Some Hardy type inequalities in the Heisenberg group. Han, Yazhou; Niu, Pengcheng — 2003 JIPAM. Journal of Inequalities in Pure & Applied Mathematics [electronic only]
A Hardy inequality with remainder terms in the Heisenberg group and the weighted eigenvalue problem. Dou, Jingbo; Niu, Pengcheng; Yuan, Zixia — 2007 Journal of Inequalities and Applications [electronic only]
Morrey estimates for parabolic nondivergence operators of Hörmander type Sufang Tang; Pengcheng Niu — 2010 Rendiconti del Seminario Matematico della Università di Padova