Design of exponential control charts based on average time to signal using a sequential sampling scheme

Exponential charts based on time-between-events (TBE) data are widely investigated and applied in various fields. The average time to signal (ATS) is used instead of the average run length to evaluate the performance of TBE charts, since the ATS involves both the number and the time of samples inspected until a signal occurs. An ATS-unbiased exponential control chart is proposed when the in-control parameter is known. Considering the need in practice to start monitoring a production process as soon as possible, a sequential sampling scheme is adopted and the in-control parameter is estimated by an unbiased and consistent estimator. Some specific guidelines to stop updating control limits are obtained from the relationship between the phase I sample size and the actual false alarm rate. Finally, two real examples are given to illustrate the implementation and efficiency of the proposed method.     

A Study of Control Chart for Monitoring Exponentially Distributed Characteristics Based On Type‐II Censored Samples

In this paper, control charts for monitoring the exponential type‐II censoring samples are investigated. Such data are very common in many practical inspection scenarios in reliability context when items are replaced in groups after a period of time. The average time to signal, which involves both the number and the time of samples inspected until a signal occurs, is a good criterion to evaluate the performance of control charts. We propose an average time to signal‐unbiased control chart with known parameter and compare the proposed method with the traditional ones. The results indicate the proposed control chart is more sensitive to system deterioration. Then the effects of parameter estimation on the proposed control charts are evaluated. Because the control limits with estimated parameters result in more false alarms, an adjusted control chart with estimated parameters is proposed and the self‐starting control chart based on a sequential sampling scheme is adopted to solve the phase I problem. Finally, two examples are given to illustrate the implementation of the proposed approach. Copyright © 2017 John Wiley & Sons, Ltd.     

The Run Sum Hotelling's χ2 Control Chart with Variable Sampling Intervals

Control charts are widely used for process monitoring and quality control in manufacturing industries. Implementing variable sampling interval (VSI) control schemes on control charts rather than traditional fixed sampling interval procedure can significantly improve the control chart's efficiency. In this paper, the VSI run sum (RS) Hotelling's χ² chart is proposed. The optimal scores and parameters of the proposed chart are determined using an optimization technique to minimize the following: (i) out‐of‐control average time to signal (ATS); (ii) adjusted ATS (AATS), when the exact shift size can be specified; (iii) expected ATS; or (iv) expected AATS, when the exact shift size cannot be specified. The Markov chain method is used to evaluate the zero‐state ATS and expected ATS, and steady‐state AATS and expected AATS of the proposed chart. The results show that the VSI RS Hotelling's χ² chart significantly outperforms the standard RS Hotelling's χ² chart and the former also performs well compared with other competing charts. By adding more scoring regions, the efficiency of the VSI RS Hotelling's χ² chart can be further enhanced. An illustrative example using data from a manufacturing process is presented to demonstrate the application of the VSI RS Hotelling's χ² chart. The application of the proposed chart in a quality improvement program can be extended to management and service industries. Copyright © 2016 John Wiley & Sons, Ltd.     

Adaptive charting schemes based on double sequential probability ratio tests

Sequential probability ratio test (SPRT) control charts are shown to be able to detect most shifts in the mean or proportion substantially faster than conventional charts such as CUSUM charts. However, they are limited in applications because of the absence of the upper bound on the sample size and possibly large sample numbers during implementation. The double SPRT (2‐SPRT) control chart, which applies a 2‐SPRT at each sampling point, is proposed in this paper to solve some of the limitations of SPRT charts. Approximate performance measures of the 2‐SPRT control chart are obtained by the backward method with the Gaussian quadrature in a computer program. On the basis of two industrial examples and simulation comparisons, we conclude that the 2‐SPRT chart is competitive in that it is more sensitive and economical for small shifts and has advantages in administration because of fixed sampling points and a proper upper bound on the sample size. Copyright © 2008 John Wiley & Sons, Ltd.     

