Abstract: A hardware random number generator (RNG) (10) comprises a source of entropy (12) for providing a bit stream (DIS) comprising successive bits of a first state and a second state and a first digital corrector circuit (28). The first circuit being configured to provide from two successive bits in the bit stream an output bit of an output bit stream (34) according to a first scheme to ensure that bits in the output bit stream (34) are independent from one another. A serially connected second digital corrector circuit (28) ensures that the bits in the output bit stream are also unbiased, so that the output bit stream is truly random. A Gaussian generator 40 connected to an output of either the first corrector or the second corrector generates from the output bit stream (34) words having standard Gaussian deviates.

Abstract: A subterranean excavation such as a mine working is cooled by a refrigeration plant having a heat rejection system at an upper station and a heat absorption system in the excavation, the refrigerant medium being ammonia. The system includes a surge drum at the upper station and maybe also at the excavation. Safety measures include the location of the vapor and liquid pipes in a borehole separate from the mine shaft or shafts.