1,721,007 research outputs found
ESR of free radical reactions in gamma-irradiated ethylene–propylene-based terpolymers. II
No full textThe gamma irradiation at liquid nitrogen temperature of dicyclopentadiene, 2-methylennorbornene, and cyclopentadienyl-5-endo-norbor-2-enyl-methane-based ethylene–propylene terpolymers leads to the formation of macroradicals of the alkyl type by loss of hydrogen atoms from the ethylene–propylene chains. When warmed almost to glass transition temperature these primary alkyl species decay and generate new radicals by the double-bond addition and/or H abstraction from the unsaturations. The nature of the radical products was determined by ESR and MO methods
Studies on Polymerizations Initiated by Syncatalytic Systems Based on Aluminium Organic Compounds, 4
No full textElectron spin resonance of radicals in .gamma.-irradiated mono- and polycyclic olefins. 4. Electronic structure and electron spin resonance properties of a norbornenyl fused cyclopentadienyl radical
No full textESR study of .gamma.-irradiated substituted norbornanes in thiourea clathrate and adamantane matrix. Novel 2-norbornyl-type radicals
No full textThe ..gamma.. irradiation at 77/sup 0/K of 2-methyl-2-ethylbicyclo(2.2.1)heptane and of 2-methylene-2-ethylidenebicyclo(2.2.1)heptene in the state of thiourea adducts leads to formation of 2-methyl- and 2-ethylnorbornyl radicals by loss of hydrogen atoms at the substituent sites or by partial hydrogenation of the double bonds. On warming above 77/sup 0/K after irradiation, the 2-alkylnorbornyls add to double bonds of neighboring molecules yielding new adduct radicals alkylnorbornyl. The reactions can be reversed by uv irraidation at 77/sup 0/K, thus suggesting that the addition does not proceed beyond the first step. A reaction model based on the geometrical control by the molecular packing within the clathrate channels has been proposed. The irradiation of 2-ethylidenenorbornene in the state of thiourea clathrate or trapped in adamantane matrix yields an allyl-type radical by loss of a hydrogen atom from the methyl group. The structure and ESR properties of 2-alkylnorbornyls and of the allylnorbornyl have been investigated by MO methods to the INDO and extended Hueckel levels of approximation
Electron spin resonance of radicals in γ-irradiated ethylene-propylene-polyene terpolymers
No full textThe ESR spectra resulting from γ-irradiation of the following terpolymers: ethylene-propylene-5-ethylidene-2-norbornene (EPENB), ethylene-propylene-l-isopropylidendicyclopentadiene (EPIPDCP) and ethylene-propylene-tricyclo-5.2.1.02.6-deca-2.5.8-triene (EPDDCP) have been investigated. Measurements with ethylene-propylene copolymer and isotactic polypropylene have been made for comparison. The results suggest that, during the irradiation at 77 K, most of the radicals can be accounted for in terms of loss of hydrogen atoms from the main EP chains. On warming above the glass transition temperature, some of the primary radicals react with termonomer units yielding new allyl type radicals. The dominant mechanism of reaction seems to be double bond addition in the case of EPIPDCP and EPDDCP and hydrogen abstraction in the case of EPENB
Electron spin resonance study of radicals in γ-irradiated mono- and poly-cyclic olefins. Part III. Allyl and pentadienyl radicals from dienes and trienes with strained ring structures
No full textAn e.s.r. study of the radicals produced by low temperature γ-irradiation of dicyclopentadiene and 1-isopropylidenetetrahydroindene in an adamantane–thiourea matrix leads to the identification of the species dicyclopentadien-9-yl (II) and 1-(tetrahydroinden-1-ylidene)ethyl (I) respectively. The origin, structure, and e.s.r. properties of these radicals are discussed on the basis of the results of progressive thermal annealing experiments and of SCF MO calculations performed to the INDO and HMO (McLachlan) levels of approximation
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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