Adaptive detection technique for optical wireless communication over strong turbulence channels

Optical wireless communication (OWC) systems use the atmosphere as a propagation medium, so the atmospheric turbulence effects lead to fading related with signal intensity. The received signal of OWC over strong turbulence channels is assumed to be a mixture of K-distributed fading and Gaussian distributed thermal noise. Second-order spectral analysis is unable to separately estimate the mixed signal. In order to mitigate the fading induced by turbulence, the decision threshold-updating algorithm based on second and higher order cumulants is proposed and is able to operate in an unknown turbulence environment. The performance of the adaptive processing scheme has been evaluated by means of Monte Carlo simulations. Simulation results show the improvement of the bit error rate (BER) performance.     

MRAS在油膜轴承动态特性辨识中的应用

将模型参考自适应系统（ＭＫＡＳ）用于辨识轴承的８个线性化系数。每个轴承座在水平和垂直方向均简化为质量－弹簧－阻尼系统。在多跨转子系统的在线辨识和诊断中，这种方法有其独特的优点。此方法的可行性经计算机模拟和实验得到证明。     

两位控制系统稳态特性的一种计算方法

本文提出的两位控制系统稳态特性的计算方法,能比较全面和准确地计算出系统进入稳态后被控变量的波动过程。对于传递函数比较复杂的被控对象,只要能写出其幅频和相频特性的公式,都可以用本文提出的方法计算。     

Governing equations, experiments, and the experimentalist

It is argued that the most important test of the understanding of any experiment is whether or not the results are consistent with the equations and boundary conditions believed to govern the flow. If they are not, then either the measurements are incorrect, the equations or boundary conditions are wrong, or the experiment performed was not the one believed to have been done. It is suggested that many apparently contradictory experimental results are, in fact, the result of the latter and have not been recognized as such because of a failure to apply the governing equations to the data. The arguments are supported by examples from turbulent shear flow experiments.     

宽量程测色仪器的光电转换特性

从颜色测量原理出发,讨论了光电积分式测色仪器的光电转换特性以及采取的各种处理:(1)滤色片一探测器的匹配;(2)测量量程的实现;(3)放大及修正电路的设计;(4)内部接收器的灵敏度校准。最后,对系统精度进行了分析。     

Critical mass of bacterial populations and critical temperature of self-gravitating Brownian particles in two dimensions

We show that the critical mass M_c=8π of bacterial populations in two dimensions in the chemotactic problem is the counterpart of the critical temperature T_c=GMm/4k_B of self-gravitating Brownian particles in two-dimensional gravity. We obtain these critical values by using the Virial theorem or by considering stationary solutions of the Keller-Segel model and Smoluchowski-Poisson system. We also consider the case of one-dimensional systems and develop the connection with the Burgers equation. Finally, we discuss the evolution of the system as a function of M or T in bounded and unbounded domains in dimensions d=1, 2 and 3 and show the specificities of each dimension. This paper aims to point out the numerous analogies between bacterial populations, self-gravitating Brownian particles and, occasionally, two-dimensional vortices.     

光栅常数对向列相液晶响应特性的影响

通过二波耦合实验研究了C60掺杂向列相液晶中光栅形成的响应特性与光栅常数的关系。实验发现，在光栅常数较小时，光致电荷在扩散和漂移机制作用下能够很快移动到暗区形成空间电荷场，相位光栅响应较快；当光栅常数较大时，光致电较慢。荷移动到暗区时需要更长的时间，相位光栅的响应较慢。     

Variational analysis of the disc-loaded waveguide slow-wave structures

The variational method is applied to calculate the dispersion characteristics of disc-loaded waveguide slow-wave structures. The parameters describing the waveguide discontinuities in disc-loaded waveguide are calculated by the variational method. Then the dispersion characteristics of slow-wave structures are obtained using lossless microwave quadrupole theory. Good agreement was observed between results of the variational method and those of field matching method and high frequency structure simulator. In the case of broad band, results of the variational method are better than those of field matching method.     

人文社科研究在地方经济发展中作用的思考

地方高校的人文社科研究,要充分发挥高校在当地的人才和信息优势,结合地方历史文化特色及社会经济发展实际,使社科研究成果转化为促进经济发展的生产力,为地方的经济建设服务,使地方高校的人文社科研究工作步入富有特色的发展之路.     

Numerical calculations of three-dimensional turbulent vortex breakdown

Numerical solutions to the three-dimensional, unsteady, incompressible Reynolds-averaged Navier-Stokes equations have been obtained for bubble-type vortex breakdown. Two different turbulence models were employed: (1) standard K-ε and (2) an explicit, regularized algebraic Reynolds stress model. Results are computed at a Reynolds number of 10,000. The algebraic Reynolds stress model produced a breakdown bubble with a larger length-to-diameter ratio than did the K-ε model. Breakdown also occurred at lower levels of adverse pressure gradient for the algebraic stress model than for the K-ε model. In each case single-cell breakdown structures resulted. This is contrasted with numerical calculations for laminar breakdown which reveal the existence of complex multicell bubble breakdown structures.