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Register a new userApplications of Grassmannian and graph flows to nonlinear systems
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We show how many classes of partial differential systems with local and nonlocal nonlinearities are linearisable. By this we mean that solutions can be generated by solving a corresponding linear partial differential system together with a linear Fredholm integral equation. The flows of such nonlinear systems are examples of linear flows on Fredholm Stiefel manifolds that can be projected onto Fredholm Grassmann manifolds or of further projections onto natural subspaces thereof. Detailed expositions of such flows are provided for the Korteweg de Vries and nonlinear Schrodinger equations, as well as Smoluchowskis coagulation and related equations in the constant frequency kernel case. We then consider Smoluchowskis equation in the additive and multiplicative frequency kernel cases which correspond to the inviscid Burgers equation. The solution flow in these cases prompts us to introduce a new class of flows we call ``graph flows. These generalise flows on a Grassmann manifold from sets of graphs of linear maps to sets of graphs of nonlinear maps. We include a detailed discussion of directions in which these flows can be generalised to include many other partial differential systems with local and nonlocal nonlinearities.
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We derive continuum limits of atomistic models in the realm of nonlinear elasticity theory rigorously as the interatomic distances tend to zero. In particular we obtain an integral functional acting on the deformation gradient in the continuum theory which depends on the underlying atomistic interaction potentials and the lattice geometry. The interaction potentials to which our theory applies are general finite range models on multilattices which in particular can also account for multi-pole interactions and bond-angle dependent contributions. Furthermore, we discuss the applicability of the Cauchy-Born rule. Our class of limiting energy densities consists of general quasiconvex functions and the class of linearized limiting energies consistent with the Cauchy-Born rule consists of general quadratic forms not restricted by the Cauchy relations.
This paper addresses the mathematical models for the heat-conduction equations and the Navier-Stokes equations via fractional derivatives without singular kernel.
We prove a local Faber-Krahn inequality for solutions $u$ to the Dirichlet problem for $Delta + V$ on an arbitrary domain $Omega$ in $mathbb{R}^n$. Suppose a solution $u$ assumes a global maximum at some point $x_0 in Omega$ and $u(x_0)>0$. Let $T(x_0)$ be the smallest time at which a Brownian motion, started at $x_0$, has exited the domain $Omega$ with probability $ge 1/2$. For nice (e.g., convex) domains, $T(x_0) asymp d(x_0,partialOmega)^2$ but we make no assumption on the geometry of the domain. Our main result is that there exists a ball $B$ of radius $asymp T(x_0)^{1/2}$ such that $$ | V |_{L^{frac{n}{2}, 1}(Omega cap B)} ge c_n > 0, $$ provided that $n ge 3$. In the case $n = 2$, the above estimate fails and we obtain a substitute result. The Laplacian may be replaced by a uniformly elliptic operator in divergence form. This result both unifies and strenghtens a series of earlier results.
We consider nonlinear reaction systems satisfying mass-action kinetics with slow and fast reactions. It is known that the fast-reaction-rate limit can be described by an ODE with Lagrange multipliers and a set of nonlinear constraints that ask the fast reactions to be in equilibrium. Our aim is to study the limiting gradient structure which is available if the reaction system satisfies the detailed-balance condition. The gradient structure on the set of concentration vectors is given in terms of the relative Boltzmann entropy and a cosh-type dissipation potential. We show that a limiting or effective gradient structure can be rigorously derived via EDP convergence, i.e. convergence in the sense of the Energy-Dissipation Principle for gradient flows. In general, the effective entropy will no longer be of Boltzmann type and the reactions will no longer satisfy mass-action kinetics.
An averaging method is applied to derive effective approximation to the following singularly perturbed nonlinear stochastic damped wave equation u u_{tt}+u_t=D u+f(u)+ u^alphadot{W} on an open bounded domain $DsubsetR^n$,, $1leq nleq 3$,. Here $ u>0$ is a small parameter characterising the singular perturbation, and $ u^alpha$,, $0leq alphaleq 1/2$,, parametrises the strength of the noise. Some scaling transformations and the martingale representation theorem yield the following effective approximation for small $ u$, u_t=D u+f(u)+ u^alphadot{W} to an error of $ord{ u^alpha}$,.
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