On 27 January, Donald Trump signed an executive order denying Syrian refugees entry to the US, suspending all refugee admissions for 120 days and blocking citizens of seven nations from entering the US for at least 90 days. Scientists are among those affected, with some speaking out about its impact. "While one can understand security imperatives, a broad ban that restricts movement of widely defined groups can hold back important scientific progress; progress that can solve some of our most urgent problems," says one professor at a leading US university. A dual citizen of one of the countries on the list, he says he will probably have to cancel research trips, as well as a visit to see his mother.
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