Jacob Kogan and A. Leizarowitz, "Frequency domain criterion for robust stability of interval time-delay systems", Automatica, 1995, Vol. 31, No. 3, pp. 463-469.
Stability conditions for time-delay systems are of great importance for industrial applications. Delays often occur in the transmission of information or material between different parts of a system. Transportation systems, communication systems, chemical processing systems, metallurgical processing systems, environmental systems, and power systems are examples of time-delay systems. The mathematical formulation of a time-delay system results in a system of delay-differential equations. Any mathematical model of an engineering system possesses the unavoidable inaccuracy. The existence of the inaccuracies implies that the analysis of stability and performance as well as system design, based on a nominal model only, may not be meaningful in applications.
In this paper, a new criterion is described for robust stability of interval time-delay systems.
From the authors' summary