“…The equation (1.6) has been considered in several papers, see for instance [19,20,23,29,14,21,1,13], the review paper [30] and the recent monograph [22]. For the homogeneous boundary conditions (u = 0 at both ends, corresponding to J b = 0), it is well known that the initial-boundary value problem for (1.6) is well-posed for initial data (u 0 , ∂ t u 0 ) ∈ H 1 0 (I) × L 2 (I), for k(x) ∈ L ∞ (I) with k(x) ≥ 0, and decay estimates for the energy are obtained, either exponential or polynomial.…”