DURHAM, N.C. -  Duke has a new leader at point guard and his name is Quinn Cook.  The sophomore played every minute of last evening's game, going up against one of the most ballyhooed guards in the nation in Buckeye Aaron Craft.  And the numbers speak for themselves.  Craft struggled from the field all night long while Cook took over in the second half, nailing six consecutive free throws down the stretch and tallying 12 points while dishing out eight dimes on the evening.  The emergence of Cook this season has allowed Seth Curry and Rasheed Sulaimon to play off the ball while Tyler Thornton serves in the sixth man role.  Cook is the type of player that gets better as the game goes on.  Perhaps this is still part of the learning curve, for he is far from a finished product, but make no mistake: he is here to stay.  And the best is yet to come.