RESUMEN

The concentration C(  x,t ) of a solute in a saturated porous medium is governed by a second-order parabolic equation. n the case that b s periodic and divergence free, and Dij are constants and  (( D_ij )) positive definite, the concentration is asymptotically Gaussian for large times. This article analyzes the dependence of the dispersion matrix K of the limiting Gaussian distribution on the velocity parameter U_o and the period “a”. It is shown that each coefficient Kii is asymptotically quadratic in aU_o if b_i - b_i has a nonzero component in the null space and asymptotically constant belongs to the range of   b. It is shown in a more general context that K epends only on aUo. An asymptotic expansion of the Cramer–Edgeworth type is derived for concentration refining the Gaussian approximationPrincipio del formulario

We provide non-ergodicity criteria for denumerable continuous time Markov processes in terms of test functions. Two examples are given where the non-ergodicity criteria are applied.