1,720,962 research outputs found
Kinetics of the reaction of toluene with benzyl alcohol over a Nafion-silica composite
No full textThe title reaction, a set of concurrent-consecutive steps, was studied in a slurry batch reactor at 50, 65, and 75 degrees C, using cyclohexane as solvent and Nafion SAC-13 as solid acid catalyst. The final products were found to be dibenzylether, the isomers of benzyltoluene and dibenzyltoluenes and small amounts of unidentified byproducts. The kinetic results were interpreted by a Langmuir-Hinshelwood model, evaluating the main kinetics and adsorption coefficient involved in the reactions and their temperature dependence. (c) 2004 Elsevier B.V. All rights reserved
SYNTHESIS OF [2.2]PARACYCLOPHANE VIA HOFMANN ELIMINATION - A KINETIC-STUDY OF THE HOMOGENEOUS REACTION
No full textParacyclophane (PCP) and byproducts were obtained from (p-methylbenzyl)trimethylammonium hydroxide (QOH) by reaction with NaOH in concentrated water solutions. The system presents a miscibility gap: selectivities and kinetics were separately studied in a NaOH-rich ("Na") region, a QOH-rich ("Q") region, and a "dilute" region, at temperatures in the range 70-110 °C. The reaction rate is much higher in the Na region, particularly at high levels of NaOH concentration, but selectivity to PCP is better in the other regions. The dependence of the reaction rate on the alkali concentration is discussed, relating it to the poor solvation of OH- ions
Toluene Disproportionation Catalysed by Various Zeolites
No full textToluene disproportionation in the gas/solid phase was performed in a flow reactor (carrier H2 or N2) over some partially exchanged X and Y zeolites and, more systematically, over decationated Y, ZSM-5 and ZSM-11 zeolites. Activity, selectivity and stability of the catalysts were tested at temperatures up to 500°C, but mostly in the range 350°–400°C. Two samples HZSM-5 showed a considerably different catalytic behaviour: with one of them, shape-selectivity effects, favouring p-xylene, were observed during progressive deactivation (carrier N2); the other one, of higher and stable activity, gave xylenes in the equilibrium isomeric ratios. Using the latter zeolite, kinetic measurements were carried out in a differential reactor at 240°–300°C (carrier H2). A few kinetic models were tested
COMPARISON OF DIFFERENT SAMPLES OF HZSM-5 AS CATALYSTS FOR TOLUENE DISPROPORTIONATION
No full textToluene disproportionation was performed at 300°-360°C in a fixed-bad reactor (carrier H2) over samples of HZSM-5 differing in surface acidity, organic compound used for the synthesis, crystal size and procedure used for decationation. Xylene isomers in the product were in equilibrium ratios. The catalyst activity was found to be clearly dependent on surface acidity. An interpretation is given, in terms of a slow toluene disproportionation within the zeolite pores, followed by fast xylene isomerization on the external surface. Measurements of the reaction rate at 300°C over one of the catalysts confirmed a kinetic model as previously suggested
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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