“…Therefore χ is an important number that characterizes the asymptotic behavior of the solutions to Timoshenko system. This was proved to memory viscoelastic constitutive laws in [1,3,4,6,8,12]; to thermoelastic constitutive laws with Fourier law and also to thermoelastic dissipation of type III in [10,12,23]; to Timoshenko system with boundary dissipation in [15,16] and also with locally distributed dissipation [18][19][20]. Of course, since Timoshenko system is a two-by-two system of hyperbolic equations, if there exist two dissipative mechanisms, we always get the exponential stability, no matter if the velocities of propagations are equal or not, see [13,14,21].…”