Volume 83, Number 4, August 2008
Article Number 48001
Number of page(s) 6
Section Interdisciplinary Physics and Related Areas of Science and Technology
Published online 19 August 2008
EPL, 83 (2008) 48001
DOI: 10.1209/0295-5075/83/48001

Unstable dynamical systems: Delays, noise and control

J. G. Milton1, J. L. Cabrera2 and T. Ohira3

1  Joint Science Department, The Claremont Colleges - Claremont, CA 91711, USA
2  Centro de Física I. V. I. C. - Caracas 1020-A, Venezuela
3  Sony Computer Science Laboratories, Inc. - Tokyo, 141-0022, Japan

received 4 November 2007; accepted in final form 30 June 2008; published August 2008
published online 19 August 2008

Escape from an unstable fixed point in a time-delayed dynamical system in the presence of additive white noise depends on both the magnitude of the time delay, $\tau$, and the initial function. In particular, the longer the delay the smaller the variance and hence the slower the rate of escape. Numerical simulations demonstrate that the distribution of first passage times is bimodal, the longest first passage times are associated with those initial functions that cause the greatest number of delayed zero crossings, i.e. instances where the deviations of the controlled variable from the fixed point at times t and t-$\tau$ have opposite signs. These observations support the utility of control strategies using pulsatile stimuli triggered only when variables exceed certain thresholds.

87.18.Tt - Noise in biological systems.
02.30.Ks - Delay and functional equations.
02.50.Ey - Stochastic processes.

© EPLA 2008