Modelling the dynamics of microbubble undergoing stable and inertial cavitation : delineating the effects of ultrasound and microbubble parameters on sonothrombolysis

Sonothrombolysis induces clot breakdown using ultrasound waves to excite microbubbles. Despite the great potential, selecting optimal ultrasound (frequency and pressure) and microbubble (radius) parameters remains a challenge. To address this, a computational model was developed to investigate the bubble behaviour during sonothrombolysis. The blood and clot were assumed to be non-Newtonian and porous, respectively. The effects of ultrasound and microbubble parameters on flow-induced shear stress on the clot surface during stable and inertial cavitation were investigated. It was found that microbubble translation towards the clot and the shear stress on the clot surface during stable cavitation were significant when the bubble was about to undergo inertial cavitation. While insonation of large microbubble (radius of 1.6

Ambientes virtuais de aprendizagem em química

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia de Produção.Este trabalho idealiza e acompanha o desenvolvimento de um projeto envolvendo a informática em uma situação de aprendizagem a fim de facilitar a compreensão da estrutura da matéria, correlacionando a sua compreensão com o entendimento contextualizado sobre o meio ambiente. A evolução das idéias referentes à estrutura da matéria, as ferramentas computacionais disponíveis para mediarem o processo de ensino- aprendizagem e o estado da arte dos ambientes virtuais de aprendizagem de Química foram abordados a partir de um levantamento bibliográfico. Em seguida, são traçados os fundamentos da metodologia de projetos e feita a descrição do desenvolvimento do projeto: A qualidade do ar e da água no município de Divinópolis-MG . Com esse trabalho é possível gerar situações de ensino-aprendizagem de Química entre outras disciplinas, estabelecer conexões entre as abordagens macro e sub-microscópicas da matéria, fomentar a cooperação docente e discente, trabalhar as diversas habilidades dos alunos e elaborar uma leitura crítica da realidade. Dentre as principais limitações para desenvolver o projeto pode-se destacar a rigidez da estrutura curricular tradicional, a questão da avaliação e as dificuldades próprias de se trabalhar com situações novas e complexas. Para o desenvolvimento de futuros trabalhos sugere-se que haja maior flexibilização do currículo com a participação efetiva de todas as disciplinas e que a Escola possa estar sempre aberta ao desafio de interagir com a comunidade. Uma perspectiva de continuidade desse projeto surge na pesquisa de soluções para os problemas ambientais detectados na fase inicia

Studies of ocular heat transfer using the boundary element method

Ocular heat transfer is a promising area of research. The continual fascination with ocular temperature may be attributed to its potential use in monitoring the physiological and health conditions of the human eye. Mathematical modeling has proven to be a reliable technique in the studies of ocular heat transfer. This has been attributed to the advancement of computational technology that enables complex mathematical problems to be modeled accurately. The incapability of infrared thermography (which is the current method in ocular thermometry) to measure intraocular temperatures in particular, may also contribute to the rising popularity of mathematical modeling. Majority of the ocular heat transfer studies in the past have been carried out using the finite element method. The boundary element method, which has been established as a leading alternative to the commonly used finite element method in engineering analysis, is rarely used. Since some aspects of the boundary element method have been found to be advantageous over the finite element method, it may be worth exploring the performance and feasibility of the boundary element method in the studies of ocular heat transfer. For this purpose, four specific problems involving heat transfer inside the human eye are investigated.DOCTOR OF PHILOSOPHY (MAE

Thermal and thermal damage responses during switching bipolar radiofrequency ablation employing bipolar needles : a computational study on the effects of different electrode configuration, input voltage and ablation duration

