Viscoelastic material design with negative stiffness components using topology optimization

An application of topology optimization to design viscoelastic composite materials with elastic moduli that soften with frequency is presented. The material is a two-phase composite whose first constituent is isotropic and viscoelastic while the other is an orthotropic material with negative stiffness but stable. A concept for this material based on a lumped parameter model is used. The performance of the topology optimization approach in this context is illustrated using three examples.     

模糊控制在光纤熔缩棒控制系统中的应用

将模糊控制技术应用于光纤熔缩机熔缩棒压力控制,建立了光纤熔缩机模糊控制系统,并对该控制系统的硬件构成和软件实现作了具体分析,系统实现了联机调试,实现了熔缩棒的压力控制。     

回转体头部压力分布规律及其对转捩点的影响

以圆头回转体为研究对象,头部线型采用双参数椭圆曲线,利用面元法求解绕流势流流场,利用F.W.Scholkemeier的积分方法,确定该压力分布下的层流边界层,利用P.S.Granville方法求解边界层转捩点.通过变换头部线型参数,以最小压力系数绝对值的下降方向为搜索方向,研究不同头型压力分布的变化规律及其对转捩点的影响.结果表明:最小压力系数绝对值越小的头型其最小压力点离头部驻点的距离越近;不同头型的转捩点不光与其压力分布有关,而且还与其头部长径比有关.     

Crack propagation of pipeline steel exposed to a near-neutral pH environment under variable pressure fluctuations

This investigation attempts to understand the corrosion fatigue crack propagation behavior of pipeline steels exposed to near-neutral pH environments. The fatigue loading was designed to simulate the underload-type variable amplitude pressure fluctuations found during pipeline operation. The effects of amplitudes (R ratios) of underload and minor cycles were investigated. It has been found from this investigation that the crack growth rate is enhanced significantly through load interaction of the variable amplitude fatigue. The acceleration factor is found to be up to 2.7 and 5.3 for tests in air and in the near-neutral pH solution, respectively. The crack growth rate decreases with R ratios of underload and minor cycles for tests both in air and in near-neutral pH environments. The latter could enhance crack propagation by a factor of up to 11, as compared with the crack growth rate in air. The critical R ratio of minor cycles at which the minor cycles do not contribute to crack propagation through load interaction was determined to be as high as 0.982, which is much lower than the threshold determined by constant amplitude fatigue. This critical R ratio could be utilized to demarcate stress corrosion cracking and corrosion fatigue, and should be incorporated as one of the design principles for components/structures subjected to variable amplitude cyclic loading.     

水分对分子筛结构及吸附性能的影响

分子筛是变压吸附制氧过程中最重要的组分,使用中该组分常出现吸水失效问题,极大地影响了氧产量及浓度.针对此问题,本文以HD-1型和PU-8型分子筛为原料,通过在不同温度(100、200、300、400℃)下活化得到不同含水量的分子筛,并通过对不同材料的结构形貌、热性能及吸附性能的表征分析了水分对分子筛结构及吸附性能的影响.研究结果表明:水分不会破坏分子筛的骨架结构,但会增大晶胞参数,并导致HD-1型分子筛中阳离子迁移;分子筛中的物理吸附水和化学结晶水会影响其吸附性能,其中物理吸附水的影响最大;活化有效提高了分子筛的吸附性能,且温度越高,含水量越少,吸附性能越好;在150~180℃下活化,将物理吸附水脱附后,分子筛的吸附能力可恢复70%,可在此温度下进行吸附器内低温活化;在400℃下活化,脱除化学结晶水,分子筛吸附性能可100%恢复,400℃为两种分子筛的最佳活化温度.     

A discrete-time on–off source queueing system with negative customers

This paper studies a discrete-time single-server infinite-capacity queueing system with correlated arrivals, geometrically distributed service times and negative customers. Positive customers are generated by a Bernoulli bursty source, with geometrically distributed lengths of the on-periods and off-periods. Negative customers arrive to the system according to a geometrical arrival process which is independent of the positive arrival process. A negative customer removes a positive customer in service if any, but has no effect on the system if it finds the system empty. We analyze the Markov chain underlying the queueing system and evaluate the performance of the system based on generating functions technique. Closed-form expressions of some performance measures of the system are obtained, such as stationary probability generating functions of queue length, unfinished work, sojourn time distribution and so on. Finally, the effect of several parameters on the system is shown numerically.     

基于S7-300／400PLC的冗余控制系统在变压吸附（PSA）制氢装置中的应用

本文介绍了分别基于西门子S7—300PLC和S7—400PLC的两种冗余控制系统在荆门石化和鞍钢变压吸附制氢装置中的应用。概述了工艺过程和工艺对控制系统的要求,着重对上述两套系统的硬件配置和软件编程组态实施方案进行了描述。运行结果表明,上述系统稳定可靠,控制效果良好,能满足工艺要求。     

Effects of differences in office chair controls, seat and backrest angle design in relation to tasks

In this study the influence of chair characteristics on comfort, discomfort, adjustment time and seat interface pressure is investigated during VDU and non-VDU tasks: The two investigated office chairs, both designed according to European and Dutch standards are different regarding: 1) seat cushioning and shape, 2) backrest angle and 3) controls. Thirty subjects in total, both male and female, participated in two experiments: twenty in the first and ten in the second.Significant differences are found for ease of adjustment and adjustment time of controls, independent of the tasks. Related to tasks, a significant difference was found for the backrest range of motion. For non-VDU tasks a larger range of backrest motion was preferred by 70% of the subjects. The chair design differences were most clear for comfort and adjustment time of controls, followed by comfort of backrest angle. No differences are found between seat pan comfort and discomfort, first impressions and peak interface pressure.     

<Emphasis Type="Italic">New-Age</Emphasis>: A Negative Bias Temperature Instability-Estimation Framework for Microarchitectural Components

Degradation of device parameters over the lifetime of a system is emerging as a significant threat to system reliability. Among the aging mechanisms, wearout resulting from Negative Bias Temperature Instability (NBTI) is of particular concern in deep submicron technology generations. While there has been significant effort at the device and circuit level to model and characterize the impact of NBTI, the analysis of NBTI’s impact at the architectural level is still at its infancy. To facilitate architectural level aging analysis, a tool capable of evaluating NBTI vulnerabilities early in the design cycle has been developed that evaluates timing degradation due to NBTI. The tool includes workload-based temperature and performance degradation analysis across a variety of technologies and operating conditions, revealing a complex interplay between factors influencing NBTI timing degradation.     

A new solution for a queueing model of a manufacturing cell with negative customers under a rotation rule

In this paper, we consider a queueing model extension for a manufacturing cell composed of a machining center and several parallel downstream production stations under a rotation rule. A queueing model is extended with the arrival processes of negative customers to capture failures of production stations, reorganization of works and disasters in the manufacturing cell. We present an exact solution for the steady-state probabilities of the proposed queueing model. The solution does not require the approximation of the infinite sum. In addition, it provides an alternative way to compute the rate matrix for the matrix-geometric method as well.