Hindawi Publishing Corporation Mathematical Problems in Engineering Volume 2009, Article ID 610574, 13 pages doi:10.1155/2009/610574 Research Article Intermittent Behavior and Synchronization of Two Coupled Noisy Driven Oscillators ˆ Angela Maria dos Santos, 1, 2 S´ ergio Roberto Lopes, 1 and Ricardo Luiz Viana 1 1 Departamento de F´ ısica, Universidade Federal do Paran´ a, Caixa Postal 19044, 81531-990 Curitiba, Paran´ a, Brazil 2 Setor Escola T´ ecnica, Universidade Federal do Paran´ a, UNED Paranagu´ a, 83215-750 Paranagu´ a, Paran´ a, Brazil Correspondence should be addressed to Ricardo Luiz Viana, viana@fisica.ufpr.br Received 12 September 2008; Revised 18 November 2008; Accepted 23 February 2009 Recommended by Elbert E. Neher Macau The coupled system of two forced Li´ enard-type oscillators has applications in diode-based electric circuits and phenomenological models for the heartbeat. These systems typically exhibit intermittent transitions between laminar and chaotic states; what affects their performance and, since noise is always present in such systems, dynamical models should include these effects. Accordingly, we investigated numerically the effect of noise in two intermittent phenomena: the intermittent transition to synchronized behavior for identical and unidirectionally coupled oscillators, and the intermittent transition to chaos near a periodic window of bidirectionally coupled oscillators. We found that the transition from a nonsynchronized to a synchronized state exhibits a power-law scaling with exponent 3/2 characterizing on-off intermittency. The inclusion of noise adds an exponential tail to this scaling. Copyright q 2009 ˆ Angela Maria dos Santos et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1. Introduction Intermittency is a ubiquitous phenomenon in nonlinear dynamics. It consists of the intermittent switching between a laminar phase of regular behavior and irregular bursts. In one-dimensional quadratic-type maps it was first associated with a saddle-node bifurcation by Pomeau and Manneville, who also described its scaling characteristics 1. A comprehensive theory of intermittency for such systems is now available 2. Another context in which intermittency appears is related to the synchronization of coupled nonlinear oscillators. Synchronization of nonlinear oscillators is a subject with a venerable history dating back from the early observation by Huygens that two pendula suspended from the same