arXiv subjects

Hiroyasu Hamada

Publications and source records attributed to Hiroyasu Hamada.

9 recordsLinked to original sources

arXiv2021

C*-algebras generated by multiplication operators and composition operators with self-similar maps

Let $K$ be a compact metric space and let $γ= (γ_1, \dots, γ_n)$ be a system of proper contractions on $K$. We study a C*-algebra $\mathcal{MC}_{γ_1, \dots, γ_n}$ generated by all multiplication operators by continuous functions on $K$ and composition operators $C_{γ_i}$ induced by $γ_i$ for $i=1, \dots, n$ on a certain $L^2$ space. Suppose that $K$ is self-similar. We consider the Hutchinson measure $μ^H$ of $γ$ and the $L^2$ space $L^2(K, μ^H)$. Then we show that the C*-algebra $\mathcal{MC}_{γ_1, \dots, γ_n}$ is isomorphic to the Cuntz algebra $\mathcal{O}_n$ under some conditions.

math.OA↗

arXiv2021

C*-algebras generated by multiplication operators and composition operators by functions with self-similar branches II

Let $K$ be a compact metric space and let $φ: K \to K$ be continuous. We study a C*-algebra $\mathcal{MC}_φ$ generated by all multiplication operators by continuous functions on $K$ and a composition operator $C_φ$ induced by $φ$ on a certain $L^2$ space. Let $γ= (γ_1, \dots, γ_n)$ be a system of proper contractions on $K$. Suppose that $γ_1, \dots, γ_n$ are inverse branches of $φ$ and $K$ is self-similar. We consider the Hutchinson measure $μ^H$ of $γ$ and the $L^2$ space $L^2(K, μ^H)$. Then we show that the C*-algebra $\mathcal{MC}_φ$ is isomorphic to the C*-algebra $\mathcal{O}_γ(K)$ associated with $γ$ under the open set condition and the measure separation condition. This is a generalization of our previous work, in which we studied the case where $γ$ satisfied the finite branch condition.

math.OA↗

arXiv2019

C*-algebras generated by multiplication operators and composition operators by functions with self-similar branches

Let $K$ be a compact metric space and let $φ: K \to K$ be continuous. We study C*-algebra $\mathcal{MC}_φ$ generated by all multiplication operators by continuous functions on $K$ and a composition operator $C_φ$ induced by $φ$ on a certain $L^2$ space. Let $γ= (γ_1, \dots, γ_n)$ be a system of proper contractions on $K$. Suppose that $γ_1, \dots, γ_n$ are inverse branches of $φ$ and $K$ is self-similar. We consider the Hutchinson measure $μ^H$ of $γ$ and the $L^2$ space $L^2(K, μ^H)$. Then we show that the C*-algebra $\mathcal{MC}_φ$ is isomorphic to the C*-algebra $\mathcal{O}_γ(K)$ associated with $γ$ under some conditions.

math.OA↗

arXiv2019

On $Λ$-Elastica

In this paper, we investigate a transition from an elastica to a piece-wised elastica whose connected point defines the hinge angle $ϕ_0$; we refer the piece-wised elastica $Λ_{ϕ_0}$-elastica or $Λ$-elastica. The transition appears in the bending beam experiment; we compress elastic beams gradually and then suddenly due the rupture, the shapes of $Λ$-elastica appear. We construct a mathematical theory to describe the phenomena and represent the $Λ$-elastica in terms of the elliptic $ζ$-function completely. Using the mathematical theory, we discuss the experimental results from an energetic viewpoint and numerically show the explicit shape of $Λ$-elastica. It means that this paper provides a novel investigation on elastica theory with rupture.

physics.class-ph↗

arXiv2018

An algebraic description of screw dislocations in SC and BCC crystal lattices

We give an algebraic description of screw dislocations in a crystal, especially simple cubic (SC) and body centered cubic (BCC) crystals, using free abelian groups and fibering structures. We also show that the strain energy of a screw dislocation based on the spring model is expressed by the Epstein-Hurwitz zeta function approximately.

math-ph↗

arXiv2017

Mathematics in Caging of Robotics

It is a crucial problem in robotics field to cage an object using robots like multifingered hand. However the problem what is the caging for general geometrical objects and robots has not been well-described in mathematics though there were many rigorous studies on the methods how to cage an object by certain robots. In this article, we investigate the caging problem more mathematically and describe the problem in terms of recursion of the simple euclidean moves. Using the description, we show that the caging has the degree of difficulty which is closely related to a combinatorial problem and a wire puzzle. It implies that in order to capture an object by caging, from a practical viewpoint the difficulty plays an important role.

math.MG↗

arXiv2015

C*-algebras generated by multiplication operators and composition operators with rational symbol

Let $R$ be a rational function of degree at least two, let $J_R$ be the Julia set of $R$ and let $μ^L$ be the Lyubich measure of $R$. We study the C$^*$-algebra $\mathcal{MC}_R$ generated by all multiplication operators by continuous functions in $C(J_R)$ and the composition operator $C_R$ induced by $R$ on $L^2(J_R, μ^L)$. We show that the C$^*$-algebra $\mathcal{MC}_R$ is isomorphic to the C$^*$-algebra $\mathcal{O}_R (J_R)$ associated with the complex dynamical system $\{R^{\circ n} \}_{n=1} ^\infty$.

math.OA↗

arXiv2011

Quotient algebras of Toeplitz-composition C*-algebras for finite Blaschke products

Let R be a finite Blaschke product. We study the C*-algebra TC_R generated by both the composition operator C_R and the Toeplitz operator T_z on the Hardy space. We show that the simplicity of the quotient algebra OC_R by the ideal of the compact operators can be characterized by the dynamics near the Denjoy-Wolff point of R if the degree of R is at least two. Moreover we prove that the degree of finite Blaschke products is a complete isomorphism invariant for the class of OC_R such that R is a finite Blaschke product of degree at least two and the Julia set of R is the unit circle, using the Kirchberg-Phillips classification theorem.

math.OA↗

arXiv2008

Toeplitz-composition C*-algebras for certain finite Blaschke products

Let R be a finite Blaschke product of degree at least two with R(0)=0. Then there exists a relation between the associated composition operator C_R on the Hardy space and the C*-algebra associated with the complex dynamical system on the Julia set of R. We study the C*-algebra generated by both the composition operator C_R and the Toeplitz operator T_z to show that the quotient algebra by the ideal of the compact operators is isomorphic to the C*-algebra associated with the complex dynamical system, which is simple and purely infinite.

math.OA↗