A short circuit arc welding system is disclosed. The message authentication function can be used to authenticate data transmitted between the first processor and a third processor. The dopants provide optical gain responsive to pump radiation provided to the fiber device by a pump source. The remaining groups of switches are selected, in turn, until all of the TDO signals have been transmitted. When the receiver senses the brake command, it implements it by applying the brakes of the train from the car in which the receiver is placed. The copolymers are useful as cold flow improvers in fuel oils.