[MT 2] Relations between PL exponents

Realistically, the effective medium of the cell should be described by a frequency dependent elastic modulus



For simplicity we assume a purely elastic medium with x=1, so that the bead displacement is directly proportional to the momentary sum of forces. Then the PL exponents are related as follows:

Mean squared displacement:



Velocity Autocorrelation:



Velocity power spectral density:



Force power spectral density:




In our case we get for diffusive motion lambda=2 and for ballistic motion lambda=3. According to

P.Bursac et al., Nature Materials 4, 557 (2005)

a lambda of 2 is characteristic for force fluctuations that are finite but discontinuous (a series of force steps), whereas lambda=4 corresponds to uniformly continous fluctuations.

This could be checked by evolving the random phases in v(w) and then analyzing the resulting x(t) ~ F(t).