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We use Brownian dynamics simulations of colloidal systems to explore new nonequilibrium collective e ects. Colloids driven over a symmetric ashing periodic substrate undergo a ratcheting behavior which can be used to fractionate di erent particle species. The addition of nondriven colloids can increase the drift velocity of the driven colloids due to collective interactions. We show that colloids in optical trap lattices can be used to create an arti cial spin ice system which shows a rich variety of ice rule and other orderings. Our study of an interstitial point defect in a two-dimensional colloidal crystal shows that it is more mobile than a vacancy defect due to the more two-dimensional character of the di usion. We also demonstrate that a bidisperse, phase segregated colloid system can be mixed e ciently in the absence of temperature by driving the colloids over a random substrate and inducing plastic ow.

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Andras Libal is an Associate Professor at the Mathematics and Computer Science Department of the Babes-Bolyai University in Cluj, Romania. His current research topics include soft matter systems such as colloids and granular systems. He is also interested in simulations concerning spin ice, frustrated systems and magnetic modelling.

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