoptera order in station No. 7, 9, 10 and 13 stated low quality of environment in comparison with upstream stations. Confirmation of effects quality and quantity for point and non-point sources of imported pollutants require specific management considerations in order to present exploitations, pollutants control and emergencies for river monitoring in forthcoming years.
    Description: Iranian Fisheries Science Research Institute
    Description: Published
    Keywords: River ; Pollution ; Aquaculture ; EPTC ; Assessment ; Macroinvertebrates ; Chemistry ; Microbiology
    Repository Name: AquaDocs
    Type: Report , Refereed
    Format: 138pp.
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  • 133
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    Scavenging and transport of thorium radioisotopes in the North Atlantic Ocean (2018)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-25
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2018
    Description: Many chemical constituents are removed from the ocean by attachment to settling particles, a process referred to as “scavenging.” Radioisotopes of thorium, a highly particle-reactive element, have been used extensively to study scavenging in the ocean. However, this process is complicated by the highly variable chemical composition and concentration of particles in oceanic waters. This thesis focuses on understanding the cycling of thorium as affected by particle concentration and particle composition in the North Atlantic. This objective is addressed using (i) the distributions 228,230,234Th, their radioactive parents, particle composition, and bulk particle concentration, as measured or estimated along the GEOTRACES North Atlantic Transect (GA03) and (ii) a model for the reversible exchange of thorium with particles. Model parameters are either estimated by inversion (chapter 2-4), or prescribed in order to simulate 230Th in a circulation model (chapter 5). The major findings of this thesis follow. In chapters 2 and 3, I find that the rate parameters of the reversible exchange model show systematic variations along GA03. In particular, 𝑘1, the apparent first-order rate "constant" of Th adsorption onto particles, generally presents maxima in the mesopelagic zone and minima below. A positive correlation between 𝑘1 and bulk particle concentration is found, consistent with the notion that the specific rate at which a metal in solution attaches to particles increases with the number of surface sites available for adsorption. In chapter 4, I show that Mn (oxyhydr)oxides and biogenic particles most strongly influence 𝑘1 west of the Mauritanian upwelling, but that biogenic particles dominate 𝑘1 in this region. In chapter 5, I find that dissolved 230Th data are best represented by a model that assumes enhanced values of 𝑘1 near the seafloor. Collectively, my findings suggest that spatial variations in Th radioisotope activities observed in the North Atlantic reflect at least partly variations in the rate at which Th is removed from the water column.
    Description: This work was supported by the US National Science Foundation. Two US NSF grants have supported the research in this thesis (OCE-1232578 and OCE-155644).
    Keywords: Thorium ; Chemistry
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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    The crust and upper mantle structure of central and West Antarctica from Bayesian inversion of Rayleigh Wave and receiver functions (2018)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 123 (2018): 7824-7849, doi:10.1029/2017JB015346.
    Description: We construct a new seismic model for central and West Antarctica by jointly inverting Rayleigh wave phase and group velocities along with P wave receiver functions. Ambient noise tomography exploiting data from more than 200 seismic stations deployed over the past 18 years is used to construct Rayleigh wave phase and group velocity dispersion maps. Comparison between the ambient noise phase velocity maps with those constructed using teleseismic earthquakes confirms the accuracy of both results. These maps, together with P receiver function waveforms, are used to construct a new 3‐D shear velocity (Vs) model for the crust and uppermost mantle using a Bayesian Monte Carlo algorithm. The new 3‐D seismic model shows the dichotomy of the tectonically active West Antarctica (WANT) and the stable and ancient East Antarctica (EANT). In WANT, the model exhibits a slow uppermost mantle along the Transantarctic Mountains (TAMs) front, interpreted as the thermal effect from Cenozoic rifting. Beneath the southern TAMs, the slow uppermost mantle extends horizontally beneath the traditionally recognized EANT, hypothesized to be associated with lithospheric delamination. Thin crust and lithosphere observed along the Amundsen Sea coast and extending into the interior suggest involvement of these areas in Cenozoic rifting. EANT, with its relatively thick and cold crust and lithosphere marked by high Vs, displays a slower Vs anomaly beneath the Gamburtsev Subglacial Mountains in the uppermost mantle, which we hypothesize may be the signature of a compositionally anomalous body, perhaps remnant from a continental collision.
    Description: National Science Foundation Grant Numbers: PLR‐1142518, PLR‐1246712, PLR 1246151, PLR‐1246416, PLR‐1744883, PLR‐ 1744883
    Description: 2019-03-22
    Keywords: Seismology ; Crust and uppermost mantle ; Ambient noise tomography ; Antarctica ; Transantarctic Mountains ; Gamburtsev Mountains
    Repository Name: Woods Hole Open Access Server
    Type: Article
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    Assessment of seabed seismic systems (2018)
    Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-26
    Description: This project was initiated to accomplish the necessary research and documentation of existing seismic techniques and systems for the study of sediments and sedimentary structures in the oceans. In this respect , it is an 'inventory' of methods and techniques for looking at small-scale features or changes in structures lying from 10 to 1000 m beneath the sea floor. It attempts to assess the vertical and lateral resolution capabilities of existing and technically feasible seismic systems. Some of the questions posed are: how closely can we determine vertical variation such as sediment layer thickness and vertical variation with depth; also lateral coherence or its disruption by such agents as facies changes, thinning or thickening, slumping, faulting; the nature of the basement structure, its areal coherence, velocity structure and associated anomalies?
