1,721,340 research outputs found
Reactions and Separations in Green Solvents
No full textMost chemical processes involve solvents in the reaction and the separation step. These solvents give rise to a heavy environmental and economical burden. Moreover, these solvents are based on non-sustainable resources like petroleum. The aim of this thesis has been to develop a number of alternative processes based upon green (sustainable) solvents, and to demonstrate that these processes can be economically and ecologically advantageous. The green solvents investigated were water (polar, protic), supercritical carbon dioxide (apolar, aprotic) and ionic liquids. Water was used for the recovery of soda and molybdate by eutectic freeze crystallization from an industrial waste stream, leading to a zero waste discharge process. Supercritical carbon dioxide was shown to be an excellent solvent for the extraction of natural products like cannabis, for the foaming of polystyrene and for the dyeing of cotton. In a number of reactions ionic liquids were good replacements for traditional solvents. The first generation ionic liquids are based upon petroleum chemicals. In this thesis ionic liquids based upon natural products were synthesized and successfully applied. Based upon these results it can be concluded that the replacement of oil based solvents by green solvents is only a question of time.Process and EnergyMechanical, Maritime and Materials Engineerin
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
Sustainable Production of Cannabinoids with Supercritical Carbon Dioxide Technologies
No full textThis thesis concerns the production of natural compounds from plant material for pharmaceutical and food applications. It describes the production (extraction and isolation) of cannabinoids, the active components present in cannabis. Many cannabinoids have medicinal properties but not all cannabinoids are available in the (large) quantities necessary to develop new medicines, because so far, for large scale production, there are no economically and technically viable methods to extract those cannabinoids present in low quantities in the plant. Moreover, the currently used production process for the most important cannabinoid, tetrahydrocannabinol (?9-THC), has many drawbacks, such as the large use of the organic solvents, which is not only a burden to the environment but also to the safety of the operators, the production costs as well as the treatment of the produced waste. In this thesis, an alternative process using supercritical carbon dioxide is presented for the production of cannabinoids, including ?9-THC, cannabinol (CBN), cannabigerol (CBG) and cannabidiol (CBD). One of the steps of ?9-THC production from cannabis plant material, is the decarboxylation reaction, transforming the ?9-THC-acid naturally present in the plant into the psychoactive ?9-THC. Experiments showed a pseudo first order reaction, with an activation barrier of 85 kJ.mol-1 and a pre-exponential factor of 3.7x108 s-1. Using molecular modeling, two options for an acid catalysed ?-keto acid type mechanism were identified. Each of these mechanisms might play a role, depending on the actual process conditions. Formic acid was shown to be a good model for a catalyst of such a reaction. A direct keto-enol mechanism catalyzed by formic acid seems to be the best explanation for the observed activation barrier and the pre-exponential factor of the decarboxylation of ?9-THC-acid. Evidence for this was found by performing an extraction experiment with Cannabis Flos. It revealed the presence of short chain carboxylic acids supporting this hypothesis. Then, in order to develop the supercritical fluid extraction process, the solubility of ?9-THC, CBN, CBG and CBD in supercritical carbon dioxide has been determined using an analytical method with a quasi-flow apparatus. First the solubility of ?9-THC has been determined at 315, 327, 334 and 345 K and in the pressure range from 13.2 to 25.1 MPa. The molar solubility for ?9-THC ranged from 0.20 to 2.95x10-4. Then, the solubility of CBN, CBG and CBD in supercritical carbon dioxide has been determined at 314, 327 and 334 K and in the pressure range from 11.3 to 20.6 MPa. The molar solubility of CBN, CBG and CBD ranged from 1.26 x 10-4 to 4.16 x 10-4, from 1.17 to 1.91 x 10-4 and from 0.88 to 2.69 x 10-4, respectively. These solubility data have been compared to each other. The solubility of the different cannabinoids in supercritical CO2 increases at 326 K in the following order: ?9-THC < CBG < CBD < CBN. The solubility data were correlated using the Peng-Robinson equation of state in combination with Van der Waals mixing rules. To continue, supercritical fluid extraction (SFE) using carbon dioxide was performed with Cannabis Sativa L. in a pilot scale set-up at 313 and 323 K in the pressure range from 18 to 23 MPa. The SFE yield of ?9-THC is at maximum 98 %, which is comparable to classical hexane extraction. CBN and CBG can be extracted in higher amounts with SFE than with hexane extraction. Waxes are co-extracted with the cannabinoids. They can be easily removed via a winterization step. The purity of the final extract after winterization was 85 % ?9-THC at the optimal experimental conditions found in these experiments. With a two-steps extraction, it is possible to selectively extract minor cannabinoids (i.e. CBN, CBD and CBG) in a first step at low pressure (~15 MPa), and ?9-THC in a second step at higher pressure (~20 MPa). The last step of the process is performed using Centrifugal Partition Chromatography. It uses a two-phase liquid system, instead of a solid stationary phase, as it is the case in High Pressure Liquid Chromatography (HPLC). Separation is realized by the partitioning of compounds between the two phases. With this technique, a successful separation of ?9- THC, CBN and CBG is presented using the two-phase system hexane / acetone / acetonitrile. A purity higher than 99% is achieved with ?9- THC. With CBN and CBG the best purity obtained is higher than 90%. To conclude, an economical and ecological evaluation of two production routes to obtain pure ?9-THC is presented: the current process using organic solvents is compared with the alternative process using supercritical carbon dioxide developed in this thesis. The alternative process is significantly cheaper than the current one, although the high price of the starting material cannabis dominates the ultimate cost price. From an ecological point of view, the alternative process is also more sustainable as it consumes less energy and generates less waste. Therefore, this alternative process is preferred from an economical and ecological point of view.Process and EnergyMechanical, Maritime and Materials Engineerin
Plant bioassay to assess the effects of allelochemicals on the metabolome of the target species Aegilops geniculata by an NMR-based approach
No full textA metabolomic-based approach for the study of allelopathic interactions in the Mediterranean area is proposed using Aegilops geniculata Roth (Poaceae), a Mediterranean herbaceous plant, as test species. Its metabolome has been elucidated by 1D and 2D NMR experiments. Hydroponic plant cultures of A. geniculata were treated with specific compounds of known allelopathic potential: catechol, coumarin, p-coumaric acid, p-hydroxybenzoic acid, ferulic acid and juglone. The metabolic variations due to the presence of allelochemicals have been analyzed and measured. All of the compounds showed the strongest effects at the highest concentration, with coumarin and juglone as the most active compounds, causing an increase of several metabolites. The metabolome changes in test plants confirmed the allelochemicals' reported modes of action. The results demonstrated that the proposed method is a promising tool. It can be applied to plant extracts, making it possible to evidence the metabolites responsible for the activity, as well as their mechanisms of action. © 2013 Elsevier B.V
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
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