1,721,126 research outputs found
Laser-generated plasma investigation by electrostatic quadrupole analyzer
No full textA study of different metallic targets ablation, in vacuum, by using a 3ns Nd:YAG laser radiation, 532nm wavelength, is reported. Laser pulse with a high intensity generates a plasma at the target surface, with high non-isotropic emission of neutral and ion species, mainly emitted along the normal to the target surface. Mass quadrupole spectrometry, associated to the electrostatic ion deflection, allows an estimation of the emitted charge states energy distributions, within the plasma plume, for a fixed incident laser energy. Neutrals show Boltzmann-like distributions while ions show Coulomb-Boltzmann- shifted distributions. Time-of-flight measurements were also performed by using an ion collector consisting of a collimated Faraday cup placed along the normal to the target surface. The plasma is investigated in terms of velocity, kinetic energy, ion charge state and temperature of the ejected particles. A special regard is given to the parameters that influence the plasma properties, such as the evaporation latent heat, the electrical conductivity and the electron density of the ablated elements, to the plasma temperature and density and to the evaluation of the electric field producing the ion acceleration inside the plasma
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
Characteristic modification of UHMWPE by laser-assisted ion implantation
No full textThe purpose of this work is the characteristic modification by ion implantation of ultra high molecular weight polyethylene, and a preliminary study of its surface. This biomedical material has been chosen for its excellent chemical and physical properties. An ultraviolet-pulsed laser of 248 nm was employed to produce, by laser ablation, C and Ti ions of different charges with current densities of the order of 10 mA/cm(2). The ions were accelerated by the application of a positive high voltage, 30 kV, on the target support to accelerate ions to implant the polyethylene surfaces up to a depth of about 200 nm. Preliminary results about surface properties indicate that implanted surfaces have higher wettability and micro-hardness values with respect to unimplanted one
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