Working towards programmable matter: Unexpected behavior discovered in active particles

Investigating systems consisting of self-propelled particles—so-called active particles—is a rapidly growing area of research. In theoretical models for active particles, it is often assumed that the particles' swimming speed is always the same. This is not so, however, for particles produced in many experiments, for example for those propelled by ultrasound for medical applications. In these cases, the propulsion speed depends on the orientation.