1,720,957 research outputs found
Scanning electrochemical microscopy (SECM) study of pH changes at Pt electrode surfaces in Na2SO4 solution (pH 4) under potential cycling conditions
No full textpH Changes in the vicinity of a platinum electrode immersed in a 10(-4) mol dm(-3) H2SO4+0.5 mol dm(-3) Na2SO4 solution have been probed with a scanning electrochemical microscope (SECM). Experiments were carried out in the tip substrate voltammetric mode where the faradaic current flowing to the tip is recorded while cycling the potential of the substrate. The tip current was made pH-sensitive by holding the tip potential in a region where a pH-dependent reaction occurs. Three reactions were considered: hydrogen evolution, Pt oxide formation and oxygen evolution. The results provide direct evidence of a pH decrease close to the substrate during hydrogen desorption, oxide formation and oxygen evolution. Conversely, a pH increase is observed during oxide reduction, hydrogen adsorption and hydrogen evolution. A quantitative assessment of pH changes is proposed; variations as large as one pH unit were observed
Scanning electrochemical microscopy (SECM): Study of the adsorption and desorption of hydrogen on platinum electrodes in Na2SO4 solution (pH=7)
No full textHydrogen adsorption and desorption at polycrystalline platinum electrodes in a neutral Na2SO4 solution were studied with a scanning electrochemical microscope. Experiments were carried out with the tip-substrate voltammetry mode, where the faradaic current flowing to the tip is recorded while cycling the potential of the substrate, and with the tip-substrate chronoamperometry mode, where the tip faradaic current is recorded as a function of time following the application of a potential step to the substrate. The tip current was made pH sensitive by holding the tip potential in a region where a pH- dependent reaction occurs. Proton reduction was used to monitor pH decrease, whereas platinum oxide formation was selected to detect pH increase. The results showed that a transient pH decrease as high as 2.3 pH units exists during hydrogen desorption and that a great pH increase occurs during hydrogen adsorption. The mechanisms of hydrogen adsorption and desorption were analysed by comparing tip current vs. substrate potential curves, which reflect the exchange of H+ between the adsorbed layer and the solution, with substrate current vs. substrate potential curves, which reflect the exchange of electrons between the adsorbed layer and the electrode. New conclusions have been drawn
Scanning electrochemical microscopy (SECM): study of the formation and reduction of oxides on platinum electrode surfaces in Na2SO4 solution (pH=7)
No full textThe formation and reduction of oxides on polycrystalline platinum were studied in a neutral solution with a scanning electrochemical microscope (SECM). Experiments were carried out with tip-substrate voltammetry where the faradaic current flowing to the tip is recorded while cycling the potential of the substrate, and with tip-substrate chronoamperometry where the faradaic tip current is recorded against time following the application of a potential step to the substrate. The tip current was made pH sensitive by holding the tip potential in a region where a pH dependent reaction occurs. Hydrogen evolution was used to probe pH decreases, oxygen evolution was used for the detection of pH increases and Pt oxide formation was used to detect both pH increases and decreases. The results showed that oxide formation occurs in two stages, each involving the transfer of electrons and the release of protons into the solution. During the first stage the release of H+ precedes the transfer of electrons, while in the second stage H+ release and electron transfer proceed simultaneously. Results are analysed in terms of the formation of PtOH during stage 1 and PtO during stage 2. However stage 2 behaves differently under slow potential changes and the release of protons lags behind the transfer of electrons. This is interpreted as the result of a place-exchange mechanism from PtOH to HOPt prior to stage 2, followed by the oxidation of HOPt to OPt during stage 2. Similarly, oxide reduction was found to occur in two stages, each involving the transfer of electrons and the consumption of protons. During the first stage, the consumption of H+ precedes the transfer of electrons. The results suggest that during the transfer of electrons, protons diffuse from the outer layer of the oxide (OPt) into the inner layer to form HOPt. For the second stage results are analysed in terms of a place exchange mechanism from HOPt to PtOH running in parallel with the consumption of H+, followed by a surface reduction from PtOH2+ to Pt metal
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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