A weighted $L_p$-theory for second-order elliptic and parabolic partial   differential systems on a half space
  In this paper we develop a Fefferman-Stein theorem, a Hardy-Littlewood theorem and sharp function estimations in weighted Sobolev spaces. We also provide uniqueness and existence results for second-order elliptic and parabolic partial differential systems in weighed Sobolev spaces. 
Kyeong-Hun Kim and Kijung Lee
math.AP