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  • American Association for the Advancement of Science (AAAS)  (130)
  • Institute of Physics (IOP)  (58)
  • International Union of Crystallography (IUC)  (34)
  • 1
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    Atomic structure of sensitive battery materials and interfaces revealed by cryo-electron microscopy (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-10-27
    Description: Whereas standard transmission electron microscopy studies are unable to preserve the native state of chemically reactive and beam-sensitive battery materials after operation, such materials remain pristine at cryogenic conditions. It is then possible to atomically resolve individual lithium metal atoms and their interface with the solid electrolyte interphase (SEI). We observe that dendrites in carbonate-based electrolytes grow along the 〈111〉 (preferred), 〈110〉, or 〈211〉 directions as faceted, single-crystalline nanowires. These growth directions can change at kinks with no observable crystallographic defect. Furthermore, we reveal distinct SEI nanostructures formed in different electrolytes.
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    CRISPR-Cas9 delivery to hard-to-transfect cells via membrane deformation (2015)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2015-08-16
    Description: The CRISPR (clustered regularly interspaced short palindromic repeats)–Cas (CRISPR-associated) nuclease system represents an efficient tool for genome editing and gene function analysis. It consists of two components: single-guide RNA (sgRNA) and the enzyme Cas9. Typical sgRNA and Cas9 intracellular delivery techniques are limited by their reliance on cell type and exogenous materials as well as their toxic effects on cells (for example, electroporation). We introduce and optimize a microfluidic membrane deformation method to deliver sgRNA and Cas9 into different cell types and achieve successful genome editing. This approach uses rapid cell mechanical deformation to generate transient membrane holes to enable delivery of biomaterials in the medium. We achieved high delivery efficiency of different macromolecules into different cell types, including hard-to-transfect lymphoma cells and embryonic stem cells, while maintaining high cell viability. With the advantages of broad applicability across different cell types, particularly hard-to-transfect cells, and flexibility of application, this method could potentially enable new avenues of biomedical research and gene targeting therapy such as mutation correction of disease genes through combination of the CRISPR-Cas9–mediated knockin system.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
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    Tailoring pathway modularity in the biosynthesis of erythromycin analogs heterologously engineered in E. coli (2015)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2015-05-30
    Description: Type I modular polyketide synthases are responsible for potent therapeutic compounds that include avermectin (antihelinthic), rapamycin (immunosuppressant), pikromycin (antibiotic), and erythromycin (antibiotic). However, compound access and biosynthetic manipulation are often complicated by properties of native production organisms, prompting an approach (termed heterologous biosynthesis) illustrated in this study through the reconstitution of the erythromycin pathway through Escherichia coli . Using this heterologous system, 16 tailoring pathways were introduced, systematically producing eight chiral pairs of deoxysugar substrates. Successful analog formation for each new pathway emphasizes the remarkable flexibility of downstream enzymes to accommodate molecular variation. Furthermore, analogs resulting from three of the pathways demonstrated bioactivity against an erythromycin-resistant Bacillus subtilis strain. The approach and results support a platform for continued molecular diversification of the tailoring components of this and other complex natural product pathways in a manner that mirrors the modular nature of the upstream megasynthases responsible for aglycone polyketide formation.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Microstructural evolution associated with martensitic transformation in Ni-Mn-Ga alloy (2015)
    Institute of Physics (IOP)
    Details
    Publication Date: 2015-04-26
    Description: Based on the spatially resolved electron backscatter diffraction technique, the microstructural evolution accompanying the martensitic transformation (austenite to 7M martensite) and the intermartensitic transformation (7M martensite to NM martensite) was studied on a polycrystalline Ni53Mn22Ga25 alloy. Results show that the 7M martensite plate groups transformed from initial austenite have a diamond-shape with four twin-related variants. The 7M to NM intermartensitic transformation was accompanied by the thickening of martensite plates. With the experimental results, the characteristics of microstructural evolution during the phase transformations were further analyzed.
