Ergin Erdem

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A Finite Mixture GARCH Approach with EM Algorithm for Energy Forecasting Applications

Energies, 2021

Enhancing forecasting performance in terms of both the expected mean value and variance has been ... more Enhancing forecasting performance in terms of both the expected mean value and variance has been a critical challenging issue for energy industry. In this paper, the novel methodology of finite mixture Generalized AutoRegressive Conditional Heteroskedasticity (GARCH) approach with Expectation–Maximization (EM) algorithm is introduced. The applicability of this methodology is comprehensively evaluated for the forecasting of energy related time series including wind speed, wind power generation, and electricity price. Its forecasting performances are evaluated by various criteria, and also compared with those of the conventional AutoRegressive Moving-Average (ARMA) model and the less conventional ARMA-GARCH model. It is found that the proposed mixture GARCH model outperforms the other two models in terms of volatility modeling for all the energy related time series considered. This is proven to be statistically significant because the p-values of likelihood ratio test are less than 0....

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A Clustering Approach for Missed Opportunity Risk Assessment

The primary care clinics of the U.S. Department of Veterans Affairs (VA) have long suffered the a... more The primary care clinics of the U.S. Department of Veterans Affairs (VA) have long suffered the adverse effect of missed opportunity risks which are mainly reflected by patient no-shows. This calls for quantitative tools that can identify and assess the missed opportunity risk. In this study, we apply the Glowworm Swarm Optimization (GSO) approach to group VA primary care clinics into clusters with different levels of missed opportunity risk based on the historical patient no-show data. The GSO based approach can simultaneously decide the optimal number of clusters and select the best candidate for each cluster. The VA primary care clinics are divided into several clusters with different patient no-show risk levels, where the similarity of risks between facilities in the same cluster is maximized, while the similarity of risks between facilities in different clusters is minimized. Meanwhile, we also investigate the selection of objective function related to the GSO algorithm, in whi...

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Stochastic Price-Based Unit Commitment in Wind Power Generating Company

In this paper, we propose a stochastic mixed-integer programming model to obtain the best day-ahe... more In this paper, we propose a stochastic mixed-integer programming model to obtain the best day-ahead dispatch strategy for a generating company (GENCO) with wind and storage units. The strategy development is based on the formulized price-based unit commitment (PBUC) problem, which considers the volatility of wind speed and electricity price. The model is then solved through an integration of Monte Carlo simulation and genetic algorithm approach. In addition, a scenario analysis is applied to investigate the impact of wind speed and electricity price forecasting on the optimized unit commitment. Our preliminary results show that the accuracy of wind speed and electricity price forecasting can greatly affect the optimal unit commitment and dispatch and the profit of generation companies.

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Column Generation Approach to the Convex Recoloring Problem on a Tree

Modeling and Optimization: Theory and Applications, 2017

The convex recoloring (CR) problem is to recolor the nodes of a colored graph at minimum number o... more The convex recoloring (CR) problem is to recolor the nodes of a colored graph at minimum number of color changes such that each color induces a connected subgraph. We adjust to the convex recoloring problem the column generation framework developed by Johnson et al. (Math Program 62:133–151, 1993). For the convex recoloring problem on a tree, the subproblem to generate columns can be solved in polynomial time by a dynamic programming algorithm. The column generation framework solves the convex recoloring problem on a tree with a large number of colors extremely fast.

Effect of Notifying Expected Waiting Time on Telephone System Performance

In a telephone system, the notification of expected waiting time brings valuable information to t... more In a telephone system, the notification of expected waiting time brings valuable information to the callers so that they can make timely decision on whether to keep waiting or call back later. In this study, we investigate how the realization of this scheme affects the performance of a VA (Veteran Affairs) telephone system. In the proposed scheme, the callers are notified before joining the queue regarding the expected waiting time for the telephone service. A formula based on the number of callers currently in the system is used for providing the approximate expected waiting time. Four scenarios are formed based on different levels of exogenous patience time before abandoning the call and presence of advanced notification scheme. The investigation is carried out using discrete event simulation analysis. The results indicate that the effect of such notification scheme is scenario dependent, in which the patience level of callers plays a significant role on determining the potential ...

