关于Nyquist判据特殊应用的研究

Nyquist判据是经典控制理论中的重要方法,本文对Nyquist判据在两种特殊情况下的应用进行了详细分析.当出现闭环极点位于复平面[s]内虚轴上的临界情况时,通过判断该极点是否位于虚轴上原点处以及是否同时有极点位于右半平面,可具体判别出闭环系统属于稳定、临界稳定或是不稳定三种状态.在复平面[s]内构造恰当的Nyquist轨迹,该判据还可用于分析闭环极点在特定区域内的分布情况,从而满足系统相对稳定性的要求.本文的方法简单易学,内容可作为对相关教材的补充.     

无人机紧密编队协同控制设计与仿真

研究了紧密编队无人机所受气动耦合的影响以及三维环境下的编队控制方法,分析了在气动耦合影响下编队的动力学特性和运动学特性,建立了紧密编队控制的数学模型。根据编队飞行实体试验的工程控制方法,采用经典PID控制设计了紧密编队控制系统。仿真实验表明,设计的控制系统能够较好地实现无人机紧密编队队形形成与保持,并且具有编队形成速度快、编队误差小的优点。     

美军Link-16数据链在近距空中支援作战中应用研究

近距空中支援作战在现代战争中的地位日益凸显,通过战术数据链网络为 CAS 任务提供高效的战场态势、指挥引导、空地协同等信息交互能力,能够缩短 CAS 任务从发起到打击所需时间、提高打击精度和效率,成为美军发展的重点的方向。本文以 Link-16 战术数据链为切入点,结合近距空中支援作战流程,对美军 CAS 作战中 Link-16 数据链的组网应用和信息交互进行研究。     

废纸造纸污水的封闭循环和零排放

本文通过对造纸废水的来源及主要污染成分的分析，提出如何实现造纸废水．特别是白水的封闭循环和零排放     

近距定位系统的物联网案例分析与方案设计

从介绍基于无线技术的人员近距定位系统适应的各种应用场景入手,对基于无线技术的人员近距定位系统的多项物联网案例进行了分析,并基于ZigBee技术给出了一种适合高端养老院的人员近距定位解决方案。     

波纹管型自调式制冷器设计研究

对波纹管型自调式制冷器的设计技术进行了研究，并针对制冷器出现的流量稳定性问题，提出关闭预紧力的设计构想。即认为制冷流量变化必然是由于针阀开度变化引起，而针阀开度变化则是由于调节器受力关系发生变化造成的，若在制冷器的设计中预留一当量预紧力，即可望解决制冷器的稳定性问题；即总的思路来讲，以力的变化换取当量位移的变化，从而实现针阀开度的不变，并最终实现制冷流量的稳定。     

基于Matlab的三相桥式SPWM逆变器建模与仿真

对三相桥式逆变电路原理及其SPWM控制原理进行简单的分析,针对开环SPWM电压的不稳定提出一种电压闭环SPWM控制模型。在Matlab/Simulink软件环境中分别建立了三相SPWM逆变器开环仿真模型和具有电压调节作用的SPWM闭环仿真模型,分别对其进行仿真分析。仿真结果表明电压闭环SPWM控制比开环SPWM控制具有更好的动静态特性。得出的结论对三相桥式逆变器的原理的理解、参数的确定、电路的设计有一定的参考价值和指导意义。     

简单图像闭合外边缘轮廓提取

提出了一种在较简单图像中提取多个完整图形闭合外边界的方法.利用方向边缘检测、方向数学形态学方法和拟态流水侵蚀法得到了较好的完整图形闭合外边界.通过实验验证了该方法不仅适用于简单图像,而且适用于较复杂的图像.在一定程度上具有去除非闭合曲线段及噪声的能力.同时,通过使用拟态流水侵蚀法使处理速度和效果明显优于常用的处理方法.实验结果证明了所提供的算法在图像闭合区域边界提取方面是有效的.     

High-performance detector read-out at very low temperatures

An infra-red detection system must be physically colder than the objects it needs to observe. As some of the objects to be observed by the European Space Agency's Infra-red Space Observatory (ISO) might be as cold as a few tens of degrees Kelvin, it is essential that the ISO's detectors should themselves operate at temperatures close to absolute zero. To avoid problems with electromagnetic interference, it is also necessary that detector read-out (i.e. first-stage signal amplification) be located as close as possible to the detectors. As conventional amplifiers cannot work at temperatures close to absolute zero, special techniques had to be used for the ISO's detectors     

Quantized conductance in a Si/Si0.7Ge0.3 split-gate device and impurity-related magnetotransport phenomena

We have defined a quantum point-contact by the split-gate technique in a Si/SiGe heterostructure containing a two-dimensional electron gas with an elastic mean free path of about 1.3 μm. The conductance of this device shows typical steps very close to multiples of 4e² h⁻¹. Upon application of a perpendicular magnetic field the spin and valley degeneracies are lifted and magnetic depopulation of the one-dimensional subbands can be observed. The appearance of Aharonov-Bohm oscillations for B ≥ 2T and of resonant tunneling peaks close to “pinch-off” indicates the presence of impurities close to the constriction.     

