1,720,964 research outputs found
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
Electrochemical incineration of glucose as a model organic substrate. Part 1: role of the electrode material
No full textIn the frame of study on the electrochemical incineration of organic pollutants, the reactivity of glucose toward mineralization was studied under different electrolysis conditions. The process was followed at Pt, SnO2-Pt composite, and PbO2 electrodes, at different current densities and temperatures. In all cases, the supporting electrolyte was 2N H2SO4. Chemical oxygen demand and total organic carbon content of the solutions and amount of oxygen evolved were measured as functions of the electrolysis time.
From these data, an initial electrochemical oxidation index (EOI) was evaluated following standard methods. Larger values for this
parameter were found at the PbO2 electrodes under all conditions of current density and temperature. At Pt and SnO2-Pt, in the
room-temperature range, the efficiency of the electrochemical mineralization of glucose was low, particularly at longer electrolysis times. The situation improved by increasing the temperature to 56°C. The extent of mineralization was quite low at SnO2-Pt electrodes under all conditions explored. At Pt and SnO2-Pt electrodes, the main oxidation intermediate was glucaric acid, apparently quite stable toward further attack at these electrodes. In the case of PbO2 electrodes, smaller concentrations of intermediates were detected. Gluconic and 2-ketogluconic acids were also present in amounts comparable with that of glucaric acid. Study of the initial electrochemical oxidation index for gluconic acid and glucaric acid was also carried out, confirming the stability of the latter at Pt and SnO2-Pt electrodes. At PbO2, on the contrary, it was found to be even more reactive than glucose. An explanation for the reactivity of carboxylic acids toward mineralization at the PbO2 electrodes is proposed
Electrochemical incineration of glucose as a model organic substrate II. Role of active chlorine mediation
No full textThe electrochemical incineration of glucose mediated by active chlorine in alkaline media has been studied under different electrolysis conditions. For the sake of comparison, the electrolysis has been carried out in the presence of 1 M Na2SO4 + 0.01 M NaOH at Pt, SnO2-Pt composite electrodes and PbO2 electrodes in the absence of sodium chloride. At the first two electrode materials, only partial oxidation could be achieved and complete mineralization was observed only at PbO2 electrode. While the other parameters remain constant, addition of NaCl to the solution causes a sharp increase of the reactivity of glucose and its oxidation intermediates, toward the electrochemical incineration. At a NaCl concentration as low as 1 g dm-3 , the mediation of the incineration process by active chlorine is already significant. A maximum is achieved at [NaCl] = 5 g dm-3 (in 0.01 M NaOH). At this sodium chloride concentration, the chemical oxygen demand of glucose solutions has been found to decrease faster, the lower the solution temperature and the higher the current density. This acceleration of the mineralization is accompanied by an increase of faradaic efficiency
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
Electrochemical incineration of glucose
No full textThe possibility of eliminating organic pollutants from industrial wastes, by anodic mineralization or “incineration” has been discussed in recent years (1-3). The mineralization process takes place as an extreme case of anodic oxidation, together with the oxygen evolution reaction. The formation of adsorbed hydroxyl radicals is a necessary condition for the oxidative attack of the organic substrate to take place and also for the oxygen evolution (3). At high oxygen overvoltage anodes, like PbO2, Sb- or F-doped SnO2 , typically the anodic mineralization of organic substrates takes place with better faradaic yields. Both electrodes have however short service life.
Accordingly, it may be of interest to investigate the possibility to use stable anodes, like galvanic Pt, IrO2-based DSA’s®, improving the faradaic yield of the electrochemical mineralization. This aim may be achieved using inorganic mediators of the oxidation of the organic substrate. In this respect active chlorine may be of particular interest, and has been discussed for the case of electrochemical mineralization of phenol (4). An important drawback of electrolytic treatments in chloride solutions may be the formation of chlorinated species. In such cases an electrochemical treatment would result in an increase in toxicity of the wastewater and, possibly, also in stability of the residual chlorinated substrates. Accordingly, it is important to study the mechanism of oxidative degradation of different organic molecules, in different chloride-containing media, and at different anodes, to find optimal conditions for the electrochemical treatment, ensuring good faradaic yields for mineralization process, avoiding the formation of chlorocompounds.
In the present work glucose has been chosen as a model substrate, of interest considering that saccharides are important components in food industry effluents, like for instance olive-mill wastewaters. Experiments on electro-oxidation of glucose have been carried out at Ti/Pt and Ti/PbO2 elec-trodes, in absence and in presence of NaCl. In the presence of NaCl, at Ti/Pt electrodes complete mineralization of glucose could be achieved at current densities > of 500 A m-2. At Ti-PbO2 electrodes a substantially similar situation was found. At Ti/Pt electrodes, in the absence of NaCl, the abatement of COD was very small even after long electrolysis times. At PbO2, on the contrary, complete mineralization was achieved, even without the active chlorine mediator.
