1,720,971 research outputs found
Eco- fingerprinting of Borghiella dodgei (Dinoflagellata): experimental evidence of a narrow environmental niche
Full text linkThe dinoflagellate Borghiella dodgei Moestrup, Hansen et Daugbjerg, was cultivated in the laboratory under different temperature, nutrients, and light conditions. Growth rates, cell biovolume, cyst formation, pigment content, and MAAs were determined. Experiments showed that this algae grew well at low temperatures, and grew slowly without organic supplements. While it was not able to grow in the dark, Borghiella survived for long periods without a light source.
In particular, Borghiella grew well at temperatures of <6 °C. Cell yields increased ten fold with organic supplements and increasing irradiance levels had a positive effect on growth.
Cell volume was not affected by light conditions but increased with an increase in temperature or a lack of nutrients. The formation of thick-walled resting cysts was enhanced by an increase in temperature while light conditions did not effect encystment. Chlorophyll a content per cell was inversely related to irradiance levels. Cultures with a high number of resting cysts were characterized by a red-brick colour and altered peridinin/chlorophyll contents. Even after several years of culturing, Borghiella was still capable of MAA synthesis.
The temporal spatial occurrence of this species in Lake Tovel was confronted with results from in vitro experiments. Borghiella’s growth requirements make it well suited to the unique habitat of Lake Tovel
Environmental controls of epilithic diatom depth-distribution in an oligotrophic lake characterized by marked water-level fluctuations
No full textThe depth-distribution of epilithic diatoms in a carbonate meromictic lake (south-eastern Alps), characterized by marked water-level fluctuations, was investigated. Fixed stations were placed along a depth-profile at intervals of 2-3 m and sampled throughout the year using scuba diving. Diatom analysis included quantification of living cells (biovolume calculations) and the estimation of fucoxanthin concentration, which, coupled with the analysis of digested material, permitted taxonomic determination at specific or subspecific level. Multivariate analyses indicated the following variables to be significant: water-level fluctuations, photosynthetically active radiation, silica and nitrates. Diatoms had distinct depth-distributions. Quantification of densities, biovolumes and Chl a, and physiological (senescence index, fucoxanthin), functional (photosynthetic efficiency), and community structure (diversity) parameters allowed the definition of three depth-distribution zones (shallow, mid-depth and deep). The different diatom communities in these zones were confirmed by ANOSIM (analysis of similarity). The shallow, mid-depth, and deep zone were characterized by disturbance due to water-level fluctuations, high stability with favourable growth conditions and severe light limitation, respectively. Community composition and diversity depth-distribution features remained relatively stable throughout the year, while marked changes in benthic diatom biovolumes were modulated by competition for light with phytoplankton. Fucoxanthin was strongly correlated with epilithic diatom biovolumes. The results indicate that depth-distribution patterns should be considered when performing lake diatom biodiversity inventories and integrity evaluations because water-level fluctuations are likely to increase in many lakes due to increased withdrawal of water and climate change in the future. © 2009 British Phycological Society
On-line identification of secondary metabolites in freshwater microalgae and cyanobacteria by combined liquid chromatography-photodiode array detection-mass spectrometric techniques
No full textThe analysis and identification of a wide range of secondary metabolites biosynthesized by different algal taxa and cyanobacteria has been performed through a selective and sensitive methodology, mainly based on reversed-phase HPLC coupled both to UV photodiode array detection and to atmospheric pressure mass spectrometric techniques (HPLC-DAD-APIMS). Results are reported here with special attention to the analyses carried out both on the natural phytoplankton (mixed populations) of Lake Tovel (Northern Italy, Brenta Dolomites) and on enclosure-produced biomass of the dinoflagellate Glenodinium sanguineum Marchesoni (1941). This analytical procedure might represent a powerful tool for the fast screening of the taxonomic composition (broad groups, e.g. divisions) of natural mixed populations of phytoplankton, by providing a reliable distribution of accessory pigments extracted from microalgae, such as carotenoids and chlorophyll derivatives. Furthermore, we showed that in the same chromatographic analysis other classes of natural products, such as galactolipids, alkaloids, sterols and mycosporine-like amino acids, can be detected by using combined optical and mass spectrometric techniques. These metabolites represent distinctive biochemical signatures, sometimes even at the species level. © 2005 Elsevier B.V. All rights reserved
A new method for the identification and the structural characterisation of carotenoid esters in freshwater microorganisms by liquid chromatography/ electrospray ionisation tandem mass spectrometry
No full textLiquid chromatography/electrospray ionisation mass spectrometry (LC/ESI-MS) has been employed to identify carotenoid esters present in raw organic extracts of pigmented freshwater microalgae and to gain structural information on these compounds. In particular, acyl carotenoid derivatives of Haematococcus pluvialis and Euglena sanguinea have been characterised by tandem mass spectrometry (MS/MS) in a quadrupole ion trap. ESI-MS/MS allows recognition of the presence of carotenoid esters in complicated mixtures without any initial chromatographic work-up and without the need to use UV-V is photo-diode array (PDA) detectors. Product ion scans of the [M + Na]+ ion lead to known neutral losses of the C7H8 and C8H10 residues from the conjugated polyene moiety of the carotenoid unit, that permit the unambiguous identification of the carotenoid itself. These structurally relevant ions are not observed in positive or negative ion APCI (atmospheric pressure chemical ionisation) mass spectra. Moreover, the several product ions observed in positive and/or negative ion ESI-MS/MS not only are a diagnostic signature of the main structural features of the acyl chains such as length, position and unsaturation, but also display the nominal mass of the parent xanthophyll. Our methodology has been validated (i) by using esters of astaxanthin obtained from off-line purification of the H. pluvialis extracts and structurally elucidated through proton nuclear magnetic resonance (1H-NMR) spectroscopy and (ii) by product analysis of esters by alkaline hydrolysis. The characterisation of the unknown carotenoid esters of E. sanguinea is a demonstration of the capabilities of this methodology. Copyright © 2008 John Wiley & Sons, Ltd
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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