1,721,027 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
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Linking the Genetic Signature of Asymbiotic Soil Diazotrophs with Nitrogen Fixation under Land-use Change in the Amazon Rainforest
Get PDFNet primary productivity and carbon sequestration are dependent on an adequate source of nitrogen (N) in terrestrial ecosystems. Biological nitrogen fixation, the microbially-mediated conversion of atmospheric N2 to biochemically reactive ammonia (NH3) serves as an important source of new N to many natural ecosystems. Despite its crucial role in global biogeochemistry, controls over the rate of this microbially mediated process remain poorly understood. This is particularly true in the context of land use (LU) alteration, a major driver of climate change and ecological disruption. In the Amazon Basin, LU change from primary tropical forest to agricultural operations, particularly cattle pasture, has been prevalent and ongoing for decades. To better understand shifts in N inputs resulting from LU change, this dissertation investigates the activity and diversity of free-living soil diazotrophic communities across the LU dichotomy of forest and pasture in the Amazon Basin. First, to establish a broader perspective on the microbial response to LU change in the Amazon, we performed a comprehensive review of all studies investigating microbial communities or microbially mediated processes across variable LUs and successional states in the region, highlighting both generalized and repeated findings, as well as points of disagreement which may indicate regional heterogeneity or methodological biases. This meta-analysis revealed that although trends in the alpha-diversity of microbial communities vary somewhat across studies, spatial biotic homogenization in pastures compared to primary forests has been a near-universal finding among prokaryotes, fungi, and several other taxonomic or functional subgroups. Additionally, a large proportion of studies have identified soil Al3+ content and extractable acidity to be major factors shaping community structure, emphasizing the importance of tropical mineralogy. Significant shifts in microbially-driven biogeochemical cycling with LU change have been identified as well. Most studies have found that soil C stocks increase slightly with pasture conversion, simultaneous with elevated methane emissions and a decline in the community proportion and taxonomic richness of methanotrophs. However, the most drastic and consequential nutrient cycle shift has been to the N cycle. Studies have found that rates of net mineralization and nitrification decline sharply in maturing pastures, coincident with reductions in nitrous oxide emissions and inorganic N pools. Recent studies have indicated that free-living diazotrophs increase in abundance and diversity with pasture conversion, but measurements of asymbiotic nitrogen fixation (ANF) have not been made across LUs to bolster these community findings. Addressing this knowledge gap in conjunction with community profiling was a primary focus of the original research presented here.To fulfill this aim, we surveyed three primary forests and three pastures (converted in or around 1972) in the state of Rondônia, Brazil near the end of the wet season in April of 2017. At each site, we established a 100 m2 quadrat and collected four replicate soil cores (0-10 cm in depth) from seven locations each. After homogenization, fresh soil was utilized for 15N2 gas incubations to calculate soil N incorporation attributable to ANF. Additionally, preserved soil samples were used for nucleic acid extraction and analysis, quantifying a suite of physicochemical measurements, and profiling the bulk soil metabolome. Community nucleic acids were utilized for marker-gene targeted amplification to serve as a proxy of absolute abundance and functional community structure, as well as to obtain profiles of potential diazotrophs within the broader soil metagenome.
From this analysis, we concluded that soil ANF is indeed stimulated (47x increase) in active cattle pastures coincident with an augmentation in soil nifH copy number (18x increase; in line with previous observations), but that the two are not directly related within LUs. Using soil physicochemical parameters (including various pools of C and N, natural isotopic abundance, soil texture, pH, P, cation exchange capacity, and enzyme metallocluster constituents including Mo and V) for variable selection in multiple linear regression, we were unable to identify variables strongly associated with nifH community augmentation from forest to pasture. Substantially lower soil NO3- concentrations provided significant, but modest value in explaining the stimulation of ANF in mature, active cattle pastures compared to primary forests. Additionally, when forests were considered separately from pastures, nifH copy number and ANF rates (which were consistently near zero) were poorly explained by physicochemical parameters. Together these findings indicate that factors such as high inorganic N concentration as well as alternative, more productive N input pathways (i.e., canopy lichens, nodules, or the surface litter layer), which were not measured in this study, could largely suppress the activity of potential diazotrophic bacteria in primary forests. Within pasture soils, however, we found that nifH copy number was primarily associated with C pools. We found a modest, but significant association between pasture soil ANF rate and the ratio of low molecular weight extractable organic C to N, as well as the fraction of total N in the dissolved organic form, suggesting that this energy-intensive reaction is stimulated by a limited availability of N combined with sufficient fuel in the form of low molecular weight C compounds. Additionally, using a multigene approach to profile soil diazotrophs within the broader microbial community revealed that the genetic potential for asymbiotic diazotrophy is one of the most (if not the most) enriched soil microbial functions accompanying pasture conversion. This realization speaks to the immense influence that large-scale LU change can have on microbial communities, and the strong pressure for N replenishment in grazed (but unfertilized) pastures of the Amazon Basin.
