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Relaxation oscillations are ubiquitous in various fields of natural science and engineering technology. Exploring possible routes to relaxation oscillations is one of the important issues in the study of relaxation oscillations. Recently, the pulse-shaped explosion (PSE), a novel mechanism which can lead to relaxation oscillations, has been reported. The PSE means pulse-shaped sharp quantitative changes related the variation of system parameters in branches of equilibrium points and limit cycles, which leads the system’s trajectory to undertake sharp transitions and further induces relaxation oscillations. Regarding externally and parametrically excited nonlinear systems with different frequency ratios, some work on PSE has been reported. The present paper focuses on the PSE and the related relaxation oscillations in a externally and parametrically excited Mathieu-van der Pol-Duffing system. We show that if there is an initial phase difference between the slow excitations with the same frequency ratio, the fast subsystem may compose of two parts with different expressions, each of which determines a different vector field. As a result, the bistable behaviors are observed in the system. In particular, one of the vector fields exhibits two groups of bifurcation behaviors, which are symmetric with respect to the positive and negative PSE, and each can induce a cluster in the relaxation oscillations. Based on this, we present several routes to compound relaxation oscillations, and obtain new types of relaxation oscillations connected by pulse-shaped explosion, which we call compound “subHopf/fold-cycle” relaxation oscillations and compound “supHopf/supHopf” relaxation oscillations, respectively. Our results show that the two clusters in the resultant relaxation oscillations are connected by the PSE, and the initial phase difference plays an important role in transitions to different attractors and the generation of relaxation oscillations. Although the research in this paper is based on a specific nonlinear system, we would like to point out that the bistable behaviors, the PSE and the resultant compound relaxation oscillations can also be observed in other dynamical systems. The reason is that the fast subsystem composes of two different vector fields induced by the initial phase difference, which dose not rely on a specific system. The results of this paper deepen the research about PSE as well as the complex dynamics of relaxation oscillations.

The main purpose of this study is to investigate the characteristics as well as the bifurcation mechanisms of the bursting oscillations in the asymmetrical dynamical system with two scales in the frequency domain. Since the slow-fast Hodgkin-Huxley model was established to successfully reproduce the activities of neuron, the complicated dynamics of the system with multiple time scales has become a hot research topic due to the wide engineering background. The dynamical system with multiple scales often presents periodic oscillations coupled by large-amplitude oscillations at spiking states and small-amplitude oscillations at quiescent states, which are connected by bifurcations. Up to now, most of the reports concentrate on bursting oscillations in the symmetric systems, in which there exists only one form of spiking oscillations and quiescence, respectively. Here we explore some typical forms of bursting behavior in an asymmetrical dynamical system with periodic excitation, in which there exists an order gap between the exciting frequency and the natural frequency. As an example, based on the typical Chua's oscillator, by introducing an asymmetrical controller and a periodically changed current source, and choosing suitable parameter values, we establish an asymmetrical dynamical system with two scales in the frequency domain. Since the exciting frequency is much smaller than the natural frequency, the whole periodic exciting term can be regarded as a slowly-varying parameter, leading to the fast subsystem in autonomous form. Since all the equilibrium curves and relevant bifurcations are presented in the form related to the slowly-varying parameter, the transformed phase portraits describing the evolution relationship between the state variables and the slowly-varying parameter are employed to account for the mechanism of the bursting oscillations. With the variation of the slowly-varying parameter, different equilibrium states and relevant bifurcations in the fast subsystem are presented. It is found that for different parameter values, multiple balance curves of the fast subsystem may coexist, which affect the structure of the bursting attractor. For the other parameters fixed to certain values, the balance curve with the variation of the slowly-varying parameter is presented. Three typical cases with different exciting amplitudes are considered, corresponding to different situations of coexistence of equilibrium states in the fast subsystem. In the first case, there exist at most three stable equilibrium points in the fast subsystem. Bursting attractor that oscillates around the three points can be observed, in which fold and Hopf bifurcations lead to the alternations between spiking states and quiescent states, while in the second case, saddle on the limit cycle bifurcation may cause the repetitive spiking oscillations to jump to the equilibrium curve. In the third case with relatively large exciting amplitude, only two equilibrium curves may involve the bursting oscillations, in which fold bifurcations lead to the alternation between the quiescent states and spiking states. Unlike the structures of bursting oscillations in the symmetric system, different forms of asymmetrical bursting oscillations with different periodic exciting amplitudes can be observed, the mechanisms of which are presented. It is pointed out that the change of the external exciting amplitude, does not only cause the variation of the attracting basins corresponding to different stable equilibrium branches, but also leads to the change of the temporal intervals when the trajectory passes different bifurcation points, respectively, which results in different patterns of bursting oscillations. Furthermore, since the slowly-varying parameter determined by the whole exciting term changes between two extreme values determined by the amplitude, the trajectory of the bursting oscillations of the transformed phase portrait returns at the two extreme values. The properties of equilibrium branches between the two extreme values determine the forms of the moving attractors.

Since most of the work relevant to the control of Chen system is based on the same time scale, and the results associated with the coupled systems with two time scales are mainly for the cases with only one slow variable, in this paper we investigate the dynamical evolution of the Chen system with the controller described by Duffing oscillator on a slow time scale, which implies two slow variables may be involved in the coupled vector field. Different types of bursting oscillations such as the symmetric fold/fold bursting, symmetric fold/Hopf bursting, symmetric homoclinic/homoclinic bursting, and mechanism are presented, revealing that the mutual influence between the two slow variables may cause the bursting behaviors similar to those in the periodic excited systems.

