No / Various Partial Differential Equations (PDE) have been used in computer graphics for approximating surfaces of geometric shapes by finding solutions to PDEs subject to suitable boundary conditions. The PDE boundary conditions are defined as 3D curves on the surface of the shapes. We propose how to automatically derive these curves as boundaries of curved patches on the surface of the original polygon mesh. The analytic solution to the PDE used throughout this work is fully determined by finding a set of coefficients associated with parametric functions according to the particular set of boundary conditions. The PDE coefficients require an order of magnitude smaller space compared to the original polygon data and can be interactively rendered with different level of detail. It allows for an efficient exchange of the PDE shapes in 3D Cyber worlds and their web visualization. In this paper we analyze and formulate the requirements for extracting suitable boundary conditions, describe the algorithm for the automatic deriving of the boundary curves, and present its implementation as a part of the function-based extension of VRML and X3D.

Yes / Computer aided geometric design is an area where the improvement of surface generation techniques is an everlasting demand since faster and more accurate geometric models are required. Traditional methods for generating surfaces were initially mainly based upon interpolation algorithms. Recently, partial differential equations (PDE) were introduced as a valuable tool for geometric modelling since they offer a number of features from which these areas can benefit. This work summarises the uses given to PDE surfaces as a surface generation technique together

Neste trabalho analisamos, de maneira descritiva utilizando simulações, o desempenho um conjunto de estimadores para os parâmetros funcionais f, g, h e k de uma equação diferencial parcial. Para as simulações, selecionamos doze EDPs nas quais aplicaremos os estimadores as soluções dessas EDPs. Iremos medir o desempenho dos estimadores utilizando o erro quadrático entre as estimativas obtidas e os coeficientes conhecidos das EDPs. As estimativas dos coeficientes serão obtidas para soluções com e sem ruídos. Os estimadores propostos serão comparados com um grupo de estimadores diretos. Os programas para as simulações foram desenvolvidos com programas no repositório R, versão 3.2.3. Veremos que os estimadores propostos apresentaram um desempenho superior aos dos estimadores diretos, para soluções com e sem ruídos. Nas soluções com ruídos os estimadores propostos tiveram um desempenho mais significativo que para soluções sem ruídos. / In this paper we shall analyze, on a descriptive way using simulations, the performance of a set of estimators for the coefficients f, g, h and k using the following. For the simulations, we select twelve EDPs in which we will apply the estimators from the solutions from the mentioned EDPs. We will measure the performance using the quadratic error between the estimates obtained and the known coefficients from the EDPs. The estimates will be obtained for solutions with and without noises. The proposed estimators will be compared with a group of direct estimators. The programs used for the simulations were developed with the programs in the repository R, version 3.2.3. We shall see that the proposed estimators present a superior performance compared to the direct estimators, for solutions with or without noises. The proposed estimators have had a better performance in the solutions with noises than in the solutions without a noise.

Neste trabalho analisamos, de maneira descritiva utilizando simulações, o desempenho um conjunto de estimadores para os parâmetros funcionais f, g, h e k de uma equação diferencial parcial. Para as simulações, selecionamos doze EDPs nas quais aplicaremos os estimadores as soluções dessas EDPs. Iremos medir o desempenho dos estimadores utilizando o erro quadrático entre as estimativas obtidas e os coeficientes conhecidos das EDPs. As estimativas dos coeficientes serão obtidas para soluções com e sem ruídos. Os estimadores propostos serão comparados com um grupo de estimadores diretos. Os programas para as simulações foram desenvolvidos com programas no repositório R, versão 3.2.3. Veremos que os estimadores propostos apresentaram um desempenho superior aos dos estimadores diretos, para soluções com e sem ruídos. Nas soluções com ruídos os estimadores propostos tiveram um desempenho mais significativo que para soluções sem ruídos. / In this paper we shall analyze, on a descriptive way using simulations, the performance of a set of estimators for the coefficients f, g, h and k using the following. For the simulations, we select twelve EDPs in which we will apply the estimators from the solutions from the mentioned EDPs. We will measure the performance using the quadratic error between the estimates obtained and the known coefficients from the EDPs. The estimates will be obtained for solutions with and without noises. The proposed estimators will be compared with a group of direct estimators. The programs used for the simulations were developed with the programs in the repository R, version 3.2.3. We shall see that the proposed estimators present a superior performance compared to the direct estimators, for solutions with or without noises. The proposed estimators have had a better performance in the solutions with noises than in the solutions without a noise.