References
1) S. Stucki, R. Kötz, B. Carcer, W. Suter, J. Appl. Electrochem. 21, 99 (1991)
2) Ch.Comninellis and E. Plattner, Chimia 42, 250 (1988)
3) Ch. Comninellis, Electrochim. Acta 39, 1863 (1994)
4) Ch. Comninellis and A. Nerini, J. Appl. Electrochem. 25, 23 (1995
Anodic mineralization of organic substrates in chloride-containing aqueous media
No full textThe possibility of eliminating organic pollutants from industrial wastes, by anodic mineralization or “incineration” has been discussed in recent years [1-4]. The electrochemical wastewater treatment may be of particular interest when the effluent contains biorefractory organics and/or high amounts of organic carbon and requires some pre-treatment to allow further biological purification. The mineralization process takes place as an extreme case of anodic oxidation, together with the oxygen evolution reaction. The formation of adsorbed hydroxyl radicals is a necessary condition for the oxidative attack of the organic substrate to take place and also for the oxygen evolution [4]. At high oxygen overvoltage anodes, like PbO2, Sb- or F-doped SnO2 , typically the anodic mineralization of organic substrates takes place with better faradaic yields. In the case of lead dioxide, however, problems of service life and of release of lead ions in the treated effluent, may represent serious drawbacks in a practical application. For tin dioxide-based electrodes, the short service life is again an inconvenience.
While the improvement of these anodes is under investigation in several research groups, it may be of interest to investigate the possibility to use stable anodes, like galvanic platinum, iridium dioxide-based DSA’s®, improving the faradaic yield of the electrochemical mineralization. This aim may be achieved using inorganic mediators of the oxidation of the organic substrate. In this respect active chlorine may be of particular interest, and has been discussed for the case of electrochemical mineralization of phenol [5,6]. In the presence of chlorides the electrochemical treatment can be carried out at much lower potentials, compared with those required for the non-mediated (direct) anodic oxidation. Galvanic Pt and other DSA’s materials based on iridium and ruthenium oxides, can be used, the optimal choice depending on pH and other compositional features of the effluent. An important drawback of electrolytic treatments in chloride solutions may be the formation of chloroderivatives of the organic substrates and of their oxidation products. In such cases an electrochemical treatment would result in an increase in toxicity of the wastewater and, possibly, also in stability of the residual chlorinated substrates. Accordingly, it is important to study the mechanism of oxidative degradation of different organic molecules, in different chloride-containing media, and at different anodes, to find optimal conditions for the electrochemical treatment, ensuring good faradaic yields for mineralization process, avoiding the formation of chlorocompounds.
In the present work two model substrates have been studied: glucose and phenol. The first may be of interest considering that saccharides are important components in effluents from food industry (e.g.: olive mill wastewaters). The second has been studied in different researches on electrochemical abatement of organic pollutants and many results are available for comparison, including some aspects of its reactivity in chloride media.
Experiments on electro-oxidation of glucose have been carried out at Ti/Pt and Ti/PbO2 electrodes, in presence of NaCl concentrations between 0.5 and 5 g dm-3. The substrate, in COD units, was 10.000 mg O2 dm-3 have been used, in consideration of the high COD values nor-mally met in effluents like olive-mill ones. The initial solution pH was 12. Electrolyses were carried out at different temperatures between 15 and 50°C. At Ti/Pt electrodes complete mineralization of glucose could be achieved at current densities > of 500 A m-2, under different electrolysis conditions.The mineralization rate was larger the lower the electrolysis temperature. The mineralization rate of glucose was found to increase with the NaCl concentration for values between 0.5 and 3 g dm-3. Only a small influence could be observed above this value. At Ti-PbO2 electrodes a substantially similar situation was found. At Ti/Pt electrodes, in the absence of NaCl, the abatement of COD was very small even after long electrolysis times. At PbO2, on the contrary, complete mineralization was achieved, even without the active chlorine mediator. Interestingly, a treatment of glucose solutions with sodium hypochlorite allowed a decreas of COD to only one half of its initial value. An important part of the overall reaction is therefore a surface stage. No organic chlorinated compounds were detected during the electrolysis. At the end of the electrolysis it was found that part of the original chloride was converted to chlorate and hypochlorite. In the first stage of the electrolysis the main intermediate seems to be gluconic acid.
Under analogous conditions also the mineralization of phenol (1000 ppm) in alkaline media (pH 13) could be achieved. Two unidentified complex quinonic species were present during the first stages of the electrolysis. As expected from the literature, maleic, fumaric and oxalic acid are then formed. No chlorophenols or organochloro compounds were detected.
References
1 S. Stucki, R. Koetz, B. Carcer, W. Suter, J. Appl. Electrochem. 21, 99 (1991)
2 Ch.Comninellis and E. Plattner, Chimia 42, 250 (1988)
3 Ch.Comninellis and C. Pulgarin, J. Appl. Electrochem. 23, 108 (1993)
4 Ch. Comninellis, Electrochim. Acta 39, 1863 (1994)
5 A. Boscolo, F. Gottardi, M. Tavan, R. Amadelli, A. De Battisti, A. Barbieri, G. Battaglin, J. Appl. Electrochem.. 24, 1052 (1994)
6 Ch. Comninellis and A. Nerini, J. Appl. Electrochem. 25, 23 (1995
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