Grad Students/Postdocs
Joshua Enszer, Graduate Student
Personal Website
Research Interests
My research involves finding verified, or mathematically guaranteed, numerical solutions of systems of nonlinear ordinary differential equations (ODEs), seeking both dynamic (transient trajectories) and static (equilibrium) solutions. ODE systems of two or more variables may permit limit cycle trajectories, and systems of three or more variables may include solutions that are deterministically chaotic. In my research, the ODEs of interest are often those of dynamics in biochemical kinetics, physiology, and population ecology or epidemiology.
Generally, numerical solutions of systems of equations are approximations to the true solutions, so I seek to improve tools that make use of interval methods and Taylor models to perform computations that mathematically guarantee the existence of the true solution between two (machine number) bounds. The majority of my research involves the Verified Solver for Parametric ODEs (VSPODE) developed by Lin and Stadtherr to provide transient solutions to systems of ODEs with uncertain initial conditions and/or parameters.
I have used VSPODE to investigate the well-studied Rosenzweig-MacArthur model, using artificially-created scenarios with uncertain initial conditions or uncertain parameters that straddled separatrix or bifurcation points in this model. I have also used the program to seek solutions to two-point boundary value problems (TPBVPs), utilizing an interval shooting method. I aim to implement the ideas of probability distribution variables (PDVs) or probability-boxes (p-boxes) in algorithms similar to those of VSPODE to compute probabilistic bounds on uncertain variables, effectively creating a stochastic-deterministic hybrid that is less computationally expensive than Monte Carlo processes. I have completed work in this area for several areas of mathematical research, including physiology, epidemiology, and chemical engineering models.
My other major interest is in education, which I am pursuing more informally through courses and workshops at Notre Dame's Kaneb Center for Teaching and Learning and through opportunities to serve as a teaching assistant, co-instructor, and instructor for chemical engineering courses. As of the fall of 2007, I work for the Kaneb Center as a teaching associate. I am also a participant in the College of Engineering's first Teaching Apprenticeship program, working with faculty across the College in developing the first-year engineering sequence. I also actively work to assist in the department's electronic portfolio initiative for undergraduate students.
My career goal is to use my PhD to obtain a teaching position in chemical engineering, general engineering, or applied mathematics. My CV can be found here.
Advisor
Publications
Y. Lin, J. A. Enszer, M. A. Stadtherr. Enclosing All Solutions of Two-Point Boundary Value Problems for ODEs. Comput. Chem. Eng., 32:1614-1725, 2008.
J. A. Enszer, Y. Lin, S. Ferson, G. F. Corliss, and M. A. Stadtherr. Propagating Uncertainties in Modeling Nonlinear Dynamic Systems. Proceedings of the 3rd International Workshop on Reliable Engineering Computing, Georgia Institute of Technology, Savannah, GA, :89-105, 2008.
J. A. Enszer and M. A. Stadtherr. Verified Solution Method for Population Epidemiology Models with Uncertainty. Int. J. Appl. Math. Comput. Sci., 19:501-512, 2009.
J. A. Enszer and M. A. Stadtherr. Rigorous Propagation of Imprecise Probabilities in Process Models. Proceedings of the 7th International Conference on Foundations of Computer-Aided Process Design, Breckenridge, CO, :77-92, 2009.
Presentations and Posters
Rigorous Propagation of Imprecise Probabilities in Process Models
Presented on June 7, 2009 at Breckenridge, CO
- Event: 7th International Conference on Foundations of Computer-Aided Process Design
- Authors: Joshua A. Enszer, Mark A. Stadtherr
Probability Bounds Analysis in Modeling Nonlinear Ecosystem Dynamics
Presented on November 18, 2008 at Philadelphia, PA
- Event: AIChE 100th Annual Meeting
- Authors: Joshua A. Enszer, Mark A. Stadtherr
Verified Solution and Propagation of Uncertainty in Physiological Models
Presented on September 30, 2008 at University of Texas at El Paso
- Event: 13th GAMM - IMACS International Symposium on Scientific Computing, Computer Arithmetic and Verified Numerical Computations
- Authors: Joshua A. Enszer, Mark A. Stadtherr
Verified Solution of Nonlinear Dynamic Models in Epidemiology
Presented on June 30, 2008 at University College, London
- Event: 15th European Conference in Mathematics for Industry
- Authors: Joshua A. Enszer, Mark A. Stadtherr
Propagating Uncertainties in Modeling Nonlinear Dynamic Systems
Presented on February 20, 2008 at Georgia Institute of Technology, Savannah, GA
- Event: 3rd International Workshop on Reliable Engineering Computing
- Authors: Joshua A. Enszer, Youdong Lin, Scott Ferson, George F. Corliss, and Mark A. Stadtherr
Schools
University of Notre Dame, 2005-Present
Title: PhD
Degree: Chemical and Biomolecular Engineering
University of Notre Dame, 2008
Title: MS
Degree: Chemical and Biomolecular Engineering
Michigan Technological University, 2001-2005
Title: BS
Degree: Chemical Engineering, double major in Mathematics
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