Dr. Ömer Schmiel (né Özümerzifon)
Schloss Schneckenhof Ost, SO 229
68161 Mannheim
Dissertation Project
Revisiting the Queue: Empirical, Analytical, and Numercal Insights on Retrials
Date of Defense
13.02.2026
Queueing systems are used in various service systems, such as call centres, health care, emergency services, and repair facilities. In many of these service systems, customers leave the queue before being served (e.g. abandonment or balking) due to a lack of patience. However, with emerging concepts such as virtual queueing and callback options, impatient users may join the system at a later time point. My research deals with the analysis and optimization of such retrial queueing systems with time-dependent and stochastic demand and capacities.
- Özümerzifon, Ö., B. Legros, and R. Stolletz (2024): Should we account for retrials in time-dependent queues?. Working Paper.
- Sun, Y., AI-Khazrage, L., and Ö. Özümerzifon (2021): Generating High Quality Samples of Process Cases in Internal Audit. In: Polyvyanyy A., Wynn M.T., Van Looy A., Reichert M. (eds) Business Process Management Forum. BPM 2021. Lecture Notes in Business Information Processing, Springer, Cham, vol 427, 63–279.
Özümerzifon, Ö., B. Legros, and R. Stolletz (2025): When customers call back: The impact of retrial distribution, 34th QBWL Workshop, Pfronten-Rehbichl, Germany, March 2025
Özümerzifon, Ö., B. Legros, and R. Stolletz (2024): Revisiting the Queue: Approximation of Call Centers with Retrials, 11th Workshop on Queueing Theory, Obergurgl, Austria, December 2024.
Özümerzifon, Ö., B. Legros. R. Stolletz (2024): Impact of retrial distribution in stationary and time-dependent queues, SMMSO 2024, Naples, Italy, June 2024.
Özümerzifon, Ö., B. Legros, and R. Stolletz (2024): Time-dependent queues with retrials, 15th Workshop on Supply Chain Management & Production, Obergurgl, Austria, March 2024.
Özümerzifon, Ö., B. Legros, and R. Stolletz (2023): Impact of retrial distribution in time-dependent queues, 10th Workshop on Queueing Theory, Obergurgl, Austria, December 2023.
Özümerzifon, Ö., B. Legros, and R. Stolletz (2023): Analysis of time-dependent queues with retrials: Impact of retrial distribution, INFORMS APS 2023, Nancy, France, June 2023.
Özümerzifon, Ö., B. Legros,, and R. Stolletz (2023): Time-dependent queues with retrials, 14th Workshop on Supply Chain Management & Production, Obergurgl, Austria, March 2023
Özümerzifon, Ö., B. Legros, and R. Stolletz (2022): Performance Analysis of Retrial Queues, 9th Workshop on Queueing Theory, Obergurgl, Austria, December 2022.
Özümerzifon, Ö. and R. Stolletz (2022): Performance Analysis of Time-Dependent Retrial Queues, 31. Workshop für quantitative Betriebswirtschaftslehre, (online). March 2022.
Education
05/
2021 – present
Doctoral Studies in Business Administration, Chair of Production Management (Prof. Stolletz), University of Mannheim05/
2017 – 12/ 2020
Industrial Engineering and Management (M.Sc., with distinction), Karlsruhe Institute of Technology (KIT)
10/2013 – 05/ 2017
Industrial Engineering and Management (B.Sc.), Karlsruhe Institute of Technology (KIT)
09/2009 – 05/ 2013
Takev German-Turkish High School, Izmir, TurkeyProfessional experience
05/
2021 – present
Research Assistant, Chair of Production Management (Prof. Stolletz), University of Mannheim
10/2020 – 04/ 2021
Data Scientist & Risk Consultant, KPMG AG Wirtschaftsprüfungsgesellschaft
01/2019 – 09/ 2020
Junior Data Scientist & Risk Consultant, KPMG AG Wirtschaftsprüfungsgesellschaft
12/2018 – 03/ 3019
Student Assistant, Research Group for Efficient Algorithms, Institute of Applied Informatics and Formal Description Methods
06/2018 – 11/ 2018
Data Science Intern, KPMG AG Wirtschaftsprüfungsgesellschaft
09/2017 – 03/ 2018
Student Assistant, Chair of Stochastic Optimization, Institute of Operations Research
10/2017 – 02/ 2018, 10/ 2016 – 02/ 2017
Student Assistant, Research Group for Business Information Systems, Institute of Applied Informatics and Formal Description Methods
09/2016 – 10/ 2016
Logistics Intern, Mercedes Benz Türk A.Ş.