1,720,963 research outputs found
The Fundamental and Underrated Role of the Base Electrolyte in the Polymerization Mechanism. The Resorcinol Case Study
Full text linkThe Kane-Maguire polymerization mechanism is disassembled at a molecular level by using DFT-based quantum mechanical calculations. Resorcinol electropolymerization is selected as a case study. Stationary points (transition states and intermediate species) leading to the formation of the dimer are found on the potential energy surface (PES), and elementary reactions involved in the dimer formation are characterized. The latter allow to further propagate the polymerization chain reaction, when applied recursively. In this paper, the fundamental role of the sulfate anion (a typical base electrolyte) is addressed. Investigation of the PES in terms of both stationary-state properties and of ab initio molecular dynamics results (dynamic reaction coordinate) allows the appreciation in detail of the critical role of the base electrolyte anion in making the proton dissociation from the initial radical ion, a feasible (downhill in energy) process
Dissociation Dynamics of Asymmetric Alkynyl(Aryl)Iodonium Radicals. An ab-initio DRC Approach to Predict the Surface Functionalization Selectivity.
No full textThe dissociation process of neutral open-shell [4-F-(C(6)H(4))-I-C C-(CH(2))(4)-Cl] and [4-NO(2)-(C(6)H(4))-I-C C-(CH(2))(4)-Cl] asymmetric iodonium radicals was studied theoretically Vertical electron affinities and DRC (dynamic reaction coordinate) results were obtained and compared with experimental evidence. In particular, the fluorine and nitro substituent groups were selected because of (i) their opposite electron-withdrawing/electron-donating effects and (ii) experimental evidence that the grafting ability, in terms of alkynyl/aryl grafting ratio, increases with decreasing electron-withdrawing nature of the para-position substituent on the phenyl ring. DRC results show that the dissociation dynamics of the iodine-alkynyl carbon bond, for the nitro-substituted iodonium, occurs on a longer time scale than that of the fluorine-substituted iodonium. This finding is in agreement with the overall experimental results
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
Charge Transfer in Molecular Cocrystals: A Plane Wave vs Localized-Orbital View─Structural Information Obtained from Calculated Raman and IR Phonons
Full text linkThis article aims at laying the foundation for the development of electronic structure-property relationships in the field of charge-transfer (CT) organic semiconductors by studying the low-frequency phonon response of donor-acceptor (DA) compounds. In this article, it is shown and discussed how and why phonon frequencies and their delocalization depend on the interplay between single-molecule properties and crystal structures. These results are obtained by combining results from state-of-the-art quantum-mechanical calculations, carried out within both localized orbitals and a plane wave paradigm, with simple classical models. CT compounds obtained from perylene (Pery) as the donor and FnTCNQ (n = 0, 4) as the acceptors are considered
Electrochemical growth of PAH-dendrimers supramolecular films. An integrated experimental-theoretical approach
No full textThe electrochemical oxidation of a polyphenylene-based dendrimer containing 96 sp2 carbon atoms (PPD) allows
obtaining a more extended conjugated carbon framework, polymer PPD (pPPD), starting from the parent fused-
benzene-based PPD. The structure and electronic properties of the polymeric thin film obtained by electrochemical
oxidation have been characterized by Near Edge X-Ray Absorption Fine Structure (NEXAFS) spectroscopy.
Structural properties of the thin film formed upon electrochemical oxidation of PPD, are characterized
by Matrix-Assisted Laser Desorption/Ionization (MALDI-TOF) and Gel-Permeation Chromatography (GPC)
measurements. The degree of order of the layers as well as the virtual, and occupied, electronic states are
addressed and exploited to obtain information on conjugation and oligomer size within the polymeric pPPD film.
The experimental results are compared with DFT, B3LYP/6–31G(d), calculations. The overall results suggest that
the thin film formed on the electrode surface is mainly formed by PPD dimer and trimer upon electrochemical
oxidation
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