Abstract: In Chapter 1 we consider the following system of semilinear elliptic equations: LU = F(x, U) + T? + H(x), U = 0, where l = diag (L, L), T E 2, L is a 2nd order elliptic operator in the divergent form, H is a fixed vector-function in C?(?) x C?(?) and <P~ is a positive eigenfunction of ?'1 the dual operator of L. Using the Monotonic Iteration Method and Degree Theory, we find a curve r that splits the plane into two disjoint unbounded domains E and N ( 2 = E U N U ) such that: ... Note: The complete abstract is available with the full electronic digital thesis or dissertations Ver menos