The Effect of Parameter Estimation on Upper‐sided Bernoulli Cumulative Sum Charts

The Bernoulli cumulative sum (CUSUM) chart has been shown to be effective for monitoring the rate of nonconforming items in high‐quality processes where the in‐control proportion of nonconforming items (p₀) is low. The implementation of the Bernoulli CUSUM chart is often based on the assumption that the in‐control value p₀ is known; therefore, when p₀ is unknown, accurate estimation is necessary. We recommend using a Bayes estimator to estimate the value of p₀ to incorporate practitioner knowledge and to avoid estimation issues when no nonconforming items are observed in phase I. We also investigate the effects of parameter estimation in phase I on the upper‐sided Bernoulli CUSUM chart by using the expected value of the average number of observations to signal (ANOS) and the standard deviation of the ANOS. It is found that the effects of parameter estimation on the Bernoulli CUSUM chart are more significant than those on the Shewhart‐type geometric chart. The low p₀ values inherent to high‐quality processes imply that a very large, and often unrealistic, sample size may be needed to accurately estimate p₀. A methodology to identify a continuous variable to monitor is highly recommended when the value of p₀ is low and the required phase I sample size is impractically large. Copyright © 2012 John Wiley & Sons, Ltd.     

Traceable Nanoparticles with Dual Targeting and ROS Response for RNAi‐Based Immunochemotherapy of Intracranial Glioblastoma Treatment

The chemotherapy of glioblastoma is severely hindered by the immunosuppressive tumor microenvironment, especially the tumor growth factor β (TGF‐β), an immunosuppressive cytokine. In this study, it is proposed to employ RNAi‐based immunomodulation to modify the tumor immune microenvironment and improve the effect of chemotherapy. Herein, a nanotheranostic system (Angiopep LipoPCB(Temozolomide+BAP/siTGF‐β), ALBTA) with dual targeting and ROS response is established for intracranial glioblastoma treatment. The traceable nanoparticles exhibit strong siRNA condensation, high drug loading efficiency, good serum stability, and magnetic property. They can efficiently cross the blood–brain barrier and target to glioblastoma cells via receptor‐mediated transcytosis. The zwitterionic lipid (distearoyl phosphoethanol‐amine‐polycarboxybetaine lipid) in ALBTA promotes endosomal/lysosomal escape, and thus enhances the cytotoxicity of temozolomide and improves gene silencing efficiency of siTGF‐β. ALBTA significantly improves the immunosuppressive microenvironment and prolongs the survival time of glioma‐bearing mice. Moreover, ALBTA can be accurately traced by MRI in brain tumors. The study indicates that this immunochemotherapeutic platform can serve as a flexible and powerful synergistic system for treatment with brain tumors as well as other brain diseases in central nervous system.     

Properties of the exponential EWMA chart with parameter estimation

Count rates may reach very low levels in production processes with low defect levels. In such settings, conventional control charts for counts may become ineffective since the occurrence of many samples with zero defects would cause control statistic to be consistently zero. Consequently, the exponentially weighted moving average (EWMA) control chart to monitor the time between successive events (TBE) or counts has been introduced as an effective approach for monitoring processes with low defect levels. When the counts occur according to a Poisson distribution, the TBE observations are distributed as exponential. Although the assumption of exponential distribution is a reasonable choice as a model of TBE observations, its parameter, i.e. the mean (also the standard deviation), is rarely known in practice and its estimate is used in place of the unknown parameter when constructing the exponential EWMA chart. In this article, we investigate the effects of parameter estimation on the performance measures (average run length, standard deviation, and percentiles of the run length distribution) of the exponential EWMA control chart. A comprehensive analysis of the conditional performance measures of the chart shows that the effect of estimation can be serious, especially if small samples are used. An investigation of the marginal performance measures, which are calculated by averaging the conditional performance measures over the distribution of the parameter estimator, allows us to provide explicit sample size recommendations in constructing these charts to reach a satisfactory performance in both the in‐control and the out‐of‐control situation. Copyright © 2009 John Wiley & Sons, Ltd.     

Economic‐Statistical Design of Acceptance Control Chart

Acceptance control charts are effective tools to monitor capable processes in which the fraction of the produced nonconforming items is very low. In these charts, some controlled changes in the process mean are allowed, and the production of a specified number of defectives is tolerated. Designing these acceptance control charts by considering the cost of sampling, detecting, and investigating out‐of‐control signals as well as the probable correction of assignable cause(s) can result in economic advantages. Moreover, the statistical properties of the control charts can be satisfied. In this article, an economic‐statistical model is developed to design acceptance control charts. An illustrative example is used to compare the results of economic versus economic‐statistical design of the acceptance control charts. In addition, a comprehensive sensitivity analysis is conducted on the basis of the parameters of the model. Copyright © 2012 John Wiley & Sons, Ltd.     

