Eigenvalue asymptotics for Sturm--Liouville operators with singular   potentials
  We derive eigenvalue asymptotics for Sturm--Liouville operators with singular complex-valued potentials from the space $W^{\al-1}_{2}(0,1)$, $\al\in[0,1]$, and Dirichlet or Neumann--Dirichlet boundary conditions. We also give application of the obtained results to the inverse spectral problem of recovering the potential from these two spectra. 
Rostyslav O. Hryniv and Yaroslav V. Mykytyuk