Princeton University in New Jersey (its science library shown here) is one of four institutions to which the US National Science Foundation began restricting research grants last month. Credit: EQRoy/Alamy Update: On 28 May, the day after this story was published, the NSF’s OAM removed from its database the note “Future Awards to Organization on Hold” for Duke, Harvard and Yale. And a few grants for researchers at Harvard and Duke have been released, according to agency staff members who spoke to Nature. The US National Science Foundation (NSF) — a major funder of basic research — has restricted the flow of new research grants to a group of elite universities, Nature has learnt.…