In many situations, employees' performance decrements have generally been attributed to fatigue, and a flexibly designed work-break schedule can reduce their fatigue effect. This paper focuses upon the development and solution of model which minimises the actual completion time of all jobs, subject to a given fixed workload, through the selection of optimal work-break schedules. In this paper, several break periods are considered where each break activity is scheduled after a periodic time interval, and the employees' work rate first maintains a certain level and then declines during the work period. We propose a mathematical programming model and a heuristic algorithm to solve this problem. Our analysis finds that compared to the actual completion time of an employee without having a break, setting several reasonable fixed breaks makes work efficiency increased and improves employee satisfaction and reduces the makespan. Our findings light on the importance of understanding and setting break time in the work periods, and contribute to the improvement of employee satisfaction.

This paper considers a supply chain in which an upstream supplier sells a component to a downstream manufacturer facing a price and quality sensitive demand. The supplier has a chance to make investment in the manufacturer, which can not only enable the supplier to hold equity shares in the manufacturer and thus achieve profit sharing with the manufacturer, but also provide resources for the manufacturer to improve its product quality. Under any given investment strategy of the supplier, the equilibrium decisions of the two chain members on wholesale price and profit margin are characterized. Then, the supplier's optimal investment strategy is derived. The paper considers three competition models: supplier Stackelberg (SS), manufacturer Stackelberg (MS), and vertical Nash (VN) models, which correspond to different market power structures. The paper shows that the investment can always increase the market demand. Moreover, in both the SS and VN models, the value of the supplier's investment for the entire supply chain, comes from not only the quality improvement but also the profit sharing caused by equity holding; while in the MS model, the investment value comes only from the quality improvement.