Boundary asymmetry, curvature, and corner
Active pressure depends of shape of non-spherical particles through reorientation at the boundary.
Are there macroscopic consequences of activity for spherical particles (no wall-induced reorientation)?
N. Nikola, A.P. Solon, Y. Kafri, M. Kardar, J. Tailleur, R. Voituriez, Phys. Rev. Lett. 117, 098001 (2016);
Asymmetric boundaries:
Tangential Ratchet force: Asymmetric walls support a current and net tangential force:
Random motions of bacteria:
(R. Di Leonardo, et al PNAS 2010)
(Another macroscopic consequence of the absence of time reversibility at microscopic scale.)
Curving boundaries:
Normal force variations for sinusoidal wall:
(Density along and into the wall is non-uniform, depending on curvature as well as potential)
Variation of pressure with curvature is reminiscent of Laplace's law, implying an activity-induced line (surface) tension:
Sharp corners:
Scale invariant currents and density variations:
Simulations: 
Conserved density is the only slow variable in this system
Analogy to electrostatics (dipolar field sourced at corner):
The strength of resulting currents and corresponding pressure depend on the opening angle.
Bendable soft boundary:
+ stabilizing nonlinearities
Reduction in line tension leads to modulation instability:
Confirmation for a granular chain held on a vibrating plate of shaken particles (Physics Viewpoint)
G. Junot, G. Briand, R. Ledesma-Alonso, and O. Dauchot, PRL 119, 028002 (2017)
