1,720,955 research outputs found
Mechanistic and kinetic study of limona ketone oxidation initiated by hydroxyl radical: impact of indoor air pollution
No full textInternational audienceDegradation of air quality in the atmosphere is mainly caused by air pollution and represents a major health risk. Limona ketone (LK) (C9H14O, 4-acetyl-1-methyl-1-cyclohexene) is emitted by alpha-pinene, which is massively present in the indoor environment and a major atmospheric source of secondary organic aerosols (SOAs), and has attracted attention in the field of atmospheric chemistry. The OH-addition and H-abstraction reactions of LK by OH radicals have been investigated using M06-2X, omega B97X-D, MP2 and CCSD(T) with the 6-311+G(d,p) basis set. Its degradation channels and reactions with O2, NO and HO2 radicals have been explored using quantum chemical methods. The reaction kinetics were studied theoretically over the temperature range of 278-350 K by employing canonical variational transition state theory with the small curvature tunnelling (CVT/SCT) method for both barrierless channels and channels with barriers. The addition of OH at the C1 position of LK at the endocyclic double bond was shown to be the most favourable, with a small relative energy barrier of -7.27 kcal mol-1, and H-abstraction at the C4 position exhibited a relative energy barrier of -1.65 kcal mol-1 at the M06-2X/6-311+G(d,p) level of theory. Our calculated energy results show that the OH addition reactions are more dominant than the H-abstraction channel through electronic rearrangement. The obtained overall rate coefficient at 298 K is 4.77 x 10-10 cm3 molecule-1 s-1, which is in good agreement with the experimental rate coefficient of kOH = (1.29 +/- 0.33) x 10-10 at 296 +/- 2 K and similar to 735 Torr determined by Atkinson et al. Addition of the OH radical at the C1 position predominates over all the other reaction channels, with a branching ratio of 56.20% at 298 K. Our theoretical results suggest that the atmospheric lifetime is similar to 0.58 hours and the formation of stable product 1-(hydroperoxy-4-methylcyclohex-3-en-1-yl) ethenone is thermodynamically exothermic in nature. This work provides valuable information regarding the degradation mechanism and atmospheric fate of LK in the reaction initiated by the OH radical. Degradation of air quality in the atmosphere is mainly caused by air pollution and represents a major health risk
Environmental implications of oxalic and malonic acids with tropospheric oxidants
No full textInternational audienceDicarboxylic acids (DCAs) are major players in the formation of secondary organic aerosols (SOAs) and climate change. DCAs have potential impact on human health and environmental issues ranging from local scale to global scale participate mainly in the cloud condensation. In this context, oxalic acid (OA) and malonic acid (MA) are the most dominant DCAs in the atmosphere. A full atmospheric degradation mechanism of OA and MA with the most reactive tropospheric oxidants, namely, OH, Cl and NO3 radicals, were studied using M06‐2X, ωB97XD/cc‐pVTZ and 6‐311++G(2df,2p) level of theories. To evaluate the atmospheric influence, this study enables us to deep investigation of fate of OA and MA with respect to the mentioned radicals and their subsequent secondary reactions. The latter result in the formation of carbon dioxide (CO2), formic acid (HCOOH), which contributes to the formation of SOA and climate change. The reaction mechanism in this study was initiated through H‐abstraction reaction, followed by dehydrogenation and decarboxylation reaction of both DCAs. The rate coefficients of OA, MA with OH, Cl and NO3 radicals are determined theoretically using variational transition state theory (VTST) with Eckart tunnelling method in the temperature range of 278–1000 K. At 298 K, the rate coefficient of OA with OH, Cl and NO3 are 2.48 × 10−15, 2.37 × 10−20, 6.16 × 10−23 in cm3 molecule−1 s−1, whereas MA with OH, Cl and NO3 are 9.76 × 10−14, 1.01 × 10−12 and 5.89 × 10−18 in cm3 molecule−1 s−1, respectively. Our present results shed light on the atmospheric implications of two DCAs and provide the significant insight for the atmospheric pathways
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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