Abstract
Sharing the sam principle of tracking the bright spots in the time-series images, single particle/molecule tracking (SPT/SMT) and particle tracking velocimetry (PTV) makes contrast in the typical quantity of interest. Namely, characteristics of random motion is also of great importance in the SPT/SMT, whereas PTV solely focus on the velocity field. Brownian motion, the random motion basically caused by the thermal fluctuation in the system, is evaluated as some kinds of diffusion by sampling sufficient data in terms of amount as well as the resolution and precision. The diffusion coefficients are usually evaluated by the mean squared displacements (MSDs) as a function of time. On the other hand, it is often the case that the system of interest exhibits multiple modes of diffusion. While the time evolution of the whole MSD tells us the representative single value, it is often insufficient for the discussion to address the mechanism that results in the multimodal diffusion. Furthermore, it is often desired to detect the multimodality if it exists in the system of interest. Here I would like to introduce the simple method, “logarithmic measure” of diffusion, to enable such detection and evaluation without any prior knowledge of the system.
