1,721,020 research outputs found
Structure and growth control of a nonionic surfactant micelle by adding a phospholipid
No full textWe have studied the effects of a phospholipid (DL-alpha -phosphatidylcholine dimyristoyl: DMPC), which forms an extended flat bilayer aggregate (nearly zero spontaneous curvature), on the spherical-cylindrical shape of nonionic surfactant micelles (pentaethylene glycol mono-n-dodecyl ether; C12E5) in terms of an aggregation number, critical micellization concentration (cmc), second virial coefficient (A(2)), and hydrodynamic diameter (D-H) by laser light scattering. The aggregation number and critical micellization concentration increase as the amount of DMPC is increased. On the basis of the cmc values, the total free energy per micelle of C12E5/DMPC mixtures is estimated. The free energy per micelle of C12E5/DMPC mixtures decreases as DMPC is added. This is consistent with the decrease of A(2) and the strong hydrophobicity of DMPC compared with that of C12E5. The average contour length, the diffusion coefficient, and the end-cap energy of mixed micelles are estimated on the basis of the cmc and molecular specific volumes of the moiety. The end-cap energy of the mixed micelles and the average contour length increase as DMPC is added, which is also reasonable considering the molecular structure of DMPC. Furthermore, the diffusion coefficients obtained from dynamic laser light scattering are in excellent agreement with the estimated diffusion coefficients obtained from a one-dimensional growth model based on static light scattering measurements
Nano-control of self-assembled biomolecular structures
No full textWe have controlled the structure of self-assembled systems by introducing charges (charge effect) and polymeric tails (steric effects) on a spherical-cylindrical shape of nonionic surfactant micelles. In detail. we studied the effects of a phospholipid (DL-alpha-phosphatidycholine dimyristol: DMPC) on the shape of nonionic surfactant micelles (penta-ethyleneglycol mono-n-dodecyl ether: C12E5), which has been studied in terms of an aggregation number. critical micellization concentration (CMC), second virial coefficient (A(2)), and hydrodynamic diameter (D-H) by laser light scattering. DMPC, DOPC (DL-alpha-phosphatidylcholine dioleoyl), and DMPE (DL-a-phosphoethanolamin dimyristol) molecules added in C12E5 micelle solutions decrease the spontaneous curvatures. leading to an increase of the end-cap energy E, that favors micellar growth. Based on the CMC values, the total free energy per micelle of C12E5/DMPC mixtures is estimated. The free energy per micelle of C12E5/DMPC mixtures decreases as DMPC is added. This is consistent with the decrease of A(2) and the strong hydrophobicity of DMPC compared with C12E5. The average contour length, the diffusion coefficient, and the end-cap energy of mixed micelles are estimated based on the CMC and molecular specific volumes of the moiety. The end-cap energy of the mixed micelles and the average contour length increase as DMPC is added, which is also reasonable considering the molecular structure of DMPC. Furthermore. the diffusion coefficients obtained from dynamic laser light scattering are in excellent agreement with the estimated diffusion coefficients obtained from a one-dimensional growth model based on static light scattering measurements. Charged lipid (1,2-dioleo,1-3-trimethylammonium-propane) and polymer lipid (1.2-dimyristol-sn-glycero-3-phosphoethanolamine-[poly(ethylene glycol)]) increase the spontaneous curvatures, resulting in breaking micelles into small size. When the lipids are added, the hydrodynamic diameter of the micelles of C12E5/lipids is nearly temperature independent due to the strong charge or steric repulsion. (C) 2002 Published by Elsevier Science B.V
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
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