Completeness, Ricci blowup, the Osserman and the conformal Osserman   condition for Walker signature (2,2) manifolds
  Walker manifolds of signature (2,2) have been used to provide examples of Osserman and of conformal Osserman manifolds of signature (2,2). We study questions of geodesic completeness and Ricci blowup in this context. 
M. Brozos-Vazquez, P. Gilkey, E. Garcia-Rio, and R. Vazquez-Lorenzo