1,720,971 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
The effect of permafrost thaw on merucry- and methane-cycling microbes and their potential interactions
Get PDFThesis (M.S.) University of Alaska Fairbanks, 2024In this study, I investigated potential interactions between methane and mercury cycles in boreal forest soils. Additionally, I examined the changes in these cycles relative to shifts in soil moisture along an environmental soil moisture gradient. This investigation is pertinent due to the escalating rate of permafrost thaw driven by climate change in Arctic and subarctic ecosystems. Permafrost thaw leads to increased soil moisture, fostering favorable conditions for anaerobic microbial processes such as mercury methylation, methanogenesis, and anaerobic methanotrophy. Microbial mercury methylation creates monomethylmercury, a neurotoxin that accumulates in aquatic food webs. Methane cycling results in the production of greenhouse gases that can create a climate-warming feedback loop. In this study, I explored the mercury and methane cycles and analyzed the microbial communities involved in these cycles along an environmental soil moisture gradient. Microbial communities were analyzed by quantifying the relative abundance of taxonomic groups and by quantifying functional genes associated with mercury methylation, methanogenesis, and anaerobic methanotrophy. The relationship between soil water content and functional gene quantities was not significant. However, my findings did reveal a significant relationship between relative beta diversity and gravimetric water content along the environmental soil moisture gradient. The functional potential was predicted by quantifying net methane and net monomethylmercury production through incubations designed to measure total production in completely saturated, anoxic conditions I found that total mercury increases as soil moisture increases, methane efflux increases as soil moisture increases, and carbon dioxide efflux increases as soil moisture increases. This suggests that the activity of the mercury and methane cycles may change as permafrost continues to thaw and soil moisture content increases. In a changing climate, continuing to monitor these cycles in Alaska is pertinent due to its robust fishing industry, indigenous communities, subsistence fishing practices.Alaska INBRE Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health under grant number 120GM103395Chapter 1: General introduction -- 1.1 Introduction -- 1.1.1 Methane cycle -- 1.1.2 Mercury cycle -- 1.2 Cycle interactions -- 1.3 Functional potential of mercury and methane cycles -- 1.4 Microbial community composition -- 1.5 References. Chapter 2: Microbial potential for mercury methylation and methane efflux across a soil moisture gradient -- 2.1 Abstract -- 2.2 Introduction -- 2.3 Methods -- 2.3.1 Soil core collection -- 2.3.2 Soil properties -- 2.3.3 Total mercury concetrations -- 2.3.4 Net greenhouse gas efflux -- 2.3.5 Inhibition experiments -- 2.3.6 Statistical analysis -- 2.4 Results -- 2.4.1 Total mercury concentrations -- 2.4.2 Net greenhouse gas efflux -- 2.4.3 Inhibition experiments -- 2.5 Discussion -- 2.6 References. Chapter 3: Impacts of soil moisture on functional gene abundance and community composition -- 3.1 Abstract -- 3.2 Introduction -- 3.3 Methods -- 3.3.1 Soil core collection -- 3.3.2 Soil properties -- 3.3.3 DNA extraction and community composition -- 3.3.4 Functional gene quantities -- 3.4 Results -- 3.4.1 Community composition -- 3.4.2 Relative abundance of taxonomic groups -- 3.4.3 Functional gene quantities -- 3.5 Discussion -- 3.6 References. Chapter 4: General conclusion -- 4.1 Introduction -- 4.2 Findings -- 4.3 Implications -- 4.4 References
Spéciation hépatique et distribution tissulaire et sub-cellulaire du mercure: effets sur la toxicité chez les poissons.
