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. 2015 Jun 19;6:7470. doi: 10.1038/ncomms8470

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(a) Snapshot of a vortex of rollers. The dark dots show the position of one half of the ensemble of rollers. The blue vectors represent their instantaneous speed (R_c=1.35 mm, φ₀=5 × 10⁻²). (b) Average polarization plotted versus the average packing fraction for different confinement radii. Open symbols: experiments. Full line: best fit from the theory. Filled circles: numerical simulations (b=3a, R_c=1 mm). (c) Time-averaged polarization field (R_c=1.35 mm, φ₀=5 × 10⁻²). (d) Time average of the local packing fraction (R_c=1.35 mm, φ₀=5 × 10⁻²). (e) Time-averaged packing fraction at the centre of the disc, normalized by and plotted versus the average packing fraction. Error bars: one standard deviation. (f) Fraction of the disc where versus the average packing fraction. Open symbols: experiments. Full line: theoretical prediction with no free fitting parameter. Filled circles: numerical simulations (b=3a, R_c=1 mm). (g) Radial density profiles plotted as a function of the distance to the disc centre r. All the experiments correspond to φ₀=0.032±0.002, error bars: 1σ. (h) Open symbols: same data as in g. The radial density profiles are rescaled by and plotted versus the rescaled distance to the centre r/R_c. All the profiles are seen to collapse on a single master curve. Filled symbols: Numerical simulations. Solid line: theoretical prediction. All the data correspond to E₀/E_Q=1.1.

Inline graphic — (a) Snapshot of a vortex of rollers. The dark dots show the position of one half of the ensemble of rollers. The blue vectors represent their instantaneous speed (R_c=1.35 mm, φ₀=5 × 10⁻²). (b) Average polarization plotted versus the average packing fraction for different confinement radii. Open symbols: experiments. Full line: best fit from the theory. Filled circles: numerical simulations (b=3a, R_c=1 mm). (c) Time-averaged polarization field (R_c=1.35 mm, φ₀=5 × 10⁻²). (d) Time average of the local packing fraction (R_c=1.35 mm, φ₀=5 × 10⁻²). (e) Time-averaged packing fraction at the centre of the disc, normalized by and plotted versus the average packing fraction. Error bars: one standard deviation. (f) Fraction of the disc where versus the average packing fraction. Open symbols: experiments. Full line: theoretical prediction with no free fitting parameter. Filled circles: numerical simulations (b=3a, R_c=1 mm). (g) Radial density profiles plotted as a function of the distance to the disc centre r. All the experiments correspond to φ₀=0.032±0.002, error bars: 1σ. (h) Open symbols: same data as in g. The radial density profiles are rescaled by and plotted versus the rescaled distance to the centre r/R_c. All the profiles are seen to collapse on a single master curve. Filled symbols: Numerical simulations. Solid line: theoretical prediction. All the data correspond to E₀/E_Q=1.1.