基于奇异值分解和小波阈值方法的地震资料处理方法

奇异值分解是一种基于代数特征值的提取方法,小波变换是一种时间频率域的去噪方法,两者在去噪方面各有特点。将奇异值分解和小波阈值去噪的方法有机地结合起来,用于消除地震勘探资料中的随机噪声。仿真实验显示对于较低信噪比资料仍有很好的处理效果。     

Observations on the leader-return stroke of cloud-to-ground lightning with the broadband interferometer

Radio frequency observations of cloud-to-ground lightning (CG) were made in 1999 in Guangdong Province with the broadband lightning interferometer. In this paper, radiation source locations and electric field waveforms are analyzed for different types of breakdown events, including the preliminary breakdown of in-cloud activities, the stepped leaders of initial strokes to ground and activities during and following return strokes. It is shown that the structure and development of lightning discharges and associated breakdown processes can be reconstructed by using this new type of lightning radiation source location system. The detectable radiation of lightning was primarily produced by the negative breakdown process. The channel was concentrated with few branches during the preliminary breakdown stage of CG lightning flashes. The radiation sources appeared generally at the tip of the channel. During the late period of the stepped leader, the radiation sources were dispersed with branches extended away from the main channel. The radiation sources were in a certain length segment of the channel and the altitude of the segment descended along with the propagation of the leader to the ground. During the preliminary breakdown and the stepped leader of initial strokes to the ground, a sequence of fast negative streamers were observed to start continually from or farther away the lightning-initiated region and propagate along the developed leader channel, which may supply negative charge that assisted the leader’s development. The progression speed of fast negative streamers was about ten times faster than the average speed of lightning channel.     

Chaotic behaviour in a low-order unforced,inviscid barotropic model

A low-order model of the unforced, inviscid barotropic model is examined as a dynamical system. Analytic solutions, consisting of linear and nonlinear oscillations (Rossby waves), are obtained in appropriate limiting initial conditions. These solutions are periodic. With less restrictive initial conditions the system shows quasi-periodic behaviour at low energies and chaotic behviour at high energies. This transition is accompanied by frequency-locking and period-doubling. Quasi-periodic and chaotic behaviour may coëxist in phase space for the same values of the model invariants. The results are interpreted in terms of perturbed integrable Hamiltonian systems. Considerations of the low-frequency variability of the atmosphere are also made.     

Numerical results to the Sitnikov-problem

We present numerical results of the so-called Sitnikov-problem, a special case of the three-dimensional elliptic restricted three-body problem. Here the two primaries have equal masses and the third body moves perpendicular to the plane of the primaries' orbit through their barycenter. The circular problem is integrable through elliptic integrals; the elliptic case offers a surprisingly great variety of motions which are until now not very well known. Very interesting work was done by J. Moser in connection with the original Sitnikov-paper itself, but the results are only valid for special types of orbits. As the perturbation approach needs to have small parameters in the system we took in our experiments as initial conditions for the work moderate eccentricities for the primaries' orbit (0.33e _primaries 0.66) and also a range of initial conditions for the distance of the 3 ^rd body (= the planet) from very close to the primaries orbital plane of motion up to distance 2 times the semi-major axes of their orbit. To visualize the complexity of motions we present some special orbits and show also the development of Poincaré surfaces of section with the eccentricity as a parameter. Finally a table shows the structure of phase space for these moderately chosen eccentricities.     

基于一类离散动力系统的混沌加密研究

研究了一类具有良好隐蔽性的一元三次离散动力系统的混沌序列产生情况，提出了混沌序列的异或和置乱加密算法。实验结果证明，该系统所生成的混沌序列有密钥复杂、安全性较高的特点，具有推广应用的价值。     

古气候变化吸引子维数对比研究

对世界上不同地区的多条古气候曲线 ,采用相同的间距和同一种算法进行关联维数计算 ,结果表明各系统均具有非线性作用产生的混沌现象。与太阳辐射曲线关联维数对比表明 ,太阳辐射控制了气候变化的基本格局 ,在此基础上叠加了区域性特征。     

基于三维混沌序列的DEM置乱与还原方法

DEM是地形的真实表达,蕴含着丰富的地理空间信息。如何保证涉密DEM在网络环境中的安全传输是当前亟待解决的关键问题之一。本文采用三维混沌序列,对DEM文件先后进行高程置乱、位置置乱和文件头置乱,可使置乱后的数据失去高程变化的空间连续性与数值连续性。置乱数据经网络传输后,接收方仅凭用户密钥就可以实现置乱DEM数据的无损、盲式还原。基于ASCII格式DEM的置乱与还原试验表明:本文方法可以有效破坏原始DEM数据的空间形态特征和空间连续性,并具有较高的安全性。此外,在无原始数据参与的情况下,用户可以将置乱数据恢复至初始形态,且不会造成任何精度损失。本文算法特性基本满足了DEM数据在安全传输、封装存储等方面的应用需求。     

分数阶混沌系统与整数阶混沌系统之间的同步

基于追踪控制的思想,利用分数阶系统稳定性理论,实现了分数阶混沌系统与整数阶混沌系统之间的混沌同步,给出了补偿器和反馈控制器的选择方法. 以三维分数阶Chen系统和三维整数阶Lorenz混沌系统之间的混沌同步为例进行了数值仿真和电路仿真. 研究表明了该同步方法的有效性.     

Theoretical and experimental study of Chen chaotic system with notch filter feedback control

Since the past two decades, the time delay feedback control method has attracted more and more attention in chaos control studies because of its simplicity and efficiency compared with other chaos control schemes. Recently, it has been proposed to suppress low-dimensional chaos with the notch filter feedback control method, which can be implemented in a laser system. In this work, we have analytically determined the controllable conditions for notch filter feedback controlling of Chen chaotic system in terms of the Hopf bifurcation theory. The conditions for notch filter feedback controlled Chen chaoitc system having a stable limit cycle solution are given. Meanwhile, we also analysed the Hopf bifurcation direction, which is very important for parameter settings in notch filter feedback control applications. Finally, we apply the notch filter feedback control methods to the electronic circuit experiments and numerical simulations based on the theoretical analysis. The controlling results of notch filter feedback control method well prove the feasibility and reliability of the theoretical analysis.     

Nonlinear feedback synchronisation control between fractional-order and integer-order chaotic systems

This paper focuses on the synchronisation between fractional-order and integer-order chaotic systems. Based on Lyapunov stability theory and numerical differentiation, a nonlinear feedback controller is obtained to achieve the synchronisation between fractional-order and integer-order chaotic systems. Numerical simulation results are presented to illustrate the effectiveness of this method.