General decay of the solution for a viscoelastic wave equation with a   time-varying delay term in the internal feedback
  In this paper we consider a viscoelastic wave equation with a time-varying delay term, the coefficient of which is not necessarily positive. By introducing suitable energy and Lyapunov functionals, under suitable assumptions, we establish a general energy decay result from which the exponential and polynomial types of decay are only special cases. 
Wenjun Liu
math.AP math.OC