The article outlines the advantages of active cooling as compared to passive heat sinks in reducing the volume and weight of power op amps in industrial applications. The relative reliability of passive vs. active cooling is summarized. The advantages of pre-assembled amplifier and heat sink combinations are illustrated. Unless your equipment is in outer space all cooling is ultimately accomplished by convection. In outer space there is no air so cooling is accomplished by radiation, but back here on earth the heat collected by whatever means is ultimately dumped into a cooler atmosphere. Liquids, for example, may carry heat away from power devices but in the end the heat passes through a radiator where cool outside air carries away the heat of the liquid. In a passive heat sink the heat generated in the power device is initially conducted through the metal body of the heat sink but convection eventually carries the heat from the heat sink fins to the atmosphere. True, back here on earth, there is a component of cooling resulting from radiation (and that's why passive heat sinks are black, to simulate black body radiation) but overwhelmingly heat is carried away by convection.