**Simulations of Transient Active Matter**

Simulations employing the model of *Active Brownian Particles* (ABP):

Force and pressure can be computed from the density of particles in a wall potential:

For non-interacting ABPs:

** Non-interacting active particles, agitated (from rest) between walls separated by L: **

Active particles condense on a repulsive surface!

The evolution of the

mean density profilecan be modelled by:

Interactions between inclusionsare similarly dominated by changes in the mean density with time

**What about the fluctuation-induced transient force?**

A local equilibrium assumption suggests

There is no fluctuation force for non-interacting particles (

P''=0)

Simulations for an interacting gas (initial condition corresponding to infinite temperature):

The transient force due to relaxation of the mean density profile decays with time exponentially

The long time decay of the force is due to the (repulsive) contribution of transient density fluctuations.