On Hermite-Hadamard Type Integral Inequalities for preinvex and   log-preinvex functions
  In this paper, we extend some estimates of the left hand side of a Hermite- Hadamard type inequality for nonconvex functions whose derivatives absolute values are preinvex and log-preinvex. 
Mehmet Zeki Sarikaya, Hakan Bozkurt and Necmettin Alp
math.FA