A mechanical optical switch provides an active switching mechanism and an active latching mechanism that are both actuated by piezoelectric elements. Therefore, the series-connected packaged bags can be transferred with the portions swollen due to a packed material of the bags not contacting the receiving blade. The invention determines, in the node, a channel occupancy during the first time interval, after counting the messages, and then adaptively adjusts, in the node, the contention interval based on the channel occupancy. The body portion is also flexible and may be made integrally with the rib elements by an injection-moulding process. If desired, the operating speed pattern can be repeated to continue the pulsatile blood flow pattern. A method to retrieve a hollow device from an undersea flow pipe uses a flexible pig driven by a flow flowing into flow pipe to retrieve hollow device from a location where hollow device operates.