1,721,116 research outputs found
Photochemical Organocatalytic Synthesis of Thioethers from Aryl Chlorides and Alcohols
No full textThioethers, often found in pharmaceuticals and natural compounds, typically involve metal cross-coupling reactions, high temperatures, and the use of disagreeable thiols for their synthesis. Here we present a straightforward, thiol-free organocatalytic protocol that uses mild conditions to stitch together inexpensive alcohols and aryl chlorides, yielding a diverse array of aryl alkyl thioethers. Central to this approach was the discovery that tetramethylthiourea can serve as a simple sulfur source upon intercepting photochemically generated aryl radicals. To form radicals, we used a readily available indole thiolate organocatalyst that, when excited with 405 nm light, gained a strongly reducing power, enabling the activation of typically unreactive aryl chlorides via single-electron transfer. Radical trapping by the thiourea, followed by an alcohol attack via a polar path, resulted in the formation of thioether products
A General Light‐Driven Organocatalytic Platform for the Activation of Inert Substrates
No full textDue to their strong covalent bonds and low reduction potentials, activating inert substrates is challenging. Recent advances in photoredox catalysis offered a number of solutions, each of which useful for activating specific inert bonds. Developing a general catalytic platform that can consistently target a broad range of inert substrates would be synthetically useful. Herein, we report a readily available indole thiolate organocatalyst that, upon excitation with 405 nm light, acquires a strongly reducing power. This excited-state reactivity served to activate, by single-electron reduction, strong C-F, C-Cl, and C-O bonds in both aromatic and aliphatic substrates. This catalytic platform was versatile enough to promote the reduction of generally recalcitrant electron-rich substrates (E-red<-3.0 V vs SCE), including arenes that afforded 1,4-cyclohexadienes. The protocol was also useful for the borylation and phosphorylation of inert substrates with a high functional group tolerance. Mechanistic studies identified an excited-state thiolate anion as responsible of the highly reducing reactivity
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
No full text“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
No full textWe 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
Numerical Study on the Behaviors of Localized Surface Plasmon Resonances of Au Nanoparticles
No full text本論文中，我們利用數值模擬計算金奈米柱、金奈米環、金奈米
球殼在其侷域表面電漿子共振模態時的散射、吸收截面積以及單位體
積散射、吸收截面積。其中，金奈米柱、金奈米環、金奈米球殼的模
擬結構及尺寸皆著重在現今製程容許度以及合理之波段範圍。數值結
果顯示金奈米柱的吸收截面積及散射截面積小於金奈米環及金奈米球
殼。而在單位體積散射、吸收截面積的計算中，金奈米柱則為三者中
最高，金奈米環次之，金奈米球殼則為最低者。
我們另外計算了金奈米顆粒在溶液或組織中的隨機指向分布狀態
所產生的效應，可以發現在隨機指向分布時的金奈米顆粒的侷域表面
電漿子共振強度會依其模態所對應的軸向幾何對稱性而有所衰減，另
外，藉由改變金奈米環的高度，我們有效設計一個金奈米環，使其在
隨機指向分布的狀態下，其散射、吸收截面積衰減的效應能有效的減
小。In this thesis, the numerical results of overall absorption and
scattering cross sections and cross sections per metal volume of Au nanorod
(NRO), nanoring (NRI), and nanoshell (NS), based on the commonly used
localized surface plasmon (LSP) resonance modes, with various sizes and
aspect ratios (ARs) in the reasonable ranges, which are determined by the
practical fabrication capability and application wavelength ranges, are
compared. The results show that the overall absorption and scattering cross
sections of NRO are generally smaller than those of NRI and NS. However,
in terms of cross section per Au volume, those of NRO are the highest
among the three types of Au nanoparticle (NP), followed by NRI and then
NS. We also evaluate the effects of NP random orientation distribution in a
solution or tissue in practical applications. It is found that with random
orientation, the reduction range of extinction cross section depended on the
geometry symmetry property of the electron oscillation axis in the
concerned LSP resonance mode. Then, we designed an Au NRI to make the
resonance wavelengths of its symmetric dipole mode and axial dipole mode
the same by increasing the ring height. In such an Au NRI of a large ring height, the reduction ranges of scattering and absorption cross sections were
significantly decreased
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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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