An Inventory Model with Two Classes of Customers in On-line Rental Service: Consumer Model Approach

This short version of the paper offers a model and analysis of the rental process at a subscription-based business like Netflix. We analyze a priority scheduling scheme, currently in use, that gives priority to light renters over heavy renters and show that, in some situations, it may be more profitable for the firm to give priority to heavy renters which is opposite to the Netflix’s current practice. The conditions determining the optimal initial inventory are proved analytically. Extensions are briefly discussed

Time-partitioning heuristic algorithm for optimal production, inventory, and transportation planning with direct shipment

We developed a mixed integer linear programming model for an integrated decision problem of production, inventory, and transportation planning. Our model combines the direct shipment into the production, inventory, and distribution planning. The objective was to minimize the total operation cost which is comprised of production setup cost, inventory holding cost, transportation cost, and reorder cost. The model is solved to optimality using the leading optimization software, IBM ILOG CPLEX (CPLEX), but the software shows a limited capability to solve large size problems. A time-partitioning heuristic algorithm is proposed to efficiently solve the problem. Numerical experiments are extensively conducted to test the proposed algorithm. In our numerical experiments, the proposed algorithm can solve many large size problems, whereas CPLEX fails to solve them. The numerical experiment shows that a company can gain a significant saving by optimally incorporating the direct shipment. The proposed heuristic algorithm performs well in most cases in terms of a total cost and the computation time

MULTI-PERIOD SUPPLY CHAIN COORDINATION USING TRADE PROMOTION: COMPLEMENTARY SLACKNESS APPROACH

In this paper, a two-level supply chain network with a single manufacturer supplying a single product to a single retailer is studied. This research uses a trade promotion strategy to coordinate the supply chain by finding the optimal pre-announced multi-period wholesale prices that can induce the retailer’s decentralized decisions to be the same as the retailer’s centralized decisions with the minimum total cost for the supply chain. The manufacturer makes production, inventory, and wholesale price decisions. The retailer makes ordering and inventory decisions. A procedure is proposed to determine optimal wholesale prices to pre-announce in each period to the retailer, coordinating the supply chain using complementary slackness conditions. The results show the coordination benefits for a supply chain when the setup or reorder cost is high but the average demand is low. Finally, the performance of the proposed method is compared with the performance of the “Every Day Low Price” wholesale price policy

Nurse scheduling in a hospital emergency department: A case study at a Thai university hospital

Common problems of Thai nurses are low quality of life, working long hours, and a high turnover rate. The workload imbalance among nurses also worsens the turnover rate. With careful schedule planning, nurses do not have to work in consecutive shifts and can rest more. We interviewed and collected data from an emergency department at a hospital administered by a Thai university, related to objectives and constraints of monthly nurse scheduling, and actual monthly schedules. A multi-objective mathematical model was developed using the open source “OpenSolver” software in MS-Excel for nurse schedulers to freely use. We tested the model using actual data collected from the department and found that the schedules created by the model tended to provide more balanced workloads and more days off compared to the schedules created manually by a real scheduler. The model also suggested an easy policy to increase the number of nurses for future expansion

HEURISTIC PROCEDURE FOR MULTI-WORKDAY VEHICLE ROUTING PROBLEM WITH PRE-ASSIGNED WORKERS AND MANUAL UNLOADING

This paper deals with the multi-workday vehicle routing problem (MW-VRP) where delivery workers are pre-assigned to vehicles. At customer locations, workers must manually unload goods from vehicles. For each worker, the daily accumulated physical workload depends on the number of customers served by the vehicle and load demands at those customers. The MW-VRP is intended to determine daily delivery routes for a given set of vehicles over the multi-workday delivery period such that the maximum average percent residual energy (PRE) among all workers is minimized. A heuristic procedure is developed to firstly determine delivery routes for vehicles. Next, a greedy exchange algorithm is used to decrease the maximum average PRE among workers and total travel distance of vehicles. The results from the given numerical example show that the heuristic procedure is able to generate the routing solution with the same maximum average PRE as that from the optimal solution, but with a slightly greater total travel distance (11.57%)

A Multi-Objective Unit Commitment Model for Setting Carbon Tax to Reduce CO2 Emission: Thailand's Electricity Generation Case

Carbon tax policy is a cost-effective instrument for emission reduction. However, setting the carbon tax is one of the challenging task for policy makers as it will lead to higher price of emission-intensive sources especially the utility price. In a large-scale power generation system, minimizing the operational cost and the environmental impact are conflicting objectives and it is difficult to find the compromise solution. This paper proposes a methodology of finding a feasible carbon tax rate on strategic level using the operational unit commitment model. We present a multi-objective mixed integer linear programming model to solve the unit commitment problem and consider the environmental impacts. The methodology of analyzing of the effect of carbon tax rates on the power generation, operating cost, and CO2 emission is also provided. The trade-off relationship between total operating cost and total CO2 emission is presented in the Pareto-optimal curve to analyze the feasible carbon tax rate that is influencing on electricity operating cost. The significant outcome of this paper is a modeling framework for the policy makers to determine the possible carbon tax that can be imposed on the electricity generation