Spectral and Homogenization Problems

In this dissertation we will address two types of homogenization problems. The first one is a spectral problem in the realm of lower dimensional theories, whose physical motivation is the study of waves propagation in a domain of very small thickness and where it is introduced a very thin net of heterogeneities. Precisely, we consider an elliptic operator with epsilon-periodic coefficients and the corresponding Dirichlet spectral problem in a three-dimensional bounded domain of small thickness delta. We study the asymptotic behavior of the spectrum as epsilon and delta tend to zero. This asymptotic behavior depends crucially on whether epsilon and delta are of the same order (delta ≈ epsilon), or epsilon is of order smaller than that of delta (delta = epsilon tau, tau < 1), or epsilon is of order greater than that of delta (delta = epsilontau, tau > 1). We consider all three cases.;The second problem concerns the study of multiscale homogenization problems with linear growth, aimed at the identification of effective energies for composite materials in the presence of fracture or cracks. Precisely, we characterize (n + 1)-scale limit pairs (u, U ) of sequences {(uepsilon LN&fll0;W ,Du3&fll0;W &parr0;&cubr0;3>0 ⊂ M&parl0;W;R d&parr0;xM&parl0;W; RdxN &parr0; whenever {uepsilon}epsilon>0 is a bounded sequence in BV(O; Rd ). Using this characterization, we study the asymptotic behavior of periodically oscillating functionals with linear growth, defined in the space BV of functions of bounded variation and described by n ∈ N microscales.