Examinando por Materia "Light"
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Ítem ¿Cómo se forma el fuego?(2017) Londoño Restrepo, Néstor Mauricio; Arango Hurtado, Carolina; Muriel Gil, Luisa Fernanda; Londoño Rivera, Ana MaríaÍtem Effect of CeO2 content in morphology and optoelectronic properties of TiO2-CeO2 nanoparticles in visible light organic degradation(ELSEVIER SCI LTD, 2019-02-01) Cano-Franco, JC; Alvarez-Lainez, M; Universidad EAFIT. Departamento de Ingeniería de Diseño; Ingeniería de Diseño (GRID)TiO2 is a semiconductor widely used in photocatalytic degradation of organic pollutants due to its band gap energy. However, its absorption range is restricted only to UV radiation that is less than 10% of solar light. With the aim of increasing the adsorption area on TiO2 nanoparticles a modified sol-gel method was used to produce a smaller particle size, and to extend the absorption range to the visible spectrum, TiO2 nanoparticles were synthesized with different CeO2 contents to generate semiconductor heterojunction between them. The crystallographic, morphological, and optoelectronic characteristics of these TiO2-CeO2 nanoparticles were studied, and two crystalline phases were differentiated: anatase for TiO2 and fluorite for CeO2. An increase in the CeO2 content produced crystallite sizes between 6.5 nm and 12.0 nm. TiO2-CeO2 nanoparticles showed morphological properties such as small particle size, heterogeneous surface and high BET surface area compared to bare commercial TiO2. These features involve a positive effect of CeO2 in TiO2 nanoparticles surface, thus TiO2-CeO2 nanoparticles exhibit enhanced optoelectronic properties caused by a decrease in the effective band gap and red-shift in the electromagnetic spectrum. In addition, methylene blue degradation showed that TiO2-CeO2 nanoparticles are suitable for high photocatalytic activity application under visible light. © 2018 Elsevier LtdÍtem Foto-degradación de fenol sobre catalizadores de TiO2 y Mo/TiO2. La metodología de superficie de respuesta como herramienta de optimización(Centro de Informacion Tecnologica, 2014-01-01) López-Zamora, S.M.; GilPavas, E.; Gómez-García, M.Á.; Dobrosz-Gómez, I.; López-Zamora, S.M.; GilPavas, E.; Gómez-García, M.Á.; Dobrosz-Gómez, I.; Universidad EAFIT. Departamento de Ingeniería de Procesos; Procesos Ambientales (GIPAB)In this work, the response surface methodology was applied as a tool for the optimization of the operational conditions of phenol photo-degradation over TiO2 and 2% wt Mo/TiO2 catalysts. A multifactorial experimental design was proposed, including the following variables: phenol initial concentration (Ci), catalyst loading (Cat) and pH. The apparent reaction rate constant and the percentage of phenol degradation were chosen as the response variables. When TiO2 was used as catalyst, the following optimal operational conditions were found: Ci=10ppm, Cat=0.7g/L and pH=8 for both UV and visible light. For 2% wt Mo/TiO2 catalyst, the optimal operating conditions strongly depended on the applied radiation source. Thus, under UV radiation: Ci=10 ppm, Cat=0.7 g/L and pH=8 were found as the optimum conditions. Using visible light, and the following optimized conditions, Ci=10 ppm, Cat=0.1 g/L, pH =3.6, the Mo containing catalyst showed to be the most efficient. Under these conditions, the amount of 2% wt. Mo/TiO2 was 7 times lower than that of unsupported TiO2.Publicación Generación y caracterización de vórtices ópticos mediante moduladores espaciales de luz(Universidad EAFIT, 2015) Echeverri Chacón, Santiago; Restrepo Gómez, René; Ángel Toro, Luciano AlbertoLa generación de haces de luz con vorticidad óptica usando moduladores espaciales de luz, es una capacidad que desde hace más de 10 años le ha permitido a instituciones de alto prestigio como por ejemplo, la Universidad de Glasgow, generar innovaciones tecnológicas que han revolucionado campos de la biomedicina -- Entre estas innovaciones se encuentran las pinzas ópticas para micromanipulación de objetos microscópicos [43], y nuevas técnicas de microscopía de fase mejoradas con vórtices ópticos (VOs) [14] -- En este trabajo se presentan los resultados de un proyecto del Laboratorio de Fotónica del Grupo de Óptica Aplicada de la Universidad EAFIT, en el cual logramos implementar las herramientas y métodos necesarios para la generación de VOs que puedan ser usados para la investigación en estas áreas -- En primera instancia, se desarrolló y caracterizó un montaje experimental en el cual los VOs son generados al proyectar máscaras de fase sobre un modulador espacial de luz de transmisión -- Esto implicó comprender el funcionamiento de este tipo de dispositivos e implementar técnicas y herramientas para su caracterización, que garantizaran una modulación de fase y amplitud adecuada -- Una vez cumplido el objetivo de generar VOs de forma experimental, se desarrolló un método novedoso de reconstrucción de fase basado en la técnica de Diversidad de Fase (PD) para la caracterización de las aberraciones ópticas del sistema que distorsionan sus distribuciones de intensidad -- La novedad del método resulta del uso de máscaras de fase espiral como diversidades de fase, de tal forma que los mismos VOs distorsionados sirven para la detección de las aberraciones que los están deformando -- Finalmente, se presentan VOs de calidad, generados experimentalmente, y en los cuales se ha introducido y corregido una aberración conocida como demostración de las capacidades adquiridasÍtem Improving on-axis optical vortex generation by transmissive spatial light modulator using coherent phase diversity(OSA - The Optical Society, 2016-01-01) Cuartas-Vélez, C.; Restrepo, R.; Echeverri-Chacón, S.; Uribe-Patarroyo, N.