Energy decay rates for solutions of the wave equation with boundary damping and source term

In this paper, we consider the wave equation $$u'' - \Delta u = |u|^\rho u$$ with the following nonlinear boundary condition $$\frac{\partial u}{\partial \nu} + \int\limits^t_0 k(t-s,x)u'(s){\rm d}s + a(x)g(u') = 0.$$ We show energy decay rates for solutions of the wave equation in bounded domain with nonlinear boundary damping and source term.