Abstract: An erasable optical data storage medium has an embedded servo track and a subsurface recording interface. An erasable recording structure having two dyed polymer layers is separated from the servo track by a compression layer. The servo track is formed in a hard substrate which provides mechanical support for the medium. The medium is adapted to form non-vesicular data bumps projecting into the compression layer when exposed to a write laser beam of predetermined wavelength projected through the substrate and compression layer. The embedded servo track and recording interface are sufficiently close to each to be read simultaneously in the same focal plane.

Abstract: The apparatus includes a cylindrical retainer form spaced inwardly of the wall of the shaft by the desired thickness of the liner to be poured and having overlapping edges which seal against concrete flow but permit the form to be contracted to a smaller circumference after the liner has hardened and is self-supporting. A curb ring extends downwardly and outwardly toward the shaft wall from the bottom of the retainer form to define the bottom surface of each poured liner section. An inflatable toroid forms a seal between the curb ring and the shaft wall. A form support gripper ring having gripper shoes laterally extendable under hydraulic power to engage the shaft wall supports the retainer form, curb ring and liner until the newly poured liner section becomes self-supporting. Adjusting hydraulic cylinders permit the curb ring and retainer form to be properly aligned relative to the form support gripper ring.