1,721,020 research outputs found
Stopped-flow polymerizations of ethene and propene in the presence of the catalyst system rac-Me2Si(2-methyl-4-phenyl-1-indenyl)2ZrCl2/methylaluminoxane
No full textThe kinetics of ethene and propene polymn. at 20-60° in the presence of the homogeneous catalyst system rac-Me2Si(2-methyl-4-phenyl-1-indenyl)2ZrCl2/methylaluminoxane was investigated by means of stopped-flow techniques. The specific rate of chain propagation, measured at the very short reaction times typical of this method, turned out to be ≈102 times higher for ethene than for propene; this suggests that diffusion limitations through the poly(ethylene) pptg. at longer reaction times may be responsible for the fact that the two monomers polymerize instead at comparable rates under "std." conditions. The concn. of active sites is significantly lower than the anal. Zr concn
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
Cross- talk between testicular steroidogenesis and spermatogenesis
No full textSpermatogenesis is regulated by a complex interplay between endocrine signals and local interactions of tubules with the interstitial tissue, mainly androgen producing Leydig cells (LC). We hypothesized that the functional phenotype of LC reflects the developmental environment in which these cells grow and interact with other testicular cells, including both somatic and germ cells. As experimental model, we used the organotypic culture of 2.5dpp mouse testicular fragments in the presence of 10% KSR (Knockout Serum Replecement), which is essential to maintain the entire spermatogenetic process from spermatogonia to spermatids in vitro up to 5-6 weeks. At different times we analyzed: 1) testicular morphology, to assess germ cell differentiation; 2) LC proliferation by KI67 immunostaining; and 3) LC maturation, by measuring androgens and INSL3 secreted into the medium. LC were identified by immunostaining of specific markers, including 3βHSD, c-Kit and INSL3. In the presence of KSR, testosterone significantly increased from the first to the second week and was maintained up to the fifth week, in association with germ cell differentiation up to haploid elongated spermatids. On the contrary, in the absence of KSR, testosterone markedly declined during the fourth week, together with an altered spermatogenesis. These results indicate that LC undergo normal development and function in vitro, provided that culture conditions maintained spermatogenesis. We also addressed the regulation of LC function in humans, using fresh and cryopreserved testicular biopsies obtained from beating heart organ donors. Having assessed several culture conditions, we set up a new system biology model allowing to successfully in vitro culture testicular fragments for three hours and to analyze the differential LC response to LH and hCG in terms of testosterone secretion. The study of the age-dependent LC response is in progress, comparing young (15-40 years) and elderly (60-85 years) donors
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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