1,721,036 research outputs found
Application of Scattering Techniques in the Domain of Amphiphiles
No full textLight and neutron scattering techniques are discussed in connection with experiments on micellar solutions of gangliosides - amphiphilic molecules of biological origin, Micellar properties, like molecular weight, hydrodynamic radius and shape, are obtained with precise scattering measurements in conditions of negligible intermicellar interactions. It has also been verified that the GM1 ganglioside micelle does not change molecular weight and shape on addition of salt. Scattering techniques are also shown to be useful in studying intermicellar interactions, like the Coulomb repulsion between GM1 micelles, in the regime of the long-range interactions obtainable at very low ionic strength
Static and Dynamic Light Scattering Study of Solutions of Strongly Interacting Ionic Micelles
No full textDilute solutions of ionic micelles formed by biological glycolipids (gangliosides) have been investigated at very low ionic strength by static and dynamic light scattering. With no added salt the effect of electrostatic interactions is so strong that both the scattered intensity and the measured diffusion coefficient are different by an order of magnitude with respect to the values obtained for weakly interacting micelles. The electric charge of the micelle is derived by a fit of the experimental structure-factor data which uses the hypernetted chain approximation for the radial distribution function. The dependence of the diffusion coefficient on the ionic strength is partially explained by considering, in addition to hydrodynamic interactions, effects due to the non-negligible size of the Na+ and Cl- ions. The measured intensity correlation function deviates from exponential behaviour at extremely low ionic strength
AGGREGATION PROPERTIES OF SEMISYNTHETIC GD1A GANGLIOSIDE (IV(3)NEU5ACII(3)NEU5ACGGOSE(4)CER) CONTAINING AN ACETYL GROUP AS ACYL MOIETY
No full textGD1a ganglioside containing an acetyl group as acyl moiety, GD1a(acetyl), was synthesized from natural GD1a. The aggregative properties in aqueous solution of GD1a(acetyl) have been studied by static and dynamic laser light-scattering measurements. GD1a(acetyl) spontaneously aggregates as small micelles showing a hydrodynamic radius and molecular mass of 33 Angstrom and 96 kDa, respectively. Vibrio cholerae sialidase showed a very high activity on the micelles of GD1a(acetyl), compared to GD1a. This has been explained as a consequence of the high surface curvature of the the small micelles. High resolution proton NMR spectra were recorded from micelles of GD1a(acetyl) in deuterated water. The low overall correlation time of the GD1a(acetyl) micelles was calculated to be about 2 x 10(-8) s, a value one order of magnitude lower than that determined for natural GD1a
Static and Dynamic Properties of Solutions of Strongly Interacting Ionic Micelles
No full textThe authors report on light scattering measurements performed on ionic micelles of biological glycolipids in very low ionic strength aqueous solution. The system differs fundamentally with respect to solutions of macromolecules or inorganic colloids, because the micelle is a spontaneous aggregate, its electric charge is unknown a priori, and the system may present an intrinsic polydispersity. The static and dynamic light scattering data are compared with calculations based on the HNC approximation
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
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