Fluid Mechanics for Biomedical Applications: Weakly Viscoelastic Electrospray, Flow Focusing and Collapsible Channel Models

Three different research topics are discussed in this thesis: i) weakly-viscoelastic electrospray, ii) the emergence of whipping effect on the Flow Focusing technique, and iii) fluid-structure interaction (FSI) phenomena implementing a 2D collapsible channel model. i) A systematic, theoretical comparison of a Newtonian fluid, and a non-Newtonian one modelled using an Oldroyd-B model was performed, resulting in a better understanding of how the properties of this type of material influence aspects such as meniscus shrinking, the agreement with a 1D-slenderness model, or the minimum flow rate value defining the boundary between electrospray and electrospinning. ii) In order to use Flow Focusing for some applications (e.g. XFEL), chaotic oscillations on the jet, known as whipping, must be avoided. A stability map for axisymmetric and lateral perturbation modes was obtained and compared to previous experimental data, examining the effect of different nozzle geometries on the emergence of the whipping effect and jetting-to-dripping configuration physical boundary. iii) In the last paper, the implemented model overcame some limitations presented in other 2D collapsible channel models, leading to analysis using a non-negligible membrane thickness and large deformations on the flexible wall segment. The multiplicity of solutions and their folding points, and the quantification of the effect of physical parameters such as wall thickness and inertia values on the emergence of self-excited oscillations were investigated.En esta tesis se abordan tres temas de investigación diferentes: i) electrospray débilmente viscoelástico, ii) la aparición del efecto whipping en la técnica de Flow Focusing, y iii) la interacción fluido-estructura (FSI) implementando un modelo de canal colapsable 2D. i) Se ha realizado una comparación sistemática y teórica entre un fluido newtoniano y uno no newtoniano modelado mediante un modelo Oldroyd-B, lo que ha permitido comprender mejor cómo las propiedades de este tipo de material influyen en aspectos como la contracción del menisco, la concordancia con un modelo de esbeltez (slenderness) 1D o el valor mínimo de la tasa de flujo que define la frontera entre el electrospray y el electrospinning. ii) Para poder utilizar el Flow Focusing en algunas aplicaciones (por ejemplo, el XFEL), deben evitarse las oscilaciones caóticas en el chorro, conocidas como whipping. Se obtuvo un mapa de estabilidad para los modos axisimétrico y de perturbación lateral y se comparó con datos experimentales anteriores, examinando el efecto de diferentes geometrías de boquillas en la aparición del efecto whipping y en la frontera física de la configuración de jetting-to-dripping. iii) En el último artículo, el modelo implementado superó algunas limitaciones presentadas en otros modelos de canales colapsables 2D, lo que llevó al análisis de estabilidad global del sistema utilizando un espesor de membrana no despreciable y grandes deformaciones en el segmento de pared flexible. Se investigó la multiplicidad de soluciones y sus folding-points, así como la cuantificación del efecto de parámetros físicos como el grosor de la pared y los valores de inercia en la aparición self-excited oscillations

A robust numerical framework for the analysis of material failure of fibre reinforced soft tissue

In this work, robustness and stability of continuum damage models applied to material failure in soft tissues are addressed. In the implicit damage models equipped with softening, the presence of negative eigenvalues in the tangent elemental matrix degrades the condition number of the global matrix, leading to a reduction of the computational performance of the numerical model. Two strategies have been adapted from literature to improve the aforementioned computational performance degradation: the IMPL-EX integration scheme [Oliver,2006], which renders the elemental matrix contribution definite positive, and arclength-type continuation methods [Carrera,1994], which allow to capture the unstable softening branch in brittle ruptures. The IMPL-EX integration scheme has as a major drawback the need to use small time steps to keep numerical error below an acceptable value. A convergence study, limiting the maximum allowed increment of internal variables in the damage model, is presented. Finally, numerical simulation of failure problems with fibre reinforced materials illustrates the performance of the adopted methodology

