任意型一维FIR数字滤波器设计新方法

本文介绍了一种设计任意型（宽带、窄带、低阶、高阶、低通、高通、带通、带阻）一维FIR数字滤波器新方法．给出设计不同类型滤波器的统一方法。各种类型滤波器脉冲响应的设计公式简单、计算方便。该方法消除了Gibbs现象．不仅克服了优化设计中收敛速度、设计精度及初值选取等问题，而且减少设计高阶滤波器的时间。最后，本文给出了各种类型滤波器设计的仿真结果。     

Vibrations of stretched damped beams under non-ideal boundary conditions

A simply supported damped Euler-Bernoulli beam with immovable end conditions are considered. The concept of non-ideal boundary conditions is applied to the beam problem. In accordance, the boundaries are assumed to allow small deflections and moments. Approximate analytical solution of the problem is found using the method of multiple scales, a perturbation technique.     

A critique of internal oxidation in alloys during the post-wagner era

Wagner's classical treatment of internal oxidation (generic name allowing for reaction with oxygen, nitrogen, carbon or sulfur) assumed ideal conditions such as uninhibited dissolution of the gas, formation of spherical particles, diffusion of the oxidant in the solvent as the rate-controlling step, equilibrium conditions, etc. However, during the 45 years since his treatment, many observations have been made to complicate the idealized situation suggested by Wagner. This paper examines the most important modifications with respect to Wagner's original analysis. The following items are discussed. (a) The role of solute concentration: The parabolic kinetics are much higher than expected for Ni–Al alloys due to rapid interfacial diffusion of oxygen along the interfaces between cylindrical rods of Al₂O₃ (perpendicular to the surface) and the matrix. (b) Precipitate morphology: Spherical precipitates seem almost to be the exception. A wide variety of forms have been observed, including Widmanstätten platelets, cylindrical rods, hexagonal plates, dendritic or fishbone products, etc. The competition between nucleation and growth is useful to explain the observed structures. (c) Intergranular internal oxidation: Rapid oxygen diffusion in grain boundaries may lead to a wide variety of intergranular-precipitate structures. (d) Internal-oxide bands: Wavy, approximately parallel bands form at a finite distance beneath the surface in certain alloys having very reactive solutes, e.g., Ag–Mg. It is postulated that high stresses generated by precipitation play a major role. (e) Surface nodules of pure solvent metal: High stresses generated during precipitation cause extrusion of solute through dislocation pipes, leading to extensive nodule formation on either grain boundaries or on the grains (or both), depending on the alloy and oxidizing conditions. (f) Nonstoichiometric precipitates: Either hypo- or hyperstoichiometric particles can form as very small clusters in certain alloys (Ag–Al). The nature of precursors and changes in stoichiometry during reaction are discussed. (g) Trapping of oxidant: Diffusion of the oxidant may be slowed appreciably by trapping with the solute, although no precipitates need to form. Lower-than-expected kinetics (based on normal diffusivities of the oxidant) result. (h) High-solubility-product precipitates: Concentration profiles of solute, oxidant and precipitate are quite different than those expected for low-solubility-product precipitates as considered by Wagner. In particular, a variable mole fraction of precipitate exists, and further precipitation occurs in the reaction zone after the front has passed by. Linear kinetics have been observed for some Nb-base alloys at very high temperatures and low oxygen pressures. The rate-controlling step is the arrival of oxygen at the surface and not oxygen diffusion in the metal. (i) Dual oxidants: Two gases may diffuse·simultaneously and each forms its own product with the solute. The thermodynamically most-stable compound forms near the surface, and the less-stable compound deeper in the alloy. The less-stable compound is subsequently converted to the more-stable compound with a concomitant release of the second oxidant. Although numerous examples have been reported of systems which do not behave as predicted by Wagner, his theory still remains as the cornerstone of our understanding and is still the starting point for virtually every study in internal oxidation.     

