1,721,020 research outputs found
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
Iron and sulfur isotope constraints on pyrite formation in Lake Cadagno, an analog to ancient oceans
No full textPaleoenvironmental reconstructions rely on the study of ancient sedimentary rocks, recording information about the water column, associated biomass, as well as continental and atmospheric inputs. Modern analog of ancient oceanic systems offer the opportunity to study biogeochemical cycles from the water column to the sediments and improve our interpretation of the geological record. This thesis focuses on Lake Cadagno, a stratified lake with permanently anoxic and sulfidic deep waters, frequently used as an analog for ancient oceans. Building on prior works, we used stable isotope geochemistry to investigate pyrite (FeS2) formation in the lake’s sediments. Isotope geochemistry is a powerful tool for disentangling biogeochemical processes and tracing elemental sources.
We employ both Fe and S isotope systematics to gain a detailed understanding of pyrite formation pathways in Lake Cadagno sediments and assess the influence of early diagenesis on pyrite isotope signatures. We combine conventional bulk analyses with spatially resolved isotopic measurements by ion microprobe. The results reveal the heterogeneity of isotope composition distributions at the microscale, helping to identify the underlying processes.
Our sulfur isotope data, when compared with previously published values for dissolved species in the water column, show a significant isotopic shift of sulfide over the past decades, both in the porewaters and the overlying water column. Furthermore, microscale sulfur isotope compositions in pyrite show a relatively narrow range of variation, with little evidence for high 34S depletion or enrichment. These patterns reflect the interplay of high organic matter availability and low sulfate concentrations, driving rapid sulfate depletion via microbial sulfate reduction coupled to both organic matter degradation and anaerobic methane oxidation. Sulfide produced under these conditions accumulates and tends to isotopically homogenize, resulting in moderate isotopic variation in pyrite. In this context, the temporal shift observed in the isotope composition of sulfide likely reflect an increase in upward diffusing 34S-enriched sulfide flux. Importantly, pyrite formed near the sediment surface records this temporal evolution. Depth-dependent variation in pyrite sulfur isotopes is further influenced by episodic turbidite deposition and fluctuating iron input. The sulfur isotope composition of pyrite appears to be primarily controlled by organic matter input rather than water column processes, highlighting the need to assess the sedimentary context in paleoenvironmental reconstructions.
Iron isotope signatures reveal a more complex picture. While the iron isotopic composition of framboidal pyrite is consistent with well-known processes such as dissimilatory iron reduction, sulfidation of iron oxides, and kinetic pyrite formation, some irregular pyrite grains are unusually enriched in 56Fe, which remains difficult to reconcile with existing models. These unusual iron isotope compositions indicate that additional processes may influence pyrite formation in Lake Cadagno. Overall, iron isotope compositions of pyrite appear to be modified during early diagenesis.
This thesis highlights the crucial role of local sedimentary conditions, such as organic matter and iron availability, in shaping the sulfur and iron isotope signatures of pyrite in euxinic systems. Our findings emphasize the importance of considering early diagenetic processes and microscale heterogeneity when using pyrite isotopes as proxies in paleoenvironmental reconstructions. Future work should aim to better constrain the mechanisms behind extreme iron isotope fractionation
Biomineralization and diagenesis of iron sulfides produced by sulfate-reducing bacteria : experimental approaches
No full textLes sulfures de fer sont omniprésents dans les roches sédimentaires et se sont révélés particulièrement utiles pour reconstruire l'évolution des paléoenvironnements terrestres. Leur propension à receler des biosignatures, en particulier celles des micro-organismes sulfato-réducteurs, est également utilisée pour tracer l'évolution de la biogéosphère mais reste souvent débattue. En effet, dans les environnements modernes, les bactéries sulfato-réductrices (SRB) jouent un rôle clé dans la réduction des sulfates en sulfures qui peuvent, en présence de métaux, précipiter des minéraux comme la pyrite (FeS2). Cependant, l'implication directe des SRB dans la formation de pyrite sédimentaire est encore mal comprise en raison des échecs à obtenir cette réaction dans des cultures monospécifiques en laboratoire. L'étude en laboratoire est pourtant une étape essentielle pour pouvoir préciser les mécanismes de formation des sulfures de fer, le rôle des SRB et en extraire des biosignatures robustes. Au cours de ce travail de thèse, plusieurs approches expérimentales ont été explorées afin de caractériser les processus de biominéralisation de sulfures de fer par les SRB ainsi que leur évolution diagénétique. Une première approche s'est appuyée sur des enrichissements bactériens (plurispécifiques) réalisés à partir des eaux anoxiques et ferrugineuses du lac Pavin (Massif Central). Elle a montré que les SRB pouvaient se développer dans des milieux pauvres en sulfates et avoir un rôle important dans la biominéralisation des phases porteuses de fer grâce aux interactions avec d'autres métabolismes microbiens et à la mise en place d'un cycle cryptique du soufre. Une seconde approche s'est focalisée sur des cultures monospécifiques d'une