1,720,972 research outputs found
Cobaltaelectro‐Catalyzed C–H Activation for Central and Axial Double Enantio‐Induction
No full textIn recent years, enantioselective electrocatalysis has surfaced as an increasingly‐effective platform for sustainable molecular synthesis. Despite indisputable progress, strategies that allow the control of two distinct stereogenic elements with high selectivity remain elusive. In contrast, we, herein, describe electrochemical cobalt‐catalyzed C–H activations that enable the installation of chiral stereogenic centers along with a chiral axis with high levels of enantio‐ and diastereoselectivities. The developed electrocatalysis strategy allowed for C–H/N–H activations/annulations with cyclic and non‐cyclic alkenes providing expedient access to various central as well as atropo‐chiral dihydroisoquinolinones paired to the valuable hydrogen evolution reaction. Studies on the atropo‐stability of the obtained compounds demonstrated that the exceedingly mild conditions ensured by the electrocatalytic process were key for the achieved high stereoselectivities
Cobaltaelektro‐katalysierte C−H‐Aktivierung für zentrale und axiale doppelte Enantioinduktion
No full textAbstract In den letzten Jahren hat sich die enantioselektive Elektrokatalyse zunehmend als eine effektive Methode für die nachhaltige molekulare Synthese herausgestellt. Trotz unbestreitbarer Fortschritte bleiben Strategien zur Kontrolle über zwei unterschiedliche stereogene Elemente mit hoher Selektivität schwer fassbar. Im Gegensatz dazu beschreiben wir hier elektrochemische Cobalt‐katalysierte C−H‐Aktivierungen, welche die Installation chiraler stereogener Zentren zusammen mit einer chiralen Achse mit hoher Enantio‐ und Diastereoselektivität ermöglichen. Die entwickelte elektrokatalytische Strategie erlaubte C−H/N−H‐Aktivierungen/Anellierungen mit cyclischen und acyclischen Alkenen und gewährte einen direkten Zugang zu vielseitigen sowohl zentralen als auch atropo‐chiralen Dihydroisochinolinonen gepaart mit der wertvollen Wasserstoffbildungsreaktion. Studien zur Atropo‐Stabilität der erhaltenen Verbindungen demonstrierten, dass die äußerst milden Bedingungen, gewährleistet durch den elektrokatalytischen Prozess, entscheidend für die hohen erzielten Stereoselektivitäten waren.Deutsche Forschungsgemeinschaft https://doi.org/10.13039/501100001659HORIZON EUROPE European Research Council https://doi.org/10.13039/100019180Werner Siemens-Stiftung https://doi.org/10.13039/100016964Fonds der Chemischen Industrie https://doi.org/10.13039/10001899
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Structural evolution of Lithium Manganate cathodes during charge/discharge cycles
No full textSurface Nanoparticles modifications have been observed on alumina coated LiMn2O4(LMO) cathodes with respect to the uncoated nanoparticles cathodes during the first charge/discharge cycles. During discharging (lithiation), at low voltages the disproportionation reaction is favoured, scanning electron microscopy has revealed the presence of holes formation in LMO nanoparticles while similar effects were not visible in other phases of the voltammogram. We put in relation this observation with the nonuniform Al2O3coating on the nanoparticles used for the electrode where the channel of ions transport is activated, contrarily to uncoated nanoparticles, showing a deep reaction of the carbon-based electrolyte with the oxide, on a larger extent than usually considered for the cathode electrolyte interphase. The non- thermodynamic proton transfer process at the basis of the present effect was recently predicted by Choi et at [1] by first-principle density functional calculations. The x-ray absorption analysis (Mn L2,3, F and O K-edge) was also able to describe the chemistry at the interphase formed at the high voltages when strong fluorinated by-products are differently observed along with the vertical profile at variance with the coatings. Al2O3 coating results fully effective for stopping the strong reduction processes occurring during charging at a high voltage of the battery, when O-Mn couple react with organic species, making Mn capture and electrolyte reaction with the oxide surface possible, and electrolyte interphase and Mn dissolution might occur. We followed the transition by Raman scattering to detect the signatures of the transformation, observing a reversible modification of the surface character of the nanoparticle from spinel to a layered. In conjunction with soft X-ray spectroscopy study is particularly suitable to detect modification of the active material at the frontier of the nanoparticle, where the interphase between the electrolyte and active nanoparticle is formed, during phases of oxidation/reduction that are crucial for the cyclability and safety of the whole battery
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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