Dynamic performance and cost measures with setup determination under state-age-dependent deterioration

Many manufacturing processes and production systems suffer from progressive degradation with usage and age and are subject to random failures resulting from such deterioration. Traditional models for evaluating the reliability and performance of a process/system use binary-state models, with working success or failure, to classify the states of the process/system that are unrealistic. This article proposes the classification of discrete multiple states of the deterioration process. A nonhomogeneous continuous-time Markov process is employed for modelling the process deterioration because we assume that the time for which a process stays in certain state depends not only on the current state but also on the time for which the process has been in the current state. For major and minor deteriorations, we present symbolic solutions of several differential equations by using MATLAB to estimate the probability of the process being in each state at time t. We contribute dynamic performance and cost measures for the state-age-dependent process deterioration to assess the severity of the deterioration at some point in time as well as the total severity that it causes over the entire process. The optimal setup time is determined in order to estimate the minimum total expected cost during the production period. A practical application of the proposed methodology is illustrated throughout this article.     

GeoBuilder: A Geometric Algorithm Visualization and Debugging System for 2D and 3D Geometric Computing

Algorithm visualization is a unique research topic that integrates engineering skills such as computer graphics, system programming, database management, computer networks, etc., to facilitate algorithmic researchers in testing their ideas, demonstrating new findings, and teaching algorithm design in the classroom. Within the broad applications of algorithm visualization, there still remain performance issues that deserve further research, e.g., system portability, collaboration capability, and animation effect in 3D environments. Using modern technologies of Java programming, we develop an algorithm visualization and debugging system, dubbed GeoBuilder, for geometric computing. The GeoBuilder system features Java's promising portability, engagement of collaboration in algorithm development, and automatic camera positioning for tracking 3D geometric objects. In this paper, we describe the design of the GeoBuilder system and demonstrate its applications.     

Surface tension driven flow for open microchannels with different turning angles

Present study examines the flow characteristics of open microchannels with sharp turns by experimental and numerical methods. For the open channel system in microscale, the flow is mainly driven by surface tension at atmospheric pressure. The open channels are of various aspect ratios of depth-to-width, ranging from 0.75 to 3, and of turning angles from 45° to 135°. It is found that the turning angle and the aspect ratio of depth-to-width play major roles in the velocity of liquid front advancing, the meniscus of liquid–gas interface shape, and head loss of flow due to turning. Besides, the radius of curvature of the liquid front is reduced as the liquid front travels downstream and over the turning elbow. The loss coefficient remains the same for turning angles less than 75°, whereas it is increased further and is even more pronounced for turning angles larger than 105°. Numerical predications based on conservation laws agree with the experimental observations, and the flow characteristics are well described for open channel in microscale, as the aspect ratio is greater than or near to 1.5.     

Manufacturing process performance evaluation for fuzzy data based on loss-based capability index

Process capability indices have been introduced for measuring process reproduction capability of a manufacturing industry. The loss-based capability index C_pmC_{pm} takes into account the degree of process targeting (centering), which essentially measures the process performance on the basis of average process loss. Generally, the underlying manufacturing process data are obtained from the output responses of continuous quantities, which are always assumed to be real numbers. However, in a practical situation, the data collected by output process measurements are often imprecise (fuzzy data). We propose a constructive methodology for obtaining the fuzzy estimate of C_pmC_{pm} using fuzzy data, which is based on “resolution identity” in fuzzy sets theory. We propose four decision rules to judge the process condition by simultaneously introducing randomness and fuzziness. Finally, we present a sequence of testing steps for assessing manufacturing process performance using the critical value of C_pmC_{pm} with fuzzy data and can be easily implemented in real situations.     

Using intuitionistic fuzzy sets for fault-tree analysis on printed circuit board assembly

Fault-tree analysis (FTA) is a powerful technique used to identify the root causes of undesired event in system failure by constructing a tree of sub-events, spreading into bottom events, procreating the fault and finally heading to the top event. From integrating expert’s knowledge and experience in terms of providing the possibilities of failure of bottom events, an algorithm of the intuitionistic fuzzy fault-tree analysis is proposed in this paper to calculate fault interval of system components and to find the most critical system component for the managerial decision-making based on some basic definitions. The proposed method is applied for the failure analysis problem of printed circuit board assembly (PCBA) to generate the PCBA fault-tree, fault-tree nodes, then directly compute the intuitionistic fuzzy fault-tree interval, traditional reliability, and the intuitionistic fuzzy reliability interval. The result of this proposed method is compared with the existing approaches of fault-tree methods.     

Exposure of Hong Kong residents to PBDEs and their structural analogues through market fish consumption

High concentrations of polybrominated diphenyl ethers (PBDEs) and their structural analogues (such as methoxylated (MeO) and hydroxylated (OH) PBDEs) had been observed in environmental samples and human tissues. This study evaluated the occurrence, potential source and human exposure of these organobrominated compounds via market fish consumption in Hong Kong. The contamination of 22 PBDEs, 7 MeO-BDEs, 15 OH-BDEs and 3 bromophenols (BRPs) were analyzed in 20 fish species (279 samples). The estimated daily intakes of PBDEs, MeO-BDEs, OH-BDEs and BRPs via fish consumption ranged from 4.4 to 14, 0.50 to 4.3, 0.02 to 0.43 and 0 to 0.21 ng/kg day for Hong Kong residents, respectively, based on 50^th and 95^th centile concentrations. BDE-47 and 99 were found to be the major PBDE congeners while 2′-MeO-BDE-68, 6-MeO-BDE-47 and 3-MeO-BDE-47 were the dominant MeO-BDEs. Concentrations of OH-BDEs and BRPs were 10-100-fold less than those of PBDEs, with small frequencies of detection (max 36.7%). Dietary intake of PBDEs via fish consumption by Hong Kong residents was greater than many developed countries, such as the USA, UK, Japan and Spain. To our knowledge, this is the first report to estimate the dietary intake of MeO/OH-BDEs and BRPs via fish consumption. Our results indicated that the toxicity potential of these compounds should not be neglected.     

A secure multi-item e-auction mechanism with bid privacy

The recent focus within the auction field has been multi-item auctions where bidders are not restricted to buying only one item of the merchandise. It has been of practical importance in Internet auction sites and has been widely executed by them. In this paper, we concentrate on the use of the multi-item auction for task assignment scenarios and propose a novel PUPA auction protocol to solve the problem of bid privacy in multi-item auctions. A verifiable technique of shared key chain is proposed to find the winners without revealing the losing bid and bidder’s privacy. It can be shown that our new scheme is robust against cheating bidders.     

Storage assignment problem with travel distance and blocking considerations for a picker-to-part order picking system

Order picking is a key operation in managing a warehouse efficiently. Most previous studies on picking only considered single-picker operation; however, many pickers frequently work concurrently in the same region. Since congestion may occur in such a multi-picker system, waiting time must be taken into account together with travel time and distance when evaluating the efficiency of picking operations. The picking model under investigation can be formulated as a queueing network, and a heuristic storage assignment policy that considers both the travel time and the waiting time simultaneously by minimizing the average order fulfillment time is developed in the paper. An approximation method and a simulation model using eM-plant software are presented to implement the proposed heuristic algorithm and to compare the mean travel time for different storage assignment polices as well. The results indicate that the proposed heuristic policy outperforms existing storage assignment policies in a multi-picker warehouse environment.