“…Stability of evolution equations of hyperbolic type with linear or nonlinear autonomous feedbacks has been the object of many works. Let us quote the stability of the wave equation [29,30,32,33,35,40,64], of the elastodynamic system [1,8,18,19,20,22,36,61], of the Petrovsky system [17,33,34], of Mawxell's system [5,15,31,54,59] or combination of them [13,25,53], see also the references cited in the aforementioned works. On the contrary the case of nonautonomous damping is less considered in the literature, let us quote [14,23,45,46,47,49,50,51,60] for the wave equation and [6,7] for the Lamé systems.…”