@article {1449, title = {Modeling the pharmacodynamics of nandrolone doping drug and implications for anti-doping testing}, journal = {System Dynamics Review}, volume = {36}, year = {2020}, pages = {467-496}, abstract = {

Abstract We model the pathways of nandrolone in the body, an anabolic steroid widely used as a performance enhancing drug (PED). The model generates the dynamics of nandrolone and its metabolites. PED tests check for the presence of a primary metabolite of nandrolone, 19-NA in urine. To cheat in these tests, PED users typically use inhibitors that reduce the urinary concentration of 19-NA. One such inhibitor is finasteride. Finasteride{\textquoteright}s main effect in the body is the inhibition of reductase enzymes that turn nandrolone into its metabolite 19-NA. To capture this effect, we include structures for finasteride and reductase enzymes in the model. The model is tested by fundamental structure validity tests. We also show that the model behavior is consistent with experimental data in the literature. We finally investigate the potential ways by which the drug users may cheat in PED tests and make suggestions for improved testing as counter-measures. {\textcopyright} 2021 System Dynamics Society

}, doi = {https://doi.org/10.1002/sdr.1672}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/sdr.1672}, author = {Sahin, {\"O}zge and Feyyaz {\c S}ent{\"u}rk and Yaman Barlas and Yasarcan, Hakan} } @inbook {1451, title = {Credibility, Validity and Testing of Dynamic Simulation Models}, booktitle = {Simulation and Modeling Methodologies, Technologies and Applications}, year = {2018}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, address = {Cham}, abstract = {

Also called {\textquoteleft}model validity{\textquoteright} testing, model credibility evaluation has always been a controversial issue in any modeling methodology. We briefly discuss why this important notion is so controversial. To this end, we classify major types of models, particularly as they impact the notion of model credibility: i- Purely statistical forecasting (black box) models, and ii- Causal-descriptive policy (transparent) models. We then focus on what makes causal-descriptive model credibility and evaluation unique and quite difficult, compared to short-term forecasting models. One important result is that causal-descriptive model credibility consists of two different aspects: structural and behavioral. In most simulation modeling (particularly system dynamics policy simulation), establishing structure credibility must strictly precede behavior credibility; the latter has no value without the former. We thus discuss Structural tests and output behavior tests for dynamic simulation models separately. Structure tests can further be classified into direct and indirect structure tests. We place special emphasis on indirect structure tests. We also provide a quick overview of recent model testing software developed in SESDYN Laboratory at Bo{\u g}azi{\c c}i University. Finally we discuss model credibility in broader context and some implementation issues.

}, isbn = {978-3-319-69832-8}, author = {Yaman Barlas} } @article {1450, title = {Queuing systems in a feedback environment: Continuous versus discrete-event simulation}, journal = {Journal of Simulation}, volume = {12}, year = {2018}, pages = {144-161}, abstract = {

AbstractThe discrete stochastic nature of typical queuing problems calls for discrete-event simulation, rather than continuous simulation that would ignore the discrete details that may be important in queuing dynamics. However, continuous simulation can perhaps be suitable for certain large queuing systems that involve feedback interactions and time delays. This study examines this question by a series of simulation experiments with queuing systems. We start with an M/M/2 system with state-dependent arrivals. Since continuous simulation represents the system states by continuous variables, when these variables (number of entities) revolve around small integer values, discrete and continuous simulation approaches exhibit significant differences in their output dynamics. However, when the system scale is increased (many servers, many entities), errors caused by continuity assumption drop significantly and the two simulation approaches yield much closer outputs. Finally, when a delay is introduced before the state of the system influences the arrival rates, the system behaviour becomes oscillatory, involving even sustained oscillations when the delay is discrete. We show that in such settings, continuous simulation can be superior to discrete simulation, since the system exhibits far-from-equilibrium dynamics driven by the endogenous system structure, rather than by discrete stochastic events. Our results have various real-life modelling implications.

