1,721,014 research outputs found
Synthesis and comparative characterization of Al, B, Ga, and Fe containing Nu-1-type zeolitic framework
No full textWe synthesized four different Nu-1-type zeolites containing, respectively, Al, B, Ga, and Fe as the trivalent element. With the exception of B-Nu-1, the synthesis is difficult because of the competitive formation of other crystalline phases as sodalite, ZSM-39-type, or glassy phases. The trivalent elements isomorphous substitution was demonstrated by X-ray powder diffraction, FTi.r., e.s.r., u.v.-Vis., and 27Al, 11B, and 71Ga-MAS-n.m.r. By the same techniques and t.g.a. measurements, we evaluated the thermal stability of the different Nu-1-type zeolites
VANADIUM MIXED-OXIDE CATALYSTS FOR THE OXIDATIVE COUPLING OF METHANE
No full textThe improvement of methane conversion and C2+ selectivity for the oxidative coupling of methane has been pursued by evaluating a series of new polyfunctional oxide catalysts. The catalysts included: (i) a transition metal oxide, (ii) an alkaline earth metal oxide (CaO or MgO), and (iii) an inert oxide support (Al2O3, SiO2, TiO2, or ZrO2) to stabilize the active phases. Vanadium oxide was chosen from the set of transition metal oxides having a standard free energy change lower than zero for the reaction methane+metal oxide→ 1 2 ethene+water+reduced metal oxide. The molar composition of the catalysts was the following: 68Mg(Ca)/2V/30Al(Ti,Si,Zr). Several catalysts were tested before and after alkali impregnation (lithium with MgO and sodium with CaO). Impregnation of alkali caused an increase in the methane conversion in the CaO-based catalysts. The catalysts were examined by electron spin resonance and UV-visible spectroscopy to find relationships between vanadium species and catalytic activity. The spectroscopic analyses did not show a correlation between VIV species and catalytic activity, whereas the (V = O)3+ species seems to play an important role in the reaction
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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