Global Practical Tracking for High-Order Uncertain Nonlinear Systems with Unknown Control Directions. - XueHua Yan; YunGang Liu (SIAM J. Control. Optim., 2010)

Global practical tracking by output-feedback for nonlinear systems with unknown growth rate. - XueHua Yan; YunGang Liu (Sci. China Inf. Sci., 2011)

The further result on global practical tracking for high-order uncertain nonlinear systems. - XueHua Yan; YunGang Liu (J. Syst. Sci. Complex., 2012)