# Nonlinear Meeting 2021

Zoom, March 22-23, 2021

The NLM2021 is the 6th of a series of annual workshops focusing on nonlinear analysis and differential problems. This edition's common thread will cover theoretical topics on reaction-diffusion equations and dynamical systems with possible applications to biology or physics.

### Invited speakers

 Henri BerestyckiEHESS-CAMS-CNRS Paris Christian KuehnTechnical University of Munich Elaine CrooksSwansea University Peter PoláčikUniversity of Minnesota Frank HilkerUniversity of Osnabrück Pedro J. TorresUniversity of Granada

### Program

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#### Monday, March 22

15:30 16:30 Henri BerestyckiTBA Elaine CrooksTBA TBA Break Christian Kuehn"Geometric Singular Perturbation Theory for Fast-Slow PDEs" Systems with multiple time scales appear in a wide variety of applications. Yet, their mathematical analysis is challenging already in the context of ODEs, where about four decades were needed to develop a more comprehensive theory based upon invariant manifolds, desingularization, variational equations, and many other techniques. Yet, for PDEs progress has been extremely slow due to many obstacles in generalizing several ODE methods. In my talk, I shall report on two recent advances for fast-slow PDEs, namely the extension of slow manifold theory for unbounded operators driving the slow variables, and the design of a blow-up method for PDEs, where normal hyperbolicity is lost [1-2]. This is joint work with Maximilian Engel and Felix Hummel. [1] "Blow-up analysis of fast-slow PDEs with loss of hyperbolicity", M. Engel and C. Kuehn, https://arxiv.org/abs/2007.09973 [2] "Slow manifolds for infinite-dimensional evolution equations", F. Hummel and C. Kuehn, https://arxiv.org/abs/2008.10700

#### Tuesday, March 23

15:30 16:30 Pedro J. TorresPeriodic solutions of the Lorentz force equation The Lorentz force equation governs the motion of a charged particle under the effect of an electromagnetic field. In spite of that it plays a fundamental role in Classical Electromagnetism together with Maxwell equations, the application of the most known methods in Nonlinear Analysis and Dynamical Systems is still under development. The purpose of this talk is to present some recent results on the existence of periodic solutions when the electromagnetic field is periodic in time, and to identify several open problems. Frank Hilker"Mathematical models of a social-ecological system: coupling lake pollution dynamics and human behavior" From global warming over land-use change to pollution, the world is facing many environmental problems. While the causes are mostly well-known from a natural sciences point of view, the challenge is the implementation of possible solutions. Societal demands, human behavior, and economic aspects not only impact the environmental state, but are reversely affected by the environment. Mathematical models can be helpful in better understanding mutual feedbacks in coupled human-environment systems. In this talk, I will introduce a system of two nonlinear differential equations, one describing lake water pollution and the other one describing human behavior of discharging pollutants. The latter uses approaches from evolutionary game theory. Stability analysis reveals up to four alternative attractors as well as limit cycle oscillations. Numerical bifurcation analysis suggests the existence of Bogdanov-Takens and saddle-node homoclinic bifurcations. In addition, some very preliminary results will be shown to indicate potential effects of discontinuous policy instruments. (Joint work with Anthony Sun.) Break Peter Poláčik"Quasiperiodic partially localized solutions of nonlinear elliptic equations on the entire space" In this joint project with Dario Valdebenito, we study positive partially localized solutions of elliptic equations on the entire space. "Partially localized" means that the solutions decay to zero in all but one variable; we examine their behavior in the remaining variable. Our goal is to prove the existence of solutions which are quasiperiodic in the nondecay variable. In the lecture, I will discuss our techniques and report on recent progress.

### Registration

Participation in the meeting is free upon registration.
The registration for the NLM2021 is open!

For more information, please write to gidoni[at]utia[dot]cas[dot]cz.

### Information

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