A Semiparametric Mixed Model Approach to Phase I Profile Monitoring

Profile monitoring is an approach in quality control best used where the process data follow a profile (or curve). The majority of previous studies in profile monitoring focused on the parametric (P) modeling of either linear or nonlinear profiles, with both fixed and random effects, under the assumption of correct model specification. More recently, in the absence of an obvious P model, nonparametric (NP) methods have been employed in the profile monitoring context. For situations where a P model is adequate over part of the data but inadequate of other parts, we propose a semiparametric procedure that combines both P and NP profile fits. We refer to our semiparametric procedure as mixed model robust profile monitoring (MMRPM). These three methods (P, NP and MMRPM) can account for the autocorrelation within profiles and treat the collection of profiles as a random sample from a common population. For each approach, we propose a version of Hotelling's T² statistic for use in Phase I analysis to determine unusual profiles based on the estimated random effects and obtain the corresponding control limits. Simulation results show that our MMRPM method performs well in making decisions regarding outlying profiles when compared to methods based on a misspecified P model or based on NP regression. In addition, however, the MMRPM method is robust to model misspecification because it also performs well when compared to a correctly specified P model. The proposed chart is able to detect changes in Phase I data and has easily calculated control limits. We apply all three methods to the automobile engine data of Amiri et al.⁵ and find that the NP and the MMRPM methods indicate signals that did not occur in a P approach. Copyright © 2012 John Wiley & Sons, Ltd.     

The Performance of the Adaptive Exponentially Weighted Moving Average Control Chart with Estimated Parameters

The adaptive exponentially weighted moving average (AEWMA) control chart has the advantage of detecting balance mixed range of mean shifts. Its performance has been studied under the assumption that the process parameters are known. Under this assumption, previous studies have shown AEWMA to provide superior statistical performance when compared with other different types of control charts. In practice, however, the process parameters are usually unknown and are required to be estimated. Using a Markov Chain approach, we show that the performance of the AEWMA control chart is affected when parameters are estimated compared with the known‐parameter case. In addition, we show the effect of different standard deviation estimators on the chart performance. Finally, a performance comparison is conducted between the exponentially weighted moving average (EWMA) chart and the AEWMA chart when the process parameters are unknown. We recommend the use of the AEWMA chart over the ordinary EWMA chart especially when a small number of Phase I samples is available to estimate the unknown parameters. Copyright © 2012 John Wiley & Sons, Ltd.     

Smart self-healing anti-corrosion vanadia coating for magnesium alloys

Eco-friendly vanadia based chemical conversion coating was applied for improving the corrosion resistance of a newly developed magnesium AZ31 HP-O alloy. The effect of vanadia solution concentrations (10, 30 and 50 g/l) and pH (neutral pH 7 and pH 9) on the corrosion protection performance of a magnesium substrate were investigated. EIS and linear polarization techniques were used to evaluate the electrochemical behavior in 3.5% NaCl. The results showed a marked increase in the localized corrosion resistance after applying vanadia surface treatment of 50 g/l due to self-healing effect. The optimum conditions to obtain protective coatings for AZ31 HP-O with a self-healing ability were determined. Changes in surface morphology, composition and microstructure of the conversion coatings were followed by SEM-EDS and macroscopic imaging techniques.     

3-D aluminum nanostructure with microhole array synthesized by femtosecond laser radiation for enhanced light extinction

This article presents 3-D aluminum micro-nanostructures for enhanced light absorption. Periodic microhole arrays were created by firing a train of femtosecond laser pulses at megahertz pulse frequency onto the surface of an aluminum target at ambient conditions. The laser trains ablated the target surface and created microholes leading to the generation of deposited nanostructures inside and around the microholes. These micro-nanostructures showed enhanced light absorption, which is attributed to surface plasmonics induced by the generation of both nano- and microstructures. These micro-nanostructures may be promising for solar cell applications.     

Techniques for the extraction of phytosterols and their benefits in human health: a review

This review summarizes the information on the health-promoting effects of phytosterols and the techniques for their extraction. The extraction and analysis processes of phytosterols are complex and have not been fully established. Phytosterols have significant roles in the areas of foods, nutrition, pharmaceuticals, and cosmetics. Free phytosterols extracted from plant sources are widely used in fortified foods and dietary supplements. Most phytosterols are extracted from plant matrices using organic solvents which are health and environmental hazards. However, the application of supercritical fluid in the extraction of phytosterols has offered a promising green technology in overcoming the limitations of conventional extraction.     

Oxidative Cyclization-Induced Activation of a Phosphoinositide 3-Kinase Inhibitor for Enhanced Selectivity of Cancer Chemotherapeutics

In this work, we designed a prodrug that reacts with cellular oxidative equivalents leading to ether cleavage and cyclization to release an active phosphatidylinositol 3-kinase (PI3K) inhibitor. We show that the compound reduces affinity for PI3KA relative to the PI3K inhibitor, is slow to intercellularly oxidize, and is resistant to liver microsomes. We observed modest activity in untreated acute myeloid leukemia cells and 14-fold selectivity relative to non-cancerous cells. The cellular activity of the compound can be modulated by the addition of antioxidants or oxidants, indicating the compound activity is sensitive to cellular reactive oxygen species (ROS) state. Co-treatment with cytosine arabinoside or doxorubicin was used to activate the compound inside cells. We observed strong synergistic activity specifically in acute myeloid leukemia (AML) cancer cells with an increase in selective anticancer activity of up to 90-fold. Thus, these new self-cyclizing compounds can be used to increase the selectivity of anticancer agents.     

Derivation of creepage distance in terms of ESDD and diameter ofthe contaminated insulator

In designing EHV transmission systems, specific knowledge about the creepage distance of the insulator, which is subjected to adverse environmental contamination, is important. Various system components' configurations can be properly coordinated through the appropriate application of the relationship between insulator creepage distance, the equivalent salt deposit density (ESDD), and the insulator diameter. In this paper, a general relationship between the creepage distance, ESDD, and diameter of the insulator has been proposed using the dimensional analysis technique     

Performance Evaluation of Generalized Selection Combiners Over Slow Fading with Estimation Errors

In this paper we derive closed-form expressions for the single-user adaptive capacity of generalized selection combining (GSC) system, taking into account the effect of imperfect channel estimation at the receiver. The channel considered is a slowly varying spatially independent flat Rayleigh fading channel. The complex channel estimate and the actual channel are modelled as jointly Gaussian random variables with a correlation that depends on the estimation quality. Three adaptive transmission schemes are analyzed: (1) optimal power and rate adaptation; and (2) constant power with optimal rate adaptation, and (3) channel inversion with fixed rate. In addition to deriving an exact expression for the capacity of the aforementioned adaptive schemes, we analyze the impact of channel estimation error on the capacity statistics and the symbol error rate for GSC systems. The capacity statistics derived in this paper are the moment generating function, complementary cumulative distribution function and probability density function for arbitrary number of receive antennas. Moreover, exact closed-form expressions for M-PAM/PSK/QAM employing GSC are derived. As expected, the channel estimation error has a significant impact on the system performance.     

Syngas Production via Bi-Reforming of Methane Over Fibrous KCC-1 Stabilized Ni Catalyst

Topics in Catalysis - Bi-reforming of methane (BRM) technology has the potential to serve as an alternative energy source while also mitigating greenhouse gas emissions. However, the main hurdle in...