Recent studies have demonstrated the effectiveness of switching bipolar radiofrequency ablation (bRFA) in treating liver cancer. Nevertheless, the clinical use of the treatment remains less common than conventional monopolar RFA – likely due to the lack of understanding of how the tissues respond thermally to the switching effect. The problem is exacerbated by the numerous possible switching combinations when bRFA is performed using bipolar needles, thus making theoretical deduction and experimental studies difficult. This article addresses this issue via computational modelling by examining if significant variation in the treatment outcome exists amongst six different electrode configurations defined by the X-, C-, U-, N-, Z- and O-models. Results indicated that the tissue thermal and thermal damage responses varied depending on the electrode configuration and the operating conditions (input voltage and ablation duration). For a spherical tumour, 30 mm in diameter, complete ablation could not be attained in all configurations with 70 V input voltage and 5 minutes ablation duration. Increasing the input voltage to 90 V enlarged the coagulation zone in the X-model only. With the other configurations, extending the ablation duration to 10 minutes was found to be the better at enlarging the coagulation zone. © 2020 John Wiley & Sons, Ltd

Numerical investigation of the meshless radial basis integral equation method for solving 2D anisotropic potential problems

The radial basis integral equation (RBIE) method is derived for the first time to solve potential problems involving material anisotropy. The coefficients of the anisotropic conductivity require the gradient term to be modified accordingly when deriving the boundary integral equation so that the flux expression can be properly accounted. Analyses of the behavior of the anisotropic fundamental solution and its spatial gradients showed that their variations along the subdomain boundaries may be large and they increase as the diagonal components of the material anisotropy become larger. The accuracy of the anisotropic RBIE was found to depend primarily on the accuracy of the influence coefficients evaluations and this precedes the number of nodes used. Root mean squared errors of less than 10(-4)% can be obtained if evaluations of the influence coefficients are sufficiently accurate. An alternative formulation of the anisotropic RBIE was derived. The levels of accuracy obtained were not significantly different from the standard formulation. (C) 2014 Elsevier Ltd. All rights reserved

Shape-shifting thermal coagulation zone during saline-infused radiofrequency ablation: A computational study on the effects of different infusion location

Background and objective: The majority of the studies on radiofrequency ablation (RFA) have focused on enlarging the size of the coagulation zone. An aspect that is crucial but often overlooked is the shape of the coagulation zone. The shape is crucial because the majority of tumours are irregularly-shaped. In this paper, the ability to manipulate the shape of the coagulation zone following saline-infused RFA by altering the location of saline infusion is explored. Methods: A 3D model of the liver tissue was developed. Saline infusion was described using the dual porosity model, while RFA was described using the electrostatic and bioheat transfer equations. Three infusion locations were investigated, namely at the proximal end, the middle and the distal end of the electrode. Investigations were carried out numerically using the finite element method. Results: Results indicated that greater thermal coagulation was found in the region of tissue occupied by the saline bolus. Infusion at the middle of the electrode led to the largest coagulation volume followed by infusion at the proximal and distal ends. It was also found that the ability to delay roll-off, as commonly associated with saline-infused RFA, was true only for the case when infusion is carried out at the middle. When infused at the proximal and distal ends, the occurrence of roll-off was advanced. This may be due to the rapid and more intense heating experienced by the tissue when infusion is carried out at the electrode ends where Joule heating is dominant. Conclusion: Altering the location of saline infusion can influence the shape of the coagulation zone following saline-infused RFA. The ability to ‘shift’ the coagulation zone to a desired location opens up great opportunities for the development of more precise saline-infused RFA treatment that targets specific regions within the tissue. © 2019 Elsevier B.V

Dynamic fracture simulations using the scaled boundary finite element method on hybrid polygon-quadtree meshes

In this paper, we present an efficient computational procedure to model dynamic fracture within the framework of the scaled boundary finite element method (SBFEM). A quadtree data structure is used to discretise the domain, and 2:1 ratio between the cells is maintained. This limits the number of patterns in the quadtree decomposition and allows for efficient computation of the system matrices. The regions close to the boundary are discretised with arbitrary sided polygons so as to facilitate accurate modelling of the curved boundaries. The stiffness and the mass matrix over all the cells are computed by the SBFEM. Moreover, the semi-analytical nature of the SBFEM enables accurate modelling of the asymptotic stress fields in the vicinity of the crack tip. An efficient remeshing algorithm that combines the quadtree decomposition with simple Boolean operations is proposed to model the crack propagation. The remeshing is restricted only to a small region in the vicinity of the crack tip. The efficiency and the convergence properties of the proposed framework are demonstrated with a few benchmark problems. © 2015 Elsevier Ltd. All rights reserved

