1,720,971 research outputs found
Electro-oxidation of Some Phenolic Compounds by Electrogenerated O<sub>3</sub> and by Direct Electrolysis at PbO<sub>2</sub> Anodes
No full textThe oxidative degradation of phenolic compounds (4-chlorophenol and 4-nitrophenol) was studied using different electrochemical systems involving ozone formation at PbO2 anodes: (i) direct electrolysis at constant current; (ii) ex-situ use of O3 and (iii) combined use of anodically generated stream of O3/O2 fed into the cathode where H2O2 is electrogenerated by O2 reduction. We show that the latter advanced oxidation method gives the best results: it is a Fenton-type degradation of the target pollutants taking place in the cathodic compartment by reason of the highly oxidizing environment brought about by radicals that are formed mainly in the reactions of O3 with OH− and HO2
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Electrochemical oxidation of trans-3,4-dihydroxycinnamic acid at PbO2 electrodes: Direct electrolysis and ozone mediated reactions compared
No full textA comparative study of the oxidative degradation of trans-3,4-dihydroxycinnamic acid was carried out using three different methods, two of which have in common the use of electrogenerated ozone as a potential oxidant: (i) direct
electrolysis; (ii) external cell chemical reactions with O3; and (iii) a ‘cathodic oxidation’ in which an O2:O3 mixture is fed into the cathodic compartment containing the organic substrate; H2O2 produced reacts with ozone to yield radicals that bring about the demolition of the organic compound. The nature products formed by the direct electrochemical oxidation depends on potential. The degradation of dihydroxy-acid is observed only at relatively high
potentials, where radical oxygen species are formed in a high amount by the oxidation of water. At relatively lower potentials the process shows stirring dependence and leads essentially to one oxidation product which is adsorbed on the electrode. A comparative examination of the results, considering also the requested amount of ozone as a parameter, shows that the external cell and cathodic oxidation are the most efficient methods. This confirms our previous data on the oxidation of phenolic compounds, and the cathodic oxidation with ozone emerges as a promising approach in the abatement of pollutants
INFLUENCE OF THE ELECTRODE HISTORY AND EFFECTS OF THE ELECTROLYTE COMPOSITION AND TEMPERATURE ON O2 EVOLUTION AT BETA-PbO2 ANODES IN ACID MEDIA
No full textAn investigation is reported on O2 electrogeneration at b-PbO2 electrodes in HClO4, H2SO4 and CF3SO3H (TFMSA) using steady-state and impedance measurements. It is established that desorption of reaction intermediates is rate limiting in all the cases examined, and it is proposed that elementary reactions leading to oxygen evolution take place at a surface consisting of crystal line (PbO2) and hydrous zones. ...Different important factors are found to affect the electrochemical process: (i) pre-treatment of the electrode....; (ii) the temperature at which electrodeposition of PbO2 is carried out....; (iii) electrolite anions are adsorbed and inhibit desorption of reaction intermediates....; (iv) fluoride added to the electrolyte is strognly adsorbed and suppresses or modifies the structure of the hydrous layer .....; (v) a low electrolite temperature also inhibits O2 evolution ...
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
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