1,720,959 research outputs found
The Role of Cu-0 in Surface-Initiated Atom Transfer Radical Polymerization: Tuning Catalyst Dissolution for Tailoring Polymer Interfaces
No full textThe availability of catalytic/reducing sites at metallic Cu( )(0)sources during supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) is regulated by the components of the polymerization mixture, including ligand (L), alkyl halide initiator (R-X), and Cu-II-based deactivator. Their contributions were analyzed by quantifying the dissolution of Cu species within a quartz crystal microbalance with dissipation (QCM-D), subjecting a Cu-0-coated sensor to different polymerization mixtures. The control of catalyst diffusion from Cu-0 was subsequently exploited to fabricate structured polymer brushes with diverse compositions, when ATRP was performed from surface-immobilized initiators in the presence of a Cu-0 plate, placed at a determined distance (d) from the substrate. Surface-initiated ATRP in the presence of Cu-0 (Cu-0-SI-ATRP) is compatible with a broad variety of monomers, including oligo(ethylene glycol) acrylate (OEGA), methyl acrylate (MA), and acrylamide (AAm). The kinetics of brush growth is finely tuned by the independent variation of d, polymerization time, and concentration of added deactivator. Modulation of these parameters allowed us to generate homopolymer and multiblock copolymer brush gradients featuring a variety of morphologies and controlled interfacial properties, with unprecedented spatial resolution over the brush structure
Design and characterization of ultrastable, biopassive and lubricious cyclic poly(2-alkyl-2-oxazoline) brushes
No full textBilayer polymer brushes presenting surface-bound poly(glycidyl methacrylate) (PGMA) films and interfacial cyclic poly(2-alkyl-2-oxazoline) (PAOXA) brushes show excellent biopassivity and lubrication, while displaying long-term stability in chemically harsh aqueous environments. Due to their lower radii of gyration (R-g), cyclic poly(2-methyl-2-oxazoline)s (PMOXAs) and poly(2-ethyl-2-oxazoline)s (PEOXAs) react at high temperatures with PGMA grafts producing similar to 50% denser brushes compared to linear analogues featuring comparable molar masses. This generates significantly more hydrated brush interfaces, which quantitatively prevent unspecific surface contamination by biomolecules after several hours of exposure. In addition, the more compact and denser character of cyclic brushes imparts excellent lubricating properties to the bilayered coatings, with the more hydrophilic cyclic PMOXA interfaces reaching a coefficient of friction (mu) of 0.05 against a silica AFM probe in aqueous medium. In addition to their unique physico-chemical properties, cyclic PMOXA and PEOXA brushes grafted on PGMA layers demonstrate extremely robust films, which could withstand one month incubation in phosphate buffered saline (PBS) solution, tap water or water from Lake Zurich
Loops and Cycles at Surfaces: The Unique Properties of Topological Polymer Brushes
No full textGrafting synthetic polymers to inorganic and organic surfaces to yield polymer brushes has represented a revolution in many fields of materials science. Polymer brushes provide colloidal stabilization to nanoparticles (NPs), prevent and/or regulate the adsorption of proteins on biomaterials, and significantly reduce friction when applied to two surfaces sheared against each other. Can the performance of polymer brushes as steric stabilizers and boundary lubricants be improved? The answer to this question encompasses the application of polymer grafts presenting different chain topologies, beyond linearity. In particular, grafted polymers forming loops and cycles at the surface have been recently demonstrated to enable the modulation of interfacial physicochemical properties, including nanomechanical and nanotribological, to an extent that is difficultly addressed by using their linear counterparts. Loop and cyclic polymer brushes provide enhanced steric stabilization to surfaces, increase their biopassivity and show superlubricious behavior. Their distinctive structure, the methods applied to fabricate them and their application in several technologically relevant fields of materials science are reviewed in this contribution
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
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
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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