An ultrasonic transducer array comprising individual transmit MUT elements and receive MUT elements includes the transmit MUT elements and the receive MUT elements distributed in two dimensions over the array. One implementation involves maintaining a cache in a local cluster file system and caching local file data in the cache by fetching file data on demand from the remote cluster file system into the local cached file system over the network. The piston body has a crown portion with an upper combustion surface, a pair of skirts which depend from the crown surface, a pair of pin bosses for receiving a wrist pin and a plurality of pin boss bridges which extend from the pin bosses to the skirts. The transducer is configured to receive interrogation signals from a controller and to transmit signals in response to the interrogation signals. Thus, the operational information is available in response to attributes of the operational information.