1,720,990 research outputs found
Laser surface texturing of ceramics and ceramic composite materials – A review
Full text linkThe surface texturing of ceramics is generally performed through acid-based etching and machining; however, laser texturing may be considered as a more precise, reproducible and eco-friendly process. Furthermore, laser ablation may be used to produce complex patterns on ceramic surfaces, thus offering new surface engineering opportunities. The studies so far conducted on this topic have mainly been application-driven, and since a wide variety of lasers have been used for surface texturing, it is difficult to have a comprehensive understanding of this technique applied to ceramics and ceramic composite materials. Laser texturing requires a great deal of knowledge of the material and the laser source parameters to optimise the process in order to obtain the expected results. It is therefore important to expand the research on the laser texturing of ceramics and CMCs in order to build a relevant amount of literature that can be used to identify the most appropriate parameters for each application. This review provides an overview of most of the technological aspects considered relevant for the laser surface texturing of ceramics and CMCs, and includes the fundamentals of laser-material interactions and a summary of the used equipment and parameters. Furthermore, most of the techniques related to the modifications of surface material induced by a laser are critically reviewed, and the new horizons that are opening up, in the context of the modification of surfaces to improve the performances of materials for several applications, are discussed
Surface modification of SiC to improve joint strength via a Corona plasma treatment
Full text linkThe high mechanical and chemical properties of SiC make it difficult to texture and modify its surface using such conventional methods as mechanical machining and wet etching. Among possible alternative strategies, Atmospheric Pressure Plasmas (APPs) could be used, cutting cost and time, but much still has to be understood about their feasibility for the surface treatment of ceramic materials. In this work, the effectiveness of a commercial corona discharge system in modifying the surface of SiC has been evaluated, focusing on its positive effect on the joint strength of adhesively bonded plasma-treated SiC. The objective of the study has been to observe the surface changes, in terms of chemical composition and texture, that take place as a result of exposure to corona plasma and to compare the obtained results with previous studies on laser and low-pressure plasma textured SiC samples. These very first results, derived from characterization and mechanical testing, suggest that this approach could be a promising alternative
Ytterbium disilicate-based glass-ceramic as joining material for ceramic matrix composites
Full text linkA key aspect of ceramic matrix composites integration is related to a reliable joining technique. An ytterbium disilicate based glass-ceramic material is processed by reactive viscous flow sintering between a barium aluminium borosilicate glass and ytterbium oxide and it is used to join SiC/SiC and C/SiC composites. The joining temperature and the in situ formation of the Yb2Si2O7 is optimised at 1200°C without pressure, on the basis of the sintering and crystallisation mechanisms. The mechanical characterization of SiC/SiC and C/SiC joined with the ytterbium disilicate-based glass-ceramic, tested by single-lap offset at RT, exhibits an apparent shear strength of 35 MPa, similar to their interlaminar shear strength. The proposed system displays self-healing behaviour at 1000 °C and 1150 °C, as demonstrated by the partial and complete sealing of induced cracks by Vickers indentation on its surface at different loads, thus suggesting that it can effectively be used as promising joining material for CMCs
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
Mechanical and thermal characterization of an epoxy foam as thermal layer insulation for a glass fiber reinforced polymer
Full text linkWe have investigated the formulations and curing parameters to obtain an epoxy foam to be used as thermal insulator layer
for a glass fiber reinforced polymer (GFRP). A relevant decrease (50%) of the apparent density of the foam was achieved by adding up
to 5 wt % of foaming agent without affecting the glass-transition temperature (Tg). The mechanical properties were inevitably affected
by the foaming, but a remarkable reduction down to 30% of the original value of the thermal conductivity was achieved. Morphological
analysis by scanning electron microscopy showed a continuous interface between the epoxy GFRP and the foamed layer
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
- …
