改进的灰色模型在光催化数据预测中的应用

光催化去除水中污染物的研究通常得到的是小样本的离散数据,利用拟一级动力学模型对实验结果进行模拟和分析,有时拟合效果较差,且无法用于数据预测.本研究在离散灰色预测模型(DGM(1,1))的基础上,考虑数据的非线性特征并结合等维信息替代思想建立了非线性动态离散灰色模型(EDGM(1,1,α)),利用该模型对三元复合材料Bi...     

Goal-oriented adaptivity based on a model hierarchy of mean-field and full-field homogenization methods in linear elasticity

Homogenization methods are drawing increasing attention for simulation of heterogeneous materials like composites. For balancing the accuracy and the numerical efficiency of such strategies, we deal with both model and discretization errors of the finite element method (FEM) on a macroscale. Within a framework of goal-oriented adaptivity, we consider linear elastic heterogeneous materials, for which first-order homogenization schemes apply. A novel model hierarchy is proposed based on mean-field and full-field homogenization methods. For the former, we consider several well-established schemes like Mori-Tanaka or self-consistent as basic models, and for the latter, as superior models, unit cell problems are solved via the FEM under an a priori chosen boundary condition. For a further stage of the model hierarchy, we consider hierarchical unit cells within the frame of the FEM toward an adaptive selection of the unit cell size. By means of several numerical examples, we illustrate the effectiveness of the proposed adaptive approach.     

On autoregressive model selection for the exponentially weighted moving average control chart of residuals in monitoring the mean of autocorrelated processes

With the development of automation technologies, data can be collected in a high frequency, easily causing autocorrelation phenomena. Control charts of residuals have been used as a good way to monitor autocorrelated processes. The residuals have been often computed based on autoregressive (AR) models whose building needs much experience. Data have been assumed to be first-order autocorrelated, and first-order autoregressive (AR(1) ) models have been employed to obtain residuals. But for a p th-order autocorrelated process, how the AR(1) model affects the performance of the control chart of residuals remains unknown. In this paper, the control chart of exponentially weighted moving average of residuals (EWMA-R) is used to monitor the p th-order autocorrelated process. Taking the mean and standard deviation of run length as performance indicators, two types of EWMA-R control charts, with their residuals obtained from the p th-order autoregressive AR(p) and AR(1) models, respectively, are compared. The results of the numerical experiment show that for detecting small mean shifts, EWMA-R control charts based on AR(1) models outperform ones based on AR(p) models, whereas for detecting large shifts, they are sometimes slightly worse. A practical application is used to give a recommendation that a large number of samples are necessary for determining an EWMA-R control chart before using it.     

Phase II monitoring of survival times with categorical covariates

Monitoring surgical outcomes is of paramount importance especially by accounting for health conditions of the patients prior to surgery. However, the problem arises as the effect of some covariates is pronounced but cannot be measured. In this paper, in order to deal with the effect of measured and unmeasured (categorical) covariates simultaneously, a class of survival analysis regression models called accelerated failure time (AFT) model and discrete frailty models is integrated and some Phase II risk-adjusted control schemes are devised to monitor the patients' lifetime. Three monitoring procedures including the cumulative sum (CUSUM), exponentially weighted moving average (EWMA), and probability limits-based control charts are developed in the presence and absence of censored observations. The performance analysis reveals that the proposed AFT frailty-based CUSUM control chart outweighs the competing counterparts in detecting shifts under various scenarios. Subsequently, two CUSUM control charts have been constructed corresponding to the cases of neglecting both the unmeasured and measured covariates and ignoring just the unmeasured covariate. The results clearly indicate that the detection ability for both of the mentioned CUSUM control charts declines, and including the unmeasured and measured covariates is critical while monitoring surgical outcomes. Finally, a real case study in a cardiac surgical center in the United Kingdom has been provided to investigate the application of the proposed AFT frailty-based CUSUM control scheme.     

Improving the performance of CUSUM charts

The control chart is an important statistical technique that is used to monitor the quality of a process. Shewhart control charts are used to detect larger disturbances in the process parameters, whereas CUSUM and EWMA charts are meant for smaller and moderate changes. Runs rules schemes are generally used to enhance the performance of Shewhart control charts. In this study, we propose two runs rules schemes for the CUSUM charts. The performance of these two schemes is compared with the usual CUSUM, the weighted CUSUM, the fast initial response CUSUM and the usual EWMA schemes. The comparisons revealed that the proposed schemes perform better for small and moderate shifts, whereas they reasonably maintain their efficiency for large shifts as well. Copyright © 2010 John Wiley & Sons, Ltd.     

