Near-optimal modified base stock policies for the capacitated inventory problem with stochastic demand and fixed cost

In this study, we investigate a single-item, periodic-review inventory problem where the production capacity is limited and unmet demand is backordered. We assume that customer demand in each period is a stationary, discrete random variable. Linear holding and backorder cost are charged per unit at the end of a period. In addition to the variable cost charged per unit ordered, a positive fixed ordering cost is incurred with each order given. The optimization criterion is the minimization of the expected cost per period over a planning horizon. We investigate the infinite horizon problem by modeling the problem as a discrete-time Markov chain. We propose a heuristic for the problem based on a particular solution of this stationary model, and conduct a computational study on a set of instances, providing insight on the performance of the heuristic. © 2014 World Scientific Publishing Co

Developing a Collaborative Planning Framework for Sustainable Transportation

Currently, as being the highest petroleum consuming sector in the world, transportation significantly contributes to the total greenhouse gas emissions in the world. Road transportation not only is responsible for approximately 20% of the total emissions of carbon dioxide in the EU and in the US but also has a steadily increasing trend in contributing to global warming. Initiatives undertaken by authorities, such as Emission cap and trade in the EU, limit the emissions resulted from the actions of the companies and also give economic incentives to companies to reduce their emissions. However, in logistics systems with multiple entities, it is difficult to assess the responsibilities of the companies both in terms of costs and emissions. In this study, we consider a delivery network with multiple customers served by a single carrier, which executes a delivery plan with the minimum transportation cost, and allocate the resulting costs and the emissions among the customers in a fair manner. We develop allocation mechanisms for both costs and emissions. In order to develop a mechanism that provides further reduction of the emissions, we study a setting where the carrier takes the responsibility of the emissions and reflects the resulting inefficiencies while charging the customers

Rassal talep altında sabit ısmarlama maliyetli kapasiteli envanter modeli

M.S. - Master of Scienc

Solving the integrated shipment routing problem of a less-than-truckload carrier

Due to copyright restrictions, the access to the full text of this article is only available via subscription.We study a less-than-truckload (LTL) transportation network and investigate the potential benefits of implementing an integrated solution approach for shipment routing throughout this network. In LTL transportation, shipments are first delivered to local hubs to be consolidated, then transferred to another hub, and finally sent to their destinations. This routing planning process involves three routing decisions: (i) from origins to hubs,(ii) between hubs, and (iii) from hubs to destinations. These decisions are usually handled in a sequential manner due to the complexity of these individual problems, which may result in suboptimal solutions. In this study, we develop an integrated framework for solving all of these decision problems simultaneously. We propose an optimization-driven approach that can efficiently handle large instances with thousands of loads and provides solutions with significant cost savings over the sequential approach

A game theoretical framework for allocating cost and gas emission responsibilities in a collaborative setting

Global warming poses significant risks to our planet and has a tremendous impact on our daily lives. Unless severe precautions are taken, these adverse effects are most likely to increase drastically and threaten other aspects of our lives and the environment. We consider a shippers’ network in a full-truckload transportation setting. We develop a framework to allocate the resulting cost of this network to the shippers’ while determining the gas emission responsibilities. We conduct a computational analysis to test the effectiveness and the time efficiency of this mechanism in comparison with the proportional-based allocation method and the Shapley Value allocation method.Publisher's Versio

Managing platelet supply through improved routing of blood collection vehicles

Due to copyright restrictions, the access to the full text of this article is only available via subscription.In this paper, we study the routing of blood collection vehicles for improving the platelet supply in the blood supply chain. In order to extract platelets, donated blood has to be processed at a central processing facility within six hours of donation time. Blood collection organizations have to dispatch collection vehicles and schedule pickups from the donation sites so that the donated units can be used in platelet production. Because of the accumulating behavior of donations and the six-hour processing time limit, routing of blood collection vehicles is a time-sensitive routing problem. We analyze the routing decisions in such a setting and propose an integrated clustering and routing framework to collect and process the maximum number of donations for platelet production. In our analysis, motivated by the practices in real-life, we cluster the donation sites so that only a single vehicle serves the donation sites in each cluster. In the proposed framework, we make the clustering and routing decisions in an integrated manner so that we can foresee the impact of adding a donation site to a cluster on the routing decisions. For the routing step, we propose several heuristic algorithms, two of which have a greedy nature and the others are based on a priori tour generation and selection scheme. To evaluate the performances of the proposed heuristics, we develop an upper bound by relaxing the number of vehicles so that one vehicle is available for each donation site. Using the proposed heuristic algorithms, we obtain solutions with around 15% optimality gaps with respect to the upper bound.TÜBİTA

Coordinating collection and appointment scheduling operations at the blood donation sites

Due to copyright restrictions, the access to the full text of this article is only available via subscription.According to the regulations imposed by the U.S. Food and Drug Administration and the American Association of Blood Banks, in order to extract platelets, donated blood units have to be processed at a processing center within six hours of donation time. In this paper, considering this processing time requirement of donated blood units for platelet production we study collection and appointment scheduling operations at the blood donation sites. Specifically, given the blood donation network of a blood collection organization, we try to coordinate pickup and appointment schedules at the blood donation sites to maximize platelet production. We call the problem under consideration Integrated Collection and Appointment Scheduling Problem. We first provide a mixed integer linear programming model for the problem. Then, we propose a heuristic algorithm called Integer Programming Based Algorithm. We perform a computational study to test the performance of the proposed model and algorithm in terms of solution quality and computational efficiency on the instances from Gulf Coast Regional Blood Center located in Houston, TX.TÜBİTA

Lane-exchange mechanisms for truckload carrier collaboration

Due to copyright restrictions, the access to the full text of this article is only available via subscription.Because of historically high fuel prices, the trucking industry's operating expenses are higher than ever and thus profit margins are lower than ever. To cut costs, the trucking industry is searching for and exploring new ideas. We investigate the potential of collaborative opportunities in truckload transportation. When carriers serve transportation requests from many shippers, they may be able to reduce their repositioning costs by exchanging one or more of them. We develop optimization models to determine the maximum benefit that can be derived from collaborating. We also develop various exchange mechanisms which differ in terms of information sharing requirements and side payment options that allow carriers to realize some or all of the costs savings opportunities.NS

Near-optimal modified base stock policies for the capacitated inventory problem with stochastic demand and fixed cost

Due to copyright restrictions, the access to the full text of this article is only available via subscription.In this study, we investigate a single-item, periodic-review inventory problem where the production capacity is limited and unmet demand is backordered. We assume that customer demand in each period is a stationary, discrete random variable. Linear holding and backorder cost are charged per unit at the end of a period. In addition to the variable cost charged per unit ordered, a positive fixed ordering cost is incurred with each order given. The optimization criterion is the minimization of the expected cost per period over a planning horizon. We investigate the infinite horizon problem by modeling the problem as a discrete-time Markov chain. We propose a heuristic for the problem based on a particular solution of this stationary model, and conduct a computational study on a set of instances, providing insight on the performance of the heuristic

Integrated blood collection and appointment scheduling

Due to copyright restrictions, the access to the full text of this article is only available via subscription.Considering the processing requirements of donated blood, we study an integrated blood collection and appointment scheduling problem. We develop a mixed integer programming model to maximize the amount of donated blood that can be delivered to the processing center before spoilage as well as determine the schedule of donation appointments. Since the problem complexity and the computational time of MIP formulation is exponentially increasing by including more donation sites, we propose an insertion/saving heuristic algorithm to find a good feasible solution and develop a large neighborhood search method to improve the solution further