Most existing network design and facility location models have focused on the trade-off between t... more Most existing network design and facility location models have focused on the trade-off between the fixed costs of locating facilities and variable transportation costs between facilities and customers. However, operational performance measures such as service levels and lead ...
European Journal of Operational Research, Sep 1, 2009
We consider a two-stage supply chain with a production facility that replenishes a single product... more We consider a two-stage supply chain with a production facility that replenishes a single product at retailers. The objective is to locate distribution centers in the network such that the sum of facility location, pipeline inventory, and safety stock costs is minimized. We explicitly model the ...
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
In recent years, supply chain networks have been increasing in complexity due to the globalizatio... more In recent years, supply chain networks have been increasing in complexity due to the globalization of manufacturing operations. In a capacitated planning problem with intermediate distribution centers (DCs), decisions must be made for production lot sizes, production schedules, shipment amounts between locations and more. These models generally consist of a non-linear objective and are difficult to solve. In this paper, we formulate the Capacitated Production, Inventory, and Distribution Problem (CPIDP) for multiple products on a single production line in the supply chain network and develop an efficient simulated annealing (SA) algorithm and various improvement heuristics. We then present the computational results that demonstrate the reliable and robust performance of our approach.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
In this paper we consider a centralized logistics system in which a single company owns the produ... more In this paper we consider a centralized logistics system in which a single company owns the production facility and the set of retailers and establishes warehouses that will replenish the retailers' inventories. We analyze the potential savings that the company will achieve by allowing its retailers to be sourced by more than one warehouse probabilistically, through the use of information technology. We facilitate the discussion on the impact of multisourcing by introducing a capacitated location-inventory model that minimizes the sum of the fixed warehouse location costs, the transportation costs, and the inventory costs. The model is formulated as a nonlinear integer-programming problem that has a cost term that is neither concave nor convex. We propose a Lagrangian relaxation solution algorithm to solve the model and successfully test the algorithm on problems with 88 and 150 retailers. Based on the model properties and the sensitivity analysis results, we conclude that multi...
In this article, we introduce the capacitated warehouse location model with risk pooling (CLMRP),... more In this article, we introduce the capacitated warehouse location model with risk pooling (CLMRP), which captures the interdependence between capacity issues and the inventory management at the warehouses. The CLMRP models a logistics system in which a single plant ships one type of product to a set of retailers, each with an uncertain demand. Warehouses serve as the direct intermediary between the plant and the retailers for the shipment of the product and also retain safety stock to provide appropriate service levels to the retailers. The CLMRP minimizes the sum of the fixed facility location, transportation, and inventory carrying costs. The model simultaneously determines warehouse locations, shipment sizes from the plant to the warehouses, the working inventory, and safety stock levels at the warehouses and the assignment of retailers to the warehouses. The costs at each warehouse exhibit initially economies of scale and then an exponential increase due to the capacity limitations. We show that this problem can be formulated as a nonlinear integer program in which the objective function is neither concave nor convex. A Lagrangian relaxation solution algorithm is proposed. The Lagrangian subproblem is also a nonlinear integer program. An efficient algorithm is developed for the linear relaxation of this subproblem. The Lagrangian relaxation algorithm provides near-optimal solutions with reasonable computational requirements for large problem instances.
Purpose – The growing presence of foods that are labelled “locally/ecologically produced” leads t... more Purpose – The growing presence of foods that are labelled “locally/ecologically produced” leads to the question of how many consumers consider the impact of their food purchases. Do they value local/ecologically-produced food sufficiently to drive their purchasing behaviour, even if such foods are more costly? Can consumer segments be identified and, if so, what are their characteristics? This paper aims to focus on these questions. Design/methodology/approach – In an exploratory study, the authors surveyed over 400 students from a public university in California asking them to select between apples based on a combination of price, origin and presence/absence of an ecological indicator. The authors collected information on their shopping attitudes, their affinity for international trade and demographic identifiers. Findings – Evidence is found for three consumer segments: the deep green, the price conscious and switchers. The latter are the most prevalent category across demographic...
International Journal of Applied Decision Sciences, 2009
In this paper, we propose a genetic algorithm as an alternative technique for solving the capacit... more In this paper, we propose a genetic algorithm as an alternative technique for solving the capacitated facility location problem with risk pooling (CLMRP). The CLMRP is a joint location-inventory problem involving a single supplier and multiple retailers that face stochastic demand. Due to the stochasticity of demand associated with each retailer, risk pooling may be achieved by allowing some retailers to serve as distribution centres (DCs). This is a combinatorial optimisation problem that has been shown to be NP-hard. A genetic algorithm that is computationally very efficient is developed to solve the problem. A computational experiment is conducted to test the performance of the developed technique and computational results are reported. The algorithm can easily find optimal or near optimal solutions for benchmark test problems from the literature, where the Lagrangian relaxation approach was used.
