The structure of the collection of processes may be pictured as \setlength{\unitlength}{0.01cm} \nop{ ) } \hspace{0.4cm} \mbox{ \begin{picture}(1000,350)(0,0) \put(200,200){\circle{100}} \put(400,200){\circle{100}} \put(600,200){\makebox(0,0){...}} \put(800,200){\circle{100}} \put( 250,200){\vector(4,0){ 100}} \put( 450,200){\vector(4,0){ 100}} \put( 650,200){\vector(4,0){ 100}} \put(200,100){\makebox(0,0){driver}} \put(400,100){\makebox(0,0){sieve1}} \put(800,100){\makebox(0,0){sieve_n}} \end{picture} }\n where each arrow represents a channel.