    Description: Prepared for the Sandia Laboratories under Contract 13-9944.
    Keywords: Seismology ; Ocean bottom
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
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    Microearthquake activity on the Orozco Fracture Zone : preliminary results from Project ROSE (2018)
    Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-26
    Description: Also published as: Journal of Geophysical Research 86 (1981): 3783- 3790
    Description: We present preliminary hypocenter determinations for 52 earthquakes recorded by a large multiinstitutional network of ocean bottom seismometers and ocean bottom hydrophones in the Orozco Fracture Zone in the eastern Pacific during late February to mid-March 1979. The network was deployed as pan of the Rivera Ocean Seismic Experiment, also known as Project ROSE. The Orozco Fracture Zone is physiographically complex, and the pattern of microeanhquake hypocenters at least partly reflects this complexity. All of the well-located epicenters lie within the active transform fault segment of the fracture zone. About lialf of the recorded earthquakes were aligned along a narrow trough that extends eastward from the northern rise crest intersection in the approximate direction of the Cocos-Pacific relative plate motion; these events appear to be characterized by strike-slip faulting. The second major group of activity occurred in the central portion of the transform fault; the microearthquakes in this group do not display a preferred alignment parallel to the direction of spreading, and several are not obviously associated with distinct topographic features. Hypocentral depth was well resolved for many of the earthquakes reported here. Nominal depths range from 0 to 17 km below the seafloor.
    Description: Prepared for the Office of Naval Research under Contract N00014-79-C-0071; NR 083-004.
    Keywords: Natural disasters ; Seismology
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
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    A geophysical survey within the Mesozoic magnitic anomaly sequence south of Bermuda (2018)
    Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-26
    Description: Also published as: Journal of Geophysical Research 84 (1979): 5487-5496
    Description: This geophysical survey of an approximate 1° square covers Mesozoic magnetic anomalies M0, M2, and M4 south of Bermuda. Bathymetry, magnetics, seismic reflection profiling, and seismic refraction data are presented. The isochron trend within the survey area at magnetic anomaly M4 time is 025°. Two left lateral fracture zones exist: the southern fracture zone has an offset of 〈10 km at M4 time and 33 km at M0 time. The northern fracture zone has an offset of 37 km at M4 time and 26 km at M0 time. These changes in offset are accounted for by asymmetric spreading, an 11° change in trend of anomaly M0 relative to M4, and by M0 time, growth of a small right lateral fracture zone. Seismic refraction data provide poor control on the shallow crustal structure but suggest the presence of significant lateral inhomogeneities within layer 2.
    Description: Prepared for the Office of Naval Research under Contract N00014-74-C-0262; NR 083-004.
    Keywords: Submarine geology ; Seismology
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
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    Rupture evolution of the 2006 Java tsunami earthquake and the possible role of splay faults (2018)
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Tectonophysics 721 (2017): 143-150, doi:10.1016/j.tecto.2017.10.003.
    Description: The 2006 Mw 7.8 Java earthquake was a tsunami earthquake, exhibiting frequency-dependent seismic radiation along strike. High-frequency global back-projection results suggest two distinct rupture stages. The first stage lasted ~65 s with a rupture speed of ~1.2 km/s, while the second stage lasted from ~65 to 150 s with a rupture speed of ~2.7 km/s. High-frequency radiators resolved with back-projection during the second stage spatially correlate with splay fault traces mapped from residual free-air gravity anomalies. These splay faults also colocate with a major tsunami source associated with the earthquake inferred from tsunami first-crest back-propagation simulation. These correlations suggest that the splay faults may have been reactivated during the Java earthquake, as has been proposed for other tsunamigenic earthquakes, such as the 1944 Mw 8.1 Tonankai earthquake in the Nankai Trough.
    Description: W.F. is currently supported by the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution, with funding provided by the Weston Howland Jr. Postdoctoral Scholarship.
