Gas turbine engine systems involving hydrostatic face seals with back-up seals are provided. Information used for transmission control is read from a received datagram and the information that are thus read are used to generate an identification key. Refrigerant is compressed in two stages. Thereafter, each activated PCPD can be used in a transaction with a merchant who submits the transaction to an acquirer for processing by a transaction handler who requests an issuer of the account of the PCPD to obtain payment for the transaction from the account corresponding to the PCPD. The pixel circuit further includes a compensating circuit which detects a decrease in the driving current attendant on a secular change of the drive transistor from a side of the output node and feeds back a result of the detection to a side of the input node to compensate for the decrease.