Impact of defects on the decomposition of chemical warfare agent simulants in Zr-based metal organic frameworks

Metal organic frameworks (MOFs) containing zirconium secondary building units (SBUs) in UiO-67 and related MOFs, are highly active for neutralizing both the chemical warfare agents and simulants, such as dimethyl methylphosphonate (DMMP). However, two recent publications gave conflicting reports of DMMP reaction with UiO-67 under ultra high vacuum (UHV) conditions, with one reporting chemisorption and reaction (Wang et al., J Phys Chem C, 2017, 121, 11261–11272) and the other reporting only physisorption and reversible desorption (Ruffley et al., J Phys Chem C, 2019, 123, 19748–19758) from very similar temperature programmed desorption experiments. We show that the discrepancy between these experiments may be explained by different levels of missing linker defects in the UiO-67 samples. We present density functional theory calculations showing that SBU sites having two-adjacent missing linkers exhibit reaction barriers that are about 30 kJ/mol lower than SBU sites having a single missing linker. We also show that topology of the undercoordinated sites plays an important role in the reaction barrier under UHV conditions.     

Multiphase topology optimization with a single variable using the phase-field design method

In this study, a multimaterial topology optimization method using a single variable is proposed by combining the solid isotropic material with penalization method and the reaction-diffusion equation. Unlike ordinary multimaterial optimization, which requires several variables depending on the number of material types, this method intends to represent various materials as one variable. The proposed method combines two special functions in the sensitivity analysis of the objective function to converge the design variable into prespecified density values defined for each of the multimaterials. The composition constraint based on a normal distribution function is also introduced to estimate the distribution of each target density value in a single variable. It enables density exchange between multiple materials by increasing or decreasing the amount of a specific material. The proposed method is applied to structural and electromagnetic problems to verify its effectiveness, and its usefulness is also confirmed from the viewpoint of cost and computation time.     

基于FAHP的机械振动WSN均衡拓扑构建方法

针对机械振动无线传感器网络因拓扑不均衡导致传输时延和网络传输能耗增加的问题,提出了一种基于模糊层次分析(fuzzy analytic hierarchy process,简称FAHP)的均衡拓扑构建方法,该方法由构建模糊判断矩阵和计算权重向量组成。首先,传感器节点进行簇内通信获取信标广播信息,将信标节点网络决策因子统一量纲化,利用网络决策因子构建模糊判断矩阵;其次,检验模糊判断矩阵一致性,采用行和归一化处理或拉格朗日最小二乘法计算权重向量;最后,传感器节点通过权重向量计算出各个信标节点综合权值,关联最优信标节点为父节点加入网络,将提出的模糊层次分析拓扑构建方法与基于链路质量单准则构建网络拓扑机制进行对比。实验结果表明,该方法能有效改善传输时延和机械振动无线传感器节点网络寿命。     

An engineering method for complex structural optimization involving both size and topology design variables

This work presents an engineering method for optimizing structures made of bars, beams, plates, or a combination of those components. Corresponding problems involve both continuous (size) and discrete (topology) variables. Using a branched multipoint approximate function, which involves such mixed variables, a series of sequential approximate problems are constructed to make the primal problem explicit. To solve the approximate problems, genetic algorithm (GA) is utilized to optimize discrete variables, and when calculating individual fitness values in GA, a second-level approximate problem only involving retained continuous variables is built to optimize continuous variables. The solution to the second-level approximate problem can be easily obtained with dual methods. Structural analyses are only needed before improving the branched approximate functions in the iteration cycles. The method aims at optimal design of discrete structures consisting of bars, beams, plates, or other components. Numerical examples are given to illustrate its effectiveness, including frame topology optimization, layout optimization of stiffeners modeled with beams or shells, concurrent layout optimization of beam and shell components, and an application in a microsatellite structure. Optimization results show that the number of structural analyses is dramatically decreased when compared with pure GA while even comparable to pure sizing optimization.     

