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Se encontraron 2733 resultados en recursos

Imagen de apoyo de  Spatial models with random covariance structure = Modelos espaciales con estructura de covarianza aleatoria

Spatial models with random covariance structure = Modelos espaciales con estructura de covarianza aleatoria

Por: Danna Lesley Cruz Reyes | Fecha: 2021

Abstract: The conditional autoregressive model (CAR model) is the most popular distribution for jointly modeling the \textit{a priori} uncertainty over spatially correlated data. In general, it is used in hierarchical spatial models where it models the uncertainty about random spatial effects. A limitation of the CAR model is its inability to produce high correlations between neighboring areas. We propose a robust model for area data that alleviates this problem. We represent the map by an undirected graph where nodes represent areas and edges connect neighboring nodes on the map. We assign distinct and random weights to the edges. The model is based on a spatially structured $t-$Student multivariate distribution, in which the precision matrix is indirectly constructed assuming a multivariate distribution for the random weights of the edges. Such t- Student distribution spatially correlates the edge weights and induces another $t$-Student model for the spatial effects of the areas that correlates them and is able to accommodate outliers and heavy tail behavior for these effects. More importantly, the proposed model can produce a higher marginal correlation between spatial effects than the CAR model, overcoming one of the main limitations of this model. We adjusted the proposed model to map the incidence of some types of cancer in southern Brazil and compared its performance with several alternative models proposed in the literature. The results show that the proposed model is competitive and provides similar and, in some cases, better results than those obtained by fitting models commonly used to analyze this type of data. In the second proposal, we approach the problem of dimensionality reduction in regression models. One of the most used methods to avoid overfitting and to select relevant variables in regression models with many predictors is the penalized regression technique. Under suchapproaches, variable selection is performed in a non-probabilistic way using some optimization criterion. Bayesian approaches to penalized regression have been proposed assuming an \textit{a priori} distribution for the regression coefficients that plays a role similar to the penalty term in classical statistics: compressing towards zero non-significant coefficients and putting a probability mass significant in coefficients that can be grouped. Generally, such a priori distributions, called shrinkage priors, assume independence between the effects of the covariates, which may not bean appropriate assumption in many cases. In this work, we focus on the dimensionality reduction of categorical variables with many levels. These variables are included in the model through variables dummy inducing sparsity in the design matrix, which can generate overfitting and difficulties in interpreting the results. The effect of the levels of these categorical variables are naturally correlated. To deal with this problem, we propose two a priori shrinkage distributions for the coefficients associated with the levels of categorical variables, correlating them. The proposed distributions are properand, in addition to sparsity, they have the property of grouping similar effects. We illustrate the use of these distributions by applying them to dimensionality reduction in a linear regression. Their performances are analyzed and compared to pre-existing methods through simulated data studies and considering housing price data available on Airbnb. Resumen: El modelo autorregresivo condicional (modelo CAR) es la distribución más popular para modelar conjuntamente la incertidumbre \ textit {apriori} sobre datos correlacionados espacialmente. En general, se utiliza en modelos espaciales jerárquicos donde modela la incertidumbre sobre los efectos espaciales aleatorios. Una limitación del modelo CAR es su incapacidad para producir altas correlaciones entre áreas vecinas. Proponemos un modelo robusto para datos de área que alivia este problema. Representamos el mapa mediante un gráfico no dirigido donde los nodos representan áreas y los bordes conectan los nodos vecinos en el mapa. Asignamos pesos distintos y aleatorios a los bordes. El modelo se basa en una distribución multivariante $ t- $ Student estructurada espacialmente, en la que la matriz de precisión se construye indirectamente asumiendo una distribución multivariante para los pesos aleatorios de los bordes. Tal distribución t-Student correlaciona espacialmente los pesos de los bordes e induce otro modelo $ t $ -Student para los efectos espaciales de las áreas que los correlaciona y es capaz de acomodar valores atípicos y un comportamiento de cola pesada para estos efectos. Más importante aún, el modelo propuesto puede producir una mayor correlación marginal entre los efectos espaciales que el modelo CAR, superando una de las principales limitaciones de este modelo. Ajustamos el modelo propuesto para mapear la incidencia de algunos tipos de cáncer en el sur de Brasil y comparamos su desempeño con varios modelos alternativos propuestos en la literatura. Los resultados muestran que el modelo propuesto es competitivo y proporciona resultados similares y, en algunos casos, mejores que los obtenidos mediante el ajuste de modelos comúnmente utilizados para analizar este tipo de datos. En la segunda propuesta abordamos el problema de la reducción de dimensionalidad en modelos de regresión. Uno de los métodos más utilizados para evitar el sobreajuste y seleccionar variables relevantes en modelos de regresión con muchos predictores es la técnica de regresión penalizada. Bajo tales enfoques, la selección de variables se realiza de forma no probabilística utilizando algún criterio de optimización. Se han propuesto enfoques bayesianos para la regresión penalizada asumiendo una distribución \ textit {a priori} para los coeficientes de regresión que juega un papel similar al término de penalización en la estadística clásica: comprimir hacia cero coeficientes no significativos y poner una masa de probabilidad significativa en coeficientes que se pueden agrupar. Generalmente, tales distribuciones a priori, llamadas a priori de contracción, asumen independencia entre los efectos de las covariables, lo que puede no ser una suposición apropiada en muchos casos. En este trabajo, nos enfocamos en la reducción de dimensionalidad de variables categóricas con muchos niveles. Estas variables se incluyen en el modelo a través de variables ficticias que inducen escasez en la matriz de diseño, lo que puede generar sobreajustes y dificultades en la interpretación de los resultados. El efecto de los niveles de estas variables categóricas está naturalmente correlacionado. Para abordar este problema, proponemos dos distribuciones de contracción a priori para los coeficientes asociados a los niveles de variables categóricas, correlacionándolos. Las distribuciones propuestas son adecuadas y, además de escasa, tienen la propiedad de agrupar efectos similares. Ilustramos el uso de estas distribuciones aplicándolas a la reducción de dimensionalidad en una regresión lineal. Sus resultados se analizan y comparan con métodos preexistentes a través de estudios de datos simulados y teniendo en cuenta los datos de precios de la vivienda disponibles en Airbnb.
Fuente: Biblioteca Virtual Banco de la República Formatos de contenido: Tesis
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Spatial models with random covariance structure = Modelos espaciales con estructura de covarianza aleatoria

