1,720,962 research outputs found
Circular Dichroism Spectra (350-185 nm) of a New Series of 4-Substituted [2.2] Paracyclophanes: a Quantitative Analysis within the De Voe Polarizability Model
No full textThe CD spectra of a new series of 4-substituted [2.2]paracyclophanes 1b- e have been measured down to 185 nm. Polarizability calculations within the DeVoe model satisfactorily reproduce the CD features over all the spectral range. In addition, the analysis of the complete CD spectrum allowed a phenomenological interpretation of the dependence of the sign of [α](D) on the nature of the substituents, at least for X=F, OH, I
Definition of green synthetic tools based on safer reaction media, heterogeneous catalysis, and flow technology
No full textGreen/Sustainable Chemistry is the scientific platform where chemists are contributing from different areas to develop modern and efficient processes aimed at minimizing the environmental impact of chemical production. To reach these goals scientists, from both academia and industry, need to strongly focus their fundamental and innovative research towards the application of modern principles of Green Chemistry. In this contribution a description of our efforts in this direction is presented
Sustainable Protocol for the Reduction of Nitroarenes by Heterogeneous Au@SBA-15 with NaBH4 under Flow Conditions
No full textA gold-incorporated SBA-15 catalyst was prepared by a solvent-free ball-milling approach. The catalyst showed high reactivity and selectivity in the reduction of a variety of nitroarenes to anilines operating in absolute EtOH with NaBH4 as reducing agent. The catalyst was reused in batch conditions over five consecutive runs without any losses of activity or selectivity. Considering the high chemical stability and reusability of the catalytic system, a continuous-flow protocol was also investigated and defined to minimize the generation of waste and optimize the continuous reuse of the catalyst. Benefits of flow conditions were proven by turnover numbers that increased from 47.5 to 1902 and also by the minimization of both leaching (9.5 vs. 1 ppm) and E-factor values (8 vs. 23 in batch)
A heterogeneous and recoverable palladium catalyst to access the regioselective C-H alkenylation of quinoline N -oxides
No full textHerein, we disclose the first C-2-selective C-H alkenylation of quinoline N-oxides catalyzed using a heterogeneous palladium catalyst. The protocol does not require the use of an external oxidant and it is applicable to an ample substrate scope always showing excellent site selectivity. This process is made accessible by the use of a specific 1,2,3-triazolium-tagged heterogeneous polymeric catalytic system. The catalyst can be efficiently recovered and reused with no decrease of its catalytic performance and hot filtration and mercury poisoning tests suggest that its mechanism of action is operatively heterogeneous. In addition, mechanistic studies revealed that C-H activation reaction pathways are operative, setting the stage for the direct synthesis of 2-functionalized quinolines using N-oxide functionality as both a directing group and an oxidant
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
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