Get PDFLe mercure est un contaminant d'intérêt mondial, car il affecte même des
environnements éloignés comme l'Alaska et l'extrême-arctique canadien. La
consommation de poissons contaminés est la principale source de mercure chez les
humains et la faune et cela entraîne des effets négatifs sur la santé. Le mercure est
également toxique pour les poissons eux-mêmes. Les poissons sont principalement
exposés au mercure, comme le méthylmercure, via leurs régimes alimentaires. Le
méthylmercure ingéré traverse la paroi intestinale de manière plus efficace que le
mercure inorganique. Suite à son ingestion, il est distribué par la veine porte vers le
foie. C’est pour cette raison, que la majorité du mercure dans le foie des poissons
devrait être sous la forme de méthylmercure, mais des recherches récentes suggèrent
que ce n'est pas toujours le cas. En raison du positionnement stratégique du foie dans
le système circulatoire, il joue un rôle important dans la détoxication du mercure avant
d'atteindre d'autres tissus du poisson.
La première partie de cette thèse décrit une nouvelle méthode afin de déterminer la
spéciation du mercure dans les tissus des poissons par un analyseur de mercure direct.
Le méthylmercure dans le foie et les muscles des poissons est estimé par la différence
des mesures directes du mercure inorganique dans un extrait acide et du mercure total
dans les tissus entiers. La méthode a été validée par l’analyse d'une substance de
référence certifiée (DOLT-4, le foie d’aiguillat), et la comparaison des résultats obtenus
sur les tissus de poissons contaminés naturellement, avec une méthode de spéciation
du mercure traditionnelle (chromatographie en phase gazeuse couplée à la
spectrométrie de fluorescence atomique à vapeur froide). Le rendement du mercure
organique de DOLT-4, estimé par différence, est en moyenne 99 ± 5 % de la valeur
moyenne certifiée pour le méthylmercure. Dans la majorité des échantillons de foie et
dans tous les échantillons de muscles, les estimations de mercure organique à partir de
la méthode proposée étaient indiscernables des mesures directes de spéciation de
méthylmercure (99 ± 6 %). L’estimation de mercure organique par différence entre le
mercure et le mercure inorganique totale était moins précise dans les échantillons de
foie comportant des proportions de mercure inorganique élevées (≥90 %).
Par la suite, la nouvelle méthode a été utilisée pour déterminer les proportions relatives
de méthylmercure dans les foies de plusieurs poissons osseux, représentant des
espèces primitives et des plus évoluées. Dans les trois espèces de salmonidés, la
majorité du mercure total hépatique était présente sous forme de méthylmercure.
Inversement, le barbue de rivière (Ictalurus punctatus) et deux espèces primitives, le
lépisostée tacheté (Lepisosteus oculatus) et le poisson-castor (Amia calva),
comportaient des proportions élevées de mercure inorganique dans leurs foies. Pour
les autres espèces de poissons, le méthylmercure composait environ la moitié du
mercure hépatique totale. Chez une espèce de poisson donnée, la spéciation hépatique
du mercure observée était similaire sur toute la gamme de concentrations de mercure
total mesurées. Les différences entre espèces peuvent être issues de différences
alimentaires ou encore de métabolismes différents du mercure pour chaque espèce de
poisson.
Les agrégats de mélano-macrophages (MA) sont des collections de cellules
spécialisées du système immunitaire de poissons. Dans les foies de certaines espèces,
les MA augmentent en taille et en nombre en fonction de l'exposition aux contaminants,
et peuvent être impliqués dans le métabolisme et le stockage du mercure.
Afin d'élucider la relation entre les MA et l'exposition aux métaux, nous avons
échantillonné des sébastes aux yeux jaunes (Sebastes ruberrimus), une espèce à vie
longue qui vit en milieu côtier; l’échantillonnage a eu lieu à l‘est et à l’ouest de l'île
Prince of Wales, en Alaska. Les concentrations en métaux (c.-à-d., le méthylmercure, le
mercure inorganique, le sélénium, le nickel, le cadmium, le cuivre, le zinc) dans le foie,
ainsi que leurs corrélations avec la superficie globale des mélano-macrophages, ont été
déterminées. Des sections de tissu hépatique ont été analysées par spectrométrie de
masse à plasma induit couplée à l’ablation laser afin de déterminer la répartition des
métaux entre les hépatocytes et les MA. La concentration de mercure inorganique dans
tout le tissu était le meilleur facteur prédictif de la superficie globale des mélanomacrophages
dans le foie et la rate des sébastes aux yeux jaunes. Comparativement
aux hépatocytes, les mélano-macrophages comportaient des concentrations
relativement plus élevées pour la plupart des métaux mesurés. Cependant, tous les
métaux n’ont pas été accumulés de la même manière dans les macrophages, comme
indiqué par les différences de proportions de métaux dans les macrophages par rapport
aux hépatocytes. Les données d'ablation laser ont été corroborées avec les résultats
d’imagerie obtenus par la spectrométrie de fluorescence X sur d'une section du foie
d’un sébaste aux yeux jaunes, ces mesures ayant été obtenues sur le synchrotron
canadien à Saskatoon.