}, doi = {10.1080/17477778.2018.1465153}, url = {https://doi.org/10.1080/17477778.2018.1465153}, author = {Yaman Barlas and Onur {\"O}zg{\"u}n} } @proceedings {1190, title = {Modeling the Long Term Dynamics of Obesity as a Societal Epidemic}, journal = {34th International Conference of the System Dynamics Society}, year = {2016}, address = {Delft, the Netherlands}, author = {Akta{\c s}, Gizem and Nefel Tellio{\u g}lu and Yaman Barlas and Hakan Ya{\c s}arcan} } @article {1168, title = {Sensitivity analysis for models with multiple behavior modes: a method based on behavior pattern measures}, journal = {System Dynamics Review}, volume = {32}, year = {2016}, pages = {332{\textendash}362}, author = {Hekimo{\u g}lu, Mustafa and Yaman Barlas} } @article {._zba__2014, title = {Modeling and Simulation of the Endogenous Dynamics of Housing Market Cycles}, journal = {Journal of Artificial Societies and Social Simulation}, volume = {17}, number = {1}, year = {2014}, pages = {19}, abstract = {

The purpose of this study is to model and analyze by simulation the dynamics of endogenously created oscillations in real estate (housing) prices. A system dynamics simulation model is built to understand some of the structural sources of cycles in the key housing market variables, from the perspective of construction companies. The model focuses on the economic balance dynamics between supply and demand. Because of the unavoidable delays in the perception of the real estate market conditions and construction of new buildings, prices and related market variables exhibit strong oscillations. Two policies are tested to reduce the oscillations: decreasing the construction time, and taking into account the houses under construction in starting new projects. Both policies yield significantly reduced oscillations, more stable behaviors.

}, keywords = {Housing Cycles, Price Oscillations, Real Estate Modeling, Socio-Economic Simulation, System Dynamics}, issn = {1460-7425}, url = {http://jasss.soc.surrey.ac.uk/17/1/19.html}, author = {Birnur {\"O}zba{\c s} and Onur {\"O}zg{\"u}n and Yaman Barlas} } @proceedings {ozgun, title = {Effects of Delay, Nonlinearity and Feedback on the Overall Complexity of a Stock Management Game}, journal = {30th International Conference of the System Dynamics Society}, year = {2012}, author = {Onur {\"O}zg{\"u}n and Yaman Barlas} } @proceedings {ozgun, title = {Systemic Complexity of a Growth Management Game: Comparative Analysis of Decision Heuristics and Experimental Results}, journal = {30th International Conference of the System Dynamics Society}, year = {2012}, author = {Onur {\"O}zg{\"u}n and Yaman Barlas} } @article {Yucel2011, title = {Automated parameter specification in dynamic feedback models based on behavior pattern features}, journal = {System Dynamics Review}, volume = {27}, number = {2}, year = {2011}, pages = {195{\textendash}215}, publisher = {Wiley Online Library}, keywords = {Calibration}, doi = {10.1002/sdr}, url = {http://onlinelibrary.wiley.com/doi/10.1002/sdr.457/full}, author = {G{\"o}nen{\c c} Y{\"u}cel and Yaman Barlas} } @article {barlas2011demand, title = {Demand forecasting and sharing strategies to reduce fluctuations and the bullwhip effect in supply chains}, journal = {Journal of the Operational Research Society}, volume = {62}, number = {3}, year = {2011}, pages = {458{\textendash}473}, publisher = {Nature Publishing Group}, author = {Yaman Barlas and Baris Gunduz} } @proceedings {nisa3, title = {Modeling the Dynamics of Academic Publications and Citations}, journal = {29th International Conference of the System Dynamics Society}, year = {2011}, author = {Nisa {\"O}nsel and Yaman Barlas} } @proceedings {seker, title = {Modeling the Dynamics of Thyroid Hormones and Related Disorders}, journal = {29th International Conference of the System Dynamics Society}, year = {2011}, author = {Oylum {\c S}eker and Yaman Barlas and Faruk Alag{\"o}l} } @article {Yucel2010, title = {Dynamics of the North{\textendash}South welfare gap and global sustainability}, journal = {Technological Forecasting and Social Change}, volume = {77}, number = {4}, year = {2010}, pages = {594{\textendash}614}, publisher = {Elsevier Inc.}, keywords = {north, south welfare gap}, issn = {00401625}, doi = {10.1016/j.techfore.2009.11.004}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0040162509001887}, author = {G{\"o}nen{\c c} Y{\"u}cel and Yaman Barlas} } @article {FBE-IE-02-2008-02, title = {Measurement, Analysis and Evaluation of Academic Publications and Citations}, number = {FBE-IE-02/2008-02}, year = {2008}, institution = {Bo{\u g}azi{\c c}i University}, author = {Yaman Barlas and B. K{\"u}{\c c}{\"u}k and Nisa {\"O}nsel and A. S. Kocaman} }