Índice de empleabilidad para Colombia

Este trabajo tiene como objetivo construir una herramienta que facilite el diagnóstico de las personas que se encuentran buscando un trabajo en el mercado laboral colombiano, haciendo énfasis en las barreras que presentan. Adicionalmente, este instrumento permitirá identificar los programas y acciones específicos que buscador necesita para mitigar sus barreras y mejorar sus posibilidades de acceder a un puesto de trabajo, al igual que permitirá identificar barreras comunes a grupos específicos y diseñar nuevas políticas que sean aplicadas de manera transversal a estos grupo

Two dimensional fluidized bed dynamics

There are different equipments where solid-gas reactions can take place. One of the most used equipments for these processes, are the uidized beds due to their high reaction rate per unit reactor volume. This complex gas-solid flow is often difficult to model because of the very different length scales that are present, so that additional fundamental investigations are needed before reliable models can be developed for the performance of fluidized beds. Among the different aspects in need of additional research, this PhD thesis focuses on the experimental investigation of the uid dynamics of the fluidized bed by use of pressure probes as well as nonintrusive measurements, based on Particle Image Velocimetry (PIV) and Digital Image Analysis (DIA) techniques, to characterize the flow in a two-dimensional experimental facility. In particular, the DIA technique is employed for the interpretation of images taken with a high-speed camera for different operating conditions. A clear difference between the dense phase and the bubble phase is established, thereby enabling different bubble parameters such as equivalent diameter, bubble mass center and bubble velocity to be quantified. In addition, the selected DIA technique allows us to detect and characterize dynamical bubble phenomena including bubble formation, growth and coalescence. In addition, to characterize the in fluence of the bubbles on the dense phase, the dense phase velocity has been measured with use made of the PIV technique. This PhD thesis reports relevant results with the aim to a better understanding of the dense and bubble phases interaction for different operation conditions, distributor design, fixed bed height, particle size and bed thickness. As a novel result, the circulation time was obtained, yielding an order-of-magnitude estimate for the mixing degree within the reactor. The present work also analyzes the effect of the bed thickness in the minimum uidization velocity, since this value is one of the most important parameters for reactor-design purposes. The influence regions promoted by the bubbles in the dense phase have been calculated, identifying and measuring the upwards and downwards solid movement regions around the bubble. The bubble size and the bubble velocity have been correlated with the volumetric dissipation of kinetic energy in the dense phase, providing information about the attrition phenomena responsible of the mechanical stress which leads to the gradual degradation of the individual bed particles, which in turn affects the fluidized bed behavior. Also, the influence of the grid configuration has been investigated. It has been proved that two uniform multi-orifice distributors, having the same pressure drop but different grid configurations yield the same dynamical bubble pattern and global bed behavior when the beds are operated at the same fluidization conditions. Consequently for the fluidization conditions covered, the overall bed dynamics for uniform gas distribution, do not depend on the grid configuration.---------------------------------------------------------------------------------------------------------------------------------------------Actualmente existen multitud de procesos en los que se pueden encontrar reacciones sólido-gas. Los reactores de lecho fluidizado se muestran como uno de los sistemas más adecuados para este tipo de reacciones debido a su alta capacidad de mezcla por unidad de volumen. Precisamente esta característica hace que en los lechos fluidos presenten diferentes longitudes de escalas haciendo muy compleja su modelización, de ahí la importancia de los estudios fundamentales sobre lechos fluidos a la hora de ayudar en el modelado y diseño de este tipo de reactores. De entre los diferentes campos de investigación en los lechos fluidos, esta tesis se centra en el estudio experimental de la dinámica de un lecho fluido bidimensional mediante el uso de sondas de presión así como de técnicas no intrusivas de medida basadas en la Velocimetría por Imágenes de Partículas (PIV) y en Análisis Digital de Imágenes (DIA), para diferentes condiciones de operación. En concreto, se ha utilizado la técnica DIA para el tratamiento digital de las imágenes capturadas mediante una cámara de alta velocidad , pudiendo así hacer una clara separación entre la fase densa y la fase burbuja, caracterizando las burbujas mediante su diámetro equivalente, posición de centro de masas y velocidad. La técnica DIA permite además observar de manera detallada los fenómenos de formación, crecimiento y coalescencia de las burbujas a lo largo del lecho. Además, para caracterizar la influencia de la burbuja sobre la fase densa, se ha utilizado la técnica de PIV para medir la velocidad de ésta. Esta tesis aporta resultados relevantes con el objetivo de ayudar a entender mejor la interacción entre ambas fases del lecho para diferentes condiciones de operación, tipos de distribuidor, altura de lecho fijo, tamaño de partícula y espesor del lecho. Como resultado novedoso se ha calculado el tiempo de recirculación medio de las partículas del lecho, pudiendo así definir el grado de mezcla del reactor. Este trabajo también estudia la influencia del tamaño del espesor del lecho en la velocidad de mínima fluidización, ya que este valor es uno de los parámetros de diseño más importantes. También se ha calculado la región de influencia que una burbuja provoca a su paso en la fase densa, identificando y midiendo el movimiento de los sólidos alrededor de la burbuja. Se ha establecido una relación entre el tamaño y velocidad de la burbuja con la disipación de energía cinética en la fase densa, esta relación está directamente relacionada con los procesos de degradación de la materia. Este fenómeno es de gran importancia ya que la degradación de la fase densa genera partículas de menor tamaño y esto influye directamente en el comportamiento general del lecho. En esta tesis también se ha investigado la influencia de la distribución de orificios a lo largo del distribuidor. Se ha comprobado que dos distribuidores multi-orificio homogéneamente distribuidos, con la misma perdida de carga pero diferente disposición de orificios, generan, bajo las mismas condiciones de operación, la misma respuesta dinámica del lecho. Podemos entonces concluir que para las condiciones de operación de este trabajo y una distribución de gas uniforme, el comportamiento global del lecho fluido no depende de la disposición de orificios a lo largo del distribuidor

