类星体PKS 1510-089的X射线流量变化周期特性

使用罗西X射线时变探测器的数据,得到了类星体PKS 1510-089从1996年1月到2009年12月在X射线的1.5-12 keV能段上的光变曲线.运用离散相关函数方法、小波分析方法和功率谱方法分析和认证类星体PKS 1510-089的光变周期值,结果表明类星体PKS 1510-089 在X射线的1.5-12 keV能段具有(0.94±0.08)a的平均光变周期.采用不同模型对观测到的周期性光变进行分析后的结果表明,超大质量双黑洞模型是目前解释类星体PKS 1510-089周期性光变较为理想的模型,应用 关键词： 类星体PKS 1510-089 X射线流量变化 双黑洞模型     

基于近似熵的斯隆数字化巡天中类星体光变复杂性分析

光变是类星体的重要观测特征之一,类星体在多个波段存在剧烈的光变现象.光变非常复杂,具有非线性特征.以斯隆数字化巡天(Sloan digital sky survey, SDSS) stripe 82天区中的类星体为研究对象,利用近似熵方法分析了类星体光变的复杂性.首先应用模拟信号检验了近似熵方法对周期序列、白噪声序列、混沌序列和组合序列的区分能力,验证了近似熵方法是一种识别不同类型时间序列的有效方法.再计算了SDSS第7次释放数据中光谱证认过的类星体光变的近似熵,并分析了它们的复杂性.结果表明:SDSS类星体光变的近似熵值最大值为0.58,类星体光变的复杂性介于周期序列和白噪声序列的复杂性之间,近一半样本的复杂性与混沌序列基本一致.     

基于聚合经验模态分解方法的OJ 287 射电流量变化周期分析

BL Lac 天体OJ 287 是一个重要的Blazar天体, 光变具有准周期特点. 本文从密歇根大学射电天文台数据库收集了OJ 287射电波段4.8, 8.0和 14.5 GHz超过30年时间的观测数据. 由于天文观测资料的复杂性, 一些传统寻找周期的方法不是太理想. 近几年迅速发展起来的聚合经验模态分解(EEMD) 特别适合于具有非线性和非平稳动态变化特性的Blazar天体光变规律的研究. 运用EEMD方法对OJ 287 的3个射电波段流量分别进行多时间尺度分解, 各获得6个代表不同时间尺度局部特征信息的本征模态函数分量和一个趋势项. 研究结果表明: 4.8 GHz射电流量变化的主要周期是18.9, 11.9, 5.7 和2.4年; 8.0 GHz 的主要周期是12.2, 5.2和2.4 年; 14.5 GHz的主要周期是21.8, 12.0, 4.3和 2.4 年. 尽管3个波段流量变化主要周期大小有一定的差别, 但是存在着近似相同的变化周期12.0 和2.4年, 说明这3个波段可能来源于相同的辐射机制, 也证实了OJ 287 射电波段和光学波段具有相同的长光变周期12.0 年. 这些结论表明: EEMD 作为一种全新的非线性、非平稳信号处理方法, 可以更精确地提取Blazar天体中不同光变周期的分量. 关键词： OJ 287 光变周期 聚合经验模态分解     

耀变体S5 0716+714的混沌特性研究

长期观测显示,耀变体S5 0716+714具有复杂的光变行为.本文运用混沌理论,研究了S5 0716+714四个较大爆发阶段的射电、光学和X波段的光变曲线.分别计算了它们的关联维和Lyapunov指数.结果表明:1)光变曲线的关联维和Lyapunov指数都介于纯混沌系统与随机噪声之间;2)相轨迹是一个与Rossler吸引子相似的混沌系统,由于受到各种内在或外在因素的影响产生噪声,导致关联维和Lyapunov指数均比Rossler吸引子大,相轨迹出现紊乱.从这两个混沌判据上看,三个波段均表现出很强的混沌特性,因此推断S50714+716的光变是一个混沌现象.     