Many outpatient clinics are experimenting with open access scheduling. Under open access, patient... more Many outpatient clinics are experimenting with open access scheduling. Under open access, patients see their physicians within a day or two of making their appointment request, and long term patient booking is very limited. The hope is that these short appointment lead times will improve patient access and reduce uncertainty in clinic operations by reducing patient no-shows. Practice shows that successful implementation can be strongly influenced by clinic characteristics, indicating that open access policies must be designed to account for local clinical conditions. The effects of four variables on clinic performance are examined: (1) the fraction of patients being served on open access, (2) the scheduling horizon for patients on longer term appointment scheduling, (3) provider care groups, and (4) overbooking. Discrete event simulation, designed experimentation, and data drawn from an intercity clinic in central Indiana are used to study the effects of these variables on clinic throughput and patient continuity of care. Results show that, if correctly configured, open access can lead to significant improvements in clinic throughput with little sacrifice in continuity of care.
We consider a two-stage supply chain with a production facility that replenishes a single product... more We consider a two-stage supply chain with a production facility that replenishes a single product at retailers. The objective is to locate distribution centers in the network such that the sum of facility location, pipeline inventory, and safety stock costs is minimized. We explicitly model the ...
The first capacitated location-inventory model we introduce in this dissertation assigns each ret... more The first capacitated location-inventory model we introduce in this dissertation assigns each retailer to a single distribution center. We formulate this model as a nonlinear integer program in which the objective function is neither concave nor convex. Feasible solutions for this ...
This study concerns the execution of open access appointment scheduling system at an urban outpat... more This study concerns the execution of open access appointment scheduling system at an urban outpatient clinic. The clinic underwent a change of its patient appointment scheduling policy from the traditional up-to-one- year fixed booking to the same-day appointment open access system. In this study, we developed a queueing network and a simulation model that help the decision making process of the clinic's scheduling policy. From the analytical results and anecdotal evidence, we also discovered the important factors for successfully implementing of open access. Large outpatient healthcare clinics schedule thousands of patient appointments each year, and the effectiveness of processes used have direct and critical impacts on the efficiency of clinical resource use and patient satisfaction. It is not unusual in traditional scheduling systems for appointments to be made months in advance of the patient visit, even when the clinic supply and demand are balanced in the sense that the number of new appointments scheduled equals the number of visits completed each day. Furthermore, no-show patients, who fail to report at their scheduled time, may number as much as 42% of the total which introduces enormous volatility in clinic operations that squanders critical availability of physicians and other clinical staff.(1) Open Access Scheduling has been introduced in the past decade to address some of these challenges. Instead of booking well ahead, a substantial fraction of patients are asked to call in for appointments within a day or two of the time they wish to see their physician. If appointment slots are available the patient is scheduled immediately, thus avoiding the long delay of advanced booking and substantially reducing no-shows in many settings. Despite its apparent appeal, implementations of open access scheduling often fail or prove far less successful than anticipated because the system has not been optimized for the environment in the particular clinic tested. For example, indigent or aged patients may have much more difficulty with some forms of open access than more up- scale populations. Work patterns of physicians - especially when residents are included - may prevent or complicate the ability of open access scheduling to preserve continuity of care between the patient and his/her regular doctor. Also, a certain fraction of patients, such as those returning for follow-up visits, may require advance appointments like the traditional system; the number of slots reserved for such patients must be optimized for different settings. This paper details the development of modeling and analysis tools that are used to best configure an open access patient scheduling system for an outpatient clinic of a teaching hospital situated in Midwest urban area. In the spring of 2005, the clinic was experiencing an average of 23% of patients defaulting on scheduled appointments. A nearby outpatient clinic successfully implemented an open access scheduling system and saw both patient no-show rates and wait times decrease, prompting the clinic under study to consider open access. We were approached by the teaching clinic to help develop a tool for analyzing an open access setting for their clinic. Our approach consisted of developing a queueing network model to analyze clinic operation under steady state conditions. A simulation model evaluating an open access scheduling system parameters was developed in parallel to determine the impact of various factors on the delivery of care. The subsequent sections of this paper include a literature review, methodologies used in the study, an analysis of results and the current status of the clinic.
Historically, the improvement of modern health care delivery was almost exclusively championed by... more Historically, the improvement of modern health care delivery was almost exclusively championed by interdisciplinary teams of health care professionals and researchers from within the health care domain. Only recently have researchers from nonmedical disciplines begun to actively and consistently
Most existing network design and facility location models have focused on the trade-off between t... more Most existing network design and facility location models have focused on the trade-off between the fixed costs of locating facilities and variable transportation costs between facilities and customers. However, operational performance measures such as service levels and lead ...
