A new approach to detecting weak signal in strong noise based on chaos system control

In this paper, a chaos system and proportional differential control are both used to detect the frequency of an unknown signal. In traditional methods the useful signal is obtained through the Duffing equation or other chaotic oscillators. But these methods are too complex because of using a lot of chaos oscillators. In this paper a new method is presented that uses the R?ssler equation and proportional differential control to detect a weak signal frequency. Substituting the detected signal frequency into the R?ssler equation leads the R?ssler phase state to be considerably changed. The chaos state can be controlled through the proportional differential method. Through its phase diagram and spectrum analysis, the unknown frequency is obtained. The simulation results verify that the presented method is feasible and that the detection accuracy is higher than those of other methods.     

Upper bound for the time derivative of entropy for a stochastic dynamical system with double singularities driven by non-Gaussian noise

A stochastic dynamical system with double singularities driven by non-Gaussian noise is investigated. The Fokker--Plank equation of the system is obtained through the path-integral approach and the method of transformation. Based on the definition of Shannon's information entropy and the Schwartz inequality principle, the upper bound for the time derivative of entropy is calculated both in the absence and in the presence of non-equilibrium constraint. The present calculations can be used to interpret the effects of the system dissipative parameter, the system singularity strength parameter, the noise correlation time and the noise deviation parameter on the upper bound.     

Variational iteration method for solving compressible Euler equations

This paper applies the variational iteration method to obtain approximate analytic solutions of compressible Euler equations in gas dynamics.This method is based on the use of Lagrange multiplier for identification of optimal values of parameters in a functional.Using this method,a rapid convergent sequence is produced which converges to the exact solutions of the problem.Numerical results and comparison with other two numerical solutions verify that this method is very convenient and efficient.     

Paramagnetism in Cu-doped ZnO

Zn0.98 Cu0.02 O powders are prepared by the sol-gel method.A small number of CuO impurity phases are observed by the x-ray diffraction,indicating the solubility of Cu in ZnO is less than 2 at.%.The Zn0.98 Cu0.02 O powders exhibit diamagnetism at 300 K and paramagnetism at 5 K.After subtracting the diamagnetic contribution of ZnO bulk and the paramagnetic contribution of defects,Cu ions exhibit weak paramagnetism.By codoping Cu with Co or Mn in ZnO,only paramagnetism is observed at room temperature.     

Generation of millimeter-wave sub-carrier optical pulse by using cascaded all-pass cavities

A novel scheme is proposed to transform an ultra-short optical pulse to a millimeter-wave frequencymodulated pulse by using the cascaded all-pass cavities （APCs）. The envelope waveform of the generated pulse train is calculated, showing effective improvement by APC cascading. The extinction ratio is analyzed with different input pulses, different cavity reflectivities, and different cascading numbers. It is shown that the cascading does not introduce much effect on the extinction ratio. Two designs by using Gires-Tournois cavity and waveguide ring resonators are proposed to realize the cascaded APC.     

The role of refocusing in dynamic X-wave formation during femtosecond laser filamentation in water

<正>With the evolution of a laser pulse in water,the formation of a nonlinear X wave during femtosecond filamentation is investigated based on numerical simulations.In particular,we analyze the far-field angularly resolved spectra obtained for different temporal portions of the ultrashort pulse during its propagation. Our result shows that the refocusing of ultrashort pulse leads to the formation of dynamic X wave which essentially manifests itself as conical emission.     

Fast generation of cluster states in a linear ion trap

We propose a practical scheme to generate cluster states by simultaneously accomplishing two-qubit conditional gating on an array of equidistant ions by using transverse modes. Our operation is robust to heating and insensitive to Lamb--Dicke parameter. Meanwhile, as it is carried out in a geometric quantum computing fashion, our scheme enables the fast and high-fidelity generation of cluster states. The experimental feasibility is discussed with sophisticated ion trap techniques.     

Negative differential resistance behaviour in N-doped crossed graphene nanoribbons

By using first-principles calculations and nonequilibrium Green’s function technique, we study elastic transport properties of crossed graphene nanoribbons. The results show that the electronic transport properties of molecular junctions can be modulated by doped atoms. Negative differential resistance (NDR) behaviour can be observed in a certain bias region, when crossed graphene nanoribbons are doped with nitrogen atoms at the shoulder, but it cannot be observed for pristine crossed graphene nanoribbons at low biases. A mechanism for the negative differential resistance behaviour is suggested.     

预处理对355nm激光作用下熔石英损伤增长的影响

测试了经化学蚀刻、紫外激光预处理及其共同处理后的熔石英355 nm激光损伤阈值;研究了处理前后其损伤斑面积随激光辐照脉冲数的增长情况。结果表明,处理后熔石英355 nm激光损伤阈值得到了提高,且损伤斑面积增长变慢。利用CO2激光对熔石英表面损伤点进行了修复处理,修复后的损伤点R-on-1抗损伤阈值和基底阈值相当,损伤增长得到有效抑制。     

欧姆定律教学难点的突破

分析了欧姆定律的适用条件,结合教学中应用欧姆定律的疑难案例,从电路和能量的角度探讨了如何突破含电解槽、电动机、电容器、二极管等非纯电阻电路教学难点的策略.