1,720,964 research outputs found
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
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
Metagenome-based analysis of the functional potential of a marine sediment community dominated by ANME-2c
Full text linkMethane is the most abundant hydrocarbon in the atmosphere and after CO2; it contributes for 14% of global greenhouse gas emissions. Marine sediments are a large reservoir of methane where approximately 80% of the methane is formed through a biological process known as methanogenesis by methanogenic archaea. Despite the high rates of CH4 production in marine sediments, about 90% of methane flux from sediment is recycled through the microbial process, anaerobic oxidation of methane (AOM) with sulfate. The AOM is catalyzed by uncultivated anaerobic methanotrophic archaea (ANME-1, 2 and 3) which thus have a crucial role regulating the flux of methane from marine environments to the atmosphere. In this study, the functional potential of an ANME2c-dominated sediment horizon at 20-22cm below the seafloor in the G11 pockmark at Nyegga has been investigated using a metagenomic approach. Total DNA was applied to 454-pyrosequencing and 142.8 MB (1001981 sequence reads) sequence information was assembled into 22706 contigs. The assembled contigs were clustered into 4 bins based on multivariate statistics of tetra-nucleotide frequencies combined with the use of interpolated Markov models, using Metawatt binner tool. Three of the metagenomic bins were imported into RAST for annotation. From the bins, genes encoding phylogenetic marker genes, 16S rRNA, Adenylylsulfate reductase (AprAB) and Methyl CoM reductase (Mcr) subunit A (McrA) were extracted. Phylogenetic analysis suggested that metagenomic bin II was of ANME2c and bin I was of Desulfobacteraceae. A complete set of genes encoding enzymes involved in reverse methanogenesis including Coenzyme F420-dependent N5N10-methylene tetrahydromethanopterin reductase (Mer) and Methyl CoM reductase (Mcr) was observed in the ANME2c bin. In the Desulfobacteraceae bin, the enzymes involved in three enzymatic reactions of the dissimilatory sulfate reduction pathway, Sulfate adenylyltransferase (Sat), Adenylylsulfate reductase (AprAB) and Dissimilatory sulfite reductase (DsrABC) were identified. Furthermore, the electron transporter proteins, QmoABC (quinone-interacting membrane-bound oxidoreductase) and DsrMJKOP complexes known to donate electron to AprAB and DsrABC, respectively, were found in this bin. The presence of CO-dehydrogenase/acetyl-CoA synthase (Fd2−red), the key enzyme of acetyl-coenzyme A (CoA) pathway, in the Desulfobacteraceae and ANME-2c bins indicated a potential for CO2 fixation via this pathway in both groups of microorganisms. The obtained data did not reveal any information about substrate spectrum by the Desulfobacteraceae as no genes encoding an uptake hydrogenase, formate dehydrogenase and lactate dehydrogenase were identified. The metagenomic analyses did not support the use of other electron acceptors like nitrate of iron/manganese by the ANME2c population. However, the presence of gene fragments of a nitrogen fixation pathway in methanogenic archaea in the metagenomic data indicated a potential for this process in the community. Altogether, this study has fortified the partnership of ANME-2c and sulfate-reducing bacteria from the Desulfobacteraceae family, and revealed new information about other possible aspects of syntrophy, in addition to the methane oxidation coupled to sulfate reduction, in the Nyegga sediments
Using induced pluripotent stem cells for modeling POLG mitochondrial disease : Stamceller som modellsystem for å behandle mitokondriesykdom
Full text linkBackground: More than 90% of the energy required to sustain life is provided by mitochondria through the process of oxidative phosphorylation (OXPHOS). The role of mitochondria, however, is not restricted to supplying cellular energy; they are also involved in many other cellular processes including differentiation and cell death. Mitochondrial functional impairment is also associated with a wide spectrum of devastating diseases known as mitochondrial diseases.
Among the most common mitochondrial disorders are POLG-related diseases. These comprise a large number of different phenotypes with age of onset ranging from infancy to adulthood. These complicated and incurable disorders are caused by mutations in the POLG gene which encodes the catalytic subunit of DNA polymerase gamma (POLG). The enzyme POLG is involved in mitochondrial DNA (mtDNA) replication, and despite being present in all cells, the main disease manifestations show tissue and cell type-specificity. The patho-mechanisms underlying POLG-disease remain poorly documented mostly due to the lack of reliable animal models and limited access to affected tissues. Human induced pluripotent stem cells (iPSC) with the capacity of self-renewal and differentiation into all relevant tissues provide a promising tool for modeling POLG-related diseases and investigating possible treatments.
