Esma Gel | University of Nebraska Lincoln (original) (raw)
Papers by Esma Gel
Social Science Research Network, 2022
arXiv (Cornell University), May 18, 2023
Increasing workload is one of the main problems that surgical practices face. This increase is no... more Increasing workload is one of the main problems that surgical practices face. This increase is not only due to the increasing demand volume but also due to increasing case complexity. This raises the question on how to measure and predict the complexity to address this issue. Predicting surgical duration is critical to parametrize surgical complexity, improve surgeon satisfaction by avoiding unexpected overtime, and improve operation room utilization. Our objective is to utilize the historical data on surgical operations to obtain complexity groups and use this groups to improve practice.Our study first leverages expert opinion on the surgical complexity to identify surgical groups. Then, we use a tree-based method on a large retrospective dataset to identify similar complexity groups by utilizing the surgical features and using surgical duration as a response variable. After obtaining the surgical groups by using two methods, we statistically compare expert-based grouping with the data-based grouping. This comparison shows that a tree-based method can provide complexity groups similar to the ones generated by an expert by using features that are available at the time of surgical listing. These results suggest that one can take advantage of available data to provide surgical duration predictions that are data-driven, evidence-based, and practically relevant.
Operations Research, Jun 1, 2010
We consider the problem of evaluating the quality of solution sets generated by heuristics for mu... more We consider the problem of evaluating the quality of solution sets generated by heuristics for multiple-objective combinatorial optimization problems. We extend previous research on the integrated preference functional (IPF), which assigns a scalar value to a given discrete set of nondominated points so that the weighted Tchebycheff function can be used as the underlying implicit value function. This extension is useful because modeling the decision maker's value function with the weighted Tchebycheff function reflects the impact of unsupported points when evaluating sets of nondominated points. We present an exact calculation method for the IPF measure in this case for an arbitrary number of criteria. We show that every nondominated point has its optimal weight interval for the weighted Tchebycheff function. Accordingly, all nondominated points, and not only the supported points in a set, contribute to the value of the IPF measure when using the weighted Tchebycheff function. Two- and three-criteria numerical examples illustrate the desirable properties of the weighted Tchebycheff function, providing a richer measure than the original IPF based on a convex combination of objectives.
Preventive medicine reports, Dec 1, 2022
Quality Engineering, 2006
2021 Winter Simulation Conference (WSC), Dec 12, 2021
European Journal of Operational Research, Oct 1, 2010
We present a new hybrid approach to interactive evolutionary multi-objective optimization that us... more We present a new hybrid approach to interactive evolutionary multi-objective optimization that uses a partial preference order to act as the fitness function in a customized genetic algorithm. We periodically send solutions to the decision maker (DM) for her evaluation and use the resulting preference information to form preference cones consisting of inferior solutions. The cones allow us to implicitly
Women in Industrial and Systems Engineering, 2019
We summarize the literature on dynamic quotation strategies under which a seller provides price a... more We summarize the literature on dynamic quotation strategies under which a seller provides price and/or lead time quotes to a potential buyer, who then either accepts or rejects the quote. The goal of quotation strategies is to better match supply and demand by influencing and possibly smoothing out the demand. We identify some common observations and findings in this domain, and suggest directions of future work.
Sabre Corporation, a company based out of Southlake, Texas, is a global technology leader in the ... more Sabre Corporation, a company based out of Southlake, Texas, is a global technology leader in the travel industry. Sabre began in 1960 as a joint initiative between IBM and American Airlines to create a computerized airline reservation system. Being one of the world’s largest software companies to date, Sabre’s technology is utilized by more than a billion people across the world to plan, book and travel to their desired destination as efficiently as possible.
Interfaces, 2015
The work we describe addresses the problem of deciding between project-funding opportunities unde... more The work we describe addresses the problem of deciding between project-funding opportunities under budget and headcount constraints. Although the projects lead to products that yield revenue in the market, complex interactions between the projects and products make the selection of a portfolio difficult. Furthermore, the senior managers in the company have a wealth of business intuition that can inform the required decisions. We combine modeling, simulation, and optimization techniques to provide a set of the best portfolios possible from the proposed projects and resulting products. We also provide a rich set of analysis and visualization tools for the decision makers to use in exploring the suggested portfolios and applying their intuition to make the final selection. The resulting interplay between analytics and intuition produces better business solutions through a more focused and effective debate in a shorter time than previously achieved.
