1,721,018 research outputs found
Metal vapour synthesis of stabilized transition metal nanoparticles: characterization, studies on factors affecting particle size and catalytic applications
Full text linkThis PhD thesis is focused on the synthesis, characterization and evaluation of
catalytic activity of stabilized platinum and gold nanoparticles, generated by use of
the metal vaporization technique. Metal vapour synthesis allows to obtain platinum
and gold particles with diameters in the range of few nanometers. The introduction of
suitable organic molecules at various stage of the synthesis has proven to be useful in
order to control the final size of the produced particles. The metal nanoparticles
obtained by this new approach are very stable and can be easily handled and
characterized in solution. In particular, NMR based measurement of diffusion
parameters has proven to be useful for the quick determination of particles size in
solution. The choice of organic stabilizing ligand is crucial in determining both the
particle size and the catalytic activity and selectivity of the system. Platinum particles
characterized by small diameters and good catalytic performances are obtained using
vinylsiloxanes and aromatic solvents while, in the synthesis of gold particles,
branched thiols and alkylamines demonstrated to be a better choices over linear
alkylthiols if catalytic activity is required. A new application of gold nanoparticles in
catalytic silane alcoholysis reaction has also been discovered
Design and Synthesis of Low Molecular Weight and Polymeric Surfactants for Enhanced Oil Recovery
Full text linkSurfactants are defined as molecules able to lower the surface (or interfacial)tension at the gas/liquid, liquid/liquid, and liquid/solid interfaces. Due totheir properties, they are typically employed as detergents, emulsifiers, dispersants,wetting and foaming agents. In chemical enhanced oil recovery (cEOR), surfactantsare used as flooding agents, alone or in combination with polymers, alkali, and morerecently nanoparticles, to increase the microscopic displacement efficiency. Froma chemical point of view, surfactants are amphiphiles, meaning that they bear intheir structure both hydrophilic and hydrophobic moieties. Some naturally occurringsurfactants exists, but the majority are synthetic. The availability of syntheticsurfactants, allows a big variety of structures and properties. In this chapter, the mainclasses of surfactants will be reviewed, with focus on those used or proposed foruse for chemical enhanced oil recovery. After a general introduction about surfactantsand their main structural and physico-chemical properties, specific aspects ofdesign and synthesis will be discussed. Particular emphasis will be given to the mostrecent developments, which includes zwitterionic, gemini and polymeric surfactants.Own work of the author of this chapter in the field of polymeric surfactants will behighlighted
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
Chain extension and branching of poly(ethylene terephtalate) (PET) with di- and multifunctional epoxy or isocyanate additives: an experimental and modelling study
No full textThe effect of two difunctional chain extenders, 1,6-diisocyanatohexane (NCO) and 1,4-butanediol diglycidyl ether (EPOX), in the reactive melt-processing of a post-consumer poly(ethylene terephthalate) (r-PET) was investigated. The torque evolution during processing in a batch mixer and the molecular weight of the chain-extended r-PET, as determined by SEC analysis, were comparatively evaluated. A simple mathematical model proposed here was used to fit the obtained molecular weights. Two polyfunctional chain extenders, poly(phenyl isocyanate-co-formaldehyde) (P-NCO) and a styrene-acrylate copolymer bearing epoxide groups (P-EPOX), were also used and their reactivity was compared with that of the difunctional ones by analyzing torque and melt flow rate data. The different reactivity of the two functional groups and the structure of the final polymer (either linear or branched depending on the type of chain extender) affect both crystallization behaviour and tensile properties of the modified r-PET. Fine tuning of the latter properties by suitable chain extender(s) selection and formulation is anticipated
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
- …
