Pressure of Active Matter

red ball What is active matter? Some examples:

          

Self-propelled colloidal particles                                                               Swimming Cells                              

 

Grains on vibrating plate

red ball Is there a 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)

red ball "What is the Pressure of an Active Particle Fluid?," (Is pressure well-defined?)

A. P. Solon, Y. Fily, A. Baskaran, M. E. Cates, Y. Kafri, M. Kardar, J. Tailleur, arXiv:1412.3952:

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 ball "What is the Pressure of an Active Particle Fluid?,"

A. P. Solon, Y. Fily, A. Baskaran, M. E. Cates, Y. Kafri, M. Kardar, J. Tailleur, arXiv:1412.3952 (2015):

yellow ballResponse of an active particle at a wall also needs to be 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.