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaWe present a modification of numerical optimization coherent phase diversity in order to detect and correct undesired effects of non-linear and incomplete phase modulation of transmissive spatial light modulators for on-axis optical vortices. © OSA 2016.Ítem Shack-Hartmann centroid detection using the spiral phase transform(OSA - The Optical Society of America, 2012-01-01) Vargas, J.; Restrepo, R.; Estrada, J.C.; Sorzano, C.O.S.; Du, Y.-Z.; Carazo, J.M.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaWe present a Shack-Hartmann (SH) centroid detection algorithm capable to measure in presence of strong noise, background illumination and spot modulating signals, which are typical limiting factors of traditional centroid detection algorithms. The proposed method is based on performing a normalization of the SH pattern using the spiral phase transform method and Fourier filtering. The spot centroids are then obtained using global thresholding and weighted average methods. We have tested the algorithm with simulations and experimental data obtaining satisfactory results. A complete MATLAB package that can reproduce all the results can be downloaded from [http://goo.gl/o2JhD]. © 2012 Optical Society of America.Ítem Speckle photography with different pupils in a multiple-exposure scheme(OPTICAL SOC AMER, 2000-01-01) Angel, L; Tebaldi, M; Bolognini, N; Trivi, M; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaThe use of different multiple-aperture pupils for recording each image in speckle photography is proposed. The introduction of suitable spatial frequency carriers, by internally modulating imaged speckles, allows one to selectively isolate or combine the spectral content of different images into spatially separated regions in the Fourier plane. Theoretical and experimental results extend the speckle photography technique to the depiction of several specklegrams of multiple uniform in-plane displacements. In this case, because different pupils are considered for recording, the cross-correlation functions for the amplitudes and intensities in the image plane are calculated on the basis of the statistical properties of the object. Also, the ensemble-average intensity in the Fourier plane is analytically derived, and fringe visibility is investigated. © 2000 Optical Society of America.Ítem Understanding the physical optics phenomena by using a digital application for light propagation(IOP PUBLISHING LTD, 2011-01-01) Sierra-Sosa, D.-E.; Ángel-Toro, L.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaUnderstanding the light propagation on the basis of the Huygens-Fresnel principle stands for a fundamental factor for deeper comprehension of different physical optics related phenomena like diffraction, self-imaging, image formation, Fourier analysis and spatial filtering. This constitutes the physical approach of the Fourier optics whose principles and applications have been developed since the 1950's. Both for analytical and digital applications purposes, light propagation can be formulated in terms of the Fresnel Integral Transform. In this work, a digital optics application based on the implementation of the Discrete Fresnel Transform (DFT), and addressed to serve as a tool for applications in didactics of optics is presented. This tool allows, at a basic and intermediate learning level, exercising with the identification of basic phenomena, and observing changes associated with modifications of physical parameters. This is achieved by using a friendly graphic user interface (GUI). It also assists the user in the development of his capacity for abstracting and predicting the characteristics of more complicated phenomena. At an upper level of learning, the application could be used to favor a deeper comprehension of involved physics and models, and experimenting with new models and configurations. To achieve this, two characteristics of the didactic tool were taken into account when designing it. First, all physical operations, ranging from simple diffraction experiments to digital holography and interferometry, were developed on the basis of the more fundamental concept of light propagation. Second, the algorithm was conceived to be easily upgradable due its modular architecture based in MATLAB® software environment. Typical results are presented and briefly discussed in connection with didactics of optics.