1,720,985 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
No full text“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
No full textWe 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
Functionalising lignin in crude glycerol to prepare polyols and polyurethane
No full textIn this work, crude glycerol liquefaction of lignins produced in the pulp and paper industry, as well
as an organosolv lignin (sugarcane bagasse), was studied with the ultimate aim of preparing biobased
polyols for polyurethane (PU) preparation. This is a proposed strategy to valorise the byproducts
of biodiesel and lignocellulose biorefineries. Size-exclusion chromatography revealed
that the lignins behave differently during liquefaction based on a ranging product molecular weight
(MW). The MW of the liquefaction products was concluded to be related to the phenolic and
aliphatic hydroxyl group content of the respective lignins, as well as the removal of glycerol and
monoacylglycerol during liquefaction. Lignin was modified to yield mostly a solid-phase product.
Fourier transform infrared spectroscopy suggests that crude glycerol constituents like glycerol and
fatty acid esters are bound to lignin during liquefaction through formation of ether and ester bonds.
Liquefaction yield further also varied with lignin type. The liquefaction products were effectively
employed as bio-based polyols to prepare P
Oligomerisasie van langerketting 1-alkene in die teenwoordigheid van Cp2MCl2-metalloseen-, meer komplekse Zr-metalloseen- en tridentaat bis(imino)piridienyster(II)-katalisatorsisteme
No full text1-alkenes represent a large part of the commercial market and since oligomers thereof are important intermediates for specialty chemicals, they warrant further study. Metallocene catalysts are a promising development, since metallocenes, such as Cp2ZrCl2 (Cp = cyclopentadienyl), are easily obtainable. Examples of the oligomerisation of higher 1-alkenes are limited and there is a shortage of in-depth studies on these types of catalysts [3, 8–39]. It is also very apparent that only low MAO loadings lead to the formation of oligomers, and at higher loadings, polymerisation takes place [3, 18–29]. In an effort to increase the knowledge base of the oligomerisation of 1-alkenes a series of Cp2MCl2-catalysts (M = Zr (1), Ti (2), Hf (3) and Nb(4)), more complex Zr-metallocene (5 to 7) and tridentate bis(imino)pyridine iron(II) (8 to 11) catalyst systems was investigated (Figure 4). The specific aim was to determine the oligomerisation activity and selectivity of these catalysts in the presence of MAO as co-catalyst. Several factors can influence the catalyst activity during the conversion of 1-alkenes, namely activation temperature (Ta), activation time (ta), reaction temperature (Tr), co-catalyst concentration, the transition metal (M), and the monomer (mo) concentration. All these factors were investigated for the metallocene catalysts (1 to 4). The choice of ligand and bridging compound of the metallocene catalysts influenced the properties of the polymers obtained during reactions. The three more complex metallocene catalysts, 5 to 7, were investigated for their ability to oligomerise higher 1-alkenes. An important development in 1-alkene polymerisation catalysts was the discovery of the Group 8 iron catalysts, the so-called neutral tridentate bis(imino)pyridine iron(II) catalysts. Four catalysts of this type, 8 to 11, were identified for investigation of their activity with regard to the oligomerisation of higher chain 1-alkenes. Many factors can influence the catalyst activity during the conversion of 1-alkenes; in this study, only the reaction temperature (Tr) and co-catalyst concentration were varied because they were found to be major factors in determining the catalytic activity. The activity of the catalysts and degree of oligomerisation (n) were investigated with regard to 1-heptene and 1-octeneDie oligomerisasievermoë van ’n reeks Cp2MCl2-metalloseen- (Cp = siklopentadiëniel, η
5
-C5H5;
M = Zr, Ti, Hf en Nb), meer komplekse Zr-metalloseen- en tridentaat bis(imino)piridienyster(II)-
katalisatorsisteme is ondersoek. Verskeie faktore wat die katalisatoraktiwiteit van die Cp2MCl2-
metalloseen-katalisatorsisteme gedurende die omskakeling van 1-alkene kan beïnvloed, is nagegaan. Die
faktore is: aktiveringstemperatuur (Ta), aktiveringstyd (ta), reaksietemperatuur (Tr),
kokatalisatorkonsentrasie, die tipe oorgangsmetaal (M) en die monomeerkonsentrasie (mo). Die
temperatuur, die oorgangsmetaal en die kokatalisatorkonsentrasie het die reaksietempo en die graad van
oligomerisasie dramaties beïnvloed. Die twee faktore wat die reaksietempo en graad van oligomerisasie
dramaties beïnvloed het, naamlik die kokatalisatorkonsentrasie en die reaksietemperatuur (Tr), is verder
met die meer komplekse Zr-metalloseen- en tridentaat bis(imino)piridienyster(II)-katalisatorsisteme
ondersoek. Uit die drie reekse katalisatore wat ondersoek is, is vier geïdentifiseer wat die hoogste
aktiwiteit getoon het, en die potensiaal het om vir die dimerisasie van langerketting 1-alkene gebruik te
kan wor
The development of a Cu(I)/pyrazolylpyridineamine catalyst system for the hydroxylation of aryl halides
No full textA catalyst system comprising of pyrazolylpyridineamine/Cu(I)/CsOH is reported. for the hydroxylation of aryl iodides and bromides with moderate to outstanding yields, without the use of an inert atmosphere. A comprehensive parameter optimisation study established optimum component concentrations: [Cu(MeCN)4]BF4 and 2-(1H-pyrazol-1-yl)-N-(pyridine-2-ylmethyl)ethan-1-amine (L01) (2 mol %), substrate (1 mmol), CsOH (4 mmol) and DMSO:H2O (1:1, 3 mL). Monitoring substrate conversion as a function of time revealed an induction period of 90 min, which could be eliminated through the initial in situ formation of the proposed [(L01)Cu-OH] intermediate. Eliminating the induction period resulted in complete conversion within one hour, with turnover numbers exceeding that of the benchmark catalyst system operating at an optimal catalyst loading of 0.05 mol
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
DFT investigation of the 1-octene metathesis reaction mechanism with the Phobcat precatalyst
No full textThe productive self-metathesis reaction of 1-octene in the presence of the Phobcat precatalyst [RuCl2(Phoban-Cy)2(=CHPh)] using density functional theory was investigated and compared to the Grubbs 1 precatalyst [RuCl2(PCy3)2(=CHPh)]. At the GGA-PW91/DNP level, the geometry optimization of all the participating species and the PES scans of the various activation and catalytic cycles in the dissociative mechanism were performed. The formation of the catalytically active heptylidene species is kinetically and thermodynamically favored, while the formation of trans-tetradecene is thermodynamically favore
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