HL-2A托卡马克装置CXRS光学系统设计

电荷交换复合谱(CXRS)是一项先进的测量托卡马克等离子体温度及空间分布的方法。针对我国HL-2A托卡马克装置上CXRS光谱采集系统对宽光谱范围(470?660nm)、大视场(535.34mm)、宽光束(直径110mm)、高空间分辨(14道)以及与后续导光光纤数值孔径(0.22)匹配等要求,应用ZEMAX光学设计软件优化设计了一片反射镜与四片透镜组合的光学系统,并通过将像面倾斜的方法进一步减小了像差。模拟计算表明像面最大弥散斑RMS半径为88.14?m,像方数值孔径0.217,很好地满足了使用需要。     

Effect of heat treatment on structure evolution and properties of nano zinc titanate ceramics

Nano zinc titanate ceramics are prepared using a conventional solid state method. The obtained compacts are sintered at 800, 900, 1000 and 1100 °C for 3 h. The prepared compacts are analyzed using X‐ray diffraction (XRD) and scanning electron microscopy (SEM) for structural and microstructural studies. Based on the X‐ray diffraction (XRD) data, it is observed the coexistence of ZnTiO₃ and α‐Zn₂TiO₄ phases together at low temperature (800 °C) without the presence of TiO₂ (rutile) contradicting the general mechanism stating the transformation of ZnTiO₃ to α‐Zn₂TiO₄ and TiO₂ at higher temperatures. A new mechanism is proposed to explain the formation of nano ZnTiO₃ and α‐Zn₂TiO₄ structures depending on the role of TiO₂ in achieving this mission. According to this mechanism, we propose a partial diffusion of TiO₂ in the ZnO lattice forming the ZnTiO₃ phase. The second part of TiO₂ acts as a catalyst that facilitates the transformation of nano ZnTiO₃ to nano α‐Zn₂TiO₄. The catalytic power of rutile is achieved from its enhanced tensile stress that induces the phase transition from nano ZnTiO₃ to nano α‐Zn₂TiO₄.     

Economic statistical design of a T2 control chart with double warning lines

Recent studies have shown that enhancing the common T² control chart by using variable sample sizes (VSS) and variable sample intervals (VSI) sampling policies with a double warning line scheme (DWL) yields improvements in shift detection times over either pure VSI or VSS schemes in detecting almost all shifts in the process mean. In this paper, we look at this problem from an economical perspective, certainly at least as an important criterion as shift detection time if one considers what occurs in the industry today. Our method is to first construct a cost model to find the economic statistical design (ESD) of the DWL T² control chart using the general model of Lorenzen and Vance (Technometrics 1986; 28 :3–11). Subsequently, we find the values of the chart parameters which minimize the cost model using a genetic algorithm optimization method. Cost comparisons of Fixed ratio sampling, VSI, VSS, VSIVSS with DWL, and multivariate exponentially weighted moving average (MEWMA) charts are made, which indicate the economic efficacy of using either VSIVSS with DWL or MEWMA charts in practice if cost minimization is of interest to the control chart user. Copyright © 2010 John Wiley & Sons, Ltd.     

基于参数化设计的传统纹样结构衍生及应用

目的 将传统纹样的形式规则与参数化设计方法相结合,探索传统纹样在现代设计中的衍生设计方法,为纹样文化的传承和发展提供新的思路。方法 提取传统纹样造型中的构图规则,利用现代图形设计中的函数曲线、曲线的控制点坐标参数,重构参数纹样模型。通过空间点集的形式构建纹样的空间排列结构。制定演变规则,调整可变参数,对目标纹样进行结构衍生设计。结果 以马家窑旋涡纹为例,分析并提取结构规则,在此基础上,利用参数化建模工具Grasshopper完成参数纹样建模和插件制作以及参数化纹样设计和应用。结论 传统纹样结构蕴含着有序的形式规则,具备纹样参数化设计的基本条件。构建的参数化纹样结构可更灵活高效地进行纹样衍生和设计,有利于传统纹样与现代设计的融合。     

Runaway Carbon Dioxide Conversion Leads to Enhanced Uptake in a Nanohybrid Form of Porous Magnesium Borohydride

Leveraging molecular‐level controls to enhance CO₂ capture in solid‐state materials has received tremendous attention in recent years. Here, a new class of hybrid nanomaterials constructed from intrinsically porous γ‐Mg(BH₄)₂ nanocrystals and reduced graphene oxide (MBHg) is described. These nanomaterials exhibit kinetically controlled, irreversible CO₂ uptake profiles with high uptake capacities (>19.9 mmol g^?1) at low partial pressures and temperatures between 40 and 100 °C. Systematic experiments and first‐principles calculations reveal the mechanism of reaction between CO₂ and MBHg and unveil the role of chemically activated, metastable (BH₃‐HCOO)^? centers that display more thermodynamically favorable reaction and potentially faster reaction kinetics than the parent BH₄^? centers. Overall, it is demonstrated that size reduction to the nanoscale regime and the generation of reactive, metastable intermediates improve the CO₂ uptake properties in metal borohydride nanomaterials.     

