This Letter introduces a new method-mode decomposition-for stability analysis of periodic orbits. Using this method, the stability of a periodic solution of an autonomous system, as well as the stability of synchronization within three chaotic systems with linear coupling, can be analyzed. As an example, a rigorous sufficient condition on the coupling coefficients for achieving chaos synchronization is obtained, for the case of three-coupled identical Lorenz systems. Numerical simulations are shown for demonstration.

All cell components exhibit intracellular noise due to random births and deaths of individual molecules, and extracellular noise due to environment perturbations. In particular, gene regulation is an inherently noisy process with transcriptional control, alternative splicing, translation, diffusion and chemical modification reactions, which all involve stochastic fluctuations. Such stochastic noises may not only affect the dynamics of the entire system but may also be exploited by living organisms to actively facilitate certain functions, such as cooperative behavior and communication. Results: We have provided a general model and an analytic tool to examine the cooperative behavior of a multi-cell system with both intracellular and extracellular stochastic fluctuations. A multi-cell system with a synthetic gene network is adopted to demonstrate the effects of noises and coupling on collective dynamics. These results establish not only a theoretical foundation but also a quantitative basis for understanding essential roles of noises on cooperative dynamics, such as synchronization and communication among cells.

An effective method of chaotification via time-delay feedback for a simple finite-dimensional continuous-time autonomous system is made rigorous in this paper. Some mathematical conditions are derived under which a nonchaotic system can be controlled to become chaotic, where the chaos so generated is in a rigorous mathematical sense of Li-Yorke in terms of the Marotto theorem. Numerical simulations are given to verify the theoretical analysis. Chaos has been found useful lately in various areas of science, engineering, and technology. Therefore, purposefully generating chaos (called chaotification, or anticontrol of chaos) has investigated rather intensively in the past few years. Recently, Wang, Chen, and Yu [Chaos 10, 771-779 (2000)] developed an anticontrol method via time-delay feedback for chaotifying a continuous-time dynamical system. The fundamental idea of this anticontrol method is correct and insightful, but a time-delay differential equation used therein is only approximated by a related discrete map, leaving some room for improvement. To present a mathematically rigorous approach, this paper adopts the same anticontrol idea but further improves its technical contents thereby deriving a similar yet rigorous design method for chaotificaiton. A rather general continuous-time system can be driven from nonchaotic to chaotic by using time-delay feedback perturbation on the system parameters or employing an exogenous time-delay state-feedback input, where the generated chaos is in a precise mathematical sense of Li-Yorke in terms of the Marotto theorem.

Tyson [Ann. NY Acad. Sci. 316 (1979) 279] conjectured that the stable homogeneous positive steady state may coexist with stable echo wave (meaning anti-phase wave) in linearly coupled Oregonators (and thus gave a conjecture on the bifurcation diagram of this system). In this paper, we rigorously prove stability of the in-phase wave and existence of the anti-phase wave. Our proof procedure actually gives a general method (or line) to deal with the analogous problem. For instance, to prove stability of the in-phase wave, following our line one may decompose the corresponding variational equations (a four-dimensional system) into two independent planar systems; also for instance, existence of the anti-phase wave can be concluded as existence and uniqueness of limit cycle of the associate oscillator. In addition, according to parameter regimes of existence of the anti-phase wave and the stable homogeneous positive steady state, we give their coexistence regime and specify it, and in particular give the regime of the coupled coefficient. The specified results show that the theoretical results are in good accord with Tyson's numerical results.