A Generalized Quasi-MMSE Controller for Run-to-Run Dynamic Models

This study proposes a generalized quasi-minimum mean square error (qMMSE) controller for implementing a run-to-run process control where the process input–output relationship follows a general-order dynamical model with added noise. The expression of the process output, the long-term stability conditions and the optimal discount factor of this controller are derived analytically. Furthermore, we use the proposed second-order dynamical model to illustrate the effects of mis-identification of the process I-O model on the process total mean square error (TMSE). Via a comprehensive simulation study, the model demonstrates that the TMSE may inflate by more than 150% if a second-order dynamical model with moderately large carryover effects is wrongly identified as that of a first-order model. This means that the effects of mis-identification of the process I-O model on the process total mean square error (TMSE) is not negligible for implementing a dynamic run-to-run (RTR) process control. Supplementary materials for this article are available online.     

On improved dispersion control charts under ranked set schemes for normal and non‐normal processes

In manufacturing industries, control charts are the promising statistical tools used for an efficient monitoring of processes. These charts enhance the product quality by timely signaling for special variations at any stage of the process. There are two common concerns in statistical process monitoring, location and variability of the quality characteristic of interest. Besides location parameter, the monitoring of process dispersion remained a matter of concern for researchers. The conventional simple random sampling (SRS) is a usual practice; however, ranked set sampling (RSS) schemes are very effective methods of choosing sample values. This study intends to design and investigate dispersion control charts under different RSS strategies for normal and non‐normal processes. We have considered RSS, median ranked set sampling (MRSS), and extreme ranked set sampling (ERSS) schemes to design dispersion control charts. The performance of the existing and the proposed control charts is evaluated in terms of relative efficiency and power for normal and a variety of non‐normal distributions. The comparative analysis revealed that the proposed structures outperform the existing charts. The application of the proposed procedures is also shown for a bottles filling process for an efficient and timely signaling of any special causes in the process.     

基于GRU神经网络的自相关过程残差控制图

为提升自相关过程监控的效率,提出基于门控循环单元(gated recurrent unit,GRU)神经网络的自相关过程残差控制图。采用受控下的自相关过程数据对GRU网络进行离线训练与测试,对预测误差进行监控,形成控制用残差控制图。采用训练好的GRU网络预测当前过程波动,利用控制用残差控制图判定当前过程是否失控。运用蒙特卡洛仿真法,与基于一阶自回归模型、BP神经网络以及支持向量回归构建的残差控制图进行性能对比。研究表明,过程受控时,所提残差控制图与其他3种的稳态平均运行链长相差不大,即4者的性能表现相当;而在均值偏移异常过程中,所提残差控制图的平均运行链长远小于其他3种,对自相关过程均值偏移具有较好的监控性能。     

Sono-sorption as a new method for the removal of lead ion from aqueous solution

Sorption of Pb(II) as a toxic heavy metal ion, onto styrene-divinylbenzene co-polymer resin in the presence of ultrasound (sono-sorption) and in its absence (classical method) is presented in this work. Batch experiments were conducted to study the effect of the main parameters such as the amount of sorbent, concentration of sorbate, contact time, intensity of ultrasound and temperature on this sorption process. The equilibrium between liquid and solid phase was described by Langmuir model better than the Freundlich model. The time to reach equilibrium especially in the presence of ultrasound was very fast. This indicates that the resin mentioned has a high potential for the sorption of this pollutant ion. The isotherm constants were obtained under several different conditions. These constants were used in the calculation of the thermodynamic parameters of sorption. According to the results, the kinetics of sorption was in agreement with both pseudo-first-order and first-order reversible models.     

On the robustness and efficiency of integration algorithms for a 3D finite strain phenomenological SMA constitutive model

Most devices based on shape memory alloys experience large rotations and moderate or finite strains. This motivates the development of finite‐strain constitutive models together with the appropriate computational counterparts. To this end, in the present paper a three‐dimensional finite‐strain phenomenological constitutive model is investigated and a robust and efficient integration algorithm is proposed. Properly defining the variables, extensively used regularization schemes are avoided and a nucleation–completion criterion is defined. Moreover, introducing a logarithmic mapping, a new form of time‐discrete equations is proposed. The solution algorithm as well as a suitable initial guess for the resultant nonlinear equations are also deeply discussed. Extensive numerical tests are performed to show robustness as well as efficiency of the proposed integration algorithm. Implementation of the integration algorithm within a user‐defined subroutine UMAT in the commercial nonlinear finite element software ABAQUS/Standard makes also possible the solution of a variety of boundary value problems. The obtained results show the efficiency and robustness of the proposed approach and confirm the improved efficiency (in terms of solution CPU time) when a nucleation–completion criterion is used instead of regularization schemes, as well as when a logarithmic mapping is used for the time‐discrete evolution equation instead of an exponential mapping. Copyright © 2010 John Wiley & Sons, Ltd.     

