1,720,954 research outputs found
Amino Acid Racemization Dating
No full textAmino acid racemization dating (AAR) is a valuable technique used in geochronology and archaeology for estimating the age of biological materials based on the extent of racemization of amino acids. L-amino acids and D-amino acids are the two mirror-image forms, or enantiomers, of amino acids, which are the building blocks of proteins. Racemization is the process by which the L-amino acids gradually turn into D-amino acids, changing the ratio of these enantiomers over time. Amino acid racemization dating requires a number of important processes. Initially, a sample comprising of organic components is taken from the relevant geological or archaeological site. A rock from the Bahamas served as the sample. After that, acid hydrolysis is used to extract the amino acids from the sample. A two-step derivatization procedure including capping the side chains of the amino acids extracted from the sample may be used prior to the amino acids being submitted to gas chromatography. By changing amino acids into more volatile and stable derivatives, this procedure seeks to improve amino acid separation and detection. Using thionyl chloride and 2-propanol, one amino acid side chain is capped in the first step. Then comes the second derivatization, which caps the opposite side chain and uses pyridine and trimethyl acetyl chloride. As a result, the D/L enantiomers are more suited for gas chromatographic examination since they can separate more effectively. The derivatized amino acids were dissolved in methylene chloride and injected into the GC column using an autosampler to determine the relative abundance of L- and D-amino acids
Synthesis of Porphyrin Complexes for Solar Cells
No full textIn recent years, solar energy has emerged as a key area of scientific research due to its potential for large-scale energy production. Our research focuses on the light-absorbing components of solar cells, which are often based on molecules known as porphyrins. As an initial step toward developing more complex compounds, we first synthesized a mixed porphyrin. To verify the success of this synthesis, we used proton NMR spectroscopy to confirm the formation of the desired product. Afterwards, we used preparative thin-layer chromatography (prep-TLC) to identify the porphyrin and separate it from any impurities present in the crude product. With the porphyrin compound confirmed and purified, our next objective is to perform a Sonogashira coupling reaction to attach additional functional groups to the porphyrin.. With this preliminary data, we are now prepared to couple the purified mixed porphyrin with other compounds, ultimately creating dyes suitable for use in solar cell
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
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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