At our institute in Brazil, there are students and post-doctoral fellows from many countries, from Peru to China, and Russia to Colombia. We are particularly concerned about the latter: Colombian citizens are being progressively prevented from participating in international congresses.
At least two countries — Italy and Ireland — have recently refused visas to our Colombian students. No reasons have been given. But, as only Colombians have experienced this problem, the reason must be their nationality.
It is clear that political considerations are damaging purely scientific activities.
We see no real solution to the problem. But increasing awareness in the scientific community of what is taking place is perhaps a first step.