Compounds of the following formula:wherein A, D, Q, T, U, V, W, X, Y, Z, R1, and are as defined herein. The method includes applying a first degree of braking to the train during a first period of time, and then applying a second degree of braking to the train during a second time period following the first time period so that the train is slowed in a manner effective to limit a peak deceleration rate experienced by the train. The support structure may include an elongated support member that is generally vertically disposed relative to the playing surface and a single support assembly which connects the elongated support member to the basketball goal. The apparatus can be built into a portable device, or an automated docking station for testing and calibrating gas detection and monitoring instruments, or into a fixed gas detection system for performing such functions. The devices offer the advantages of minimal conditioning requirements, fast set speeds, high reset resistances and low set resistances.