1,721,029 research outputs found
Biogeochemistry of arsenic and metals in drifting and stranded holopelagic Sargassum in the tropical Atlantic
No full textDepuis 2011, l'échouement massif de Sargasses holopélagiques est devenu un problème récurrent dans les Caraïbes et l'Atlantique tropical avec des perturbations considérables des écosystèmes côtiers et des impacts négatifs sur les économies locales. La transformation de cette nuisance en opportunité de valorisation nécessite une meilleure compréhension des processus clefs et des déterminants de la composition en arsenic (As) et en métaux toxiques, tel que le cadmium (Cd), de cette biomasse. Il s’avère en outre particulièrement important de suivre l’arsenic inorganique (Asi) qui fait l’objet d’une réglementation stricte au niveau européen et international en raison de sa toxicité élevée. Un premier objectif de ce travail a été de développer une méthode électrochimique sur fil d’or afin de disposer d’une méthode simple, rapide et accessible à des non-spécialistes pour la mesure de l’Asi dans les macroalgues brunes. En se basant sur une récolte variée de sargasses dérivant en pleine mer, stagnant dans les baies ou échouées sur les plages, nous avons pu montrer un contrôle important des teneurs en arsenic selon les conditions de limitation ou de disponibilité du phosphate et un accroissement important en éléments terrigènes (Al et Fe) dans les zones côtières. La prise en compte des trajectoires suivies au large par les radeaux a permis de mettre en évidence une route problématique amenant rapidement depuis le panache de l’Amazone et le courant de Guyane une biomasse particulièrement riche en Asi et Cd. Nos expérimentations, en vue de valoriser cette biomasse, montrent qu’un simple trempage dans de l’eau douce, accompagnée d’un pressage mécanique, permet de faire passer les teneurs en Asi sous les niveaux réglementaires de 40 ppm.Since 2011, the massive stranding of holopelagic Sargassum has become a recurring problem in the Caribbean and tropical Atlantic, with considerable disturbance to coastal ecosystems and negative impacts on local economies. Transforming this nuisance into an opportunity requires a better understanding of the key processes and determinants of the composition of arsenic (As) and toxic metals, such as cadmium (Cd), in this biomass. It is also particularly important to monitor inorganic arsenic (Asi), which is subject to strict European and international regulations due to its high toxicity. The first objective of this work was to develop a gold wire electrochemical method to provide a simple, rapid and accessible method for non-specialists to measure Asi in brown macroalgae. Based on a large sample set of Sargassum drifting in the open sea, stagnant in bays or stranded on beaches, we were able to show a significant control of arsenic levels depending on the conditions of phosphate limitation or availability and a significant increase in terrigenous elements (Al and Fe) in coastal areas. By taking into account the trajectories followed offshore by the rafts, we were able to highlight a problematic route that rapidly brings in biomass from the Amazon plume and the Guiana current that is particularly rich in Asi and Cd. Our experiments, with a view to valorise this biomass, have shown that a simple soaking in freshwater, with mechanical pressing, can reduce Asi content to below the regulatory level of 40 ppm
Fate of metals in deep-sea hydrothermal vents : dissolved-particulate partitioning and speciation in the early mixing between hydrothermal fluid and seawater
No full textQuarante ans après la découverte de la circulation hydrothermale profonde, les processus chimiques se produisant dans le mélange entre le fluide hydrothermal et l’eau de mer restent mal contraints. Ce travail de thèse, dont l’originalité repose sur l’utilisation systématique de la filtration in situ, présente le partitionnement effectif des éléments métalliques majeurs (principalement Fe, Cu, Zn, Ba et Ca) entre les phases dissoutes ( 0,45 μm) dans le mélange précoce-intermédiaire de plusieurs fumeurs du champ hydrothermal Lucky Strike (37°N, MAR). Le comportement et la spéciation du Cu dans la fraction dissoute sont ensuite explorés plus en détail par le biais de compétitions de ligands et de mesures voltamétriques. Nos résultats démontrent en premier lieu l’importance de la filtration in situ pour s’affranchir des biais induits par le prolongement des réactions de précipitation ou de redissolution pouvant se produire lors de la remontée des échantillons. L’examen des fluides collectés à différentes reprises et sur une large panoplie de fumeurs (240 échantillons) démontre une variabilité spatiale des signatures chimiques le long de l'axe est-ouest du champ hydrothermal. Parmi les métaux étudiés, Fe, Ca et Ba sont principalement mesurés sous forme dissoute tandis que Cu et Zn sont majoritairement particulaires. Dans le mélange initital (50‒150°C, dMn > 50 μM), le pool de particules est dominé par de la sphalérite (ou wurtzite) et de la chalcopyrite, avec généralement moins de pyrite. Dans cette zone, les changements chimiques semblent cinétiquement limités et les fluides échantillonnés présentent une signature chimique proche de celle du fluide pur. Cependant, à mesure que le fluide hydrothermal se mélange à l'eau de mer (4‒50°C, dMn 0.45 μm) phases in the early mixing of several black and clear smokers from the Lucky Strike vent field (37°N, MAR). The behavior and the speciation of Cu in the dissolved fraction are then deeper explored by performing ligands competition and voltammetric measurements. Our results first demonstrate the importance of the in situ filtration to restrict the bias induced by precipitation reactions or particles redissolution potentially occurring postsampling.The examination of the fluids collected at several occasions and on a wide range of smokers (240 samples) shows a spatial variability of chemical signatures along the east-west axis of the hydrothermal field. Among metals studied, most of Fe, Ca and Ba are measured as dissolved species whereas Cu and Zn are mainly found as particles. In the initial part of the mixing (50-150°C, dMn > 50 μM), the particulate pool is dominated by sphalerite (or wurtzite) and chalcopyrite, with generally lower amount of pyrite. In this zone, chemical changes seem kinetically limited and fluids collected display a chemical signature close to that of the end-members. However, as the hydrothermal fluid progressively mixes with seawater (4-50°C, dMn < 50 μm), the partitioning of some alkali and alkaline earth metals (Ca, Ba, Mg and Sr) between the two phases is deeply affected by precipitation of sulfates. Unlike thermodynamic predictions, precipitation of anhydrite, barite and potentially caminite is observed in the colder part of the mixing (4-50°C). The large increase of pH in this area also drives the beginning of Fe oxides precipitation. Finally, the dissolved Cu-ligands detected seem to be mainly inorganic sulfides originating from the hydrothermal fluid
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
