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## A. Phase diagram 

(a) 

(c) 

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(b) 

(d) 

Of principal interest in determining the phase diagram are the bulk density and the current as functions of the rates α and β . These results are summarized in Fig. 7, showing evidence of both continuous and discontinuous phase transitions, depending on the rates. We see that for low α ( α < 0 . 8 or so) and β < α the system is in the high-density phase, in which density and current depend only on β , whereas for β > α , and β < 0 . 6 or so, the system is in the low-density phase in which density 

