1,721,021 research outputs found
Phase superdiagrams of two component phospholipid membranes : pH dependence
No full textA model proposed to determine the phase diagrams of PC/PC, PE/PE and PC/PE mixtures (1, 2) has been considered to account for the phosphatidic acid (FA) mixtures too. PAs have two dissociable protons, the pK values of the phosphate group are 3.5 and 9. In the transition temperature (Tt) vs pH diagrams of the PAs the increasing ionisation results in a maximum value for Tt at pH = pK1. Small variations in Tt are observed in the regions between the pK values in spite of the large changes occurring on the surface charges of the membranes while a further pH increase abruptly decreases Tt. The proposed analysis is concerned with the intermediate pH region. Considering the free energy function of the one component system (PA) the energy term accounting for the surface contribution has been generalized and it has been observed that the pH dependence of the corresponding model parameter, L*, is of parabolic type. Other model parameters were determined comparing the experimental results of PC, PE and PA at different pH values and, for binary mixtures, the superdiagrams (SDs) could be constructed. Depending on the relationships between the chain lengths and that on the phase transition temperatures of the pure components it is possible, in these SDs, to predict the type of the phase diagrams. PC/PA and PE/PA mixtures, at different pH values, were analyzed. In the first case, increasing pH, an increase of area between the two fusion lines is found while an opposite situation is given by PE/PA mixtures. At the same pH, the region between the fusion lines is smaller in PC/PA than in PE/PA mixtures indicating a lower affinity of the components with prevalently eutectic and peritectic phase diagrams. 1) Sugar I.P. and Monticelli G. (1985) - Biophys. J. 48: 283-288. 2) Monticelli G. (1986) in "Biophysics of membrane transport" (Kuczera J. and Przestalski S. eds.), Wroclaw Univ. Publ., pp. 271-300
Impedance measurements of self-assembled lipid bilayer membranes on the tip of an electrode
No full textSupported lipid membranes were self-assembled on the tip of a freshly cleaved silver wire, in the presence of an appropriate polarization voltage, to facilitate, during the membrane formation, the organization of the lipids into an ordered structure. Radiowave impedance spectroscopy measurements have been carried out to provide information on the relaxation properties of the system. We have measured the conductometric and dielectric properties of bilayers built up of different lipids [dipalmitoylphosphatidic acid (DPPA), 1,2-dipalmitoyl-sn- glycero-3-phosphocholine (DPPC), linoleic acid (LIN)] in a wide frequency range (from 10(3) to 10(6) Hz) and in electrolyte solutions of different ionic strengths, in the presence of uni-univalent (KCl) and di-univalent (CaCl2, MgCl2, ZnCl2) electrolytes. This made it possible to measure the influence of different cations and different lipid compositions on the membrane properties. In particular, we have found a different capacitive behaviour of the supported lipid bilayer membrane (s-BLM) structure in the presence of different counterions in the electrolyte solution. This peculiarity offers the opportunity for the preparation of a variety of biosensors with diverse applications in membrane biophysics, biochemistry and biotechnology. (C) 2002 Elsevier Science B.V. All rights reserved
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
Effect of isoprenoid cyclization on the transition temperature of lipids in thermophilic archaebacteria
No full textVariations 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
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