Chinese Cryptologists Get Invitations to a U.S. Conference, but No Visas - New York Times

"SAN FRANCISCO, Aug. 16 - Last year a Chinese mathematician, Xiaoyun Wang, shook up the insular world of code breakers by exposing a new vulnerability in a crucial American standard for data encryption. On Monday, she was scheduled to explain her discovery in a keynote address to an international group of researchers meeting in California.

But a stand-in had to take her place, because she was not able to enter the country. Indeed, only one of nine Chinese researchers who sought to enter the country for the conference received a visa in time to attend."