Stochastic resonance in a bistable magnetic system

Theoretical model of magnetostochastic resonance is developed. It is shown that in the presence of noise the signal-to-noise ratio for a bistable uniaxial ferromagnetic can be a million times greater than that for a one-stable ferromagnetic. The phenomenon can be used for magnetic field measurements, detection of macroscopic quantum tunneling of magnetization and investigation of electron tunneling that depends upon magnetization     

Stochastic resonance in an asymmetric bistable system

The phenomenon of stochastic resonance in a simple bistable stochastic system, representing an overdamped Kramers oscillator featuring white noise and a periodic rectangular signal with a constant component, has been studied theoretically and using an analog model. An increase in the constant component, determining a static asymmetry of the potential, leads to a decrease in the signal to noise ratio as compared to the symmetric case.     

Deterministic stochastic resonance in a bistable semiconductor system

The phenomenon of deterministic stochastic resonance has been experimentally observed and studied for the first time in a bistable semiconductor system with an S-shaped current-voltage characteristic exhibiting a transition to chaos via intermittency. Spectral regions featuring amplification of an external signal and phase locking are determined as dependent on the frequency and amplitude of the external signal and the control parameter.     

Stochastic transitions in a bistable reaction system on the membrane

Transitions between steady states of a multi-stable stochastic system in the perfectly mixed chemical reactor are possible only because of stochastic switching. In realistic cellular conditions, where diffusion is limited, transitions between steady states can also follow from the propagation of travelling waves. Here, we study the interplay between the two modes of transition for a prototype bistable system of kinase–phosphatase interactions on the plasma membrane. Within microscopic kinetic Monte Carlo simulations on the hexagonal lattice, we observed that for finite diffusion the behaviour of the spatially extended system differs qualitatively from the behaviour of the same system in the well-mixed regime. Even when a small isolated subcompartment remains mostly inactive, the chemical travelling wave may propagate, leading to the activation of a larger compartment. The activating wave can be induced after a small subdomain is activated as a result of a stochastic fluctuation. Such a spontaneous onset of activity is radically more probable in subdomains characterized by slower diffusion. Our results show that a local immobilization of substrates can lead to the global activation of membrane proteins by the mechanism that involves stochastic fluctuations followed by the propagation of a semi-deterministic travelling wave.     

Transformation of bistable chaotic oscillations in triggers of a ring system

Equations describing a ring system of three unidirectionally coupled Chua oscillators (subsystems) are presented. Numerical analysis is performed in the case in which only one subsystem is autooscillatory. It is shown that non-auto-oscillatory subsystems (simplified to single-shot trigger type) exhibit complication of circuit oscillations that is accompanied by multiplication of the oscillation frequencies and expansion of the generated spectrum.     

Chaotic pulse trains generated by a dynamical system driven by a periodic signal

Chaotic pulse trains (rf pulses) can be generated by a dynamical system driven by a periodic signal. This possibility is demonstrated using a generator of chaotic oscillations with 2.5 degrees of freedom. By controlling the frequency of external action and selecting a constant bias (working point), it is possible to vary the width of rf pulses and their repetition rate within broad limits.     

A controllable chaotic system based on inductively coupled bistable oscillators

A mathematical model of a new controllable autooscilatory chaotic system based on inductively coupled Chua’s oscillators is described. Numerical simulations show that, using a chaotizing feedback algorithm, chaotic oscillations in this system can be excited in regimes where only regular oscillations are generated otherwise.     

非线性耦合双稳系统的振动共振与随机共振

单一双稳系统受到弱周期信号和噪声的作用能产生随机共振.而在高、低两种不同频率信号作用下则能产生振动共振,将两个双稳系统经非线性耦合而成为耦合双稳系统,并在低频、高频信号和噪声的作用下研究了耦合双稳系统对低频信号的响应特性,给出了高频信号参数和耦合系数对振动共振和随机共振的影响关系,结果表明通过调节高频信号幅值或耦合系数大小能产生振动共振或随机共振,并构建了耦合双稳系统原理框图,为随机共振的控制及其利用提供了新的理论方法,数值仿真结果与理论分析结论完全吻合.     

Controlling attractor structure in bistable chaotic oscillator

The effect of the asymmetric characteristic of a nonlinear element in the Chua oscillator on the oscillatory process in this chaotic dynamical system has been studied. The system behavior was studied under the action of irregular oscillations modeling the intrinsic noise, rather than as excited by a single impact. It is established that a growth in the asymmetry parameter of the nonlinear element characteristic leads to an asymmetry of the chaotic attractor of the Chua oscillator that maps the switching of motions between the two basins of attraction. Then, the system exhibits a bifurcation, whereby chaotic oscillations arise in one of these basins and develop into motions that correspond to a multiple limit cycle.     

外加周期信号控制下的随机共振及其应用

分析了双稳系统的Kramers逃逸率与外加周期信号参数的关系,揭示了外加周期信号通过调节Kramers逃逸率影响微弱周期信号的随机共振效应,从而人为地产生或增强随机共振,实现随机共振的有效控制.数值仿真和实验结果表明,外加周期信号控制下的随机共振,可以增强双稳系统输出功率谱在微弱周期信号频率处的谱值,检测出强噪声中的微弱信号,在涡街频率检测方面的应用是可行和有效的.     

