The present disclosure addressed apparatus and methods for forming an annular isolator in a borehole after installation of production tubing. Such sidewall is intended to promote a path of least electrical resistance. The digital power manager further comprises a user interface, such as an I2C interface, adapted to receive programming data therefrom and send monitoring data thereto. 1; : higher than 9; : higher than 18; B2O3: 4 to 15; P2O5: 0 to 5; SO3: 0 to 1; Fe2O3: 0 to 0. The slots and apertures are arranged so that regardless of the particular orientation of the housing relative to the sleeve, at least one of the apertures will be in registry with one of the slots.