De plus, des ombles chevaliers (Salvelinus alpinus) ont été échantillonnés dans quatre
lacs (c.-à-d., Small, 9-Mile, North, et Amituk) couvrant un gradient de contamination au
mercure. De la même manière que pour les sébastes aux yeux jaunes, leurs foies ont
été examinés afin de déterminer la relation entre les MA et le mercure hépatique. Les
MA des quatres populations d’ombles chevaliers étaient plus petits et moins bien définis
que ceux des sébastes aux yeux jaunes et n’étaient pas corrélés avec les
concentrations de mercure. En revanche, les MA dans le foie de l'omble chevalier
peuvent augmenter en nombre en présence de niveaux élevés de fer. Les ombles
chevaliers du lac Amituk, qui comportaient les niveaux de fer les plus bas et les
concentrations de mercure les plus élevées, possédaient moins de MA et
significativement plus d’occurrence de fibrose du foie.
Une procédure a été utilisée pour déterminer la répartition sub-cellulaire des métaux
entre les fractions potentiellement sensibles et les fractions détoxiquées, chez les foies
des ombles chevaliers des lacs Small et Amituk. Au niveau sub-cellulaire, le mercure a
été trouvé principalement dans les fractions potentiellement sensibles, ce qui indique
que les ombles chevaliers ne détoxiquent pas efficacement ce métal.
Enfin, les indices généraux de santé (facteur de condition, l'indice hépatosomatique
l'indice gonadosomatique) ont été calculés. Pour les sébastes aux yeux jaunes, les
augmentations du facteur de condition et de l'indice hépatosomatique étaient
probablement le résultat d’une augmentation de la disponibilité alimentaire. Pour l'omble
chevalier, les concentrations de mercure étaient positivement corrélées avec l'indice
hépatosomatique, qui était probablement un reflet de l'écologie alimentaire de l'omble.
L’alimentation au niveau trophique supérieur conduit à de plus grandes réserves de
lipides, mais aussi à une plus grande exposition au mercure. Le facteur de condition et
l'indice gonadosomatique n’étaient pas liés aux concentrations de mercure chez l'omble
chevalier. En conclusion, selon les indices de santé communs utilisés dans cette
étude, le mercure ne semble pas affecter négativement la santé générale des sébastes
aux yeux jaunes et de l’omble chevalier. Mercury is a contaminant of global concern as it affects even remote environments such
as Alaska and the Canadian High Arctic. Consumption of contaminated fish is the
principal source of mercury in humans and wildlife and results in negative health effects.
Mercury is also toxic to the fish themselves. Fish are primarily exposed to mercury, as
methylmercury, through their diets. Ingested methylmercury crosses the intestinal wall
much more efficiently than inorganic mercury, and is circulated via the portal vein to the
liver. Therefore, the majority of mercury in fish liver should be methylmercury, however
recent research suggests that this is not always the case. Due to the liver’s strategic
positioning within the circulatory system it plays an important role in the detoxification of
mercury before it reaches other fish tissues.
