VI. Evolution of Interfaces for the Reaction-Diffusion Equations – Part 2

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# ISP Lecture 3 Discussion

# NPDE Lecture 5 Discussion

# ISP Lecture 2 Discussion

# ISP Lecture 1 Discussion

# Dynamical Systems and Chaos Theory

In a joint work with my undergraduate research students Miss Almas Abdulla (MIT, Class of 2014) and Rashad Abdulla (UPenn, Class of 2017) we revealed a new law of the distribution of periodic orbits in chaotic regime for the one parameter family of discrete dynamical systems. We presented a new constructive proof of the result on the structure of minimal $2(2k+1)$-orbits of the continuous endomorphisms $f:I \to I$, where $I$ is a nondegenerate interval on the real line. It is proved that there are four types of digraphs with accuracy up to inverse graphs. It is demonstrated that the first appearance, as the parameter increased, of the $2(2k+1)$-periodic window within the chaotic regime in the bifurcation diagram of the one-parameter family of logistic type unimodal continuous endomorphisms is always a minimal $2(2k+1)$-orbit with Type I digraph.

In summer session of 2014 students will pursue research on the fine classification of the periodic orbits of the continuous endomorphisms and analysis of the structure of the periodic windows within the chaotic regime of the bifurcation diagram for the unimodal continuous endomorphisms. This research requires creative combination of theoretical and numerical analysis.

#### References

- A. U. Abdulla, R. U. Abdulla, U. G. Abdulla, On the Minimal 2(2k+1)-orbits of the Continuous Endomorphisms on the Real Line with Application in Chaos Theory, Journal of Difference Equations and Applications, Volume 19, 9(2013), 1395-1416.
- L. S. Block, W. A. Coppel, Dynamics in One Dimension, Springer-Verlag, Berlin, 1992.

# NPDE Lecture 1 Discussion

I. Nonlinear Diffusion Equation (Introduction)

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The importance of the nonlinear PDEs is associated with the fact that they reflect more precise nonlinear laws of the nature, while linear PDEs were derived from the linearized versions of the nonlinear laws. Despite the great advances in the theory of nonlinear PDEs it is far from being complete. It is remarkable that almost every major nonlinear PDE has its own personality and requires unique approach. However, looking to current state of art in the theory of nonlinear PDEs, one can observe a similarity with the classical linear theory in the following sense: there are some major individual nonlinear PDEs, and analysis and understanding of those PDEs is a key towards the general theory of a broad class of nonlinear PDEs. I am going to concentrate on one of those key nonlinear PDEs called the nonlinear diffusion equation, which is a generalization of the classical heat/diffusion equation.

Continue reading NPDE Lecture 1 Discussion

# Nonlinear Partial Differential Equations

Partial differential equations (PDEs) are central to mathematics, whether pure or applied. They arise in mathematical models of real world problems, where dependent variables vary continuously as functions of several independent variables, usually space and time. PDEs arising in a majority of real world applications are nonlinear. Despite its complexity, in the theory of nonlinear PDEs one can

observe key equations or systems which are essential for the development of the theory for a particular class of equations. One of those key equations is the nonlinear reaction-diffusion-convection equation:

\[u_t=(u^m)_{xx}+bu^{\beta}+c(u^{\gamma})_x,\]

where \[u=u(x,t),x\in \mathbb{R}, t>0, b,c \in \mathbb{R}, m>0, \beta>0, \gamma>0\]

It arises, for instance, in the theory of gas flow through a porous medium, heat radiation in plasmas, spatial spread of biological populations, diffusion of particles in plasma etc.

In summer session of 2014 students will pursue research on the open problem of evolution of interfaces

of solutions to the reaction-diffusion-convection equations.

Full solution of this problem for the reaction-diffusion equation is given in the following two papers by using significantly the theory of reaction-diffusion equations in general non-smooth domains developed in my JDE paper.

- U. G. Abdulla and J. R. King, Interface development and local solutions to reaction-diffusion equations, SIAM J. Math. Anal., 32, 2, 2000, 235-260.
- U. G. Abdulla, Evolution of interfaces and explicit asymptotics at infinity for the fast diffusion equation with absorption, Nonlinear Analysis, 50, 4, 2002, 541-560.
- U. G. Abdulla, Reaction-diffusion in irregular domains, J. Differential Equations, 164, 2000, 321-354.

Introductory lectures on this topic will be posted soon.

# Campus Pictures

# Welcome to Ugur Abdulla’s Mathematical Blog

Welcome to my Mathematical Blog . The purpose is to share updates in my research, discussion of mathematical ideas in the fields of my research expertise, discussion of open problems, updates and discussions on my new papers and posted lectures, and in general discussion of any math related topics. It is open to everyone in the mathematical community worldwide.

In particular, this is the weblog for the Research Experience for Undergraduates (REU) Site on Partial Differential Equations and Dynamical Systems, which I am running for 2014-2016 with the grant from the US National Science Foundation. For application, grant, and program information, please see the REU Main Page.

Each summer from 2014 to 2016, 9 undergraduate students will participate in an 8 week summer REU Site on **Partial Differential Equations** and Dynamical Systems held at the Florida Institute of Technology Mathematical Sciences Department.

The REU Site is designed to involve undergraduate students in innovative research in **nonlinear partial differential equations**, optimal control and inverse problems for systems with distributed parameters, and dynamical systems and chaos theory, while utilizing modern tools of mathematical and numerical analysis. Students will have a great opportunity to pursue hands-on, original research on the frontier of modern mathematics, which will include the evolution of interfaces for **nonlinear reaction-diffusion-convection equations**, inverse free boundary problems and optimal control of phase transition processes, and the fine classification of minimal periodic orbits of discrete dynamical systems with application in chaos theory.

For more information on the REU faculty and program, see Dr. Abdulla’s REU page. For an extended description and other related links, see the FIT Research Portal. I will post here periodically both before, during, and after the REU to communicate with other students and the community at large about our results and other interesting information.