The subject of this diploma thesis is experimental and numerical assessment of the heat transfer coefficients during condensation of water steam in simplified parts of an industrial steam turbine. This simplified part is a pipe with circular cross section, which is often used in simulations of processes inside the steam turbine. The first part of thesis describes theoretical basics of heat transfer during conduction, convection and condensation. The content of other chapters is description of methods used to determine heat transfer coefficient. These are: ex-perimental analysis performed on a measuring device and evaluated using finite element ana-lysis (FEA), computational fluid dynamics analysis (CFD) in ANSYS CFX and analytical calculations of heat transfer coefficients using mathematical models for condensation. Thesis is concluded by validation and comparison of obtained results.

La fibrilación auricular es una de las arritmias cardíacas más comunes observadas en la práctica clínica. Por lo tanto, es de vital importancia desarrollar nuevas tecnologías destinadas a diagnosticar y acabar con este tipo de arritmia, para mejorar la calidad de vida de los pacientes y reducir los costes de los sistemas nacionales de salud. En los últimos años ha aumentado el uso de las nuevas técnicas de mapeo auricular, basadas en sistemas multi-electrodo para mapear la actividad eléctrica en humanos. Dichas técnicas permiten localizar y ablacionar los impulsores de la fibrilación auricular, como son las fuentes focales o los rotores. Sin embargo, todavía existe incertidumbre sobre su precisión y los procedimientos experimentales para su análisis están limitados debido a su carácter invasivo. Por lo tanto, las simulaciones computacionales son una herramienta muy útil para superar estas limitaciones, al permitir reproducir con fidelidad las observaciones experimentales, dividir el problema bajo estudio en sub-estudios más simples, y realizar investigaciones preliminares imposibles de llevar a cabo en el práctica clínica. Esta tesis doctoral se centra en el análisis de la precisión de los sistemas de mapeo multi-electrodo a través de modelos y simulaciones computacionales. Para ello, desarrollamos modelos realistas multi-escala con el objetivo de simular actividad eléctrica auricular reentrante, en primer lugar en una lámina de tejido auricular, y en segundo lugar en las aurículas completas. Posteriormente, analizamos los efectos de las configuraciones geométricas multi-electrodo en la precisión de la localización de los rotores, mediante el uso de agrupaciones multi-electrodo con distancias inter-electrodo equidistantes, así como a través de catéteres de tipo basket con distancias inter-electrodo no equidistantes. Después de calcular los electrogramas unipolares intracavitarios, realizamos mapas de fase, detecciones de singularidad de fase para rastrear los rotores, y mapas de frecuencia dominantes. Finalmente, descubrimos que la precisión de los sistemas de mapeo multi-electrodo depende de su posición dentro de la cavidad auricular, de la distancia entre los electrodos y el tejido, de la distancia inter-electrodo, y de la contribución de las fuentes de campo lejano. Además, como consecuencia de estos factores que pueden afectar a la precisión de los sistemas de mapeo multi-electrodo, observamos la aparición de rotores falsos que podrían contribuir al fracaso de los procesos de ablación de la fibrilación auricular. / Atrial fibrillation is one of the most common cardiac arrhythmias seen in clinical practice. Therefore, it is of vital importance to develop new technologies aimed at diagnosing and terminating this kind of arrhythmia, to improve the quality of life of patients and to reduce costs to national health systems. In the last years, new atrial mapping techniques based on multi-electrode systems are increasingly being used to map the atrial electrical activity in humans and localise and target atrial fibrillation drivers in the form of focal sources or rotors. However, significant concerns remain about their accuracy and experimental approaches to analyse them are limited due to their invasive character. Therefore, computer simulations are a helpful tool to overcome these limitations since they can reproduce with fidelity experimental observations, permit to split the problem to treat into more simple substudies, and allow the possibility of performing preliminary investigations impossible to carry out in the clinical practice. This PhD thesis is focused on the analysis for accuracy of the multielectrode mapping systems through computational models and simulations. For this purpose, we developed realistic multiscale models in order to simulate atrial electrical reentrant activity, first in a sheet of atrial tissue and, then, in the whole atria. Then, we analysed the effects of the multi-electrode geometrical configurations on the accuracy of localizing rotors, by using multi-electrode arrays with equidistant inter-electrode distances, as well as multi-electrode basket catheters with non-equidistant inter-electrode distances. After computing the intracavitary unipolar electrograms, we performed phase maps, phase singularity detections