1,720,956 research outputs found
Ab initio determination of the geometric structure of oligo-2-thienyl ketones
No full textConformations, structural parameters and charge distributions of 2-acetylthiofene (THCO), di-2-thienyl ketone (2THCO) and higher oligomers (3THCO and 4THCO) have been determined by ab initio calculations at the HF/6-31G** level of theory. Electron correlation effects have been investigated at MP2/6-31G** level for THCO and at the MP2/6-311G**//HF/6-31G** level for 2THCO. The most probable conformation of oligo-2-thienylene ketones is rod-like, with a ring deviation from the main molecular plane of about 20° and with prevailing S,O-cis orientation
Conformation and electronic structure of 3-methylchalcogenothiophenes
No full textThe conformation and the electronic structure of 3-methoxythiophene (THOME) and 3-methylthiothiophene (THSME) have been determined by means of a multidisciplinary approach based on ultraviolet photoelectron and electron transmission spectroscopies and fully optimized ab initio 6-31G** and MP2/6-31G** calculations. The plots of the relative energy as a function of the X-Me torsion angle of THXME show that i) for both compounds the s-cis rotamer is an energy minimum lower in energy than the s-trans conformer; ii) the s-trans rotamer is a local minimum for THOME but a maximum for THSME; iii) the gauche conformer is calculated to be the lowest minimum for THSME but close to a maximum for THOME. These findings are rationalized in terms of a delicate balance of several effects such as the steric hindrance between the methyl group and the faced C-H group of the ring, the π*ring ← Xlp charge transfer interaction, the repulsion between the charge in the C2=C3 double bond and the in-plane heteroatom lone pair, the πring - Xlp interaction and C2-CMe electrostatic interaction. The possibility that these compounds can give rise to highly conducting polymers is briefly discussed
Ab initio and electron spectroscopy study of carbonyl derivatives
No full textThe bands present in the low ionisation energy region (Ei[less-than-or-eq] 12 eV) of the He I photoelectron spectra, and the low energy resonances of the electron transmission spectra of some substituted carbonyls XC(O)R (X = Et2N, alkyl, EtS and EtO; R = Me and CH2SR) have been assigned to the corresponding molecular orbitals by comparison with the assignments reported for simple related molecules. Fully optimized 3-21G ab initio calculations reproduce the assignment of the spectra and available geometric parameters and therefore have been used to determine the electronic charge distribution among the various atoms and groups in the studied compounds. A combined analysis of the theoretical and experimental data provides a detailed understanding of the electronic interaction among the X, CO and R groups in the molecules studied
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
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
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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