"Can one hear the shape of a drum？" This famous question about the existence of nonisometric billiards having the same spectrum of the Laplacian has been  answered by the construction of noncongruent planar isospectral pairs. Various mathematical tools are used to solve the iso-spectral problem. Physical scientists do spectral experiments in various fields. Numerical mathematician do eigenvalue computation to verify the iso-spectral. However, essentially only 17 families of examples in 2-D that say no to Kac's question were constructed in a 40 year period. And there is no answer in real 3-D case. 

Prof. Jia-Chang Sun graduated from CUST in 1964 and visited abroad for 4 years, including Department of Mathematics of UCSB and NA Group of Yale in 1980-1982, Minnesota Supercomputer Institute and Department of Mathematics of UCLA in 1988-1989, Mathematical Department of CUHK in 1993, Computer Science Department of Corolaro in 1997 and 2004, etc. He has joined in many major projects in China, such as 863 and 973 for 20 years.