Reactive wetting behavior and mechanism of AlN ceramic by CuNi-Xwt%Ti active filler metal

In order to propel the application of the developed CuNi-Xwt%Ti active filler metal in AlN brazing and get the universal reactive wetting mechanism between liquid metal and solid ceramic, the reactive wetting behavior and mechanism of AlN ceramic by CuNi-Xwt%Ti active filler metal were investigated. The results indicate that, with the increasing Ti content, surface tension for liquid CuNi-Xwt%Ti filler metal increases at low-temperature interval, but very similar at high-temperature interval, which influence the wetting behavior on AlN ceramic obviously. CuNi/AlN is the typical non-reactive wetting system, the wetting process including rapid wetting stage and stable stage. The wettability is depended on surface tension of the liquid CuNi filler metal completely. However, the wetting process of CuNi-8wt.%Ti/AlN and CuNi-16 wt%Ti/AlN reactive wetting system is composed by three stages, which are rapid wetting stage decided by surface tension, slow wetting stage caused by interfacial reaction and stable stage. For CuNi-8wt.%Ti/AlN and CuNi-16 wt%Ti/AlN reactive wetting system, although the surface tension of liquid filler metal is the only factor to influence the instant wetting angle θ₀ at rapid wetting stage, the reduced free energy caused by interfacial reaction at slow wetting stage plays the decisive role in influencing the final wettability.     

A diagnostic tool for online sensor health monitoring in air-conditioning systems

Healthy sensors are essential for the reliable monitoring and control of building automation systems (BAS). This paper presents a diagnostic tool to be used to assist building automation systems for online sensor heath monitoring and fault diagnosis of air-handling units. The tool employs a robust sensor fault detection and diagnosis (FDD) strategy based on the Principal Component Analysis (PCA) method. Two PCA models are built corresponding to the heat balance and pressure-flow balance of an air-handling process. Sensor faults are detected using the Q-statistic and diagnosed using an isolation-enhanced PCA method that combines the Q-contribution plot and knowledge-based analysis. The PCA models are updated using a condition-based adaptive scheme to follow the normal shifts in the process due to changing operating conditions. The sensor FDD strategy, the implementation of the diagnostic tool and experimental results in an existing building are presented in this paper.     

动圈式永磁平面电机平稳起浮与下降无位置传感器控制策略

针对动圈式永磁平面电机无位置传感器控制起浮过程中出现的误差过大、抖动以及下降过程中撞击定子表面等问题,分析了在实时电流分配策略下动子的移动过程,提出了"假气隙点"概念,推导出了"假气隙点"位置与期望气隙点位置的数学关系表达式和动子起浮至期望气隙点和下降至零高度的时间计算积分公式,并给出了平稳起浮和下降控制策略。"假气隙点"现象表现为动子停留在零位置时,对线圈分配"假气隙点"恒定电流,在此电流驱动下动子运行至期望气隙点处速度为0;动子悬浮在期望气隙点位置时,对线圈分配"假气隙点"恒定电流,在此电流驱动下动子运行至零位置处速度为0。控制策略利用上述现象,通过切换电流使动子在零位置和气隙点之间平稳移动。仿真结果表明,动子运行误差、抖动很小,证明了控制策略的正确性。     

Mixed H∞ and passive filtering for switched Takagi-Sugeno fuzzy systems with average dwell time

This paper investigates the mixed H_∞ and passive filtering problem for switched Takagi-Sugeno (T-S) fuzzy systems with average dwell time (ADT) in both continuous-time and discrete-time contexts. To deal with this problem, a new performance index is proposed for switched systems. This new performance index can be viewed as the mixed weighted H_∞ and passivity performance index. Based on this new performance index, the weighted H_∞ filtering problem and the passive filtering problem for switched T-S fuzzy systems can be solved in a unified framework. Combining the multiple Lyapunov functions approach with a matrix decoupling technique, new sufficient conditions for the existence of mixed weighted H_∞ and passive filters are obtained for switched T-S fuzzy systems. All these conditions are expressed in terms of linear matrix inequalities (LMIs). The desired filters can be constructed by solving these LMIs. Finally, numerical examples and practical examples are provided.     

Geometrically resilient color image zero-watermarking algorithm based on quaternion Exponent moments

Although research on zero-watermarking has made great progress in recent years, most of it has been focused on grayscale images rather than color ones, and cannot resist geometric attacks efficiently. In this paper, we discuss properties of quaternion Exponent moments (QEMs) in detail and propose a robust color image zero-watermarking algorithm which is robust to geometric attacks. We first compute and select robust QEMs of the original color image, and then a binary feature image is constructed using the magnitude of the selected moments. Eventually, a bitwise exclusive-or is applied on the binary feature image and a scrambled binary logo to generate the zero-watermark image. Experimental results show that the proposed zero-watermarking algorithm is robust to both geometric attacks and common image processing attacks effectively. Compared to similar zero-watermarking algorithms and traditional watermarking algorithms based on QEMs, the proposed zero-watermarking algorithm has better performance.     

