1,721,272 research outputs found
Decarboxylation of carbonyloxy radicals: a density functional study
No full textWe present a thorough theoretical investigation on the decarboxylation process of carbonyloxy radicals of general structure RC(O)O which play a key role in the decomposition of organic peroxides that are widely used as initiators in free-radical polymerizations. The effect of variation in the molecular structure (R = PhO, PhCH2 and NphO) (Nph = naphthyl) is studied systematically. Geometries, energies, and vibrational frequencies of the carbonyloxy radicals, the dissociation products, and the first-order saddle points pertinent to decarboxylation have been calculated employing density functional theory. The results are compared with recent data for the benzoyloxy radical (R = Ph). Insertion of an oxygen atom or a CH2 group between the chromophore and the CO2 moiety yields a significant reduction in the stability of the carbonyloxy radicals. Despite the structural similarity of the three compounds, the reaction coordinates are markedly different. The structural effects are discussed in terms of changes in thermochemistry, barrier heights and transition modes. The calculated data serve as essential input parameters for statistical unimolecular rate theory calculations and are crucial for the modeling of recent femtosecond pump/probe spectroscopy experiments on the carbonyloxy radical decomposition mechanism
Decomposition of tertiary alkoxy radicals
No full textRate coefficients of beta-scission reactions in tertiary alkoxy radicals, R(CH3)(2)CO (R = methyl, ethyl, tert-butyl and neo-pentyl) have been estimated via density functional theory (DFT) calculations in conjunction with statistical unimolecular rate theory. For tert-butoxy, results obtained by employing different basis sets are compared with experimental values, indicating that UB3LYP/6-31G(d,p) excellently predicts kinetic data. Rate coefficients for inter- and intramolecular hydrogen abstraction are also reported. Depending on R, the P-scission rate may vary by orders of magnitude. The predicted temperature dependence of the alcohol-to-ketone product ratios for alkoxy radical decomposition in a hydrocarbon environment is in remarkably close agreement with the corresponding ratios measured on the product mixtures from decomposition of tert-butyl and tert-amyl peroxyacetates in solution of n-heptane
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
Experimental and theoretical studies into mechanisms of ultrafast UV-induced decarboxylation in organic peroxide decomposition.
No full textExperimental and theoretical studies into mechanisms of ultrafast UV-induced decarboxylation in organic peroxide decomposition.
No full textDispelling 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
- …
