Abstract: A machine comprises a tank defining a liquid chamber for holding a liquid. A rotor is located in the liquid chamber and is mounted such that the rotor is able to rotate relative to the tank. The rotor comprises a plurality of positively buoyant first elements and a plurality of negatively buoyant second elements. The liquid chamber is able to hold the liquid so that the rotor is immersed in the liquid and the first and second elements are arranged so that the positive buoyancy of the first elements and the negative buoyancy of the second elements are able to cause the rotor to rotate.

Abstract: A multiport repeater for a local area network installation has (in addition to its conventional functions) storing access rules for the items of equipment connected to it. It reads a portion of each frame, which may be all or part of the destination address segment and/or of the source address segment and/or of the control segment of each incoming data frame, or it could be a frame or protocol identifier incorporated in opening bytes of the data segment. It compares the data that it reads with the stored access rules to determine whether the frame is permitted or not. If not, it corrupts the frame which it is in the course of re-transmitting, for example by overwriting it with meaningless digits. It may also report the source address, destination address and reason for deciding to corrupt the frame to the network controller.