<http://www.w3.org/1999/02/22-rdf-syntax-ns#first>
<http://pop.h-cdn.co/assets/cm/15/05/480x360/54cb2de3bc312_-_sound-waves-06-0314-de.jpg>
<http://www.popularmechanics.com/military/g1458/7-amazing-things-you-can-do-with-sound-waves/>