基于Simulink的语音通信调制解调仿真实验

窄带随机过程是“随机信号分析“课程中重要的知识点。本文以调制信号这种典型的窄带随机过程为例,利用Simulink仿真软件模拟了语音通信的全过程,并在调制信号被高斯白噪声污染的情况下比较了相干解调与包络解调的信号质量。将Simulink软件引入“随机信号分析“的计算机仿真教学实验,既可加深学生对该课程中抽象理论的认识和理解,也可锻炼学生分析问题和解决问题的能力。     

成都电信提升宽带网速 全力打造无线上网城

本刊讯3月15日,成都地区的百万宽带用户告别了多年的512K下传速度,迎来一个互联网信息生活中具有里程碑意义的日子:中国电信成都分公司对全城ADSL宽带用户全部免费提速,512k提升到1M,1.5M提升到2M,并以此作为成都电信宽带10周年的庆典。从512K提升到M速度,是成都电信宽带发展10年后的再次"亮剑",从而使成都成为西部地区宽带平均速     

CO2滚动活塞膨胀机膨胀过程模拟计算

膨胀机工作过程模拟是以膨胀机实际工作过程为研究对象,综合各种因素,建立数学模型,利用计算机对模型进行数值求解,分析了膨胀机中工质的主要热力参数以及其能量、质量及功率等变化特性,计算了膨胀机输出功和效率等主要参数,通过分析,揭示了膨胀机的内部工作规律和改进膨胀机性能的途径.     

Saturation of Photoassociation in Cs Magneto-optical Trap

An ultrahigh resolution photoassociation spectrum of caesium atoms in a magneto-optical trap is presented. Hyperfine structure of the excited state molecule is obtained by using the lock-in method based on modulated cold atoms in this spectrum. Amplitude of resonant lines related to the rotational levels increases with photoassociation laser intensity, and saturation effect of photoassociation of cold atoms is observed in our experiment. The saturation intensity of photoassociation is deduced by fitting the experimental data to asaturation model based on scattering theory. Differences among saturation intensities of different rotational progressions in the υ=55 vibrational state of the caesium molecular long-range 0_g^- state have been found.     

基于准最大似然估计的星载海洋雷达高度计 跟踪器的实现及机载试验验证

在轨实时跟踪处理是海洋雷达高度计的关键环节,本文系统地研究了应用于海洋雷达高度计跟踪器的最大似然估计算法的原理、算法误差分析、以及α-β滤波器的工作机理.在此基础上研制了基于准最大似然算法的星载海洋雷达高度计跟踪器,该跟踪器在机载飞行试验中获得了成功,在国内首次获得了基于准最大似然算法的海洋回波曲线,为我国星载海洋雷达高度计的发展奠定了重要的基础.     

频率分辨率概念的教学探讨

频率分辨率是“数字信号处理”课程中的一个重要知识点,该概念紧贴雷达探测等领域的工程应用。但是在传统教学中,往往直接给出频率分辨率的定义和公式,缺乏对概念背后物理意义和工程应用的理解。本文从区分两个单频信号的实际需求出发,给出频率分辨率概念的起因和定义,并且从工程应用的角度对频率分辨率的概念进行了再认识。     

A NUMERICAL AND ANALYTICAL STUDY ON A TAIL-FLAPPING MODEL FOR FISH FAST C-START＊

The force production physics and the flow control mechanism of fish fast C-start are studied numerically and theoretically by using a tail-flapping model. The problem is simplified to a 2-D foil that rotates rapidly to and fro on one side about its fixed leading edge in water medium. The study involves the simulation of the flow by solving the two-dimensional unsteady incompressible Navier-Stokes equations and employing a theoretical analytic modeling approach. Firstly, reasonable thrust magnitude and its time history are obtained and checked by fitting predicted results coming from these two approaches. Next, the flow fields and vortex structures are given, and the propulsive mechanism is interpreted. The results show that the induction of vortex distributions near the trailing edge of the tail are important in the time-averaged thrust generation, though the added inertial effect plays an important role in producing an instant large thrust especially in the first stage. Furthermore, dynamic and energetic effects of some kinematic controlling factors are discussed. For enhancing the time-averaged thrust but keeping a favorable ratio of it to time-averaged input power within the limitations of muscle ability, it is recommended to have a larger deflection amplitude in a limited time interval and with no time delay between the to-and-fro strokes. The project supported by the CAS (KJCX-SW-L04)     

Preliminary research on the relationship between long-range correlations and predictability

By establishing the Markov model for a long-range correlated time series (LRCS) and analysing its evolutionary characteristics, this paper defines a physical effective correlation length (ECL) τ, which reflects the predictability of the LRCS. It also finds that the ECL has a better power law relation with the long-range correlated exponent γ of the LRCS: τ= Kexp (-γ/0.3)+Y, (0 < γ < 1) -- the predictability of the LRCS decays exponentially with the increase of γ. It is then applied to a daily maximum temperature series (DMTS) recorded at 740 stations in China between the years 1960--2005 and calculates the ECL of the DMTS. The results show the remarkable regional distributive feature that the ECL is about 10--14 days in west, northwest and northern China, and about 5--10 days in east, southeast and southern China. Namely, the predictability of the DMTS is higher in central-west China than in east and southeast China. In addition, the ECL is reduced by 1--8 days in most areas of China after subtracting the seasonal oscillation signal of the DMTS from its original DMTS; however, it is only slightly altered when the decadal linear trend is removed from the original DMTS. Therefore, it is shown that seasonal oscillation is a significant component of daily maximum temperature evolution and may provide a basis for predicting daily maximum temperatures. Seasonal oscillation is also significant for guiding general weather predictions, as well as seasonal weather predictions.