In the ¡Krst chapter, separation of variables is used to derive the explicit particular solutions for a class of singularly perturbed di¤erential equations with constant coe¢ cients on a rectangular domain. Although only the Dirichlet boundary condition is taken into account; it can be similarly extended to other boundary conditions. Based on these results, the behavior of the solutions and their derivatives can be easily illustrated. Moreover, we have proposed a model with exact solution, which can be used to explore the behavior of layer and to test numerical methods. Hence, these analytic solutions are very important to the study in this ¡Keld. In the second chapter, we study the model of Shi¤ et al. [20]. It is a biharmonic equation on the rectangular domain [¡ a; a]£ [0; b] with clamped boundary condition. We compute its most accurate numerical solution by boundary approximation method (BAM), which is a special version of spectral method or collocation method. Its convergence unfortunately is not as good as the usual spectral method with exponential decay rate. We discover that the slowdown is due to the very mild singularity at two corners not considered by BAM. We further simplify the basis functions and their partial derivatives. Using these functions we can construct several models useful for testing numerical methods. We also explore how the stress intensity factor depends on the sizes of domain a and b, and the load ¸ by reducing the original problem with three parameters lambda, a, b to that with only one parameter t.

This paper discusses how a boundary-based surface fitting approach can be utilised to smoothly reconstruct a given human face where the scan data corresponding to the face is provided. In particular, the paper discusses how a solution to the Biharmonic equation can be used to set up the corresponding boundary value problem. We show how a compact explicit solution method can be utilised for efficiently solving the chosen Biharmonic equation. Thus, given the raw scan data of a 3D face, we extract a series of profile curves from the data which can then be utilised as boundary conditions to solve the Biharmonic equation. The resulting solution provides us a continuous single surface patch describing the original face.

Nesse trabalho estudamos questões de existência, multiplicidade e concentração de soluções de uma classe de problemas elípticos biharmônicos. Nos três primeiros capítulos são utilizados métodos variacionais para estudar a existência, multiplicidade e comportamento assintótico das soluções fracas não-triviais de equações de Schrödinger estacionárias biharmônicas com diferentes hipóteses sobre o potencial e sobre a não-linearidade. No último capítulo, o método de decomposição em cones duais é empregado para obter a existência de três soluções (positiva, negativa e nodal) para uma equação biharmônica / In this work we study some problems on existence, multiplicity and concentration of solutions of biharmonic elliptic equtions. In the first three chapters, variational methods are used to study the existence, multiplicity and the asymptotic behavior of weak nontrivial solutions of stationary Schrödinger biharmonic equations under certain assumptions on the potential function and the nonlinearity. In the last chapter we use variational methods again and also the dual decomposition method to get existence of positive, negative and sign-changing solutions for a biharmonic equation

We propose the use of Partial Differential Equations (PDEs) for shape modelling within visual cyberworlds. PDEs, especially those that are elliptic in nature, enable surface modelling to be defined as boundary-value problems. Here we show how the PDE based on the Biharmonic equation subject to suitable boundary conditions can be used for shape modelling within visual cyberworlds. We discuss an analytic solution formulation for the Biharmonic equation which allows us to define a function based geometry whereby the resulting geometry can be visualised efficiently at arbitrary levels of shape resolutions. In particular, we discuss how function based PDE surfaces can be readily integrated within VRML and X3D environments

Yes / Principal component analysis (PCA) is an elegant mechanism that reduces the dimensionality of a dataset to bring out patterns of interest in it. The preprocessing of facial images for efficient face recognition is considered to be one of the epitomes among PCA applications. In this paper, we introduce a novel modification to the method of PCA whereby we propose to utilise the inherent averaging ability of the discrete Biharmonic operator as a preprocessing step. We refer to this mechanism as the BiPCA. Interestingly, by applying the Biharmonic operator to images, we can generate new images of reduced size while keeping the inherent features in them intact. The resulting images of lower dimensionality can significantly reduce the computational complexities while preserving the features of interest. Here, we have chosen the standard face recognition as an example to demonstrate the capacity of our proposed BiPCA method. Experiments were carried out on three publicly available datasets, namely the ORL, Face95 and Face96. The results we have obtained demonstrate that the BiPCA outperforms the traditional PCA. In fact, our experiments do suggest that, when it comes to face recognition, the BiPCA method has at least 25% improvement in the average percentage error rate.

