1,720,975 research outputs found
Steric control in the initiation step of the isospecific homogeneous Ziegler-Natta polymerization of propene and 1-butene
No full textA possible model of stereoregularity in the isotactic specific homogeneous Ziegler-Natta polymerization
No full textMelting behaviour of a series of diamides
No full textThe melting behaviour of diamides of general formula (n - C pH 2p+1)CONH-(CH 2) qNHCO(n - C pH 2p+1) has been investigated by calorimetric, dilatometric and IR techniques. The conformational contribution to the melting entropy, calculated from the hypothesis of complete conformational freedom of the molecules at the melting point, has been compared with the experimental data. The higher melting points of the diamides, as compared with those of the linear hydrocarbons having the same number of conformationally flexible chain bonds, are attributed to a reduction of conformational freedom of the chain segments in the liquid state (caused by the large fraction of hydrogen bonds maintained in the melt)
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
Theories and simulations of polymer-based nanocomposites: from chain statistics to reinforcement
No full textA survey of the present understanding of particle-filled polymers is presented, as obtained from either theoretical or
computational approaches. We concentrate on composites in which the nanoparticles are either spherical or statistically
isotropic aggregates, and the matrix is a homopolymer melt or a cross-linked elastomer. Recent progress has been
prompted by the preparation and careful characterization of well-defined model systems, as well as by theoretical
developments and the application of computer simulation to increasingly realistic models. After an introduction providing
the main motivations (Section 1), an overview of the basic phenomenology and recent experimental results is presented
(Section 2), with special emphasis on the Payne effect and related aspects. In Section 3, we discuss results of equilibrium
molecular dynamics and Monte Carlo simulations of polymer chains in the presence of nanoparticles. After a concise
theoretical description, these are compared with those obtained from integral equation and density functional approaches
(Section 4). The molecular origins of the inter-particle-depletion interaction are discussed, as well as the phase-separation
diagram of the nanoparticle/polymer system. The related issue of polymer chains and networks compressed between planar
surfaces is also dealt with. In Section 5 simulations and theories of polymer dynamics at the interface are discussed, with
special emphasis on the effects of surface roughness and on the vicinity of the glass transition. In Section 6 the overall
viscoelastic response of polymer nanocomposites is considered, both from the point of view of molecular-level simulations
and of continuum mechanics approaches. The concluding remarks (Section 7) discuss some of the open challenges in
the field
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