After observing that the absolute abundance of potential diazotrophs (based on DNA copy number) did not scale with ANF measurements in either LU, we aimed to further explore any meaningful relationships between diazotrophic communities and this crucial biogeochemical process they mediate. A previous analysis of the potential diazotroph community in forest and pasture soils of Rondônia found significant shifts in its structure. However, given the phylogenetic and trophic breadth of potential diazotrophs (i.e., microorganisms bearing nitrogenase-encoding genes, but not necessarily contributing to ANF), it is not clear whether these shifts have occurred independent of the larger soil prokaryotic community. By comparing potential diazotroph community structure (using DNA-based amplification of the nitrogenase marker gene, nifH) with that of all prokaryotes (by amplifying the 16S rRNA gene), we found that potential diazotroph community alpha-diversity was significantly higher in pasture soils, while the overall prokaryotic community did not reflect an increase. However, both profiles reflected a similar degree of community compositional dissimilarity with respect to LU change. Additionally, both communities exhibited significantly lower groupwise compositional dispersion in pasture compared to forest soils, agreeing with several earlier studies observing biotic homogenization of soil microbial communities with LU change. The compositional dissimilarities of both communities were associated with a similar subset of physicochemical conditions including clay content, pH, and total sulfur content, as well as the proportion of nitrogen in inorganic forms.
We further investigated how these potential diazotrophic communities relate to the subset of taxa that are both metabolically active, and actively transcribing the nitrogenase enzyme (via RNA-based sequencing of nifH), to determine if the latter community exhibits a community structural response to LU change differing from that of DNA-based communities, and whether active communities may better explain ANF activity. In contrast to our expectations, we found that active diazotrophs did not reflect an increase in alpha-diversity with LU change and exhibited only a modest compositional response with no environmental correlates. Surprisingly, active, RNA-based communities across LUs were more similar to each other than they were to their DNA-based counterparts, showing an opposite trend in community dispersion with respect to LU. This increase in dispersion was related to ANF rates; we identified 17 of 882 taxa whose relative abundance scaled linearly and significantly (Pearson r = 0.88) with ANF. Of these, two OTUs, annotated as Bradyrhizobium and Enterobacteriaceae, reflected strong correlations with ANF on individual bases and were found to have the third and twentieth highest relative abundances among active pasture taxa, respectively. While paired potential and active diazotrophic communities (i.e., derived from the same sample) reflected a high degree of compositional dissimilarity from each other overall, by far the most drastic shift observed was the more than 100x enrichment of the photosynthetic cyanobacterial family Aphanizomenonaceae in active diazotroph profiles, irrespective of LU. Therefore, soil surface diazotrophs may also play an important role in providing N to pastures and forests alike, suggesting further work is needed to capture measurements of ANF activity under lighted conditions
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Microbial diversity and carbon dynamics in a forage crop system
Get PDFDairy farms produce vast amounts of manure, which can be stored in anaerobic lagoons, facilitating the production of potent greenhouse gasses. Manure can be diverted to the field for use as fertilizer to aid in forage crop production. The viability of this practice depends on the breakdown of organic matter, making it available to the plant and soil microbial community. Microorganisms rest at the heart of this process, and assessments of how their structure and function changes throughout cropping cycles remain limited. In this thesis research, a field trial was established using three rates of manure application: high (100% of plant nitrogen stemmed from manure), low (50% plant nitrogen was provided by manure and 50% from chemical fertilizer), and zero (100% plant nitrogen came from chemical fertilizer) to grow forage crops over two years. Plots were sampled regularly, resulting in 22 sampling dates spanning agricultural milestones such as fertilizer application, plant growing season, and harvest. Here I found manure changes the soil microbial community, increasing microbial diversity, microbial biomass-carbon (MBC) and dissolved organic carbon (DOC) following application. Furthermore, manure associated microbial groups appear to be most responsive to application, increasing following application before diminishing throughout the growing season. Manure application also improves carbon use efficiency (CUE) and stable isotope probing (SIP) revealed microbial carbon incorporators temporarily increase following application before diminishing in the growing season. Assessment of functional genes in manure applied vs. zero manure soils revealed a greater abundance of genes involved in carbon metabolism and degradation in manure soils. Together, effective manure management can play a profound role in improving the structure and function of the soil microbial community, curating a more robust and efficient carbon cycle
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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