1,720,962 research outputs found
Water capacity and size data of reverse micelles formed by novel cationic surfactants
Get PDFThis paper contains data of water capacity (in terms of w 0 = molwater/molsurfactant) in reverse micelles formed by several commercial and non-commercial cationic surfactants in cyclopentane, petroleum ether, and iso-octane. Also reported are hydrodynamic diameters of the respective reverse micelles formed. Tested surfactants were (i) single-chained cationics: cetyl benzyl diethanolammonium bromide (CBDB), cetyl benzyl dimethylammonium bromide (CBMB), cetyl dibutyl ethanolammonium bromide (CDBEB), cetyl cyclohexyl dimethylammonium bromide (CCDB); and (ii) twin-chained cationics: didodecyl dimethylammonium chloride (DDMC), didodecyl diethylammonium bromide (DDEB), didodecyl dipropylammonium bromide (DDPB), didodecyl diethylammonium chloride (DDEC), dodecyl benzyl dimethylammonium bromide (DBDMB). Also reported are sizes of reverse micelles as determined by dynamic light scattering
Deoxydehydration of glycerol to allyl alcohol catalyzed by rhenium derivatives
No full textThe deoxydehydration (DODH) of glycerol is effectively catalyzed by rhenium derivatives, either in neat
glycerol or in the presence of solvents (in particular alcohols), in air or under hydrogen bubbling.
Methyltrioxorhenium (MTO) and ReO3 were the only rhenium catalysts tested that can selectively
catalyze the DODH reaction at very low temperatures (140 °C). The presence of oxygen is not necessary,
although under nitrogen the reaction requires higher temperatures to occur. On the other hand, the
presence of hydrogen often noticeably increased the selectivity versus allyl alcohol formation, reaching
the considerable value of 90% in the case of reaction conducted in 2,4-dimethyl-3-pentanol with ReO3.
The DODH reaction always exhibits a definite induction time that, in the case of MTO, corresponds more
or less to the time required for its demethylation. Metal catalysts in both high – likely rhenium(VI) – and
low oxidation states are involved. Re-addition of fresh glycerol at the end of the reaction indicates the
feasibility of the reuse of the catalysts
Gas-phase reactions of the rhenium oxide anions, [ReOx]- (x = 2 - 4) with the neutral organic substrates methane, ethene, methanol and acetic acid
Get PDFThe ion–molecule reactions of the rhenium oxide anions, [ReOx]– (x = 2–4) with the organic substrates methane, ethene, methanol, and acetic acid have been examined in a linear ion trap mass spectrometer. The only reactivity observed was between [ReO2]– and acetic acid. Isotope-labelled experiments and high-resolution mass spectrometry measurements were used to assign the formulas of the ionic products. Collision-induced dissociation and ion–molecule reactions with acetic acid were used to probe the structures of the mass-selected primary product ions. Density functional theory calculations [PBE0/LanL2DZ6-311+G(d)] were used to suggest possible structures. The three primary product channels observed are likely to arise from the formation of the metallalactone [ReO2(CH2CO2)]– (m/z 277) and H2, [CH3ReO2(OH)]– (m/z 251) and CO, and [ReO3]– (m/z 235), H2 and CH2CO
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
Two Spin-State Reactivity in the Activation and Cleavage of CO2by [ReO2]
Get PDFThe rhenium dioxide anion [ReO2](-) reacts with carbon dioxide in a linear ion trap mass spectrometer to produce [ReO3](-) corresponding to activation and cleavage of a C-O bond. Isotope labeling experiments using [(ReO2)-O-18](-) reveal that O-18/O-16 scrambling does not occur prior to cleavage of the C-O bond. Density functional theory calculations were performed to examine the mechanism for this oxygen atom abstraction reaction. Because the spins of the ground states are different for the reactant and product ions ((3)[ReO2](-) versus (1)[ReO3](-)), both reaction surfaces were examined in detail and multiple [O2Re-CO2](-) intermediates and transition structures were located and minimum energy crossing points were calculated. The computational energy results show that the intermediate [O2Re(eta(2)-C,O-CO2)](-) species most likely initiates C-O bond activation and cleavage. The stronger binding affinity of CO2 within this species and the greater instabilities of other [O2Re-CO2)](-) intermediates are significant enough that oxygen atom exchange is avoided
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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