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Optimization models for scheduling and rescheduling elective surgery patients under the constraint of downstream units

Healthcare is a unique industry in terms of the associated requirements and services provided to ... more Healthcare is a unique industry in terms of the associated requirements and services provided to patients. Currently, healthcare industry is facing challenges of reducing the cost and improving the quality and accessibility of service. Operating room is one of the biggest major cost and revenue centers in any healthcare facility. In this study, we develop optimization models and the corresponding solution strategies for addressing the problem of scheduling and rescheduling of the elective patients for surgical operations in the operating room. In the first stage, scheduling of the elective patients based on the availability of the resources is optimized. The resources considered in the study are the availability of the operating rooms, surgical teams, and the beds/equipment in the downstream post anesthesia care units (PACUs). Discrete distributions governing surgical durations for selected surgical specialties are developed for representing variability for duration of surgery. Based on the distributions, a stochastic mathematical programming model is developed. It is indicated that with the increase of problem sizes, the model may not be solved by using a leading commercial solver for optimization problems. As a result, a heuristic solution approach based on genetic algorithm is also developed. It is found out that the genetic algorithm provides close results as compared to the commercial solver in terms of solution quality. For large problem sizes, where the commercial solver is unable to solve the problem due to the memory restrictions, the genetic algorithm based approach is able to find a solution within a reasonable amount of computation time. In the second stage, the rescheduling of the elective patients due to the sudden arrival of the emergency patients is considered. A mathematical programming model for minimizing the costs related with expanding the current capacity and disruption caused by the inclusion of the emergency patient is developed. Also, two different solution approaches are brought forward, one with using the commercial solver, and the other based on genetic algorithm. Genetic algorithm based approach can always make efficient decision regarding whether to accept the emergency patients and how to minimize the reshuffling effort of the original elective surgery schedule.Department of Veterans Affairs; National Science Foundation (Award # 1126570

Towards sustainable additive manufacturing: The need for awareness of particle and vapor releases during polymer recycling, making filament, and fused filament fabrication 3-D printing

Resources, Conservation and Recycling, 2022

Fused filament fabrication three-dimensional (FFF 3-D) printing is thought to be environmentally ... more Fused filament fabrication three-dimensional (FFF 3-D) printing is thought to be environmentally sustainable; however, significant amounts of waste can be generated from this technology. One way to improve its sustainability is via distributed recycling of plastics in homes, schools, and libraries to create feedstock filament for printing. Risks from exposures incurred during recycling and reuse of plastics has not been incorporated into life cycle assessments. This study characterized contaminant releases from virgin (unextruded) and recycled plastics from filament production through FFF 3-D printing. Waste polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) plastics were recycled to create filament; virgin PLA, ABS, high and low density polyethylenes, high impact polystyrene, and polypropylene pellets were also extruded *

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Use of 3-Dimensional Printers in Educational Settings: The Need for Awareness of the Effects of Printer Temperature and Filament Type on Contaminant Releases

ACS Chemical Health & Safety, 2021

Material extrusion-type fused filament fabrication (FFF) 3-D printing is a valuable tool for educ... more Material extrusion-type fused filament fabrication (FFF) 3-D printing is a valuable tool for education. During FFF 3-D printing, thermal degradation of the polymer releases small particles and chemicals, many of which are hazardous to human health. In this study, particle and chemical emissions from 10 different filaments made from virgin (never printed) and recycled polymers were used to print the same object at the polymer manufacturer's recommended nozzle temperature ("normal") and at a temperature higher than recommended ("hot") to simulate the real-world scenarios of a person intentionally or unknowingly printing on a machine with a changed setting. Emissions were evaluated in a college teaching laboratory using standard sampling and analytical methods. From mobility sizer measurements, particle number-based emission rates were 81 times higher; the proportion of ultrafine particles (diameter <100 nm) were 4% higher, and median particle sizes were a factor of 2 smaller for hot-temperature prints compared with normal-temperature prints (all p-values <0.05). There was no difference in emission characteristics between recycled and virgin acrylonitrile butadiene styrene and polylactic acid polymer filaments. Reducing contaminant release from FFF 3-D printers in educational settings can be achieved using the hierarchy of controls: (1) elimination/substitution (e.g., training students on principles of prevention-through-design, limiting the use of higher emitting polymer when possible); (2) engineering controls (e.g., using local exhaust ventilation to directly remove contaminants at the printer or isolating the printer from students); (3) administrative controls such as password protecting printer settings and establishing and enforcing adherence to a standard operating procedure based on a proper risk assessment for the setup and use (e.g., limiting the use of temperatures higher than those specified for the filaments used); and (4) maintenance of printers.

