Two-dimensional isochronous nonstandard Hamiltonian systems
  We identify a generic class of two dimensional nonstandard Hamiltonian systems which exhibit isochronous behaviour. This class of systems belongs to the two dimensional mixed Li\'enard- type equations and is obtained by generalizing the scalar modified Emden equation (MEE) to two dimensions. We show that the generalized class of equations admits a Hamiltonian description and exhibits periodic and quasi-periodic oscillations for suitable choice of parameters and also $\emph PT$ symmetric property. 
A. Durga Devi, R. Gladwin Pradeep, V. K. Chandrasekar and M.   Lakshmanan
nlin.SI