Tympanic membrane retraction over the surface and move out along the ear canal. Even if migration along the ear canal is blocked, new cells continue to grow so the surface of the eardrum becomes larger. This process of proliferation and migration can result in enlargement of a retraction pocket so that the eardrum expands and grows deeper into the ear. The majority of tympanic membrane retractions remain stable for long periods of time, or may even resolve spontaneously so that eardrum becomes normal again. Not all retractions are able to resolve even if middle ear pressure normalizes, as the retracted segment may become
Dirac membrane Dirac membrane A model of a charged membrane introduced by Paul Dirac in 1962. Dirac's original motivation was to explain the mass of the muon as an excitation of the ground state corresponding to an electron. Anticipating the birth of string theory by almost a decade, he was the first to introduce what is now called a type of Nambu–Goto action for membranes. In the Dirac membrane model the repulsive electromagnetic forces on the membrane are balanced by the contracting ones coming from the positive tension. In the case of the spherical membrane, classical equations of motion imply that the