Uniform estimates for small volume asymptotics.

RESUMEN: We revisit the problem of  studying the impact of a perturbation of the coefficients of an elliptic PDE on a set of small size. We show that the asymptotic structure
of the perturbed solution can be described in terms of the spectrum of the Poincaré variational operators defined by the perturbations. This approach turns out to be
useful in obtaining estimates which are uniform in the coefficient contrast.