Polynomial filtering for nonlinear stochastic systems with state‐ and disturbance‐dependent noises

This article is concerned with the polynomial filtering problem for a class of nonlinear stochastic systems governed by the Itô differential equation. The system under investigation involves polynomial nonlinearities, unknown‐but‐bounded disturbances, and state‐ and disturbance‐dependent noises ((x,d)‐dependent noises for short). By expanding the polynomial nonlinear functions in Taylor series around the state estimate, a new polynomial filter design method is developed with hope to reduce the conservatism of the existing results. In virtue of stochastic analysis and inequality technique, sufficient conditions in terms of parameter‐dependent linear matrix inequalities (PDLMIs) are derived to guarantee that the estimation error system is input‐to‐state stable in probability. Moreover, the desired polynomial matrix can be obtained by solving the PDLMIs via the sum‐of‐squares approach. The effectiveness and applicability of the proposed method are illustrated by two numerical examples with one concerning the permanent magnet synchronous motor.     

Time dependent failure probability estimation of the solid oxide fuel cell by a creep-damage related Weibull distribution model

In present paper, a new model is proposed and embedded into the finite element software ABAQUS to estimate the time dependent failure probability of the solid oxide fuel cell stack. The results show that sealant is the potential failure region of the solid oxide fuel cell stack, while the failure probability of the anode, electrolyte and cathode are very small within the operation time of 50,000 h. The creep and damage distribution of the components reflect that the proposed model can reasonably predict the time dependent failure probability of the solid oxide fuel cell stack. Increasing either the characteristic strain, Weibull modulus or decreasing the operating temperature can decrease the failure probability of the SOFC stack. For the sealant, to ensure the high temperature integrity of the SOFC stack, the characteristic strain should be larger than 0.01 or Weibull modulus should be higher than 8.0 under the operating temperature of 600 °C.     

弯载下砂岩声发射特征值时间效应

为探索开采速度对采空区顶板破断特征影响的力学机制，设定不同加载速率，开展砂岩3点弯曲和声发射试验，研究砂岩弯曲折断过程的力学行为及其受加载速度影响的时间效应和折断前兆特征。结果表明，加载速率越快，砂岩显著初始损伤声发射发生的应力条件越高，积累的应变能越高;岩石折断前，前兆声发射时间长度与加载速率呈指数负相关，加载速度越快，前兆声发射时间越短，可预测性越差;加载速率与砂岩折断声发射峰值能量及破坏载荷呈指数正相关，与砂岩折断声发射峰值计数呈指数负相关，加载速度越快，岩石折断所需的破坏荷载越大，峰值声发射计数越少，一次性释放的能量越高。上述岩石弯曲声发射特征值是加载速率的函数，存在时间效应。从机理上解释了煤矿开采速度越高，顶板岩体动力灾害危险性相对越高，可预测性越差的原因。     

Influence of anion structure on thermal,mechanical, dielectric and electrochemical properties of ZrO2 nanoparticle-pyrrolidinium ionic liquid hybrid electrolytes for the application in energy storage devices

Influence of the two different anion structures viz. bis(fluorosulfonyl)imide (FSI^?) and bis(trifluoromethanesulfonyl) imide (TFSI^?), on the thermophysical, dielectric and electrochemical properties of ZrO₂-nanoparticle tethered pyrrolidinium based nanoscale hybrid ionic fluids (NHIFs) was investigated. Thermal and mechanical properties of NHIFs were found to depend strongly upon the structure of anions and TFSI^? comprising NHIF showed better thermal and mechanical stability then its FSI^? analogue. Temperature dependent electrical conductivity, dielectric and electrochemical properties of different NHIFs were studied. FSI-NHIF displayed higher ionic conductivity, associated with faster structural relaxation dynamics. At all the measured temperature, FSI-NHIF displayed superior electrochemical cycling performance than its TFSI-equivalent. While, electrochemical cell with TFSI-NHIF showed 81% capacitance retentivity after 5000 charge/discharge cycles, FSI-NHIF cell was found to retain >90% of its initial specific capacitance value after the same. Results obtained from the study optimize the applicability of pyrrolidinium based hybrid ionic fluids as electrolytes in secondary energy storage devices.     