souche modèle de SRB (Desulfovibrio desulfuricans) en présence de différentes sources de fer (ferreux dissous ou nanoparticules de phosphate ferrique). Les deux conditions ont conduit à la formation rapide (une semaine) de monosulfures de fer (FeS) présentant cependant des différences morphologiques. En effet, en présence de fer dissous, les sulfures de fer précipitaient sous forme de particules micrométriques rappelant des bactéries encroûtées alors qu'en présence de phosphate de fer, ils ont pris la forme d'un biofilm minéralisé. Après un mois, des pyrites sont apparues au sein de ce biofilm tandis que les cultures en présence de fer dissous n'ont pas évolué. Ces résultats, qui comptent parmi les rares synthèses de pyrites biogéniques, ont permis de préciser les mécanismes de formation des pyrites en lien avec l'activité des SRB. Dans les mêmes conditions de culture, les compositions isotopiques des sulfates, FeS et pyrites ont été mesurées afin de préciser les fractionnements isotopiques liés à la production de sulfures de fer par les SRB, là où les études précédentes s'étaient arrêtées à la formation de sulfure d'hydrogène. Nos résultats ont montré que la sulfato-réduction microbienne détermine le fractionnement majeur par rapport à la précipitation des sulfures de fer. Par ailleurs, des résultats préliminaires en multi-isotopie du soufre ont révélé des signatures distinctes sur la masse 36 selon la source de fer utilisée dans les cultures. Finalement, la diagenèse expérimentale des sulfures de fer abiotiques et biogéniques précédemment obtenus a conduit dans les deux cas à la formation de pyrite mais une nouvelle fois, une dichotomie majeure a été observée concernant leur morphologie. Là où les pyrites obtenues à partir des sulfures de fer abiotiques formaient des cristaux euhédriques semblables à ceux observés dans les sédiments pauvres en matière organique, celles obtenues à partir des produits des cultures ressemblaient à des agrégats sphérulitiques. Ces agrégats, distincts des framboïdes, pourraient avoir été négligés jusqu'à présent dans les environnements sédimentaires et leur recherche permettrait d'ouvrir une nouvelle voie vers l'identification des pyrites biogéniques dans les environnements naturels.Iron sulfides are ubiquitous in sedimentary rocks and have proven particularly useful in reconstructing paleoenvironments evolution. Their propensity to harbor biosignatures, in particular those of sulfate-reducing microorganisms, is also used to trace the geobiosphere evolution but remains often debated. Indeed, in modern environments sulfate-reducing bacteria (SRB) play a key role in the reduction of sulfate to sulfide that can then precipitate minerals such as pyrite (FeS2) in the presence of metals. However, the direct involvement of SRB in the formation of sedimentary pyrite is still poorly understood due to failures in achieving this reaction in laboratory pure cultures. However, laboratory studies are crucial to assess the mechanisms of iron sulfides formation, the role of SRB and to determine robust biosignatures. In this PhD work, several experimental approaches were explored in order to characterize iron sulfide biomineralization processes in SRB cultures and their diagenetic evolution. A first approach was based on microbial enrichments carried out from anoxic and ferruginous waters of Lake Pavin (Massif Central). It showed that SRB could thrive in sulfate-poor environments and have an important contribution in the biomineralization of iron-bearing phases thanks to interactions with other microbial metabolisms through a cryptic sulfur cycle. A second approach focused on pure cultures of a model strain of SRB (Desulfovibrio desulfuricans) in the presence of different iron sources (dissolved ferrous iron or nanoparticulate ferric phosphate). Both conditions led to the rapid formation (one week) of iron monosulfide (FeS) exhibiting however morphological differences. Indeed, in the presence of dissolved ferrous iron, iron sulfide precipitated as micrometric particles reminiscent of encrusted bacteria, whereas in the presence of ferric iron phosphate, it appeared as a mineralized biofilm. After one month, pyrite nucleated within this biofilm while the cultures with dissolved iron did not evolve further. These results, which are among the rare laboratory syntheses of biogenic pyrites, allowed to clarify the mechanisms of pyrite formation in association with SRB activity. Under the same culture conditions, isotopic compositions of sulfates, FeS and pyrites were measured in order to determine the isotopic fractionations related to the production of iron sulfides by SRB, while previous studies focused on the formation of hydrogen sulfide (with no biomineralization). Our results showed that microbial sulfate reduction determined the main fractionation with respect to iron sulfide precipitation. Furthermore, preliminary results on sulfur multi-isotopes revealed distinct signatures on the mass 36, linked to the nature of the iron source supplied in cultures. Finally, experimental diagenesis of abiotic and biogenic iron sulfides both led to the formation of pyrite, but once more a major dichotomy of pyrite morphology was noticed. While pyrite obtained from abiotic iron sulfides displayed euhedral crystals similar to those reported in organic-poor sediments, those obtained from culture products were spherulitic aggregates. These aggregates, distinct from the well-known framboids, may have been overlooked so far in the sedimentary record and their investigation might pave the way to new identification of biogenic pyrites in natural environments
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
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