折臂式随车起重机转台的拓扑优化设计

为了使折臂式随车起重机转台在最大应力不超过材料许用应力的前提下实现轻量化设计的目的,通过ADAMS软件仿真确定其极限工况,对转台进行静力学分析及拓扑优化。通过拓扑优化得到了理想的材料分布。基于优化结果调整转台结构,并对改进后的转台进行静力学分析。结果表明,优化后的转台能够满足实际的使用需求。同时,转台质量降低了12%,证明了优化设计的有效性和可行性,并为折臂式随车起重机的相关设计提供了一定的借鉴。     

Void region restriction for additive manufacturing via a diffusion physics approach

A longstanding challenge in additive manufacturing (AM), the presence of void regions in additively manufactured components, causes two main issues: the enclosing of build material powder in powder bed fusion techniques and limiting tool access in critical post-processing operations to remove sacrificial support structures. As topology optimization has embraced and overcome many of the obstacles of incorporating AM constraints into the underlying numerical optimization statement, there exist few solutions that directly address this fundamental void region issue. By developing computationally efficient and effective solutions to this problem, the integration of these two advanced technologies can be fully realized. Drawing on inspiration from the principles of diffusion physics, a particle diffusion void restriction (PDVR) method is presented in this work that is capable of encouraging the optimization scheme to generate final designs that are fully accessible. Additionally, this method empowers the user to choose the type of post-processing method to clear support material (eg, three-axis or five-axis milling operations, number and orientation of part set-ups) and, therefore, quantify the level of costs associated with the post-processing operation. The PDVR optimization framework is demonstrated on multiple two- and three-dimensional test problems, with physically manufactured examples depicting the real-world benefits this method admits.     

基于残差决策的自动飞行控制系统远程实时故障诊断

针对自动飞行控制系统结构复杂、关联部件众多,发生故障时诊断时间长,从而影响飞机运行效率的问题,提出一种基于飞机通信寻址报告系统(ACARS)的远程实时故障诊断方案。首先,分析自动飞行控制系统的故障特点,设计搭建检测滤波器;然后,利用ACARS数据链实时发送的自动飞行控制系统的关键信息进行相关部件的残差计算,并根据残差决策算法进行故障诊断及定位;最后,针对不同故障部件残差间的差异大、决策门限无法统一的缺点,提出基于二次差值的残差决策改进算法,减缓了检测对象的整体变化趋势,降低了随机噪声和干扰的影响,避免了将瞬态故障诊断为系统故障的情况。实验仿真结果表明,基于二次差值的改进残差决策算法避免了多决策门限的复杂性,在采样时间为0.1 s的情况下,故障检测所需时间大约为2 s,故障检测时间大幅降低,有效故障检测率大于90%。     

浅谈高压变频调速变压器及高压变频系统结构

介绍了高压变频调速变压器及高压变频器系统的基本原理及结构,详细论述了系统各组成部分的功能,并进行了举例说明。     

基于消息队列的通信系统异步传送控制仿真

传统方法对通信系统异步传送控制效果不佳,存在信号干扰及传送时间间隔较长等问题。为此引入消息队列技术,提出一种新的传送控制方法来解决以上问题。对通信系统的空时信道进行空时编码设计,实现空时信道的编码增益与分集增益;利用空时编码实现通信系统中继节点的空间分集,根据空间分集结果制订异步空时传送方案;采用消息队列技术构建通信系统异步传送控制模型,实现通信系统的异步传送控制。为了验证所提方法异步传送控制效果,设计对比实验。实验结果表明,上述方法的传送时间间隔较短,抗干扰能力强,平均分集增益高,说明所提方法更适用于通信系统的异步传送控制。     

Looking at both sides of relationship dynamics in virtual communities: A social exchange theoretical lens

This study draws on social exchange theory to investigate the relationship dynamics of the member–community dyad in virtual community settings. Using a longitudinal design and multiple measurement sources, the findings indicate that social and task communication styles have unique effects on members’ community commitment velocity, which in turn influences member gratitude and entitlement behaviors. A moderated path analysis demonstrates that the effects of social and task communication styles on community commitment velocity are both positively moderated by attachment anxiety and attachment avoidance. It also reveals that members’ level of popularity augments the influence of community commitment velocity on member entitlement behavior.