1,720,959 research outputs found
Ovali di un piano di Galois di ordine pari dotate di un gruppo di collineazioni transitivo sui loro punti
No full textExperimental Aspects of Solid State Circular Dichroism
No full textThe interest of circular dichroism in the solid state is stimulated by several needs, such as the desire to get solvent free spectra, the insolubility of the sample or the intrinsic process in which the sample itself is prepared or manipulated. We approach the argument on the basis of the sampling technique, since each different case calls for specific care in getting proper results
Catalytic hydroformylation of (1S,5S) -( - ) - and (1R,5R) -( +) -β-pinene: Stereoselective synthesis and spectroscopic characterization of (1S,2R,5S) -, (1S,2S,5S) -, (1R,2R,5R) - and (1R,2S,5R) -10-formylpinane
No full text(1S,5S)-( - )- and (1R,5R)-( + )-β-pinene have been hydroformylated in toluene to give (1S,2R,5S)- and (1R,2S,5R)-10-formylpinane with up to 95% diastereoselectivity using bimetallic CoRh(CO)7 as a catalyst; the latter was generated in situ from preformed Co2Rh2(CO)12 or a stoichiometric mixture of either [Rh4(CO)12] or [Rh6(CO)16] and [Co2(CO)8]. At 70-125°C and under 60 atm of syngas, the yields of hydroformylated products do not exceed 30% because of the concomitant isomerization of β-to α-pinene. In all cases the catalyst is recovered as a mixture of soluble cobalt carbonyl derivatives and a crystalline precipitate that contains most of the rhodium, mainly as [Rh6(CO)16]. Comparable yields and diastereoselectivities were obtained from reactions in tetrahydrofuran with a mixture of [Rh4(CO)12] and [N(PPh3)2]Cl as the catalyst precursor. The corresponding (1S,2S,5S)- and (1R,2R,5R)-10-formylpinanes, along with the corresponding alcohols, were obtained diastereoselectively by use of bimetallic Co-Rh or homometallic Rh carbonyl catalysts modified with bis(diphenylphosphine)ethane (dppe). When unidentate phosphines such as triphenylphosphine were used in place of dppe, as the ligand/metal (L/M) ratio was raised the diastereoselectivity of both the hetero- and the homo-metallic catalytic system fell progressively, and was completely lost for L/M ≥ 4. However, a further increase in L/M to ca. 70-100 allows chemio- and diastereo-selective synthesis of both the (1S,2S,5S)- and (1R,2R,5R)-10-formylpinane. The (1S,2R,5S)-, (1S,2S,5S)-, (1R,2R,5R)- and (1R,2S,5R)-10-formylpinane diastereomers were isolated by distillation under reduced pressure and fully characterized by IR, UV, 1H and 13C NMR and circular dicroism (CD) spectroscopy, and mass spectrometry. The possible factors favouring the diastereoselective hydroformylation of β-pinenes under the conditions used are discussed
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
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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