Browsing by Author "Castro Hernández, Sebastián Andrés"

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    Multiscale modeling of cardiac electrophysiology : a non-linear diffusion approach to the electrical excitation of cardiac tissue
    (2015) Castro Hernández, Sebastián Andrés; Hurtado Sepúlveda, Daniel; Pontificia Universidad Católica de Chile. Escuela de Ingeniería
    El comportamiento electrofisiológico de componentes biológicas ha sido, tradicionalmente, modelado utilizando el modelo de cable. Para representar la naturaleza de las ondas eléctricas, practicamente todas las formulaciones electrofisiológicas propuestas a la fecha consideran una difusión lineal del flujo basada en materiales óhmicos, conocida en biología como la ley de Fick. En este trabajo, inspirados por la naturaleza porosa de las uniones gap ubicadas en los discos intercalados de los cardiomiocitos, los cuales controlan el flujo intercelular, proponemos una nueva formulación de electrofisiología cardiaca que incorpora un término de difusión no lineal del tipo medio-poroso. El sistema resultante de ecuaciones diferenciales parciales no lineales es resuelto utilizando un método implícito con elementos finitos, el cual es adecuado para simulaciones a gran escala. Los resultados obtenidos con la utilización del modelo de medio poroso muestran potenciales de acción con frentes de onda bien definidos y que viajan con una velocidad finita. También se muestra que este modelo captura las características de restitución de un músculo cardiaco de igual manera que la ecuación de cable lo hace. Finalmente mostramos las capacidades de nuestro método simulando la secuencia de activación en un modelo tridimensional del corazón humano, donde importantes microestructuras fueron incorporadas, como la orientación de los cardiomiocitos, el haz de His y la red de Purkinje.
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    Seismic risk assessment of human evacuations in buildings
    (National Information Centre of Earthquake Engineering, 2017) Poulos Campbell, Alan John; Castro Hernández, Sebastián Andrés; Llera Martin, Juan Carlos de la; Mitrani-Reiser, Judith
    Major earthquakes may require people to evacuate immediately from buildings as recently observed in the 2015 Mw 8.3 Illapel earthquake in Chile. The building may suffer damage, thus affecting the evacuation process. Perhaps due to its apparent complexity, this interaction has not been taken into account when computing seismic risk variables that are intrinsically coupled, such as evacuation times and number of injured people. This limitation can be addressed by simulating the evacuation processes and the physical damage together using agent-based modelling. The evacuation of the building emerges from a set of rules that govern the interaction between agents and with their (damaged) physical surrounding. This research focuses first on modeling evacuations when no physical damage occurs, and uses real evacuation drills performed in a K-12 school and an office building as validation. The comparison was carried out under a low level of uncertainty in the initial conditions of the occupants, i.e., their initial positions and pre-evacuation times were relatively well known, resulting in prediction errors in total evacuation time of only 5.9% and 5.7% for the school and office building, respectively. The evacuation model is then extended to consider building damage and used in an integrated methodology to evaluate the seismic risk of building occupants. This assessment was divided into five steps: (i) seismic hazard, (ii) structural response, (iii) building damage, (iv) evacuation, and (v) risk assessment. First, probabilistic seismic hazard analysis was used to compute the frequency of different levels of local earthquake intensity, characterized herein by the spectral acceleration at the fundamental period of the structure. Ground motions accelerograms matching these intensities were then used in dynamic analyses of the inelastic structure to compute the building response. Story drifts and floor accelerations of the building were related to the damage of non-structural components (e.g., ceilings and partition walls) using appropriate fragility curves. The estimated damage state of the building was used to feed an agent-based evacuation model and assess the evacuation response of the building occupants in this new environment. The outputs of the model are probability distributions of different performance measures and losses, such as evacuation times and number of injured people. These results can better inform decision making processes to mitigate the consequences that future earthquakes will have on buildings and their inhabitants, as well as provide useful information in modeling other larger scale city evacuation scenarios.