The present invention relates to novel azetidine derivatives, processes for preparing them, pharmaceutical compositions containing them and their use as pharmaceuticals as modulators of sphingosine-1-phosphate receptors. The cleaner has a main body with a ferrule insertion hole extending from a ferrule insertion port at its distal end face toward the proximal end of the cleaner. Burnt gases from the engine such as a jet engine no longer fit for flying are directed into a duct where the exchangers are located. The probe assembly has a street tee with an inlet port to receive outlet gas from the gas analyzer and a sintered metal outer housing, through a catalyst cartridge for reaction.