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Imagen de apoyo de  Steering Hexanol Formation in a Continuous Chain Elongation Process

Steering Hexanol Formation in a Continuous Chain Elongation Process

Por: Santiago Daniel; Leeuw Delgado Tovar | Fecha: 2021

Abstract: Chain elongation fermentation in open cultures systems can tolerate complex organic waste and convert it into useful biochemicals (commodities) such as caproic acid. In previous chain elongation research, fatty alcohols such as hexanol have been also documented. Hexanol has a potential application as biofuel, is less corrosive, watersoluble, and toxic than caproic acid. Moreover, the hexanol market size seems more attractive than the one of caproic acid. This research aims to produce hexanol via a chain elongation process in an upflow anaerobic sludge blanket (UASB) system. Granular sludge formation was also considered due to its advantages such as high biomass concentration and settleability. The highest selectivity (based on total carbon products in the effluent) and productivity of caproate was 82.49 % on day 35 and 10.25 g L-1 d -1 on day 33, whereas for hexanol was 1.66 % and 0.19 g L-1 d -1 , both on day 77. CO2 supply had a positive effect on chain elongation activity and hexanol formation. Selectivity and productivity of hexanol was not negatively affected despite methane formation. Throughout the whole study, suspended biomass was the dominant form. A thick biofilm layer on the inner wall of the reactor was present from day 19 to 76 and black aggregates became more visible from day 76 onwards, although not significantly. The process was severely inhibited by substrate (ethanol) toxicity during the last phase (36.77 ± 3.23 g L-1 ).
Fuente: Biblioteca Virtual Banco de la República Formatos de contenido: Tesis
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Steering Hexanol Formation in a Continuous Chain Elongation Process

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Imagen de apoyo de  The Gender Perspective and the Truth Commissions: Learning from the Cases of Peru and East Timor

The Gender Perspective and the Truth Commissions: Learning from the Cases of Peru and East Timor

Por: Soraya Estefan Vargas | Fecha: 2017

Abstract: The transition from armed conflicts or oppressive regimes to contexts of peace and democracy requires a thorough investigation of what happened during the time of violence. This crucial responsibility of clarifying a past period of abuses has been undertaken by truth commissions. However, the reconstruction of this truth cannot forget the inequalities women had to endure historically and the different impacts they suffer during wartime. In that sense, the truth-seeking work that truth commissions performed needs to incorporate a gender perspective, in order to fight the discrimination against women, and to include their point of view in the version of a country’s truth. Thus, two of the strongest truth commissions in the world have developed particular measures regarding women: Peru and East Timor. For that reason, this research identifies and analyse such actions. This with the aim of recognising the learnings of these experiences in gender issues and, based on them, build a proposal on how a truth commission should incorporate the gender perspective in its truth-seeking work.
Fuente: Biblioteca Virtual Banco de la República Formatos de contenido: Tesis
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The Gender Perspective and the Truth Commissions: Learning from the Cases of Peru and East Timor