The Factory Operations portion of the 2001 International Technology Roadmap for Semiconductors (I... more The Factory Operations portion of the 2001 International Technology Roadmap for Semiconductors (ITRS) indicates that real time scheduling is one of the potential solutions for the semiconductor industry to preserve the decades-long trend of 30% per year reduction in cost per function. However, scheduling wafer fabrication facilities is a very difficult problem. There are several main features that complicate scheduling these systems including: a large number of processing steps, re-entrant flows, batch tools, planned and unplanned equipment downtimes, sequence-dependent tool setups, high levels of automation, and the fact that some processing steps require auxiliary resources (e.g. reticles). The Semiconductor Research Corporation (SRC) and International SEMATECH recently created the Factory Operations Research Center (FORCe). As one of the initial set of FORCe projects, a team of researchers from two US and three German institutions were funded to investugate a shiftingbottleneck heuristic-based approach to scheduling wafer fabrication facilities. In this paper, we briefly describe the FORCe program and discuss the four major research tasks associated with the three year scheduling project.
2021 Winter Simulation Conference (WSC), 2021
2020 Winter Simulation Conference (WSC), 2020
SSRN Electronic Journal, 2021
We present a novel framework to characterize the probability that an offered appointment with k-d... more We present a novel framework to characterize the probability that an offered appointment with k-days' access delay will be booked and subsequently attended by a patient. We refer to this probability as the "probability of realization'" of an offered appointment, and demonstrate how empirical characterizations of this measure can be used to identify improved policies for managing patient demand and enabling the most intentional use of clinical care resources. We consider the estimation problem in the context of new patients looking to establish care at a clinic, and offer a model of patient responses during an appointment scheduling encounter with an agent. We define different cases of data availability and demonstrate the effectiveness of framework in each case to ensure generalizability. We first demonstrate the accuracy of estimations using simulated data, and then highlight behavioral differences between different patient groups using real-life transactional data from two clinical departments. Finally, we clearly demonstrate a practical use case for the obtained realization probabilities by showing that they can be reliably used as input to a novel time windows-based patient prioritization protocol that allows effective management of demand from different classes by explicitly considering wait sensitivities of patients.
Social Science Research Network, 2022
arXiv (Cornell University), May 18, 2023
Increasing workload is one of the main problems that surgical practices face. This increase is no... more Increasing workload is one of the main problems that surgical practices face. This increase is not only due to the increasing demand volume but also due to increasing case complexity. This raises the question on how to measure and predict the complexity to address this issue. Predicting surgical duration is critical to parametrize surgical complexity, improve surgeon satisfaction by avoiding unexpected overtime, and improve operation room utilization. Our objective is to utilize the historical data on surgical operations to obtain complexity groups and use this groups to improve practice.Our study first leverages expert opinion on the surgical complexity to identify surgical groups. Then, we use a tree-based method on a large retrospective dataset to identify similar complexity groups by utilizing the surgical features and using surgical duration as a response variable. After obtaining the surgical groups by using two methods, we statistically compare expert-based grouping with the data-based grouping. This comparison shows that a tree-based method can provide complexity groups similar to the ones generated by an expert by using features that are available at the time of surgical listing. These results suggest that one can take advantage of available data to provide surgical duration predictions that are data-driven, evidence-based, and practically relevant.
Operations Research, Jun 1, 2010
We consider the problem of evaluating the quality of solution sets generated by heuristics for mu... more We consider the problem of evaluating the quality of solution sets generated by heuristics for multiple-objective combinatorial optimization problems. We extend previous research on the integrated preference functional (IPF), which assigns a scalar value to a given discrete set of nondominated points so that the weighted Tchebycheff function can be used as the underlying implicit value function. This extension is useful because modeling the decision maker's value function with the weighted Tchebycheff function reflects the impact of unsupported points when evaluating sets of nondominated points. We present an exact calculation method for the IPF measure in this case for an arbitrary number of criteria. We show that every nondominated point has its optimal weight interval for the weighted Tchebycheff function. Accordingly, all nondominated points, and not only the supported points in a set, contribute to the value of the IPF measure when using the weighted Tchebycheff function. Two- and three-criteria numerical examples illustrate the desirable properties of the weighted Tchebycheff function, providing a richer measure than the original IPF based on a convex combination of objectives.
