Spatiotemporal dynamics of avalanche structural rearrangements through the interplay of structural heterogeneities, multiscale thermal acoustic wave excitations, and their intermittent synchronizations in cold dusty plasma liquids around freezing

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题名:	Spatiotemporal dynamics of avalanche structural rearrangements through the interplay of structural heterogeneities, multiscale thermal acoustic wave excitations, and their intermittent synchronizations in cold dusty plasma liquids around freezing
作者:	胡皓為;Hu, Hao-Wei
贡献者:	物理學系
关键词:	微粒電漿;微觀冷液體;基礎物理
日期:	2022-01-10
上传时间:	2022-07-13 19:38:54 (UTC+8)
出版者:	國立中央大學
摘要:	雪崩性行為(Avalanche activities)廣泛存在於不同強耦合系統之中，例如受壓固體或玻璃、地震、金融危機、大範圍停電、傳染病爆發、以及雪山上的雪崩，這類系統蘊含強交互作用及背景擾動，當一局部事件被激發，其影響能藉強交互作用傳遞，在時空間形成具冪次律(power law)大小分布群簇，了解雪崩性行為的普世動力學行為是重要議題，發展能預測具極端尺寸群簇之指標亦尤為重要。至微觀尺度，接近凝固點之液體為一強耦合系統，交互作用及熱擾動的競爭下，冷液體具不同大小及晶格方向之晶粒(crystalline ordered domains)，其各晶粒間蘊含缺陷團簇以補償不對齊晶格線。粒子傾向蘊含小振幅擾動，因其近鄰形成之位能井。當背景生成建設性熱擾動，粒子受其激發以脫離位能井並集體躍動(cooperative hopping)，造成雪崩性結構重整，研究冷液體中結構重整能幫助了解雪崩性事件的普世行為。本論文將藉由實驗系統，微粒電漿冷液體，從多尺度聲波角度探討上述議題。利用希爾伯特-黃轉換(Hilbert-Huang transform)，拆解粒子間的相對縱向位移成多尺度聲波模態，以取得傳遞於冷液體中聲波之動力資訊。發現結構重整主發於由相鄰同方向旋轉晶粒誘發之剪切帶(shear strip)上，剪切帶上的局部結構重整沿其錯位缺陷(dislocation defect)之柏格斯向量(Burgers vector)滯-滑式(stick-slip)傳遞，並在時空間形成具冪次律分布樹枝狀團簇，於時空間傳播之多尺度聲波模態的相位同步(synchronization)及不同步(desynchronization)為剪切帶滯-滑式傳遞之關鍵。大型團簇傾向發生於具多個且散佈之錯位缺陷區域，在團簇發生前，已激發之低頻聲波模態逐步變形區域結構，進而誘發高頻聲波模態激發，促成後續不同尺度聲波模態的相位同步及團簇發生，證明錯位缺陷及低頻聲波模態振幅為預測大型團簇之關鍵。 ;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.
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