1,721,463 research outputs found
Metal matrix composites reinforced with SiC long fibers and carbon nanomaterials produced by electrodeposition
Get PDFThe research work of this PhD thesis was done on the study, production and characterization of two types of metal matrix composites: 1) fiber reinforced metal matrix composites and, 2) carbon nanomaterials reinforced metal matrix composites. In fiber reinforced metal matrix composites, a metal or an alloy is reinforced with continuous or discontinuous fibers in order to improve the specific strength and stiffness at high temperatures. For example superalloys are the typical materials for the hot parts of aeronautic engines. They are very important in the aerospace field as they offer high temperature mechanical strength together with a good resistance to oxidation and corrosion. But due to high temperatures involved in the service conditions, buckling of the material may occur. In order to avoid this high temperature buckling phenomena, a reinforcement of the superalloy could be needed to maintain the mechanical properties. For this reason it was thought to investigate the possibility of realizing continuous fibers reinforced metal matrix composites over the superalloys that can further improve the high temperature properties. Due to its simplicity and viability, electrochemical deposition was chosen as the production technique to produce this kind of composite materials. The selected substrate for electrodepositing the nickel matrix composite was nickel based superalloy Inconel-718, and monofilament continuous silicon carbide fibers were chosen as reinforcement. First of all chemical compatibility was studied between the nickel matrix, superalloy and silicon carbide fibers, both in the uncoated form, and coated with carbon or carbon/titanium diboride. Both theoretical calculations and experiments were conducted, suggesting the use of a carbon coating over fibers and a buffer layer of nickel to increase the interface quality as well as to avoid unwanted reactions between substrate and silicon carbide fibers. After studying the chemical feasibility of all the related components, electrodeposition of the composites was performed in order to demonstrate the practical feasibility of the process. Then final composites were deposited on the dog-bone shaped specimens of Inconel-718. The produced composites were subjected to mechanical tests in order to evaluate the mechanical properties at room temperature and at high temperatures (400 °C and 600 °C). Evaluation of the results shows improvement in the yield strength of the produced composites with respect to the superalloy alone at room temperature. There is a decrease in the yield strength at high temperatures due to the failure of the interface between the superalloy and the composite layer but it is demonstrated that if a hot pressing treatment is done, then the interface strength is retained at high temperature and thus yield strength values will also increase. Fracture analysis and EDS analysis were also performed on the fractured surfaces of the samples with the help of field emission scanning electron microscope in order to study the fracture mechanisms involved and the composition of the interface after their testing at high temperatures. The fracture mechanisms in Ni/SiC composite layer was of debonding and pull out type which is typical characteristic of the fiber reinforced composites. The superalloy fractures with ductile behavior at room temperature. At temperatures of 400 °C and 600 °C, the superalloy fails with more ductile character after extensive amount of plastic deformation before its fracture. Carbon nanomaterials are widely being used to reinforce the metallic materials in order to improve their electrical, thermal, corrosion, wear and friction resistance for particular applications. In this part of the research work, graphene nanoplatelets (GNPs) and graphene oxide (GO) were chosen as nano reinforcements to produce nickel matrix nanocomposites with the intention to evaluate their wear and friction behavior. Gr
Design of Single-Channel Sampling-Rate Reconfigurable Asynchronous SAR and Dual-Mode Noise-Shaping SAR ADCs for Space Applications
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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
Contribution Based Author Categorization to Calculate Author Performance Index
Get PDFDespite the widely used author contribution criteria, unethical authorship practices such as guest, ghost, and honorary authorship remains largely unsolved. We have identified six major reasons by analyzing 78 published papers addressing unethical authorship practice. Those are lack of: (i) awareness about and (ii) compliance with authorship criteria, (iii) universal definition and scope for determining authorship, (iv) common mechanisms for positioning an author in the list, (v) quantitative measures of intellectual contribution; and (vi) pressure to publish. As a possible measure to control unethical practice, we have evaluated the possibility to adopt an author categorization scheme – proposed according to the common understanding of how first-, co-, principal-, or corresponding- author is perceived. Based on an online opinion survey, the proposed scheme was supported by ~80% of the respondents (n=370). The impact of the proposed categorization was then evaluated using a novel mathematical tool to measure “Author Performance Index (API)” that can be higher for those who might have authored more papers as primary and/or principal authors than those as coauthors. Hence, if adopted, the proposed author categorization scheme together with the API would provide a better way to evaluate the credit of an individual as a primary and principal author
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