Fractional Sobolev-Poincare inequalities in irregular domains
  This paper is devoted to the study of fractional (q,p)-Sobolev-Poincare inequalities in irregular domains. In particular, we establish (essentially) sharp fractional (q,p)-Sobolev-Poincare inequality in s-John domains and in domains satisfying the quasihyperbolic boundary conditions. When the order of the fractional derivative tends to 1, our results tends to the results for the usual derivative. Furthermore, we verified that those domains that support the fractional (q,p)-Sobolev-Poincare inequality together with a separation property are s-diam John domains for certain s, depending only on the associated data. We also point out an inaccurate statement in [2]. 
Chang-Yu Guo
math.FA