1,720,997 research outputs found
Hydrocracking of long chain linear paraffins
Full text linkThe hydrocracking reactivity of two model compounds, namely n-C(16)H(34) (n-C16) and n-C(28)H(58) (n-C28), was investigated on a Pt/SiO(2)-Al(2)O(3) catalyst. Conversion and products distribution have been determined under a wide range of operating conditions (i.e. pressure: 20-80 bar; temperature: 270-330 degrees C; weight hourly space velocity: 0.33-1.0 h(-1): H(2)/n-paraffin feeding ratio 0.05-0.15 wt/wt). The latter were changed according to a central composite design. The present paper summarises the results obtained on both the model paraffins, depending on the reaction conditions. A first, simple kinetic elaboration is also presented, based on an ideal PFR model and a first order kinetics. The reaction confirmed to be first order with respect to the n-paraffin. Experimental data showed that for both n-C16 and n-C28 conversion was affected by H(2)/n-paraffin ratio. The change of conversion was explained in terms of vapour liquid equilibrium (VLE), which in turn is affected by the H(2)/n-paraffin ratio, so leading to a different vaporisation degree of reactant. In agreement with the VLE data, the effect of H(2)/n-paraffin on conversion was lower for n-C28. VLE calculations have been carried out to estimate the H(2) partial pressure and degree of vaporisation of the normal paraffin. The reaction order for hydrogen was -1 and -0.5 for n-C16 an n-C28, respectively. However, in the case of n-C16 the data obtained at the lower bound of the pressure range examined displayed an increase of the reaction order. The apparent activation energy was calculated after correction of the contact time taking into account the liquid-vapour equilibrium: similar values have been estimated for n-C16 and n-C28, ca. 32 and 31 kcal/mol, respectively
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
Liquid fuels from Fischer-Tropsch wax hydrocracking: Isomer distribution
No full textConsidering the current need of low emission fuels for the automotive market and the need of renewable
fuels that will emerge in the very next future, Fischer-Tropsch (FT) based technologies should be
considered a valid option to accomplish both low emission and renewable fuel production targets. A
hydrocracking step is necessary for obtaining high quality fuels from FT wax. Isomerisation is an
important reaction that takes place during the hydroconversion process. The amount and the type of the
isomers in the produced fuels heavily influence both cold flow properties and cetane number. In this
paper the results of a detailed method of analysis which allows the distinction between mono-branched
and multi-branched isomers in fuels obtained from an FT wax hydrocracking process, are presented and
discussed. In particular the influence of the operating conditions and the wax conversion on the isomer
distribution is pointed out
Introduction of a Breakage Probability Function in the Hydrocracking Reactor Model
No full textThis paper shows how a breakage probability function for the C-C bonds, elaborated from experimental evidence reported in literature, is introduced in the reactor model for the hydrocracking of Fischer-Tropsch waxes. The results demonstrate a better response to the variation of the operating conditions (especially as concerns temperature) and show product distributions closer to the experimental ones than those predicted by the previous model [Pellegrini, L. A. et al. Chem. Eng. Sci. 2008, 63, 4285]. The agreement with the experimental data has also been enhanced introducing a dependence on temperature (in addition to the dependence on the number of carbon atoms) in the expressions for the Langmuir constants and giving the equilibrium constants for isomerization reactions a new function derived from a thermodynamic study
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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