Improved design of robust exponentially weighted moving average control charts for autocorrelated processes

Residual‐based control charts for autocorrelated processes are known to be sensitive to time series modeling errors, which can seriously inflate the false alarm rate. This paper presents a design approach for a residual‐based exponentially weighted moving average (EWMA) chart that mitigates this problem by modifying the control limits based on the level of model uncertainty. Using a Bayesian analysis, we derive the approximate expected variance of the EWMA statistic, where the expectation is with respect to the posterior distribution of the unknown model parameters. The result is a relatively clean expression for the expected variance as a function of the estimated parameters and their covariance matrix. We use control limits proportional to the square root of the expected variance. We compare our approach to two other approaches for designing robust residual‐based EWMA charts and argue that our approach generally results in a more appropriate widening of the control limits. Copyright © 2010 John Wiley & Sons, Ltd.     

Investigation into real-time pressure sensing properties of SnO2, TiO2, and TiO2/ZnO thick films with interdigitated electrodes

The pressure sensing properties of nanocomposite SnO₂, TiO₂, and TiO₂/ZnO thick film capacitors with interdigitated electrodes are investigated. To form the dielectric layers, the metal oxides powders were respectively mixed with isopropanol, wet ball milled for 24 h, then the mixtures were dried at 120 °C and further the powders were placed under 2 tonnes of pressure to form pellets, which were fired at 1250 °C (rate of 5 °C/min) in a vacuum of 6 × 10⁻³ mbar for 5 h, followed by cooling (rate of 3 °C/min). After firing, the resultant nanopowders were mixed with 7 wt.% of polyvinyl butyral (binder) and suitable amount of ethylenglycolmonobutylether (solvent) to form the pastes. These were screen-printed over the Ag electrodes on alumina substrates to form SnO₂, TiO₂, and TiO₂/ZnO capacitor pressure sensors accordingly. The evaluation of pressure sensing properties of these sensors was performed using a HP 4192A Impedance Analyser, which recorded the changes in the values of the capacitances under different mechanical stresses. At the applied load of 5 kPa, the response times of 2.5 s, 5.6 s and 4 s were recorded for SnO₂, TiO₂, and TiO₂/ZnO sensors, respectively. In addition to instant response times, these pressure sensors have the advantage of being reusable, as their electrical properties were restored to the original value after annealing for 2 h at 80 °C. Moreover, one year later after the initial testing, the sensors were still operational and produced similar time responses to pressure.     

复杂形体超高层钢框架-混凝土核心筒混合结构减震的研究

以拟建超高宁夏电视塔(NXTVT)工程为背景,利用SAP2000建立其三维有限元分析模型。超高宁夏电视塔呈现底部小、上部大、中部略呈细腰形的花瓶状复杂形体;而且,楼层的不连续分布导致结构质量和侧向刚度沿竖向分布的不均匀。因此,整体结构形式复杂,对抗震要求高。首先,对结构的动力特性进行分析研究。在此基础上,使用振型分解反应谱法和FNA动力时程法对该结构的地震反应进行多维分析。接着,对安装非线性液体粘滞阻尼器(NFVDs)结构进行动力时程分析,以评价NFVDs对该结构的多维减震性能。通过大量的计算分析与比较,综合出了许多有益的结论与建议,为该实际工程或类似工程的减震设计提供参考依据。     

基于自适应蚁群优化的Volterra核辨识算法研究

提出了一种基于自适应蚁群优化(AACO)的Volterra核辨识方法。该方法将蚁群算法应用于Volterra时域核的辨识,并能够随着进化次数的增加,自适应调整基本蚁群算法的参数。同时,与相应的基于蚁群优化(ACO)的Volterra核辨识方法进行了对比分析。仿真结果表明,本文提出的方法与蚁群优化辨识方法不论在无噪声环境下,还是在有噪声干扰下,都能得到很好的辨识精度、收敛稳定性和较强的鲁棒抗噪性能,然而,在收敛速度方面,本文提出的方法优于蚁群优化辨识方法。     

基于位移反馈控制的主动增加时滞补偿方法及其试验验证

时滞是结构振动主动控制系统中普遍存在的现象,时滞不仅会降低控制系统的性能,严重时会造成系统失稳、控制发散。针对此问题,本文研究以下三方面内容：首先基于单自由度系统时滞的稳定性理论分析,确定系统最大允许时滞量的解析解,该阈值可以作为确定何时应用时滞补偿技术的一个评判指标;其次,当作动器实际时滞量大于最大允许时滞量时,常规时滞补偿方法将会失效,提出了基于位移反馈的主动增加时滞的补偿新方法,并定性结合定量详细分析了主动控制算法的参数影响规律;最后,以单层剪切型框架结构为被控对象,进行了多种输入激励下基于位移反馈的主动增加时滞补偿试验验证。大量仿真分析和试验结果表明本文所提方法能够在保证系统稳定性的同时获得一定可观的控制效果     

基于压电智能材料的自适应吸声实验研究

提出了用压电材料进行水下主动宽带低频吸声的方法,用PVDF复合智能材料作为主动吸声系统中的吸声材料,在滤波-X LMS算法基础上,研究了一种在工程中实现简便的次级通道建模方法——通道时延估计法。构建了数字时延控制系统,直接从实际声场中分离入射声波与反射声波作为控制系统的参考信号和误差信号,在脉冲声管中进行了管道声有源吸声控制实验。实验结果表明,在施加控制的情况下PVDF压电智能材料能有效地对低频入射声进行吸收。     

不同柔性链丙烯酸松香环氧树脂性能比较

以丙烯酸松香二缩水甘油酯(ARE)、丙烯酸松香乙二醇二缩水甘油醚(AR-EDGE)和丙烯酸松香丁二醇二缩水甘油醚(AR-BDGE)为研究对象,通过测定固化反应的凝胶时间、固化产物的耐热性、力学性能及耐溶剂性,研究了不同柔性链对松香基环氧树脂性能的影响。结果表明,松香基的稠环结构有着优异的耐热性,然而也会带来较大的脆性,需引入合适长度的柔性链。三种体系中,AR-EDGE综合性能最好,虽耐热性不及ARE,但其力学性能强于另两种体系;柔性链稍短的ARE因脆性大力学性能不好;柔性链稍长的AR-BDGE耐热性及耐丙酮性不佳,力学性能一般。     

关于自由基聚合几个值得关注的问题

总结了自由基聚合教学中的几个值得关注的问题,包括自由基聚合时不同引发剂类型的选择和确定、聚合温度及其区间选择及确定、聚合时间的确定、溶剂选择等。同时阐述了这些相关因素在自由基聚合研究方案设计时的相互关系。旨在使学生对自由基聚合的认识更为深刻和系统,培养学生独立进行自由基聚合研究方案设计的能力。     

基于瞬时输入能量时变特征的SDOF体系位移历程模拟

目前地震能量分析方法的研究多集中于对结构总输入能与总滞回耗能的简化估计,忽略了能量沿时间轴输入历程的不同所导致的结构反应的差别。该文以瞬时输入能量在时间轴上的分布特征（瞬时输入能量时变特征）来描述地震能量输入历程的特点,并通过建立瞬时输入能量时变特征与结构位移历程之间的联系,获得了基于能量参数的结构位移历程求解方法。为...