Robust stability of the linear time-delay systems with indefinite delay

Usually physical control systems such as that of stabilization of the current in tokamaks, or that of stabilization of the form of the plasma in tokamaks should operate adequately in presence of various of uncertain factors. These factors include both the uncertainty in the mathematical description of the processes and some external perturbations of the system under consideration. This note is devoted to the qualitative analysis of control dynamical systems subjected to the parametrical type of uncertainty. The main goal of the note is to obtain some new bounds on system delay within which the system preserves Such qualitative characteristics as, for example, given stability margin, or (and) given oscillation margin. Results presented in the note may have direct application in analysis and synthesis of robust regulators described by differential-difference equations.