一种低复杂度的正交频分复用水声信道估计方法

高可靠性、低复杂度的信道估计是实现正交频分复用(OFDM)数据通信的必要前提。由于水声信道是时间、频率高度散射的信道,传统的基于维纳滤波的信道估计复杂度过高,参考无线信道的广义平稳非相关散射(WSSUS)模型,本文提出了一种基于最小均方误差(MMSE)准则的低复杂度OFDM水声信道估计方案,其运算复杂度明显降低,并被实际实验证明是可行、有效的。     

A Time Splitting Space Spectral Element Method for the Cahn-Hilliard Equation

We propose and analyse a class of fully discrete schemes for the Cahn-Hilliard equation with Neumann boundary conditions. The schemes combine large-time step splitting methods in time and spectral element methods in space. We are particularly interested in analysing a class of methods that split the original Cahn-Hilliard equation into lower order equations. These lower order equations are simpler and less computationally expensive to treat. For the first-order splitting scheme, the stability and convergence properties are investigated based on an energy method. It is proven that both semi-discrete and fully discrete solutions satisfy the energy dissipation and mass conservation properties hidden in the associated continuous problem. A rigorous error estimate, together with numerical confirmation, is provided. Although not yet rigorously proven, higher-order schemes are also constructed and tested by a series of numerical examples. Finally, the proposed schemes are applied to the phase field simulation in a complex domain, and some interesting simulation results are obtained.     

CO2跨临界循环带膨胀压缩机系统热力学分析

膨胀压缩机是一种膨胀功回收装置，膨胀机的膨胀功全部用于提供给辅助压缩机作为输入功，以驱动压缩机完成压缩过程。膨胀压缩机在系统中可以与主压缩机串联和并联，由于布置形式不同，则压缩机的流量和压比改变，导致系统循环性能系数也发生变化。本文利用简单的压缩机模型，对CO2跨临界循环带膨胀压缩机的两种不同布置系统形式进行了分析，并在理想等熵情况和考虑压缩机和膨胀机效率情况下进行了对比，得出串联模式系统的中间压力不能达到系统最优中间压力，串联模式系统COP总是高于并联模式系统。     

用三维离散元实现混凝土Ⅰ型断裂模拟

为了进行从连续介质到非连续介质转化的数值模拟,实现结构破坏全过程的仿真分析,本文基于三维变形体离散元法,分别采用弥散的旋转裂缝模型和分离裂缝模型分析了混凝土、岩石等准脆性材料的受拉开裂行为。通过单轴拉伸算例和对比三点弯梁试验的数值计算与试验结果,说明在确定的断裂能情况下,两种断裂模型均能够合理预测结构的荷载位移响应;并且基于离散单元法的分离裂缝模型不仅可以获得裂缝开裂过程荷载位移全曲线,而且可以实现系统部分或完全失效溃决过程的仿真分析。     

Robustness properties of Cuscore statistics for monitoring a nonstationary system

We investigate the performance of cumulative score (Cuscore) charts in monitoring a nonstationary process subject to minimum mean‐squared error (MMSE) feedback control. Specifically, we have previously designed Cuscore statistics to discover spike or step signals hidden in a nonstationary noise disturbance for feedback‐controlled processes. Here, we study the properties of the proposed policies in terms of their robustness to process model misspecification, to deviations from assumed values for their parameters, to model misspecification for the disturbance as well as to model misspecification for the signal. We found that, in general, the Cuscore charts are fairly robust to process and signal model misspecification. However, they are less robust to departures from its true parameter values. We present a numerical example to demonstrate the importance of understanding the Cuscore's robustness as well as its construction and application. Copyright © 2008 John Wiley & Sons, Ltd.     

An Efficient Certificateless Aggregate Signature Scheme Designed for VANET

The Vehicular Ad-hoc Network (VANET) is the fundamental of smart transportation system in the future, but the security of the communication between vehicles and vehicles, between vehicles and roadside infrastructures have become increasingly prominent. Certificateless aggregate signature protocol is used to address this security issue, but the existing schemes still have many drawbacks in terms of security and efficiency: First, many schemes are not secure, and signatures can be forged by the attacker; Second, even if some scheme are secure, many schemes use a large number of bilinear pairing operation, and the computation overhead is large. At the same time, the length of the aggregated signature also increases linearly with the increase of user numbers, resulting in a large communication overhead. In order to overcome the above challenges, we propose a new certificateless aggregate signature scheme for VANET, and prove the security of the scheme under the random oracle model. The new scheme uses pseudonym to realize the conditional privacy protection of the vehicle’s information. The new scheme does not use bilinear pairing operation, and the calculation efficiency is high. At the same time, the length of the aggregate signature of the new scheme is constant, thereby greatly reducing the communication and storage overhead. The analysis results demonstrate that the new scheme is not only safer, but also superior in performance to the recent related schemes in computation overhead and communication cost.     