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Incorporating Autodesk Moldflow as a Tool for Promoting Engaged Student Learning

2017 ASEE Annual Conference & Exposition Proceedings

In this paper, we provide a discussion on implementation of Autodesk Moldflow TM Software for enh... more In this paper, we provide a discussion on implementation of Autodesk Moldflow TM Software for enhancing and promoting teaching activities and enhancing course content offered as one of mandatory courses in Manufacturing Engineering curriculum of one of the Higher Education Institution in United States. The target audience of the course is undergraduate students at junior or senior level. In the paper, implementation of Autodesk Moldflow TM as an instructional tool for promoting a dynamic interactive classroom environment and providing seamless integration of classroom activities such as traditional classroom teaching, computer simulation of manufacturing process, and actual physical laboratory experience related with the process. In that regard, Autodesk Moldflow TM is used as one of the tools that would be used for promoting positive outcomes associated with the student learning. Autodesk Moldflow TM is used for modeling and simulating of the plastic injection molding process. During computer simulation laboratories, specific examples of Autodesk Moldflow TM is introduced for providing ideas to students on how the manufacturing process would be improved by employing the tools based on computer simulation of associated process. In that regard, corresponding examples on discovering potential manufacturing problems that might arise are introduced. Role of software for providing visual aid for understanding filling, packing, and cooling stages of the manufacturing process is emphasized. In order for promoting active learning experience, and providing association between classroom teaching, physical laboratory demonstration, and computer simulation of plastic injection molding process, required references are made. Feedback obtained from the oral communication and Student Evaluation of Instruction Report indicate that suggested approach help achieving learning outcomes and promote a classroom environment conducive to engaged student learning.

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A Statistical Approach for Process Optimisation of Digital Light Processing (DLP) 3D Printing Process

International Journal of Rapid Manufacturing, 2020

This study focuses on experimental design-based approach for process optimisation of a custom-mad... more This study focuses on experimental design-based approach for process optimisation of a custom-made digital light processing 3D printer. Output measures are developed taking precision and accuracy into consideration. Initial runs were conducted to identify the prominent factors which might play role on output measures. The results indicate that the layer thickness plays a significant role for the two of the developed output measures, photopolymerisation time for one measure, and sequence time for two measures as the interaction-effects also play a role to some. A composite figure that considers all three output measures simultaneously is also developed and a stepwise regression analysis is conducted to identify significant factors. The regression model has moderate R 2 value (68.12%), also indicating that layer thickness and photopolymerisation period play a role. The recommended levels for layer thickness is found to be 0.2 millimetres and photopolymerisation period as 12 seconds based on the composite figure.

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Expanding Role of Telephone Systems in Healthcare

Reshaping Medical Practice and Care with Health Information Systems

The telephone systems in healthcare settings serve as a viable tool for improving the quality of ... more The telephone systems in healthcare settings serve as a viable tool for improving the quality of service provided to patients, decreasing the cost, and improving the patient satisfaction. It can play a pivotal role for transformation of the healthcare delivery for embracing personalized and patient centered care. This chapter presents a systematic review of new developments of healthcare telephone system operations in various areas such as tele-health. Current research on topics such as tele-diagnosis, tele-nursing, tele-consultation is outlined. Specific issues associated with the emerging applications such as underreferral, legal issues, patient acceptance, on-call physician are discussed. Meanwhile, the architecture and underlying technologies for healthcare telephone systems are introduced, and the performance metrics for measuring the system operations are provided. In addition, challenges and opportunities related with improving the healthcare telephone systems are identified,...

Comparison of Two ARMA-GARCH Approaches for Forecasting the Mean and Volatility of Wind Speed

Springer Proceedings in Physics, 2014

In this study, we develop two ARMA-GARCH models for predicting the mean and volatility of wind sp... more In this study, we develop two ARMA-GARCH models for predicting the mean and volatility of wind speed. The first model employs the standalone ARMA-GARCH model for modeling the mean wind speed and the variance simultaneously. For the second model, in the first step, the current wind vector is decomposed into lateral and longitudinal components by using the prevailing wind direction. The mean and variance of the two components are then modeled using two separate ARMA-GARCH processes. Thereafter, the two components are combined back to form the resultant single wind vector. A large wind dataset is employed for model building and prediction so that the two approaches can be compared. It shows that the standalone ARMA-GARCH model is more accurate for predicting the wind speed, whereas the component ARMA-GARCH model performs better for predicting the wind variance.

Profitability Analysis of Residential Wind Turbines with Battery Energy Storage

Springer Proceedings in Physics, 2014

Residential wind turbines are often accompanied by an energy storage system for the off-the-grid ... more Residential wind turbines are often accompanied by an energy storage system for the off-the-grid users, instead of the on-the-grid users, to reduce the risk of black-out. In this paper, we argue that residential wind turbines with battery energy storage could actually be beneficial to the on-the-grid users as well in terms of monetary gain from differential pricing for buying electricity from the grid and the ability to sell electricity back to the grid. We develop a mixed-integer linear programming model to maximize the profit of a residential wind turbine system while meeting the daily household electricity consumption. A case study is designed to investigate the effects of differential pricing schemes and sell-back schemes on the economic output of a 2-kW wind turbine with lithium battery storage. Overall, based on the current settings in California, a residential wind turbine with battery storage carries more economical benefits than the wind turbine alone.