A nonlinear circuit model with periodic switching is established. The fold bifurcation and Hopf bifurcation sets of the subsystems are derived via the analysis of the relevant equilibrium points as well as the stabilities. Complex dynamical behaviors caused by periodic switching in various equilibrium states of subsystems are investigated. The results show that there exist two types of destabilizing cases, i.e., period-doubling bifurcation and saddle-node bifurcation, in the variation of periodic solution to the switching system with parameter, leading to different forms of chaotic oscillations correspondingly. Furthermore, by analyzing the the phase trajectory and its corresponding bifurcation, the mechanisms for different types of oscillations are presented, which can explain some phenomena of the switched dynamical system.

Based on the classical Chua's circuit, a four-dimensional Generalized Chua's circuit with multiple interfaces is established by introducing feedback elements. For the appropriate condition, there exists a difference in order of magnitude between the variables of state and a fast-slow coupled system, thereby forming a fast- and slow-coupled system at time scale. Analyzing the equilibrium points and the characteristics of the fast subsystems, and combining the theory of Clarke differential inclusions, the singularities on the non-smooth boundaries are explored. Two types of periodic bursting phenomena for different conditions are presented. Fast-slow analysis is employed to explore the special cluster phenomenon while the system trajectory passes across multiple interfaces. The coexisting different bursting mechanisms for the case with multiple attractors are explored in detail, while the influence of non-smooth bifurcations on bursting behavior is revealed.

Based on the production kinetics of oxide-trapped charge and interface-trapped charge and the microscopic mechanism of radiation damage, a model of post-irradiation threshold voltage drift due to oxide trap and interface trap as a function of radiation dose is proposed. This model predicts that the post-irradiation threshold voltage drift due to oxide trap and interface trap would be linear in dose at low dose levels. At high dose levels, the post-irradiation threshold voltage drift due to oxide trap tend to be saturated, its peak value has no correlation with radiation dose, and the post-irradiation threshold voltage drift due to interface trap has an exponential relationship with radiation dose. In addition, the model indicates that the oxide-trapped charge and the interface-trapped charge start a saturation phenomenon at different radiation doses, and the saturation phenomenon of oxide-trapped charge appears earlier than interface-trapped charge. Finally, the experimental results accord well with the model. This model provides a more accurate prediction for radiation damage in metal-oxide-semiconductor field effect transistor.

By introducing the electrical controlling circuit composed of inductance and capacitance, a fourth order model of generalized Chuas circuit with fast-slow effect has been established for certain parameter conditions. The conditions for fold bifurcation as well as Hopf bifurcation of the fast subsystem are investigated with the variation of the slow variable. Furthermore, the dynamical evolution of the entire system is explored, in which the fast-slow effect existing in the system is focused. Two types of bursting phenomenon, namely, the symmetric fold/fold and fold/Hopf periodic bursters, as well as their mechanism, are presented, which discloses the difference between the two burstings from the view point of bifurcation.

For a fourth-order autonomous nonlinear electric circuit, we present two evolution patterns to complexity associated with the three coexisting equilibrium points. In the first pattern, stable periodic movement with symmetric structure can be observed by Hopf bifurcation from the unstable equilibrium point, which may lead to chaos via cascading of period-doubling bifurcations. All the attractors, including the chaos, keep the symmetric property. While in the second evolution pattern, two limit cycles symmetric to each other may occur via Hopf bifurcations from the other two stable equilibrium points, which may also lead to two chaotic attractors, respectively. Comparing with the two evolution procedures associated with the two stable equilibrium points, not only the bifurcations keep the same pace, but also the attractors including the two final chaotic attractors are still symmetric to each other. With further variation of the parameters, the two chaotic attractors may interact with each other to form another enlarged chaotic attractor, which is qualitatively equivalent to the chaos in the first evolution pattern.

The dynamical evolution process of the coupled system connecting two nonlinear electrical circuits with suitable circuit is investigated. The bifurcation behavior as well as the ways to chaos of the two subsystems is presented. It is pointed out when both of the two subsystems behave as periodic, the coupled system may also be led to chaos via cascading of period-doubling bifurcations. Meanwhile, in the chaotic region, critical increase of period as well as period-adding bifurcation can be observed. As to the interaction between periodic movement and the chaotic oscillation, the original periodic subsystem may chaotically oscillate around the original orbit. The amplitude associated with the oscillation increases rapidly, resulting in the obvious chaotic characteristics. On the contrary, the periodic subsystem may not only cause the instability of the chaotic subsystem, but also lead to change of the chaotic structures.

The averaged binding energy, energy gap, atomic charge and total charge density of the MgO nanotube clusters were calculated with B3LYP method at 6-31G（d） level. The calculations show that the everaged binding energy decreases approximately linearly with increasing coordination. The structural stability increases in company with length of MgO nanotube clusters, and the most stable structure is 3MR species. The charge transfer increases with length of MgO nanotube clusters, the averaged atomic charges of 2, 3 and 3 converge to 1298, 1270, 1306, respectively. Mixed covalent and ionic bonding property always exist in MgO nanoclusters.

The synchronization problem for a chemical reaction system composed of two continuous stirring tank reactorv is explored. Based on Lyapunov stability theory, a new method is proposed to design the controlling function. The range of the coupling strength to realize the synchronization between the two chemical systems is investigated both for the case with static velocity and with periodically disturbed velocity of the input material. Numerical simulations are then performed to demonstrate the effectiveness of the proposed scheme, which show that the method is suitable for both the autonomous system and the non-autonomous system with periodic perturbation.