1,721,010 research outputs found
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
Gaussian to rectangular light beam redistribution using computer generated phase elements
No full textSome considerations on the design of computer generated phase elements applied to the intensity redistribution of Gaussian light beams are presented in this paper. The computer generated phase elements are designed using an iterative transform algorithm for Fresnel domain. Parameters which influence the performances of these algorithms and the computation time are discussed. Results obtained by computer simulations are presented for three different Gaussian beam shaping (flat-top, 2 shifted gaussians, acronym)
Laser trapping and micro-manipulation using optical vortices
No full textThe aim of this work is to investigate the usefulness of the Laguerre-Gaussian (LG) beams, often referred to as optical vortices, for laser trapping and manipulation experiments that cannot be performed using Gaussian beams. Laguerre-Gaussian beams, exhibiting "doughnut"-like transversal intensity distributions and carrying orbital angular momentum (OAM), greatly extended the capabilities of laser tweezers. These beams can be obtained by converting the Gaussian beam generated by a common laser source, by means of property designed diffractive optical elements (DOEs). We present two trapping systems, the first one based on amplitude DOEs, the second one based on phase DOEs. In both cases the DOE is implemented on a liquid crystal display. Trapping of small dielectric high-index particles on the "doughnut" profile is demonstrated. OAM transfer to trapped particles, that are caused to rotate, is observed as well. Moreover, low-index particles, that would be rejected by a conventional Gaussian beam, are trapped in the zero intensity region of the doughnut
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
Phase diffractive elements for three dimensional spot arrays generation
No full textWe propose a combined analytical - iterative optimization approach to design phase diffractive elements that generate three - dimensional array of light spots The validity of this method is demonstrated by computer simulations for an array of eight spots positioned in two planes separated by 500 mum along the optical axis
Design and fabrication of diffractive optical elements for optical tweezer arrays by means of e-beam lithography
No full textOptical tweezer arrays generated by diffractive optical elements can extend the capabilities to manipulate and organize microscopic particles into complex structures, to sort them intelligently and to study collective behavior in many-body systems materials. We describe new design methods, based on iterative algorithms, to calculate phase-only diffractive optical elements able to generate planar and three-dimensional arrays of tweezers. Experimental results showing the validity of the design approach are presented for an array of eight gaussian spots
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
Two-dimensional Photonic Crystal Waveguide obtained by e-beam direct writing of SU8-2000 Photoresist
No full textWe report on the direct electron-beam patterning of a negative tone resist SU8-2000 for the fabrication of a two-dimensional photonic crystal (2D-PC) waveguide. The high refractive index of the SU8-2000 (about 1.69), its transparency above 360 nm, the good mechanical stability and the possibility of direct patterning by electron-beam lithography, make such resist ideal for the direct realization of high-resolution photonic crystal waveguides. The fabrication of a triangular array of sub-micron pillars (lattice constant of 300 nm and filling factor of 0.35) suitable for the realization of a 2D-PC waveguide on a glass substrate is reported. The energy dispersion diagram, calculated by the plane wave expansion technique, shows that this 2D-PC structure has a small photonic band gap (PBG) for the TM-like modes
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