1,721,158 research outputs found
Nanocatalysts from Ionic Liquid Precursors for the Direct Conversion of CO2 to Hydrocarbons
Get PDFThe direct conversion of carbon dioxide (CO2) into lower olefins (C2-C4) is a highly desirable process as a sustainable production route. Lower olefins, i.e., ethylene, propylene and butenes (C2-C4), are key building blocks in the current chemical industry. The reaction proceeds via two main consecutive reactions: Reverse Water Gas Shift (RWGS) to produce CO followed by the further conversion of CO to hydrocarbons via the Fischer−Tropsch reaction2. This process is achieved by a multifunctional iron-based catalyst supported on zeolites providing three types of active sites (Fe3O4, Fe5C2 and acid sites), which cooperatively catalyse a tandem reaction1.To date, attempts at synthesising a suitable catalyst for the direct hydrogenation reaction follow a conventional precipitation procedure, whereby Iron Oxide Nanoparticles (IONs) are produced and then embedded within a zeolite structure by granule mixing. This method provides no control over the size and shape of the IONs formed; a characteristic of imperative importance due to its significant effect on the hydrocarbon product distribution obtained. In our novel approach, ionic liquids are utilised for the synthesis of the IONs resulting in better control over size and morphology of the nanostructured material, and as a consequence, better conversion and selectivity towards the olefins. <br/
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
Taak specifieke ionische vloeistoffen voor het oplossen van metaalverbindingen
Get PDFThe main goal of this PhD thesis was to design new task-specific ionic liquids with the ability to dissolve metal compounds. Despite the large quantity of papers published on ionic liquids, not much is known about the mechanisms of dissolving metals in ionic liquids or about metal-containing ionic liquids. Additionally, many of the commercially available ionic liquids exhibit a very limited solubilizing power for metal compounds, although this is for many applications like electrodeposition and catalysis one of the essential features. To enhance the ability of ionic liquids to incorporate metals in ionic liquids, functional groups that are able to coordinate to the metal ions are required. Task-specific ionic liquids combine, in the best case, a solubilizing power that is comparable with organic solvents with the “green” character of ionic liquids, which makes them environmental friendly solvents. Before these compounds will be applicable on larger scale, these functionalized ionic liquids have to be cheap and easily accessible.
Firstly, a protonated betaine bistriflimide, [Hbet][Tf2N], was introduced. This is a cheap and easily accessible functionalized ionic liquid with the ability to dissolve large quantities of metal oxides and metal hydroxides. The metal solubilizing power of this compound is selective. Soluble are: oxides of the trivalent rare earths, uranium(VI) oxide, zinc(II) oxide, cadmium(II) oxide, mercury(II) oxide, nickel(II) oxide, copper(II) oxide, palladium(II) oxide, lead(II) oxide and silver(I) oxide. Insoluble or very poorly soluble are iron(III) and manganese(II) oxides, cobalt(II) oxides, as well as aluminium oxide. The metals can be stripped from the ionic liquid by treatment of the ionic liquid with an acidic aqueous solution. After transfer of the metal ions into the aqueous phase, the ionic liquid can be separated and recycled. Betainium bistriflimide forms one phase with water at high temperatures, whereas phase separation occurs below 55.5 °C (“phase switching” behavior). The mixtures of the ionic liquid with water also show a pH-dependent phase switching behavior: two phases occur at low pH, whereas one phase is present under neutral or alkaline conditions. The structures, the energetics and the charge distribution of the betainium cation, the bistriflimide anion, as well as of the cation-anion pairs were studied by density functional theory calculations (DFT). Additionally, the crystal structures of two modifications of this ionic liquid were determined.
A range of crystal structures of the metal complexes obtained from the above mentioned functionalized ionic liquid were examined. This study revealed a rich structural variety especially of oligonuclear complexes, whereas in the literature mainly monomeric or polymeric complexes with this type of ligands are known. Dimeric betaine bistriflimide structures were found for the dysprosium(III) compound; the europium(III) compound and for the copper(II) compound; a trimeric betaine bistriflimide structure for the cobalt(II) compound; a tetrameric betaine bistriflimide structure for the manganese(II) compound; a pentameric betaine bistriflimide structure for the nickel(II) compound; , a cluster formation for the lead(II) compound; and polymeric structures for the cadmium(II) compound; and the silver(I) compound. In the crystal structure of cobalt(II) betaine bistriflimide, pure ionic liquid [Hbet][Tf2N] co-crystallized. The cation-anion interaction found in the crystal structure of the pure ionic liquid remained in the metal complex. No hydrogen bonding between the ionic liquid and the metal complex could be observed. It was demonstrated that ionic liquids might be good media for crystal engineering.
In order to modify the physical properties of the betainium ionic liquid, structural modifications have been introduced. Different kinds of cations, all bearing a carboxylic functional group, were applied. Six cations with a positively charged nitrogen ion – l-carnitine, pyrrolidinium, morpholinium, pyridinium, piperidinium, imidazolium and one with a positively charged phosphonium ion - tributylphosphonium, were studied. Despite the rich structural variation, surprisingly small differences in physical properties of these ionic liquids were observed. This can be explained by the strong and dominating influence of the carboxylic group on the physical properties.
To study the influence of the carboxylic group, an ionic liquid with a hydroxyl group instead of the carboxylic group, choline bistriflimide, was introduced. Due to this hydroxyl group, the ionic liquid showed only a limited solubility towards metal compounds. This hydrophobic ionic liquid also shows a “phase switching” behavior; this occurred at higher temperatures than in the case of the betainium bistriflimide ionic liquid. Due to the absence of a conjugated system, this ionic liquid possesses a high UV-transparency. This can be an interesting property for the application of this choline bistriflimide ionic liquid as medium for photophysical reactions or as a solvent for spectroscopy.
Choline saccharinate and choline acesulfamate are two examples of hydrophilic ionic liquids, which can be prepared from easily available starting materials (choline chloride and a non-nutritive sweetener). The (eco)toxicity of these ionic liquids in aqueous solution is very low in comparison with other types of ionic liquids. A general method for the synthesis and purification of hydrophilic ionic liquids has been demonstrated. The method implies a silver-free metathesis reaction, followed by the purification of the ionic liquids by ion-exchange chromatography. The crystal structures show a marked difference in hydrogen bonding between the two ionic liquids [Chol][Sac] and [Chol][Ace], although the saccharinate and the acesulfamate anions show structural similarities. The optimized structures, the energetics and the charge distribution of cation-anion pairs in the ionic liquids were studied by density functional theory (DFT). For a qualitative picture of the Lewis structure the occupation of the non-Lewis orbitals was considered. The calculated interaction energies and the dipole moments for the ion-pairs in the gas phase have been discussed.
In the last chapter, a different strategy to incorporate metals into ionic liquids was introduced. A lanthanide thiocyanate anion was synthesized and used as component for an ionic liquid. By using this anion in combination with a 1-butyl-3-methylimidazolium (C4mim) cation the first lanthanide-containing ionic liquids were obtained. These compounds have melting points ranging from 28 °C (Nd) to 39 °C (Y). The general formula for these compounds is [C4mim]status: Publishe
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
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