1,721,007 research outputs found
Homo- and copolymers of hexafluoisopropyl methacrylate and alfa-fluoacrylate with alkyl vivyl ethers: microstructure and thermal properties
No full textA study is reported, dealing with the microstructure and thermal behavior of the homopolymers of 1,1,1,3,3,3-hexafluoroisopropyl methacrylate (HFIM) and 1, 1,1,3,3,3-hexafluoroisopropyl alpha -fluoroacrylate (HFIFA), as well as of their copolymers with various vinyl ethers. The aim of this work was a better understanding of the role that fluorine content and distribution-first in the monomer and then along the ensuring macromolecular chain-play in determining the polymerizability of the selected vinyl monomers, and the final properties of the polymeric material. Primary (n-butyl, isobutyl, 2-ethylhexyl), secondary (cyclohexyl), and tertiary (tert-butyl) vinyl ethers were employed as the comonomers. A general tendency towards comonomer alternation was observed upon radical initiated copolymerization with HFIFA. On the other hand, the relatively more electron-rich HFIM did not usually yield strictly alternating sequences, unless the bulky tert-butyl vinyl ether was employed. The incorporation of electron-rich vinyl ether monomers within a partially fluorinated polymeric chain by simple radical initiated process was considered particularly interesting in view of the possible application of these materials as water-repellent protective coatings. In this case, the fluorinated units should provide the low energy surface (water repellency) and, possibly, photo- and thermostability, whereas the vinyl ether counits should grant improved adhesion and adequate film-forming properties
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
Nucleotide diversity and population differentiation of the melanocortin 1 receptor gene, MC1R
No full textBACKGROUND: The melanocortin 1 receptor gene (MC1R) is responsible for normal pigment variation in humans and is highly polymorphic with numerous population-specific alleles. Some MC1R variants have been associated with skin cancer risk.
RESULTS: Allele frequency data were compiled on 55 single nucleotide polymorphisms from seven geographically distinct human populations (n = 2306 individuals). MC1R nucleotide diversity, pi, was much higher (10.1 x 10-4) than in other genes for all subjects. A large degree of population differentiation, determined by FST, was also present, particularly between Asia and all other populations, due to the p.R163Q (c.488 G>A) polymorphism. The least amount of differentiation was between the United States, Northern Europe, and Southern Europe. Tajima's D statistic suggested the presence of positive selection in individuals from Europe.
CONCLUSION: This study further quantifies the degree of population-specific genetic variation and suggests that positive selection may be present in European populations in MC1R
Copolymers of 1H, 1H, 2H, 2H,- perfluorodecylmethacrylate with nonfluorinated methacrylates for stone protection
No full textAdapting the Properties of New Fluorinated Acrylic Polymers to suit the Conservation of Ancient Monuments
No full textThe polymer structures considered traditionally for the formulation of protective coatings for the
conservation of ancient monuments are generally inadequate to satisfactorily fulfill all the specific
requirements for this use, such as durability, water repellence, vopour permeability etc. The results are
reported of continuing systematic study of the influence of the macromolecular structure of new acrylicbased
fluorinated materials on their photostability end the effectiveness of their protection when
employed as coatings for different types of stone. Copolymers of 1,1,2,2-perfluorodecylmethacrylote
(XFDM) and of 2,2,2-trifluoroethylmethacrylote (TFEM) with either linear or branched nonfluorinated
methacrylates and acrylates were tested and compared with the parent non-fluorinated polymers in
order to assess the influence of the number, size and distribution of fluorinated side chains on the
ultimate properties of the coating material applied on to different types of stone
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
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