Scheduling multistage hybrid flowshops with multiprocessor tasks by an effective heuristic

This study considers the scheduling problem of multistage hybrid flowshops with multiprocessor tasks, which is a core topic for numerous industrial applications. An effective and efficient heuristic, namely the heuristic of multistage hybrid flowshops (HMHF) is proposed to solve this problem. To verify the developed heuristic, computational experiments are conducted on a well-known benchmark problem set. The results are compared with 10 constructive heuristics and a tabu search (TS) based meta-heuristic from the relevant literature. These computational results show that the proposed HMHF heuristic is highly effective when compared to these algorithms for this problem on the same benchmark instances.     

Scheduling identical wafer sorting parallel machines with sequence-dependent setup times using an iterated greedy heuristic

Wafer sorting is one of the most critical processes involved in semiconductor device fabrication. This study addresses the wafer sorting scheduling problem (WSSP), with minimisation of total setup time as the primary criterion and minimisation of the number of testers used as the secondary criterion. In view of the strongly NP-hard nature of this problem, a simple and effective iterated greedy heuristic is presented. The performance of the proposed heuristic is empirically evaluated by 480 simulation instances based on the characteristics of a real wafer testing shop-floor. The experimental results show that the proposed heuristic is effective and efficient as compared to the state-of-art algorithms developed for the same problem. It is believed that this study has developed an approach that is easy to comprehend and satisfies the practical needs of wafer sorting.     

Metal toxicity to Chlorella pyrenoidosa assessed by a short-term continuous test

This study presents the metal toxicity as revealed by Chlorella pyrenoidosa using a short-term continuous test and the conventional batch test. Toxicity tests were conducted in a chemostat with a test duration of 1 day. Toxicity data of five different metals (Cd, Pb, Co, Ni, and Zn) derived from the continuous test were compared against results from the conventional batch tests. The batch test is characterized by its saturated nutrient status for algal growth and, on the other hand, the continuous test is conducted at a nutrient-limiting condition simulating more closely to the aquatic field environment. The continuous test consistently yielded smaller EC(50) values, which indicated that alga in the chemostat is approximately four to six times more sensitive than those from the batch culture. Similar phenomena between the two types of tests were observed based on the NOEC values. Compared to literature data (US EPA ECOTOX Database) from the same species of alga, differences in test sensitivity between the batch tests and chemostat technique varied from 9.25 to 160 times. Such distinct differences indicate that current toxicity database may not adequately reflect the impact of various metal toxicants on C. pyrenoidosa. The continuous test method presented herein is a sensitive and rapid assessment technique and, therefore, has a potential for more general applications such as routine checkup for regulatory purposes.     

Noise Characteristics of ZnO-Nanowire Photodetectors Prepared on ZnO:Ga/Glass Templates

In this paper, we report the fabrication of vertically well-aligned ZnO nanowire ultraviolet (UV) photodetectors on ZnO:Ga/glass templates. With 1 V applied bias, it was found that dark current density of the device was only 1.37times10^-7 A/cm². It was also found that UV-to-visible rejection ratio of the fabricated photodetector was around 1000 with a maximum quantum efficiency of 12.6%. It was also found that noise equivalent power and normalized detectivity of the ZnO nanowire photodetector were 5.73times10^-11 W and 6.17times10⁹ cmHz^0.5W^-1, respectively.     

A method of combining rigid body displacements for the determination of rigid body rotations of structural members in the slope‐deflection method

Abstract

In this paper we investigate the stresses and displacements around an advancing face of a tunnel in an elastic half‐space as well as the induced three‐dimensional ground surface subsidence. An indirect boundary integral formulation for the analysis of tunnels in an elastic half‐space is derived and the half‐space fundamental solution (Mindlin's solution) is adopted to satisfy the traction‐free condition on the ground surface. For the evaluation of the non‐singular integral in the numerical implementation, a simple and efficient algorithm to automatically search for integration orders is developed by basing on the upper bound of error in Gaussian quadrature. Numerical results for some tunnel problems are studied to demonstrate the accuracy and versatility of the proposed method. In addition, the stresses, displacements, and the induced ground surface subsidence for an advancing circular tunnel in an elastic half‐space are calculated and presented in detail.