Figure 4: Power spectra of time series obtained by Discrete Fourier Transform.
From: Self-charging of identical grains in the absence of an external field
(a) Power spectrum of 
; (b) power spectrum of Δz(t). Main plots in (a) and (b) show breathing state: χe = η = 1, and insets show the non-breathing state: χe = 0.6, η = 1. Horizontal axes of power spectrum plots are identical.
