Uniform Approximation of Discrete-Time Periodically Varying Systems

It is shown that the elements of a large class of discrete-time periodically varying nonlinear input-output maps can be uniformly approximated arbitrarily well, over infinite time intervals, using a certain structure that can be implemented in many ways using, for example, radial basis functions, polynomial functions, piecewise linear functions, sigmoids, or combinations of these functions. For the special case in which these functions are taken to be certain polynomial functions, the input-output map of our structure is a generalized finite discrete-time Volterra series. Results are given for the case in which inputs and outputs are defined on the integers. The case in which inputs and outputs are defined on the nonnegative integers is also addressed.     

Rapid thermal annealing effects on the photoluminescence properties of molecular beam epitaxy-grown GaIn(N)As quantum wells with Ga(N)As spacers and barriers

This article describes the effects of rapid thermal annealing (RTA) on the photoluminescence (PL) emission from a series of GaIn(N)As quantum wells. Indium compositions of both 20% and 32% were examined with nominal N compositions of 1% or 2%. The N location was varied within our quantum structure, which can be divided into three regions: (1) quantum well, (2) Ga(N)As spacer layers at the barrier-to-well interface and well-to-barrier interface, and (3) barriers surrounding each quantum well. Eight combinations of samples were examined with varying In content, Ga(N)As spacer layer thickness, N content, and N location in the structure. In the best cases, the presence of these Ga(N)As spacer layers improves the PL properties, due to annealing, with a reduction in the emission wavelength blueshift by ～400 Å, a reduction of the decrease in the full-width at half-maximum (FWHM) by ～5 meV, and a threefold reduction of the increase in integrated intensity. It was also observed that relocating N from the quantum wells to the barriers produces a comparable emission wavelength both before and after annealing. Our results further show that the composition of incorporated N in the material is most influential during the stages of RTA in which relatively small amounts of thermal energy is present from our lower annealing times and temperatures. Hence, we believe a low thermal-energy anneal is responsible for the recovery of the plasma-related crystal damage that was incurred during its growth. However, the In composition in the quantum well is most influential during the latter stages of thermal annealing, at increased times and temperatures, where the wavelength blueshift was roughly independent of the amount of incorporated N. As a result, our investigations into the effects of RTA on the PL properties support other reports that suggest the wavelength blueshift is not due to N diffusion.     

基于光纤传感实验仪的设计与扩展性实验

光纤传感实验仪是一种适合于高等院校光电子技术、微电子技术、电子工程等专业的实验教学仪器设备,具有十分优良的实验拓展性。为适应提高学生素质和能力培养的教学目标,本文重点阐述了如何在光纤传感实验仪所能够完成的5个基本实验的基础上进行深入的开发与扩展,以进一步完成更多的设计性、研究性实验。给出了在光纤传感实验仪的基础上所设计开发的光纤压力、温度、液位等实验。     

基于修正SSIM的SAR干扰效果评估方法

该文提出了一种基于修正结构相似度的合成孔径雷达干扰效果评估方法。该方法不仅巧妙地利用了结构相似度作为主客观评价的连接纽带,而且结合梯度模与人眼视觉系统多通道特性相匹配的特点,通过非线性处理得到了修正的评估指标GSSIM。仿真结果表明,GSSIM较均方误差、峰值信噪比及相关系数等传统评估指标具有明显的优势,不仅能够更好地反映出干扰对图像ROI的影响,而且能够与人类视觉系统保持高度一致,进一步提升了整套评估系统的效率和准确率。     

基于灰度世界和白点检测的自动白平衡算法

针对常见的自动白平衡算法存在的图像场景适应性不足或算法复杂度过高的问题,提出了一种新的自动白平衡算法.该方法综合考虑了灰度世界模型和白点检测算法的各自优势,采用一种自适应的控制流程来计算图像三分量的增益系数并进行白平衡校正,在此基础上,运用软硬件协同设计来实现该算法,降低了硬件的开销,提高了算法的灵活性.实验结果表明,...     

基于瑞萨微控制器的温度控制系统设计

为了提高传统温度控制系统的性能,将PID控制理论与嵌入式系统相结合,采用瑞萨电子公司的H8S/2166作为核心处理器,AD公司的AD7705以及热敏电阻温度传感器作为温度检测单元,利用4×6小键盘、LCD显示器和S1D13305液晶控制器达到良好的人机交互,设计出了一个应用于化工领域的嵌入式实时温度控制系统。相比于传统温度控制系统,该系统提供了更强的计算能力和可扩展能力,采用增量PID控制算法实现复杂控制。通过实验,该系统能达到0.1℃的温度控制精度以及小于120 s的温度稳定时间。     

有源阵列天线的系统噪声

有源阵列天线系统的噪声是有源相控阵雷达、通讯等系统噪声的主要成分,本文从微波网络理论入手,结合统计理论对有源阵列天线的噪声温度进行理论分析,为有源阵列天线系统噪声的分析、设计和测试提供了完整的数学模型和方法.     

非线性及粒子空间效应对交流电渗流泵的影响

在交流电渗流(ACEO)泵的研究中,一般采用Debye-Huckel(D-H)线性近似法。但该方法只在电压很小时才成立,这和实际情况不符;此外,交流电渗流泵在大电压、高频率下的反向流现象也不能由D-H近似法给出正确的预测。当电压较大时,一般采用非线性的Poisson-Boltzmann(P-B)模型。但是,P-B模型也无法对交流电渗流泵在大电压、高频率下的反向流现象进行预测。在P-B模型中,溶液粒子被当作一个空间点,忽略了粒子间的相互作用以及粒子本身的空间体积效应。实际的粒子都有一定的空间体积,当电压较大、溶液浓度较高时,粒子的空间体积不应被忽略。由于粒子的空间体积,通过引入粒子空间效应对P-B模型进行修正后,给出了交流电渗流泵在较大电压下的数值模型,并对交流电渗流泵在较大电压下的高频率反向流现象进行了成功的预测。     

Structural and optoelectronic properties of sprayed Sb:SnO_2 thin films:Effects of substrate temperature and nozzle-to-substrate distance

The influence of substrate temperature and nozzle-to-substrate distance（NSD） on the structural,morphological, optical and electrical properties of Sb:SnO₂ thin films prepared by chemical spray pyrolysis has been analyzed.The structural,morphological,optical and electrical properties were characterized by using XRD,SEM, UV-visible spectrophotometry and Hall effect measurement techniques.It was seen that the films are polycrystalline, having a tetragonal crystal structure with strong orientation along the（200） reflection.The pyramidal crystallites formed due to coalescence were observed from SEM images.The values of highest conductivity,optical transmittance and figure of merit of about 1449（Ω·cm）^-1,70%and 5.2×10^-3□/Ω,respectively,were observed for a typical film deposited using optimal conditions（substrate temperature = 500℃and NSD = 30 cm）.     

基于LabVIEW的LED显示屏箱体温度测控系统设计

利用LabVIEW作为系统开发平台,以AD590作为温度传感器,以USB2002作为数据采集卡,设计温度调理电路和温度控制电路.实现了LED显示屏箱体温度数据的采集与处理、温度曲线显示、数据分析与保存、温度范围控制等多种功能,极大增强了LED显示屏箱体的温度控制能力,提高了LED显示屏的使用寿命.