    Keywords: Earthquake ; Tsunami ; Back-projection ; Splay faults ; Java ; Seismology
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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    Least-squares reverse time migration in elastic media (2017)
    Oxford University Press
    Details
    Publication Date: 2017-01-01
    Description: Elastic reverse time migration (RTM) can yield accurate subsurface information (e.g. PP and PS reflectivity) by imaging the multicomponent seismic data. However, the existing RTM methods are still insufficient to provide satisfactory results because of the finite recording aperture, limited bandwidth and imperfect illumination. Besides, the P - and S -wave separation and the polarity reversal correction are indispensable in conventional elastic RTM. Here, we propose an iterative elastic least-squares RTM (LSRTM) method, in which the imaging accuracy is improved gradually with iteration. We first use the Born approximation to formulate the elastic de-migration operator, and employ the Lagrange multiplier method to derive the adjoint equations and gradients with respect to reflectivity. Then, an efficient inversion workflow (only four forward computations needed in each iteration) is introduced to update the reflectivity. Synthetic and field data examples reveal that the proposed LSRTM method can obtain higher-quality images than the conventional elastic RTM. We also analyse the influence of model parametrizations and misfit functions in elastic LSRTM. We observe that Lamé parameters, velocity and impedance parametrizations have similar and plausible migration results when the structures of different models are correlated. For an uncorrelated subsurface model, velocity and impedance parametrizations produce fewer artefacts caused by parameter crosstalk than the Lamé coefficient parametrization. Correlation- and convolution-type misfit functions are effective when amplitude errors are involved and the source wavelet is unknown, respectively. Finally, we discuss the dependence of elastic LSRTM on migration velocities and its antinoise ability. Imaging results determine that the new elastic LSRTM method performs well as long as the low-frequency components of migration velocities are correct. The quality of images of elastic LSRTM degrades with increasing noise.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    The dynamic response of prone-to-fall columns to ambient vibrations: comparison between measurements and numerical modelling (2017)
    Oxford University Press
    Details
    Publication Date: 2017-01-01
    Description: Seismic noise measurements (ambient vibrations) have been increasingly used in rock slope stability assessment for both investigation and monitoring purposes. Recent studies made on gravitational hazard revealed significant spectral amplification at given frequencies and polarization of the wave-field in the direction of maximum rock slope displacement. Different properties (resonance frequencies, polarization and spectral ratio amplitudes) can be derived from the spectral analysis of the seismic noise to characterize unstable rock masses. The objective here is to identify the dynamic parameters that could be used to gain information on prone-to-fall rock columns’ geometry. To do so, the dynamic response of prone-to-fall columns to seismic noise has been studied on two different sites exhibiting cliff-like geometry. Dynamic parameters (main resonance frequency and spectral ratio amplitudes) that could characterize the column decoupling were extracted from seismic noise and their variations were studied taking into account the external environmental parameter fluctuations. Based on this analysis, a two-dimensional numerical model has been set up to assess the influence of the rear vertical fractures identified on both sites on the rock column motion response. Although a simple relation was found between spectral ratio amplitudes and the rock column slenderness, it turned out that the resonance frequency is more stable than the spectral ratio amplitudes to characterize this column decoupling, provided that the elastic properties of the column can be estimated. The study also revealed the effect of additional remote fractures on the dynamic parameters, which in turn could be used for detecting the presence of such discontinuities.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Imaging of first-order surface-related multiples by reverse-time migration (2017)
    Oxford University Press
    Details
    Publication Date: 2017-01-01
    Description: Surface-related multiples have been utilized in the reverse-time migration (RTM) procedures, and additional illumination for subsurface can be provided. Meanwhile, many cross-talks are generated from undesired interactions between forward- and backward-propagated seismic waves. In this paper, subsequent to analysing and categorizing these cross-talks, we propose RTM of first-order multiples to avoid most undesired interactions in RTM of all-order multiples, where only primaries are forward-propagated and crosscorrelated with the backward-propagated first-order multiples. With primaries and multiples separated during regular seismic data processing as the input data, first-order multiples can be obtained by a two-step scheme: (1) the dual-prediction of higher-order multiples; and (2) the adaptive subtraction of predicted higher-order multiples from all-order multiples within local offset-time windows. In numerical experiments, two synthetic and a marine field data sets are used, where different cross-talks generated by RTM of all-order multiples can be identified and the proposed RTM of first-order multiples can provide a very interpretable image with a few cross-talks.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 142
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    Metal-catalyzed electrochemical diazidation of alkenes (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-08-11
    Description: Vicinal diamines are a common structural motif in bioactive natural products, therapeutic agents, and molecular catalysts, motivating the continuing development of efficient, selective, and sustainable technologies for their preparation. We report an operationally simple and environmentally friendly protocol that converts alkenes and sodium azide—both readily available feedstocks—to 1,2-diazides. Powered by electricity and catalyzed by Earth-abundant manganese, this transformation proceeds under mild conditions and exhibits exceptional substrate generality and functional group compatibility. Using standard protocols, the resultant 1,2-diazides can be smoothly reduced to vicinal diamines in a single step, with high chemoselectivity. Mechanistic studies are consistent with metal-mediated azidyl radical transfer as the predominant pathway, enabling dual carbon-nitrogen bond formation.
