1,720,962 research outputs found
SYNTHESIS AND CHARACTERIZATION OF Na-X, Na-A, AND Na-P ZEOLITES and HYDROXYSODALITE FROM METAKAOLINITE
No full textThe present work deals with the hydrothermal synthesis of Na zeolites (Na-A, Na-X and Na-P) and hydroxysodalite using kaolinite calcined at 650 degrees C as starting material. The focus was on definition of the most favourable conditions for the synthesis of zeolite Na-A and Na-X from metakaolin in order to economize on both energy (i.e. synthesis temperatures) and reaction time and to enlarge the field of pure and isolated synthesized phases. Metakaolin was mixed with calculated amounts of NaOH solution and sodium silicate and five sets of experiments were carried out at ambient pressure and 68 +/- 0.1 degrees C varying the SiO(2)/Al(2)O(3) ratio from 2.2 to 7. Optimal conditions for crystallization of Na-A zeolite from kaolinite were reached with a SiO(2)/Al(2)O(3) ratio of 2.2 plus 4 M NaOH without adding sodium silicate; transformation into hydroxysodalite develops after similar to 8 h. For SiO(2)/Al(2)O(3) ratios between 4 and 7, crystallization of the separate Na-X zeolite phase could be achieved and transformation into Na-P and hydroxysodalite occurred after 382 h and 190 h, respectively. For SiO(2)/Al(2)O(3) ratios between 5 and 6, transformation of metakaolin into Na-X plus Na-A, hydroxysodalite and Na-P occurred, and the field within which Na-A and Na-X zeolite exists overlapped that of the other zeolites.
The products of synthesis were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma optical emission spectrometry (ICP-OES), infrared spectroscopy (IR) and thermal analyses (TG-DTG-DTA).
Obtaining pure Na-A and Na-X zeolite from kaolinite treated at low metakaolinitization temperature (650 degrees C) and low hydrothermal synthesis temperature (68 degrees C) represents a considerable economic advantage in terms of both energy and time
Synthesis and characterization of wollastonite-2<i>M</i>by using a diatomite precursor
No full textABSTRACTSolid phase reaction synthesis of wollastonite-2Mby a natural rock precursor as the source of amorphous silica and CaCO3is reported. Chemical treatments were carried out on a diatomitic rock from Crotone (Calabria, Italy) in order to measure its reactive silica and CaCO3contents. Four series of synthesis were performed at 1000°C at ambient pressure by mixing, at different stoichiometry, the diatomitic rock with a natural limestone as a source of additive CaCO3, and sodium carbonate (Na2CO3) as triggering agent.Wollastonite-2Mwas characterized by chemo-physical, crystallographical and morphological-microtextural analyses. All these characterizations, together with infrared and nuclear magnetic resonance (29Si) responses provide values comparable to literature data. Estimation of the amorphous phase in the synthesis powders was performed through quantitative phase analysis using the combined Rietveld and reference intensity ratio methods, resulting in a final product of 96.3% wollastonite-2M.</jats:p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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