Monitoring the Shape Parameter of a Weibull Regression Model in Phase II Processes

In this paper, the interest is focused on monitoring profiles with Weibull distributed‐response and common shape parameter γ in phase II processes. The monitoring of such profiles is completely possible by taking the natural logarithm of the Weibull‐distributed response. This is equivalent to characterize the correspondent process by an extreme value linear regression model with common scale parameter σ = γ^?1. It was found out that from the monitoring of the common log‐scale parameter of the extreme value linear regression model, with the help of a simple scheme, it can be obtained important information about the deterioration of the entire process assuming the β coefficients as nuissance parameters that do not have to be known but stable. Control charts are based on the relative log‐likelihood ratio statistic defined for the log‐scale parameter of the log‐transformation of the Weibull‐distributed response and its respective signed square root. It was also found out that some existing adjustments are needed in order to improve the accuracy of using the distributional properties of the monitoring statistics for relatively small and moderate sample sizes. Simulation studies suggest that resulting charts have appealing properties and work fairly acceptable when non‐large enough samples are available at discrete sampling moments. Detection abilities of the studied corrected control schemes improve when sample size increases. Copyright © 2014 John Wiley & Sons, Ltd.     

用3D离散元实现Ⅰ/Ⅱ型拉剪混合断裂的模拟

将变形体离散元分别与弥散式旋转裂缝模型和分离式裂缝模型耦合起来,采用上述两种非线性断裂力学模型分析了混凝土、岩石等准脆性材料的Ⅰ/Ⅱ型拉剪混合模式的开裂行为,以实现从连续介质到非连续介质转化的数值模拟。基于变形体离散元方法的界面接触本构关系提出了混凝土Ⅰ/Ⅱ混合型开裂的拉剪分区开裂准则;基于缝面法向开度增大对刚度强度的逐渐折减实现了界面裂缝扩展的模拟。作为数值验证,通过单边切口非对称三点弯梁试验的数值计算与试验结果对比,表明两种断裂力学模型均能够合理预测裂缝的起裂和扩展,在混合形式的荷载条件下,裂缝通常以Ⅰ/Ⅱ型拉剪混合模式起裂,而后以Ⅰ型为控制方式稳定扩展。文末指出,基于离散单元法的分离裂缝模型能够实现系统在外载作用下破坏全过程仿真。     

Fast Initial Response for CUSUM Quality-Control Schemes: Give Your CUSUM A Head Start

The fast initial response (FIR) feature for cumulative sum (CUSUM) quality-control schemes permits a more rapid response to an initial out-of-control situation than does a standard CUSUM quality-control scheme. This feature is especially valuable at start-up or after a CUSUM has given an out-of-control signal. This article presents the average run length and the distribution of run length for CUSUM schemes with the FIR feature and compares FIR CUSUM schemes to standard CUSUM schemes. The comparisons show that if the process starts out in control, the fast initial response feature has little effect; however, if the process mean is not at the desired level, an out-of-control signal will be given faster when the FIR feature is used.     

Optimal design of a distribution-free quality control scheme for cost-efficient monitoring of unknown location

Traditionally, a cost-efficient control chart for monitoring product quality characteristic is designed using prior knowledge regarding the process distribution. In practice, however, the functional form of the underlying process distribution is rarely known a priori. Therefore, the nonparametric (distribution-free) charts have gained more attention in the recent years. These nonparametric schemes are statistically designed either with a fixed in-control average run length or a fixed false alarm rate. Robust and cost-efficient designs of nonparametric control charts especially when the true process location parameter is unknown are not adequately addressed in literature. For this purpose, we develop an economically designed nonparametric control chart for monitoring unknown location parameter. This work is based on the Wilcoxon rank sum (hereafter WRS) statistic. Some exact and approximate procedures for evaluation of the optimal design parameters are extensively discussed. Simulation results show that overall performance of the exact procedure based on bootstrapping is highly encouraging and robust for various continuous distributions. An approximate and simplified procedure may be used in some situations. We offer some illustration and concluding remarks.