    Keywords: Chemistry
    Print ISSN: 0036-8075
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 143
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    Playing marble run to make methane (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-08-18
    Keywords: Chemistry
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    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 144
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    Methanogenic archaea metabolism (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-08-18
    Keywords: Chemistry
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 145
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    Methanogenic heterodisulfide reductase (HdrABC-MvhAGD) uses two noncubane [4Fe-4S] clusters for reduction (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-08-18
    Description: In methanogenic archaea, the carbon dioxide (CO 2 ) fixation and methane-forming steps are linked through the heterodisulfide reductase (HdrABC)–[NiFe]-hydrogenase (MvhAGD) complex that uses flavin-based electron bifurcation to reduce ferredoxin and the heterodisulfide of coenzymes M and B. Here, we present the structure of the native heterododecameric HdrABC-MvhAGD complex at 2.15-angstrom resolution. HdrB contains two noncubane [4Fe-4S] clusters composed of fused [3Fe-4S]-[2Fe-2S] units sharing 1 iron (Fe) and 1 sulfur (S), which were coordinated at the CCG motifs. Soaking experiments showed that the heterodisulfide is clamped between the two noncubane [4Fe-4S] clusters and homolytically cleaved, forming coenzyme M and B bound to each iron. Coenzymes are consecutively released upon one-by-one electron transfer. The HdrABC-MvhAGD atomic model serves as a structural template for numerous HdrABC homologs involved in diverse microbial metabolic pathways.
    Keywords: Chemistry
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 146
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    A water window on surface chemistry (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-08-25
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 147
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    X-ray vision spies copper on the move (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-09-01
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 148
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    Ruthenium-catalyzed insertion of adjacent diol carbon atoms into C-C bonds: Entry to type II polyketides (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-08-25
    Description: Current catalytic processes involving carbon-carbon bond activation rely on -unsaturated coupling partners. Exploiting the concept of transfer hydrogenative coupling, we report a ruthenium(0)-catalyzed cycloaddition of benzocyclobutenones that functionalizes two adjacent saturated diol carbon-hydrogen bonds. These regio- and diastereoselective processes enable convergent construction of type II polyketide substructures.
    Keywords: Chemistry
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 149
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    Slicing through both C-C and C-H bonds (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-08-25
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 150
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    Optical imaging of surface chemistry and dynamics in confinement (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-08-25
    Description: We imaged the interfacial structure and dynamics of water in a microscopically confined geometry, in three dimensions and on millisecond time scales, with a structurally illuminated wide-field second harmonic microscope. The second harmonic images reported on the orientational order of interfacial water, induced by charge-dipole interactions between water molecules and surface charges. The images were converted into surface potential maps. Spatially resolved surface acid dissociation constant (p K a,s ) values were determined for the silica deprotonation reaction by following pH-induced chemical changes on the curved and confined surfaces of a glass microcapillary immersed in aqueous solutions. These values ranged from 2.3 to 10.7 along the wall of a single capillary because of surface heterogeneities. Water molecules that rotate along an oscillating external electric field were also imaged.
    Keywords: Chemistry
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 151
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    Imaging surfaces with water (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-08-25
    Keywords: Chemistry
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    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 152
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    A molecular dance to cleaner air (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-09-01
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 153
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    Dynamic multinuclear sites formed by mobilized copper ions in NOx selective catalytic reduction (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-09-01
    Description: Copper ions exchanged into zeolites are active for the selective catalytic reduction (SCR) of nitrogen oxides (NO x ) with ammonia (NH 3 ), but the low-temperature rate dependence on copper (Cu) volumetric density is inconsistent with reaction at single sites. We combine steady-state and transient kinetic measurements, x-ray absorption spectroscopy, and first-principles calculations to demonstrate that under reaction conditions, mobilized Cu ions can travel through zeolite windows and form transient ion pairs that participate in an oxygen (O 2 )–mediated Cu I -〉Cu II redox step integral to SCR. Electrostatic tethering to framework aluminum centers limits the volume that each ion can explore and thus its capacity to form an ion pair. The dynamic, reversible formation of multinuclear sites from mobilized single atoms represents a distinct phenomenon that falls outside the conventional boundaries of a heterogeneous or homogeneous catalyst.
    Keywords: Chemistry
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  • 154
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    Hydrogenation of fluoroarenes: Direct access to all-cis-(multi)fluorinated cycloalkanes (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-09-01
    Description: All-c is -multifluorinated cycloalkanes exhibit intriguing electronic properties. In particular, they display extremely high dipole moments perpendicular to the aliphatic ring, making them highly desired motifs in material science. Very few such motifs have been prepared, as their syntheses require multistep sequences from diastereoselectively prefunctionalized precursors. Herein we report a synthetic strategy to access these valuable materials via the rhodium–cyclic (alkyl)(amino)carbene (CAAC)–catalyzed hydrogenation of readily available fluorinated arenes in hexane. This route enables the scalable single-step preparation of an abundance of multisubstituted and multifluorinated cycloalkanes, including all- cis -1,2,3,4,5,6-hexafluorocyclohexane as well as cis-configured fluorinated aliphatic heterocycles.