The first part of this research describes a novel method to determine mercury speciation
in fish tissue using a direct mercury analyzer. Methylmercury in fish liver and muscle is
estimated by difference from direct measurements of inorganic mercury in an acid
extract and total mercury in whole tissue. The method was validated by analysis of a
certified reference material (DOLT-4 dogfish liver) and naturally contaminated fish
tissues with comparison to an established mercury speciation method (gas
chromatography cold vapor atomic fluorescence spectrometry). Recovery of organic
mercury from DOLT-4, estimated by difference, averaged 99 ± 5% of the mean certified
value for methylmercury. In the majority of liver samples and all muscle samples,
estimates of organic mercury from the proposed method were indiscernible from direct
speciation measurements of methylmercury (99 ± 6%). Estimation of organic mercury
by difference between total mercury and inorganic mercury was less accurate in liver
samples with high percent inorganic mercury (90%).
The outlined method was then used to determine the relative proportions of
methylmercury in the livers of several bony fish, representing both primitive and more
evolved species. In the three salmonid species, the majority of hepatic total mercury
was present as methylmercury. Conversely, channel catfish (Ictalurus punctatus) and
the more primitive spotted gar (Lepisosteus oculatus) and bowfin (Amia calva) had
elevated proportions of inorganic mercury in their livers. In the remaining species of fish,
methylmercury made up approximately half of the total hepatic mercury. These trends in
hepatic mercury speciation are similar over a range of total mercury concentrations and
may be due to differences in diet or how mercury is metabolized. Melano-macrophage
aggregates (MA), collections of specialized cells of the innate immune system of fish. In
the livers of some species, MA increase in size and number as a result of contaminant
exposure, and may be involved in mercury metabolism and storage.
In order to elucidate further the relationship between macrophage aggregates and
metals exposure, we sampled yelloweye rockfish (Sebastes ruberrimus), a long-lived
species, from the east and west coasts of Prince of Wales Island, Alaska. Metal
concentrations in livers (methylmercury, inorganic mercury, selenium, nickel, cadmium,
copper, zinc) were determined as well as their correlations with melano-macrophage
aggregate area. Sections of liver tissue were analyzed by laser ablation inductively
coupled plasma mass spectrometry to determine how metals were spatially distributed
between hepatocytes and macrophage aggregates. The concentration of inorganic Hg
in whole tissue was the best predictor of macrophage area in yelloweye livers and
spleens. Macrophage aggregates had higher relative concentrations of most metals
compared to the surrounding hepatocytes. However, not all metals were accumulated to
the same degree as evidenced by differences in the ratios of metals in macrophages
compared to hepatocytes. Laser ablation data were corroborated with the results of Xray
synchrotron fluorescence imaging of a yelloweye liver section.
Landlocked Arctic char (Salvelinus alpinus) were sampled from four lakes (Small, 9-
Mile, North, and Amituk) spanning a gradient of mercury contamination and, similar to
yelloweye rockfish, their livers were examined to determine how melano-macrophage
aggregates were related to hepatic mercury. The melano-macrophage aggregates of
Arctic char were smaller and less well defined than those of yelloweye rockfish and
were not correlated with mercury concentrations when including fish from all four char
populations. Rather, melano-macrophage aggregates in the livers of Arctic char may
increase in number as a result of elevated levels of iron. Amituk Lake char, which had
the lowest iron and highest mercury concentrations, had relatively few melanomacrophage
aggregates and significantly greater numbers of char with liver fibrosis.
A sub-cellular partitioning procedure was employed to determine how metals were
distributed between potentially sensitive and detoxified compartments of Arctic char
livers from Small Lake and Amituk Lake. At the sub-cellular level mercury was found
mainly in potentially sensitive fractions of both Small and Amituk Lake char, indicating
that Arctic char are not effectively detoxifying this metal.
Finally, common health indices (condition factor, hepatosomatic index, gonadosomatic
index) were calculated. For yelloweye, increased condition factor and hepatosomatic
index were likely a result of food availability. For Arctic char, concentrations of mercury
were positively correlated with the hepatosomatic index, which was most likely a
reflection of the feeding ecology of char; feeding at a higher trophic position results in
greater lipid reserves, but also a greater exposure to mercury. The condition factor and
gonadosomatic index were not related to mercury concentrations in Arctic char. In
conclusion, mercury does not appear to be negatively affecting the general health of
yelloweye rockfish and Arctic char, based on the common health indices employed in
this study
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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