类星体3C345的光变周期特性

收集了类星体3C345光学B波段100多年来较为完备的观测数据,获得了其长期光变曲线.利用小波分析的方法对其中B波段28年的数据进行了多时间尺度分析,并用小波变换系数图展示了3C345光学B波段的爆发过程.通过研究发现了其中存在有450天,780天,1830天和3540天的近似光变周期.利用小波逆变换可以反映其光变在不同时间尺度上的演变特征,进而预测类星体3C345未来可能的光学爆发时间为2010年左右. 关键词： 小波分析方法 光变曲线 多时间尺度 小波变换系数图     

天体运动能超过光速吗?

按照相对论的原理,一般认为任何物体运动的速度都不能超过光速.而近十年来,射电天文学家却观测到愈来愈多的视向速度超过光速的河外星体.其中类星体3C 279的视向速度达到了 45倍光速这样惊人的数值[1]. 这种射电天文观测是在厘米波段用很长基线的干涉仪(由很长距离上分布的一些射电望远镜组成的干涉仪系统)进行的.在不同时间拍摄星系的射电像,能够给出星系各部分在相应时刻的位置,这样就可得出这些部分相对运动的速度. Pearson等人报告了他们在1977年至1980年间对类星体 3 C 273的观测结果[2].从所给出的这三年间此类星体中心区 3C 273 B…     

基于结构函数方法的类星体证认

光变巡天是搜寻类星体的一个很有效的方法.应用归一化结构函数对SDSS stripe 82中存在光变的1411个类星体和174个恒星进行分类,选取幂函数模型拟合这些样本5个波段的结构函数.综合幅值和幂指数两个物理量设置了合适的分类判据,获得了比较理想的分类结果,类星体和恒星最高分类正确率分别达到了92.2%和83.6%.结果表明,改正后的结构函数对类星体的证认有很好的效果,能节约大型望远镜宝贵的观测时间,让类星体巡天获得比较高的观测效率.分析结论支持大部分类星体的光变缘于盘的不稳定性.     

微类星体发出极高能伽马射线喷流

微类星体是具有两股相似射电喷流的双星系统,它们与类星体的射电喷流类似,只是规模要小一些。喷流的射线来源于强磁场中以相对论速度运动的粒子,不过目前对这些喷流的成分却知之甚少。西班牙、德国、意大利、阿根廷、芬兰、瑞典、英国和亚美尼亚的几位科学家在《科学》杂志上介     

振荡吸积盘的光变研究

理论研究指出随机振荡吸积盘可能引起活动天体的光变,然而观测数据分析表明光变中除了含有随机噪声外还存在混沌因素.将混沌因素引入到随机振荡吸积盘中,构成"混沌+随机"振荡吸积盘模型.通过分析扰动的相图,直观再现了混沌吸引子的状态.研究结果表明:在随机因素占主导时,光变混乱无序;随机因素与混沌因素相当时,光变上下起伏类似于心电图;混沌因素占主导时,光变具有一定有序性.模拟光变曲线的关联维与观测数据的关联维一致,表明模拟光变曲线与观测结果之间存在内在联系.     

γ噪Blazar天体的γ射线和近红外光辐射研究

收集了29个有γ噪的Blazar天体(其中有16个BL Lac天体和13个平谱射电类星体)的近红外流量密度和γ射线流量密度,获得以下主要结果:1)23个天体中的γ射线流量密度和近红外流量密度在低态时存在较强的相关性而在高态时有弱的相关性.2)在29个天体中,有6个天体只有一个观测数据点,将其认为是高态时,γ射线流量密度与近红外光流量密度之间有弱相关性,而认为是低态时有强相关性.3)29个源的γ射线流量密度与X射线流量密度在低态时有相关性,但是γ射线流量与光学流量密度,γ射线流量与射电流量密度均没有相关性.4)在16个BL Lac天体中γ射线流量与近红外光流量不论在高态还是低态都有相关性,而13个平谱射电类星体没有相关性.讨论了γ噪Blazar天体的γ射线辐射机制,认为γ射线的辐射机制主要是同步自康普顿散射.而逆康普顿散射来自绕中心核且温度约为2000K的尘埃,这些尘埃的区域大约有r=3pc,聚束的相对论电子也可能是这种尘埃模型辐射机制的一个重要补充.平谱射电类星体和BL Lac天体的γ辐射机制可能有些不同. 关键词： Blazar天体 星系γ射线观测辐射机制 非热辐射     