This paper discusses how a boundary-based surface fitting approach can be utilised to smoothly reconstruct a given human face where the scan data corresponding to the face is provided. In particular, the paper discusses how a solution to the Biharmonic equation can be used to set up the corresponding boundary value problem. We show how a compact explicit solution method can be utilised for efficiently solving the chosen Biharmonic equation. Thus, given the raw scan data of a 3D face, we extract a series of profile curves from the data which can then be utilised as boundary conditions to solve the Biharmonic equation. The resulting solution provides us a continuous single surface patch describing the original face.

Neste trabalho estudamos essencialmente problemas relacionados aos conceitos de superfícies e curvas bi-harmônicas e de superfícies de ângulo constante. Caracterizamos as curva bi-harmônicas do grupo especial linear SL(2,R). Em particular, mostramos que todas as curvas bi-harmônicas de SL(2,R) são hélices e damos suas parametrizações explícitas como curvas do espaço pseudo-Euclidiano R42. Estudamos as superfícies biconservativas (as quais representam uma grande família que inclui as superfícies bi-harmônicas) nos espaços de Bianchi-Cartan-Vranceanu, obtendo a caracterização daquelas de ângulo constante e daquelas SO(2)-invariantes. Também, caracterizamos as superfícies de ângulo constante do espaço Euclidiano tridimensional que possuem aplicação de Gauss bi-harmônica, provando que são cilindros de Hopf sobre uma clotóide. Além disto, caracterizamos as superfícies de ângulo contante de SL(2,R). Mais especificamente, damos uma descrição local explícita para estas superfícies em termos de uma determinada curva de SL(2,R) e de uma família a um parâmetro de isometrias do espaço ambiente. / In this work we mainly study some problems related to the concept of biharmonic curves and surfaces and to surfaces of constant angle. We characterize the biharmonic curves in the special linear group SL(2,R). In particular, we show that all proper biharmonic curves in SL(2,R) are helices and we give their explicit parametrizations as curves in the pseudo-Euclidean space R42</sub. We study the biconservative surfaces (which represent a large family including the biharmonic surfaces) in the Bianchi-Cartan-Vranceanu spaces, obtaining the characterization of those with constant angle and of those which are SO(2)-invariant. Furthermore, we characterize the constant angle surfaces of the three-dimensional Euclidean space which have bi-harmonic Gauss map, proving that they are Hopf cylinders over a clothoid. Also, we characterize the constant angle surfaces of SL(2,R). In particular, we give an explicit local description of these surfaces by means of a suitable curve of SL(2,R) and a 1-parameter family of isometries of SL(2,R).

Neste trabalho estudamos essencialmente problemas relacionados aos conceitos de superfícies e curvas bi-harmônicas e de superfícies de ângulo constante. Caracterizamos as curva bi-harmônicas do grupo especial linear SL(2,R). Em particular, mostramos que todas as curvas bi-harmônicas de SL(2,R) são hélices e damos suas parametrizações explícitas como curvas do espaço pseudo-Euclidiano R42. Estudamos as superfícies biconservativas (as quais representam uma grande família que inclui as superfícies bi-harmônicas) nos espaços de Bianchi-Cartan-Vranceanu, obtendo a caracterização daquelas de ângulo constante e daquelas SO(2)-invariantes. Também, caracterizamos as superfícies de ângulo constante do espaço Euclidiano tridimensional que possuem aplicação de Gauss bi-harmônica, provando que são cilindros de Hopf sobre uma clotóide. Além disto, caracterizamos as superfícies de ângulo contante de SL(2,R). Mais especificamente, damos uma descrição local explícita para estas superfícies em termos de uma determinada curva de SL(2,R) e de uma família a um parâmetro de isometrias do espaço ambiente. / In this work we mainly study some problems related to the concept of biharmonic curves and surfaces and to surfaces of constant angle. We characterize the biharmonic curves in the special linear group SL(2,R). In particular, we show that all proper biharmonic curves in SL(2,R) are helices and we give their explicit parametrizations as curves in the pseudo-Euclidean space R42</sub. We study the biconservative surfaces (which represent a large family including the biharmonic surfaces) in the Bianchi-Cartan-Vranceanu spaces, obtaining the characterization of those with constant angle and of those which are SO(2)-invariant. Furthermore, we characterize the constant angle surfaces of the three-dimensional Euclidean space which have bi-harmonic Gauss map, proving that they are Hopf cylinders over a clothoid. Also, we characterize the constant angle surfaces of SL(2,R). In particular, we give an explicit local description of these surfaces by means of a suitable curve of SL(2,R) and a 1-parameter family of isometries of SL(2,R).

