“…], we establish that the process U t,t 0 has a unique pullback attractor. However, as far as we know, there are no results in the literature concerning regularity of the pullback attractor as we will consider in this paper (for similar results for the reaction-diffusion equations see [2,4], and for the Navier-Stokes equations see [10]). The regularity results on the solutions and the attractors (that we obtain here) might be useful in the future in order to implement new methods to seek solutions of more general problems by different arguments, to gain attraction in higher norms, or for numerical purposes.…”