to track rotors, and dominant frequency maps. We finally found out that the accuracy of multi-electrode mapping systems depends on their position inside the atrial cavity, the electrode-to-tissue distance, the inter-electrode distance, and the contribution of far field sources. Furthermore, as a consequence of these factors, false rotors might appear and could contribute to failure of atrial fibrillation ablation procedures. / La fibril·lació auricular és una de les arítmies cardíaques més comuns observades en la pràctica clínica. Per tant, és de vital importància desenvolupar noves tecnologies destinades a diagnosticar i acabar amb aquest tipus d'arítmia, per tal de millorar la qualitat de vida dels pacients i reduir els costos dels sistemes nacionals de salut. En els últims anys, ha augmentat l'ús de les noves tècniques de mapeig auricular, basades en sistemes multielèctrode per a mapejar l'activitat elèctrica auricular en humans. Aquestes tècniques permeten localitzar i ablacionar els impulsors de la fibril·lació auricular, com són les fonts focals o els rotors. No obstant això, encara hi ha incertesa sobre la seua precisió i els procediments experimentals per al seu anàlisi estan limitats a causa del seu caràcter invasiu. Per tant, les simulacions computacionals són una eina molt útil per a superar aquestes limitacions, en permetre reproduir amb fidelitat les observacions experimentals, dividir el problema sota estudi en subestudis més simples, i realitzar investigacions preliminars impossibles de dur a terme en el pràctica clínica. Aquesta tesi doctoral es centra en l'anàlisi de la precisió del sistemes de mapeig multielèctrode mitjançant els models i les simulacions computacionals. Per a això, desenvolupàrem models realistes multiescala per tal de simular activitat elèctrica auricular reentrant, en primer lloc en una làmina de teixit auricular, i en segon lloc a les aurícules completes. Posteriorment, analitzàrem els efectes de les configuracions geomètriques multielèctrode en la precisió de la localització dels rotors, mitjançant l'ús d'agrupacions multielèctrode amb distàncies interelèctrode equidistants, així com catèters de tipus basket amb distàncies interelèctrode no equidistants. Després de calcular els electrogrames unipolars intracavitaris, vam realitzar mapes de fase, deteccions de singularitat de fase per a rastrejar els rotors, i mapes de freqüència dominants. Finalment, vam descobrir que la precisió dels sistemes de mapeig multielèctrode depèn de la seua posició dins de la cavitat auricular, de la distància entre els elèctrodes i el teixit, de la distància interelèctrode, i de la contribució de les fonts de camp llunyà. A més, com a conseqüència d'aquests factors, es va observar l'aparició de rotors falsos que podrien contribuir al fracàs de l'ablació de la fibril·lació auricular. / Martínez Mateu, L. (2018). Mapping of the electrical activity of human atria. Multiscale modelling and simulations [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/104604

El cerebro está constituido por numerosos elementos que se encuentran interconectados de forma masiva y organizados en módulos que forman redes jerárquicas. Ciertas patologías cerebrales, como la enfermedad de Alzheimer y el trastorno por consumo de alcohol, se consideran el resultado de efectos en cascada que alteran la conectividad cerebral. La presente tesis tiene como objetivo principal la aplicación de las técnicas de análisis de la ciencia de redes para el estudio de las redes estructurales y funcionales en el cerebro, tanto en un estado control como en un estado patológico. Así, en el primer estudio de la presente tesis se examina la relación entre la conectividad estructural y funcional en la corteza cerebral de la rata. Se lleva a cabo un análisis comparativo entre las conexiones estructurales en la corteza cerebral de la rata y los valores de correlación calculados sobre las mismas regiones. La información acerca de la conectividad estructural se ha obtenido a partir de estudios previos, mientras que la conectividad funcional se ha calculado a partir de imágenes de resonancia magnética funcional. Determinadas propiedades topológicas, y extraídas de la conectividad estructural, se relacionan con la organización modular de las redes funcionales en estado de reposo. Los resultados obtenidos en este primer estudio demuestran que la conectividad estructural y funcional cortical están altamente relacionadas entre sí. Estudios recientes sugieren que el origen de la enfermedad de Alzheimer reside en un mecanismo en el cual depósitos de ovillos neurofibrilares y placas de beta-amiloide se acumulan en ciertas regiones cerebrales, y tienen la capacidad de diseminarse por el cerebro actuando como priones. En el segundo estudio de la presente tesis se investiga si las redes estructurales que se generan con la técnica de resonancia magnética ponderada en difusión podrían ser de utilidad para el diagnóstico de la pre-demencia causada por la enfermedad de Alzheimer. Mediante el uso de imágenes procedentes de la base de datos ADNI, se aplican técnicas de aprendizaje máquina con el fin de identificar medidas de centralidad que se encuentran alteradas en