A method of converting liquid micro-biological substrate is disclosed, as is an apparatus for carrying out the method. The liquid substrate is caused to flow along a duct having a cross-sectional area which alternately decreases and increases along the flow path to cause the pressure of the substrate to alternately decrease and increase. Preferably, gas is introduced into the substrate to promote the formation of bubbles of the gas in the substrate. The gas may be so introduced as to cause the s...

To enable a passenger to ride a "roller coaster" in a standing position, the inventive device includes a seat placed between the legs of the passenger, a back member with a headrest incorporated in it, and two harnesses which provide retention of the passenger from above as well as lateral retention of his head and good front and lateral retention of his body. One of the harnesses is movable and can be swung upwardly to enable easy access to the subject device by the passenger and to enable a ve...