Statistical modeling of mains zero crossing variation in powerline communication

In this paper, authors investigate statistical modeling of measured mains Zero Crossing (ZC) non idealities in narrowband powerline communication systems (PLC) using time series approach based on autoregressive moving average model (ARMA). For this purpose, Box Jenkins analysis steps are deployed for detected ZC impulsive variations. Estimated models exhibit a good fit based on R-square metric reaching 90%. This modeling approach is extended to three measurement environment: in home, in lab and rural locations. Obtained models are useful for NB-PLC channel emulator implementation.     

Accurate sub-swarms particle swarm optimization algorithm for service composition

Service composition (SC) generates various composite applications quickly by using a novel service interaction model. Before composing services together, the most important thing is to find optimal candidate service instances compliant with non-functional requirements. Particle swarm optimization (PSO) is known as an effective and efficient algorithm, which is widely used in this process. However, the premature convergence and diversity loss of PSO always results in suboptimal solutions. In this paper, we propose an accurate sub-swarms particle swarm optimization (ASPSO) algorithm by adopting parallel and serial niching techniques. The ASPSO algorithm locates optimal solutions by using sub-swarms searching grid cells in which the density of feasible solutions is high. Simulation results demonstrate that the proposed algorithm improves the accuracy of the standard PSO algorithm in searching the optimal solution of service selection problem.     

燃气轮机燃烧室中藻类替代燃料混合物的 污染物排放和性能

在一个单头部燃气轮机燃烧室中,针对与传统航空煤油(RP-3)混合的藻类替代燃料,本文进行了实验研究。实验中使用的基于藻类的替代燃料由几种烷烃混合而成,用以模拟微型藻类的碳分布。本实验研究了各种混合物的排放性能、贫油熄火极限和喷雾特性。在实验中测试了六种燃料,包括纯航空煤油和五种替代燃料混合物。在慢车状态下进行实验,进口空气压力为460 kPa,温度为511 K,流量为0.498 kg/s。实验结果表明,各种混合物的喷雾角度随替代燃料比例的增大而略有下降。当替代燃料的质量分数达到10%时,观察到燃烧性能的显著变化,这些性能包括燃烧效率、贫油熄火极限和污染物排放。     

基于电流反馈的MSCMG轴向磁轴承低功耗控制

为了进一步降低MSCMG永磁偏置轴向磁轴承的悬浮功耗,在建立其数学模型的基础上,针对传统定气隙控制在承受负载时线圈电流增大的问题,提出了基于电流积分正反馈的轴向磁轴承变气隙控制方法。该方法利用永磁偏置混合磁轴承的位移负刚度提供悬浮力,通过电流反馈改变转子悬浮参考位置来减小磁轴承线圈电流。仿真分析和试验结果表明,该方法具有良好的稳定性,与定气隙控制方法相比,磁轴承静浮时的铜耗降低了90%以上。     

实时操作系统RTEMS的复杂网络特征与传播代价研究

本文从复杂网络的角度分析了实时操作系统RTEM中与硬件相关的C文件夹和与硬件无关的CPUKIT文件夹的结构和性质。通过计算RTEMS从4.6.0到4.10.0共22个版本的一些参数,发现RTEMS的C文件夹和CPUKIT文件夹都具有"小世界"和"无标度"性质。同时本文也计算了RTEMS版本演化过程中节点变对RTEMS可维护性的影响,并采用一种定量度量软件可维护性的概念,平均故障传播代价,计算了RTEMS的CPUKIT各个版本的可维护性。     

用于减小总谐波失真的乘法器设计

模拟乘法器是实现有源功率因数校正(APFC)的关键模块电路.为了提高APFC电路的性能,在对目前一般芯片中普遍采用校正电路的THD(总谐波失真)较大,导致功率因数较低的原因进行分析研究的基础上,给出了一种高线性度的单像限模拟乘法器,该乘法器在经典的电路结构上加以改进,采用双极型和CMOS混合工艺设计,在德国XFAB工艺厂进行流片.仿真测试和流片结果表明,该乘法器消除了传统的APFC电路总谐波失真较大的缺陷,提高了功率因数,并且没有增加版图面积,具有较高性价比,适合嵌入在中小功率APFC芯片中使用.     

基于插值矩阵技术与二维空间平滑法的近场相干声源识别研究

在研究插值矩阵技术与二维空间平滑法两种方法的基础上,将两者进行结合,提出了一种对近场相干声源进行识别的方法。首先通过插值矩阵技术把实际阵列接收到的近场信号转换为形式上的远场信号,然后通过二维空间平滑法求出阵列的平滑协方差矩阵,再由平滑协方差矩阵得到给定方向向量对应的信号功率,实现二维相干声源的识别。算例表明,该方法比传统的波束形成能更准确地定位出声源的位置。     

机场塔台模拟器视景构建研究与设计

塔台模拟器就是为高效地培养塔台管制员而研制的高逼真度的模拟训练系统。在塔台模拟器中,建立虚拟的机场三维图像,逼真的飞机运动模型和车辆模型,构筑和真实的塔台高度相似的操作台、显示画面、通讯设备、工作流程和系统响应,让学员有一个完善的场景沉浸感,从中培养合理的工作习惯和敏锐的直觉,磨砺工作技能和心理素质,对提高培训质量、缩短塔台实习时间,节省培训费用都有很大的好处。目前,该类培训已在发达国家开始实施,但是在国内还刚刚开始。本文主要从实践的角度研究塔台模拟器视景部分的构建与实现,关于它与主体控制模块的衔接也进行了一定分析,并以拉脱维亚里加机场为具体研究模型。     

宫颈上皮脱落细胞的微尺度力学性质及形貌学研究

目前临床中对宫颈脱落细胞的检查多局限于大体细胞形态学的观察.本文应用原子力显微镜及环境扫描电子显微镜对5例临床宫颈炎患者的宫颈脱落细胞进行了微区力学性质表征以及细胞表面微观形态的成像.结果显示,患者正常形态宫颈上皮脱落细胞在针尖压入深度为700 nm时杨氏模量近似正态分布,峰值在20～30kPa.且细胞表面微嵴明显,微...     

An efficient strategy for multidisciplinary reliability design and optimization based on CSSO and PMA in SORA framework

The conventional reliability-based multidisciplinary design optimization (RBMDO) integrates the reliability-based design optimization and multidisciplinary design optimization (MDO) directly, which leads to a triple-level nested optimization loop. Especially, the multidisciplinary reliability analysis in the middle layer dominates the whole efficiency of RBMDO. To tackle this problem, first of all, a sequential multidisciplinary reliability analysis (SMRA) approach that integrates the concurrent subspace optimization (CSSO) strategy and the performance measure approach is proposed, in which the multidisciplinary analysis, system sensitivity analysis and reliability analysis are decoupled and arranged sequentially, making a recursive loop. The multidisciplinary analysis and system sensitivity analysis provide the value and gradient information of limit-state function for reliability analysis respectively. As a result, a great number of repeated iterations of the whole reliability analysis are eliminated. Secondly, the CSSO has been integrated with the sequential optimization and reliability assessment (SORA) to decouple the triple-level nested RBMDO procedures into a sequence of cycles of deterministic MDO and multidisciplinary reliability analysis. Therefore, the expensive computation of the whole reliability analysis model in each iteration of RBMDO is avoided. And also, the CSSO is adopted in the deterministic MDO to deal with medium-scale and coupled multidisciplinary systems. The procedures of the proposed approaches are presented in detail. The effectiveness of the proposed strategies is demonstrated and verified with two design examples.