Active Brownian
particles refer to a theory that is used in order to model the
self-propelled
motion of biological entities such as, for example, cells migrating on
substrates. For this purpose the
friction coefficient of ordinary Langevin dynamics is assumed to be
velocity dependent, representing
the take-up of energy from some external reservoir and its conversion
into kinetic energy. Other
well-known generalizations of Langevin equations are deterministic
thermal reservoirs for which
the Nos´e-Hoover thermostat is a simple example. After
introducing these two seemingly different
concepts I will show that they are quite related to each other.
Particularly, I will focus onto
the origin of bimodal velocity distributions, which are produced by
both types of generalized
Langevin dynamics. Starting from Nos´e-Hoover thermostats, I will
argue that the bimodality can
be understood in terms of a combination of canonical with
microcanonical distributions.
Ref.:
R.Klages, Microscopic chaos, fractals and transport in nonequilibrium
statistical mechanics
(World Scientific, Singapore, 2007), Chapter 16.