1,720,992 research outputs found
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
Anomalous solvatochromic effect. Comparison between decyl and ω-hydroxydecyl 3-substituted polythiophenes
No full textThe solvatochromic behavior of chloroform solutions of poly(3-decyl-2,5-thienylene), poly[3-(10-hydroxydecyl)-2,5-thienylene] and their copolymers was studied by the addition of the non-solvent methanol. A reversed chromic transformation was found associated with the content of the hydroxyalkyl substituent. This anomalous effect was investigated using a number of non-solvents, in particular aliphatic alcohols from methanol up to decanol. In the case of a chloroform/methanol mixture, which gives the maximum anomalous effect, the effect produced by temperature variation was also examined. An explanation based on a molecular approach was attempted
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
Analysis of UV - Vis spectral profiles of solvatochromic poly[3-(10-hydroxydecyl)-2,5-thienylene]
No full textThe paper discusses a systematic study of the UV - Vis spectral profiles of poly[3-(10-hydroxydecyl)-2,5-thienylene] during its solvatochromic transformation in different solvent/non-solvent mixtures. A simulation of the overlapped spectra of the two chromophores (A less and B more conjugated) of the polymer is made through the resolution of their pure forms by means of vibronic progressions of log_normal curves. The increment of the absolute intensity observed in the transformation has been determined and related to the increment of the transition moment; its value strongly supports the hypothesis that the solvatochromic transition consists in a doubling of A chromophores. Estimation of the average length of B chromophores has made it possible to evaluate the oscillator strength in the different solvent mixtures, the Franck-Condon factor and the Huang-Rhys parameter in relation to the intensity distribution of the vibronic structure. © 2002 Elsevier Science B.V. All rights reserved
Solvent and temperature effects on the chromic behaviour of poly[3-(10-hydroxydecyl)-2,5-thienylene]
No full textThe chromic behaviour of a soluble ω-hydroxydecyl 3-substituted polythiophene has been investigated by UV-VIS spectroscopy in different solvent/non-solvent mixtures over a wide range of low temperatures. Some interesting new effects have been observed that is the first case of a reversal of the solvatochromic transformation in substituted polythiopenes and a concentration effect in dilute pure solvent solutions. A molecular approach based on solvent-polymer interactions has been adopted to study the conformational chromic transformation of the polymer. © 2001 Elsevier Science B.V
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
Clear evidence of the sensitivity of the solvatochromic effect to side chain functionalization in 3-hexyI-substituted polythiophenes
No full textThe solvatochromic properties of 3-hexyl-substituted polythiophenes functionalized with an ester, ether or hydroxy group at the end of the alkyl side chain are reported. An extraordinarily large shift, AAmax = 99 nm, and a dramatic change of the UV/ vis spectral profile are found when the carboxylate is replaced with the hydroxy group by functionalization exchange. The solvatochromic behavior of each polymer is believed to be strictly related to the type of functional group owing to different physical interactions (solvation) between groups different in polarity and solvent molecules. A unique and common chromophoric unit for the final conformation of the 3-hexyl-substituted polythiophenes, induced by the solvatochromic effect, is also suggested. © VCH Verlagsgesellschaft mbH, 71997
New 3-alkylthiophene copolymers functionalized with a NLO chromophore
No full textThe soluble polythiophenes functionalized with a non-linear optical chromophore were prepared using copolymerization. The microstructure and the composition of the copolymers was determined through nuclear magnetic resonance spectroscopy. Two different types of solvent effects were identified. The first effect was on the conformation of the thiophene backbone and the other was on the electronic transition energy of the azobenzene unit
Chromic Effects in Poly (3-(10-hexanoyloxydecyl)-2,5-thienylene) as Precursor of ω-Hydroxydecyl-functionalized Polythiophene
No full textThe preparation of a hexanoyloxydecyl 3-substituted polythiophene and its conversion to the corresponding hydroxydecyl polymer, soluble in common organic solvents, is described. Solvatochromic and thermochromic effects of the two polymers were investigated by UV-vis spectroscopy in pure solvent and in solvent/nonsolvent solutions. A very different response was found depending on the type of functional group. The carboxylate polymer requires the synergy of both nonsolvent and low temperature for a strong chromic effect comparable to that of the hydroxy polymer to be observed. A possible explanation of this behavior is discussed. © 1998 John Wiley & Sons, Ltd
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