Examinando por Materia "Optics microscopy"

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    Evaluación de la coherencia de la luz en la implementación de un sistema de microscopía óptica
    (Universidad EAFIT, 2017) Cadavid Muñoz, Juan José; Restrepo Gómez, René
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    Generación y caracterización de vórtices ópticos mediante moduladores espaciales de luz
    (Universidad EAFIT, 2015) Echeverri Chacón, Santiago; Restrepo Gómez, René; Ángel Toro, Luciano Alberto
    La 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 adquiridas
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    The mechanical behavior of dentin: importance of microstructure, chemical composition and aging
    (Universidad EAFIT, 2017) Montoya Mesa, Carolina; Ossa Henao, Alexander
    Dental fracture is one of the three most common forms of failure of restored teeth and the most common cause of tooth loss or extraction in elderly patients -- Previous investigations conducted on aging of hard tissues have identified that there is a considerable reduction in the mechanical properties (i.e. fracture toughness, fatigue and flexural resistance) of dentin with aging and that may predispose tooth fracture -- These declines in properties have been attributed to microstructural and chemical composition changes over time -- However, these aging processes have not been really quantified and related with the changes in mechanical properties -- Accordingly, the aim of this work is to evaluate the aging process of coronal dentin in terms of the evolution of microstructure, changes in chemical composition and mechanical properties from selected age groups (young and old donors) -- The changes in these properties were evaluated in three different regions (outer, middle and inner) in order to identify spatial variations within the crown -- A brief description of the main literature on composition, microstructure and mechanical behavior of dentin is presented in chapter 2 -- An extensive experimental study was carried out in chapter 3 to identify the changes in microstructure of dentin with aging by means of optical and electron microscopy; while changes in chemical composition were analyzed using Raman Spectroscopy to calculate the mineral-to-collagen ratio -- Changes in mechanical properties were measured using Vickers micro-hardness -- Chapter 4 describes the importance of tubule density to the fracture toughness of dentin for young and old donor’s groups -- An approach previously proposed to study the mechanical behavior of porous materials was used to model the fracture toughness of coronal dentin in terms of the tubule characteristics -- Results were then compared with published results from previous studies -- The time-dependent deformation response of dentin was analyzed via spherical indentation experiments at different indentation loads in Chapter 5 -- From the experimental observations was proposed a simple model to describe the time dependent deformation behavior of dentin -- This model was based on previously proposed theories for indentation of time dependent materials, showing that the effective strain rate of dentin depends on its chemical composition (i.e. mineral-to-collagen ratio) and microstructure (i.e. lumen area fraction) -- The descriptions of the model were compared with the experimental results showing good agreement -- The same model was validated with experimental results of aged dentin, finding a low change in the deformation response of dentin with aging, as presented in chapter 6 -- Finally, preliminary results made on the mechanical properties of dentin have shown that the microstructure of aged human dentin can vary depending on the ethnic background of the donor and that this quality is critically important to the mechanical properties of the tissue -- In chapter 7 preliminary results on the comparison between the microstructure, chemical composition and mechanical properties of Colombian, Chinese and American donors is presented -- Finally, conclusions for the study are presented in chapter 8