1,721,003 research outputs found
Geopolymers reinforced with natural fibers: A comparison among different sources
Full text linkThe performance of different natural fibers (hemp, kenaf and bamboo) used to formulate composites with an alkali-activated matrix based on metakaolin is evaluated. Short fibers were randomly dispersed up to about 3% of the binder weight, and the fresh and cured properties of the derived composites were determined. Up to the investigated fraction, it is still possible to obtain adequate workability without the supply of additional water or additives. Upon modification with fibers, the mechanical behavior changes from completely brittle to pseudoplastic with increased toughness. The flexural strength increases by up to 80% at the highest bamboo amount and up to 20% for kenaf. Hemp fibers have a negligible effect on flexural strength but strongly improve the materials’ toughness. Moreover, the addition of fibers does not change the manner in which the material interacts with moisture. Indeed, the water uptake of the modified samples was comparable to that of the unmodified samples, and the composites showed a decreased rate of water diffusion as the amount of fiber increased
Alkali‐activated mortars modified by epoxy‐carbon fiber composites wastes
Full text linkShort chopped fibers coated by epoxy resin of different length (5 to 10 mm length) were added at low volume content (about 4.6% on the composite) to alkali‐activated fly ash or metakaolin mortars. These uncured scraps derive from the production of carbon fiber‐reinforced polymer composites and they are not presently recycled, despite their outstanding mechanical properties. The workability, microstructure, porosity, and physical and mechanical properties (mainly flexural strength) of the derived materials were investigated. Superior flexural strength and increased toughness were obtained. An acid treatment of the scraps further improved the mechanical properties of the mortars by changing the chemical structure of the surface, thus increasing the interaction with the inorganic phase. These results foster the use of these wastes to improve the performance of low carbon footprint building materials such as alkali‐activated composites in the building industry
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
Multilevel optimization of anisogrid lattice structures for aerospace applications
No full textAerospace Structures & MaterialsAerospace Engineerin
Experimental and numerical study of vacuum resin infusion of stiffened carbon fiber reinforced panels
Full text linkLiquid resin infusion processes are becoming attractive for aeronautic applications as an alternative to conventional autoclave-based processes. They still present several challenges, which can be faced only with an accurate simulation able to optimize the process parameters and to replace traditional time-consuming trial-and-error procedures. This paper presents an experimentally validated model to simulate the resin infusion process of an aeronautical component by accounting for the anisotropic permeability of the reinforcement and the chemophysical and rheological changes in the crosslinking resin. The input parameters of the model have been experimentally determined. The experimental work has been devoted to the study of the curing kinetics and chemorheological behavior of the thermosetting epoxy matrix and to the determination of both the in-plane and out-of-plane permeability of two carbon fiber preforms using an ultrasonic-based method, recently developed by the authors. The numerical simulation of the resin infusion process involved the modeling of the resin flow through the reinforcement, the heat exchange in the part and within the mold, and the crosslinking reaction of the resin. The time necessary to fill the component has been measured by an optical fiber-based equipment and compared with the simulation results
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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