Sarah Ryan

  • Professor

Main Office

3029 Black Engr
Ames, IA 50011-2164
Phone: 515-294-4347
Fax: 515-294-3524

Interest Areas

Dr. Ryan's research examines the planning and operation of manufacturing and service systems under uncertainty. Currently, she is focusing on electric power systems and closed loop supply chains with remanufacturing. Issues under study by her research group include replacement policies of equipment under condition monitoring, expansion of fuel transport and electricity generation, and joint supply of manufactured and re-manufactured products. Her work has been supported by the National Science Foundation, including a CAREER award, and an AT&T Industrial Ecology Faculty Fellowship.

Selected Publications

A. Ghosh, S. M. Ryan, L. Wang, A. Weerasinghe, "Heavy Traffic Analysis of a Simple Closed Loop Supply Chain" Stochastic Models, in press (2010)

Ryan, S.M., A. Downward, A. Philpott, G. Zakeri, "Welfare Effects of Expansions in Equilibrium Models of an Electricity Market with Fuel Network" IEEE Transactions on Power Systems, 25 (3), 1337 – 1349 (2010) (

Wu, X. and S. M. Ryan, "Value of Condition Monitoring for Optimal Replacement in the Proportional Hazards Model with Continuous Degradation" IIE Transactions, 42 (8), 553-563 (2010) (

Wang, Y. and S. M. Ryan, "Effects of Uncertain Fuel Costs on Fossil Fuel and Electric Energy Flows in the US" Energy Systems, 1, 209-243 (2010)

Marathe, R. R. and S. M. Ryan, "Capacity Expansion under a Service Level Constraint for Uncertain Demand with Lead Times" Naval Research Logistics, 56(3), 250-263 (2009).

Quelhas, A., E. Gil, J. D. McCalley and S. M. Ryan, "A Multiperiod Generalized Network Flow Model of the U.S. Integrated Energy System, Part I – Model Description" IEEE Transactions on Power Systems, 22(2), 829-836 (2007). (

Serrato, M., S. M. Ryan and J. Gaytan , "A Markov Decision Model to Evaluate Outsourcing in Reverse Logistics" International Journal of Production Research Special Issue on Sustainable Production, 45(18&19), 4289-4315 (2007).

Vorasayan, J. and S. M. Ryan, "Optimal Price and Quantity of Refurbished Products" Production and Operations Management, 15(3), 369-383 (2006).

Marathe, R. R. and S. M. Ryan, "On the Validity of the Geometric Brownian Motion Assumption" The Engineering Economist, 50(2), 159-192 (2005).

Ryan, S. M., and J. Vorasayan, "Allocating Work in Process in a Multiple-Product CONWIP System with Lost Sales" International Journal of Production Research, 43(2), 223-246 (2005).

Ryan, S. M., J. Jackman, F. Peters, S. Olafsson, M. Huba, "The Engineering Learning Portal for Problem Solving" The Engineering Economist, 49(1), 1-19 (2004).

Ryan, S. M., "Capacity Expansion for Random Exponential Demand Growth with Lead Times" Management Science, 50(6), 740-748 (2004).