la demencia. En la segunda parte del estudio, se utilizan imágenes procedentes de la base de datos NKI para construir un modelo matemático que simule el proceso de envejecimiento normal, así como otro modelo que simule el proceso de desarrollo de la enfermedad. Con este modelado matemático, se pretende estimar la etapa más temprana que está asociada con la demencia. Los resultados obtenidos de las simulaciones sugieren que en etapas tempranas de la enfermedad de Alzheimer se producen alteraciones estructurales relacionados con la demencia. La cuantificación de la relación estadística entre las señales BOLD de diferentes regiones puede informar sobre el estado funcional cerebral característico de enfermedades neurológicas y psiquiátricas. En el tercer estudio de la presente tesis se estudian las alteraciones en la conectividad funcional que tienen lugar en ratas dependientes del consumo de alcohol cuando se encuentran en estado de reposo. Para ello, se ha aplicado el método NBS. El análisis de este modelo de rata revela diferencias estadísticamente significativas en una subred de regiones cerebrales que están implicadas en comportamientos adictivos. Por lo tanto, estas estructuras cerebrales podrían ser el foco de posibles dianas terapéuticas. La tesis aporta tres innovadoras contribuciones para entender la conectividad cerebral bajo la perspectiva de la ciencia de redes, tanto en un estado control como en un estado patológico. Los resultados destacan que los modelos basados en las redes cerebrales permiten esclarecer la relación entre la estructura y la función en el cerebro. Y quizás más importante, esta perspectiva de red tiene aplicaciones que se podrían trasladar a la práctica clínica. / The brain is composed of massively connected elements arranged into modules that form hierarchical networks. Experimental evidence reveals a well-defined connectivity design, characterized by the presence of strategically connected core nodes that critically contribute to resilience and maintain stability in interacting brain networks. Certain brain pathologies, such as Alzheimer's disease and alcohol use disorder, are thought to be a consequence of cascading maladaptive processes that alter normal connectivity. These findings have greatly contributed to the development of network neuroscience to understand the macroscopic organization of the brain. This thesis focuses on the application of network science tools to investigate structural and functional brain networks in health and disease. To accomplish this goal, three specific studies are conducted using human and rodent data recorded with MRI and tracing technologies. In the first study, we examine the relationship between structural and functional connectivity in the rat cortical network. Using a detailed cortical structural matrix obtained from published histological tracing data, we first compare structural connections in the rat cortex with their corresponding spontaneous correlations extracted empirically from fMRI data. We then show the results of this comparison by relating structural properties of brain connectivity to the functional modularity of resting-state networks. Specifically, we study link reciprocity in both intra- and inter-modular connections as well as the structural motif frequency spectrum within functionally defined modules. Overall, our results provide further evidence that structural connectivity is coupled to and shapes functional connectivity in cortical networks. The pathophysiological process of Alzheimer's disease is thought to begin years before clinical decline, with evidence suggesting pahtogenic seeding and subsequent prion-like spreading processes of neurofibrillary tangles and amyloid plaques. In the second study of this thesis, we investigate whether structural brain networks as measured with dMRI could serve as a complementary diagnostic tool in prodromal dementia. Using imaging data from the ADNI database, we first aim to implement machine learning techniques to extract centrality features that are altered in Alzheimer's dementia. We then incorporate data from the NKI database and create dynamical models of normal aging and Alzheimer's disease to estimate the earliest detectable stage associated with dementia in the simulated disease progression. Our model results suggest that changes associated with dementia begin to manifest structurally at early stages. Statistical dependence measures computed between BOLD signals can inform about brain functional states in studies of neurological and psychiatric disorders. Furthermore, its non-invasive nature allows comparable measurements between clinical and animal studies, providing excellent translational capabilities. In the last study, we apply the NBS method to investigate alterations in the resting-state functional connectivity of the rat brain in a PD state, an established animal model of clinical relevant features in alcoholism. The analysis reveal statistically significant differences in a connected subnetwork of structures with known relevance for addictive behaviors, hence suggesting potential targets for therapy. This thesis provides three novel contributions to understand the healthy and