Degeneration of algebraic hypersurfaces and applications to moduli problems : The Highest Coefficient of Det Hn and the Center at Odd Roots of 1

An important question concerning algebraic geometry and differential topology is the so-called def=diff? problem: are two complex structures on a closed compact differentiable 2n-manifold deformation of each other? In the case n=1 it is a classical result that the answer is yes, while in case n=2 the above question (Friedman-Morgan conjecture) has a positive answer in some cases, but in general is still unsolved. If we restrict to minimal algebraic surfaces of general type the above question can be interpreted in terms of properties of the moduli space of surfaces of general type. The main goal of this thesis is to study the general connectedness properties of moduli spaces of surfaces of general type and to construct some algebraic manifolds with the same underlying manifold structure that cannot be continuously deformed one in the other.