Ultrasound independent Advisory Group on Non-ionising Radiation (AGNIR) produced a report in 2010, which was published by the UK Health Protection Agency (HPA). This report recommended an exposure limit for the general public to airborne ultrasound sound pressure levels (SPL) of 70 dB (at 20 kHz), and 100 dB (at 25 kHz and above). Ultrasound Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies from person to person and is approximately 20 kilohertz (20,000
Above the Influence and increases in the perceptions that others use marijuana." In 2011, Ohio State University released the results of an independent scientific study stating that the "Above the Influence" campaign appears to have effectively reduced marijuana use by teenagers. "Evidence for the success of "Above the Influence" is especially heartening because the primary independent evaluation of its predecessor campaign, 'My Anti-Drug', showed no evidence for success", said Michael Slater, principal investigator of the new study and professor of communication at Ohio State University. "The 'Above the Influence' campaign appears to be successful because it taps into the desire by teenagers to