A memetic algorithm-based heuristic for a scheduling problem in printed circuit board assembly

This research develops a memetic algorithm to solve Printed Circuit Board (PCB) scheduling with sequence-dependent setup times on a single machine with constrained feeder capacity. The objective of the scheduling problem is to minimize the total weighted tardiness. A memetic algorithm-based heuristics is developed by integrating a genetic algorithm, Minimum Slack Time (MST) scheduling rule, “Keep Tool Needed Soonest” (KTNS) policy, and a local search procedure. Application of the MA results in two outcome plans: a scheduling plan and a feeder setup plan.Numerical experiments show that compared to a number of commonly used dispatching rules, the memetic algorithm provides better solutions in term of minimum total weighted tardiness. Even the computation is the highest, it still practical. Calibration of MA parameter values is also explored in this study.     

Inhibitory effects of Enterococcus strains obtained from a probiotic product on in vitro growth of Salmonella enterica serovar enteritidis strain IFO3313

Enterococcus faecium and Enterococcus gallinarum strains were isolated from a commercial probiotic product and the effects of these strains on the growth of Salmonella enterica serovar Enteritidis strain IFO3313 were investigated. Viable cell counts of Salmonella Enteritidis in mixed cultures with the probiotic product isolate of E. faecium were significantly (P < 0.05) lower than those in pure cultures after 6, 8, and 24 h when the cultures were incubated in heart infusion broth at 37 and 41 degrees C. Significant differences in viable cell counts of Salmonella Enteritidis in mixed cultures with the probiotic product isolate of E. gallinarum and those in pure cultures were also observed after 8 and 24 h at 37 and 41degrees C. Similar observations were shown in mixed cultures of Salmonella Enteritidis with the reference strains of E. faecium GIFU8355 and E. gallinarum ATCC 49573. Significant differences in viable cell counts of these enterococcal strains were not shown among pure and mixed cultures with Salmonella Enteritidis. The pH values in pure and mixed cultures were 7.0 or 7.5 throughout the experiments. E. faecium strains were found to harbor the genes encoding enterocins A and B and showed inhibitory zones with a diameter of 4 to 6 mm against growth of Salmonella Enteritidis in the enterocin production assays. However, the E. gallinarum strains possessed neither of the enterocin genes tested and exhibited no inhibition zone in the enterocin production assays. These results indicated that enterococcal strains exhibit inhibitory effects on the growth of Salmonella Enteritidis and these effects were due to both enterocin and nonenterocin factors.     

Control of Grid Side Converter under Unbalance Voltage Conditions for Variable Speed Wind Turbine

This paper proposes the control of a grid side converter under unbalance voltage conditions for wind turbine system. The control technique is designed to operate under unbalance voltage by independent control between positive and negative components. The converter will regulate the DC link voltage at the specific value （650 V）. To verify an operation of the proposed control, the simulation is conducted by MATLAB/SIMULINK program. The experiments are conducted on a 5 kW system composed of wind turbine simulator, machine side converter and the propose grid side converter for operation under unbalance voltage. By comparing the simulation experimentation results, it can be shown that the proposed control can be continuously operating through an extremely sag voltage without damage. Moreover the proposed control can deliver power to the grid and regulate DC link voltage under unbalance voltage.     

Electrospinnability of poly(butylene succinate): Effects of solvents and organic salt on the fiber size and morphology

Submicrosized and nanosized fibers of polymers can be formed easily by electrospinning techniques. However, bead formation can occur if inappropriate solvent systems are used. In this study, we focused on investigating the effects of solvents and organic salt on the electrospinnability of poly(butylene succinate) (PBS). Electrospun PBS fibers were obtained from single‐solvent systems, that is, systems with chloroform (CF) or dichloromethane, at various concentrations (8–30% w/v). Discrete beads and beaded fibers were still found at every PBS concentration. In this study, the electrospinnability of the PBS solutions in CF were improved by the addition of methanol (MeOH) as a cosolvent and an organic salt [alkyl ammonium ethyl sulfate (AAES)]. The obtained fibers were smooth without any beads, and the diameters were affected by the amount of MeOH and the PBS concentration. The electrospinnability of PBS could be enhanced by the addition of a cosolvent with a high dielectric constant or organic salt (AAES). Moreover, the diameters of the electrospun PBS fibers decreased with increasing AAES concentration. We found that the presence of MeOH (30 vol %) and the addition of AAES caused an increase in the crystallinity of the PBS fibers. Therefore, we concluded that bead‐free ultrafine PBS fibers could be obtained through the addition of the cosolvent and the organic salt. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42716.     

Dyeing properties of Bombyx mori silks grafted with methyl methacrylate and methacrylamide

To improve their dyeing and colorfastness properties, degummed Bombyx mori silks were chemically modified by a grafting technique with either methyl methacrylate (MMA) monomer or methacrylamide (MAA) monomer. Both commercial synthetic dyes, that is, acid and basic dyes, and natural dyes extracted from turmeric, without and with potassium aluminum sulfate mordant, were used in this study. Percentage dye uptake increased with the presence of poly(methyl methacrylate) or polymethacrylamide in the silk fibroin structure regardless of the types of the dyestuffs. Furthermore, compared to the degummed silk, the colorfastness to washing of the MMA‐grafted and MAA‐grafted silks dyed with acid, basic, and curcumin dyestuffs were greatly improved. Colorfastness to both acid and basic perspirations with acid and basic dyestuffs was slightly improved, whereas perspiration fastness remained unchanged for curcumin dyeing without and with the presence of the mordant. Also, the low‐light resistances of the degummed and grafted silks dyed by curcumin dyestuff were notably improved by the MMA and MAA grafting technique. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:1169–1175, 2006     

Integrated methodology for board assignment and component allocation in printed circuit board assembly

An approach to minimize makespan for assigning boards to production lines is described. Because of sequence-dependent set-up times, board assignment and component allocation have to be performed concurrently. An integrated methodology is developed to obtain a solution to these two problems. The methodology consists of seven phases: printed circuit board grouping, family decomposition, subfamily sequencing, Keep Tool Needed Soonest (KTNS) procedure, component set-up determination, component allocation and board assignment. Application of the methodology to industrial problems demonstrates that it can solve large-scale problems efficiently. In addition, the effect of two key parameters, feeder capacity and threshold value, on the performance of the solution procedure was examined. The results indicate that feeder capacity has an impact on total workload imbalance but not on the global makespan. Threshold value, a measure of effectiveness of joining a component type to a component group for a printed circuit board family, has a significant effect on the global makespan. The interactions of threshold value, and variations in printed circuit board requirement and component usage also affect global makespan.