考虑电池储能老化和需求侧响应的交直流混合配电网动态重构方法

现有的电池储能模型一方面认为电池的充放电功率和效率为固定不变的,另一方面有关电池储能的充放电过程对循环老化的影响缺少考虑,这与电池单元本体的非线性等效电路模型相违背。因此,考虑电池储能的循环老化成本、需求侧响应,提出了交直流混合配电网动态重构方法。通过对实际电池储能的充放电功率的运行区域进行采样,在凸包络的采样点集合中将非理想状态下的电池储能模型重构为线性模型。在此基础上,分别建立了基于累积吞吐电量和放电深度的循环老化成本模型,构建了综合成本最小化的交直流混合配电网动态重构模型。并采用混合整数二阶锥规划方法求解。在改进的33节点算例上仿真验证了所提基于放电深度的循环老化成本模型的经济性,分析了交直流混合配电网重构方法经济性的影响因素。     

基于DFT的旋变软件解码非理想偏差标定方法

针对目前旋变软件解码中的采样包络面存在非理想偏差问题,从理论推导了幅值偏差、直流偏差会对旋变软件解码的输出角度叠加一个2倍频波动,正交偏差会叠加一个同频波动。提出了基于离散傅里叶变换(DFT)的矫正方法,利用该方法实现了幅值偏差、直流偏差和正交偏差的提取,并对这3种偏差设计了相应的矫正环节。同时又推导了存在转速误差条件下使用DFT方法提取到的幅值偏差、直流偏差存在一个和旋变包络面初始相位相关的波动误差,并通过取一段时间内波动平均值的方法解决了该误差对提取结果的影响。最后通过仿真试验验证了推导的正确性,搭建了拖台架并进行旋变标定试验,对比标定前后数据,表明偏差矫正后的锁相环输出的角度线性度更好,转速波动更小,相应的dq轴电流的指定阶次波动也更小。     

协同频谱感知在非理想报告信道中的性能

针对非理想报告信道环境中的认知无线电多用户协同频谱感知问题,建立了协同感知三层模型;以单用户为例,分析了报告信道传输错误对单用户感知性能的影响;同时,基于Newman—Pearson准则推导了统计值传输和判决值传输条件下的最优协同频谱感知方法,并给出了平坦瑞利衰落环境下感知性能的上限。     

LTE-Advanced系统小基站的增强技术研究

小基站已成为运营商为用户提供更高数据业务速率和容量的重要技术手段，但随着小基站部署密度的增大，会导致很多问题的出现，如频繁的切换失败，回程链路的非理想化等等。通过进一步研究小基站的增强技术，可以更好地改善这种多层混合组网的整体性能。为解决这些问题，文章针对不同场景进行了增益分析，并给出了潜在解决方案，最后通过分析对比，找到比较合适的小基站增强技术。     

一种基于电流反馈的分段式PWM控制无刷直流电机转矩波动抑制方法

无刷直流电机伺服系统具有广泛的应用场合,但转矩波动限制了其在高精度场合的应用。针对非理想反电动势引起的无刷直流电机转矩波动提出了一种基于电流反馈的分段式PWM控制方法。该方法通过线反电动势观测器获得产生目标转矩值的参考电流,以实现对电机转矩的直接控制。同时,针对电机高速与低速运行状态分别采用不同的PWM控制策略来有效消除换相转矩波动,系统具有低转矩波动和高转矩输出的特点。通过在Matlab/Simulink环境下建立系统仿真模型,对该控制方法的转矩直接控制能力进行检验,并对转矩波动进行了对比;搭建实验平台对具有非理想反电动势的无刷直流电机进行了驱动实验。仿真和实验结果表明,该文所提出的控制方法能有效减小转矩波动,提高无刷直流电机伺服系统输出转矩的稳定性和位置控制精确度。     

Assessing the impact of non-ideal optical factors on optimized solar dish collector system with mirror rearrangement

An optimized solar dish collector (OPSDC) system was proposed in our previous work, which can achieve excellent the optical efficiency and flux uniformity under ideal optics. On this basis, the impacts of the non-ideal optical factors on the optical performance of OPSDC system with a cylindrical and conical receiver are studied in detail and compared with the conventional solar dish collector (COSDC) system in this paper. Where the non-ideal optical factors considered are relatively comprehensive, including the mirror slope error, tracking error, installation error of the mirror and receiver, and receiver's absorptivity degeneration. An optical model with the non-ideal optical factors is built in detail by the ray tracing method, and the corresponding ray tracing codes are developed and verified by literatures and optical software OptisWorks 2012. The results show that the OPSDC system not only has a significantly smaller peak local concentration ratio (LCR) and non-uniformity factor than the COSDC system under the same non-ideal optical factor, but also has excellent optical performance. This means that OPSDC system can effectively avoid the heat absorber generating high-temperature hot spots, thus significantly improving its working reliability and service lifetime. In addition, the tracking error, installation error of the receiver and mirror all lead to the increase of the peak LCR and non-uniform factor, while the mirror slope error and absorber's absorptivity degeneration are conducive to reducing the peak LCR and non-uniform factor. This work can provide a reference for error control of COSDC system and OPSDC system in manufacturing, installation and operation.