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The complex mechanisms of marine mucilage formation by spectroscopic investigation of the structural characteristics of natural and synthetic mucilage samples.
No full textFormation of incubated marine mucilages investigated by FTIR and UV–VIS spectroscopy and supported by two-dimensional correlation analysis
No full textThis study describes some specific aspects of the mechanisms of chemical reactions involved in the formation of marine mucilage aggregates obtained from several living organisms incubated in laboratory under static conditions in absence of water and air circulation. After appearance, the synthetic mucilages were sampled daily during the evolution of the aggregation process and for each sample infrared (FTIR) and ultraviolet visible (UV-VIS) spectra were collected. Then the spectra were examined by two-dimensional correlation analysis (2DCORR), a powerful tool for the study of the dynamic structural and compositional changes of a molecular system caused by any possible external perturbation. This approach showed specific peculiarities concerning the role played by each class of biomolecules and metals present in the aggregation of organic matter leading to mucilages. In more detail, synchronous 2DCORR applied to FTIR spectra showed that the hydrogen bond interactions played mainly by hydroxyl groups of carbohydrates and proteins, were a constant factor present in all the steps of the aggregation process, even more significant than polymerization reactions involving mono and oligosaccharides, aminoacids and oligopeptides. Disrelation 2DCORR spectra suggested that lipids such as fatty and ester fatty acids played a different role during aggregation. This different role of lipids may consist of bridging small aggregates by means of micelle formation (i.e., the so called cross-linking role) whereas their interaction with metals was negligible.
The role played by metals in the aggregation of mucilages was well described by the joint use of FTIR and UV-VIS spectra for two-dimensional correlation analysis which in this case, is called heterogeneous two-dimensional correlation analysis (2HDCORR), ([Noda, I., Ozaki, Y. Two-Dimensional Correlation Spectroscopy, Application in vibrational and optical spectroscopy, J. Wiley & Sons, Chichester UK, 2004.]). This approach showed that in presence of high concentrations of bivalent cations (Cu, Pb) and As in seawater,negatively charged polar groups of carbohydrates and proteins interact with metals to form aggregates whereas lipids do not interact with metals; in addition, interactions of lipids with polar groups of carbohydrates and proteins resulted modified or reduced. The use of two-dimensional correlation analysis for the elaboration of FTIR and UV-VIS spectra of synthetic mucilages support the evidence concerning the different roles played by carbohydrates proteins, lipids and metals during the aggregation of natural soil organic matter (SOM) and mucilages
Fulvic acids in microlayer waters of the Gerlache Inlet Sea (Anmtartica):Their distribution in dissolved and particulate phases
No full text
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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