1,720,989 research outputs found
An insoluble polymer-bound phosphoramidite for the copper-catalysed enantioselective 1,4-addition of ZnEt2 to 2-cyclohexenone
Full text linkThe preparation of a chiral phosphoramidite ligand anchored to a Merrifield resin has been studied and its use in the copper-catalysed heterogeneous enantioselective conjugate addition of ZnEt2 to 2-cyclohexenone investigated. The insoluble polymer bound ligand could be recovered quantitatively by filtration, affording e.e. values in the range 65–84% in the course of successive recycle runs
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Excited state properties of organic sensitizers for DSSC evaluated at the PCM/TD-DFT level
No full textA Waste-Minimized Approach to Cassar-Heck Reaction Based on POLITAG-Pd0 Heterogeneous Catalyst and Recoverable Acetonitrile Azeotrope
No full textThree different Pd0-based heterogeneous catalysts were developed and tested in the Cassar–Heck reaction (i. e., copper-free Sonogashira reaction) aiming at the definition of a waste minimized protocol. The cross-linked polymeric supports used in this investigation were designed to be adequate for different reaction media and were decorated with different pincer-type ionic ligands having the role of stabilizing the formation and dimension of palladium nanoparticles. Among the ionic tags tested, bis-imidazolium showed the best performances in terms of efficiency and durability of the metal catalytic system. Eventually, aqueous acetonitrile azeotrope was selected as the reaction medium as it allowed the best catalytic efficiency combined with easy recovery and reuse. Finally, the synergy between the selected catalyst and reaction medium allowed to obtain highly satisfactory isolated yields of a variety of substrates while using a low amount of metal catalyst. The high performance of the designed POLymeric Ionic TAG (POLITAG)-Pd0, along with its good selectivity achieved in a copper-free process, also led to a simplified purification procedure allowing the minimization of the waste generated as also proven by the very low E-factor values (1.4–5) associated
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
Sustainable Pd-Catalyzed Direct Arylation of Thienyl Derivatives with (Hetero)aromatic Bromides under Air in Deep Eutectic Solvents
Full text linkAn optimized protocol for the Pd-catalyzed direct arylation of 3,4-ethylenedioxythiophene (EDOT) and other substituted thiophenes with (hetero)aromatic bromides in a deep eutectic solvent made of a mixture of choline chloride/glycerol (1:2) is presented. The coupling reactions have been successfully run under air, in nonanhydrous conditions, using PdCl2 as a palladium source, with a catalyst loading as low as 1 mol %. The adjustment of each reaction component allowed finding robust conditions for the introduction of both electron-poor and electron-rich (hetero)aryl bromides with moderate-to-high yields. The sustainability of the protocol was established through calculations of green metrics, such as Eco-scale and E-factor, and compared with the literature, when possible. Remarkably, such procedure can be successfully applied for the simple preparation of conjugated organic compounds with potential applications in optoelectronics, as we have shown, by obtaining two molecules previously reported as a hole transport material for perovskite solar cells and the final intermediate of a photosensitizer for dye-sensitized solar cells
Excited state geometries and vertical emission energies of solvated dyes for DSSC: a PCM/TD-DFT benchmark study
No full textThe ability of Time-Dependent Density Functional Theory (TD-DFT) to provide excited state geometries and reproduce emission energies of organic D-π-A dyes designed for DSSC applications is evaluated. The performance of six functionals (CAM-B3LYP, MPW1K, ωB97X-D, LC-BLYP, LC-ωPBE, and M06-HF) in combination with three basis sets (cc-pVDZ, 6-31+G(d,p), and 6-311+G(2d,p)) has been analyzed. Solvent effects have been taken into account by means of a Polarizable Continuum Model in both LR and SS formalisms. Our LR-PCM/TD-DFT results show that accurate emission energies are obtained only when solvent effects are included in the computation of excited state geometries and when a range separated hybrid functional is used. Vertical emission energies are reproduced with a mean absolute error of at most 0.2 eV. The accuracy is further improved using the SS-PCM formalism. © 2014 American Chemical Society
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