Homological Region Adjacency Tree for a 3D Binary Digital Image via HSF Model

Given a 3D binary digital image I, we define and compute an edge-weighted tree, called Homological Region Tree (or Hom-Tree, for short). It coincides, as unweighted graph, with the classical Region Adjacency Tree of black 6-connected components (CCs) and white 26- connected components of I. In addition, we define the weight of an edge (R, S) as the number of tunnels that the CCs R and S “share”. The Hom-Tree structure is still an isotopic invariant of I. Thus, it provides information about how the different homology groups interact between them, while preserving the duality of black and white CCs. An experimentation with a set of synthetic images showing different shapes and different complexity of connected component nesting is performed for numerically validating the method.Ministerio de Economía y Competitividad MTM2016-81030-

Infrared spectra of crystalline and glassy silicates and application to interstellar dust

The infrared spectra of crystalline minerals predicted in theoretical condensation sequences do not match the astronomical observations. Since the astronomical spectra are a closer match to glassy silicates, the authors undertook a study to measure the infrared spectra of glassy silicates that have compositions similar to silicate minerals predicted in theoretical condensation sequences. The data should support observations aimed at elucidating condensation chemistry in dust forming regions. The authors measured the mass absorption coefficients, from 2.5 to 25 microns, of ground samples of olivine, diopside, and serpentine and also smoke samples that were prepared from these minerals. The smoke samples prepared in this way are predominantly glassy with nearly the same composition as the parent minerals. The crystalline samples consisted of pure olivine ((Fe(0.1)Mg(0.9))(2)SiO(4)), serpentine, diopside. Sample purity was confirmed by x ray diffraction. Each mineral was ground for 10 hours and a measured mass of the powder was mixed with KBr powder for absorption measurements using the method of Borghesi et a. (1985). The smoke samples were prepared from the same samples used for grinding by vaporizing the minerals using pulsed laser radiation in air. The smoke samples formed by condensation of the resulting vapor. The smoke settled onto infrared transparent KRS-5 substrates and onto a quartz crystal microbalance used to obtain mass measurements. A description of the preparation method is given in Stephens (1980). The glassy diopside showed only diffuse electron diffraction peaks and hence was nearly amorphous, while the serpentine smoke showed a weak diffraction pattern corresponding to MgO. The smoke from olivine showed a weak diffraction pattern corresponding to Fe2O3 and/or Fe3O4. The mass absorption coefficients, from 2.5 to 25 microns, of crystalline diopside, olivine, and serpentine and their corresponding smoke samples are shown in figures

IR emission from circumstellar envelopes of C-rich stars

The reliability of a theoretical model that solves the radiative transfer equation in dust clouds surrounding a central star is checked. In particular, it is found that both classical scattering by dust and the back-heating effects are negligible in the radiative transfer when envelopes similar to IRC+10216 are taken into consideration. In addition, new fits of IRC+10216 spectra are presented which were obtained, when the source is in different luminosity phases, under the assumption that amorphous carbon grains are in the circumstellar envelope. The same model is currently used to simulate the emission from carbon-rich sources showing the silicon carbide feature at 11.3 microns

Texture Extraction Techniques for the Classification of Vegetation Species in Hyperspectral Imagery: Bag of Words Approach Based on Superpixels

