1,720,954 research outputs found
Problems in extraction and spectrophotometric determination of chlorophyll from epilithic microbial biofilms: towards a standard method
No full textA variety of methods are available to extract chlorophyll from epilithic biofilms using solvents. The relative efficiency of these has not been determined simultaneously and there is no recognized standard procedure. In this paper techniques for sample collection, storage, preparation and extraction are reviewed and compared experimentally.Extraction of chlorophyll was incomplete unless biofilms were fully hydrated. This factor was highly significant for all the solvents tested, with at least three times more pigment being extracted from hydrated samples than from dry ones. Methanol was the most efficient solvent, releasing over 96% of the total chlorophyll during a single extraction; hot ethanol extracted 86%, while acetone extracted less than 50%. Sonicating samples during extraction did not release any additional pigment. Centrifuging to remove suspended material did not alter estimates and was not advantageous. Rugose rock surfaces released more chlorophyll than smooth ones. However, a simple method to quantify surface rugosity at an appropriate scale was not available.Based on these observations, a standard method for chlorophyll extractions from epilithic biofilms using 100% methanol at room temperature (20°C) is proposed. This technique requires considerably less supervision than previously preferred methods and gave a chlorophyll extract which was stable for 15 h
Biologically generated habitat provision and diversity of rocky shore organisms at a hierarchy of spatial scales
No full textThe diversity and abundance of intertidal organisms found on moderately exposed shores were compared between biologically generated complex and less complex habitats at four different spatial scales. For macrobiota, comparisons were made between Fucus clumps and open areas (barnacle covered or bare rock) and then between barnacle covered rock and ‘bare’ rock. Microbiota were compared on barnacle plates and on the rock surface and at a finer resolution on the plates themselves and pits in the plates. Macrobiota were quantified at two levels of resolution by direct observation and under low power magnification. Microbiota were examined at two levels of resolution with a scanning electron microscope. For macrobiota the average number of species was significantly greater in complex habitats at both levels of resolution. The average number of individuals associated with the Fucus clumps was significantly lower than that on adjacent areas of barnacle covered and bare rock. However, the average number of individuals associated with the barnacle matrix was significantly greater than that on surrounding rock. The differences were entirely caused by a greater abundance of barnacles and species associated with the barnacle matrix on exposed rock outside the Fucus clumps. For microbiota there were large differences in species composition; cyanobacteria were predominant on the rock surface whilst diatoms dominated the barnacle plates. The diversity of this assemblage was low and no differences in species numbers were apparent between the two habitats. At a finer scale, abundance of individuals was much greater in the pits than on flat areas of the surrounding plates and there was a slightly elevated average number of species per sampling unit. This paper illustrates the importance of using a variety of resolutions to measure biodiversity and the importance of biological habitat provision in maintaining biodiversity
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
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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