Two bridges over the Fox River in Green Bay became stuck Wednesday.  The city blames the cold temperatures.  The Ray Nitschke Memorial Bridge was raised at about 8:30 a-m to allow a tugboat to pass through, but one side of the bridge stayed up.  That stopped all traffic on Main Street.  A public works crew says a breaker in the computerized control system tripped — possibly caused by the extreme cold.  Later in the day the Donald Tilleman Bridge couldn’t be raised when a lock on the center span froze.