1,721,123 research outputs found
Spatter reduction in nanosecond fibre laser drilling using an innovative nozzle
No full textPulsed wave fibre lasers are becoming a popular industrial tool in microprocessing due to their many positive features, such as high beam quality, high reliability and high productivity, which are fundamental to machining small, precise features of industrial applications. However, the lasers’ use in the machining of ultra-precise features, such as small holes, is hindered by the fact that commercial pulsed wave fibre lasers commonly operate with pulse durations in the nanosecond regime. Such long pulse durations mean that the material is thermally removed, which results in the production of a melted layer and thermal damage in the bulk material. Consequently, the typical thermal defects of the melting regime, such as spattering of recast material around the hole, taper, heat-affected zone and poor hole circularity, are found in materials machined with these lasers.
This paper proposes a design for an innovative nozzle that combines the high productivity of nanosecond fibre lasers with an improvement in the quality of the machined holes by reducing the spatter production in titanium laser percussion drilling. The innovative nozzle is based on the suction effect created by the Venturi principle that prevents the deposition of melted and vaporised material on the workpiece surface. The influence of the nozzle configuration and shielding gas on hole quality is investigated after the laser percussion drilling of 0.5 mm-thick titanium sheets, in which the process conditions that allow maximum productivity are used. The innovative nozzle produces a remarkable decrease in spatter on the entrance hole surface without affecting the other quality features, such as hole diameter, circularity and taper, while preserving the high productivity obtainable with a standard nozzle
I fattori per lo sviluppo della P.A. nella Net Economy: sostenibilità, trasferibilità e credibilità nell'esperienza lecchese
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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
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