1,720,960 research outputs found
Réactivité des terpènes avec le radical nitrate : études cinétique et mécanistique en chambres de simulation atmosphérique
No full textBiogenic volatile organic compounds (BVOC) are strongly emitted by forests and crops in the atmosphere. They are very reactive towards nitrate radical, the main tropospheric oxidant during the night, and play a key role in atmospheric chemistry. These reactions lead to the formation of a variety of functionalized products (organic nitrates, carbonyl compounds ...) and to large amounts of secondary organic aerosols. Organic nitrates are the main nitrogen oxides reservoir. They directly influence reactive nitrogen and ozone budgets. Secondary organic aerosol has direct and indirect impacts on climate, due to its formation, its optical and hygroscopic properties and its chemical composition. The aim of this work is to understand these processes at the molecular scale, through kinetic and mechanistic studies of NO3 radical oxidation of several BVOCs.Kinetic and mechanistic studies have been performed for three monoterpenes ((C10H16), γ- and α-terpinene and terpinolene) and one sesquiterpene ((C15H24), β-caryophyllene) in atmospheric simulation chambers. These compounds have been chosen to highlight the influence of their chemical structures on their reactivities and to fill the lack of experimental data about their chemistry in the literature.For the kinetic part, rate constants have been measured with both relative and absolute methods. Due to their high reactivities, this study has requiered the development on the simulation chamber of an IBB-CEAS ((Incoherent Broad Band Cavity Enhanced Absorption Spectroscopy) analysis pathway to measure nitrate radical at the ppt level. Mechanistic studies have been also conducted to identify and quantify the main reaction products. Organic nitrates and SOA yields have been calculated. Detected products allowed proposing reaction mechanisms.Les composés organiques volatils biogéniques (COVB) sont fortement émis dans l’atmosphère par les forêts et les cultures. Très réactifs vis-à-vis du radical nitrate NO3, principal oxydant nocturne dans la troposphère, ils ont une importance majeure dans la chimie atmosphérique. En effet, cette réaction mène à la formation d’un large panel de produits de réaction en phase gazeuse fonctionnalisés (nitrates organiques, composés carbonylés, ...) et une large fraction d’aérosols organiques secondaires. Les nitrates organiques constituent des espèces réservoirs d’oxydes d’azote dans l’atmosphère et influencent directement le bilan d’azote réactif et ainsi les niveaux d’ozone. L’aérosol organique secondaire, de par sa formation, ses propriétés optiques et hygroscopiques ainsi et sa composition chimique a un impact direct et indirect sur le climat. Ce travail a pour but la compréhension de ces processus à l’échelle moléculaire à travers une étude cinétique et mécanistique des réactions d’oxydation de plusieurs COVB par le radical NO3.Ainsi, les réactions d’oxydation par le radical NO3 de trois monoterpènes ((C10H16), γ- et α-terpinène et le terpinolène) et un sesquiterpène ((C15H24), le β-caryophyllène) ont été invesitguées en chambre de simulation atmosphérique. Les composés ont été choisis d’une part pour mettre en évidence l’influence de leur structure chimique sur leur réactivité et d’autre part, pour combler les manques de données expérimentales dans la littérature sur la chimie de ces composés.Pour la partie cinétique, les constantes de vitesse ont été mesurées à la fois par la méthode de cinétique absolue et par celle de cinétique relative. Les réactions chimiques étudiées étant très rapides, cette étude a nécessité au préalable le développement sur la chambre de simulation atmosphérique d’une voie d’analyse spectroscopique IBB-CEAS (Incoherent Broad Band Cavity Enhanced Absorption Spectroscopy) pour la mesure des radicaux nitrates dans la gamme du ppt. Des études mécanistiques ont également été menées afin d’identifier et de quantifier les principaux produits de réaction. Les rendements de nitrates organiques, d’AOS ont été calculés. Les produits détectés ont permis d’établir des mécanismes réactionnels
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
