1,720,972 research outputs found
Air‐Stable Bis‐Cyclometallated Iridium Catalysts for Ortho‐Directed C( sp 2 )−H Borylation
No full textAbstract
We report a class of isolable bis‐cyclometallated iridium precatalysts (ImIr) and their use in regioselective
ortho
−C−H borylation of aromatic, heteroaromatic, acrylic, and aliphatic systems. The catalysts consist of two imine ligands and an acetate coordinated to an iridium (III) center. The isolable character of ImIr warrants its compatibility with high‐throughput experimentation, a prerequisite for applications in late‐stage functionalization (LSF) of complex substrates. Initial mechanistic studies point towards an inner‐sphere mechanism involving bis‐cyclometallated species shedding light on the general mechanistic understanding of
ortho
‐selective C−H borylations.Syngenta International https://doi.org/10.13039/50110001076
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
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
Digest of "Implementation Possibilities of SMD Capacitors for High Power Applications"
No full textFocus is on implementation possibilities of surfacemount device (SMD) to be used in high power applications. SMD capacitors reduce the size and dimensions of a power circuit and increase the flexibility of placement of other components. Ceramic and electrolytic capacitors are compared by means of voltage ripple, volume, labour-intensity and impedance. A 1 kW experimental setup of a quasi-Z-Source inverter (qZSI) based converter was built to compare SMD capacitor performance in the quasi-Z-source (qZS) network. Operation waveforms in both input voltage extremes showed that no significant visual differences exist in the performance of the two types of capacitors. Differences in voltage ripple were found in the electrolytic and ceramic capacitor case. This fact could be caused by high temperature on the electrolytic capacitors when the voltage ripple damping capability decreases. The heat reduction could be achieved by selecting capacitors with smaller impedance and higher permissible ripple current. If labour intensity and price are not essential, then SMD ceramic capacitors can be recommended for high power applications. Electrolytic capacitors could be implemented only in the case of paralleling them in order to reduce total impedance
Cyclometallated iridium catalysts for ortho-directed C–H borylation
No full textAu cours des deux dernières décennies, la borylation C–H a continué d'évoluer, passant des premiers exemples de réactions stœchiométriques à la synthèse de blocs de construction à l'échelle du kilogramme.1 Plus récemment, l'accent a été mis sur la borylation dirigée permettant un meilleur contrôle de la régiosélectivité dans des molécules plus complexes (Figure 1B).2,3 Généralement, cela est réalisé par une conception astucieuse du ligand introduisant des groupements chélateurs sur le ligand permettant l'interaction ligand-groupe directeur du matériau de départ (Figure 1A, II). La deuxième approche consiste à concevoir des ligands hétérobidentés qui fonctionnent par la formation d'iridacycles insaturés permettant la coordination du groupe directeur (Figure 1B-III)4-6 Cependant, la comparaison directe entre différents groupes directeurs (GD) est rarement démontrée, ce qui rend difficile la prédiction de la réactivité dans des molécules complexes. Le précurseur métallique le plus utilisé [Ir(COD)OMe]2 est également sensible à l'air et à l'humidité, ce qui complique son utilisation pour le criblage à haut débit. Nous avons cherché à résoudre ces deux problèmes en développant des catalyseurs à base d'iridium hautement sélectifs et stables à l'air. En utilisant ces nouveaux catalyseurs, nous avons criblé une multitude de GD différents et nous avons réussi à fonctionnaliser des molécules complexes de manière prévisible.C–H borylation has continued to evolve from early examples of stoichiometric reactions to a method employed for building block synthesis on a kilogram scale. However, challenges remain for its wider application. We have developed new bis-cyclometallated iridium complexes exhibiting an improved reactivity and air-stability. These complexes have been used for the ortho-directed C–H borylation of arenes, heterocycles, and acrylamides, achieving average to high yields. By combining these new catalysts with high-throughput screening, we rapidly evaluated the reactivity of different directing groups, enabling predictions for the functionalization of substrates with multiple directing groups. Mechanistic studies revealed the details how these new bis-cyclometallated complexes are activated during the reaction. Subsequently, we investigated ligand free borylation and found a wide range of compatible substrates. We then investigated miniaturization of C-H borylation reactions and successfully conducted them on micromolar scale. By integrating our findings with those from the literature, we designed a screening platform comprising eight different reaction conditions. This platform was used to screen a vast array of small molecules, as well as more complex substrates. The results revealed differences between the catalytic systems and allowed us to successfully functionalize complex molecules. These findings highlight the widespread of ligand-free borylation as well as the limitations of the current state-of-the-art methods
Operation of Resonant DC/DC Converter in the BUCK Operation Regime
No full textThe series resonant DC/DC converter with isolation transformer is investigated. When switching frequency of input inverter bridge is above the resonant one a shortening of the naturally half-waves of current through a L-C resonant circuit takes place resulting in a circulating current through the DC supply source reducing a mean value of supply current and also reducing load voltage in respect to the one at normally resonant case. The main relations for the case with strong voltage supply source are obtained and operation regimes at raised switching frequency investigated using a computer modeling. Some conclusions are made for proper calculation of parameters. It is shown that the shape of the resonant circuit current at raised frequency grows to the triangular one and that asks for proper correction of the expressions obtained for sinusoidal case. Applying qZ input link processes quite differ from observed for the strong supply – arise charging of the capacitors of the link by influence of circulating current and this phenomena impedes to reducing of the load voltage. That qZ link does not allow to create proper regulation of load parameters.
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
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