Fig. 9. Centered particles are transported more efficiently. Four simulations were run in which we measured the final position after a single cycle of a single particle placed at the mouth at time zero. The brown particle was assumed to move at mean fluid velocity as in previous simulations. The green and red particles move at 1.4 and 2.0 times mean fluid velocity, respectively, and the blue particle moves at the calculated velocity of the fluid at the center of the lumen, which varies from 2.2 to 3.5 times mean velocity depending on how open the lumen is at a particular moment. See text for further explanation.