| dc.description.abstract | Avalanche activities commonly occur in many strongly coupled systems. Cracking in stressed solids or glasses, earthquakes in seismic systems, financial crisis, blackouts of the electrical power network, epidemic spreading, and avalanches flowing down the mountains are good examples. These many-body systems typically possess heterogeneous structures and associated complicated interactions between the elements, which serve as channels for propagating the information. Once a local source is excited by a certain perturbation, it can spread and terminate in the network formed by those strongly coupled elements. These avalanche-type events thereby form clusters with various sizes and the associated cluster size distribution typically follows a power-law distribution. Investigating the generical dynamical behavior of avalanche activities is an important but challenging issue. In particular, identifying the precursor of the extreme avalanche activities with extreme cluster sizes is very important for preventing the great loss caused by the catastrophic events mentioned above.
Down to the microscopic level, the cold liquid close to the freezing point is also a strongly coupled system. The competition between mutual interaction and the reduced thermal agitation causes the formation of crystalline ordered domains with various sizes and orientations, which are surrounded by defect clusters due to the lattice mismatch. Dynamically, dust particles temporally exhibit small-amplitude rattling in the caging well set by neighbors. The cooperative hopping of particles rearranging the local structure and spreading in the xyt space can be excited once the constructive perturbation is accumulated. These avalanche-type behaviors make the cold liquid system a good model system for investigating the generic dynamical behavior of avalanche activities.
In this work, we experimentally investigate avalanche activities and, especially, extreme avalanche activities from the view of multiscale-acoustic waves, using a quasi-2D cold dusty plasma liquid as the experimental platform. The cold dusty plasma liquid can be formed by negatively charged particles suspended in a low-pressure Ar rf discharge. The particles with 7 mum diameter can be directly captured by a top view CCD with a standard optical microscope. By tracking local structural rearrangement sites induced by cooperatively hopping particles, avalanche activities in the form of structural rearrangement clusters with various sizes in the xyt space can be identified. By multidimensional complementary ensemble empirical mode decomposition from Hilbert-Huang transform, the relative transverse displacements of the dust particles are decomposed into traveling wave modes with different spatiotemporal scales. It is found that structural rearrangement clusters exhibit a power-law cluster size distribution. Larger clusters with sizes in the distribution tail are formed by networks of dendritic shear strips associated with co-rotating crystalline domains. The shear strip can propagate along the Burgers vector of the dislocation defect in a stick-slip fashion. The phase synchronization and desynchronization of the large-amplitude traveling wave modes with different scales are the keys for the stick-slip type propagation. If a region exhibits widely-distributed dislocation defects, it facilitates the excitation of the low-frequency wave modes that can further deteriorate the local structure without changing the topology. This feedback loop with the excitation of high-frequency wave modes causes the sequential excitation from low to high-frequency modes. The average local structural order, defect number, and the amplitude of the low-frequency modes can serve as reliable precursors of the extreme clusters. | en_US |