1,720,953 research outputs found
Dynamic covalent surfactants
No full textIn this thesis the development of surfactant aggregates with fast exchange dynamics between the aggregated and non-aggregated state is described. Dynamic surfactant exchange plays an important role in natural systems, for instance in cell signaling, cell division, and uptake and release of cargo. Remarkably, dynamic surfactant exchange in synthetic systems has received relatively little attention. In this thesis we have shown that surfactants and surfactant aggregates with diverse morphologies with fast exchange dynamics could be obtained by making use of dynamic covalent surfactants. These dynamic covalent surfactants were formed in water by mixing of two isotropic solutions of a surfactant precursor. As surfactant precursors we used hydrophilic aldehyde functionalized building blocks and hydrophobic, but water soluble, amine building blocks. By mixing both building blocks in water, surfactants were formed in situ by the formation of reversible imine bonds between the two precursor building blocks. These surfactants form surfactant aggregates above their critical aggregation concentration (CAC). By following this approach, we have shown that spherical micelle formation can be switched on and off by reversible displacement of the equilibrium between the nonamphiphilic building blocks and their single tailed surfactant counterparts. Also double tailed surfactants could be obtained by this approach, from aqueous solutions of a bisaldehyde functionalized head group and an amine functionalized apolar tail through the in-situ formation of dynamic covalent imine bond between the precursors. The reversible nature of the dynamic covalent imine bond made the bilayer of the resulting vesicle assemblies highly dynamic, which is quite unusual for vesicles composed of double tailed surfactants. Due to the fast formation and dissociation kinetics of the imine bond, these dynamic covalent vesicles are highly responsive to changes in their environment, resulting for instance in complete dissociation upon dilution or changes in pH. Since dynamic covalent surfactants are capable of reversible formation due to the presence of reversible dynamic covalent bonds in the molecular structure, it was assumed that surfactant mixtures would be able to change composition in response to a change in their environment, on account of their continuous building block exchange. To test this hypothesis, we chose a micelle forming dynamic covalent surfactant system and a vesicle forming dynamic covalent surfactant system as a starting point. Next, we combined these systems, in such a way that there is building block competition between a micelle forming hydrophobic tail and a vesicle forming hydrophobic tail for binding with a hydrophilic head group or for a micelle forming head group and a vesicle forming head group for a single hydrophobic tail . Here, we show that vesicle forming surfactants and vesicles self-select from a mixture of aldehyde and amine functionalized non-surface active surfactant precursors, which are capable of forming multiple aggregate types and surfactants. We were able to describe the experimental data with a thermodynamic model, which strongly suggests that the selection of bilayer-forming surfactants and bilayer morphologies is thermodynamically controlled. We believe that these results bear some significance for the mechanisms behind the formation of bilayer compartments in prebiotic systems. We have shown that also dynamic covalent wormlike micellar morphologies can be obtained by imine bond formation upon mixing of simple water soluble gemini-surfactant precursors. Analogous to the previously obtained micelles and vesicles, these dynamic covalent wormlike micelles could be associated and dissociated upon changing the pH or temperature, using the fast association and dissociation of the imine bond. Also, exchange of the mono-functional amine tail for a diamine derivative in the vesicle-forming system led to the formation of crosslinked networks of dynamic vesicles, gelling the surrounding solvent. These vesicle gels are highly responsive to changes in their environment, but also partly self-heal after removal of any perturbation. The work in this thesis provides a new approach for the development of responsive surfactant assemblies that are easily formed by simple mixing of isotropic aqueous precursor solutions. The resulting surfactant assemblies show fast dissociation kinetics and switchable surfactant morphologies. In the future, this work might find application in the development of dynamic encapsulation and release materials.DelftChemTechApplied Science
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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