    Keywords: Chemistry
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    A charged approach to forming C-N bonds (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-08-11
    Keywords: Chemistry
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    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 156
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    Keeping all fluorines on the same side (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-09-01
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 157
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    Locked synchronous rotor motion in a molecular motor (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-06-02
    Description: Biological molecular motors translate their local directional motion into ordered movement of other parts of the system to empower controlled mechanical functions. The design of analogous geared systems that couple motion in a directional manner, which is pivotal for molecular machinery operating at the nanoscale, remains highly challenging. Here, we report a molecular rotary motor that translates light-driven unidirectional rotary motion to controlled movement of a connected biaryl rotor. Achieving coupled motion of the distinct parts of this multicomponent mechanical system required precise control of multiple kinetic barriers for isomerization and synchronous motion, resulting in sliding and rotation during a full rotary cycle, with the motor always facing the same face of the rotor.
    Keywords: Chemistry
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  • 158
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    A modular and enantioselective synthesis of the pleuromutilin antibiotics (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-06-02
    Description: The tricyclic diterpene fungal metabolite (+)-pleuromutilin has served as a starting point for antibiotic development. Semisynthetic modification of its glycolic acid subunit at C14 provided the first analogs fit for human use, and derivatization at C12 led to 12- epi -pleuromutilins with extended-spectrum antibacterial activity, including activity against Gram-negative pathogens. Given the inherent limitations of semisynthesis, however, accessing derivatives of (+)-pleuromutilin with full control over their structure presents an opportunity to develop derivatives with improved antibacterial activities. Here we disclose a modular synthesis of pleuromutilins by the convergent union of an enimide with a bifunctional iodoether. We illustrate our approach through synthesis of (+)-12- epi -mutilin, (+)-11,12-di- epi -mutilin, (+)-12- epi -pleuromutilin, (+)-11,12-di- epi -pleuromutilin, and (+)-pleuromutilin itself in 17 to 20 steps.
    Keywords: Chemistry
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  • 159
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    Gearing up molecular rotary motors (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-06-02
    Keywords: Chemistry
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 160
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    Coupled motion in a light-activated rotor (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-06-02
    Keywords: Chemistry
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 161
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    Two different combs from a single source (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-06-16
    Keywords: Chemistry
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 162
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    Dual-comb spectroscopy of water vapor with a free-running semiconductor disk laser (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-06-16
    Description: Dual-comb spectroscopy offers the potential for high accuracy combined with fast data acquisition. Applications are often limited, however, by the complexity of optical comb systems. Here we present dual-comb spectroscopy of water vapor using a substantially simplified single-laser system. Very good spectroscopy measurements with fast sampling rates are achieved with a free-running dual-comb mode-locked semiconductor disk laser. The absolute stability of the optical comb modes is characterized both for free-running operation and with simple microwave stabilization. This approach drastically reduces the complexity for dual-comb spectroscopy. Band-gap engineering to tune the center wavelength from the ultraviolet to the mid-infrared could optimize frequency combs for specific gas targets, further enabling dual-comb spectroscopy for a wider range of industrial applications.
    Keywords: Chemistry
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    Trifluoromethylation via broken C-F bonds (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-06-23
    Keywords: Chemistry
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  • 164
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    A catalytic fluoride-rebound mechanism for C(sp3)-CF3 bond formation (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-06-23
    Description: The biological properties of trifluoromethyl compounds have led to their ubiquity in pharmaceuticals, yet their chemical properties have made their preparation a substantial challenge, necessitating innovative chemical solutions. We report the serendipitous discovery of a borane-catalyzed formal C(sp 3 )-CF 3 reductive elimination from Au(III) that accesses these compounds by a distinct mechanism proceeding via fluoride abstraction, migratory insertion, and C-F reductive elimination to achieve a net C-C bond construction. The parent bis(trifluoromethyl)Au(III) complexes tolerate a surprising breadth of synthetic protocols, enabling the synthesis of complex organic derivatives without cleavage of the Au-C bond. This feature, combined with the "fluoride-rebound" mechanism, was translated into a protocol for the synthesis of 18 F-radiolabeled aliphatic CF 3 -containing compounds, enabling the preparation of potential tracers for use in positron emission tomography.
    Keywords: Chemistry
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  • 165
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    Iodide management in formamidinium-lead-halide-based perovskite layers for efficient solar cells (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-06-30
    Description: The formation of a dense and uniform thin layer on the substrates is crucial for the fabrication of high-performance perovskite solar cells (PSCs) containing formamidinium with multiple cations and mixed halide anions. The concentration of defect states, which reduce a cell’s performance by decreasing the open-circuit voltage and short-circuit current density, needs to be as low as possible. We show that the introduction of additional iodide ions into the organic cation solution, which are used to form the perovskite layers through an intramolecular exchanging process, decreases the concentration of deep-level defects. The defect-engineered thin perovskite layers enable the fabrication of PSCs with a certified power conversion efficiency of 22.1% in small cells and 19.7% in 1-square-centimeter cells.