Preventive medicine reports, Dec 1, 2022
Quality Engineering, 2006
2021 Winter Simulation Conference (WSC), Dec 12, 2021
European Journal of Operational Research, Oct 1, 2010
We present a new hybrid approach to interactive evolutionary multi-objective optimization that us... more We present a new hybrid approach to interactive evolutionary multi-objective optimization that uses a partial preference order to act as the fitness function in a customized genetic algorithm. We periodically send solutions to the decision maker (DM) for her evaluation and use the resulting preference information to form preference cones consisting of inferior solutions. The cones allow us to implicitly
Women in Industrial and Systems Engineering, 2019
We summarize the literature on dynamic quotation strategies under which a seller provides price a... more We summarize the literature on dynamic quotation strategies under which a seller provides price and/or lead time quotes to a potential buyer, who then either accepts or rejects the quote. The goal of quotation strategies is to better match supply and demand by influencing and possibly smoothing out the demand. We identify some common observations and findings in this domain, and suggest directions of future work.
Sabre Corporation, a company based out of Southlake, Texas, is a global technology leader in the ... more Sabre Corporation, a company based out of Southlake, Texas, is a global technology leader in the travel industry. Sabre began in 1960 as a joint initiative between IBM and American Airlines to create a computerized airline reservation system. Being one of the world’s largest software companies to date, Sabre’s technology is utilized by more than a billion people across the world to plan, book and travel to their desired destination as efficiently as possible.
Interfaces, 2015
The work we describe addresses the problem of deciding between project-funding opportunities unde... more The work we describe addresses the problem of deciding between project-funding opportunities under budget and headcount constraints. Although the projects lead to products that yield revenue in the market, complex interactions between the projects and products make the selection of a portfolio difficult. Furthermore, the senior managers in the company have a wealth of business intuition that can inform the required decisions. We combine modeling, simulation, and optimization techniques to provide a set of the best portfolios possible from the proposed projects and resulting products. We also provide a rich set of analysis and visualization tools for the decision makers to use in exploring the suggested portfolios and applying their intuition to make the final selection. The resulting interplay between analytics and intuition produces better business solutions through a more focused and effective debate in a shorter time than previously achieved.
The Factory Operations portion of the 2001 International Technology Roadmap for Semiconductors (I... more The Factory Operations portion of the 2001 International Technology Roadmap for Semiconductors (ITRS) indicates that real time scheduling is one of the potential solutions for the semiconductor industry to preserve the decades-long trend of 30% per year reduction in cost per function. However, scheduling wafer fabrication facilities is a very difficult problem. There are several main features that complicate scheduling these systems including: a large number of processing steps, re-entrant flows, batch tools, planned and unplanned equipment downtimes, sequence-dependent tool setups, high levels of automation, and the fact that some processing steps require auxiliary resources (e.g. reticles). The Semiconductor Research Corporation (SRC) and International SEMATECH recently created the Factory Operations Research Center (FORCe). As one of the initial set of FORCe projects, a team of researchers from two US and three German institutions were funded to investugate a shiftingbottleneck heuristic-based approach to scheduling wafer fabrication facilities. In this paper, we briefly describe the FORCe program and discuss the four major research tasks associated with the three year scheduling project.
2021 Winter Simulation Conference (WSC), 2021
2020 Winter Simulation Conference (WSC), 2020
SSRN Electronic Journal, 2021
We present a novel framework to characterize the probability that an offered appointment with k-d... more We present a novel framework to characterize the probability that an offered appointment with k-days' access delay will be booked and subsequently attended by a patient. We refer to this probability as the "probability of realization'" of an offered appointment, and demonstrate how empirical characterizations of this measure can be used to identify improved policies for managing patient demand and enabling the most intentional use of clinical care resources. We consider the estimation problem in the context of new patients looking to establish care at a clinic, and offer a model of patient responses during an appointment scheduling encounter with an agent. We define different cases of data availability and demonstrate the effectiveness of framework in each case to ensure generalizability. We first demonstrate the accuracy of estimations using simulated data, and then highlight behavioral differences between different patient groups using real-life transactional data from two clinical departments. Finally, we clearly demonstrate a practical use case for the obtained realization probabilities by showing that they can be reliably used as input to a novel time windows-based patient prioritization protocol that allows effective management of demand from different classes by explicitly considering wait sensitivities of patients.