Dynamics of two coupled chaotic multimode Nd:YAG lasers with intracavity frequency doubling crystal

The effect of coupling two chaotic Nd:YAG lasers with intracavity KTP crystal for frequency doubling is numerically studied for the case of the laser operating in three longitudinal modes. It is seen that the system goes from chaotic to periodic and then to steady state as the coupling constant is increased. The intensity time series and phase diagrams are drawn and the Lyapunov characteristic exponent is calculated to characterize the chaotic and periodic regions.     

Periodic orbit analysis at the onset of the unstable dimension variability and at the blowout bifurcation

Many chaotic dynamical systems of physical interest present a strong form of nonhyperbolicity called unstable dimension variability (UDV), for which the chaotic invariant set contains periodic orbits possessing different numbers of unstable eigendirections. The onset of UDV is usually related to the loss of transversal stability of an unstable fixed point embedded in the chaotic set. In this paper, we present a new mechanism for the onset of UDV, whereby the period of the unstable orbits losing transversal stability tends to infinity as we approach the onset of UDV. This mechanism is unveiled by means of a periodic orbit analysis of the invariant chaotic attractor for two model dynamical systems with phase spaces of low dimensionality, and seems to depend heavily on the chaotic dynamics in the invariant set. We also described, for these systems, the blowout bifurcation (for which the chaotic set as a whole loses transversal stability) and its relation with the situation where the effects of UDV are the most intense. For the latter point, we found that chaotic trajectories off, but very close to, the invariant set exhibit the same scaling characteristic of the so-called on-off intermittency.     

心率变异性谱成分的非线性本质

提出了分频段相位随机化替代数据方法,与噪声滴定法相结合,观察了不同频率成分对心搏混沌的影响.结果显示心率变异性高频成分相位随机化的替代数据使混沌强度显著降低,提示谱分析的频率成分中蕴含着信号的非线性特性.提出的方法能有效分析不同频率成分对非线性的贡献,该法不仅适用于心率变异性还适用于其他确定性信号的特性分析. 关键词： 分频段相位随机化替代数据 混沌 滴定法 心率变异性     

基于广义局部频率的Duffing系统频域特征分析

针对传统功率谱在频率概念上的局限性及傅氏变换的固有缺陷, 提出一种新的广义局部频率概念,在自适应峰值分解方法的基础上, 研究周期激励下Duffing系统随阻尼参数r变化的频域动力学特征,发现了频率分岔现象, 并且不同参数r下的混沌时间序列在中心频率附近出现连续频段, 其形状具有相似性.通过厄米解调分析,总结出混沌时间序列具有频率调制特性和频率调制的相似性. 上述研究表明:提出的基于自适应峰值分解的广义局部频率方法, 能够有效提取Duffing系统的频域特征,为观察非线性系统混沌状态下频率连续分布规律提供一种新方法.     

Crisis-induced unstable dimension variability in a dynamical system

Unstable dimension variability is an extreme form of non-hyperbolic behavior in chaotic systems whose attractors have periodic orbits with a different number of unstable directions. We propose a new mechanism for the onset of unstable dimension variability based on an interior crisis, or a collision between a chaotic attractor and an unstable periodic orbit. We give a physical example by considering a high-dimensional dissipative physical system driven by impulsive periodic forcing.     