Reactivity of terpenes with nitrate radical : kinetic and mechanistic studies in atmospheric simulation chambers
No full textLes composés organiques volatils biogéniques (COVB) sont fortement émis dans l’atmosphère par les forêts et les cultures. Très réactifs vis-à-vis du radical nitrate NO3, principal oxydant nocturne dans la troposphère, ils ont une importance majeure dans la chimie atmosphérique. En effet, cette réaction mène à la formation d’un large panel de produits de réaction en phase gazeuse fonctionnalisés (nitrates organiques, composés carbonylés, ...) et une large fraction d’aérosols organiques secondaires. Les nitrates organiques constituent des espèces réservoirs d’oxydes d’azote dans l’atmosphère et influencent directement le bilan d’azote réactif et ainsi les niveaux d’ozone. L’aérosol organique secondaire, de par sa formation, ses propriétés optiques et hygroscopiques ainsi et sa composition chimique a un impact direct et indirect sur le climat. Ce travail a pour but la compréhension de ces processus à l’échelle moléculaire à travers une étude cinétique et mécanistique des réactions d’oxydation de plusieurs COVB par le radical NO3.Ainsi, les réactions d’oxydation par le radical NO3 de trois monoterpènes ((C10H16), γ- et α-terpinène et le terpinolène) et un sesquiterpène ((C15H24), le β-caryophyllène) ont été invesitguées en chambre de simulation atmosphérique. Les composés ont été choisis d’une part pour mettre en évidence l’influence de leur structure chimique sur leur réactivité et d’autre part, pour combler les manques de données expérimentales dans la littérature sur la chimie de ces composés.Pour la partie cinétique, les constantes de vitesse ont été mesurées à la fois par la méthode de cinétique absolue et par celle de cinétique relative. Les réactions chimiques étudiées étant très rapides, cette étude a nécessité au préalable le développement sur la chambre de simulation atmosphérique d’une voie d’analyse spectroscopique IBB-CEAS (Incoherent Broad Band Cavity Enhanced Absorption Spectroscopy) pour la mesure des radicaux nitrates dans la gamme du ppt. Des études mécanistiques ont également été menées afin d’identifier et de quantifier les principaux produits de réaction. Les rendements de nitrates organiques, d’AOS ont été calculés. Les produits détectés ont permis d’établir des mécanismes réactionnels.Biogenic volatile organic compounds (BVOC) are strongly emitted by forests and crops in the atmosphere. They are very reactive towards nitrate radical, the main tropospheric oxidant during the night, and play a key role in atmospheric chemistry. These reactions lead to the formation of a variety of functionalized products (organic nitrates, carbonyl compounds ...) and to large amounts of secondary organic aerosols. Organic nitrates are the main nitrogen oxides reservoir. They directly influence reactive nitrogen and ozone budgets. Secondary organic aerosol has direct and indirect impacts on climate, due to its formation, its optical and hygroscopic properties and its chemical composition. The aim of this work is to understand these processes at the molecular scale, through kinetic and mechanistic studies of NO3 radical oxidation of several BVOCs.Kinetic and mechanistic studies have been performed for three monoterpenes ((C10H16), γ- and α-terpinene and terpinolene) and one sesquiterpene ((C15H24), β-caryophyllene) in atmospheric simulation chambers. These compounds have been chosen to highlight the influence of their chemical structures on their reactivities and to fill the lack of experimental data about their chemistry in the literature.For the kinetic part, rate constants have been measured with both relative and absolute methods. Due to their high reactivities, this study has requiered the development on the simulation chamber of an IBB-CEAS ((Incoherent Broad Band Cavity Enhanced Absorption Spectroscopy) analysis pathway to measure nitrate radical at the ppt level. Mechanistic studies have been also conducted to identify and quantify the main reaction products. Organic nitrates and SOA yields have been calculated. Detected products allowed proposing reaction mechanisms
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
