1,721,006 research outputs found
Local Aromaticity of the Six-Membered Rings in Pyracylene. A Difficult Case for the NICS Indicator of Aromaticity
No full textIn this work, we have analyzed the local aromaticity of the six-membered rings (6-MRs) of planar
and pyramidalized pyracylene species through the structurally based harmonic oscillator model of
aromaticity (HOMA), the electronically based para-delocalization index (PDI), and the magneticbased
nucleus independent chemical shift (NICS) measurements, as well as with maps of ring
current density. According to ring currents and PDI and HOMA indicators of aromaticity, there is
a small reduction of local aromaticity in the 6-MRs of pyracylene with a bending of the molecule.
In the case of NICS, the results depend on whether the NICS value is calculated at the center of
the ring (NICS(0)) or at 1 Å above (NICS(1)out) or below (NICS(1)in) the ring plane. While NICS-
(1)out values also indicate a slight decrease of aromaticity with bending, NICS(0) and NICS(1)in
wrongly point out a large increase of aromaticity upon distortion. We have demonstrated that the
NICS(0) reduction in the 6-MRs of pyracylene upon bending is due to (a) a strong reduction of the
paratropic currents in 5-MRs and (b) the fact that, due to the distortion, the paratropic currents
point their effects in other directions
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
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
Computational Insights into the Regioselectivity of 1,3-Dipolar Cycloadditions inside Carbon Nanotubes
No full textNature’s enzymes exhibit remarkable substrate specificity and catalytic efficiency by transforming substrates within confined active sites. To emulate this, various molecular containers, including zeolites, cyclodextrins, calix[n]arenes, cavitands, cucurbit[n]urils, metal-organic frameworks, covalent organic frameworks, and carbon nanotubes (CNTs), have been explored. Among these, CNTs are notable for their unique physical and chemical properties, enabling them to control reactions through spatial confinement. This study investigates the effect of CNT encapsulation on metal-free 1,3-dipolar Huisgen cycloaddition reactions between benzyl azide and substituted alkynes. Experimental results showed that CNTs significantly enhance the selectivity for the 1,4-triazole product. Computational studies using density functional theory further elucidate the impact of CNT confinement on reaction mechanisms and regioselectivity. The findings reveal that confinement within CNTs alters potential energy surfaces, favoring 1,4-triazole formation over 1,5-triazole, driven by steric and electronic factors. Additionally, comparative analyses highlight the influence of CNT diameter on activation energies and product stability, particularly with energy decomposition analysis and noncovalent interaction plots. This research underscores the potential of CNTs as nanoscale reactors for controlled synthesis, providing insights into the design of new catalytic systems and advancing the field of molecular encapsulation for selective organic transformations
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
Unravelling Enzymatic Features in a Supramolecular Iridium Catalyst by Computational Calculations
No full textNon-biological catalysts following the governing principles of enzymes are attractive systems to disclose unprecedented reactivities. Most of those existing catalysts feature an adaptable molecular recognition site for substrate binding that are prone to undergo conformational selection pathways. Herein, we present a non-biological catalyst that is able to bind substrates via the induced fit model according to in-depth computational calculations. The system, which is constituted by an inflexible substrate-recognition site derived from a zinc-porphyrin in the second coordination sphere, features destabilization of ground states as well as stabilization of transition states for the relevant iridium-catalyzed C−H bond borylation of pyridine. In addition, this catalyst appears to be most suited to tightly bind the transition state rather than the substrate. Besides these features, which are reminiscent of the action modes of enzymes, new elementary catalytic steps (i. e. C−B bond formation and catalyst regeneration) have been disclosed owing to the unique distortions encountered in the different intermediates and transition states
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