This dissertation is a contribution to the equilibrium theory in incomplete financial markets. It shows that, under appropriate conditions, an equilibrium exists and is unique in a general class of incomplete Brownian market environments either composed of exponential-utility-maximizing agents or populated by a class of convex-risk-measure-minimizing agents. We first use the Dynamic Programming Principle to deduce the Hamilton-Jacobi-Bellman (HJB) equation for each agent, and solve the individual optimization problem, to identify the optimal control. Using the optimal portfolio, we establish the equivalence between the existence of a stochastic equilibrium in an incomplete Brownian market and solvability of a non-linearly coupled parabolic PDE system with a homogeneously-quadratic non-linear structure. To solve this PDE system, we work mainly in anisotropic Hölder spaces. There, we construct a proper class of Hölder subspaces, where potential solutions to the equilibrium PDE system are expected to “live”. These turn out to be convex and compact under the uniform topology, thanks to the help of an Arzela-Ascoli-type theorem for unbounded domains. We then define an approapriate functional on the subspace, and show that, if we choose the parameters associated with the subspace carefully, this functional maps the subspace back to itself. After that, we apply Schauder’s fixed point theorem on a constructed subset of the subspace, and establish the existence of solutions to the PDE system, therefore equivalently, the existence of market equilibria in these general incomplete Brownian market environments. To prove the uniqueness of the solution to the parabolic PDE system, we utilize classical L2-type energy estimates and the Gronwall’s inequality. This way, we also establish the uniqueness of a market equilibrium within a class of smooth Markovian markets. / text

In this thesis, we consider parabolic partial differential equations such as the heat equation, the Fokker-Planck equation, and the porous media equation. Our aim is to develop methods that provide a priori estimates for solutions with singular initial data. These estimates are obtained by understanding the time decay of norms of solutions. First, we derive regularity results for the heat equation by estimating the decay of Lebesgue norms. Then, we apply similar methods to the Fokker-Planck equation with suitable assumptions on the advection and diffusion. Finally, we conclude by extending our techniques to the porous media equation. The sharpness of our results is confirmed by examining known solutions of these equations. The main contribution of this thesis is the use of functional inequalities to express decay of norms as differential inequalities. These are then combined with ODE methods to deduce estimates for the norms of solutions and their derivatives.

We take a model for Ferromagnetic Superconductors based on a variational energy functional, and search for radially symmetric minimizers. First we define what it means for a solution to the Euler-Lagrange equations to be admissible, before relating these admissible solutions to an appropriate function space. We then use a variational approach to prove the existence of minimizers. Since it is not clear at first whether or not the energy is bounded below, the direct method of the calculus of variations does not apply. Instead, we first prove existence in a case where the energy is bounded below, namely when the Zeeman coupling constant g vanishes. We then use the implicit function theorem to prove the existence of physically relevant minimizers for small values of g. / Thesis / Master of Science (MSc)

Yes / This work presents an efficient and fast method for achieving cyclic animation using Partial Differential Equations (PDEs). The boundary-value nature associ- ated with elliptic PDEs offers a fast analytic solution technique for setting up a framework for this type of animation. The surface of a given character is thus cre- ated from a set of pre-determined curves, which are used as boundary conditions so that a number of PDEs can be solved. Two different approaches to cyclic ani- mation are presented here. The first consists of using attaching the set of curves to a skeletal system hold- ing the animation for cyclic motions linked to a set mathematical expressions, the second one exploits the spine associated with the analytic solution of the PDE as a driving mechanism to achieve cyclic animation, which is also manipulated mathematically. The first of these approaches is implemented within a framework related to cyclic motions inherent to human-like char- acters, whereas the spine-based approach is focused on modelling the undulatory movement observed in fish when swimming. The proposed method is fast and ac- curate. Additionally, the animation can be either used in the PDE-based surface representation of the model or transferred to the original mesh model by means of a point to point map. Thus, the user is offered with the choice of using either of these two animation repre- sentations of the same object, the selection depends on the computing resources such as storage and memory capacity associated with each particular application.

No / Mass production of components with micro and nano scale surface features is known as micromoulding and is very sensitive to a number of variables that can cause important changes in the surface geometry of the components. The surface itself is regarded as a key element in determining the product's functionality and as such must be subject to thorough quality control procedures. To that end, a number of surface measurement techniques have been employed namely, White Light Interferometry (WLI) and Atomic Force Microscopy (AMF), whose resulting data is given in the form of large and rather unmanageable Cartesian point clouds. This work uses Partial Differential Equations (PDEs) as means for characterizing efficiently the surfaces associated with these data sets. This is carried out by solving the Biharmonic equation subject to a set of boundary conditions describing outer surface contours extracted from the raw measurement data. Design parameters are expressed as a function of the coefficients associated with the analytic solution of the Biharmonic equation and are then compared against the design parameters describing an ideal surface profile. Thus, the technique proposed here offers means for quality assessment using compressed data sets.

Yes / Direct parameterisation is among the most widely used facial animation techniques but requires complicated ways to animate face models which have complex topology. This paper develops a simple solution by introducing a PDE-based facial animation scheme. Using a PDE face model means we only need to animate a group of boundary curves without using any other conventional surface interpolation algorithms. We describe the basis of the method and show results from a practical implementation. / EPSRC