    Keywords: Chemistry
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  • 166
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    Lighting the way to carbon borylation (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-07-21
    Keywords: Chemistry
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 167
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    Photoinduced decarboxylative borylation of carboxylic acids (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-07-21
    Description: The conversion of widely available carboxylic acids into versatile boronic esters would be highly enabling for synthesis. We found that this transformation can be effected by illuminating the N -hydroxyphthalimide ester derivative of the carboxylic acid under visible light at room temperature in the presence of the diboron reagent bis(catecholato)diboron. A simple workup allows isolation of the pinacol boronic ester. Experimental evidence suggests that boryl radical intermediates are involved in the process. The methodology is illustrated by the transformation of primary, secondary, and tertiary alkyl carboxylic acids as well as a diverse range of natural-product carboxylic acids, thereby demonstrating its broad utility and functional group tolerance.
    Keywords: Chemistry
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  • 168
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    Highly elastic binders integrating polyrotaxanes for silicon microparticle anodes in lithium ion batteries (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-07-21
    Description: Lithium-ion batteries with ever-increasing energy densities are needed for batteries for advanced devices and all-electric vehicles. Silicon has been highlighted as a promising anode material because of its superior specific capacity. During repeated charge-discharge cycles, silicon undergoes huge volume changes. This limits cycle life via particle pulverization and an unstable electrode-electrolyte interface, especially when the particle sizes are in the micrometer range. We show that the incorporation of 5 weight % polyrotaxane to conventional polyacrylic acid binder imparts extraordinary elasticity to the polymer network originating from the ring sliding motion of polyrotaxane. This binder combination keeps even pulverized silicon particles coalesced without disintegration, enabling stable cycle life for silicon microparticle anodes at commercial-level areal capacities.
    Keywords: Chemistry
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  • 169
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    Experimentally realized mechanochemistry distinct from force-accelerated scission of loaded bonds (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-07-21
    Description: Stretching polymer chains accelerates dissociation of a variety of internal covalent bonds, to an extent that correlates well with the force experienced by the scissile bond. Recent theory has also predicted scenarios in which applied force accelerates dissociation of unloaded bonds and kinetically strengthens strained bonds. We report here unambiguous experimental validation of this hypothesis: Detailed kinetic measurements demonstrate that stretching phosphotriesters accelerates dissociation of the unloaded phosphorus-oxygen bond orthogonal to the pulling axis, whereas stretching organosiloxanes inhibits dissociation of the aligned loaded silicon-oxygen bonds. Qualitatively, the outcome is determined by phosphoester elongation and siloxane contraction along the pulling axis in the respective rate-determining transition states. Quantitatively, the results agree with a simple mechanochemical kinetics model.
    Keywords: Chemistry
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  • 170
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    Low-temperature CO removal (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-07-28
    Keywords: Chemistry
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  • 171
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    Atomic-layered Au clusters on {alpha}-MoC as catalysts for the low-temperature water-gas shift reaction (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-07-28
    Description: The water-gas shift (WGS) reaction (where carbon monoxide plus water yields dihydrogen and carbon dioxide) is an essential process for hydrogen generation and carbon monoxide removal in various energy-related chemical operations. This equilibrium-limited reaction is favored at a low working temperature. Potential application in fuel cells also requires a WGS catalyst to be highly active, stable, and energy-efficient and to match the working temperature of on-site hydrogen generation and consumption units. We synthesized layered gold (Au) clusters on a molybdenum carbide (α-MoC) substrate to create an interfacial catalyst system for the ultralow-temperature WGS reaction. Water was activated over α-MoC at 303 kelvin, whereas carbon monoxide adsorbed on adjacent Au sites was apt to react with surface hydroxyl groups formed from water splitting, leading to a high WGS activity at low temperatures.
    Keywords: Chemistry
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  • 172
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    Accumulating evidence for the Zundel motif (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-08-04
    Keywords: Chemistry
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  • 173
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    Forcing polymers to be semiconductors (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-08-04
    Keywords: Chemistry
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 174
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    Mechanochemical unzipping of insulating polyladderene to semiconducting polyacetylene (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-08-04
    Description: Biological systems sense and respond to mechanical stimuli in a complex manner. In an effort to develop synthetic materials that transduce mechanical force into multifold changes in their intrinsic properties, we report on a mechanochemically responsive nonconjugated polymer that converts to a conjugated polymer via an extensive rearrangement of the macromolecular structure in response to force. Our design is based on the facile mechanochemical unzipping of polyladderene, a polymer inspired by a lipid natural product structure and prepared via direct metathesis polymerization. The resultant polyacetylene block copolymers exhibit long conjugation length and uniform trans-configuration and self-assemble into semiconducting nanowires. Calculations support a tandem unzipping mechanism of the ladderene units.
