1,720,966 research outputs found
Innovative approach to the development of conductive hybrid composites for Selective Laser Sintering
Full text linkSelective Laser Sintering (SLS) was used to manufacture electrically conductive polymer composites made of polyamide 12 reinforced with carbon fibres and graphite (PA12/CF/GP). Since material design is critical in developing conductive polymer composites, an innovative experimental technique is proposed to preliminary evaluate the electrical behaviour of the powders before SLS processing and select the most performing hybrid compositions. The properties of starting powders and the microstructure, mechanical and electrical behaviour of PA12/CF/GP composites were studied. Results reveal that the addition of graphite lowers the flowability and mechanical properties of the composites compared to the carbon fibres reinforced counterparts. Hybrid composites display great enhancements in the electrical conductivity with respect to the neat PA12 up to anti-static and conductive range; however, no synergistic effect between the two fillers was observed
Composition and Workability of Plastic Fractions Recovered from Commingled Waste Discarded by a Composting Plant
Full text linkThis paper deals with the recovery of plastic fractions from waste discarded by an industrial composting plant that processes the organic fraction of municipal solid waste. Polymeric fractions (PE, PP and PET) were sorted from this discarded waste using a NIR separator. The polymeric fractions were then washed to remove residual contaminants and characterized with the aim of assessing their composition. A process of pelletizing and injection molding suitable for producing specimens made of 100% of these recovered materials was set up. The tensile strength and stiffness, as well as the microstructure of the recycled plastics, were investigated. The mechanical features of samples fully made of recycled PE and PP were like those characteristic of virgin polymers. Samples made of PET did not show completely satisfactory properties, as they displayed rather poor elastic modulus and ductility
Optimization of selective laser sintering process conditions using stable sintering region approach
Full text linkThe optimization of process parameters represents one of the major drawbacks of selective laser sintering (SLS) technology since it is largely empirical and based on performing a series of trial-and-error builds. This approach is time con-suming, costly, and it ignores the properties of starting powders. This paper provides new results into the prediction of processing conditions starting from the material properties. The stable sintering region (SSR) approach has been applied to two different polymer-based powders: a polyamide 12 filled with chopped carbon fibers and polypropylene. This study shows that the laser exposure parameters suitable for successful sintering are in a range that is significantly smaller than the SSR. For both powders, the best combination of mechanical properties, dimensional accuracy, and porosity level are in fact, achieved by using laser energy density values placed in the middle of the SSR
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
Thermal shock resistance of a NiCrAlY-coated Alloy 625 system produced by laser powder bed fusion
No full textAdditive Manufacturing offers an innovative route for producing high-quality parts in various fields. A bi-material system, consisting in a NiCrAlY bond coat deposited onto a Ni-based Alloy 625 substrate, was manufactured by laser powder bed fusion (LPBF). Test samples were prepared and included sol-gel ceramic ZrO2(Y2O3) top coats as well as a specific grain boundary serration (GBS) heat treatment for promoting high temperature resistance. These specimens were subjected to very severe thermal shock cycles between 950 °C and 300 °C, characterized by steep heating and air quenching rates in a state-of-the-art burner rig designed to render gas turbine conditions, and their integrity was compared. While LPBFed NiCrAlY coatings were relatively spared from degradations due to thermal shocks, ceramic top coats exhibited clear spallation. Poor bonding was particularly experienced by specimens subjected to the GBS heat treatment due to the unavoidable formation therein of surface oxides. Numerous cracks were detected within NiCrAlY bond coats, both in tested specimens as well as in pre-cycled as-built ones, which suggested a dominant role of the LPBF process known for generating residual stress. Heat treated specimens exhibited nearly no cracking. Hardness was found to significantly increase within as-built NiCrAlY bond coats as a result of heat exposure during thermal shock cycling and was attributed to precipitations. The fully recrystallized microstructure of heat treated specimens, on the other hand, was found more stable. The present study completes a series of investigations demonstrating the great potential for manufacturing excellent high temperature structural components by means of LPBF as opposed to more constraining conventional routes
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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