Energetics of single active diffusion trajectories
1 Department of Mathematical and Life Science, Graduate School of Science, Hiroshima University Kagamiyama, Higashi-Hiroshima 739-8526, Japan
2 Department of Computational Science, Graduate School of System Informatics, Kobe University Rokkodai, Kobe 657-8501, Japan
Received: 8 November 2013
Accepted: 22 January 2014
The fundamental insight into Brownian motion by Einstein is that all substances exhibit continual fluctuations due to thermal agitation balancing with the frictional resistance. However, even at thermal equilibrium, biological activity can give rise to non-equilibrium fluctuations that cause “active diffusion” in living cells. Because of the non-stationary and non-equilibrium nature of such fluctuations, mean square displacement analysis, relevant only to a steady-state ensemble, may not be the most suitable choice as it depends on the choice of the ensemble; hence, a new analytical method for describing active diffusion is desired. Here we discuss the stochastic energetics of a thermally fluctuating single active diffusion trajectory driven by non-thermal random forces. Heat dissipation, usually difficult to measure, can be estimated from the active diffusion trajectory; guidelines on the analysis such as criteria for the time resolution and driving force intensity are shown by a statistical test. This leads to the concept of an “instantaneous diffusion coefficient” connected to heat dissipation that may be used to analyse the activity and molecular transport mechanisms of living systems.
PACS: 05.40.Jc – Brownian motion / 05.70.Ln – Nonequilibrium and irreversible thermodynamics / 87.10.Mn – Stochastic modeling
© EPLA, 2014