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Imagen de apoyo de  Assessment of recent tectonic activity of the Sabanalarga Fault System, Western Antioquia – Colombia

Assessment of recent tectonic activity of the Sabanalarga Fault System, Western Antioquia – Colombia

Por: John Jairo Gallego Montoya | Fecha: 2018

Abstract: Recent seismic activity can be expressed by different forms of tectonic deformation in non-consolidated fluvial-lacustrine and debris-flow deposits. We study such deposits along the Interandean Cauca River Canyon in the Antioquia State in western Colombia as a proxy for paleoearthquakes related to the recent activity of Sabanalarga Fault System (SFS), which is one of the most prominent active faults in western Medellin city. Our aim is to evaluate the recent tectonic activity through three complementary aspects: I) a geo-morphotectonic evaluation of the surface traces of the SFS, lineament analysis and calculation of geomorphological indices of active tectonics; II) a paleoseismological assessment of three trenches and outcrops with evidence of recent (Middle Pleistocene to Holocene) faulting and liquefaction in fluvial-lacustrine and alluvial sediments; and III) a preliminary regional compilation of historical seismicity from the colonial epoch archives and assessment of the social perception regarding earthquakes and landslide-dams along the Cauca River canyon. Based on a 10-m resolution hydrologically-corrected DEM, manually-drawn lineaments and field observations, we redefined the faults systems along the Cauca River canyon, between the municipalities of Sabanalarga and Sabanalarga in the Antioquia State, and extracted in a GIS environment evidence for tectonic activity and morphotectonic parameters. Morphotectonic outcomes reveal active tectonic deformation for the SFS and significant changes in relief, topography, and drainage-mountain front geomorphic indices values, suggesting a major active strike-slip faulting and high-uplift patterns regarding a vertical secondary component. An active tectonic framework has been established for the study area with the existence of around 30 sites with indications of Quaternary faulting. Using a combination of Optically Stimulated Luminescence (OSL), Infrared Stimulated Luminescence (IRSL), and radiocarbon dating along with trenching, we estimated the timing of the identified paleoearthquakes related to the SFS and subsidiaries faults. We found evidence for at least three paleoearthquakes in the last ~30 kyr with moment magnitudes Mw ranging from 5.7 to 7.0. The last two seismic events identified in the Cauca River canyon, occurred around 4 and 1.1 kyr ago, respectively, indicating an average Holocene earthquake recurrence interval of ∼3 kyr. Twenty semi-structured face-to-face interviews were conducted with local inhabitants to answer: I) what is the perception of the native population concerning damages and origin of geohazards, especially earthquakes? And II) is there any evidence in people's memory for ancient damming of the Cauca River? The locals determined several risk-scenarios for the Cauca River canyon as a result of their historical memory that has been inherited through generations, finding some myths and legends that preserve memories of the occurrence of historical earthquakes in the region. Additionally, based on the exploration Beneficiario COLFUTURO 2015 VI of historical archives of the Spanish colonial epoch and previous studies, we compiled the historical seismicity of the Antioquia State and reports of earthquake damage caused since the 18th century. Moreover, no evidence of seismic events in the colonial epoch between the 16th and 18th centuries was found for the surroundings of the study area. However, there is an earthquake reported in the Cali region that occurred in 1566 AD, in the southwest of the Antioquia State. The historical document is located in the folios of the Indias Archive of the "Audiencia de Quito" and it is considered as the oldest historically reported earthquake in Colombia. The evidence of recent tectonic activity (Upper Quaternary) in the Cauca River canyon, which is localized at less than 50-km distance to the city of Medellin with a population of 4 million, should be considered by the governmental agencies in future seismic hazard assessment in the region. Additionally, a plausible scenario with landslides along the river canyon triggered by the occurrence of a large earthquake must be taken into account, as it was demonstrated recently by the severe problems for the hydro-Ituango project, which is located 60 km downstream from the study area, caused by high-instability conditions (landslides occurrence). The results of this study clearly show the potentiality of the faults located along the Cauca River canyon to generate large earthquakes. Due to the slow slip-rates of these structures, the instrumental and historical seismic records are not providing a sufficiently long temporal coverage. Thus, it is necessary to characterize better the activity and the earthquake history of the faults employing paleoseismological studies. Resumen: La actividad sísmica reciente se evidencia mediante varias formas de deformación tectónica en depósitos fluvio-lacustres y aluviales no consolidados. Dentro de la investigación, se estudiaron estos depósitos a lo largo del cañón Interandino del Rio Cauca en el noroccidente de Colombia en el noroccidente del departamento de Antioquia, como una aproximación al entendimiento de los