    Keywords: Chemistry
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  • 175
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    Large-amplitude transfer motion of hydrated excess protons mapped by ultrafast 2D IR spectroscopy (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-08-04
    Description: Solvation and transport of excess protons in aqueous systems play a fundamental role in acid-base chemistry and biochemical processes. We mapped ultrafast proton excursions along the proton transfer coordinate by means of two-dimensional infrared spectroscopy, both in bulk water and in a Zundel cation (H 5 O 2 ) + motif selectively prepared in acetonitrile. Electric fields from the environment and stochastic hydrogen bond motions induce fluctuations of the proton double-minimum potential. Within the lifetime of a particular hydration geometry, the proton explores a multitude of positions on a sub-100-femtosecond time scale. The proton transfer vibration is strongly damped by its 20- to 40-femtosecond population decay. Our results suggest a central role of Zundel-like geometries in aqueous proton solvation and transport.
    Keywords: Chemistry
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  • 176
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    Synthesis of mixed hypermetallic oxide BaOCa+ from laser-cooled reagents in an atom-ion hybrid trap (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-09-30
    Description: Hypermetallic alkaline earth (M) oxides of formula MOM have been studied under plasma conditions that preclude insight into their formation mechanism. We present here the application of emerging techniques in ultracold physics to the synthesis of a mixed hypermetallic oxide, BaOCa + . These methods, augmented by high-level electronic structure calculations, permit detailed investigation of the bonding and structure as well as the mechanism of its formation via the barrierless reaction of Ca ( 3 P J ) with BaOCH 3 + . Further investigations of the reaction kinetics as a function of collision energy over the range 0.005 kelvin (K) to 30 K and of individual Ca fine-structure levels compare favorably with calculations based on long-range capture theory.
    Keywords: Chemistry
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  • 177
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    A chilly meeting of barium and calcium (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-09-30
    Keywords: Chemistry
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 178
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    A direct look at halogen bonds (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-10-13
    Keywords: Chemistry
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 179
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    Aqueous Au-Pd colloids catalyze selective CH4 oxidation to CH3OH with O2 under mild conditions (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-10-13
    Description: The selective oxidation of methane, the primary component of natural gas, remains an important challenge in catalysis. We used colloidal gold-palladium nanoparticles, rather than the same nanoparticles supported on titanium oxide, to oxidize methane to methanol with high selectivity (92%) in aqueous solution at mild temperatures. Then, using isotopically labeled oxygen (O 2 ) as an oxidant in the presence of hydrogen peroxide (H 2 O 2 ) , we demonstrated that the resulting methanol incorporated a substantial fraction (70%) of gas-phase O 2 . More oxygenated products were formed than the amount of H 2 O 2 consumed, suggesting that the controlled breakdown of H 2 O 2 activates methane, which subsequently incorporates molecular oxygen through a radical process. If a source of methyl radicals can be established, then the selective oxidation of methane to methanol using molecular oxygen is possible.
    Keywords: Chemistry
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  • 180
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    Imaging the halogen bond in self-assembled halogenbenzenes on silver (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-10-13
    Description: Halogens are among the most electronegative elements, and the variations in size and polarizability of halogens require different descriptions of the intermolecular bonds they form. Here we use the inelastic tunneling probe (itProbe) to acquire real-space imaging of intermolecular-bonding structures in the two-dimensional self-assembly of halogenbenzene molecules on a metal surface. Direct visualization is obtained for the intermolecular attraction and the "windmill" pattern of bonding among the fully halogenated molecules. Our results provide a hitherto missing understanding of the nature of the halogen bond.
    Keywords: Chemistry
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  • 181
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    Addressing supply issues for natural products in the clinic (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-10-13
    Keywords: Chemistry
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 182
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    Visualizing halogen bonding (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-10-13
    Keywords: Chemistry
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  • 183
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    A radical route from methane to methanol (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-10-13
    Keywords: Chemistry
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  • 184
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    Hydrogen from methane in molten metal (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-11-17
    Keywords: Chemistry
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  • 185
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    Purifying ethylene with flexible zeolites (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-11-24
    Keywords: Chemistry
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  • 186
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    Control of zeolite framework flexibility and pore topology for separation of ethane and ethylene (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-11-24
    Description: The discovery of new materials for separating ethylene from ethane by adsorption, instead of using cryogenic distillation, is a key milestone for molecular separations because of the multiple and widely extended uses of these molecules in industry. This technique has the potential to provide tremendous energy savings when compared with the currently used cryogenic distillation process for ethylene produced through steam cracking. Here we describe the synthesis and structural determination of a flexible pure silica zeolite (ITQ-55). This material can kinetically separate ethylene from ethane with an unprecedented selectivity of ~100, owing to its distinctive pore topology with large heart-shaped cages and framework flexibility. Control of such properties extends the boundaries for applicability of zeolites to challenging separations.
