  A new definition of discrete-time negative imaginary (NI) systems is
provided. This definition characterizes the dissipative property of a
zero-order hold sampled continuous-time NI system. Under some assumptions,
asymptotic stability can be guaranteed for the closed-loop interconnection of
an NI system and an output strictly negative imaginary system, with one of them
having a one step advance. In the case of linear systems, we also provide
necessary and sufficient frequency-domain and LMI conditions under which the
definition is satisfied. Also provided is a simple DC gain condition for the
stability results in the linear case.
