Pressure of Active Matter

red ball Active matter? Some examples:

          

Self-propelled colloidal particles                                                               Swimming Cells                              

 

Grains on vibrating plate

red ball Is there fluctuation-induced force in active matter?

yellow ball "Fluctuation-Induced Casimir Forces in Granular Fluids,"

C. Cattuto, R. Brito, U.M.B. Marconi, F. Nori, and R. Soto, Phys. Rev. Lett. 96, 178001 (2006)

yellow ball "Nonadditivity of Fluctuation-Induced Forces in Fluidized Granular Media,"

M.R. Shaebani1, J. Sarabadani, and D.E. Wolf, Phys. Rev. Lett. 108, 198001 (2012)

yellow ball "Casimir effect in actice mtter systems,"

D. Ray, C. Reichhardt, and C.J. Olson Reichhardt, Phys. Rev. E 90, 013019 (2014)

yellow ballThe answer appears to be no long-ranged correlations or interaction.

red ball What is the Pressure of an Active particle fluid? Does it behave like an equilibrium system?

A. P. Solon, J. Stenhammar, R. Wittkowski, M. Kardar, Y. Kafri, M. E. Cates, J. Tailleur, Phys. Rev. Lett. 114, 198301 (2015);

A. P. Solon, Y. Fily, A. Baskaran, M. E. Cates, Y. Kafri, M. Kardar, J. Tailleur, Nature Phys. 11, 673 (2015)

yellow ballTwo common models are Run and Tumble Particles, and Active Brownian Particles:

yellow ballForce and pressure can be measured by introducing a wall potential:

yellow ballReorientation of an active particle close to a wall can be independently specified:

yellow ballNo equation of state since pressure depends on the wall potential!

yellow ballFor non-interacting ellipses, pressure decreases when the torque increases:

    

vs.