What type of mask is best? Brais Seara/Moment via Getty Images Laura (Layla) H. Kwong, University of California, Berkeley Do masks work? And if so, should you reach for an N95, a surgical mask, a cloth mask or a gaiter? Over the past year and a half, researchers have produced a lot of laboratory, model-based and observational evidence on the …

Tony Walker, La Trobe University The 20th anniversary of the September 11 terrorist attacks on New York and Washington carries with it two punctuation marks. The first are the attacks themselves on the World Trade Centre and the Pentagon. These shocked a country that was both psychologically and physically unprepared for such a brazen assault on American soil. The second …

Un miembro de la policía afgana y soldados estadounidenses cerca del aeródromo de Kandahar. Brendan Smialowski/AFP via Getty Images Neta C. Crawford, Boston University Estados Unidos invadió Afganistán a finales de 2001 para destruir a Al Qaeda, apartar a los talibanes del poder y rehacer la nación. El 30 de agosto de 2021, Estados Unidos completó la retirada de sus …