Merdan, Huseyin
(2004)
Renormalization Group Methods in Applied Mathematical Problems.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
This work presents the application of the methods known as renormalization group (RG) and scaling in the physics literature to applied mathematics problems after a brief review ofthe methodology.The first part of the thesis involves an application to a class of nonlinear parabolic differential equations. We consider equationsof the form $u_{t}=frac{1}{2}u_{xx}+varepsilonN(x,u,u_{x},u_{xx})$ where $varepsilon$ is a small positive number and $N$ is dimensionally consistent without additional dimensional constants. First, RG methods are described fordetermining the key exponents related to the decay of solutions to these equations. The determination of decay exponents is viewed asan asymptotically selfsimilar process that facilitates an RG approach. These methods are extended to higher order in the smallcoefficient of the nonlinearity. The RG calculations lead to the result that for large space and time, the solution is characterized by $u(x,t)sim t^{frac{1}{2}alpha }u^{ast}(xt^{1/2},1)$ where the exponent $alpha$ is a simple function of the exponents of the terms in $N$. Finally, the RG results are verified in some cases by rigorous proofs and other calculations.In the second part, the application of renormalization technique to systems of equations describing interface problems are presented. The temporal evaluation of an interface separating twophases is analyzed for large time. We study the standard sharp interface problem in the quasistatic regime. The characteristic length, $R(t)$, of a selfsimilar system that is the timedependent length scale characterizing the pattern growth is calculated by implementing a renormalization procedure. It behaves as t^β where β has values in the continuous spectrum [1/3,1/2] when the dynamical undercooling is nonzero, and β in [1/3,∞] when the undercooling is set atzero. The single value of β=1 is extracted from this continuous spectrum as a consequence of boundary conditions that impose a plane wave. It is also shown that in almost all of thesecases, the capillarity length (arising from surface tension) is irrelevant for the large time behavior even though it has a crucial role at the early stage evolution of an interface.end{abstract}
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Item Type: 
University of Pittsburgh ETD

Status: 
Unpublished 
Creators/Authors: 

ETD Committee: 

Date: 
24 September 2004 
Date Type: 
Completion 
Defense Date: 
28 May 2004 
Approval Date: 
24 September 2004 
Submission Date: 
31 July 2004 
Access Restriction: 
No restriction; Release the ETD for access worldwide immediately. 
Institution: 
University of Pittsburgh 
Schools and Programs: 
Dietrich School of Arts and Sciences > Mathematics 
Degree: 
PhD  Doctor of Philosophy 
Thesis Type: 
Doctoral Dissertation 
Refereed: 
Yes 
Uncontrolled Keywords: 
Asymptotic selfsimilarity; Capilarity length; Interface dynamics; Nonlinear parabolic equations; Quasistatic regime; Renormalization group 
Other ID: 
http://etd.library.pitt.edu/ETD/available/etd07312004200513/, etd07312004200513 
Date Deposited: 
10 Nov 2011 19:55 
Last Modified: 
15 Nov 2016 13:47 
URI: 
http://dscholarship.pitt.edu/id/eprint/8752 
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