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# ACMD Seminar: Modeling Diffusion and Capture

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Alan Lindsay*University of Notre Dame*

Tuesday, June 13, 2017, 11:00 - 12:00Building 101, Lecture Room BGaithersburg

Tuesday, June 13, 2017, 09:00 - 10:00Room 1-4058Boulder

Presentation Slides

**Host:** Michael Mascagni

**Abstract:** Diffusion is a fundamental transport mechanism whereby spatial paths are determined from probabilistic distributions. In examples such as the pollination of a flower or immune response to infection, the arrival of a single particle can initiate a cascade of events. The movement of these particles is driven by random motions, yet these systems largely function in an ordered and predictable way. This process, and others like it, can be modeled as a problem for the arrival time of a diffusing molecule to hit a small absorbing target.In this talk I will discuss the mathematical models of this phenomenon and introduce the governing equations which are PDEs of parabolic and elliptic type with a mix of Dirichlet (Absorbing) and Neumann (Reflecting) boundary conditions. A particular feature of cellular problems is that the absorbing set has a large number of very small sites. I will present a new homogenized theory which replaces the heterogeneous configuration of boundary conditions with a uniform Robin type condition. To verify this limit, I will describe a novel spectral boundary element method for the exterior mixed Neumann-Dirichlet boundary value problem. The numerical formulation reduces the problem to a linear integral equation supported on each of the absorbing sites. Real biological systems feature thousands of absorbing sites and our numerical method can rapidly resolve this realistic limit to high accuracy.

**Bio:** Alan Lindsay is an Assistant Professor at the University of Notre Dame in South Bend, Indiana. His research interests are in applied and computational math, in particular using mathematical modeling, perturbation analysis, dynamical systems theory and numerical computation to understand and predict complex spatio-temporal phenomena in engineering, physical, and biological problems. His recent work focuses on diffusive signalling and first passage time problems in immune recognition.

Alan completed his B.Sc at the University of Edinburgh in 2005 and Ph.D at the University of British Columbia in 2010. Following that, he was the Hanno Rund postdoctoral fellow at the University of Arizona from 2010-2012. From 2012-2013 he was a lecturer of Applied Math at Heriot-Watt university and since 2013 has been on the faculty at the University of Notre Dame.

Mathematics and statistics

## Contacts

                -  Prof. Michael Mascagni  michael.mascagni@nist.gov      (301) 975-2051   

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