1,721,039 research outputs found
DETERMINATION OF ANTIMONY IN SEAWATER BY CATHODIC STRIPPING VOLTAMMETRY
No full textThe method proposes to determine subnanomolar levels of antimony in freshwater and seawater by cathodic stripping voltammetry preceded by adsorptive deposition of complexes with catechol. Dc-polarographic and cyclic voltammetric experiments indicated that the complex of catechol with Sb(III) is adsorbed prior to the scan, and is reduced to Sb(0) in a single reduction step. The optimized analytical conditions include a catechol concentration of 0.002 M and pH 6. The deposition potential is selected at -1.0 V. rather than at a more positive potential, in order to eliminate interference by uranium in seawater by including an amalgamation step in the preconcentration procedure. This is followed by a re-oxidation period of 20 s at -0.2 V to allow amalgamated Sb to become re-oxidized and form an adsorbed layer of Sb(III)-catechol complexes. The scan is then initiated in a negative direction using a linear sweep of 50 mV/s. The limit of detection lies near 0.2 nM Sb with a deposition time of 3 min, whereas the sensitivity can be increased by extending the deposition time. Interference by copper, lead and cadmium is eliminated by adding EDTA to the solution. Both Sb(III) and Sb(V) can be determined with identical sensitivity. © 1987
Single-electronic cleavage of a carbon-sulphur bond in the cathodic reduction of 2,3-bis(phenylsulphonyl)-1,4-dimethylbenzene in dimethyl sulphoxide
No full text2,3-Bis(phenylsulphonyl)-1,4-dimethylbenzene, dissolved in dimethyl sulphoxide, undergoes a one-electron single reduction wave at -1.6 V with respect to Ag-Ag+ (0.01 M). The reduction was studied by differential pulse polarography, cyclic voltammetry, and controlled-potential electrolysis. Fast chemical steps follow the initial reduction and the isolated products are 1,4-dimethyldibenzothiophene 5,5-dioxide and 1,4-dimethyl-2-(phenylsulphonyl) benzene. In some experiments small percentages of 5a,9a-dihydro-1,4- dimethyldibenzothiophene 5,5-dioxide are also obtained. The results argue in support of the electron-transfer mechanism previously proposed for the photoinduced reactions of the same substrate with sodium arenethiolates in dimethyl sulphoxide
Ottimizzazione della voltammetria di ridissoluzione anodica ad onda quadra (SWASV) per la determinazione di Cd, Pb e Cu in acqua di mare.
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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
Cross-validation, influential observations and selection of variables in chemometric studies of wines by principal components analysis
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