paleo-terremotos relacionados con la actividad reciente del Sistema de Fallas de Sabanalarga (SFS), el cual es uno de los sistemas de fallas más prominentes al oeste de la ciudad de Medellín. El estudio se basó en la evaluación de la actividad tectónica reciente a través de tres aspectos complementarios: I) la geo-morfotectónica de las trazas superficiales del SFS, análisis de lineamientos y cálculo de índices geomorfológicos de tectónica activa; II) la paleosismología de tres trincheras y afloramientos con evidencias de fallamiento y licuefacción reciente (del Pleistoceno Medio al Holoceno) en sedimentos fluvio-lacustres y aluviales; y III) la compilación regional preliminar de la sismicidad histórica de los archivos de la época colonial y la evaluación de la percepción social respecto a los terremotos y represamiento por deslizamientos a lo largo del cañón del río Cauca. Se redefinieron los sistemas de fallas a lo largo del cañón del Rio Cauca, entre los municipios de Sopetrán y Sabanalarga en el departamento de Antioquia, con base en un Modelo de Elevación Digital de 10 m de resolución, la identificación de lineamientos y observaciones de campo, además, se calcularon en un ambiente SIG varios parámetros morfotectónicos como evidencia de tectónica activa. Los resultados morfotectónicos revelan una deformación tectónica activa espacialmente variable para el SFS y cambios significativos en los valores de los índices geomórficos del relieve, la topografía y el drenaje, lo que sugiere un fallamiento activo de rumbo y patrones de levantamiento con respecto a un componente secundario de fallamiento vertical. Adicionalmente, se estableció un marco de tectónica activa para el área de estudio con la existencia de alrededor de 30 sitios con indicios de fallamiento Cuaternario. Se estimaron las edades de ocurrencia de varios paleo-terremotos relacionados con el SFS y sus fallas secundarias, mediante la combinación de varios métodos de datación: luminiscencia ópticamente estimulada (OSL), luminiscencia estimulada por infrarrojo (IRSL) y radiocarbono, junto con herramientas paleosismológicas y apertura de trincheras. Se encontraron evidencias de por lo menos tres paleo-terremotos en los últimos 30 mil años con magnitudes Mw que van desde 5.7 y 7.0. Los dos eventos sísmicos más recientes identificados en el cañón del Rio Cauca, ocurrieron dentro del Holoceno, alrededor de 4000 y 1100 años, respectivamente, lo que indica un intervalo de recurrencia promedio de 3000 años. Se realizaron 20 entrevistas semiestructuradas a los habitantes del cañón del Rio Cauca con el objetivo de responder principalmente las siguientes preguntas: I) ¿Cuál es la Beneficiario COLFUTURO 2015 VIII percepción de la población nativa sobre los desastres y el origen de la amenaza geológica, especialmente terremotos?; y II) ¿existe alguna evidencia en la memoria de la población de un antiguo represamiento del Rio Cauca? Como resultado, los lugareños determinaron varios escenarios de riesgo dentro del cañón del Rio Cauca, a partir de su memoria histórica que ha sido heredada por generaciones, encontrando algunos mitos y leyendas que conservan los recuerdos sobre la ocurrencia de terremotos históricos en la región. Además, con base en la exploración de archivos históricos de la época colonial española y estudios históricos previos, se compilaron datos acerca de la sismicidad histórica del departamento de Antioquia y los informes de daños causados por terremotos desde el siglo XVIII. Sin embargo, no fueron encontrados registros de eventos sísmicos de la época colonial entre los siglos XVI y XVIII en los alrededores de la zona de estudio. No obstante, si se halló un documento físico que registra el terremoto más antiguo reportado históricamente en Colombia, dentro de los folios del Archivo de Indias de la "Audiencia de Quito". Este sismo ocurrió entre los departamentos del Cauca y Valle del Cauca en el año de 1566 DC. Las evidencias de la actividad tectónica reciente (Cuaternario Superior) en el cañón del Rio Cauca, que se localiza a menos de 50 km de distancia de la ciudad de Medellín y su área metropolitana (con una población de 4 millones de habitantes), tienen implicaciones relevantes sobre cómo las entidades gubernamentales deben contemplar la amenaza sísmica en la región. Se hace necesario caracterizar mejor la actividad y el historial de terremotos de las fallas en los estudios de amenaza a partir de estudios paleosismológicos Adicionalmente, teniendo en cuenta estos resultados, se debe evaluar el posible escenario en donde se generen grandes movimientos en masa a lo largo del cañón del Rio Cauca, desencadenados por un evento sísmico de alta magnitud, así también como las implicaciones directas sobre la presa del proyecto hidroituango, ubicada 60 km aguas abajo de la zona de estudio, debido a la inestabilidad y debilitamiento de la obra por los deslizamientos ocurridos entre mayo y julio de 2018. Los resultados de este estudio demuestran el potencial de las fallas ubicadas a lo largo del cañón del Rio Cauca para generar grandes terremotos. Debido a las bajas tasas de desplazamiento de estas estructuras geológicas y a los registros sísmicos instrumentales e históricos que no proporcionan una cobertura temporal lo suficientemente larga.
Fuente: Biblioteca Virtual Banco de la República Formatos de contenido: Tesis
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Assessment of recent tectonic activity of the Sabanalarga Fault System, Western Antioquia – Colombia

