I have just run a major programme at the Isaac Newton Institute for Mathematical Sciences in Cambridge. Three Iranians, graduate students and postdocs in the US, were unable to attend because of highly restrictive US visa rules. All are doing work that would have made a considerable contribution. We and they were thus deprived of the chance to participate in normal scientific dialogue and are all the poorer as a result.
Visa restrictions are an insidious form of academic boycott that sit ill with the increasing globalisation of the scientific community.
Caroline Series
University of Warwick