The present invention discloses a method and a system for non-periodic feedback in a carrier aggregation scenario. A user can perform leg extension exercises and leg curl exercises with the leg exercise arm assembly. The method is particularly useful for treating premature ejaculation. The filter drain conduit may be in fluid communication with the filter chamber substantially at a lower portion of the fuel filter, and may include a valve located externally of the fuel tank. Preferably, a volumetric capacity of the pressure generation chambers is changed in accordance with a change in the pressure, to eject an ink droplet from the nozzle orifice. Aging tokens are used to tracking the age of a system as a whole, as well as its individual constituents, in the context of stochastic Petri nets.