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Imagen de apoyo de  Understanding the Experience of Latin American Asylum-seeking Women in Quebec: A Feminist Approach

Understanding the Experience of Latin American Asylum-seeking Women in Quebec: A Feminist Approach

Por: Laura Gallo Tapias | Fecha: 2021

Resumen: Esta tesis consta de dos capítulos. El primero es una reflexión teórica sobre la relación entre los estudios feministas y el campo de la investigación en salud mental de los refugiados. En él, sostengo que los enfoques feministas pueden contribuir a la investigación sobre la salud mental de los refugiados cuestionando algunos de sus límites y supuestos epistemológicos, haciendo visibles a las comunidades marginadas y amplificando sus voces, y reconociendo las implicaciones sociales y políticas de este tipo de investigación. Este esfuerzo pretende alinear las perspectivas de la academia y el activismo de una manera que resulte relevante para los sujetos implicados. El segundo artículo es un trabajo de investigación empírica que se basa en un estudio cualitativo realizado con nueve mujeres solicitantes de asilo de América Latina en el que se adoptó un enfoque feminista. Contribuye a la investigación actual sobre las mujeres refugiadas al ocuparse de la narración de la experiencia vivida por las mujeres colombianas y venezolanas llegadas a Quebec como de asilo en términos de su corporeidad. A partir de entrevistas en profundidad con estas mujeres, sostengo que la salud mental y el bienestar no son incorpóreos, sino que están anclados en roles de género, prácticas, rituales y normas sociales que tienen una dimensión corporal y son culturalmente específicos. Considerar el lugar del cuerpo en la experiencia de la migración implica examinar sus dimensiones sensoriales, táctiles, somáticas y quinestésicas. De esta manera, esta investigación ofrece nuevas posibilidades para un análisis crítico de las intersecciones entre género, bienestar emocional y asilo. Abstract: This thesis consists of two chapters. The first paper is a theoretical reflection about the relationship between feminist scholarship and the field of refugee mental health research. Here, I argue that feminist approaches can contribute to refugee mental health research by questioning some of its epistemological boundaries and assumptions, by rendering marginalized communities visible and amplifying their voices, and by recognizing the social and political implications of this type of research, in an attempt to align academia and activism in ways that are relevant for the implicated subjects. The second paper is an empirical research paper drawing from a qualitative study conducted with nine women asylum seekers from Latin America in which a feminist approach undertaken. It contributes to the current research on refugee women by examining the narration of the lived experience of Colombian and Venezuelan women arrived in Quebec as asylum claimants in terms of their corporeality. Drawing from indepth interviews with these women, I argue that mental health and wellbeing are not disembodied, but rather anchored in gender roles, practices, rituals, and norms that have a corporeal dimension and are culturally specific. Considering the place of the body in the experience of migration implies examining its sensorial, tactile, somatic and kinesthetic dimensions. This brings about new possibilities for a critical analysis of the intersections between gender, wellbeing and asylum.
Fuente: Biblioteca Virtual Banco de la República Formatos de contenido: Tesis
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Understanding the Experience of Latin American Asylum-seeking Women in Quebec: A Feminist Approach