pathological brain connectivity under the perspective of network science. The results obtained in this thesis underscore that brain network models offer further insights into the structure-function coupling in the brain. More importantly, this network perspective provides potential applications for the diagnosis and treatment of neurological and psychiatric disorders. / El cervell està constituït per nombrosos elements que es troben interconnectats de forma massiva i organitzats en mòduls que formen xarxes jeràrquiques. Certes patologies cerebrals, com la malaltia d'Alzheimer i el trastorn per consum d'alcohol, es consideren el resultat d'efectes en cascada que alteren la connectivitat cerebral. La present tesi té com a objectiu principal l'aplicació de les tècniques d'anàlisi de la ciència de xarxes per a l'estudi de les xarxes estructurals i funcionals en el cervell, tant en un estat control com en un estat patològic. Així, en el primer estudi de la present tesi s'examina la relació entre la connectivitat estructural i funcional en l'escorça cerebral de la rata. Es du a terme una anàlisi comparativa entre les connexions estructurals en l'escorça cerebral de la rata i els valors de correlació calculats sobre les mateixes regions. La informació sobre la connectivitat estructural s'ha obtingut a partir d'estudis previs, mentre que la connectivitat funcional s'ha calculat a partir d'imatges de ressonància magnètica funcional. Determinades propietats topològiques, i extretes de la connectivitat estructural, es relacionen amb l'organització modular de les xarxes funcionals en estat de repòs. Els resultats obtinguts en este primer estudi demostren que la connectivitat estructural i funcional cortical estan altament relacionades entre si. Estudis recents suggereixen que l'origen de la malaltia d'Alzheimer resideix en un mecanisme en el qual depòsits d'ovulets neurofibrilars i plaques de beta- miloide s'acumulen en certes regions cerebrals, i tenen la capacitat de disseminar-se pel cervell actuant com a prions. En el segon estudi de la present tesi s'investiga si les xarxes estructurals que es generen amb la tècnica de la imatge per ressonància magnètica ponderada en difusió podrien ser d'utilitat per al diagnòstic de la predemència causada per la malaltia d'Alzheimer. Per mitjà de l'ús d'imatges procedents de la base de dades ADNI, s'apliquen tècniques d'aprenentatge màquina a fi d'identificar mesures de centralitat que es troben alterades en la demència. En la segona part de l'estudi, s'utilitzen imatges procedents de la base de dades NKI per a construir un model matemàtic que simule el procés d'envelliment normal, així com un altre model que simule el procés de desenrotllament de la malaltia. Amb este modelatge matemàtic, es pretén estimar l'etapa més primerenca que està associada amb la demència. Els resultats obtinguts de les simulacions suggereixen que en etapes primerenques de la malaltia d'Alzheimer es produeixen alteracions estructurals relacionats amb la demència. La quantificació de la relació estadística entre els senyals BOLD de diferents regions pot informar sobre l'estat funcional cerebral característic de malalties neurològiques i psiquiàtriques. A més, a causa de la seua naturalesa no invasiva, és possible comparar els resultats obtinguts entre estudis clínics i estudis amb animals d'experimentació. En el tercer estudi de la present tesi s'estudien les alteracions en la connectivitat funcional que tenen lloc en rates dependents del consum d'alcohol quan es troben en estat de repòs. Per a realitzar-ho, s'ha aplicat el mètode NBS. L'anàlisi d'aquest model de rata revela diferències estadísticament significatives en una subxarxa de regions cerebrals que estan implicades en comportaments addictius. Per tant, estes estructures cerebrals podrien ser el focus de possibles dianes terapèutiques. La tesi aporta tres innovadores contribucions per a entendre la connectivitat cerebral davall la perspectiva de la ciència de xarxes, tant en un estat control com en un estat patològic. Els resultats destaquen que els models basats en les xarxes cerebrals permeten aclarir la relació entre l'estructura i la funció en el cervell. I potser més important, esta perspectiva de xarxa té aplicacions que es podrien traslladar a la pràcti / Díaz Parra, A. (2018). A network science approach of the macroscopic organization of the brain: analysis of structural and functional brain networks in health and disease [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/106966

