Stability implications of delay distribution for firstorder and
secondorder systems
Gábor Kiss  Department of Engineering Mathematics, University of Bristol, Bristol BS8 1TR, United Kingdom (email) Abstract: In application areas, such as biology, physics and engineering, delays arise naturally because of the time it takes for the system to react to internal or external events. Often the associated mathematical model features more than one delay that are then weighted by some distribution function. This paper considers the effect of delay distribution on the asymptotic stability of the zero solution of functional differential equations  the corresponding mathematical models. We first show that the asymptotic stability of the zero solution of a firstorder scalar equation with symmetrically distributed delays follows from the stability of the corresponding equation where the delay is fixed and given by the mean of the distribution. This result completes a proof of a stability condition in [Bernard, S., Bélair, J. and Mackey, M. C. Sufficient conditions for stability of linear differential equations with distributed delay. Discrete Contin. Dyn. Syst. Ser. B, 1(2):233256, 2001], which was motivated in turn by an application from biology. We also discuss the corresponding case of secondorder scalar delay differential equations, because they arise in physical systems that involve oscillating components. An example shows that it is not possible to give a general result for the secondorder case. Namely, the boundaries of the stability regions of the distributeddelay equation and of the meandelay equation may intersect, even if the distribution is symmetric.
Keywords: Differential Equations, Distributed Delay, Hybrid testing.
Received: February 2009; Revised: August 2009; Available Online: December 2009. 
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