1,720,955 research outputs found
Manganese uptake in the epiphytic lichens Hypogymnia physodes and Lecanora conizaeoides
No full textExposure of the foliose epiphytic lichen Hypogymnia physodes to 100 mM MnCl2 led to rapid absorption to extracellular cation exchange sites; saturation was reached within about 50 min. Intracellular uptake was constant in samples exposed to 100 mM MnCl2 for 10-120 min and analyzed for their Mn concentration after 1 day of recovery in the growth chamber. About 15 times as much Mn was bound extracellularly than was taken up intracellularly. Both 50 mM CaCl2 and 50 mM MgCl2 applied together with 100 mM MGCl(2) significantly reduced Mn uptake intracellularly and binding in the extracellular exchange sites. CaCl2 was more effective than MgCl2 at reducing Mn uptake intracellularly; extracellularly, CaCl2 and MgCl2 reduced Mn absorption equally. In the assays with MnCl2, alone or in combination with CaCl2, the amount of extracellularly bound Mg decreased, as did the content of Ca in MnCl2 alone or in combination with MgCl2. The results support the hypothesis that the alleviating effects of Ca and Mg on Mn toxicity, documented in previous culture experiments with H. physodes, were, at least in part, due to reduced Mn uptake. H. physodes bound significantly more Mn from 1 to 100 mM MnCl2 solutions on its extracellular exchange sites than did the crustose Lecanora conizaeoides. Further, H. physodes, but not L. conizaeoides released significant amounts of Ca and Mg from the extracellular exchange sites during Mn uptake. Intracellular Mn concentrations increased and the Ca/Mn and the Mg/Mn ratios decreased with increasing Mn supply in either species. The intracellular Mg/Mn ratio was higher in L. conizaeoides than in H. physodes. Its lower extracellular Mn uptake combined with lower losses of Ca and Mg as well as the higher intracellular Mg/Mn ratio may contribute to higher Mn tolerance of L. conizaeoides in the field, which was observed in spruce forests of the Harz Mountains, northern Germany. Neither H. physodes nor L. conizaeoides had significant amounts of extracellularly bound Mn3+ or Mn4+ when compared with the concentration of Mn2+. Thus, immobilization of Mn2+ by oxidizing, as known from non-lichenized green algae, is unlikely as tolerance mechanism in L. conizaeoides. (C) 2002 Elsevier Science B.V. All rights reserved
Effects of manganese on the viability of vegetative diaspores of the epiphytic lichen Hypogymnia physodes
No full textSoredia of the lichen Hypogymnia physodes cultivated with Bold's basal medium on agar plates for 8 days exhibited decreasing growth rates along with increasing Mn concentrations above 3 mM. Ca and Mg added separately or in combination, alleviated Mn toxicity. The chlorophyll a and b content of the soredia was reduced under the influence of Mn and was positively correlated with the rate of grown soredia. Trebouxia cells of the soredia grown with excess Mn were smaller than control cells, had reduced chloroplasts and were partly collapsed; fungal hyphae were shortened and strongly swollen. Disintegrated cell walls occurred both in algal and fungal cells. Excess Mn was sequestered in extracellular encrustations together with phosphate as corresponding anion. Intracellularly, Mn was accumulated in polyphosphate granules both in algal and fungal cells. Mn uptake was correlated with significant loss of Na, Mg and Ca, particularly from the mycobiont. Fungal cell walls also lost significant amounts of P. The same damage symptoms occurred in cells of soredia both grown or not, but the former had a higher share of intact cells. Damaged cells of both types of soredia had equally increased Mn concentrations, whereas the total Mn content was higher in not grown soredia than in the grown ones due to the greater amount of damaged cells in the former. The Si-Mn ratio in cell walls of intact Trebouxia cells was significantly higher than in collapsed cells. The experimental evidence of Mn sensitivity of If. physodes soredia corresponds to studies of epiphyte vegetation in montane spruce forests of northern Germany that revealed decreasing cover values of H. physodes with an increasing Mn content of the substrate. (C) 2002 Elsevier Science B.V. All rights reserved
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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