1,720,964 research outputs found
Photodegradation of lignin: The role of singlet oxygen
No full textThe photochemical irradiation of some phenoxyacetophenone derivatives in
the presence of oxygen by using visible light did not produce any
decomposition product. In the presence of singlet oxygen, sensitized by
using Bengal Rose, decomposition products were obtained. The products
obtained were similar to those obtained by direct beta-C-O cleavage on
the substrate. In this case, the observed behavior can be explained
assuming an attack of singlet oxygen on a phenoxy part of the molecule
Theoretical study of photoinduced ring-isomerization in the 1,2,4-oxadiazole series
No full textA theoretical study of photoinduced ring-isomerization of 3-amino-5-methyl- and 3-amino-5-phenyl-1,2,4-oxadiazoles is reported. The results well agree with the reported experimental data: in particular, they explain the ring-photoisomerization into the corresponding 2-amino-1,3,4-oxadiazoles through a ring contraction-ring expansion route; moreover, the occurrence of competing pathways involving both the ring contraction and the internal cyclization–isomerization mechanism during irradiation of the 5-alkyl substituted substrates in the presence of a base has been also substantiated
SINGLET OXYGEN IN THE PHOTODEGRADATION OF LIGNIN MODELS
No full textThe photochemical oxidation of lignin models in the presence of singlet
oxygen nas studied. The treatment of the non-phenolic beta-O-4 aryl
ether derivatives 6, 7, and 8 in the presence of both oxygen and Rose
Bengal gave products deming from a formal beta-C-O cleavage formation.
By this way the derivatives 12. 13, and 15 were obtained, The
photochemical oxidation of the phenolic beta-O-4 aryl ehter 9 gave the
same type of product confirming that, in this case, the presence of the
carbonyl group is not indispensable to have the cleavage reaction. The
use of the model compound 10 showed that. When the phenoxy part of the
molecule shows a lower reactivity towards singlet oxygen, the oxidation
of the phenol moiety to hydroquinone call occur. The photochemical
behaviour of these model compounds can be rationalised from a reaction
of singlet oxygen with the phenoxy part of the molecule. (C) 1997
Published by Elsevier Science Ltd
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
Unusual (4+2)-cycloaddition reaction between electron poor 1,2-diaza-1,3-dienes and electron poor alkenes: useful entry to novel tetrahydropyridazines
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
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