Koji Furuta. Integral representations of positive definite functions on convex sets of certain semigroups of rational numbers. Nihonkai Mathematical Journal. 2017. 28. 79-88
Koji Furuta. A moment problem on rational numbers. Hokkaido Mathematical Journal. 2017. 46. 2. 209-226
古田公司, 榊原暢久. Operator moment problems on abelian *-semigroups. Mathematica Japonica. 2000. Vol. 51. No.3. 433-441
K. Furuta, N. Sakakibara. An example of a positive definite function which is not of positive type on Z^2. Mathematical Journal of Ibaraki University. 1999. 31. 43-46