1,720,988 research outputs found
New lamellar structure formed by an adamantyl derivative of cholic acid
No full textThe self-aggregation of the sodium salt of a new adamantyl amide of the 3 beta-amino derivative of cholic acid (Na-AdC) in aqueous solution has been investigated by surface tension, dynamic light scattering, fluorescence, small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) measurements. These last two techniques suggest that a lamellar phase, consisting of charged bilayers of Na-AdC separated by solvent and periodically stacked, is formed in aqueous solution. The structure of the bilayer is inferred from the resolution of the crystal of the compound in its acid form. The adamantyl moieties, which are mutually interlocked, reside in the central region of the bilayer, and the carboxylic groups are directed toward the hydrophilic region. The structure is open enough to allow water molecules to interact with a fluorescence probe located at the central hydrophobic region
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
Diarmed (adamantyl/alkyl) surfactants from nitrilotriacetic acid
No full texttThe compounds presented here constitute a clear example of molecular biomimetics as their designis inspired on the structure and properties of natural phospholipids. Thus novel double-armedsurfactants have been obtained in which nitrilotriacetic acid plays the role of glycerol in phospho-lipids. The hydrophobic arms are linked to the head group through amide bonds (which is also thecase of sphingomyelin): (R1NHCOCH2)(R2NHCOCH2) NCH2CO2H (R1being CH3(CH2)11, CH3(CH2)17,CH3(CH2)7CH CH(CH2)8, and adamantyl, and R2= adamantyl). The dependence of the surface tensionwith concentration shows the typical profile of surfactants since a breaking point, which corresponds tothe critical aggregation concentration (cac), is observed in all cases. The cac of these diarmed derivativesare about 1–3 orders of magnitude lower than those of classical monoalkyl derivatives used as referencecompounds. In contrast to conventional surfactants, reversed trends in cac values and molecular areasat the solution–air interface have been observed. This anomalous behavior is tied to the structure of thesurfactants and suggests that long and flexible alkyl chains should self-coil previous to the aggregation oradsorption phenomena. Above cac all compounds form large aggregates, globular in shape, which tendto associate forming giant aggregates.tThe compounds presented here constitute a clear example of molecular biomimetics as their designis inspired on the structure and properties of natural phospholipids. Thus novel double-armedsurfactants have been obtained in which nitrilotriacetic acid plays the role of glycerol in phospho-lipids. The hydrophobic arms are linked to the head group through amide bonds (which is also thecase of sphingomyelin): (R1NHCOCH2)(R2NHCOCH2) NCH2CO2H (R1being CH3(CH2)11, CH3(CH2)17,CH3(CH2)7CH CH(CH2)8, and adamantyl, and R2= adamantyl). The dependence of the surface tensionwith concentration shows the typical profile of surfactants since a breaking point, which corresponds tothe critical aggregation concentration (cac), is observed in all cases. The cac of these diarmed derivativesare about 1–3 orders of magnitude lower than those of classical monoalkyl derivatives used as referencecompounds. In contrast to conventional surfactants, reversed trends in cac values and molecular areasat the solution
Supramolecular Structures Generated by a p-tert-Butylphenylamide Derivative of Deoxycholic Acid. From Planar Sheets to Tubular Structures through Helical Ribbons
No full textThe formation of supramolecular structures initiated by a p-tert-butylphenylamide derivative of deoxycholic acid (Na-t-butPhDC) is investigated. At 1.18 mM concentration of Na-t-butPhDC and 37 degrees C, initial flat ribbons are observed which sell-transform into helical ribbons (with a mean pitch angle of 47 +/- 6) which finally originate molecular tubes with an external diameter of 241 +/- 28 inn. Most of the molecular tubes show helical markings with a pitch angle value of 45 +/- 4 degrees, in full agreement with predictions of simple models based on chiral elastic properties of the membrane. A lateral association mechanism is proposed to account or the growth of the external diameter (from 225 +/- 32 to 546 +/- 59 nm) of tubes with time at 3.99 mM
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
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