Fig. 2
Fluidization of the granular medium at a high-filling fraction Φ = 0.679. The particles now fill the whole sample cell and hexagonal order can be observed on the ground and in microgravity (a). The distributions of the measured transmitted intensities follow Γ-distribution, which are predicted for intensity fluctuations emerging from random phase shifts (b). The IACFs accordingly decay in a single, nearly exponential decay, with no measurable contributions from local packing fraction fluctuations (c). Although the samples are forced to take the same filling fraction Φ and packing fraction ϕ in both the cases, the IACFs do not superpose. The amplitude \(\tilde E\) of the IACF on the ground is only half as high as the amplitude measured in microgravity. Also shown in c are the autocorrelation functions measured samples at Φ = 0.68, which is achieved with a minute compression by the piston of 20 μm compared to Φ = 0.679. No decay in correlation can be observed, thus the samples become fully arrested