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Institute of Physics (IOP)
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  • 5
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    Thermodynamically stabilized {beta}-CsPbI3-based perovskite solar cells with efficiencies 〉18% (2019)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2019
    Description: 〈p〉Although β-CsPbI〈sub〉3〈/sub〉 has a bandgap favorable for application in tandem solar cells, depositing and stabilizing β-CsPbI〈sub〉3〈/sub〉 experimentally has remained a challenge. We obtained highly crystalline β-CsPbI〈sub〉3〈/sub〉 films with an extended spectral response and enhanced phase stability. Synchrotron-based x-ray scattering revealed the presence of highly oriented β-CsPbI〈sub〉3〈/sub〉 grains, and sensitive elemental analyses—including inductively coupled plasma mass spectrometry and time-of-flight secondary ion mass spectrometry—confirmed their all-inorganic composition. We further mitigated the effects of cracks and pinholes in the perovskite layer by surface treating with choline iodide, which increased the charge-carrier lifetime and improved the energy-level alignment between the β-CsPbI〈sub〉3〈/sub〉 absorber layer and carrier-selective contacts. The perovskite solar cells made from the treated material have highly reproducible and stable efficiencies reaching 18.4% under 45 ± 5°C ambient conditions.〈/p〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 6
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    Exceptional oxygen evolution reactivities on CaCoO3 and SrCoO3 (2019)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2019
    Description: 〈p〉We investigated the roles of covalent bonding, separation of surface oxygen, and electrolyte pH on the oxygen evolution reaction (OER) on transition metal oxides by comparing catalytic onset potentials and activities of CaCoO〈sub〉3〈/sub〉 and SrCoO〈sub〉3〈/sub〉. Both cubic, metallic perovskites have similar Co〈sup〉IV〈/sup〉 intermediate spin states and onset potentials, but a substantially smaller lattice parameter and shorter surface oxygen separation make CaCoO〈sub〉3〈/sub〉 a more stable catalyst with increased OER activity. The onset potentials are similar, occurring where H〈sup〉+〈/sup〉 is removed from surface -OH〈sup〉–〈/sup〉, but two competing surface reactions determine the catalytic activity. In one, the surface -O〈sup〉–〈/sup〉 is attacked by electrolyte OH〈sup〉–〈/sup〉 to form the surface -OOH〈sup〉–〈/sup〉; in the other, two -O〈sup〉–〈/sup〉 form a surface peroxide ion and an oxygen vacancy with electrolyte OH〈sup〉–〈/sup〉 attacking the oxygen vacancy. The second pathway can be faster if the surface oxygen separation is smaller.〈/p〉
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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  • 7
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    Discovery of log-periodic oscillations in ultraquantum topological materials (2018)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2018
    Description: 〈p〉Quantum oscillations are usually the manifestation of the underlying physical nature in condensed matter systems. Here, we report a new type of log-periodic quantum oscillations in ultraquantum three-dimensional topological materials. Beyond the quantum limit (QL), we observe the log-periodic oscillations involving up to five oscillating cycles (five peaks and five dips) on the magnetoresistance of high-quality single-crystal ZrTe〈sub〉5〈/sub〉, virtually showing the clearest feature of discrete scale invariance (DSI). Further, theoretical analyses show that the two-body quasi-bound states can be responsible for the DSI feature. Our work provides a new perspective on the ground state of topological materials beyond the QL.〈/p〉
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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  • 8
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    Intermolecular dialkylation of alkenes with two distinct C(sp3)boxhH bonds enabled by synergistic photoredox catalysis and iron catalysis (2019)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2019
    Description: 〈p〉The functionalization of unactivated C(sp〈sup〉3〈/sup〉)H bonds represents one of the most powerful and most atom-economical tools for the formation of new carbon-based chemical bonds in synthesis. Although cross-dehydrogenative coupling reactions of two distinct CH bonds for the formation of carbon-carbon bonds have been well investigated, controlled functionalizations of two or more different C(sp〈sup〉3〈/sup〉)H bonds across a functional group or a molecule (e.g., an alkene or alkyne) in a single reaction remain challenging. Here, we present a three-component dialkylation of alkenes with common alkanes and 1,3-dicarbonyl compounds via synergistic photoredox catalysis and iron catalysis for the synthesis of two functionalized 1,3-dicarbonyl compounds. Mechanistic studies suggest that the photoredox catalysis serves as a promotion system to allow the dialkylation to proceed under mild conditions by reducing the oxidation and reduction potentials of the iron intermediates and the reaction partners.〈/p〉
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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  • 9
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    Cell type-dependent bimodal p53 activation engenders a dynamic mechanism of chemoresistance (2018)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2018
    Description: 〈p〉Studies of drug resistance mostly characterize genetic mutation, and we know much less about phenotypic mechanisms of drug resistance, especially at a quantitative level. p53 is an important mediator of cellular response to chemotherapy, but even p53 wild-type cells vary in drug sensitivity for unclear reasons. Here, we elucidated a new resistance mechanism to a DNA-damaging chemotherapeutic through bimodal modulation of p53 activation dynamics. By combining single-cell imaging with computational modeling, we characterized a four-component regulatory module, which generates bimodal p53 dynamics through coupled feed-forward and feedback, and found that the inhibitory strength between ATM and Mdm2 determined the differential modular output between drug-sensitive and drug-resistant cancer cell lines. We further showed that the combinatorial inhibition of Mdm2 and Wip1 was an effective strategy to alter p53 dynamics in resistant cancer cells and sensitize their apoptotic response. Our results point to p53 pulsing as a potentially druggable mechanism that mediates chemoresistance.〈/p〉
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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  • 10
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    Subunit cell-level measurement of polarization in an individual polar vortex (2019)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2019
    Description: 〈p〉Recently, several captivating topological structures of electric dipole moments (e.g., vortex, flux closure) have been reported in ferroelectrics with reduced size/dimensions. However, accurate polarization distribution of these topological ferroelectric structures has never been experimentally obtained. We precisely measure the polarization distribution of an individual ferroelectric vortex in PbTiO〈sub〉3〈/sub〉/SrTiO〈sub〉3〈/sub〉 superlattices at the subunit cell level by using the atomically resolved integrated differential phase contrast imaging in an aberration-corrected scanning transmission electron microscope. We find, in vortices, that out-of-plane polarization is larger than in-plane polarization, and that downward polarization is larger than upward polarization. The polarization magnitude is closely related to tetragonality. Moreover, the contribution of the PbO bond to total polarization is highly inhomogeneous in vortices. Our precise measurement at the subunit cell scale provides a sound foundation for mechanistic understanding of the structure and properties of a ferroelectric vortex and lattice-charge coupling phenomena in these topological ferroelectric structures.〈/p〉
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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