浅谈Profibus总线电缆的安装规范

通过调研,对Profibus现场总线电缆在奇瑞汽车安装中暴露的问题进行了分析,指出Profibus现场总线常见的接线不规范现象及可能产生的后果.提出了Profibus现场总线电缆的合理安装规范,克服了总线电缆安装出现的问题.     

遥感相机姿态控制轴的动平衡结构设计与验证

多个遥感相机固定在一颗遥感卫星上,调整其中一个遥感相机工作姿态的反作用力产生的角动量会改变遥感卫星的姿态,进而影响其他遥感相机的工作姿态。为了在遥感相机姿态控制轴内自平衡该角动量,减小影响,设计了一种遥感相机姿态控制轴动平衡机械机构。该机构主要由一个驱动电机、一个主轴、一个传动齿轮系、一个增速器及一个角动量平衡轮组成。机构工作时,电机转子驱动主轴带动遥感相机姿态控制轴调整相机姿态,同时,电机定子的反作用力通过传动齿轮系、增速器逐级传递,驱动角动量平衡轮旋转。通过调整角动量平衡轮的质量放大比或者增速器的增速比可得适当量值的平衡轮角动量,实现机构内部动平衡。基于角动量守恒定律和理论力学基本原理,证明了机构设计的正确性。最后,建立了遥感相机姿态控制动平衡机构的三维动态仿真模型,根据机构的实际参数,设定了机构的仿真参数,在给定负载的条件下进行了仿真验证和结果分析,进一步验证了设计的可行性。     

A novel process with the characteristics of low-temperature bonding and high-temperature resisting for joining Cf/SiC composite to GH3044 alloy

Taking advantages of reaction composite brazing, transient liquid phase bonding (TLP) and partial transient liquid phase bonding (PTLP), a novel process with the characteristics of low-temperature bonding and high-temperature resisting was developed for joining C_f/SiC composite to GH3044 alloy by using (Cu-Ti) + C + Ni mixed powder filler. Under the bonding temperature (980 °C), the reaction between the liquid Cu-Ti alloy and C particles (reaction composite mechanism), composition homogenizations between the joining layer and Ni particles (PTLP mechanism) as well as Ni-based substrate (TLP mechanism) occurred to complete the transformation (Cu,Ti)_l + C_s + Ni_s → TiC_s + (Cu,Ni)_s. Thereby, a joint with high-temperature resistance and excellent mechanical properties was obtained in relatively short holding time. The melting-point of the joint (1050 °C) was obviously higher than that of Cu-Ti alloy (898 °C) in the filler. The bonded joints exhibited shear strengths of 229, 225 and 104 MPa at room temperature, 600 °C and 1000 °C, respectively.     

基于改进蚁群算法的移动机器人路径规划研究

针对蚁群算法在复杂环境下收敛速度慢且易陷入局部最优值的问题,提出一种改进的蚁群优化算法。该方法依据起始点和目标点位置信息选择全局有利区域增加初始信息素浓度,提高前期蚂蚁搜索效率;增加避障策略,避免蚂蚁盲目搜索产生大量交叉路径并有效减少蚂蚁死锁数量;采用动态参数控制的伪随机转移策略,提出优质蚂蚁信息素更新原则,自适应调整挥发系数,提高算法全局性;进行二次路径规划,优化路径并降低移动机器人能耗的损失。实验结果表明,该算法有较高的全局搜索能力,收敛速度明显加快,并且可以有效提高移动机器人工作效率,验证了该算法的有效性和优越性。     

一种基于环形振荡器的轻量级高效率的真随机数发生器

真随机数发生器(TRNG)作为芯片中重要的安全组件,在现代加密系统中扮演着越来越重要的角色。对于TRNG的设计,关键是需要熵提取器可以在恶劣的环境变化(如工艺波动、电压和温度(PVT))下稳定地生成熵值。基于Xilinx FPGA平台提出了一种基于环形振荡器的低成本,高效率真随机数发生器。TRNG一方面通过快速进位逻辑来提高熵提取的效率,另一方面通过优化电路结构和延迟,在以相对较低的资源开销情况下实现可观的吞吐量和随机性。TRNG分别在多块Xilinx Virtex6 FPGAs和Xilinx Spartan6 FPGAs上进行验证,实验数据测试结果表明,所提出的TRNG能够在广泛的PVT范围内表现出良好的鲁棒性,且生成的随机比特流不仅以相当高P值通过NIST SP800-22统计测试套件,而且可以通过最新的NIST SP800-90B测试。