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Imagen de apoyo de  Reconstructing the limit. Urban revival via architecture and landscape design in war-damaged Mosul, Iraq = Reconstrucción del límite. Renacimiento urbano a través del diseño arquitectónico y paisajismo en Mosul, Iraq

Reconstructing the limit. Urban revival via architecture and landscape design in war-damaged Mosul, Iraq = Reconstrucción del límite. Renacimiento urbano a través del diseño arquitectónico y paisajismo en Mosul, Iraq

Por: Nicolás; Dogari Bello Melo | Fecha: 2021

Abstract: Because there is nothing intelligent to say about a massacre. Everybody is supposed to be dead, to never say anything or want anything ever again. Everything is supposed to be very quiet after a massacre, and it always is, except for the birds.” All wars are atrocious, and the task of incorporating such inglorious events into a nation’s collective identity becomes understandably hard. But it needs to be done, otherwise, the memory of the war might be trivialized and forgotten and, hence, are more prone to be repeated. War is bound to replicate itself without confrontation and awareness. Mosul city was established on the western bank of the Tigris River in the 6th Century, just across the water from the ruins of the Assyrian city of Nineveh. The city flourished during the ancient era establishing itself as an epicentre of the Islamic world, therefore it is rich with ancient ruins and cultural heritage. The war which erupted in Iraq didn’t aim to destroy only its defence, but also its identity. Entire urban blocks of Mosul’s city were damaged so severely, that when it comes to reconstruction it cannot simply restore the former fabrics, either of space or architecture. The war has changed everything, and most critically the structure of society itself. The spatial reconstruction will mostly require more than just physical rehabilitation and restoration of the cities devastated infrastructure and housing. In order to provide sensations for the need of diversity and unity, more urgent concern should be given to restoring public facilities and daily utilities. Architectural and landscape design can be judiciously used in healing the social structure. How can common spaces be rearranged to create conditions for a peaceful and creative coexistence among citizens which survived such horrors? How can the location and the design of such utilities be done in a way as to meet the needs for intimacy and peace? This thesis study intends to recommend an urban and architectural regeneration project, to be taken upon during the redevelopment of the old city of Mosul. Furthermore, a set of strategies that may ensure the preservation of the urban identity of the area, while redeveloping and coping with the environmental, socioeconomic and political changes have been identified for reclaiming the urban identity and promoting the sense of belonging.
Fuente: Biblioteca Virtual Banco de la República Formatos de contenido: Tesis
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Reconstructing the limit. Urban revival via architecture and landscape design in war-damaged Mosul, Iraq = Reconstrucción del límite. Renacimiento urbano a través del diseño arquitectónico y paisajismo en Mosul, Iraq

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Imagen de apoyo de  Evaluation of Copper Mining Companies for Investment Purposes = Evaluación de compañías mineras para propósitos de inversión

Evaluation of Copper Mining Companies for Investment Purposes = Evaluación de compañías mineras para propósitos de inversión

Por: Álvaro Humberto Gómez Mafla | Fecha: 2019

Abstract: Thanks to its durable, reliable, versatile, ductile and recyclable characteristics, copper is an essential metal for several industries, being the preferred electrical and thermal conductor. While it is naturally exposed to industrial cycles, from a long-term standpoint, copper demand has seen consistent growth, associated to the annuity of global population growth, which has allowed a constant need for copper-containing consumer products. More recently, copper has become a strategic metal for the future of clean technology, as the continuous global warming concerns due to greenhouse gasses emissions have forced governments and companies to combat climate change and intensify the actions and investments needed for a sustainable low carbon future. As such, the adoption of renewable sources of energy and electric vehicles have seen significant global penetration in recent years, and it is expected to increase at a higher rate, raising concerns on the ability of current and future producers to supply the inevitable growing demand in the near future. The purpose of this study is to evaluate three copper focused mining companies, two operators and one developer, aiming to identify the stock that represents the most attractive opportunity for long-term focused investors with exposure to the copper sector. For this purpose, the author uses the last ten years of financial data from the companies (when available) to evaluate their financial performance and current financial health, as well as the management and operational information to analyse the companies’ portfolio of mines and projects.
Fuente: Biblioteca Virtual Banco de la República Formatos de contenido: Tesis
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Evaluation of Copper Mining Companies for Investment Purposes = Evaluación de compañías mineras para propósitos de inversión