Optimal Designs of the Variable Sample Size Chart Based on Median Run Length and Expected Median Run Length

The variable sample size (VSS) chart, devoted to the detection of moderate mean shifts, has been widely investigated under the context of the average run‐length criterion. Because the shape of the run‐length distribution alters with the magnitude of the mean shifts, the average run length is a confusing measure, and the use of percentiles of the run‐length distribution is considered as more intuitive. This paper develops two optimal designs of the VSS chart, by minimizing (i) the median run length and (ii) the expected median run length for both deterministic and unknown shift sizes, respectively. The 5th and 95th percentiles are also provided in order to measure the variation in the run‐length distribution. Two VSS schemes are considered in this paper, that is, when the (i) small sample size (n_S) or (ii) large sample size (n_L) is predefined for the first subgroup (n₁). The Markov chain approach is adopted to evaluate the performance of these two VSS schemes. The comparative study reveals that improvements in the detection speed are found for these two VSS schemes without increasing the in‐control average sample size. For moderate to large mean shifts, the optimal VSS chart with n₁ = n_L significantly outperforms the optimal EWMA chart, while the former is comparable to the latter when n₁ = n_S. Copyright © 2016 John Wiley & Sons, Ltd.     

Design of a Molecular Hybrid of Dual Peptide Inhibitors Coupled on AuNPs for Enhanced Inhibition of Amyloid β‐Protein Aggregation and Cytotoxicity

Aggregation of amyloid‐β protein (Aβ) is a pathological hallmark of Alzheimer's disease (AD), so the inhibition of Aβ aggregation is an important strategy for the prevention and treatment of AD. Herein, we proposed to design molecular hybrids of peptide inhibitors by combining two peptide inhibitors, VVIA and LPFFD, into single sequences and examined their effects on Aβ₄₂ aggregation and cytotoxicity. The hybrid peptides exhibit increased but moderate inhibitory activity as compared to their two precursors. By conjugating the peptides onto gold nanoparticles (AuNPs), however, the inhibition activity of the corresponding peptide@AuNPs against Aβ₄₂ aggregation and cytotoxicity is greatly improved. Among them, VVIACLPFFD (VCD10)@AuNP is the most effective, which increases cell viability from 48% to 82% at a dosage as low as 0.1 nmol L^?1 (NPs) or 40 nmol L^?1 (peptide). The superior capacity of VCD10@AuNPs is considered due to its branched dual‐inhibitor sequence, and its special surface orientation and conformation. These structural features promote its synergetic interactions with Aβ on AuNP surface, leading to strong inhibitions of Aβ oligomerization and fibrillation and the cytotoxicity caused by the aggregation species. The findings suggest that potent inhibitors can be derived by hybridization of multiple peptide inhibitors with the hybrid products coupled onto nanoparticles.     

α‐Ni(OH)2 Originated from Electro‐Oxidation of NiSe2 Supported by Carbon Nanoarray on Carbon Cloth for Efficient Water Oxidation

Development of effective oxygen evolution reaction (OER) electrocatalysts has been intensively studied to improve water splitting efficiency and cost effectiveness in the last ten years. However, it is a big challenge to obtain highly efficient and durable OER electrocatalysts with overpotentials below 200 mV at 10 mA cm^?2 despite the efforts made to date. In this work, the successful synthesis of supersmall α‐Ni(OH)₂ is reported through electro‐oxidation of NiSe₂ loaded onto carbon nanoarrays. The obtained α‐Ni(OH)₂ shows excellent activity and long‐term stability for OER, with an overpotential of only 190 mV at the current density of 10 mA cm^?2, which represents a highly efficient OER electrocatalyst. The excellent activity could be ascribed to the large electrochemical surface area provided by the carbon nanoarray, as well as the supersmall size (≈10 nm) of α‐Ni(OH)₂ which possess a large number of active sites for the reaction. In addition, the phase evolution of α‐Ni(OH)₂ from NiSe₂ during the electro‐oxidation process was monitored with in situ X‐ray absorption fine structure (XAFS) analysis.