Texture information allows characterizing the regions of interest in a scene. It refers to the spatial organization of the fundamental microstructures in natural images. Texture extraction has been a challenging problem in the field of image processing for decades. In this paper, different techniques based on the classic Bag of Words (BoW) approach for solving the texture extraction problem in the case of hyperspectral images of the Earth surface are proposed. In all cases the texture extraction is performed inside regions of the scene called superpixels and the algorithms profit from the information available in all the bands of the image. The main contribution is the use of superpixel segmentation to obtain irregular patches from the images prior to texture extraction. Texture descriptors are extracted from each superpixel. Three schemes for texture extraction are proposed: codebook-based, descriptor-based, and spectral-enhanced descriptor-based. The first one is based on a codebook generator algorithm, while the other two include additional stages of keypoint detection and description. The evaluation is performed by analyzing the results of a supervised classification using Support Vector Machines (SVM), Random Forest (RF), and Extreme Learning Machines (ELM) after the texture extraction. The results show that the extraction of textures inside superpixels increases the accuracy of the obtained classification map. The proposed techniques are analyzed over different multi and hyperspectral datasets focusing on vegetation species identification. The best classification results for each image in terms of Overall Accuracy (OA) range from 81.07% to 93.77% for images taken at a river area in Galicia (Spain), and from 79.63% to 95.79% for a vast rural region in China with reasonable computation timesThis work was supported in part by the Civil Program UAVs Initiative, promoted by the Xunta de Galicia and developed in partnership with the Babcock Company to promote the use of unmanned technologies in civil services. We also have to acknowledge the support by Ministerio de Ciencia e Innovación, Government of Spain (grant number PID2019-104834GB-I00), and Consellería de Educación, Universidade e Formación Profesional (ED431C 2018/19, and accreditation 2019-2022 ED431G-2019/04). All are cofunded by the European Regional Development Fund (ERDF)S

Experimental evidence for amorphous carbon grains in comets

Amorphous carbon grains similar to those produced in the laboratory, but with a higher hydrogen content, appear to be good candidates to simulate both the IR continuum emission and the 3.4 micron band measured for P/Halley. The comparison of the cometary features with those detected in the laboratory for carbon grains characterized by various sp(exp 2)/sp(exp 3) ratios seems to indicate that a prevalent diamond-like (sp(exp 3)) structure should be present in cometary particles. These kinds of solid particles seem also suitable to explain the daily and monthly variations of the 3.4 micron band intensity, relative to the continuum, and, at the same time,- to fulfill the abundance constraints. The same grains appear to be able to reproduce the absorption bands detected in the IR galactic source IRS 7. This result may be considered as a first experimental evidence of a relation existing between interstellar dust and cometary materials

Torrente de civilización. Una aproximación a Argirópolis y sus conexiones con las ideas educativas de Sarmiento

Partiendo de una breve presentación del contexto de producción del ensayo sarmientino Argirópolis, se exhibe primeramente su estructura sustentada en el binomio crítica-propuesta. En un segundo momento, se examina si este rasgo, común a las utopías, es suficiente para identificar al mencionado escrito con ellas. En tercer lugar, se aborda el original sentido de la insularidad propuesta por Sarmiento para la futura capital de los Estados Unidos del Río de la Plata. A partir de allí, podemos desbrozar el camino hacia la comprensión del proyecto de nación sarmientino, donde la dicotomía civilización-barbarie funge de dato central en su imaginario. Se pasa entonces a tratar los nexos con las ideas del sanjuanino en torno a la educación: primero, espigando una concepción amplia de lo educativo que nos sugiere la obra estudiada; luego, complementando lo anterior con su insistencia en una política educativa activa, para lo cual se trae a colación su polémica con Juan Bautista Alberdi. En las palabras finales se sopesa lo que dice y no dice Argirópolis respecto a la educación, enfatizando la continuidad de las ideas de Sarmiento en el marco de un proyecto de nación orientado hacia la civilización

Las miradas poéticas de Narciso y Medusa: la transformacion de lo real

Al ser director tanto académico como artístico de este proyecto europeo Crossing Stages, esta doble condición me lleva a tomar la palabra desde estos dos lugares, es decir, desde lo académico y desde lo artístico. Desde dos lugares entonces casi antagónicos. La toma de la palabra académica responde en cierta forma a ciertas máximas de claridad y precisión, suele tender a ser un discurso mesurado, ordenado y equilibrado, que en cierta forma busca un conocimiento erudito por medio de procedimientos científicos lo más objetivos y sólidos posibles. Mientras que la toma de la palabra artística es todo lo contrario, es una palabra oscura, confusa, hiperbólica, amanerada, completamente desmesurada y caótica, y basada en experiencias y caprichos inminentemente subjetivos. Se me plantea entonces desde qué lugar hablar: