T. Ishiwata

Motion of non-convex polygons by crystalline curvature and almost convexity phenomena

The behavior of solution polygons to generalized crystalline curvature flow is discussed. The conditions to guarantee that the solution polygon keeps its admissibility as long as enclosed area of solution polygon is positive are clarified. We also show that the solution polygon becomes “almost convex” before the extinction time.

On the bolw-up rate for fast bolw-up solutions arising in an anisotropic crystalline motion

We consider the asymptotic behavior of motion of polygonal convex curves by crystalline curvature in the plane. There appear spontaneously two types of singularity: one is single point extinction and the other is degenerate pinching. We mainly discuss degenerate pinching singularity and show the exact blow-up rate for a fast blow-up solution which arises in an equivalent blow-up problem.

Three-dimensional numerical simulation of helically propagating combustion waves

In the present paper, by using a mathematical model for self-propagating high-temperature synthesis, we reveal the three-dimensional structure of so-called spin combustion wave on the inside of cylindrical sample. It is shown that an isothermal surface of regular spin combustion wave has some wings of which number is the same as that of reaction spots on the cylindrical surface and that the isothermal surface with helical wings rotates down with time. Because of this propagating pattern, in this paper, we adopt the more suitable term “helical wave.” We also obtain the following existence conditions of a helical wave: If physical parameters are set so that a pulsating wave exists stably for the one-dimensional problem, then a helical wave takes the place of a pulsating wave when the radius of cylindrical sample becomes large.

Motion of non-convex polygon by crystalline curvature flow and its generalization

The motion of polygons by crystalline curvature is discussed. We also mention the “convexity phenomena” and show examples of non-existence of non-convex self-similar solutions.