1,720,966 research outputs found
Method based on the double sideband technique for the dynamic tracking of micrometric particles
Full text linkDigital holography (DH) methods are of interest in a large number of applications. Recently, the double sideband (DSB) technique was proposed, which is a DH based method that, by using double filtering, provides reconstructed images without distortions and is free of twin images by using an in-line configuration. In this work, we implement a method for the investigation of the mobility of particles based on the DSB technique. Particle holographic images obtained using the DSB method are processed with digital picture recognition methods, allowing us to accurately track the spatial position of particles. The dynamic nature of the method is achieved experimentally by using a spatial light modulator. The suitability of the proposed tracking method is validated by determining the trajectory and velocity described by glass microspheres in movement.Fil: Ramirez, Claudio. Universitat Autònoma de Barcelona; EspañaFil: Lizana, Ángel. Universitat Autònoma de Barcelona; EspañaFil: Iemmi, Claudio César. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Campos, Juan. Universitat Autònoma de Barcelona; Españ
Inline digital holographic movie based on a double-sideband filter
Full text linkThis Letter proposes a new optical architecture based on a double-sideband filter, simultaneously applied at the Fourier plane, for inline digital holography. The proposed architecture not only allows removal of the conjugate images in the reconstruction process but also reduces the distortions that usually appear when using a single-sideband filter. We first introduce the mathematical model that explains the method and then describe the optical setup used for the implementation. The optical system includes a parallel aligned liquid crystal display placed at the Fourier plane that simultaneously filters positive and negative frequencies, when properly combined with linear polarizers. This feature makes the device useful to register dynamic processes. Finally, we tested the setup by registering a holographic movie of microscopic moving objects placed at different planes.Fil: Ramirez, Claudio. Universitat Autònoma de Barcelona; EspañaFil: Lizana, Ángel. Universitat Autònoma de Barcelona; EspañaFil: Iemmi, Claudio César. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Campos, Juan. Universitat Autònoma de Barcelona; Españ
Optimization and performance criteria of a Stokes polarimeter based on two variable retarders
Full text linkIn this paper we present the analysis, optimization and implementation of several Stokes polarimeter configurations based on a setup including two variable retarders. The polarimeter analysis is based on the Mueller-Stokes formalism, and as a consequence, it is suitable to deal with depolarized light. Complete Stokes polarimeters are optimized by minimizing the amplification of simulated errors into the final solution. Different indicators useful to achieve this aim, as the condition number or the equally weighted variance, are compared in this paper. Moreover, some of the optimized polarimeters are experimentally implemented and it is studied the influence of small deviations from the theoretical ones on the amplification of the Stokes component error. In addition, the benefit of using incomplete polarimeters, when detecting specific ranges of states of polarization, is discussedFil: Peinado, Alba. Universitat Autonoma de Barcelona; EspañaFil: Lizana, Ángel. Universitat Autonoma de Barcelona; EspañaFil: Vidal, Josep. Universitat Autonoma de Barcelona; España. ALBA Synchrotron Light Source Facility; EspañaFil: Iemmi, Claudio Cesar. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Campos, Juan. Universitat Autonoma de Barcelona; Españ
The minimum Euclidean distance principle applied to improve the modulation diffraction efficiency in digitally controlled spatial light modulators
Full text linkDigital addressing of the electrical signal in spatial light modulators, as it is the case in present liquid crystal on silicon (LCoS) displays, may lead to temporal phase fluctuations in the optical beam. In diffractive optics applications a reduction in the modulation diffraction efficiency may be expected. Experimental work is done characterizing the fluctuations amplitude and phase depth for three different digital addressing sequences. We propose a diffractive model to evaluate the modulation diffraction efficiency of phase diffractive optical elements (DOEs) in the presence of phase fluctuations. Best results are obtained for the most stable electrical sequence even though its phase depth is as small as 280°. The results show good agreement with the numerical calculation given by the model.Fil: Lizana, Ángel. Universitat Autonoma de Barcelona; EspañaFil: Márquez, A.. Universidad de Alicante; EspañaFil: Lobato, L.. Universitat Autonoma de Barcelona; EspañaFil: Rodange, Y.. Universitat Autonoma de Barcelona; EspañaFil: Moreno, I.. Universidad de Miguel Hernandez; EspañaFil: Iemmi, Claudio Cesar. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Campos, Juan. Universitat Autonoma de Barcelona; Españ
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
Optimization, tolerance analysis and implementation of a Stokes polarimeter based on the conical refraction phenomenon
Full text linkRecently, we introduced the basic concepts behind a new polarimeter device based on conical refraction (CR), which presents several appealing features compared to standard polarimeters. To name some of them, CR polarimeters retrieve the polarization state of an input light beam with a snapshot measurement, allow for substantially enhancing the data redundancy without increasing the measuring time, and avoid instrumental errors owing to rotating elements or phase-to-voltage calibration typical from dynamic devices. In this article, we present a comprehensive study of the optimization, robustness and parameters tolerance of CR based polarimeters. In addition, a particular CR based polarimetric architecture is experimentally implemented, and some concerns and recommendations are provided. Finally, the implemented polarimeter is experimentally tested by measuring different states of polarization, including fully and partially polarized light.Fil: Peinado, Alba. Universidad Autonoma de Barcelona. Facultad de Física; EspañaFil: Lizana, Ángel. Universidad Autonoma de Barcelona. Facultad de Física; EspañaFil: Turpín, Alejandro. Universidad Autonoma de Barcelona. Facultad de Física; EspañaFil: Iemmi, Claudio César. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: Kalkandjiev, Todor K.. Universidad Autonoma de Barcelona. Facultad de Física; EspañaFil: Mompart, Jordi. Universidad Autonoma de Barcelona. Facultad de Física; EspañaFil: Campos, Juan. Universidad Autonoma de Barcelona. Facultad de Física; Españ
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
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