I need to make a boolean operation (AND) between two messages. Is it possible?

Anyone can tell me how to implement in pd a digital waveguide model for i.e. a string or a tube?

Sorry, I was not clear enough... What I want to implement is a digital waveguide model of a human vocal tract, which is like a tube with a variable section along x axis. But the first step is to do it for a constant section tube.