Wu, Qiliang2013-08-022013-08-022013-05https://hdl.handle.net/11299/154985University of Minnesota Ph.D. dissertation. May 2013. Major: Mathematics. Advisor: Arnd Scheel. 1 computer file (PDF); vi, 112 pages, appendices A-B.This paper is concerned with formation mechanisms of patterns and contains two main parts. The first one is about defects of patterns. Specifically, we study grain boundaries in the Swift-Hohenberg equation. Grain boundaries arise as stationary interfaces between roll solutions of different orientations. Our analysis shows that such stationary interfaces exist near onset of instability for arbitrary angle between the roll solutions. This extends prior work in [1] where the analysis was restricted to large angles, that is, weak bending near the grain boundary. The main new difficulty stems from possible interactions of the primary modes with other resonant modes. We generalize the normal form analysis in [1] and develop a singular perturbation approach to treat resonances. In the second part, we investigate dynamics near Turing patterns in reaction-diffusion systems posed on the real line. Linear analysis predicts diffusive decay of small perturbations. We construct a "normal form" coordinate system near such Turing patterns which exhibits an approximate discrete conservation law. The key ingredients to the normal form is a conjugation of the reaction-diffusion system on the real line to a lattice dynamical system. At each lattice site, we decompose perturbations into neutral phase shifts and normal decaying components. As an application of our normal form construction, we prove nonlinear stability of Turing patterns with respect to perturbations that are small in L1 ∩ L∞, with sharp rates, recovering and slightly improving on results in [2, 3].en-USDynamical systemGrain boundariesNonlinear stabilityPartial differential equationPattern formationTuring patternsThesis or Dissertation