Itinerant memory dynamics and global bifurcations in chaotic neural networks

We have considered itinerant memory dynamics in a chaotic neural network composed of four chaotic neurons with synaptic connections determined by two orthogonal stored patterns as a simple example of a chaotic itinerant phenomenon in dynamical associative memory. We have analyzed a mechanism of generating the itinerant memory dynamics with respect to intersection of a pair of alpha branches of periodic points and collapse of a periodic in-phase attracting set. The intersection of invariant sets is numerically verified by a novel method proposed in this paper.     

动力学变换法探测连续系统不稳定周期轨道

本文利用动力学变换方法和庞加莱截面方法对两种连续混沌动力学系统进行不稳定周期轨道探测研究, 并对Lorenz系统进行了替代数据法检验.结果表明:基于庞加莱截面的动力学变换改进算法 可有效探测连续混沌动力学系统中的不稳定周期轨道.     

Hysteresis-induced bifurcation and chaos in a magneto-rheological suspension system under external excitation

The magneto-rheological damper(MRD) is a promising device used in vehicle semi-active suspension systems, for its continuous adjustable damping output. However, the innate nonlinear hysteresis characteristic of MRD may cause the nonlinear behaviors. In this work, a two-degree-of-freedom(2-DOF) MR suspension system was established first, by employing the modified Bouc–Wen force–velocity(F –v) hysteretic model. The nonlinear dynamic response of the system was investigated under the external excitation of single-frequency harmonic and bandwidth-limited stochastic road surface.The largest Lyapunov exponent(LLE) was used to detect the chaotic area of the frequency and amplitude of harmonic excitation, and the bifurcation diagrams, time histories, phase portraits, and power spectrum density(PSD) diagrams were used to reveal the dynamic evolution process in detail. Moreover, the LLE and Kolmogorov entropy(K entropy) were used to identify whether the system response was random or chaotic under stochastic road surface. The results demonstrated that the complex dynamical behaviors occur under different external excitation conditions. The oscillating mechanism of alternating periodic oscillations, quasi-periodic oscillations, and chaotic oscillations was observed in detail. The chaotic regions revealed that chaotic motions may appear in conditions of mid-low frequency and large amplitude, as well as small amplitude and all frequency. The obtained parameter regions where the chaotic motions may appear are useful for design of structural parameters of the vibration isolation, and the optimization of control strategy for MR suspension system.     

Bifurcation analysis of the logistic map via two periodic impulsive forces

The complex dynamics of the logistic map via two periodic impulsive forces is investigated in this paper. The influences of the system parameter and the impulsive forces on the dynamics of the system are studied respectively. With the parameter varying, the system produces the phenomenon such as periodic solutions, chaotic solutions, and chaotic crisis. Furthermore, the system can evolve to chaos by a cascading of period-doubling bifurcations. The Poincare′ map of the logistic map via two periodic impulsive forces is constructed and its bifurcation is analyzed. Finally, the Floquet theory is extended to explore the bifurcation mechanism for the periodic solutions of this non-smooth map.     

Dynamical Behaviour of the Bonhoeffer-van der Pol Model

The dynamical behaviour and the threshold phenomenon for the Bonhoeffer-van der Pol model of a nerve membrane stimulated by a constant and a periodic currents are investigated. For the constant current lo, there are two Hopf bifurcations at I₀ = I_L and I₀ = I_H, respectively. At I₀ = I_L an infinite long train of nerve impulses (threshold phenomenon) is found. For the periodic current, there are an ordinary period-dou bling to chaotic state, and a mode-locking state, as well as a reversed period-doubling from chaotic state to period-1 state. A phase diagram for the threshold phenomenon in the parameter space (I₁ and ω, amplit ude and frequency) is obtained. In our discussion we conclude that the period-n oscillations correspond to the n-shaped impulse trains, and the chaotic oscillation corresponds to the infinite-shaped impulse trains. All of these impulses of the BVP model system code the information process of the nerve fibre in neural tissue.