Degradation of Polycarbonate Properties Under Thermal Aging

Journal of Failure Analysis and Prevention - The aim of this paper is to characterize the thermal aging effect near the glass transition temperature of polycarbonate (PC) at different hold time....     

Modeling Failure Process and Quantifying the Effects of Multiple Types of Preventive Maintenance for a Repairable System

In this paper, we consider a repairable system whose failures follow a non‐homogenous Poisson process with the power law intensity function. The system is subject to corrective and multiple types of preventive maintenance. A corrective maintenance has a minimal effect on the system; however, a preventive maintenance may reduce the system's age. We assume the effects of different preventive maintenance on the system are not identical and derive the likelihood function to estimate the parameters of the failure process as well as the effects of preventive maintenance. Moreover, we derive the conditional reliability and the expected number of failures between two consecutive preventive maintenance types. The proposed methods are applied to a real case study of four trucks used in a mining site in Canada. Copyright © 2016 John Wiley & Sons, Ltd.     

Dynamical Comparison of Several Third-Order Iterative Methods for Nonlinear Equations

There are several ways that can be used to classify or compare iterative methods for nonlinear equations, for instance; order of convergence, informational efficiency, and efficiency index. In this work, we use another way, namely the basins of attraction of the method. The purpose of this study is to compare several iterative schemes for nonlinear equations. All the selected schemes are of the third-order of convergence and most of them have the same efficiency index. The comparison depends on the basins of attraction of the iterative techniques when applied on several polynomials of different degrees. As a comparison, we determine the CPU time (in seconds) needed by each scheme to obtain the basins of attraction, besides, we illustrate the area of convergence of these schemes by finding the number of convergent and divergent points in a selected range for all methods. Comparisons confirm the fact that basins of attraction differ for iterative methods of different orders, furthermore, they vary for iterative methods of the same order even if they have the same efficiency index. Consequently, this leads to the need for a new index that reflects the real efficiency of the iterative scheme instead of the commonly used efficiency index.     

Performance of Gradient-Based Optimizer for Optimum Wind Cube Design

Renewable energy is a safe and limitless energy source that can be utilized for heating, cooling, and other purposes. Wind energy is one of the most important renewable energy sources. Power fluctuation of wind turbines occurs due to variation of wind velocity. A wind cube is used to decrease power fluctuation and increase the wind turbine’s power. The optimum design for a wind cube is the main contribution of this work. The decisive design parameters used to optimize the wind cube are its inner and outer radius, the roughness factor, and the height of the wind turbine hub. A Gradient-Based Optimizer (GBO) is used as a new metaheuristic algorithm in this problem. The objective function of this research includes two parts: the first part is to minimize the probability of generated energy loss, and the second is to minimize the cost of the wind turbine and wind cube. The Gradient-Based Optimizer (GBO) is applied to optimize the variables of two wind turbine types and the design of the wind cube. The metrological data of the Red Sea governorate of Egypt is used as a case study for this analysis. Based on the results, the optimum design of a wind cube is achieved, and an improvement in energy produced from the wind turbine with a wind cube will be compared with energy generated without a wind cube. The energy generated from a wind turbine with the optimized cube is more than 20 times that of a wind turbine without a wind cube for all cases studied.     

17-4PH不锈钢在不同浓度HCl环境中的电化学腐蚀行为

为了探明17-4PH不锈钢在HCl溶液中的腐蚀行为,采用动电位极化和电化学阻抗测量了其在不同浓度HCl溶液中腐蚀性能,通过扫描电镜(SEM)、能谱(EDX)和X射线光电子能谱(XPS)等技术研究了锈层对腐蚀行为的作用机制.结果 表明:17-4PH不锈钢在HCl溶液中随着HCl浓度的增大,腐蚀电流密度(Jcorr)增大,锈层电阻和电荷转移电阻减小;当HCl浓度超过10％,腐蚀电流密度快速增加,15％ HCl溶液中的Jcorr比10％的增加1倍多.基于此,提出了2种不同的等效电路对17-4PH不锈钢的电化学阻抗谱进行了拟合.HCl溶液浓度小于等于10％时,17-4PH试样表面具有双锈层结构,其中,Cu元素富集在外层结构中;而浓度大于10％时为单一锈层结构.锈层的不同结构是腐蚀机制和性能产生差异的原因.     

简单0-1规划问题的动态DNA折纸计算模型

DNA折纸是一种全新的DNA自组装方法。将一个由DNA折纸卡槽、双态DNA机器、DNA行走机器人组装而成的动态折纸应用于求解0-1规划问题。其中DNA折纸卡槽由1条M13脚手架链和202条钉书钉链折叠而成。双态DNA机器分为不修饰和修饰金纳米颗粒两种情况,对应于0-1规划问题约束变量的取值为0或者1。DNA折纸卡槽和DNA双态机器组装成折纸基底。DNA行走机器人是7条单链折叠成的带有粘性末端的DNA折纸。在链的驱动下,DNA行走机器人在折纸基底上顺时针旋转行走,每步旋转120°。DNA行走机器人每走两步,与折纸基底上的DNA双态机器进行链置换,接收修饰的金纳米颗粒。当整个动态行走过程结束,根据透射电镜下DNA行走机器人接收的金纳米颗粒的大小和个数来判断约束变量的取值是否为可行解。该计算模型采用模块化结构,DNA折纸卡槽、双态DNA机器、DNA行走机器人等折纸均单独设计,且采用透射电镜读解,因而提高了模型实现的可行性。     

基于残差梯度法的神经网络Q学习算法

针对连续状态空间的非线性系统控制问题,提出一种基于残差梯度法的神经网络Q学习算法。该算法采用多层前馈神经网络逼近Q值函数,同时利用残差梯度法更新神经网络参数以保证收敛性。引入经验回放机制实现神经网络参数的小批量梯度更新,有效减少迭代次数,加快学习速度。为了进一步提高训练过程的稳定性,引入动量优化。此外,采用Softplus函数代替一般的ReLU激活函数,避免了ReLU函数在负数区域值恒为零所导致的某些神经元可能永远无法被激活,相应的权重参数可能永远无法被更新的问题。通过CartPole控制任务的仿真实验,验证了所提算法的正确性和有效性。     

面向脑机接口技术的属性可撤销访问控制方案

脑机接口技术(Brain-Computer Interface,BCI)在康复医学领域被广泛应用,然而其中的隐私数据保护问题常被忽略,从而引发严重的安全威胁,产生隐私泄露的隐患。针对BCI应用中的隐私保护问题,提出一种安全、高效的属性基访问控制方案。该方案利用版本号标记和代理重加密技术实现属性撤销,从而使访问策略灵活多变。实验分析表明,该方案有效地解决了BCI系统中的隐私保护问题,并提高了计算效率,降低了运算复杂度。     

一种新型污水处理剂的制备及其除铅性能研究

天然杭锦2^#土经改性活化研制成吸附剂，用于处理模拟含Pb^2 废水，探讨了吸附剂的制备方法、吸附时间、吸附率和吸附容量。实验发现用该吸附剂处理含Pb^2 废水，具有吸附量大、处理效果好等优点，经处理后的含pb^2 废水已达国家排放标准。