This manuscript demonstrates the regularity and uniqueness of some geometric heat flows with critical nonlinearity. First, under the assumption of smallness of renormalized energy, several issues of the regularity and uniqueness of heat flow of harmonic maps into a unit sphere or a compact Riemannian homogeneous manifold without boundary are established. For a class of heat flow of harmonic maps to any compact Riemannian manifold without boundary, satisfying the Serrin's condition, the regularity and uniqueness is also established. As an application, the hydrodynamic flow of nematic liquid crystals in Serrin's class is proved to be regular and unique. The natural extension of all the results to the heat flow of biharmonic maps is also presented in this manuscript.

Neste trabalho estudamos alguns resultados importantes sobre a teoria das subvariedades bi-harmônicas de espaços homogêneos tridimensionais. Existem três classes de espaços homogêneos tridimensionais simplesmente conexos dependendo da dimensão do grupo de isometrias, que pode ser: 3, 4 ou 6. No caso da dimensão ser 6, M é uma forma espacial; se a dimensão do grupo de isometrias for 4, M é isométrica a: \'H IND. 3\' (grupo de Heisenberg), SU(2) (grupo unitário especial), ~SL(2,R) (revestimento universal do grupo linear especial), ou aos espaços produtos \'S POT. 2\' × R e \'H POT. 2\' × R. Feita exceção para \'H POT. 3\', no caso da dimensão ser 4 ou 6 o espaço homogêneo é localmente isométrico a (uma parte de) \'R POT. 3\', munido de uma métrica que depende de dois parâmetros reais. Tal família de métricas aparece primeiramente no trabalho [3] de L. Bianchi e, mais tarde, nos artigos [14, 35] de É. Cartan e G. Vranceanu, respectivamente. Nesse projeto de mestrado, queremos estudar (essencialmente) resultados de existência e classificação de subvariedades bi-harmônicas nesses espaços, também conhecidos como variedades de Bianchi-Cartan-Vranceanu / In this work we study some important results about the theory of the biharmonic submanifolds of tridimensional homogeneous spaces. There exist three classes of simply connected tridimensional homogeneous spaces depending on the dimension of the group of isometries, which can be: 3, 4 or 6. In the case of dimension 6, M will be a space form; if the dimension of the group of isometries is 4, M will be isometric to: either \'H IND. 3\' (Heisenbergs group), or SU(2) (special unitary group), or ~SL(2,R) (universal recovering of the special linear group), or the product spaces \'S POT. 2\' × R and \'H POT. 2\' × R. Except for \'H POT. 3\', in the case of dimension 4 or 6 the homogeneous space is locally isometric to (a part of) \'R POT. 3\', endowed with a metric that depends on two real parameters. Such family of metrics first appears in the work [3] of L. Bianchi and later in the articles [14, 35] of ´E. Cartan and G. Vranceanu, respectively. In this master thesis, we want to study (essentially) results of existence and classification of bi-harmonic submanifolds in these spaces, also known as Bianchi-Cartan-Vranceanus manifolds