Symmetry breaking in a fixed circle and in a free-boundary problem.

<p>(<i>a</i>) Instability of a symmetric steady state of ZV model in a fixed circle: snapshots of dimensionless myosin density (pseudo-color) and actin velocities (arrows) at specified times <i>t</i> after myosin was slightly shifted left of center; computations were done for m<sub>tot</sub> = 1.5p and α = 0.5. (<i>b</i>) Transition to unidirectional motility in ZS model; dimensionless myosin concentration (pseudo-colors) and boundary velocities (arrows) are shown for the solution obtained with α = 1, <i>v</i><sub>0</sub> = 5, and m<sub>tot</sub> = 1.5p; the cell assumes steady unidirectional motility after <i>t</i> = 14 (<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1005862#pcbi.1005862.s003" target="_blank">S2 Movie</a>).</p>