1,720,954 research outputs found
Influence of pH on the kinetics of hydrolysis reactions: the case of epichlorohydrin and glycidol
Get PDFGlycidol (GL) and epichlorohydrin (EPI) are two widely used molecules in chemical, pharmaceutical and food industry applications. However, their use in aqueous environments causes the formation of compounds, like monochloropropanediol (MCPD) and dichloropropanol (DCP), reported as dangerous for human health and therefore regulated by severe law restrictions. To identify the conditions leading to such species and design the corresponding processes in order to prevent their formation, hydrolysis and chlorination of EPI and GL, together with dehydrohalogenation of DCP and MCPD, have been systematically analysed. Different reaction conditions in terms of temperature, pH and chloride ion concentration have been experimentally investigated and the concentration of the involved species was tracked over time by gas chromatography and high-performance liquid chromatography. These experimental data were fitted through a kinetic model, which allowed a general expression of the observed rate constant of each reaction as a function of temperature and pH to be quantified. In particular, the reaction rates are conveniently expressed as combinations of three contributions: alkaline, neutral and acid. The corresponding rate laws explicitly account for the critical role of pH. The developed mechanistic model exhibits good prediction ability and may represent the basis for optimising processes employing EPI and GL
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
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
Poly(amine-epichlorohydrin) synthesis : kinetic study of side reactions for by-product minimisation
No full textLAUREA MAGISTRALEL'attuale sviluppo dell'industria chimica insieme alla crescente produzione di sostanze organiche e coloranti, hanno introdotto nuove sfide per gli scienziati riguardo il miglioramento dei processi di purificazione delle acque. Coagulanti inorganici come il solfato di alluminio e il cloruro ferrico, che venivano storicamente utilizzati come flocculanti nel trattamento delle acque reflue, si stanno attualmente sostituendo con polielettroliti cationici sintetici. Questi ultimi, infatti, risultano estremamente efficaci grazie alla sinergia tra interazioni elettrostatiche e proprietà idrofile che portano ad aggregare le impurità consentendo la purificazione dell'acqua. In questa tesi verrà focalizzata l'attenzione sulla poli(EPI-DMA-EDA), una tra le poliammine più comuni utilizzate nel trattamento delle acque potabili e reflue. Essa viene sintetizzata attraverso policondensazione di dimetilammina ed epicloridrina, in cui ammine organiche, ad es. 1,2-diamminoetano, sono usate come agenti modificanti. La sintesi della poliammina, considerata non tossica, avviene però in ambiente acquoso, dove si sviluppano, in parallelo rispetto a quelle desiderate, delle reazioni collaterali. Queste portano alla formazione di composti, come monocloropropandiolo (MCPD) e dicloropropanolo (DCP), pericolosi per la salute umana e regolati da severe leggi restrittive. Per far luce sulle condizioni alla base della produzione di tali molecole e per stimolare lo sviluppo di processi più puliti, nel presente lavoro sono state analizzate l'idrolisi e la clorurazione dell'EPI, insieme alla deidroalogenazione di DCP e MCPD. Diverse condizioni operative sono state studiate sperimentalmente in termini di temperatura, pH e concentrazione di ioni cloruro, monitorando la concentrazione delle specie mediante gascromatografia e cromatografia liquida ad alta prestazione. Mediante fitting dei dati sperimentali è stato sviluppato un modello cinetico dipendente dalla temperatura e dal pH che ha permesso di definire un'espressione generale della costante di velocità per ogni reazione. Lo studio condotto sulla cinetica di formazione dei sottoprodotti ha inoltre permesso di ottimizzare la reazione di alchilazione tra EPI e ammine, necessaria per formare gli oligomeri. A tal proposito è stato sviluppato il modello di un reattore semi-batch con l'obiettivo di analizzare l'influenza di diverse variabili sulla reazione di alchilazione, tramite un'analisi parametrica. Infine, sono state analizzate le caratteristiche, in termini di viscosità e contaminanti residui, del polimero finale, variando diversi parametri di reazione, quali il rapporto molare tra epicloridrina e dimetilammina, la quantità di 1,2-diamminoetano e la temperatura di reazione. I risultati ottenuti sono alla base dell'ottimizzazione dei processi di sintesi di poli(ammina-epicloridrina) in termini di abbattimento di inquinanti.Today’s chemical industry and the giant production of synthetic organic chemicals and dyes have introduced new challenges to the scientists in the improvement of water purification processes. Historically, inorganic coagulants such as aluminium sulphate and ferric chloride have been used as flocculants in the treatment of drinking water. Nowadays, the use of synthetic cationic polyelectrolytes is preferred, due to a synergy of inherent electrostatic interactions and hydrophilic properties which brings to aggregate impurities enabling water purification. This thesis focuses on poly(EPI-DMA-EDA), which accounts for the majority of polyamines used in the water and wastewater treatment industry. It is synthesised by the polycondensation of dimethylamine and epichlorohydrin, in which organic amines, e.g. 1,2-diaminoethane, are used as modifying agents. Although the polyamine is considered non-toxic, its synthesis occurs in aqueous environment and this causes side reactions related to EPI hydrolysis to take place, leading to the formation of compounds, like monochloropropandiol (MCPD) and dichloropropanol (DCP), reported as dangerous for human health and therefore regulated by severe law restrictions. To shed light on the conditions leading to the formation of such molecules and to stimulate the development of processes capable of minimising their content, a kinetic scheme involving all the aqueous side reactions has been proposed and studied. Different reaction conditions in terms of temperature, pH and chloride ion concentration have been experimentally investigated, by tracking the concentration of the species through gas chromatography and high-performance liquid chromatography. The developed temperature and pH-dependent kinetic model allowed the definition of a general expression of the rate constant for each reaction identified by fitting the experimental data. Moreover, the obtained results made it possible to optimise the alkylation reaction between EPI and amines, necessary to form the oligomers. A model of a semi-batch reactor was developed and a parametric analysis was conducted with the aim of analysing the influence of different variables on the alkylation reaction. Finally, the characteristics of the polymer, in terms of viscosity and residual contaminants, were analysed by varying several reaction parameters, such as the molar ratio of epichlorohydrin to dimethylamine, the amount of 1,2-diaminoethane and the reaction temperature. The results of this work represent the basis for the synthesis optimisation, aimed to minimise pollutants in the final polymer
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