    Keywords: Chemistry
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  • 187
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    Benzene submits to main-group power (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-12-01
    Keywords: Chemistry
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  • 188
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    Calcium can breach benzene's defenses (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-12-01
    Keywords: Chemistry
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  • 189
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    Lighting the way to drug labeling (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-12-01
    Keywords: Chemistry
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  • 190
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    Going with the grain boundaries (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-12-01
    Keywords: Chemistry
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  • 191
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    Organocalcium-mediated nucleophilic alkylation of benzene (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-12-01
    Description: The electrophilic aromatic substitution of a C–H bond of benzene is one of the archetypal transformations of organic chemistry. In contrast, the electron-rich -system of benzene is highly resistant to reactions with electron-rich and negatively charged organic nucleophiles. Here, we report that this previously insurmountable electronic repulsion may be overcome through the use of sufficiently potent organocalcium nucleophiles. Calcium n -alkyl derivatives—synthesized by reaction of ethene, but-1-ene, and hex-1-ene with a dimeric calcium hydride—react with protio and deutero benzene at 60°C through nucleophilic substitution of an aromatic C–D/H bond. These reactions produce the n- alkyl benzenes with regeneration of the calcium hydride. Density functional theory calculations implicate an unstabilized Meisenheimer complex in the C–H activation transition state.
    Keywords: Chemistry
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  • 192
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    Selective increase in CO2 electroreduction activity at grain-boundary surface terminations (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-12-01
    Description: Altering a material’s catalytic properties requires identifying structural features that give rise to active surfaces. Grain boundaries create strained regions in polycrystalline materials by stabilizing dislocations and may provide a way to create high-energy surfaces for catalysis that are kinetically trapped. Although grain-boundary density has previously been correlated with catalytic activity for some reactions, direct evidence that grain boundaries create surfaces with enhanced activity is lacking. We used a combination of bulk electrochemical measurements and scanning electrochemical cell microscopy with submicrometer resolution to show that grain-boundary surface terminations in gold electrodes are more active than grain surfaces for electrochemical carbon dioxide (CO 2 ) reduction to carbon monoxide (CO) but not for the competing hydrogen (H 2 ) evolution reaction. The catalytic footprint of the grain boundary is commensurate with its dislocation-induced strain field, providing a strategy for broader exploitation of grain-boundary effects in heterogeneous catalysis.
    Keywords: Chemistry
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  • 193
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    Catalytic molten metals for the direct conversion of methane to hydrogen and separable carbon (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-11-17
    Description: Metals that are active catalysts for methane (Ni, Pt, Pd), when dissolved in inactive low–melting temperature metals (In, Ga, Sn, Pb), produce stable molten metal alloy catalysts for pyrolysis of methane into hydrogen and carbon. All solid catalysts previously used for this reaction have been deactivated by carbon deposition. In the molten alloy system, the insoluble carbon floats to the surface where it can be skimmed off. A 27% Ni–73% Bi alloy achieved 95% methane conversion at 1065°C in a 1.1-meter bubble column and produced pure hydrogen without CO 2 or other by-products. Calculations show that the active metals in the molten alloys are atomically dispersed and negatively charged. There is a correlation between the amount of charge on the atoms and their catalytic activity.
    Keywords: Chemistry
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  • 194
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    Designed to degrade (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-11-17
    Keywords: Chemistry
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  • 195
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    The future of plastics recycling (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-11-17
    Keywords: Chemistry
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  • 196
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    The promise of plastics from plants (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-11-17
    Keywords: Chemistry
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  • 197
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    Photoredox-catalyzed deuteration and tritiation of pharmaceutical compounds (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-12-01
    Description: Deuterium- and tritium-labeled pharmaceutical compounds are pivotal diagnostic tools in drug discovery research, providing vital information about the biological fate of drugs and drug metabolites. Herein we demonstrate that a photoredox-mediated hydrogen atom transfer protocol can efficiently and selectively install deuterium (D) and tritium (T) at α-amino sp 3 carbon-hydrogen bonds in a single step, using isotopically labeled water (D 2 O or T 2 O) as the source of hydrogen isotope. In this context, we also report a convenient synthesis of T 2 O from T 2 , providing access to high-specific-activity T 2 O. This protocol has been successfully applied to the high incorporation of deuterium and tritium in 18 drug molecules, which meet the requirements for use in ligand-binding assays and absorption, distribution, metabolism, and excretion studies.
    Keywords: Chemistry
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  • 198
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    Frozen in time (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-10-27
    Keywords: Chemistry
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  • 199
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    Femtosecond laser reshaping yields gold nanorods with ultranarrow surface plasmon resonances (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-11-03
    Description: The irradiation of gold nanorod colloids with a femtosecond laser can be tuned to induce controlled nanorod reshaping, yielding colloids with exceptionally narrow localized surface plasmon resonance bands. The process relies on a regime characterized by a gentle multishot reduction of the aspect ratio, whereas the rod shape and volume are barely affected. Successful reshaping can only occur within a narrow window of the heat dissipation rate: Low cooling rates lead to drastic morphological changes, and fast cooling has nearly no effect. Hence, a delicate balance must be achieved between irradiation fluence and surface density of the surfactant on the nanorods. This perfection process is appealing because it provides a simple, fast, reproducible, and scalable route toward gold nanorods with an optical response of exceptional quality, near the theoretical limit.
    Keywords: Chemistry
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  • 200
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    Laser-shaping nanoparticles (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2017-11-03
    Keywords: Chemistry
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