1,721,030 research outputs found
The Fascinating Coat Surrounding Mycobacteria
No full textThe mycobacterial cell envelope is fascinating in several ways. First, its composition is unique by the exceptional lipid content, which consists of very long-chain (up to C90) fatty acids, the so-called mycolic acids, and a variety of exotic compounds. Second, these lipids are atypically organized into a Gram-negative-like outer membrane (mycomembrane) in these Gram-positive bacteria, as recently revealed by CEMOVIS, and this mycomembrane also contains pore-forming proteins. Third, the mycolic acids esterified a holistic heteropolysaccharide (arabinogalacan), which in turn is linked to the peptidoglycan to form the cell wall skeleton (CWS). In slow-growing pathogenic mycobacterial species, this giant structure is surrounded by a capsular layer composed mainly of polysaccharides, primarily a glycogen-like glucan. The CWS is separated from the plasma membrane by a periplasmic space. A challenging research avenue for the next decade comprises the identification of the components of the uptake and secretion machineries and the isolation and biochemical characterization of the mycomembrane
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
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
Covariate identification in the human gut microbiome.
No full textSummary
More than eighty years after the isolation of the first gastrointestinal bacterium in 1885, research on the microbes inside our body finally took off. Since then, improvements in culturing techniques paved the way for the exploration of the complex microbial community inside our guts. In the last decades, the rapid development of sequencing approaches, allowing the identification of our microbial companions based on their DNA, has speeded up the field of gut microbiome research substantially. Sequencing-based assessment of microbial communities in human fecal material in medium-scale (N<400), cross-sectional studies have now linked alterations in gut microbiota composition to disease, as well as chronically suboptimal health and wellbeing. The discovery of these associations has stimulated the search for specific microbiome-based biomarkers for a wide range of pathologies. However, major challenges still hamper the once assumed imminent translation of microbiome monitoring into diagnostic and clinical practice. One such hurdle is the lack of knowledge on the impact of host and environmental factors on microbiota variation within a healthy population, which is essential for robust disease marker identification.
In this thesis we applied a two fold strategy to improve knowledge about the functioning and population-level variability of the gut microbial-human ecosystem in healthy individuals. First, we aimed to facilitate the scale up of faecal sampling initiatives by upgrading time and cost-efficiency of the ‘golden standard’ of fecal sampling procedures, while maintaining or improving user-experience, such that the large numbers necessary to detect a presumed signal in a background of multiple confounders can be obtained faster and with fewer resources. Second, we characterized the effect of specific parameters on the gut-ecosystem, thereby contributing to a better understanding of the factors driving it, and consequently aiding future gut microbiome studies through improved study design, confounder analyses and interpretation of results.
For the first objective, facilitating the scale up of faecal sampling initiatives, we evaluated current collection and preservation techniques of fecal samples for microbiome research on various aspects, including among others userfriendliness, cost, and effect on observed microbiota compostion. Although immediate freezing of samples can still be considered the golden standard, the substantial processing costs associated to such protocols, which mostly stem from cold chain management and aliquotting frozen material under sterile conditions in the laboratory, is the main reason to opt for buffer-based solutions (chapter 3). We designed two new, improved fecal sampling devices allowing rapid aliquotting of frozen fecal material. These devices reduce processing time and cost related to frozen fecal sampling and combine this with similar or improved user-experience for study participants. With the proposed devices large-scale, high-quality sampling would be no longer cost-prohibitive (chapter 4).
Several studies were carried out in order to characterize the effect of specific parameters on the gut-ecosystem, as stated in the second objective. Building upon the rich metadata of the Flemish Gut Flora project, a large-scale (N>1000) research effort based in Belgium and an equally scaled Dutch validation cohort, we identified a set of 69 microbiota covariates with a replication rate of over 92% and a cumulative, nonredundant effect size of 7.63%. The observed small effect size suggests the influence of additional, currently unknown covariates as well as intrinsic microbial ecological processes such as founder effects, species interactions, and dynamics. Out of a total of 503 parameters, stool consistency, as measured by self-assessed Bristol stool scale (BSS) score, emerged as the top feature covarying with fecal microbiome composition. We demonstrated in several study cohorts that stool consistency strongly correlates with all known major microbiome markers. It is negatively correlated with species richness (the number of species in a sample) and linked to the relative abundance of key species Akkermansia and Methanobrevibacter. Enterotypes, which are prevalent constellations of gut microbiome composition, are distinctly distributed over the BSS-scores, with a higher prevalence of Prevotella-enterotyped samples in the looser stool categories (chapters 5 and 6). BSS score has been put forward as an indicative measure of transit time, but also reflects water availability. Both rate of passage and water activity variation are thus potential mechanisms for niche differentiation within the colon ecosystem. By demonstrating - through water activity measurements - that fecal samples provide sufficient unbound water to support the growth of most bacteria, we however showed that the observed effects of stool consistency on colon microbiota composition are unlikely to be a result of water activity variation, but rather represent differences in transit time or other, currently unassessed variables (chapter 7).
Furthermore we assessed the effect of inulin supplementation, combining ecosystem-wide microbiome and metabolome profiling techniques, throughout a cross-over intervention aimed at improving constipation in healthy individuals. We demonstrated that the effect of inulin on the fecal microbiota is mainly restricted to changes in Anaerostipes, Bilophila, and Bifidobacterium relative abundances. Regarding fecal metabolites, only dodecanal was found to increase abundance with the inulin intervention. Hence, inulin indeed selectively influences growth of a limited number of colon bacteria, meeting the most debated criterion of the definition of prebiotics. In addition, we found first indications that reduction of Bilophila, a genus containing known pathobionts, is associated with enhanced host wellbeing and could play a role in the inulin-associated prebiotic mechanism (chapter 8).
In conclusion, the fecal sampling devices designed during this thesis together with the obtained results regarding covariates of gut microbiome composition will contribute to the development of microbiome research as a clinical and diagnostic field.status: Publishe
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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