1,720,954 research outputs found
Residual Chemical Shift Anisotropies in the Structure Determination of Small Molecules
No full textABSTRACT The determination of the relative and absolute configuration of natural compounds is a very challenging task. Among other anisotropic NMR parameters, residual chemical shift anisotropy (RCSA) induced by anisotropic media is an invaluable tool to determine relative configurations of natural and synthetic organic molecules in solution. This review introduces various RCSA‐based methodologies for the structural elucidation of natural products. The current availability of alignment media in organic solvents for RCSA measurements is also discussed as are applications of RCSAs for structural analysis of various natural products.Science and Engineering Research Board https://doi.org/10.13039/50110000184
Quantification of geometric isomers of citral and minor oleochemicals in Cymbopogon flexuosus (lemongrass) and Cymbopogon nardus (citronella) essential oils by <sup>1</sup>H qNMR method
No full textThe 1H quantitative Nuclear Magnetic Resonance (qNMR) has emerged as a powerful analytical tool due to its high sensitivity, ability to provide absolute quantification, and most importantly, its univocal structural assignment. So far, 1H qNMR has been used to quantify only the major constituents of the essential oils (EOs). Since the minor constituents of the EOs play a role in its various properties, quantification of minor constituents is essential. In this study, a 1H qNMR method is developed to quantify major and minor oleochemicals in the multifaceted Cymbopogon flexuosus (lemongrass) and Cymbopogon nardus (citronella) EOs. The 1H qNMR method is validated in terms of selectivity, linearity, robustness, and accuracy/precision using the 1H NMR spectra of citral. The use of a high-field 800 MHz NMR provides high spectral resolution, allowing discrimination between closely spaced signals. This enables in-depth analysis of the complex mixtures of essential oils, facilitating the quantification of twelve distinct components, including some at concentrations in the double-digit μg range. These results align with prior reports demonstrating the suitability of high-field NMR spectrometers for accurate quantification of analytes at low μg/mL concentrations. This method demonstrates high sensitivity, with a limit of detection (LOD) of 30.09 μg/mL and a limit of quantification (LOQ) of 90.93 μg/mL. It also proves to be highly reliable, showing a coefficient of variation (CV) of less than 1% across different acquisition and processing conditions tested. The key distinction between lemongrass and citronella oils lies in their citral content, which ranges from 72 to 74% in lemongrass oil compared to only 12–18% in citronella oil. The quantification of both major as well as minor constituents highlights the applicability of the 1H qNMR method for comprehensive profiling of EOs
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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