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: South Africa and Australia are now the two remaining countries bidding for the Square Kilometre Array (SKA), the biggest and most sensitive project ever undertaken in radio astronomy. The South African SKA is demonstrating its technology capabilities through the Karoo Array Telescope (KAT or MeerKAT). The development of KAT is taking place in stages to optimise design and minimise risks at each stage. An array of seven 12 m antennas will be complete by the end of 2009, called KAT-7. The following phase will see the construction of MeerKAT, which will lead to eighty arrayed dishes. Lightning and RFI studies for KAT-7 are the focus of this dissertation. Due to the extent and complexity of the South African demonstrator project, these studies have largely been conducted on a single structure. Parameters for the dish antenna and pedestal design changed throughout their development. To be effective, the doctoral research had to track these changes appropriately. A Method of Moments frequency domain computational electromagnetic code, FEKO, is used throughout the study. The consequences of direct and indirect lightning strikes are examined for the KAT-7 structure. Important FEKO model verification is achieved through measurement of physical scale models in an anechoic chamber. The microwave simulation code, CST, gives direct comparison of FEKO results by using a finite volume time domain method of calculation. Using frequency domain analysis on these models, the lightning down conductor design over the dish antenna bearings is optimised with cost-effectiveness as one driving parameter. RFI coupling levels for different designs are compared to each other to identify areas requiring RFI mitigation. Analysis of resonances enables evaluation of the mitigation at frequencies sensitive to radio astronomy. A Sommerfeld integral ground plane is used together with the computational model to investigate the use of the concrete foundation steel reinforcing as part of the lightning earthing electrode system. Different interconnections of the steel reinforcing elements are critically evaluated. The KAT-7 design incorporated clear lightning protection and RFI mitigation policies derived from recommendations contained within this dissertation. / AFRIKAANSE OPSOMMING: Suid-Afrika en Australie is nou die oorblywende twee lande wat bie vir die Vierkante Kilometer Reeks (SKA), die grootste en mees sensitiewe projek nog ooit in radio astronomie onderneem. Die Suid Afrikaanse SKA demonstreer sy tegnologiese bekwaamheid met die Karoo Reeks Teleskoop (KAT of MeerKAT). Die ontwikkeling van KAT vind plaas in fases om die ontwerp te optimaliseer en risikos te minimaliseer met elke fase. ’n Reeks van sewe 12 m antennas, genaamd KAT-7, sal teen die einde van 2009 klaar wees. Die volgende fase behels die konstruksie van MeerKAT, wat sal lei tot ’n tagtig-skottel reeks. Die fokus van hierdie proefskrif hanteer weerlig en radiofrekwensie steurings (RFS) vir KAT-7. As gevolg van die omvang en kompleksiteit van die Suid-Afrikaanse demonstreerder projek, is die studies hoofsaaklik op een struktuur gedoen. Parameters vir die antenna-skottel en -voetstuk ontwerp het met hul ontwikkeling deurgaans verander. Om effektief te wees, moes die doktorale navorsing hierdie veranderinge toepaslik volg. ’n Metode-van-Momente frekwensiedomein rekenaar elektromagnetiese kode, FEKO, is deurgaans met die studie gebruik. Die gevolge van direkte en indirekte weerligslae vir die KAT-7 struktuur is ondersoek. Belangrike FEKO model bevestiging is bereik met metings van skaalmodelle in ’n anego¨ıse kamer. Die mikrogolf-simulasie kode, CST, gee ’n direkte vergelyking met die FEKO resultate deur ’n eindige-volume-tyd-domein metode van berekening te gebruik. Met behulp van frekwensiedomein analise van hierdie modelle, is die weerligafleierontwerp oor die antenna-skottel laers ge-optimaliseer, met koste-effektiwiteit as een van die drywingsparameters. RFS koppelingsvlakke vir onderskeie ontwerpe is teen mekaar opgeweeg om areas te identifiseer wat RFS tempering benodig. Analise van resonansies stel die evaluering van die tempering in staat teen frekwensies wat sensitief is vir radio astronomie. ’n Sommerfeld integrale grondvlak word saam met die rekenaarmodel gebruik om die insluiting van die beton se staalversterking as deel van die aardingselektrodestelsel te ondersoek. Verskillende bindmetodes van die onderlinge staalversterkingselemente word krities ge¨evalueer. Die KAT-7 ontwerp inkorporeer duidelike weerligbeveiligings- en RFS temperingstrategie ¨e, komende van aanbevelings in hierdie proefskrif omskryf

Functional hyperaemia is an important mechanism by which increased neuronal activity is matched by a rapid and regional increase in blood supply. This mechanism is facilitated by a process known as “neurovascular coupling” – the orchestrated communication system involving the cells that comprise the neurovascular unit (neurons, astrocytes and the smooth muscle and endothelial cells lining arterioles). Blood flow regulation and neurovascular coupling are altered in several pathological states including hypertension, diabetes, Alzheimer’s disease, cortical spreading depression and stroke. By adapting and extending other models found in the literature, we create, for the first time, a mathematical model of the entire neurovascular unit that is capable of simulating two separate neurovascular coupling mechanisms: a potassium- and EET-based and a NO-based mechanism. These models successfully account for several observations seen in experiment. The potassium/EET-based mechanism can achieve arteriolar dilations similar in magnitude (3%) to those observed during a 60-second neuronal activation (modelled as a release of potassium and glutamate into the synaptic cleft). This model also successfully emulates