1,721,017 research outputs found
Carbon isotope fractionation of chlorinated ethenes during oxidation by Fe 2+ activated persulfate
Get PDFThe increased use of persulfate (S 2O 82-) for in situ chemical oxidation to treat groundwater and soils contaminated by chlorinated hydrocarbon compounds (CHCs) requires unbiased methods to assess treatment performance. Stable carbon isotope analysis offers a potential tool for assessing the in situ treatment performance of persulfate at sites contaminated with CHCs. This study investigated the extent of C isotope fractionation during oxidation of tetrachloroethene (PCE), trichloroethene (TCE) and cis-dichloroethene (cis-DCE) by persulfate activated by ferrous ion (Fe 2+). An average carbon isotope enrichment factor ε bulk of -4.9‰ for PCE, -3.6‰ for TCE and -7.6‰ for cis-DCE were obtained in batch experiments. Variations in the initial S 2O 82-/Fe 2+/CHC molar ratios did not result in any significant differences in carbon isotope fractionation. The occurrence of carbon isotope fractionation during oxidation and the lack of dependence of enrichment factors upon the S 2O 82-/Fe 2+/CHC molar ratio demonstrate that carbon isotope analysis can potentially be used at contaminated sites as an additional technique to estimate treatment efficacy during oxidation of CHCs by Fe 2+ activated persulfate. © 2012 Elsevier B.V
Carbon isotope fractionation of 1,1,1-trichloroethane during base-catalyzed persulfate treatment
No full textThe extent of carbon isotope fractionation during degradation of 1,1,1-trichloroethane (1,1,1-TCA) by a base-catalyzed persulfate (S2O82-) treatment system was investigated. Significant destruction of 1,1,1-TCA was observed at a pH of ~12. An increase in the NaOH:S2O82-molar ratio from 0.2:1 to 8:1 enhanced the reaction rate of 1,1,1-TCA by a factor of ̃5 to yield complete (>99.9%) destruction. An average carbon isotope enrichment fractionation factor which was independent of the NaOH:S2O82-molar ratio of -7.0±0.2‰ was obtained. This significant carbon isotope fractionation and the lack of dependence on changes in the NaOH:S2O82-molar ratio demonstrates that carbon isotope analysis can potentially be used in situ as a performance assessment tool to estimate the degradation effectiveness of 1,1,1-TCA by a base-catalyzed persulfate system. © 2013 Elsevier B.V
Carbon and Hydrogen Isotope Fractionation of Benzene, Toluene, and o -Xylene during Chemical Oxidation by Persulfate
Get PDFExperiments were performed to investigate the carbon and hydrogen isotope fractionation of benzene, toluene, and o -xylene (BTX) during
chemical oxidation by unactivated persulfate at two concentrations (8 and 20 g/L). Carbon enrichment ( e
C
) values of −1.7 ± 0.1‰ for benzene,
−0.64 ± 0.1‰ for toluene and −0.36 ± 0.04‰ for o -xylene were obtained. No significant hydrogen enrichment ( e
H
) was observed for benzene,
while the hydrogen enrichment for toluene and o -xylene were −20 ± 3‰ and −23 ± 2‰, respectively. The dual isotope plot ( ∆ δ
13
C vs. ∆ δ
2
H) for
benzene and o -xylene revealed a distinct fractionation trend compared to the majority of the biodegradation data compiled from the literature;
however, no unique trend was observed for toluene. The significant carbon and/or hydrogen enrichment, and the distinct trend observed on the
dual isotope plot suggest that compound specific isotope analysis (CSIA) can potentially be used to monitor the chemical oxidation of BTX by
persulfate, and to distinguish treatment areas where persulfate or biodegradation reactions are occurring for benzene and o -xylene
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
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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