1,722,815 research outputs found
Mechanistic Study of Radium Adsorption onto Goethite
No full textRadium (Ra2+) is a radioactive element with a long half-life. It is used in industry and is often found in shallow aquifers due to natural or anthropogenic leakage or spill of brine from deep subsurface. A major factor influencing the transport and fate of Ra2+ in water is the adsorption/desorption process onto soil particles. Goethite, a ubiquitous natural mineral generally present as a coating of soil particles, contributes significantly to the adsorption of Ra2+ in the subsurface. However, the chemical reactions of adsorption of Ra2+ onto goethite are not well-established, yet. Previous studies reported that Ra2+ creates either tetradentate or monodentate complexes on goethite and no distinction between outer-sphere and inner-sphere types of complexes were made. Knowledge of the type and structure of Ra-goethite surface complexes is important to predict the behavior and the fate of Ra2+ in the subsurface, e.g., upon a spill and during the remediation of a contaminated site. Here, the adsorption of Ra2+ onto goethite is investigated by density functional theory (DFT) calculations. By using a combination of geometric structure, adsorption energy, and electronic state (i.e., density of states and magnetic moment) analyses, the outer-sphere adsorption was found to dominate Ra2+ complexation on goethite, suggesting a significant effect of salinity on Ra2+ transport in the subsurface. Inner-sphere adsorption configuration was not observed to be thermodynamically favorable, resulting from ionic rather than covalent interaction between Ra2+ and goethite. Based on these results, a surface complexation model was developed and validated successfully with literature data. This study provides insights into the mechanism of Ra2+ adsorption on soils containing goethite and provides chemical reactions of Ra-goethite surface interaction that can be coupled with a transport model to predict Ra2+ migration in the subsurface
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
Mechanistic Study of Lead Adsorption on Activated Carbon
No full textActivated carbon (AC) is a carbonaceous material broadly applied in filters to remove lead (Pb(II)) from drinking water through adsorption. However, the chemical interactions between Pb(II) and the reactive sites on AC or other carbonaceous materials are not well understood, yet. The understanding of the mechanism of Pb(II) adsorption onto AC would allow to optimally design AC-based materials even in the presence of a complex liquid phase. Here, the interaction between Pb(II) and functional groups on AC was investigated at the molecular scale to help identifying the chemical reactions at the solid-liquid interface. Spectroscopic analyses and chemical quantum calculations were performed and indicated the formation of monodentate mononuclear Pb(II)-phenol and bidentate mononuclear Pb(II)-carboxyl complexes on AC. Competitive adsorption behavior was observed between Pb(II) and calcium (Ca(II)) because of their similar adsorption configurations on AC. In contrast, anions, including sulfate and phosphate, were observed to enhance Pb(II) adsorption on AC by forming ternary complexes. On the basis of these observations, a new surface complexation model of Pb(II) adsorption onto AC was formulated and validated with batch tests. Overall, this work presents a new set of chemical reactions at the solid-liquid interface between Pb(II) and AC under various conditions of interest for the application of AC or other carbonaceous materials in water treatment
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
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