Effect of sepiolite bed material on gas composition and tar mitigation during C-cardunculus L. gasification

Sepiolite, a clay mineral that is commonly used as adsorbent, is proposed as bed material for biomass gasification in a lab-scale bubbling fluidized bed. In order to compare the obtained gas composition and tar generation, silica sand has been used as reference bed material. C cardunculus L. has been employed as biomass feedstock. The operating temperature is varied from 830 to 875 degrees C, at constant equivalence ratio (ER) of 0.30. The gas produced with sepiolite as bed material has a slightly lower quality than the gas generated with silica sand, the lower heating value (LHV) is 0.4-1.4 MJ/Nm(3) lower for sepiolite than for silica sand. However, the tar generation is rather reduced in the sepiolite bed and the tar composition is also different among the bed materials: the polycyclic aromatic hydrocarbons fraction (PAH) is drastically reduced while oxygenated compounds arise in the sepiolite tests. Sepiolite properties such as surface area and morphology have been analysed by means of specific surface area (BET) and scanning electron microscopy (SEM-EDS) before and after the experiments. The fuel behaviour and the properties of sepiolite induce the adsorption of tars and molten ashes on the sepiolite surface, leading to a much better performance in terms of tar mitigation and agglomeration.The authors would like to express their gratitude to the financial support of the Spanish Ministry of Economy and Competitiveness from project ENE2014-54942-R. Alen Horvat acknowledges COST funding (short term scientific mission-STSM) under a COST STSM Reference Number: COST-STSM-FP1306-34300, supporting his exchange stay at University Carlos III of Madrid

Predicting the effect of bed materials in bubbling fluidized bed gasification using artificial neural networks (ANNs) modeling approach

The effect of different bed materials was included a as new input into an artificial neural network model to predict the gas composition (CO2, CO, CH4 and H2) and gas yield of a biomass gasification process in a bubbling fluidized bed. Feed and cascade forward back propagation networks with one and two hidden layers and with Levenberg-Marquardt and Bayesian Regulation learning algorithms were employed for the training of the networks. A high number of network topologies were simulated to determine the best configuration. It was observed that the developed models are able to predict the CO2, CO, CH4, H2 and gas yield with good accuracy (R2 > 0.94 and MSE < 1.7 × 10−3). The results obtained indicate that this approach is a powerful tool to help in the efficient design, operation and control of bubbling fluidized bed gasifiers working with different operating conditions, including the effect of the bed material

Defluidization and agglomeration of a fluidized bed reactor during Cynara cardunculus L. gasification using sepiolite as a bed material

This work studies the defluidization time and the agglomerate generation in a bubbling fluidized bed (BFB) reactor during Cynara cardunculus L. gasification using, separately, two different bed materials, silica sand and sepiolite 〖(MG〗_8 〖Si〗_12 O_30 (OH)_4 〖(OH〗_2)(_4^)8 H_2). The high adsorption capacity and the elemental composition of the sepiolite make it suitable as an alternative bed material in order to reduce agglomeration. Experiments were performed on a stainless steel lab-scale BFB reactor operating with air as a gasifying agent at different air excess ratios (u/umf). A quartz reactor was alternatively used for the visualization of bed material and biomass during gasification, allowing one to observe the agglomerate formation process. Pressure signals were analyzed both in time and frequency domain to determine the defluidization time. Furthermore, the shape and size of the bed material after the experiments were evaluated. Higher defluidization times in the case of sepiolite were measured. Particle sizes were affected by the type of bed material and the air excess and agglomerates of different shapes were formed for sepiolite and silica sand.Publicad

