1,720,958 research outputs found
Removal of cupric ions from acidic sulfate solution using reticulated vitreous carbon rotating cylinder electrodes
No full textThe potentiostatic deposition of copper from acid sulfate solutions (0.50 mol dm-3 Na2SO4 at pH 2 and 298 K) was studied at four porosity grades (10, 30, 60 and 100 pores per linear inch, ppi) of reticulated vitreous carbon (RVC) rotating cylinder electrode (RCE). The rate of removal of cupric ions from a 200 cm3 volume of electrolyte was examined as a function of the grade of RVC foam, the electrode potential and the initial cupric ion concentration. For the 100 ppi material, the product of the mass transport coefficient and the electroactive area per unit volume of electrode (kmAe) was equal to 0.28 s-1 at a potential of -500 mV vs SCE for an initial cupric ion concentration of 0.85 mmol dm-3 and a constant rotation speed of 1500 rev min-1. Under the experimental conditions, an initial dissolved copper concentration of 63.5 ppm could be reduced to <0.1 ppm in approximately 60 min using a 100 ppi RVC RCE. SEM studies showed some non-uniform deposition of metal due to heterogeneous nucleation of copper together with the development of rough deposits
Electrochemical removal of metal ions from aqueous solution: a student workshop
No full textAn environmental electrochemistry workshop program on metal ion removal is described. The program was designed for undergraduate students in chemistry, chemical engineering or environmental science and teaches environmental electrochemistry through a combination of hands-on experiments, understanding of research concepts, completion of project reports and in class discussion. The students are encouraged to quantitatively describe the performance of the electrochemical cells (containing 2-D and 3-D carbon cathodes) and to consider the advantages and shortcomings of electrochemical routes to environmental treatment
The application of reticulated vitreous carbon rotating cylinder electrodes to the removal of cadmium and copper ions from solution
No full textThe removal of cadmium and cupric ions from 0.50 mol dm-3 Na2SO4 at pH 2 and 298 K was studied using a reticulated vitreous carbon (RVC) rotating cylinder electrode (RCE). The cathode was a 100 pores per linear inch porosity grade with a radius of 0.5 cm, a height of 1.2 cm and a volume of 0.94 cm[3]. The cathode was rotated a constant speed of 1500 rev min-1. A rate enhancement of approximately three times is reported for the removal of cupric ions from a chloride solution (0.05 mol dm-3 cupric ions in 0.1 mol dm-3 NaCl at pH 7) when compared with the analogous reaction in acid sulfate solutions (0.50 mol dm-3 Na2SO4 at pH 2). SEM images of the metal deposit morphology allow the morphology of the metal deposits to be characterised. The deposits showed incomplete coverage of the RVC surface and appreciable roughness developed with time due to dendritic growths
Mass transport and flow dispersion in the compartments of a modular 10 cell filter-press stack
No full textFlow dispersion, pressure drop, and averaged mass transport measurements have been made to characterize the reaction environment in an industrial scale electrochemical reactor. The 10 cell filter-press stack was operated with a relatively low mean linear velocity in the range 0.6 to 6.2 cm s–1. Flow dispersion was studied by a perturbation–response technique by electrolyte conductivity measurements at the reactor outlet. Mass transport coefficients were evaluated from the first order reaction decay of dissolved bromine (Br3–) which was anodically generated from 1 mol dm–3 NaBr (aq). Each cell consisted of two 0.72 m2 projected area electrodes separated by a cationic membrane, and each electrolyte compartment contained a high-density polyolefin turbulence promoter. The electrodes consisted of a carbon/polyethylene core with a layer of an activated carbon–poly(vinylidene difluoride) composite on each side. Comparison is made with the mass transport characteristics of a similar system that contains five bipolar cells
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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