基于单片机控制的智能光控窗帘系统研究

设计了一种智能的光控窗帘控制系统,它能够感应周围环境的光照强度,当光照低于某一强度时窗帘自动打开,等到光照上升到某一范围时窗帘自动停止打开,当光照高于某一强度时窗帘自动关闭,直到光照下降到某一范围时窗帘自动停止关闭。     

光电系统中挠性陀螺闭环和开环应用效果的对比分析

阐述了挠性陀螺的闭环和开环两种应用方式,并从力矩刚度的角度分析了系统在两种模式下的稳定性。理论分析表明,在陀螺闭环应用时,系统的力矩刚度会受到陀螺带宽的限制;在陀螺开环应用时,系统的力矩刚度不受陀螺带宽的限制而会大大增加。仿真与试验结果表明,陀螺开环应用效果要好于陀螺闭环应用效果,提高了系统的力矩刚度,改善了系统的稳定性。该结果证明了理论分析的正确性,对工程应用具有一定的指导作用。     

Fast fractal image block coding based on local variances

In fractal image block coding, most of the time is spent on finding a close match between a range block and a large pool of domain blocks. For a large image, this effect becomes aggravated as the domain pool increases exponentially. We propose using the local variances of domain blocks to reduce the search space. By sorting the contracted domain pool according to their local variances and defining an acceptance criterion for a close match, we can confine all the potential close matches to a relatively small sized window to limit the search space. The encoding time can hence be shortened with the decoded image quality as good as that using the full search method. The speedup can be over ten times depending on the complexity of encoded images.     

Noise reduction in transferred electron oscillator modules

The FM noise performance of oscillator modules based on GaAs transferred electron devices characterized by carrier notches close to the cathode contact is presented. The notches have been incorporated into completed and encapsulated devices by ion-implantation techniques, the notches proving stable up to 400°C. Useful improvements in the FM noise performance close to the carrier are available using this technique.     

A percolative simulation of dielectric-like breakdown

Dielectric-like degradation of thin-film conductors is simulated up to final breakdown within a biased percolation model. As relevant indicators we take the damage pattern, current distribution, resistance variation, failure lifetime and relative resistance fluctuations. The results show that biased percolation predicts well several known features taking place close to the abrupt failure of thin films in close agreement with available experimental results.     

相关衰落信道下闭环发射分集方案的性能分析

未来移动通信系统采用的关键技术之一是发射分集技术，如WCDMA标准中采用了一种称作闭环发射分集的方案，用于下行信道传输。闭环发射分集方案使用了前向信道的相位与幅度的部分信息来选择天线的加权系数，在信道时变速率较小时，闭环发射分集的性能优于开环发射分集方案。在一般情况下，假设两个发射天线之间距离足够大，各个发射天线到接收天线的信道是不相关的，在基站这种假设是合理的。但如果在上行信道传输中(移动台到基站)应用闭环发射分集技术时，天线之间不相关的假设很难满足。本文基于对移动台配置多天线并应用闭环发射分集技术的考虑，研究在相关瑞利衰落信道下闭环发射分集技术的性能。蒙特卡罗仿真给出了不同相关系数下的性能曲线，并得出一个具有指导意义的结论。     

运动平台光电跟踪瞄准技术研究

提出了一种运动平台光电跟踪瞄准方案．该方案采用光电跟踪技术对机动目标进行跟踪滤波,给出了一种数字式闭环跟踪滤波设计方法．利用闭环滤波估计出目标运动参量并预测出目标未来时刻的位置。     

Lossy Distributed Source Coding Using LDPC Codes

In this paper, we propose a practical scheme for lossy distributed source coding with side information available at the decoder. Our proposed scheme is based on sending parity bits using LDPC codes. We provide the design procedure for the LDPC code that guarantees performance close to the Wyner-Ziv limit for long LDPC codes. Using simulation results, we show that the proposed method performs close to the theoretical limit for even short length codes.     

Electricity and weather modification II. Plans and programs, prospects and purpose

The international and domestic research programs described in this article may close the gap between dream and reality in weather control, especially if atmospheric and electrical scientists work together more closely than in the past. Can such cooperation also close the gap between research directed at realizing the dream and research needed to prevent a nightmare, that pollution may place the weather beyond anyone's control and create climatic instabilities that could lead to social chaos?     

Explicit formulas for the fundamental mode of a linear resonator with elliptic mirrors and construction of higher order modes

A linear resonator bounded by elliptic (hyperbolic) mirrors with noncoinciding principal curvature directions is considered. Explicit analytic formulas describing the fundamental mode of such resonator are derived in the principal approximation. A procedure of constructing higher order modes is developed. The potentialities of the technique are exemplified by considering a resonator with mirrors whose shapes are close to spheres and a resonator with elliptic mirrors whose shapes are close to each other.