Value creation through design for scalability of reconfigurable manufacturing systems

Rapid and cost-effective scalability of the throughput of manufacturing systems is an invaluable feature for the management of manufacturing enterprises. System design for scalability allows the enterprise to build a manufacturing system to supply the current demand, and upgrade its throughput in the future, in a cost-effective manner, to meet possible higher market demand in a timely manner. To possess this capability, the manufacturing system must be designed at the outset for future expansions in its throughput to enable growths in supply exactly when needed by the market. A mathematical method that maximises the system throughput after reconfiguration is proposed, and an industrial case is presented to validate the method. The paper offers a set of principles for system design for scalability to guide designers of modern manufacturing systems.     

Bayesian Network Resource for Meta‐Analysis: Cellular Toxicity of Quantum Dots

A web‐based resource for meta‐analysis of nanomaterials toxicity is developed whereby the utility of Bayesian networks (BNs) is illustrated for exploring the cellular toxicity of Cd‐containing quantum dots (QDs). BN models are developed based on a dataset compiled from 517 publications comprising 3028 cell viability data samples and 837 IC₅₀ values. BN QD toxicity (BN‐QDTox) models are developed using both continuous (i.e., numerical) and categorical attributes. Using these models, the most relevant attributes identified for correlating IC₅₀ are: QD diameter, exposure time, surface ligand, shell, assay type, surface modification, and surface charge, with the addition of QD concentration for the cell viability analysis. Data exploration via BN models further enables identification of possible association rules for QDs cellular toxicity. The BN models as web‐based applications can be used for rapid intelligent query of the available body of evidence for a given nanomaterial and can be readily updated as the body of knowledge expands.     

Power in threshold network flow games

Preference aggregation is used in a variety of multiagent applications, and as a result, voting theory has become an important topic in multiagent system research. However, power indices (which reflect how much “real power” a voter has in a weighted voting system) have received relatively little attention, although they have long been studied in political science and economics. We consider a particular multiagent domain, a threshold network flow game. Agents control the edges of a graph; a coalition wins if it can send a flow that exceeds a given threshold from a source vertex to a target vertex. The relative power of each edge/agent reflects its significance in enabling such a flow, and in real-world networks could be used, for example, to allocate resources for maintaining parts of the network. We examine the computational complexity of calculating two prominent power indices, the Banzhaf index and the Shapley-Shubik index, in this network flow domain. We also consider the complexity of calculating the core in this domain. The core can be used to allocate, in a stable manner, the gains of the coalition that is established. We show that calculating the Shapley-Shubik index in this network flow domain is NP-hard, and that calculating the Banzhaf index is #P-complete. Despite these negative results, we show that for some restricted network flow domains there exists a polynomial algorithm for calculating agents’ Banzhaf power indices. We also show that computing the core in this game can be performed in polynomial time.     

THE FLOW OF MICROEMULSIONS THROUGH PACKED BEDS AND CAPILLARY TUBES

The flow behavior of water-in-oil microemulsions through beds packed with glass spheres was studied experimentally. The microemulsions used in this study exhibited a shear thinning viscosity described by a simple power law model. The flow of the microemulsions was accompanied by significant apparent slip effects, quantified by an effective slip velocity. The effective slip velocity increased with increasing surfactant concentration, but it differed in magnitude for the packed bed and the capillary tube flows.

In the absence of apparent slip effects, the capillary-power law (CPL) model predicted the superficial velocities in the packed beds with an average error of less than 6%. This provides a direct verification of the applicability of the capillary-power law model to inelastic shear thinning fluids in the absence of “anomalous” wall effects.     

An expert system approach for quality assurance auditing

International standards for quality management systems, such as ISO 9000, define the organizational structure, the lines of responsibility, the procedures, the processes, and the resources used to manage the quality. The purpose of quality auditing is to assess the effectiveness of the implementation of the quality system and to determine the degree to which the system’s objectives are being achieved. Quality assurance auditing is one of the most important tools used to evaluate the effectiveness of a quality system.Due to the variety in quality systems, in some cases, the criteria to determine the degree to which systems objectives are being achieved are not clear-cut. Thus, the quality auditor may have to follow his best judgment.An expert system approach is proposed that can classify the results of the quality assurance auditing. It could be used for training and monitoring of novice auditing personnel, reduction of the variation between different auditing experts, and facilitate decision making during a quality audit.     

Operation of Manufacturing Systems with Work-in-process Inventory and Production Control

The operation of large manufacturing systems with buffers has two goals: to meet production target and minimize the work-in-process (WIP) inventory. This paper introduces a novel approach, based on optimal control theory, to achieve both goals simultaneously by on-line adjustment of the production rate of each machine. In this method the state variables are the buffer levels, the control variables are the machine production rates, and the output variable is the target production (the demand). The method is evaluated through simulations under various conditions, and compared with other methods in the literature. The results demonstrate that the proposed method can successfully produce low WIP inventory than other methods, while the required production demand is still fulfilled. It is also shown that the method is capable of providing feasible solutions for large manufacturing systems - a goal that is harder to achieve with the current known method.     

Purification of polyphenol oxidase and the browning control of litchi fruit by glutathione and citric acid

Polyphenol oxidase (PPO, EC 1.10.3.2) was purified to homogeneity from litchi peel yielding a single protein with a molecular weight of about 75.6 kD by Sephadex G‐100 gel filtration, and a 108‐fold purification of PPO achieved. The enzyme was determined to be composed of two similar subunits. Glutathione, L ‐cysteine and citric acid suppressed PPO activity markedly, whereas ascorbic acid and n‐propyl gallate showed a little inhibition. Moreover, the effect was enhanced by the addition of citric acid. On the basis of the inhibition of PPO activity in vitro, the use of 10 mmol l ⁻¹ glutathione and 100 mmol⁻¹ l citric acid was found to give good control of the browning of litchi fruit, and an 80–85% inhibition of PPO activity was observed. It is suggested that application of glutathione in combination with citric acid may slow down the browning of litchi fruit. © 1999 Society of Chemical Industry