We formulate an isoperimetric deformation of curves on the Minkowski plane, which is governed by the defocusing mKdV equation. Two classes of exact solutions to the defocusing mKdV equation are also presented in terms of the $tau$ functions. By using one of these classes, we construct an explicit formula for the corresponding motion of curves on the Minkowski plane even though those solutions have singular points. Another class give regular solutions to the defocusing mKdV equation. Some pictures illustrating typical dynamics of the curves are presented.
We give the following results for Pinkalls central affine curve flow on the plane: (i) a systematic and simple way to construct the known higher commuting curve flows, conservation laws, and a bi-Hamiltonian structure, (ii) Baecklund transformations and a permutability formula, (iii) infinitely many families of explicit solutions. We also solve the Cauchy problem for periodic initial data.
We prove that a plane domain which is almost isoperimetric (with respect to the $L^1$ metric) is close to a square whose sides are parallel to the coordinates axis. Closeness is measured either by $L^infty$ Haussdorf distance or Fraenkel asymmetry. In the first case, we determine the extremal domains.
We consider the punctured plane with volume density $|x|^alpha$ and perimeter density $|x|^beta$. We show that centred balls are uniquely isoperimetric for indices $(alpha,beta)$ which satisfy the conditions $alpha-beta+1>0$, $alphaleq 2beta$ and $alpha(beta+1)leqbeta^2$ except in the case $alpha=beta=0$ which corresponds to the classical isoperimetric inequality.
Given a positive lower semi-continuous density $f$ on $mathbb{R}^2$ the weighted volume $V_f:=fmathscr{L}^2$ is defined on the $mathscr{L}^2$-measurable sets in $mathbb{R}^2$. The $f$-weighted perimeter of a set of finite perimeter $E$ in $mathbb{R}^2$ is written $P_f(E)$. We study minimisers for the weighted isoperimetric problem [ I_f(v):=infBig{ P_f(E):Etext{ is a set of finite perimeter in }mathbb{R}^2text{ and }V_f(E)=vBig} ] for $v>0$. Suppose $f$ takes the form $f:mathbb{R}^2rightarrow(0,+infty);xmapsto e^{h(|x|)}$ where $h:[0,+infty)rightarrowmathbb{R}$ is a non-decreasing convex function. Let $v>0$ and $B$ a centred ball in $mathbb{R}^2$ with $V_f(B)=v$. We show that $B$ is a minimiser for the above variational problem and obtain a uniqueness result.
In this paper, we consider the evolution of spacelike graphic curves defined over a piece of hyperbola $mathscr{H}^{1}(1)$, of center at origin and radius $1$, in the $2$ dimensional Lorentz-Minkowski plane $mathbb{R}^{2}_{1}$ along an anisotropic inverse mean curvature flow with the vanishing Neumann boundary condition, and prove that this flow exists for all the time. Moreover, we can show that, after suitable rescaling, the evolving spacelike graphic curves converge smoothly to a piece of hyperbola of center at origin and prescribed radius, which actually corresponds to a constant function defined over the piece of $mathscr{H}^{1}(1)$, as time tends to infinity.