the paradoxical experimental finding that vasoconstriction follows vasodilation when the astrocytic calcium concentration (or perivascular potassium concentration) is increased further. We suggest that the interaction of the changing smooth muscle cell membrane potential and the changing potassium-dependent resting potential of the inwardly rectifying potassium channel are responsible for this effect. Furthermore, our simulations demonstrate that the arteriolar behaviour is profoundly affected by depolarization of the astrocytic cell membrane, and by changes in the rate of perivascular potassium clearance or the volume ratio between the perivascular space and astrocyte. In the modelled NO-based neurovascular coupling mechanism, NO exerts its vasodilatory effects via neuronal and endothelial cell sources. With both sources included, the model achieves a 1% dilation due to a 60-second neuronal activation. When the endothelial contribution to NO production is omitted, the arteriole is more constricted at baseline. Without the endothelial NO contribution, the arteriolar change in diameter during neuronal activity is greater (6%). We hypothesize that NO has a dual purpose in neurovascular coupling: 1) it dixxxvi rectly mediates neurovascular coupling through release by neuronal sources, and 2) it indirectly modulates the size of the neurovascular coupling response by determining the baseline tone. Our physiological models of neurovascular coupling have allowed us to replicate, and explain, some of the phenomena seen in both neurovascular coupling-oriented and clinicallyoriented experimental research. This project highlights the fact that physiological modelling can be used as a tool to understand biological processes in a way that physical experiment cannot always do, and most importantly, can help to elucidate the cellular processes that induce or accompany our most debilitating diseases.

This thesis presents a finite element methodology for simulating fluid–solid interactions in the left ventricle (LV) under LVAD support. The developed model was utilised to study the passive and active characteristics of ventricular function in anatomically accurate LV geometries constructed from normal and patient image data. A non–conforming ALE Navier–Stokes/finite–elasticity fluid–solid coupling system formed the core of the numerical scheme, onto which several novel numerical additions were made. These included a fictitious domain (FD) Lagrange multiplier method to capture the interactions between immersed rigid bodies and encasing elastic solids (required for the LVAD cannula), as well as modifications to the Newton–Raphson/line search algorithm (which provided a 2 to 10 fold reduction in simulation time). Additional developments involved methods for extending the model to ventricular simulations. This required the creation of coupling methods, for both fluid and solid problems, to enable the integration of a lumped parameter representation of the systemic and pulmonary circulatory networks; the implementation and tuning of models of passive and active myocardial behaviour; as well as the testing of appropriate element types for coupling non–conforming fluid– solid finite element models under high interface tractions (finding that curvilinear spatial interpolations of the fluid geometry perform best). The behaviour of the resulting numerical scheme was investigated in a series of canonical test problems and found to be convergent and stable. The FD convergence studies also found that discontinuous pressure elements were better at capturing pressure gradients across FD boundaries. The ventricular simulations focused firstly on studying the passive diastolic behaviour of the LV both with and without LVAD support. Substantially different vortical flow features were observed when LVAD outflow was included. Additionally, a study of LVAD cannula lengths, using a particle tracking algorithm to determine recirculation rates of blood within the LV, found that shorter cannulas improved the recirculation of blood from the LV apex. Incorporating myocardial contraction, the model was extended to simulate the full cardiac cycle, converging on a repeating pressure–volume loop over 2 heart beats. Studies on the normal LV geometry found that LVAD implementation restricts the recirculation of early diastolic inflow, and that fluid–solid coupled models introduce greater heterogeneity of myocardial work than was observed in equivalent solid only models. A patient study was undertaken using a myocardial geometry constructed using image data from an LVAD implant recipient. A series of different LVAD flow regimes were tested. It was found that the opening of the aortic valve had a homogenising effect on the spatial variation of work, indicating that the synchronisation of LVAD outflow with the cardiac cycle is more important if the valve remains shut. Additionally, increasing LVAD outflow during systole and decreasing it during diastole led to improved mixing of blood in the ventricular cavity – compared with either the inverse, or holding outflow constant. Validation of these findings has the potential to impact the treatment protocols of LVAD patients.

