1,720,960 research outputs found
Chemical composition and larvicidal activity of several essential oils from Hypericum species from Tunisia
No full textThe chemical composition of the essential oils extracted from some Tunisian Hypericum species and their larvicidal activity against Culex pipiens larvae were evaluated.
The chemical compositions of the essential oils from the aerial plant parts were analyzed using gas chromatography–mass spectrometry. One hundred and thirty-four compounds were identified, ranging between 85.1 and 95.4 % of the oil composition.
The components were monoterpene hydrocarbons, oxygenated monoterpenes, sesquiterpene hydrocarbons, oxygenated sesquiterpenes, non-terpenic hydrocarbons, and others.
The larvicidal activity of the essential oils was evaluated using a method recommended by WHO. Larvicidal tests revealed that essential oils from the Hypericum species have a significant larvicidal activity against C. pipiens, with LC50 ranging between 102.82 and 194.70 ppm. The most powerful essential oils against these larvae were Hypericum tomentosum and Hypericum humifusum samples, followed by the essential oil of Hypericum perforatu
Volatile components of Hypericum humifusum, Hypericum perforatum and Hypericum ericoides by HS-SPME-GC and HS-SPME-GCMS using nano scale injection techniques
No full textSeveral products were developed, which contain Hypericum herb or its extracts as additives and several brands of food, beverages and yoghurts include this herb. Some Tunisian Hypericum species considered rare plants in Tunisia and their sampling need in the most of cases authorization from the authorities. The study of their essential oils in Tunisia was sometimes limited by operational analysis. The analysis of full dry aerial parts of these plants from Tunisia has been carried out by headspace solid phase microextraction (HS–SPME) coupled with gas chromatography–mass spectrometry (GC–MS). The obtained results showed that the non-terpene hydrocarbon fraction dominated the chemical composition of volatiles from the three Hypericum species with clear abundance of n-undecane, accounting 44.4%, 36.2%, and 20.2% for H. humifusum, H. perfoliatum and H. ericoides, respectively. This fraction was followed by terpenic hydrocarbons, and oxygenated terpene
Chemical composition and intraspecific variability of the essential oil of five populations of Hypericum triquetrifolium Turra growing in North Tunisia
No full textThe chemical composition of the essential oils of five populations of Hypericum triquetrifolium Turra from Tunisia and their intraspecific variability were analyzed in detail by GC/MS. One hundred seventy-four compounds were identified, representing averages of 87.9 to 98.7% of the oil composition. The components are represented here by homologous series of monoterpene hydrocarbons, oxygenated monoterpenes, sesquiterpenes hydrocarbons, oxygenated sesquiterpenes, non-terpenic hydrocarbons, and others. Sesquiterpene hydrocarbons were the most abundant chemical compounds. Multivariate chemometric techniques, such as cluster analysis (CA) and principal component analysis (PCA), were used to characterize the samples according to the geographical origin. By statistical analysis, the analyzed populations were classified into four chemotype groups
Chemical Composition and Free Radical Scavenging Activity of the Essential Oil of Achillea ligustica All. Wild Growing in Lipari (Aeolian Islands, Sicily)
No full textThe chemical composition of the essential oils from aerial parts and flowers of Achillea ligustica All., collected in Lipari (Aeolian Islands) was evaluated by GC and GC-MS. (Z)-Chrysanthenyl acetate was the most abundant component of both oils (29.6% in A1 and 27.8% in F1) followed by viridiflorol (16.8% in A1 and 21.6% in F1), bornyl acetate (8.7% in A1 and 11.6% in F1) and 1,8-cineole (7.4% in A1 and 9.3% in F1). A comparison with the composition of the different populations studied so far has been done. Futhermore the free radical scavenging activity of the oil (A1) was determined by DPPH and ABTS methods
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
- …
