On the Hill's Operator with Matrix Potential
  In this article we obtain the asymptotic formulas for the eigenvalues and eigenfunctions of the self-adjoint operator generated by a system of Sturm-Liouville equations with summable coefficients and the quasiperiodic boundary conditions. Then using these asymptotic formulas, we find the conditions on the potential for which the number of gaps in the spectrum of the Hill's operator with matrix potential is finite. 
O.A.Veliev