CROSSOVER IN RESCALED-RANGE ANALYSIS AND POWER SPECTRA - MEASUREMENTSAND SIMULATIONS

We have measured and stimulated particle flow through a single pore an d made comparisons with theory. The simulations are based on an experi mental system where particles suspended in an electrolyte are caused t o flow by pressure difference through a pore. Each particle in the por e gives rise to a pulse in the measured pore resistance. The pulse hei ght is proportional to the particle Volume and the purse width is give n by the particle velocity. In dilute solutions individual particle pu lses can be detected and analysed, but at higher concentrations the pu lses start to overlap and the signal looks like noise. Measured and si mulated signals are analysed in terms of Hurst's rescaled range (the R /S analysis; where R is the range and S the standard deviation) and th e power spectrum: The signal is sampled and we find a clear crossover from persistent behavior (Hurst exponent H similar or equal to 1) for short times corresponding to the fact that particles reside a finite t ime in the pore to an independent process (H similar or equal to 0.5) corresponding to the uncorrelated entry of particles into the pore. Th e calculated effective Hurst exponent depends on the time resolution ( sampling interval) used, but R/S curves for different sampling interva ls scale when reduced time (sampling interval divided by pulse width) is included in the analysis and yields a nice data collapse for experi ments on different types of particles, flow-rates, and pore sizes.