Coherent structures and bubble-particle velocity in 2-D fluidized beds

This work presents an experimental study to characterize ascending bubbles and granular velocity in the dense phase of a 2-D fluidized bed. Three different non-intrusive techniques based on images obtained with a high speed camera are developed, and applied to the images. First the bubble paths are characterized with time-average concentration maps and the bubble velocities are obtained, using a tracking algorithm over the mass centers of the bubbles. Finally, a PIV (particle image velocimetry) method is used to characterize the particle velocity vectors. This procedure is repeated for different bed aspect ratios, and different superficial gas velocities. This study analyzes the superficial gas velocity influence on the bed behavior, and how the bubble path configuration depends on the bed aspect ratio. The PIV measurements give us information on the location of the recirculation regions and the influence of the superficial gas velocity.Publicad

Development of carbon fiber acrylonitrile styrene acrylate composite for large format additive manufacturing

The increasing interest of Large Format Additive Manufacturing (LFAM) technologies in various industrial sectors mainly lies on the attainable production of pieces reaching several cubic meters. These new technologies require the development of optimized materials with two-folded capabilities, able to satisfy functional in-service requirements but also showing a proper printability. Acrylonitrile Styrene Acrylate (ASA) is among the most interesting thermoplastic materials to be implemented in a LFAM device due to its excellent wettability and mechanical properties. This research focuses on the development and characterization of ASA and carbon fiber (CF) ASA composites suitable for LFAM. The rheological, thermal and mechanical properties of neat ASA and ASA containing 20 wt% CF are addressed. The results evidence the higher performance of the CF loaded composite compared to the raw ASA polymer (i.e., the 20 wt% CF composite shows a 350% increase in flexural Young's Modulus and a 500% increment in thermal conductivity compared with neat ASA). Additionally, both materials were successfully printed along perpendicular directions (X and Z), showing the maximum tensile strain for the composite printed along the X orientation as was expected. The results of the flexural tests are comparable or slightly higher than those of injected parts. Finally, the fracture surface was analysed, identifying different types of porosity

Requirement management in software projects in the healthcare area: state of the art.

Este artículo presenta un análisis general del estado de la gestión de requisitos en proyectos informáticos que involucren tecnología y salud. El objetivo es definir el estado actual de los requisitos de proyectos informáticos que integran las TIC y la salud. En la metodología se efectuó una revisión documental acerca de la gestión de requisitos, proyectos informáticos, salud, y TIC. Se proponen ideas y se cuestionan los enfoques de los escritos académicos relacionados con el tema consultado. El resultado permite ver que no existe una integración clara en los conceptos de salud, informática y gestión de proyectos para involucrar las TIC. Se concluye que es necesario tener en cuenta muchas premisas, variables y factores que son importantes al momento de iniciar un proyecto de salud. Las TIC, hacen parte fundamental de este proceso, contar con ellas es primordial y necesario.This article presents a general analysis of the condition of the management of requirements in IT projects that involve technology and health. The aim is to define the current condition of the requirements of IT projects that integrate the TIC and the health. In the methodology a documentary review was effected it brings over of the management of requirements, IT projects, health, and TIC. They propose ideas and there question the approaches of the written academicians related to the consulted topic. The result allows seeing that a clear integration does not exist in the concepts of health, computer science and project management to involve the TIC. One concludes that it is necessary bear in mind many premises, variables and factors that are important to the moment to initiate a project of health. The TIC, they make fundamental part of this process, rely on them it is basic and necessary.Este artigo apresenta uma análise geral do estado de gerenciamento de requisitos em projetos de software que envolve tecnologia e saúde. O objetivo é definir o estado atual dos requisitos de projetos de software que integram as TIC e a saúde. A metodologia foi uma análise documental sobre a gestão de requisitos, projetos de software, saúde e TIC. Proposta de ideias e abordagens dos escritos acadêmicos relacionados ao assunto consultado é pergunta. O resultado permite que você veja que clara sobre os&nbsp;conceitos de saúde, integração e projeto gerenciamento do computador lá é para não envolvendo as TIC. Conclui-se que é necessário ter em conta muitas instalações, variáveis e fatores que são importantes ao iniciar um projeto de saúde. As TIC, são uma parte essencial deste processo, tê-los é essencial e necessário

A global analysis of bank profitability factors

We analyze the factors that explain banks’ profitability globally and by region. With increasing globalization, knowing the different aspects of bank profitability is essential for countries’ financial stability and economic growth. This study used a sample of 2,091 commercial banks operating in 110 countries grouped into major world regions. With random effect regression models, the global results show that the internal factors that explain the bank´s profitability are listed entities, impaired loans, efficiency, gross interest margin, and capitalization. For its part, the most significant external factors are related to the position of the countries in the ranking by assets, inflation, unemployment, interest rates, and economic growth. From a regional perspective, the results allow us to deduce with high robustness the existence of variable sets that determine bank profitability in each region and that regional models outperform global models in most cases