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Imagen de apoyo de  Education in a Transnational Context: Representations of Haiti and Haitians in the Schools of the Dominican Bateyes = La educación en un contexto transnacional: representaciones de Haití y los haitianos en las escuelas de los bateyes dominicanos

Education in a Transnational Context: Representations of Haiti and Haitians in the Schools of the Dominican Bateyes = La educación en un contexto transnacional: representaciones de Haití y los haitianos en las escuelas de los bateyes dominicanos

Por: Natalia Gómez Muñoz | Fecha: 2018

Abstract: At the beginning of the 20th Century, during the boom of sugar production in Latin America, the Dominican Republic built the “bateyes”, small towns with some coarse barracks used for the temporary housing of foreign workforce, coming mainly from Haiti. These settings gradually became permanent dwelling places, and nowadays are found across the Dominican Republic. However, in spite of their complex history and contemporary particularities, mainly related with the transnational dynamics the population maintains with Haiti, the bateyes have been relatively little studied and remain underrepresented in academic research. This study seeks to contribute to fill the abovementioned void, focusing on the context of formal education. The goal of this study is analyzing the representations of Haiti and Haitians that circulate in some schools of the “bateyes”, with data gathered in public educational institutions that are mainly attended by students of Haitian origin. The focus of the study is particularly relevant since formal schooling is usually a tool of the State and its institutions to reproduce dominant and hegemonic ideologies (Gramsci, 1967; Gramsci, 1971), and such ideologies in the Dominican Republic are strongly based on anti-Haitians sentiments and a mainstream rejection of blackness (Eller, 2016; Gavigan, 1995; Hintzen, 2014; Simmons, 2010; Valdéz, 2015). The thesis presents a critical analysis of the standards and textbooks used in the Social Studies program, focusing on how topics related to Haiti are approached, and which representations and values they embrace. Then, based on ethnographical data, it examines the discourses of ten teachers regarding Haiti and their own students of Haitian descent. With the intention of presenting a general panorama at the representations of Haiti circulating in the school setting of the bateyes, this work first describes how the standards and textbooks of Social Studies largely cast Haiti as a historic enemy and as a burden to the Dominican Republic. Then, the second section explains how the teachers reproduce the dominant ideology of national identity of the Dominican Republic in their schooling practices, and how they express racist and anti-Haitian discourses, with active statements as well as with several silences and omissions in their discursive practices. The tensions, ruptures and incongruences of the teachers are central in this analysis, since according to them the students of Haitian origin do not conform categorically to the mainstream representations of Haitian identity. All the reflections are drawn from a multidisciplinary six-week fieldwork season conducted in 2017 in the municipality of Consuelo, in southern Dominican Republic, (1) to gather the educational standards and textbooks used in Social Studies in the schools, and (2) to conduct interviews with teachers of some educational institutions that have a high attendance of children of Haitian descent. The interviews initially inquired about the teachers’ handling of the schooling materials; their gendered notions on the immigration of people of Haitian origin in the country; and finally, about their views on their own students of Haitian descent. The data was analyzed having as theoretical and methodological framework the premises of Critical Discourse Analysis (CDA) that aims to bring together elements of discourse analysis and social theory to understand, uncover and ultimately transform situations of social injustice (c.f. Van Dijk, 1993).
Fuente: Biblioteca Virtual Banco de la República Formatos de contenido: Tesis
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Education in a Transnational Context: Representations of Haiti and Haitians in the Schools of the Dominican Bateyes = La educación en un contexto transnacional: representaciones de Haití y los haitianos en las escuelas de los bateyes dominicanos

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Imagen de apoyo de  Three-dimensional Printing of a multi-material model of the Knee Joint