Most existing network design and facility location models have focused on the trade-off between t... more Most existing network design and facility location models have focused on the trade-off between the fixed costs of locating facilities and variable transportation costs between facilities and customers. However, operational performance measures such as service levels and lead ...
European Journal of Operational Research, Sep 1, 2009
We consider a two-stage supply chain with a production facility that replenishes a single product... more We consider a two-stage supply chain with a production facility that replenishes a single product at retailers. The objective is to locate distribution centers in the network such that the sum of facility location, pipeline inventory, and safety stock costs is minimized. We explicitly model the ...
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
In recent years, supply chain networks have been increasing in complexity due to the globalizatio... more In recent years, supply chain networks have been increasing in complexity due to the globalization of manufacturing operations. In a capacitated planning problem with intermediate distribution centers (DCs), decisions must be made for production lot sizes, production schedules, shipment amounts between locations and more. These models generally consist of a non-linear objective and are difficult to solve. In this paper, we formulate the Capacitated Production, Inventory, and Distribution Problem (CPIDP) for multiple products on a single production line in the supply chain network and develop an efficient simulated annealing (SA) algorithm and various improvement heuristics. We then present the computational results that demonstrate the reliable and robust performance of our approach.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
In this paper we consider a centralized logistics system in which a single company owns the produ... more In this paper we consider a centralized logistics system in which a single company owns the production facility and the set of retailers and establishes warehouses that will replenish the retailers' inventories. We analyze the potential savings that the company will achieve by allowing its retailers to be sourced by more than one warehouse probabilistically, through the use of information technology. We facilitate the discussion on the impact of multisourcing by introducing a capacitated location-inventory model that minimizes the sum of the fixed warehouse location costs, the transportation costs, and the inventory costs. The model is formulated as a nonlinear integer-programming problem that has a cost term that is neither concave nor convex. We propose a Lagrangian relaxation solution algorithm to solve the model and successfully test the algorithm on problems with 88 and 150 retailers. Based on the model properties and the sensitivity analysis results, we conclude that multi...
In this article, we introduce the capacitated warehouse location model with risk pooling (CLMRP),... more In this article, we introduce the capacitated warehouse location model with risk pooling (CLMRP), which captures the interdependence between capacity issues and the inventory management at the warehouses. The CLMRP models a logistics system in which a single plant ships one type of product to a set of retailers, each with an uncertain demand. Warehouses serve as the direct intermediary between the plant and the retailers for the shipment of the product and also retain safety stock to provide appropriate service levels to the retailers. The CLMRP minimizes the sum of the fixed facility location, transportation, and inventory carrying costs. The model simultaneously determines warehouse locations, shipment sizes from the plant to the warehouses, the working inventory, and safety stock levels at the warehouses and the assignment of retailers to the warehouses. The costs at each warehouse exhibit initially economies of scale and then an exponential increase due to the capacity limitations. We show that this problem can be formulated as a nonlinear integer program in which the objective function is neither concave nor convex. A Lagrangian relaxation solution algorithm is proposed. The Lagrangian subproblem is also a nonlinear integer program. An efficient algorithm is developed for the linear relaxation of this subproblem. The Lagrangian relaxation algorithm provides near-optimal solutions with reasonable computational requirements for large problem instances.
Purpose – The growing presence of foods that are labelled “locally/ecologically produced” leads t... more Purpose – The growing presence of foods that are labelled “locally/ecologically produced” leads to the question of how many consumers consider the impact of their food purchases. Do they value local/ecologically-produced food sufficiently to drive their purchasing behaviour, even if such foods are more costly? Can consumer segments be identified and, if so, what are their characteristics? This paper aims to focus on these questions. Design/methodology/approach – In an exploratory study, the authors surveyed over 400 students from a public university in California asking them to select between apples based on a combination of price, origin and presence/absence of an ecological indicator. The authors collected information on their shopping attitudes, their affinity for international trade and demographic identifiers. Findings – Evidence is found for three consumer segments: the deep green, the price conscious and switchers. The latter are the most prevalent category across demographic...
International Journal of Applied Decision Sciences, 2009
In this paper, we propose a genetic algorithm as an alternative technique for solving the capacit... more In this paper, we propose a genetic algorithm as an alternative technique for solving the capacitated facility location problem with risk pooling (CLMRP). The CLMRP is a joint location-inventory problem involving a single supplier and multiple retailers that face stochastic demand. Due to the stochasticity of demand associated with each retailer, risk pooling may be achieved by allowing some retailers to serve as distribution centres (DCs). This is a combinatorial optimisation problem that has been shown to be NP-hard. A genetic algorithm that is computationally very efficient is developed to solve the problem. A computational experiment is conducted to test the performance of the developed technique and computational results are reported. The algorithm can easily find optimal or near optimal solutions for benchmark test problems from the literature, where the Lagrangian relaxation approach was used.
