1,720,957 research outputs found
Heterogenkatalysierte Polymerprecursor-Synthese auf Basis nachwachsender Rohstoffe
No full textThe doctoral thesis at hand was done in cooperation with Uhde Inventa-Fischer and as part of the EuroBioRef project of the European Union and is therefore divided into two parts. On one hand there was the attempt to substitute the current two-step polylactic acid (PLA) precursor production, which includes the prepolymerisation of aqueous lactic acid and the subsequent depolymerisation to lactide, by direct lactide synthesis. The catalytic effect of amorphous y-aluminia and different zeolites was investigated in a continuously running experimental plant in the gaseous phase. In addition to the experimental results catalyst characterizations such as x-ray diffraction (XRD), Brunauer-Emmett-Teller isotherm (BET), Temperature programmed desorption (TPD), Fourier transform spectroscopy (FTIR) and Thermogravimetric analysis (TG) were done. The use of heterogeneous catalysts proved the feasibility of direct lactide synthesis. The H-ZSM-5 zeolite with a module of 300 reached with 37,2% the highest yield of the screening. For the selective lactide production a high BET surface is needed beside a medium amount of low and high acid centers, which are favorable lewis acid centers. The parameter optimization in combination with the y-alumina increased the yield up to 50,8%. According to the current state of technology L-lactid isomer is needed for PLA production. Racemisation of ciral aqueous lactid acid occurred with less than 10%. The results were influenced by a low desorption rate of the heavy adsorbing high molecular products and the side products of the lactid acid. Experiments under subatmospheric pressure increased the isomer selectivity. On the other hand the esterification of renewable acrylic acid and n-butanol to n-butylacrylate was investigated. The liquid phase reaction is the current method of acrylate production and is done either homogeneously (sulfuric and sulfonic acid) or heterogeneously (ion exchange resins) catalyzed. The disadvantages of this process are the separation of the reaction mixture and the catalysts and the high retention times, which result in low space time yields. The innovative approach was to do the esterification in the gaseous phase, which was accomplished in a continuously running experimental plant with a fixed bedded catalyst. The catalyst screening was done with common esterification catalysts under atmospheric pressure. Irrespective of the catalysts, all experiments showed low yields and high catalyst deactivations. The usage of ion exchange resins, which differed in the amount of divinyl benzole and acid centers, was made possible with the help of subatmospheric pressure and low temperatures (75°C – 120°C). The resins showed selectivities up to 85% (Lewatit 2649). The yield was increased to 42,4% by the parameter optimization (S 80,0%). In addition, even in long time tests desorption problems of the products from the catalyst surface occurred. But after all a continuous and stable test run was accomplished for 24 hours. Also the production of higher molecular oxiesters was totally suppressed
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
Beschaffung technischer Dienstleistungen am Beispiel Instandhaltung: Auch vermeintlich einfache Tätigkeiten können zum Desaster führen
No full textIn general, maintenance as part of the plant management ensures the maximum efficiency and availability of production and infrastructure plants at optimal cost and under satisfactory conditions of quality, safety and protection for the environment. Furthermore, it can be divided into four tasks, such as inspection, preventive maintenance, improvement and repair. As an economically function, maintenance has to be managed in accordance to the corporate strategy. For this reason, maintenance management has a strong strategic focus and decides e.g. which services will be outsourced (buy) or insourced (make). Like any management decision, both show strength and weaknesses as well as opportunities and treats. This discussion paper deals with the external sourcing of technical services in comparison to the services done by own maintenance staff. First, the basics of maintenance and maintenance management like make or buy and the procurement process are outlined. Afterwards, the risk analysis is introduced and applied. Several potential risks were identified and explained in detail. For each risk, several compensate measures were introduced and the individual impact is discussed
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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