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Load Partition and Microstructural Evolution at High Temperature in Multiphase Lightweight Metallic Materials
No full textAluminium and titanium alloys surround our lives and are essential when weight minimization is required together with relatively high strengths. At room temperature, strength can be improved by reinforcing these alloys with ceramics phases, resulting in the formation of metal matrix composites. The introduction of rigid intermetallic phases is an alternative option when the production of the composites raises the costs.The study of the load partition between phases under the effect of external (thermo-) mechanical loads is crucial to understand the behaviour of multiphase alloys during real service conditions. The lack of scientific works analysing the load partition in Al and Ti multiphase alloys at high temperature is the main motivation of the present work.Bulk diffraction techniques capable to penetrate up to a few cm within materials are necessary to follow in situ the evolution of the load partition under the effect of external loads. Neutron sources with high flux and the third-generation synchrotron diffraction sources are ideal for this purpose compared with traditional x-ray laboratory sources. Furthermore, acquisition times up to 3 min for the neutron diffraction and below 1 s for the synchrotron diffraction make them suitable tools for in situ analysis at high temperature, where relaxation effects can play a relevant role.The aim of this work is the study of the load partition and the microstructural evolution at high temperature in selected multiphase lightweight metallic materials by means of in situ neutron and synchrotron diffraction techniques.Cast AlSi12 and AlSi10Cu6Ni2 alloys, undergoing solution treatments during 1h and 4h at 500°C, are compared with their respective as cast conditions during high temperature compression tests. The effect of the load partition between different phases is analyzed by in situ synchrotron diffraction. The eutectic Si in the aluminium piston alloy is able to bear a higher load than in the AlSi12 alloy in corresponding heat treatment conditions and for identical externally applied strains. Cu, Ni and Fe aluminides, forming highly contiguous 3D networks with the eutectic Si are responsible for this behaviour. The decrease of the load carrying capability in the AlSi12 with solution treatments is due to the disintegration of 3D Si networks, which on the other hand, is partially preserved by the aluminides after solution treatments in the AlSi10Cu6Ni2 alloy. The role played by aluminides on damage onset in the AlSi10Cu6Ni2 alloy is revealed by the sudden decrease of the load born by Al2Cu at the point of maximum strength of this alloy.In a different section, three SiC-particle reinforced composites produced by powder metallurgy, two of them by wet blending using 2124 and 6061 Al-alloys, and one by ball milling using a 2124 Al-alloy, are subjected to thermal cycling in order to explain the differences observed in their creep resistance. The effect of the blending route on the stress relaxation during thermal cycling is studied by in situ neutron diffraction. The thermal stresses partially relax at T above 90°C. The higher creep resistance of the composite produced by ball milling shows less relaxation of thermal stresses in comparison with the wet blended composites. The average axial compressive thermal stresses are approximately 50 MPa, 15 MPa and 10 MPa after heating to 230 - 300°C in the matrices of the ball milling 2124, wet blending 6061 and wet blending 2124 composites, respectively, which relax at rates smaller than 5 x 10^(-9) - 3 x 10^(-8) s^(-1).Finally, a Ti662 alloy reinforced with 12% and 20% volume fractions of TiC particles and produced by powder metallurgy, is subjected to high temperature tensile tests to compare the load bearing capability of the different phases as well as the different deformation mechanisms. Two Ti662 matrices, produced by powder metallurgy and ingot metallurgy are used as reference alloys. Synchrotron diffraction is the selected tool for this study. The smaller alpha-lamella size of the PRMs in comparison with the unreinforced powder metallurgy matrix is responsible for their higher ductility. Furthermore, the presence of the TiC particles does not play an effective reinforcing role because of their inhomogeneous spatial distribution although local strain evolution shows that they are able to bear part of the load. The beta-phase plastifies practically at the beginning of the tensile tests. The alpha-phase deforms by a mechanism of grain rotation in the Ti662 alloy produced by powder metallurgy as a consequence of the geometrical reorientation of the lamellae and crystallographic rotation within the lamellae. On the other hand, the beta-phase shows an increase of crystallographic misorientation within individual grains. The Ti662 ingot metallurgy alloy, because of its smaller grain size, allows following in situ the texture evolution
Load partition and microstructural evolution at high temperature in multiphase lightweight metallic materials
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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
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
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
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