Scientia Iranica
Volume:30 Issue: 6, Nov-Dec 2023

Numerous workers experience occupational diseases, especially musculoskeletal disorders, due to various physical, psychological, and individual factors. Among known risk factors for musculoskeletal disorders, work-rest patterns, and muscle fatigue are to be named. Assessment of muscle fatigue plays an important role, leading to a proper design for a work-rest program. This study was aimed to investigate isometric muscle strength in Iranian workers during repetitive activities based on gender and rest time. It has been attempted to present a model for isometric muscle strength. In a laboratory experiment, 31 students comprised of 19 males and 12 females participated, and muscle strength was recorded by a dynamometer. Minitab software results analysis proved that females' upper body muscles showed a higher level of resistance to fatigue rather than males. Furthermore, tests' results for each individual were more in line with cubic regression so that four models with a high R-Sq index (at least 94.4%) and high R-Sq (adj) index (at least 77.8%) were presented to predict isometric muscle strength in short-run. Finally, it has been suggested to use male workers for repetitive activities with a high workload and enough rest time and use female workers for repetitive activities with low workload and high frequency.

  The classical manufacturing systems assume that all of produced items are of perfect quality. They also does not consider rework process in manufacturing operations. Moreover, most of previous literature consider single stage production-inventory systems and do not consider multi stage options. However, in real world production-inventory systems, production of defective items is inevitable, and a fraction of produced items may be defective. In addition, to avoid extra costs and consider environmental issues, organizations tend to reworking activities. We propose single and multi stages production-inventory systems in manufacturing operations where the process is defective, rework is possible and a percent of items are scrapped. A main assumption, in current paper, is that the defective rate is assumed to be uncertain parameter. The grey systems theory, as a mathematical tool to address the uncertain information in real-world situations, is utilized to model the random defective rate via a grey nonlinear programming problem. The proposed issues are investigated via numerical examples to assess the impact of grey parameters on optimal solutions.

In recent years, many efforts have been made to provide different strategies for enhancing the scheduling and planning of the operating rooms. The efficient planning and scheduling of ORs is a complex task since it has to account for the availability of human resources, medical equipment, and medication required for each surgery but that are often shared between different ORs. This paper proposes a mathematical approach to enhance the management of OR resources. It presents a bi-objective robust optimization approach for scheduling the surgeries in the ORs and recovery room, regarding the uncertainty of the surgery time, uncertainty of hospitalization time in the recovery room, and shared resources. The first objective function aims to minimize the maximum completion time of the surgeries and the second one minimizes the sum of the earliness-tardiness of the surgical operations. The suggested approach utilizes the multi-choice goal programming approach with utility function to solve the proposed model. The proposed approach is applied to a real case in the Shahid Beheshti hospital, Babol, Iran. The obtained results show that the suggested bi-objective robust optimization approach can enhance OR scheduling and should be designed into a decision support system for OR management.