Many outpatient clinics are experimenting with open access scheduling. Under open access, patient... more Many outpatient clinics are experimenting with open access scheduling. Under open access, patients see their physicians within a day or two of making their appointment request, and long term patient booking is very limited. The hope is that these short appointment lead times will improve patient access and reduce uncertainty in clinic operations by reducing patient no-shows. Practice shows that successful implementation can be strongly influenced by clinic characteristics, indicating that open access policies must be designed to account for local clinical conditions. The effects of four variables on clinic performance are examined: (1) the fraction of patients being served on open access, (2) the scheduling horizon for patients on longer term appointment scheduling, (3) provider care groups, and (4) overbooking. Discrete event simulation, designed experimentation, and data drawn from an intercity clinic in central Indiana are used to study the effects of these variables on clinic throughput and patient continuity of care. Results show that, if correctly configured, open access can lead to significant improvements in clinic throughput with little sacrifice in continuity of care.
We consider a two-stage supply chain with a production facility that replenishes a single product... more We consider a two-stage supply chain with a production facility that replenishes a single product at retailers. The objective is to locate distribution centers in the network such that the sum of facility location, pipeline inventory, and safety stock costs is minimized. We explicitly model the ...
The first capacitated location-inventory model we introduce in this dissertation assigns each ret... more The first capacitated location-inventory model we introduce in this dissertation assigns each retailer to a single distribution center. We formulate this model as a nonlinear integer program in which the objective function is neither concave nor convex. Feasible solutions for this ...
This study concerns the execution of open access appointment scheduling system at an urban outpat... more This study concerns the execution of open access appointment scheduling system at an urban outpatient clinic. The clinic underwent a change of its patient appointment scheduling policy from the traditional up-to-one- year fixed booking to the same-day appointment open access system. In this study, we developed a queueing network and a simulation model that help the decision making process of the clinic's scheduling policy. From the analytical results and anecdotal evidence, we also discovered the important factors for successfully implementing of open access. Large outpatient healthcare clinics schedule thousands of patient appointments each year, and the effectiveness of processes used have direct and critical impacts on the efficiency of clinical resource use and patient satisfaction. It is not unusual in traditional scheduling systems for appointments to be made months in advance of the patient visit, even when the clinic supply and demand are balanced in the sense that the number of new appointments scheduled equals the number of visits completed each day. Furthermore, no-show patients, who fail to report at their scheduled time, may number as much as 42% of the total which introduces enormous volatility in clinic operations that squanders critical availability of physicians and other clinical staff.(1) Open Access Scheduling has been introduced in the past decade to address some of these challenges. Instead of booking well ahead, a substantial fraction of patients are asked to call in for appointments within a day or two of the time they wish to see their physician. If appointment slots are available the patient is scheduled immediately, thus avoiding the long delay of advanced booking and substantially reducing no-shows in many settings. Despite its apparent appeal, implementations of open access scheduling often fail or prove far less successful than anticipated because the system has not been optimized for the environment in the particular clinic tested. For example, indigent or aged patients may have much more difficulty with some forms of open access than more up- scale populations. Work patterns of physicians - especially when residents are included - may prevent or complicate the ability of open access scheduling to preserve continuity of care between the patient and his/her regular doctor. Also, a certain fraction of patients, such as those returning for follow-up visits, may require advance appointments like the traditional system; the number of slots reserved for such patients must be optimized for different settings. This paper details the development of modeling and analysis tools that are used to best configure an open access patient scheduling system for an outpatient clinic of a teaching hospital situated in Midwest urban area. In the spring of 2005, the clinic was experiencing an average of 23% of patients defaulting on scheduled appointments. A nearby outpatient clinic successfully implemented an open access scheduling system and saw both patient no-show rates and wait times decrease, prompting the clinic under study to consider open access. We were approached by the teaching clinic to help develop a tool for analyzing an open access setting for their clinic. Our approach consisted of developing a queueing network model to analyze clinic operation under steady state conditions. A simulation model evaluating an open access scheduling system parameters was developed in parallel to determine the impact of various factors on the delivery of care. The subsequent sections of this paper include a literature review, methodologies used in the study, an analysis of results and the current status of the clinic.
Historically, the improvement of modern health care delivery was almost exclusively championed by... more Historically, the improvement of modern health care delivery was almost exclusively championed by interdisciplinary teams of health care professionals and researchers from within the health care domain. Only recently have researchers from nonmedical disciplines begun to actively and consistently
Most existing network design and facility location models have focused on the trade-off between t... more Most existing network design and facility location models have focused on the trade-off between the fixed costs of locating facilities and variable transportation costs between facilities and customers. However, operational performance measures such as service levels and lead ...
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