Metered-dose inhaler stringent set of criteria, they must: In the early days of MDIs the most commonly used propellants were the chlorofluorocarbons CFC-11, CFC-12 and CFC-114. In 2008 the Food and Drug Administration announced that inhalers using chlorofluorocarbons as a propellant, such as Primatene Mist, could no longer be manufactured or sold as of 2012. This followed from the U.S. decision to agree to the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer. Phospholipids are important natural surfactant lipids used in enhancing penetration and bioavailability. Phospholipids act by reducing the high surface tension forces at the air-water interface within the
QSK operation (full break-in) QSK operation must ensure that their radio equipment includes the hardware capability for radio frequency antenna switching that operates rapidly enough to allow listening between signals at the appropriate Morse code sending speeds with appropriate lifetimes and reliability. QSK operation (full break-in) "Turning over" a communications channel is the change in communications protocol transmission status that occurs when a transmitting station releases transmitting control of a communications channel thus turning it over to allow another station to transmit. QSK or full break-in operation is one of several techniques and protocols for turning over control of a Morse code radiotelegraph communications