1,721,037 research outputs found
Modified aluminide coatings with reactive element for turbine blade protection
Full text linkIncreasing the maximum temperature of the gases introduced into the turbine increases both the efficiency and performance of a turbo-gas system; Switching from an input temperature of 900 ° C to 1250 ° C can result in a 30% increase in output power, leaving unchanged consumption. In order to ensure the structural integrity of components working in the hottest areas of the engine, research over the last decades has focused on the development of increasingly innovative technologies that aim to increase the efficiency of the system while at the same time increasing its operating life. In this thesis, it was studied a multiple modification approach of a standard aluminide coating in order to increase the oxidation and hot corrosion resistance. The first part of the study has involved the manufacturing, characterization and high temperature tests of a standard aluminide coating obtained by pack cementation. The optimized parameters were selected as deposition parameters for the modified coating: diffusion aluminide were doped with Zr and the characterization test were carried out in order to compare the standard with the modified samples. The second part of the study has involved the introduction of a modified process in order to optimize the manufacturing process of the coating. Electroless pure nickel plating were selected as pre-aluminization process in order to introduce a Ni reservoir onto the substrate surface. Otherwise, n-Al2O3 was used as nano-reinforcement in the Ni layer to improve the oxidation resistance by modifying the kinetic of oxidation. The final part of the work has involved the test of a different aluminization process. In collaboration with the University of La Rochelle, France, slurry-aluminization (low temperature) was carried out onto the standard and the electroless pure nickel samples. Oxidation results were compared with the first part of the work and an innovative production way of diffusion aluminide coating modified with Zr and electroless Ni was proposed and studied
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
Experimental validation of minimum time-jerk algorithms for industrial robots
No full textIn this paper, we present a minimum-time/jerk algorithm for trajectory planning and its experimental validation. The algorithm search for a trade-off between the need for a short execution time and the requirement of a sufficiently smooth trajectory, which is the well known necessary condition to limit the vibration during fast movements. The trade-off is achieved by adjusting the weight of two suitable functions, able to consider both the execution time and the squared-jerk integral along the whole trajectory. The main feature of this algorithm is its ability to smooth the trajectory's profile by adjusting the intervals between two consecutive via-points so that the overall time is minimally delayed. The practical importance of this technique lies in the fact that it can be implemented in any industrial manipulator without a hardware upgrade. The algorithm does not need for a dynamic model of the robot: only the mechanical constraints on the position, velocity and acceleration ranges have to be set a priori. The experimental proof is provided in this paper by comparing the results of the proposed algorithm with those obtained by adopting some classical algorithms
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