A computational model to investigate the influence of electrode lengths on the single probe bipolar radiofrequency ablation of the liver

Background and objectives: Recently, there have been calls for RFA to be implemented in the bipolar mode for cancer treatment due to the benefits it offers over the monopolar mode. These include the ability to prevent skin burns at the grounding pad and to avoid tumour track seeding. The usage of bipolar RFA in clinical practice remains uncommon however, as not many research studies have been carried out on bipolar RFA. As such, there is still uncertainty in understanding the effects of the different RF probe configurations on the treatment outcome of RFA. This paper demonstrates that the electrode lengths have a strong influence on the mechanics of bipolar RFA. The information obtained here may lead to further optimization of the system for subsequent uses in the hospitals. Methods: A 2D model in the axisymmetric coordinates was developed to simulate the electro-thermophysiological responses of the tissue during a single probe bipolar RFA. Two different probe configurations were considered, namely the configuration where the active electrode is longer than the ground and the configuration where the ground electrode is longer than the active. The mathematical model was first verified with an existing experimental study found in the literature. Results: Results from the simulations showed that heating is confined only to the region around the shorter electrode, regardless of whether the shorter electrode is the active or the ground. Consequently, thermal coagulation also occurs in the region surrounding the shorter electrode. This opened up the possibility for a better customized treatment through the development of RF probes with adjustable electrode lengths. Conclusions: The electrode length was found to play a significant role on the outcome of single probe bipolar RFA. In particular, the length of the shorter electrode becomes the limiting factor that influences the mechanics of single probe bipolar RFA. Results from this study can be used to further develop and optimize bipolar RFA as an effective and reliable cancer treatment technique. (C) 2019 Elsevier B.V. All rights reserved

Crack propagation modelling in concrete using the scaled boundary finite element method with hybrid polygon-quadtree meshes

This manuscript presents an extension of the recently-developed hybrid polygon-quadtree-based scaled boundary finite element method to model crack propagation in concrete. This hybrid approach combines the use of quadtree cells with arbitrary sided polygons for domain discretization. The scaled boundary finite element formulation does not distinguish between quadtree cells and arbitrary sided polygons in the mesh. A single formulation is applicable to all types of cells and polygons in the mesh. This eliminates the need to develop transitional elements to bridge the cells belonging to different levels in the quadtree hierarchy. Further to this, the use of arbitrary sided polygons facilitate the accurate discretization of curved boundaries that may result during crack propagation. The fracture process zone that is characteristic in concrete fracture is modelled using zero-thickness interface elements that are coupled to the scaled boundary finite element method using a shadow domain procedure. The scaled boundary finite element method can accurately model the asymptotic stress field in the vicinity of the crack tip with cohesive tractions. This leads to the accurate computation of the stress intensity factors, which is used to determine the condition for crack propagation and the resulting direction. Crack growth can be efficiently resolved using an efficient remeshing algorithm that employs a combination of quadtree decomposition functions and simple Booleans operations. The flexibility of the scaled boundary finite element method to be formulated on arbitrary sided polygons also result in a flexible remeshing algorithm for modelling crack propagation. The developed method is validated using three laboratory experiments of notched concrete beams subjected to different loading conditions

Transformation thermodynamics for heat flux management based on segmented thermal cloaks

Transformation thermodynamics has potential applications in heat flux management. The geometrical transformation used in the cloaking procedure requires materials that are inhomogeneous and thermally anisotropic. This requirement can be reduced by segmented cloaking, where materials with homogeneous and isotropic thermal properties are adopted. One of the issues when constructing a segmented cloak is reducing the number of segments and yet preserving the performance of the thermal cloak. In this study, the performances of linear and nonlinear segmented cylindrical cloaks are assessed, by comparison with the performance of a single-layer thermal cloak based on inhomogeneous and thermally anisotropic materials. The possibility of finding an optimal balance between the number of segments and the efficiency of the segmented cloak was investigated. The study shows that introducing a thin insulating layer inside the segmented cylindrical cloak improves its performance