1,721,003 research outputs found
Small angle X-ray and neutron scattering from ganglioside micellar solutions
No full textThe ganglioside GM1 is a biological amphiphile with a double tail hydrophobic part and an oligosaccharide chain headgroup. In solution it forms micelles which interact by electrostatic repulsion. The micellar parameters obtained at low concentration by light and neutron scattering are used to interpret the small angle X-ray experiments performed at high concentration. The combination of the contrast inhomogeneity inside the micelle with the sharp structure-factor peaks, due to the strong electrostatic interaction, makes X-ray scattering spectra very sensitive to small changes in the micellar parameter
Headgroup and chain melting transition in dispersed bilayers of GM3 ganglioside
No full textWe report on wide angle X-ray scattering (WAXS) and density experiments performed on the ganglioside GM3 in water solution. As compared to what usually found in lipid assemblies, GM3 bilayers show a degree of cooperativity feebler in the region of the lipid chains and stronger in the region of the headgroups. The collected WAXS spectra indicate the existence of a strong degree of order on the molecular scale, which we propose to be due to a highly constrained and symmetric disposition of the trisaccharide charged headgroups of GM3 at the bilayer surface. It is the first time that such an order in the headgroup region is seen in dispersed lipid assemblies, in normal pressure conditions. Experiments were carried out with no added salt, in the semidilute range of concentration, 5-15% bw, and in the range of temperature from 15 to 60°C. Parallel SAXS experiments indicate that on the scale of the bilayer cross section the same structure is preserved from the very dilute (0.1%) to the semidilute range of concentration
Combined small-angle X-ray and neutron scattering experiments for thickness characterization of ganglioside bilayers
No full textCombined small-angle neutron and X-ray scattering experiments on dilute solutions of the ganglioside GM3 in water are presented. The contrast profiles along the lipid and sugar portions of the ganglioside molecule for the two types of radiations are different, a feature which, added to the extension of the scattering q range to q similar to 0.4 Angstrom(-1), allows an accurate determination of the cross section of the bilayer in dilute solution. The electronic density profile of the bilayer cross section can be interpreted only by assuming thickness fluctuations, which have already been theoretically predicted for the GM3 bilayers, due to the peculiar packing properties of the monomer. Increasing temperature from room temperature to 50 degrees C has the effect of flattening the GM3 bilayer, as the thickness and the water content of the outer hydrophilic layer decrease, while the thickness of the inner hydrophobic region is almost unchange
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
Comment on "Thermotropic structural change of disialoganglioside micelles studied by using synchrotron radiation small-angle X-ray scattering"
No full textVariations 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
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