Sudden cardiac death is one of the leading causes of mortality in the western world. One of the main factors is myocardial ischaemia, when there is a mismatch between blood demand and supply to the heart, which may lead to disturbed cardiac excitation patterns, known as arrhythmias. Ischaemia is a dynamic and complex process, which is characterised by many electrophysiological changes that vary through space and time. Ischaemia-induced arrhythmic mechanisms, and the safety and efficacy of certain therapies are still not fully understood. Most experimental studies are carried out in animal, due to the ethical and practical limitations of human experiments. Therefore, extrapolation of mechanisms from animal to human is challenging, but can be facilitated by in silico models. Since the first cardiac cell model was built over 50 years ago, computer simulations have provided a wealth of information and insight that is not possible to obtain through experiments alone. Therefore, mathematical models and computational simulations provide a powerful and complementary tool for the study of multi-scale problems. The aim of this thesis is to investigate pro-arrhythmic electrophysiological consequences of acute myocardial ischaemia, using a multi-scale computational modelling and simulation framework. Firstly, we present a novel method, combining computational simulations and optical mapping experiments, to characterise ischaemia-induced spatial differences modulating arrhythmic risk in rabbit hearts. Secondly, we use computer models to extend our investigation of acute ischaemia to human, by carrying out a thorough analysis of recent human action potential models under varied ischaemic conditions, to test their applicability to simulate ischaemia. Finally, we combine state-of-the-art knowledge and techniques to build a human whole ventricles model, in which we investigate how anti-arrhythmic drugs modulate arrhythmic mechanisms in the presence of ischaemia.

This work deals with computational modelling of static and dynamic analyses of journal bearings, with analyses of stability of oil-film motion and analyses of response of the rotor assemblies. At our workplace a new theoretical approach to the modelling of the static and dynamic behaviour of the rigid rotating body in liquid is used. The approach is based on the application of the Navier-Stokes motion eq., equation of continuity and boundary conditions eqs. It is possible to separate the motion of the rigid body and liquid from each other using suitable transformation relations and then it is also possible to separate the stationary and nonstationary motions from each other. A method of control volumes is used for these analyses. The real Bézier body is used for the description of the geometrical configuration and also for the approximation of velocity and pressure functions. Combined the ALE (Arbitrary Lagrange-Euler) method is used, because it´s necessary to generate a new net (to perform new meshing) for a change of the shaft position. The additional effects of the liquid (additional mass, stiffness and damping), which we solved in dynamic analysis, are the function of the single parameter only – the shaft-centre position. There is a large advantage in comparison with the standard approach, which is based on application of the Reynolds liquid eq. Author solving the models of the long and short journal bearing with different geometry, especially the elliptical and cylindrical bearings, with incompressible and compressible journal bearing liquid. If the journal bearing problem is solved, it is possible to include the additional effect of the liquid to the right side of the motion equation of a model rotor assembly. Author analyze a model rotor assemblies with two degrees of freedom, which is supported inside of the two journal bearings on the ends of the rotor (Jeffcott rotor assembly). Author modelling and solveing a response of the model rotor assembly on the forced steady-state vibrations, which was actuating by the unbalanced matter.

