Alexandr Kuznetsov

Examples of mechanical systems are discussed, where quasi-periodic motions may occur, caused by an irrational ratio of the radii of rotating elements that constitute the system. For the pendulum system with frictional transmission of rotation between the elements, in the conservative and dissipative cases we note the coexistence of an infinite number of stable fixed points, and in the case of the self-oscillating system the presence of many attractors in the form of limit cycles and of quasi-periodic rotational modes is observed. In the case of quasi-periodic dynamics the frequencies of spectral components depend on the parameters, but the ratio of basic incommensurate frequencies remains constant and is determined by the irrational number characterizing the relative size of the elements.

Ensembles of several chaotic R¨ossler oscillators are considered. It is shown that a typical phenomenon for such systems is the emergence of invariant tori of different and sufficiently high dimension. The possibility of a quasi-periodic Hopf bifurcation and of the cascade of such bifurcations based on tori of increasing dimension is demonstrated. The domains of resonant tori are revealed whose boundaries correspond to a saddle-node bifurcation. Within areas of resonant modes the torus-doubling bifurcations and tori destruction are observed.

The model of three linear-coupled logistic maps is examined. The structure of parameter plane (coupling value—period-doubling parameter) is discussed. We select configuration of coupling and parameters so, that regimes of three-frequency quasiperiodicity become possible. Also we consider bifurcations associated with such states.

The dynamics of two coupled generators of quasiperiodic oscilltaions is studied. The opportunity of complete and phase synchronization of generators in the regime of quasiperiodic oscillations is obtained. The features of structure of parameter plane is researched using charts of dynamical regimes and charts of Lyapunov exponents, in which typical structures as resonance Arnold web were revealed. The possible quasiperiodic bifurctions in the system are discussed.

A phenomenon of interaction between three reactively coupled Van der Pol oscillators is considered in the paper. Phase equations are being obtained in second order approximation. Bifurcation analysis and Lyapunov’s exponent maps are used for illustrating system behavior. The paper consider significant features of reactive coupling. Complicated original system behavior with steering parameter growth is being considered too.

The conditions are discussed for which the ensemble of interacting oscillators may demonstrate Landau–Hopf scenario of successive birth of multi-frequency regimes. A model is proposed in the form of a network of five globally coupled oscillators, characterized by varying degree of excitement of individual oscillators. Illustrations are given for the birth of the tori of increasing dimension by successive quasi-periodic Hopf bifurcation.

Nephrons (functional units of the kidney) may be described by means of the system of order differential equations. This provides an opportunity to describe dynamics of both the individual and coupled nephrons by using the theory of dynamical systems and the bifurcation theory. Considering a model of a pair of vascular coupled nephrons the present paper examines the effect that the non-identity of nephrons, i. e. non-identity of peak-to-peak variations in their arteriolar radii in autonomous state, has on the behavior of the coupled system. We investigate the appearance possibility of so-called broadband synchronization region, where the stronger nephron starts to suppress the autonomous oscillations of the weaker nephron. We investigate also the appearance possibility of the regime of total oscillator death, where oscillations of both nephrons are abolished.

We suggest a simple two-dimensional map, parameters of which are the trace and Jacobian of the perturbation matrix of the fixed point. On the parameters plane it demonstrates the main universal bifurcation scenarios: the threshold to chaos via period-doublings, the situation of quasiperiodic oscillations and Arnold tongues. We demonstrate the possibility of implementation of such map in radiophysical device.

We examine the dynamics of the coupled system consisting of subsystems, demonstrating the Neimark–Sacker bifurcation. The study of coupled maps on the plane of the parameters responsible for such bifurcation in the individual subsystems is realized. On the plane of parameters characterizing the rotation numbers of the individual subsystems we reveal the complex structures consisting of the quasi-periodic modes of different dimensions and the exact periodic resonances of different orders.

The problem of external driving by the harmonic signal of two coupled self-oscillators is investigated. Comparison with the synchronization picture for phase oscillators is given. We discuss the configuration of periodic, two- and three-frequency regimes in the parameter space of external signal. The illustrations of three-frequency tori and resonance two-frequency tori are given. A number of significant differences from the bifurcation mechanisms for the destruction of synchronization are found compared with the case of phase oscillators.

The problem of the dynamics of phase oscillators is discussed with an increasing their numbers. We discuss the organization of the parameters plane responsible for the frequency detunings of the oscillators and amplitude of the dissipative coupled. The region of complete synchronization, quasi-periodic oscillations of different dimension and chaos are are observed. We discuss the changing of the synchronization picture with an increasing of the number of oscillators in the chain. We use the method of charts of Lyapunov exponents and modification of the method of charts of dynamical regimes visualized two-frequency resonant tori of different types.

The pulse driven Rossler system before the saddle-node bifurcation in the regime of divergence is considered. It is shown that external pulses initiate stable periodic and quasi-periodic regimes in non-autonomous system. The effect of synchronous response due interaction between external signal and own rhythm of autonomous system concerned with the «rotation» of the representation point in the three-dimensional phase space is observed. It is revealed that the torus doublings in the stroboscopic section exist in the certain area on the parameter plane of external force in this system.

In paper we suggest an example of system which dynamics is answered to conception of a «critical quasi-attractor». Besides the brief review of earlier obtained results the new results are presented, namely the illustrations of scaling for basins of attraction of elements of critical quasi-attractor, the renormalization group approach in the presence of additive uncorrelated noise, the calculation of universal constant responsible for the scaling regularities of the noise effect, the illustrations of transitions initialized by noise that are realized between coexisted attractors.