1,721,040 research outputs found
Characterization of arsenic content in marine organisms from temperate, tropical and polar environments.
No full textBioaccumulation and biotransformation of arsenic in the Mediterranean polychaete Sabella spallanzanii: experimental observations.
No full textHyperaccumulation of vanadium in the Antarctic polychaete Perkinsiana littoralis as a natural chemical defence against predation.
No full textHyperaccumulation of vanadium in the Antarctic polychaete Perkinsiana littoralis as a natural chemical defense against predation
No full textExceptionally high levels of trace metals have been reported in specific tissues of certain polychaetes. In the present
study, the Antarctic fan worm Perkinsiana littoralis was shown to hyperaccumulate vanadium in the branchial tissues, and the
hypothesis of an antipredatory strategy has been investigated
Trace metals (Ag, Al, As, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, V, Zn) were measured by atomic absorption
spectrophotometry in tissues of P. littoralis and, only for V, in two Antarctic bivalves and in various Mediterranean polychaetes.
Subcellular distribution of vanadium was investigated in P. littoralis after differential centrifugations; feeding trials with the
Antarctic rock cod Trematomus berancchii were performed to test the palatability of P. littoralis
Analyses of trace metals in tissues of P. littoralis confirmed the naturally high bioavailability of cadmium due to upwelling
phenomena in the investigated area and revealed extremely high concentrations of vanadium up to 10,000 A mu g/g, in the branchial
crowns; much lower concentrations were measured in the body portions and even less in the Antarctic bivalves and in
Mediterranean polychaetes. The subcellular distribution indicated that this metal was associated in branchial crowns with both
heavy components and vanadium binding proteins; the latter predominated in body tissues, although with a different pattern of
molecular weight. Feeding trials suggested that the elevated levels of vanadium in branchial crown of P. littoralis act as chemical
deterrents against predation in more exposed tissues
The hyperaccumulation of toxic metals might represent a common antipredatory strategy for unpalatable branchial crowns of
sabellid polychaetes, as recently hypothesized also for the high concentrations of arsenic in the Mediterranean Sabella spallanzanii.
The evolution of such adaptation and the reasons behind the possibility for different species to accumulate different metals represent
a stimulating field of investigation for future studies
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
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