Free and enclosed inertial active gas

Area of Science:

• Physics
• Soft Matter Physics
• Statistical Mechanics

Background:

• Active Brownian particles (ABPs) are model systems for self-propelled matter.
• Understanding the behavior of active matter under inertia is crucial for predicting collective phenomena.
• Previous studies often neglected translational and rotational inertia in active particle systems.

Purpose of the Study:

• To investigate the free expansion of inertial active gases in three dimensions.
• To theoretically derive and numerically corroborate key physical properties of these systems.
• To analyze the effect of inertia on particle distribution and pressure within a confined volume.

Main Methods:

• Fokker-Planck formalism to elucidate orientational correlations.
• Theoretical derivation of diffusion, mean-square speed, persistence length, and reorientation time.
• Langevin dynamics simulations for corroboration and numerical studies.
• Analysis of particle distribution and mechanical pressure in a cubic box.

Main Results:

• Inertia suppresses the accumulation of active particles at walls, leading to a more uniform distribution.
• A state equation for inertial active gases composed of spherical particles is derived.
• Theoretical predictions for diffusion, speed, persistence, and pressure were validated by simulations.
• Mechanical pressure and bulk pressure (from swim and Reynolds stresses) definitions coincide in the thermodynamic limit.

Conclusions:

• Inertia plays a significant role in modifying the spatial distribution and bulk properties of active gases.
• The derived state equation provides a fundamental description for inertial active matter.
• The study confirms the applicability of statistical mechanics principles to inertial active systems.