Three-dimensional Printing of a multi-material model of the Knee Joint

Por: Oliver Grimaldo Ruiz | Fecha: 2019

Abstract: Three-dimensional printing (3D) is an additive manufacturing technology based on material deposition layer by layer for 3D object construction. Every year, 3D Printing offers more alternatives and solutions in the healthcare field. Nowadays, applications such as 3D Printing labs in hospitals, low-cost patient-specific prosthetics, customized medical implants and manufacture of anatomical models with high dimensional accuracy are the most immediate emerging trends. Indeed, 3D Printing application is the convergence of multiple factors, including improvements in medical software, 3D printers evolution and new printing materials. In particular, anatomical models manufacturing is becoming increasingly popular and accessible due to its application in medical training and pre-operative planning. Anatomical models manufacturing is based on several data acquisition techniques such as computed tomography (CT), optical coherence tomography (OCT), magnetic resonance imaging (MRI) or 3D solid modeling through computer-aided-design (CAD) and anatomical structures 3D scanning. The Shirley Ryan Abilitylab research hospital has a full-color multi-material 3D printer Stratasys J750™. It uses Photopolymer jetting (Polyjet™ technology) for manufacture of highly realistic and functional 3D models in a wide range of colors and materials with variable durometers. Materials and methods: Polygonal mesh files (*.hm) corresponding to a finite elements (FE) model of the right knee joint reported by Dhaher et al. 2014 were the basis of this study. The 3D model included femur, tibia, patella, fibula, ligaments, articular cartilage, menisci, retinacula, patella and quadriceps tendons (PT-QT). Three anatomical models were projected and printed achieving the following objectives. (1) 3D model improvement of the right knee joint emulating the hierarchical structure of the collagen fibers matrix of the tendons and ligaments. (2) Anterior cruciate ligament reconstruction (ACL-R) model manufacturing using a bone-patellar-tendon-bone (BPTB) auto-graft and pre-operative planning to improve surgery outcomes, incorporating key surgical elements, such as orientation-architecture of the femoral and tibial tunnels and auto-graft dimensions reported by Dhaher et al. 2014. The surgical planning considers single bundle (SB) reconstruction and includes a customized surgical guide (SG) based on PT anatomy (it used in the graft harvest). The SG requirements followed the indications reported by Wang et al. 2017 with the aim to avoid graft tunnel length mismatch. (3) Total knee replacement (TKR) model manufacturing considering a cruciate sacrificing (CS) implant with customized design of symmetric tibial bearing, adjustment and assembly of standard prosthetic components in the improved 3D model emulating a TKR procedure. The selection process and printing materials matching with anatomical structures was based on stiffness and elastic modulus analysis of different Agilus30 printing material combinations. Mechanical uni-axial tensile tests were conducted in Northwestern University Kaiser Lab using an Instron S3300, Canton, MA Uniaxial Testing Instrument following ASTM test designation D412-C. The combinations No 1-4 were the most similar to real materials with elastic modulus of 1.8-0.7 and Pearson coefficients of the linear region of 0.980-0.991 respectively.
Fuente: Biblioteca Virtual Banco de la República Formatos de contenido: Tesis
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Three-dimensional Printing of a multi-material model of the Knee Joint

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Imagen de apoyo de  The effect of environmental variable selection in the prediction of Seasonal Influenza cases using machine learning

The effect of environmental variable selection in the prediction of Seasonal Influenza cases using machine learning

Por: Stefany Brigetty Guarnizo Peralta | Fecha: 2021

Abstract: Background: Seasonal Influenza is considered to be a cyclic and ordered sequence of values, influenced by external factors that can be predicted and used to detect disease outbreaks and monitoring. In machine learning, the key challenges that limit these analyses are in model explainability and limitations associated with ecological bias. Aim: Determine the best environmental variable selection method to predict Seasonal Influenza in Norway, using an environmental medicine approach combined with machine learning techniques. Methods: This is a quasi-experimental study that compares three approaches (non-variable selection, isolate component, and multipollutant mixture), represented in five methods (univariable, bivariable, multivariable AME, multivariable PCA, multivariable LDA). Per method, the best co-variable combination will be performed, following the internal rules of each method. The best covariable combination is the result of three components: variable selection, validation data set and lag. The first one involves 13 environmental variables (temperature, relative humidity, specific humidity, air pressure, wind speed, precipitation, CO, NO, NO2, O3, PM10, PM2,5 and SO2); second one compares a test dataset compiled from the data from 2019, last year (2018) and a synthetic environmental (avg. 2013-2018) data set in the validation process; and the third one compares a combination of lag from 0 to 12. All the predictions are made using ARIMA algorithm. The evaluation is given in terms of MAE, MSE, RMSE, OR. The training set is from 2 Jun 2013 (week 22/2013) to 28 May 2018 (week 21/2018), and test set is from (week 22/2018) to (week 21/2019) with a window of predictions of 52 weeks. Results: The increment of dimensionality in the environmental variable selection introduce different noise levels and optimize the prediction. Considerations that impact the explainability, usability, ecological bias and performance will be described. Conclusion: The increment of dimensionality in the variable selection has a better impact on performance than using complex algorithms.
Fuente: Biblioteca Virtual Banco de la República Formatos de contenido: Tesis
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The effect of environmental variable selection in the prediction of Seasonal Influenza cases using machine learning

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