Fig. 3.

Power spectral density (PSD) calculated for longitudinal (L) and transversal (T) oscillation modes for the hypertonic data presented in Fig. 2. The strongest peaks are indicated and the corresponding frequencies assigned. The inset presents linear dependence of higher harmonics and linear regression fit, which slope is equivalent to the basic frequency (R ² delivers determination coefficient; P < 0.0001 in all insets in Figs. 3, 4 and 5). Calculated total energy: see Table 3