We explore periodic orbits on an equilateral triangular billiard table. We prove that there is exactly one periodic orbit with odd period. For any positive integer n, there exist P d|n μ(d)P ¡ n d ¢ periodic orbits of period 2n, where μ(d) is the Möbius transformation function and P (n) = bn+2 2 c− bn+2 3 c. We count periodic orbits by introducing a new type of integer partition.

In this paper, a neutral multi-species logarithmic population model is investigated. By applying the matrixs spectral theory which is different from the methods employed in the literature, a set of sufficient conditions are obtained for the existence and uniqueness of almost periodic solution of the neutral multi-species logarithmic population model. The obtained sufficient conditions are given...

We prove that certain free products of factors of type I and other von Neumann algebras with respect to nontracial, almost periodic states are almost periodic free Araki-Woods factors. In particular, they have the free absorption property and Connes’ Sd invariant completely classifies these free products. For example, for λ, μ ∈]0, 1[, we show that (M2(C), ωλ) ∗ (M2(C), ωμ) is isomorphic to the...

It is proved that the scattering amplitude known at a fixed frequency, a fixed direction of the incident plane wave and all directions of the scattered wave in a solid angle, however small, determine uniquely the shape of a strictly convex obstacle with a smooth but not analytic boundary on which the Dirichlet boundary condition is assumed.

The global theory of transmission line networks with nonconservative junction conditions is developed from a spectral theoretic viewpoint. The rather general junction conditions lead to spectral problems for nonnormal operators. The theory of analytic functions which are almost periodic in a strip is used to establish the existence of an infinite sequence of eigenvalues and the completeness of ...

As we know, the coefficients of impulsive Lasota-Wazewska model are always assumed to be continuous, say, periodic and almost periodic. In this paper we consider the case when the coefficients are piecewise almost periodic, and establish an existence and uniqueness theorem of piecewise almost periodic positive solution for this model. Mathematics Subject Classifications: 34C27, 34A37

we consider the space of weakly almost periodic functions on a transformation semigroup (s, x , ?) and show that if x is a locally compact noncompact uniform space, and ? is a separately continuous, separately proper, and equicontinuous action of s on x, then every continuous function on x, vanishing at infinity is weakly almost periodic. we also use a number of diverse examples to show that th...

We discuss several classes of linear second order initial-boundary value problems, where damping terms appear in the main wave equation as well as in the dynamic boundary condition. We investigate their wellposedness and describe some qualitative properties of their solutions, including boundedness, stability, or almost periodicity. In particular, we are able to characterize the analyticity of ...