Made available in DSpace on 2015-03-04T18:50:51Z (GMT). No. of bitstreams: 1 thesis-FINAL-Drach.pdf: 12855630 bytes, checksum: ed8588770ebd55e99fede6e949f04cbe (MD5) Previous issue date: 2007-08-29 / In this thesis, computational modelling and numerical simulations are developed for construction architecture, to make possible project configuration evaluations and testing of possible improvements, both in the pre-occupancy and in the post-occupancy phases, aiming at comfort of building environments. These improvements are introduced here by simple changes to original designs targeting the functional quality increasing of the buildings with low financial and environmental costs. Attention is paid, in this work, to the following comfort variables: air circulation (velocity field), temperature and pollutant concentration, considering radiation, convection and building envelope materials. A coupled mathematical model is presented for velocity, temperature and concentration variables through the conservation equations for mass, momentum, energy and species, and variable boundary conditions can be used. Numerical solutions for the mathematical model are obtained by a stabilyzed mixed finite element method that allows to deal with the diffulties in constructing approximation spaces for problems with internal constraint and non-linearities of the convective type. It is also proposed in this thesis a global circulation index capable of identifying, from the simulation results, the windd intensity by level ranges and by rooms. Changes are proposed to original internal environmentes through openings locations, wall shapes and outdoor volumes placements. Some wind-catcher models, typical from north Africa, are studied, and it is suggested here the potentiality of theis usage in the hot and dry regions of Brazil. The usefulness of this alternative system is also proposed and tested here for some buildings located in the city of Rio de Janeiro. / Nesta tese, modelagem computacional e simulação numérica são desenvolvidas para arquitetura, com o objetivo de permitir avaliação de configurações de projetos e testes de possíveis melhorias, tanto na fase pré-ocupacional, como na pós-ocupacional, visando conforto em ambientes construídos. Essas melhorias são aqui introduzidas a partir de alterações de simples execução sobre os projetos originais, objetivando o incremento da qualidade funcional das construções, a baixos custos financeiros e ambientais. Este trabalho, assim, atenta para as variáveis de conforto de circulação do ar (campo de velocidades), temperatura e concentração de poluentes levando em conta radiação, convecção e materiais da envoltória. É apresentado um modelo matemático acoplado para as variáveis velocidade, temperatura e concentração através das equações de conservação de massa, de momento, de energia e de espécies; e estão previstas condições de contorno variáveis. As soluções numéricas para o modelo matemático são aqui obtidas via um método estabilizado de elementos finitos mistos, que permite lidar com as dificuldades de construção de espaços de aproximação para problemas que envolvem restrições internas e não linearidades do tipo convectivo. Propõe-se também nesta tese um índice de circulação global capaz de, a partir dos resultados das simulações, identificar a intensidade de vento, por faixas e por ambientes. São propostas alterações em projetos originais de ambientes internos através de localização de aberturas, formato de paredes e posicionamento de volumes exteriores. São estudados alguns casos de captadores de vento típicos do norte da África e indica-se, aqui, sua potencialidade para regiões quentes e secas do Brasil. Sua utilização é também proposta e testada para algumas residências da cidade do Rio de Janeiro.

Paradoxically enhanced cognitive processes in neurological disorders provide vital clues to understanding neural function. However, what determines whether the neurological damage is impairing or enhancing is unclear. Here we use the performance of patients with two disorders of the striatum to dissociate mechanisms underlying cognitive enhancement and impairment resulting from damage to the same system. In a two-choice decision task, Huntington\'s disease patients were faster and less error prone than controls, yet a patient with the rare condition of benign hereditary chorea (BHC) was both slower and more error prone. EEG recordings confirmed significant differences in neural processing between the groups. Analysis of a computational model revealed that the common loss of connectivity between striatal neurons in BHC and Huntington\'s disease impairs response selection, but the increased sensitivity of NMDA receptors in Huntington\'s disease potentially enhances response selection. Crucially the model shows that there is a critical threshold for increased sensitivity: below that threshold, impaired response selection results. Our data and model thus predict that specific striatal malfunctions can contribute to either impaired or enhanced selection, and provide clues to solving the paradox of how Huntington\'s disease can lead to both impaired and enhanced cognitive processes.