1,720,952 research outputs found
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
Microwave effects in heterogeneous catalysis: Application to gas-solid reactions for hydrogen production
No full textDue to the quest for more efficient production processes both from the energy and selectivity point of view, microwave irradiation has attracted significant scientific attention over the last three decades, as an alternative means of chemical activation. Over this period, striking process benefits, such as higher conversions and selectivities and/or a shorter reaction times, compared to the respective conventionally heated processes have been reported. The aim of this work is to investigate the influence of microwave energy on heterogeneous gas-solid catalytic reactions. As example process, the steam reforming of methanol and the water-gas shift reaction were selected. In a first step, the interaction of microwaves with different catalysts was investigated in a non-reactive environment, followed by investigation of the microwave effects on the reactions themselves. Comparison of the microwave- and electrically heated processes was performed in terms of conversion, selectivity and energy efficiency of the reactor. Contrary to other works in the literature, a two-dimensional temperature map along the centre plane of the reactor was recorded with both heating modes. The study of interaction of microwaves with the solid state catalysts revealed that the heating rate, the maximum temperature at constant power, and the heat distribution inside the catalyst bed strongly depend on the catalytic support morphology, the metal loading and the particle size of the catalyst. Moreover, the experiments proved that even small catalytic samples (~2g) experience non-uniform heat distribution inside their volume when exposed to a well-defined, mono-mode type of microwave field. These temperature gradients, although sometimes being severe, are undetectable by the commonly employed in microwave chemistry infra-red temperature sensors. These types of sensors are often built-in in the microwave applicator and serve as benchmark for the power control unit, which adjusts the power delivered into the microwave cavity. Therefore, a fibre optic based direct temperature measurement was selected as more accurate method in further stages of the research. The investigation of methanol steam reforming reaction was performed with employment of two catalysts - PdZnO/Al2O3 and CuZnO/Al2O3 – at an average reaction temperature ranging between 190oC – 250oC and 170oC – 230oC, respectively. In order to account for possible temperature gradients occurring across the catalytic bed, multi-point temperature mapping was implemented. The experiments revealed that at corresponding thermal conditions, the feed conversion in the microwave-heated process is significantly higher than in the electrically-heated process, regardless of the employed catalyst. However, the product distribution remained unaffected. Comparison of the reactor energy efficiency demonstrated that the MW-assisted process exhibits higher reactor energy efficiency than the corresponding electrically heated process for both catalysts and over the range of the studied reaction temperatures. This entails that a given conversion can be achieved with lower net heat input to the reactor under the microwave heating mode and thus indirectly confirms the selective microwave heating principle (microscale hot spot formation). Pre-conditioning of the catalyst in the presence of the microwave field prior to the reaction did not affect the reaction performance. The catalyst surface investigation showed no difference in the morphology of the catalyst used either between the microwave and the conventionally heated process, or between the preconditioned and the non-preconditioned samples. Consequently, specific non-thermal microwave effects were excluded as justification for the enhancement of the reactor performance. In order to confirm the thermal nature of the microwave effects observed in the methanol steam reforming reaction, a mildly exothermic process, a water-gas shift reaction, was investigated at the latest stage of the research. Contrary to steam reforming, the water-gas shift reaction did not exhibit significant enhancement neither in terms of conversion nor in terms of reactor energy efficiency. This is because a significant part of the net heat input to the reactor comes from the heat of reaction; therefore, the heat input from microwave irradiation and the associated local overheating of active sites diminishes. Consequently, the microwave effect is not pronounced. Based on the experimental experience obtained and the theoretical knowledge regarding the shortcomings of the available microwave types of equipment, an alternative reactor design, based on travelling microwave fields, is proposed for application to heterogeneous gas-solid catalytic reactions. The new concept may enable uniform spatial heating, improved electromagnetic energy utilization and electromagnetic field spatial localization (i.e. on the catalytic reactor walls).Process and EnergyMechanical, Maritime and Materials Engineerin
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
Microwave-assisted low temperature steam reforming of methanol for hydrogen production
No full textMicrowave effects on heterogeneous reactions are nowadays widely investigated due to the potential benefits coming from providing energy to the reaction zone in a different way. This study is focused on the investigation of the microwave effect on the low temperature steam reforming of methanol for the production of hydrogen. Therefore the performance of reactions carried out under conductive and microwave heating are compared. The microwave-assisted reactions showed a significant increase in conversion and product yields opposed to reactions carried out under conductive heating. This is attributed to the existence of temperature gradients on the micro-scale.Intensified Reaction & Separation SystemsProcess and EnergyMechanical, Maritime and Materials Engineerin
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
- …
