La thèse se compose de 3 parties. Dans la partie I, nous considérons des problèmes à lafrontière pour une EDP de Laplace dans un domaine simplement connexe de bordLispschitz continu. Depuis des données Dirichlet et Neumann suffisamment régulièresdisponibles sur une partie de la frontière, nous développons une méthode non-itérative derésolution de ce problème de Cauchy, régularisé par une contrainte en norm L2 portantsur la solution sur la partie complémentaire du bord. Notre approche par les fonctionsanalytiques de la variable complexe permet d'imposer des contraintes ponctuellessupplémentaires possédant un intêret pratique pour incorporer des mesures corrompues.La partie II concerne la structure spectrale d'un opérateur de Poisson tronqué intervenantdans diverses applications physiques. Nous établissons d'importantes propriétés dessolutions, des connexions avec d'autres problèmes, ainsi que, pour des valeursasymptotiques d'un paramètre, des formulations sous forme d'autres équations intégralesou EDO solubles. Dans la partie III, nous traitons un problème inverse particulier issud'expériences pratiques effectuées avec un microscope SQUID. Depuis des mesurespartielles de la composante verticale du champ magnétique, le but est de retrouvercertaines propriétés de l'aimantation d'un échantillon de roche. Nous présentons denouvelles méthodes utilisant les transformations de Kelvin et de Fourier pour l'estimationdu moment magnétique. / The thesis consists of three parts. In Part I, we consider partially overdeterminedboundary-value problemS for Laplace PDE in a planar simply connected domain withLipschitz boundary. Assuming Dirichlet and Neumann data available on its part to be realvaluedfunctions of certain regularity, we develop a non-iterative method for solving thisill-posed Cauchy problem choosing as a regularizing parameter L2 bound of the solutionon complementary part of the boundary. The present complex-analytic approach alsonaturally allows imposing additional pointwise constraints on the solution which, onpractical side, can help incorporating outlying boundary measurements without changingthe boundary into a less regular one. Part II is concerned with spectral structure of atruncated Poisson operator arising in various physical applications. We deduce importantproperties of solutions, discuss connections with other problems and pursue differentreductions of the formulation for large and small values of asymptotic parameter yieldingsolutions by means of solving simpler integral equations and ODEs. In Part III, we dealwith a particular inverse problem arising in real physical experiments performed withSQUID microscope. The goal is to recover certain magnetization features of a sample frompartial measurements of one component of magnetic field above it. We develop newmethods based on Kelvin and Fourier transformations resulting in estimates of netmoment components.

Mathematical theory of homogenization of partial differential equations is relatively a new area of research (30-40 years or so) though the physical and engineering applications were well known. It has tremendous applications in various branches of engineering and science like : material science ,porous media, study of vibrations of thin structures, composite materials to name a few. There are at present various methods to study homogenization problems (basically asymptotic analysis) and there is a vast amount of literature in various directions. Homogenization arise in problems with oscillatory coefficients, domain with large number of perforations, domain with rough boundary and so on. The latter one has applications in fluid flow which is categorized as oscillating boundaries. In fact ,in this thesis, we consider domains with oscillating boundaries. We plan to study to homogenization of certain optimal control problems with oscillating boundaries. This thesis contains 6 chapters including an introductory Chapter 1 and future proposal Chapter 6. Our main contribution contained in chapters 2-5. The oscillatory domain under consideration is a 3-dimensional cuboid (for simplicity) with a large number of pillars of length O(1) attached on one side, but with a small cross sectional area of order ε2 .As ε0, this gives a geometrical domain with oscillating boundary. We also consider 2-dimensional oscillatory domain which is a cross section of the above 3-dimensional domain. In chapters 2 and 3, we consider the optimal control problem described by the Δ operator with two types of cost functionals, namely L2-cost functional and Dirichlet cost functional. We consider both distributed and boundary controls. The limit analysis was carried by considering the associated optimality system in which the adjoint states are introduced. But the main contribution in all the different cases(L2 and Dirichlet cost functionals, distributed and boundary controls) is the derivation of error estimates what is known as correctors in homogenization literature. Though there is a basic test function, one need to introduce different test functions to obtain correctors. Introducing correctors in homogenization is an important aspect of study which is indeed useful in the analysis, but important in numerical study as well. The setup is the same in Chapter 4 as well. But here we consider Stokes’ Problem and study asymptotic analysis as well as corrector results. We obtain corrector results for velocity and pressure terms and also for its adjoint velocity and adjoint pressure. In Chapter 5, we consider a time dependent Kirchhoff-Love equation with the same domain with oscillating boundaries with a distributed control. The state equation is a fourth order hyperbolic type equation with associated L2-cost functional. We do not have corrector results in this chapter, but the limit cost functional is different and new. In the earlier chapters the limit cost functional were of the same type.