一种耦合区间-随机混合可靠性分析方法

考虑区间变量的耦合性，基于多椭球模型提出了一种高效的耦合区间-随机混合可靠性分析方法。为解决耦合区间变量导致的可靠性分析计算效率低的问题，采用序列迭代分析方法，将混合可靠性分析的双层耦合循环分解为概率分析与区间分析，并结合多项式插值法提出了一种适用于极限状态函数关于耦合区间变量单调与非单调两种工况的高效区间分析算法。算例结果表明，所提的混合可靠性分析方法具有较好的计算精度与计算效率。     

中国建筑话语中的“文脉”(1980年代-1990年代)

对"文脉"一词进入中国建筑话语的历史作出概览式的回顾,并分别以"阙里宾舍"和"西单商业大楼"为例,从设计者的自述与建筑界的评论入手,探讨1980年代末到1990年代初"文脉热"兴起的可能原因。指出对"复古主义"的批判和创作有"民族特色"建筑的愿望是"文脉"一词背后潜在的诉求,同时,也警醒地看到,基于特定时代背景,中国建筑界对西方后现代主义等建筑思潮不可避免地片面理解和吸收,也造成了"文脉"逐渐丧失了其本应具有的批判性与创造力。     

水文序列相依变异识别的RIC定阶准则——以自回归模型为例

水文过程相依性是水文变异的主要表现形式之一,应用自回归模型对其进行拟合时合理确定模型阶数是一个难点问题。本文在分析AIC和BIC准则的基础上,提出了一种以原序列与其相依成分的相关系数作为拟合度指标,同时借用信息熵形式的函数式,作为模型不确定性度量指标的自回归模型定阶准则(简称RIC准则)。以AR(1)、AR(2)、AR(3)和AR(4)模型为例进行统计试验,将不同序列长度下该准则的定阶准确率与其他定阶准则进行比较,试验结果表明,RIC准则对于上述模型均具有较好的适应性,且定阶准确率远高于AIC准则,其中对于前三阶模型RIC准则优于BIC准则,但四阶模型略低于BIC准则。RIC准则的优势是可以同时满足模型定阶、相依程度分级与模型检验的需求,将其应用于实测水文序列分析,结果显示,该准则能较准确地识别自回归模型的阶数,且符合提出的"相依有变异而残差无变异的最小阶数"的检验标准。     

New cardo silylated poly(azomethine)s containing 9,9′‐diphenylfluorene units as materials with Brønsted acid‐dependent fluorescence

Aromatic poly(azomethine)s have been studied due to their attractive properties such as high thermal stability, semiconducting behavior and the ability to coordinate species with their imine units (C?N). In this paper, the synthesis and characterization of two novel silylated poly(azomethine)s containing cardo units are reported. These materials were highly soluble in organic solvents such as chloroform and m‐cresol and were thermally stable, and PAzMC1 exhibited a high glass transition temperature value (287 °C), while that for PAzMC2 was not observed. UV–visible spectrophotometry revealed absorption bands related to the aromatic backbone of both PAzMCs, 300–285 nm in tetrahydrofuran and 310–301 nm in dimethylsulfoxide, and bands attributed to the conjugated imine unit at around 350 nm. In order to investigate the phenomenon of the emission of fluorescence promoted by dopant agents with regard to potential optoelectronic applications, the materials were doped with H₂SO₄ and their optical and electrochemical properties investigated. Thus, the absorption band of the imine group was suppressed due to the nitrogen atoms being protonated. Fluorescence spectroscopy analysis developed in dilute solutions of polymers showed no emission from the undoped polymers, whereas the acid‐doped species emitted fluorescence in the UV and violet regions (322 nm). Cyclic voltammetry measurements were carried out and HOMO–LUMO energies were estimated. This study provides a starting point for the development of new poly(azomethine)s with doping‐dependent emission. © 2019 Society of Chemical Industry     

Heat and mass transfer flow over a stretching surface with Ohmic heating and chemical reaction

The present study analyzes the effect of chemical reaction on an unsteady magnetohydrodynamic boundary layer viscous fluid over a stretching surface embedded in a porous medium with a uniform transverse magnetic field. A Darcy‐Forchheimer drag force model is employed to simulate the effect of second‐order porous resistance. Dissipative heat energy based on both viscous and Joule dissipation along with a heat source/sink is considered to enhance the energy equation. Similarity analysis is imposed to transform the governing differential equations into a set of nonlinear coupled ordinary differential equations. These sets of equations are solved numerically using the Runge‐Kutta fourth‐order scheme followed by the shooting algorithm. The effects of physical parameters such as magnetic field, Prandtl number, Eckert number, Schmidt number, unsteadiness parameter, and chemical reaction parameters have been discussed on velocity, temperature, and concentration fields. Computation for the coefficient of skin friction, rate of heat and mass transfer is done and presented in a table for validation of the present outcomes.