Health Information Exchange for Improving the Efficiency and Quality of Healthcare Delivery

Principles and Applications

The adoption of information technology in healthcare has progressed through a series of phases si... more The adoption of information technology in healthcare has progressed through a series of phases since the 1960s. Initially, health information systems were used in financial industry in the 1960s. These systems aided the organizations' billing, payroll, accounting, and reporting services. During this phase, the use of health information systems was limited to the elimination of clerical work. Primary care clinics took a major initiative during the 1970s in a similar direction and joined

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Performance analysis and improvement of a typical telephone response system of VA hospitals

International Journal of Operations & Production Management, 2015

Purpose – Telephone response system is the frontline of hospital operations. The purpose of this ... more Purpose – Telephone response system is the frontline of hospital operations. The purpose of this paper is to analyze a representative telephone response system of Veterans Affairs (VA) hospitals, address the existing inefficiency issues such as long call waiting time, and improve system resilience to changes. Design/methodology/approach – Resource sharing schemes are proposed to improve the system performance in answering calls related to appointment booking and medication renewal. Discrete event simulation is adopted to model the current system and the resource sharing schemes. Findings – The resource sharing schemes dramatically improve system performance reflected by the decrease of call waiting time and queue, as well as the extreme high utilization of agents in a key unit. Compared with the less desired alternative of hiring additional employees to mitigate the performance issues, the resource sharing schemes perform at par or even better. Sharing more resource during the peak ...

An Integrated Teaching Methodology for Manufacturing Processes

2015 ASEE Annual Conference and Exposition Proceedings

His research interests include; modeling for facility planning, genetic algorithms, education of ... more

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Large-scale assessment of missed opportunity risks in a complex hospital setting

Informatics for health & social care, Jan 17, 2014

In this research, we apply a large-scale logistic regression analysis to assess the patient misse... more In this research, we apply a large-scale logistic regression analysis to assess the patient missed opportunity risks at a complex VA (US Department of Veterans Affairs) hospital in three categories, namely, no-show alone, no-show combined with late patient cancellation and no-show combined with late patient and clinic cancellations. The analysis includes unique explanatory variables related to VA patients for predicting missed opportunity risks. Furthermore, we develop two aggregated weather indices by combining many weather measures and include them as explanatory variables. The results indicate that most of the explanatory variables considered are significant factors for predicting the missed opportunity risks. Patients with afternoon appointment, higher percentage service connected, and insurance, married patients, shorter lead time and appointments with longer appointment length are consistently related to lower risks of missed opportunity. Furthermore, the VA patient-related fa...

Simulation analysis on patient visit efficiency of a typical VA primary care clinic with complex characteristics

Simulation Modelling Practice and Theory, 2014

ABSTRACT

Genetic algorithm for instrument placement in smart grid

2013 World Congress on Nature and Biologically Inspired Computing, 2013

Communication Enhancement and Best Practices for Co-Managing Dual Care Rural Veteran Patients by VA and Non-VA Providers: A Survey Study

Journal of Community Health, 2013

Many rural Veteran patients receive healthcare services from both Veterans Affairs (VA) and non-V... more Many rural Veteran patients receive healthcare services from both Veterans Affairs (VA) and non-VA providers. Effective management of dual care Veteran patients to ensure the best clinical outcomes is a VA mission. The previous VA studies indicate that coordination between VA and non-VA providers has been lacking for dual care management of Veteran patients. In this study, we propose that VA proactively shares information with non-VA providers to enhance the communication process and identify the best practices to be carried out by both VA and non-VA providers for better coordination. Structured questionnaires are designed and distributed to VA and non-VA providers to obtain their evaluations on the proposed VA proactive information sharing approaches and the best practice items for dual care management. The non-VA provider respondents largely support the proposed proactive sharing items by VA, with the lowest average score being 3.96 out of a 5.0 scale on one item. In terms of the best practice items on co-managing dual care patients, three out of five items are overall rated higher than 4.0 from both sides. A pair-wise comparison between VA and non-VA perspectives further shows that the difference in average ratings of a proposed item could be significant. For such best practice items, the implementations from both sides may not be most effective.

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