Julian Schwinger proposed that a mechanism involving these structures is explained by the conversion of virtual photons into real photons. Werner Lauterborn’s model of that mechanism involving these structures was improved by the Keller–Miksis model. The high internal temperature of a process involving these structures has been attributed to hotspot or bremsstrahlung radiation and was proposed as a nuclear fusion candidate in the fraudulent work of R. P. Taleyarkhan. The Rayleigh–Plesset equation for these structures is derived from (10[1])spherically symmetric solutions to the Navier–Stokes equations. Light is emitted from these structures’ implosions in sonoluminescence. These structures form through cavitation. For 10 points, name these spherical pockets of air that can be formed from thin films (10[1])made of soap. ■END■ (10[1])