An assembly of a drug delivery device with a longitudinal axis is given, comprising a body with a proximal end and a distal end. In typical embodiments, identifying a user for a presentation includes creating a data structure representing a presentation and listing in the data structure at least one user identification. The present invention also includes a method of increasing the life of a particle in vivo in a mammal. Other aspects include systems programmed or otherwise configured to perform any embodiment of the method for generating a matrix-encoded two-channel audio signal.