1,721,579 research outputs found
Phytosterols from Dunaliella tertiolecta and Dunaliella salina: A potentially novel industrial application
No full textSterols have been extracted and analysed from Dunaliella tertiolecta and Dunaliella salina, in order to evaluate a potentially novel industrial exploitation of these microalgae as source of phytosterols. The effect of salt concentration on sterols yields has been studied varying the quantities of NaCl into culture medium. Twelve sterols were identified by Gas-chromatographic MS/MS analysis for both algal strains. The most abundant phyrosterols were (22E,24R)-methylcholesta-5,7,22-trien-3 beta-ol (ergosterol) and (22E,24R)-ethylcholesta-5,7,22-trien-3 beta-ol (7-dehydroporiferasterol). The whole sterol fraction consisted mainly of phytosterols (C(28) and C(29) sterols). Good yields of total sterols were achieved at lower salt concentration (1.3% and 0.89% of dry weight in D. tertiolecta and D. salina, respectively, at 0.6 M NaCl), while an increase in salt concentration resulted in a significant decrease in total sterols yield. (C) 2010 Elsevier Ltd. All rights reserved
Tunable microwave-assisted aqueous conversion of seaweed-derived agarose for the selective production of 5-hydroxymethyl furfural/levulinic acid
No full textA simple, highly efficient and tunable microwave-assisted conversion of seaweed-derived agarose into 5-hydroxymethyl furfural (5-HMF) or levulinic acid (LA), depending on the reaction conditions, is reported. The proposed system could be fine-tuned for the selective production of 5-HMF (ca. 51% yield) in the absence of any catalyst or alternatively to levulinic acid (64% yield) with the simple addition of 1% v/v sulfuric acid, both under optimized aqueous microwave irradiation conditions (10 min, 180 °C). Additionally, galactose could also be generated as the main product (45-77%) depending on the temperature and the addition of catalytic amounts of sulfuric acid. A plausible reaction mechanism is provided in which the formation of intermediates from the hydrolysis of agarose is critical to obtain 5-HMF and LA as final products
Continuous Flow Hydrogenation of Lignin‐model Aromatic Compounds over Carbon‐supported Noble Metals
No full textAn efficient continuous-flow (CF) protocol was designed for the hydrogenation of lignin-derived aromatics to the corresponding cycloalkanes derivatives. A parametric analysis of the reaction was carried out by tuning the temperature, the H-2 pressure and the flow rate, and using diphenyl ether (DPE) as a model substrate, commercial Ru/C as a catalyst, and isopropanol as a solvent: at 25 degrees C, 50 bar H-2, and a flow rate of 0.1 mL min(-1), dicyclohexyl ether was achieved in an 86 % selectivity, at quantitative conversion. By-products from the competitive C-O bond cleavage of DPE, cyclohexanol and cyclohexane, did not exceed 14 % in total. Remarkably, prolonged experiments demonstrated an excellent stability of the catalyst whose performance was unaltered for up to 420 min of time-of-stream. A substrate scope evaluation proved that under the same conditions used for DPE, a variety of substrates including alkoxy-, allyl-, and carbonyl-functionalized phenols, biphenyl, aryl benzyl- and phenethyl ethers (10 examples) yielded the ring-hydrogenated products with selectivity up to 99 % at complete conversion
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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