A method and apparatus for selectively publishing user-provided content items to other users is provided. The ion removal mechanism can be included in an ion optics assembly, which connects an ion mobility filter to a mass analyzer. Each node has N selection switches, which are provided at input terminals thereof, to each of which are input Jth outputs of two mutually adjacent cross-bar switches among the first to th cross-bar switches. The brake-control module further includes a second-trailer interface for connection of a second trailer that is coupled to the first trailer. The first word gate comprises a first control gate coupled to the first edge and a second control gate coupled to the second edge. A communication is established between a backend server and a plurality of mobile devices belonging to a respective user of a cellular phone network.