Mimi Dai, Ph.D. - US grants

Magnetic reconnection is a fundamental process in highly conducting plasmas, which allows for rapid changes in the configuration of the magnetic flux lines, with the conversion of magnetic to kinetic energy. Solar flares, violent events with significant impact to telecommunications and the electric grid, may involve magnetic reconnection in a large scale. Magnetic reconnection is inherently a multi-scale process and causes difficulties in laboratory experimental study, satellite observations, and computational simulations. During magnetic reconnection, the magnetic force can create thin localized region wherein the elevated voltage difference generates intense electric currents and dissipation - the Hall effect. The Hall Magnetohydrodynamics (Hall MHD) model has recently received increasing attention because of its improvements in predicting the fast-changing nature of magnetic reconnection compared to other models. Nevertheless, the mathematical theory of this model is far from being complete. This project will address fundamental mathematical questions for the Hall MHD model and provide theoretical insights for experiments and numerical simulations. The project will involve a graduate student in the research.

The Hall MHD model is mathematically challenging due to the usual convective nonlinearities and the additional source term given by the Hall effect. The main objectives are: 1) Explore the largest possible space of well-posedness corresponding to the major scalings in the system. 2) Search the optimal Sobolev spaces in which the model is well-posed. 3) Examine ill-posedness of solutions in some physically relevant spaces. 4) Seek minimal conditions for weak solutions to satisfy energy identity. 5) Study the asymptotic behavior of solutions and stability of the steady state. The project will combine known tools from harmonic analysis and partial differential equations, and develop new methods to study these questions.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

This award provides funding for US participation in four installments of the conference series "Midwest Partial Differential Equations Seminar" that will be held at University of Wisconsin, Madison in Spring 2018, University of Indiana, Bloomington in Fall 2018, Purdue University, West Lafayette in Spring 2019, and another midwestern university, to be determined, in Fall 2019.

The conference focuses on recent developments in Analysis, especially in the field of partial differential equations. A number of distinguished mathematicians have agreed to attend and speak at this conference series. This award gives early career researchers, members of underrepresented groups, researchers not funded by NSF and the like an opportunity to attend and participate in this conference. The organizing committee will strive to make this funding opportunity known to target groups through a number of different activities. More information will be made available at: http://homepages.math.uic.edu/~jlewis/midwpde/

Magnetic reconnection is a fundamental process in highly conducting plasmas that involves rapid changes in the configuration of the magnetic flux lines, with the conversion of magnetic to kinetic energy. Solar flares, violent events with significant impact to telecommunications and the electric grid, may involve magnetic reconnection in a large scale. Magnetic reconnection is inherently a multi-scale process and causes difficulties in laboratory experimental study, satellite observations, and computational simulations. During magnetic reconnection, the magnetic force can create thin localized region wherein the elevated voltage difference generates intense electric currents and dissipation - the Hall effect. The Hall magnetohydrodynamics (Hall MHD) model has recently received increasing attention because of its improvements in predicting the fast-changing nature of magnetic reconnection compared to other models. Nevertheless, the mathematical theory of this model is far from being complete. This project will further advance the fundamental theoretical understanding of the Hall MHD model by addressing the issues such as existence and uniqueness of solutions, anomalous dissipation, and long-time behavior of the solutions. The project will provide opportunities for students to participate in the research.

The Hall MHD model couples the Navier-Stokes equations and Maxwell's equations. The Hall MHD system is mathematically challenging due to the usual convective nonlinearities and the additional source term given by the Hall effect. The project includes investigations on the conservation or anomalous dissipation of energy and magnetic helicity for weak solutions, uniqueness, or lack thereof for weak solutions, weak-strong type of uniqueness, and asymptotic uniqueness in energy space within the framework of determining wavenumber.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.