1,720,990 research outputs found
STRUCTURE OF ALPHA-POLYPIVALOLACTONE - A REFINEMENT BASEDON THE RIETVELD METHOD
No full textA comparative study is carried out on the structure of the alpha-form of polypivalolactone obtained (i) from the analysis of oriented-fibre X-ray diffraction diagrams, (ii) from conformational energy calculations and (iii) by refining the first two models through best fitting on the powder X-ray diffraction profile according to the Rietveld method. A single refined model is obtained that shows very good agreement both with experimental fibre intensities and with the powder profile. This result is discussed in terms of the accuracy of structural parameters derived from the Rietveld method compared with the much more numerous determinations based on X-ray diffraction from oriented samples
THE THERMAL TRANSITIONS OF POLY[BIS (4-ISOPROPYLPHENOXY)PHOSPHAZENE] - A DIFFERENTIAL SCANNING CALORIMETRY AND X-RAY-DIFFRACTION STUDY
No full textTHE STRUCTURE OF ONE CRYSTALLINE FORM OF ISOTACTIC 1,4-CIS-POLY(2-METHYL-1,3-PENTADIENE) - AN APPLICATION OF THERIETVELD METHOD
No full text(E)-2-Methyl-1,3-pentadiene was polymerized with the AlEt2Cl-Nd(OCOC7H15)3-Al(iBu)3 system to a polymer consisting of 98–99% 1,4-cis-structure. The crude polymer was fractionated by successive extractions with boiling diethyl ether, heptane and toluene. Examination of the soluble fractions and of the residue to toluene extraction by NMR, X-ray and DSC techniques indicated that the crude polymer consists of macromolecules differing in stereoregularity. Evidence is reported that the crystalline residue after the toluene extraction has a 1,4-cis-isotactic structure. The existence of two different crystalline phases is shown and the respective cell parameters have been determined. α-Phase: a = 10,74, b = 13,04, c = 7,87 Å (−120°C), space group Pbca, Z = 8, Dc = 1,00 g · cm−3. β-phase: a = 9,30, b = 7,73, c = 7,90 Å (25°C), space group P212121 Z = 4, Dc = 0,96 g · cm−3
Aryltriazenido complexes. Crystal and molecular structure of trans-carbonyl(1,3-di-ptolyltriazenido)bis(triphenylphosphine)iridium(I)
No full textThe structure of the title compd. was detd. by x-ray crystallog. and refined by least-squares to R 0.032 using 2835
independent reflections. The orange crystals of the complex are monoclinic, space group C2/c, with a 22.121, b 19.190,
c 10.111Å, and 92.77°; Z = 4. The triazenido ligand is unidentate and trans to the CO in this square-planar complex.
Ir-N and Ir-C(carbonyl) bond lengths are 2.16 and 1.79Å, resp
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
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