新SH-COS混沌弱信号检测系统设计

将混沌理论应用于弱信号检测,设计了一种由三维混沌和余弦函数合成的全新的混沌弱信号检测系统——SH-COS系统,并对其进行了动力学特性的理论分析,用Matlab及Muhisim进行了电路仿真分析.与目前广泛探讨的Duffing混沌弱信号检测系统以及锁相放大器的性能相比,新设计的混沌弱信号检测系统抗噪性能强、检测精度高,而且具有信号检测的广域多样性,弥补了检测系统混沌与大周期状态难以区分、大周期状态不稳定等不足.新系统输出的大周期态具有收敛性,仿真对比结果验证了设计方法的正确性,进一步改善了混沌系统的弱信号检测性能,使定量检测成为可能,因而更适合应用于实际工程领域.     

On a driven nonlinear circuit and chaotic behaviour

Abstract

The chaotic behaviour of the sinusoidally driven nonlinear circuit proposed by Hunt is investigated. The results are compared with those from other driven nonlinear circuits.     

Features of induced synchronization of a bistable oscillator with chaotic dynamics

The features of induced synchronization of a Chua oscillator with a nonlinear element admitting cubic approximation have been numerically simulated for a system where the autonomous operation admits regular or chaotic regimes determined by losses in the oscillatory circuit. The cases of deterministic synchronization (under the action of a harmonic external driving signal) and chaotic synchronization (chaotic control) have been considered. It is established that, outside the band of synchronous oscillations that corresponds to the deterministic synchronization, the external harmonic signal stimulates the transformation of regular oscillations into chaos with the motions switched between two attractors. In cases of chaotic synchronization, there is a residual “noise” in the form of differential chaotic oscillations, which grows with increasing non-identity of the driving and driven signals.     

Separation of the informative component from a chaotic signal of a time-delay system

A new method is proposed for determining the parameters of time-delay systems using the observable time series. With this method, it is possible to reveal communications in the case of data transmission based on the nonlinear mixing of the informative signal and a chaotic signal of the time-delay system.     

Phase synchronization of switchings in stochastic and chaotic bistable systems

We study synchronization of switching processes in stochastic and chaotic bistable systems driven by a periodic signal in terms of phase synchronization. By introduction of instantaneous phases of transitions between metastable states and of the periodic forcing we show explicitly the effect of phase locking. The dynamics of phase difference appears to be qualitatively equivalent to that of a synchronized classical self-sustained oscillator. We have found that the degree of phase coherence between the input signal and the response estimated employing the effective diffusion constant is maximal at an optimal noise level in a stochastic bistable system or at an optimal value of a control parameter in a purely deterministic case. We also consider the effect of mutual synchronization of the switching processes in coupled stochastic and chaotic bistable systems.     

基于遗传算法的涡街信号随机共振检测方法

涡街流量计在工业现场工作时,输出信号易叠加噪声,尤其在小流量测量时,涡街信号易被现场噪声淹没,导致测量受限.针对涡街信号处理,提出一种基于遗传算法的双调制随机共振方法.该方法对输入信号进行频率和幅值双调制后进入非线性双稳系统,以系统输出信号的信噪比为适应度函数,通过二进制编码,将调制频率和幅值组合成一个二进制字符串,同...     

Stochastic resonance in a tunnel diode circuit

An experiment on the stochastic resonance in a bistable circuit with a tunnel diode is reported. In contrast to previous studies, the signal-to-noise ratio was measured across the load resistance. An additional narrow peak is observed in the signal-to-noise ratio plotted as function of the noise intensity. A brief explanation of the effect is given.     

耦合双稳系统随机共振的轴承故障检测方法

耦合双稳系统由两个双稳系统经非线性方式耦合而成.分析了影响耦合双稳系统随机共振产生的Kramers逃逸率及平均跃迁频率与耦合系数的关系,提出了通过调节耦合系数大小来产生和增强随机共振的方法,并将该方法应用于轴承故障信号检测中.数值仿真和实验结果表明,在系统参数固定时,调节耦合系数能增强系统输出功率谱在特征频率处的谱值,可检测出单一双稳系统随机共振所不能检测出的微弱轴承故障信号频率,该方法在轴承故障信号检测中的应用是有效的.     

Ferromagnetic resonance driven by spin transfer torque

We study spin-torque-driven ferromagnetic resonance (ST-FMR) in point contacts. Point contacts as small as a few nanometers in size are used to inject microwave currents into F/N/F spin valves where two ferromagnetic (F) layers are separated by a nonmagnetic (N) metal spacer. High densities of injected currents produce the spin-transfer torque on magnetic moments and drive FMR in the F-layers. The resonance is detected electrically when a small rectified dc voltage appears across the point contact. Here we focus on the origin of this rectified signal and study ST-FMR in point contacts to spin valves with different ferromagnets (Py and Co) and single ferromagnetic (Py) films, as well as in spin-valve wires patterned by electron beam lithography. We find that this voltage can be explained by the resistance variations which originate from giant magnetoresistance in point contacts to spin valves and involve effects of anisotropic magnetoresistance and extraordinary Hall effect on the propagation of microwave currents in continuous F-films and microwires.