1,721,044 research outputs found
New findings on the ecology and ultrastructure of Cymbella ancyli cleve
No full textCymbella ancyli is a diatom species inhabiting oligotrophic lakes with a carbonate substratum. C. ancyli has a relatively wide geographic distribution and is considered to be rare in present day assemblages, while it is more common in subfossil material (particularly in the Ancylus Clay). During a comprehensive investigation on the ecology and depth distribution of benthic diatoms of Lake Tovel, C. ancyli was found to colonise stone and rock surfaces in the intermediate depth zone of the lake. The intermediate depth zone is stable, because it is not influenced by water level fluctuations, temperatures are low and nearly constant, and light is attenuated but sufficient. This niche may constitute a relict refugium for Cymbella ancyli. Analysis of the ultrastructure of C. ancyli revealed that apical pores were present, not only at the footpole, but also the headpole. This finding gives further support to the opinion that this taxon is closer taxonomically to Cymbella sensu lato than to Gomphocymbella. © 2003 Taylor & Francis Group, LLC
Three new fragilaria species (Bacillariophyta) from low-conductivity mountain freshwaters (alps and apennines)
No full textMore or less needle-shaped species of Fragilaria s.S. are difficult to identify. Here we contribute to the taxonomy of this difficult group by describing three species new to science from very low conductivity mountain freshwater environments. Two of the new species resemble taxa established by Kützing in the early 19th century: F. Rumpens and F. Vaucheriae. Fragilaria spinaspeciosa sp. Nov., from a seepage (helocrenic spring) in the northern Apennines, is superficially similar to F. Rumpens, but has a lower stria density. Fragilaria tridentina sp. Nov. is distinguished from F. Gracilis by its smaller lengthto-breadth ratio and more closely spaced areolae. Fragilaria vaucheriaeraetica sp. Nov. is distinguished from F. Vaucheriae and F. Microvaucheriae by its outline and denser striae. These last three species also have distinctly different ecologies. Fragilaria vaucheriaeraetica sp. Nov. is found in very low conductivity, very low nitrate, ultra-oligotrophic waters, while F. vaucheriae and F. Microvaucheriae are found in medium conductivity, high total phosphorus, and relatively high nitrate streams. Accurate species identification and knowledge of each species’ ecological preferences are critically important if diatoms are to be used effectively as indicators of environmental impact and climate change. Weakly buffered, low alkalinity, low nutrient and low conductivity mountain freshwater habitats are sensitive to human disturbance and biotopes for many rare (Red List) diatoms. As such, they serve as valuable early warning systems for detecting the effects of climate change and other human activities
Neidiomorpha gen. nov. (Bacillariophyta): A new freshwater diatom genus separated from Neidium Pfitzer
No full textComparative morphological (including plastids) and ultrastructural (frustule) analyses of numerous taxa within the established diatom genus Neidium Pfitzer led to the conclusion that N. binodiforme Krammer and N. binodis (Ehrenberg) Hustedt can be identified as striking exceptions. They would be more coherently allocated in a new freshwater benthic diatom genus, Neidiomorpha gen. nov. This proposed genus differs from Neidium mainly by the longitudinal structures (shallow "caves" in the mantle instead of distinct canals at the junction between valve face and mantle), by areolation pattern (including the absence of renilimbi on the internal valve surface), and raphe endings (no silica flaps causing a bifurcate appearance of the polar endings and no central endings deflected towards opposing directions). Chloroplast number and arrangement (two valve- and girdle-appressed chloroplasts placed fore and aft in the two halves of the cell), overall valve outline, and ecology (preference for medium to high conductivity freshwaters) are likely to be further relevant distinctive elements. Observations on the distribution, and habitat and choriotope preference of the two species combined with the new genus are also provided
FIGURE 3. Hexanchorus angeli n in Two new Larainae species from Guayana region, Venezuela (Coleoptera: Elmidae)
No full textFIGURE 3. Hexanchorus angeli n. sp. male and female ventral view.Published as part of Laššová, Kristína, Čiampor, Fedor & Čiamporová-Zaťovičová, Zuzana, 2014, Two new Larainae species from Guayana region, Venezuela (Coleoptera: Elmidae), pp. 187-195 in Zootaxa 3753 (2) on page 190, DOI: 10.11646/zootaxa.3753.2.8, http://zenodo.org/record/22780
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
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