Primary clinical experiments have shown that the high energy demanding tissues such as brain, liver and skeletal muscle are severely affected, however, cardiac tissue appear clinically unaffected. Understanding this paradox is important as it can increase our understanding of the tissue specific nature of these diseases.
Aim: The main aim of this project was to model POLG-related disease using iPSCs derived from patient fibroblasts and differentiated into different cell types. We planned to differentiate them to cardiac and neuronal cells to investigate the impact of POLG mutations on mitochondrial function.
Methods: In paper I, we modified neuronal differentiation protocols to generate neural stem cells (NSC), and investigate the impact of POLG mutation on mitochondrial function by comparing different mitochondrial parameters in control and mutant NSCs. We employed different methods including flow cytometry, PCR, western blotting and Liquid Chromatography/Mass Spectrophotometry (LC/MS) to investigate the mitochondrial content, mtDNA level, respiratory chain complexes and NAD+ metabolism, ROS generation and activation of mitophagy. In the second project, we established a high throughput method for differentiating cardiomyocytes in 96well plate format in order to monitor mitochondrial changes during early stages of cardiac differentiation (paper 2). In the third paper, we differentiated human pluripotent stem cells (PSC) towards mesoderm, cardiac progenitors and later to cardiomyocytes using the protocol established in paper II. We used this to investigate changes of mitochondrial content and mtDNA copy number during early stages of mesoderm differentiation using different methods including flowcytometry and qPCR. We also studied mitochondrial function and metabolic remodeling by seahorse analysis and flow cytometry.
Results: The comparison of different mutant and control cell types including fibroblasts, iPSCs and NSCs in paper 1 showed that only NSCs manifested all the features that were seen in patient post-mortem tissues including mtDNA depletion and complex I deficiency. Using our iPSC-derived NSC model, we also showed the impact of POLG mutation on the overproduction of ROS and impairment of NAD+ metabolism, and how this led to increased cellular senescence.
In the second part of the study, we established a high-throughput cardiomyocyte differentiation protocol with low variation of differentiation efficiency between wells and between runs of differentiation. We also showed that the differentiated cardiomyocytes generated by our micro plate format were fully functional and expressed the correct cardiomyocyte markers. We used this protocol in the third project to study the mitochondrial changes during early mesoderm differentiation towards cardiac lineage. We confirmed the previous reported metabolic remodeling during mesoderm differentiation, however, in contrast to previous studies, and our expectations, we showed that mitochondrial content and mtDNA copy number decreased during the early stages of cardiomyocyte differentiation.
Conclusion: Our NSC model of POLG disease is the first that faithfully replicates the findings observed in patient post mortem tissues. Using this model, we showed that NSC developed mtDNA depletion and complex 1 deficiency and we confirmed the metabolic impact of this by demonstrating the changes in the NAD+/NADH ratio. We could also examine the downstream consequences of POLG mutation on aspects of mitochondrial function such as ROS production and show that the combined effects led to increased cellular senescence. Considering the regenerative capacity of NSCs, our aim is to use this robust model system for drug screening and identification of possible treatment for POLG diseases.
In our work with cardiomyocytes, we showed that our method using the 96 well microplate format was robust and efficient with low inter well variation. This means that it too can be used for high throughput experiments such as studying the early stages of cardiac development and drug screening.
In contrast to earlier reports, we detected a significant reduction in mitochondrial mass and mtDNA level during mesoderm differentiation towards cardiac lineage. Despite the remarkable mitochondrial reduction, we showed that differentiated cells nevertheless had a higher capacity to generate energy through OXPHOS. Overall our results suggested a unique mitochondrial remodeling process in which the metabolic switch from glycolysis to OXPHOS occurs without an increase in mitochondrial mass and mtDNA level. In the other words, metabolic remodeling is associated with mitochondrial maturation and increased mitochondrial activity rather than elevated mitochondrial mass and mtDNA level
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
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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