| dc.description.abstract | AbstractThe aim of this thesis is to invest the jamming state of active nematics system. Unlike thermal equilibrium system, active system shows rich phases and emergent patterns. Among these states, active jamming is happened in the high agent density where all of the local active force are balanced. We use surface swarming bacteria system to investigate the formation process and the local dynamics of this unique jamming state. Motility is one of the charming features of living organism. From physics point of view, active-matter is composed of large number of individual active agents with simple rules of movement leading to complex collective behaviors. Due to the experimental difficulties of manufacturing identical active agents, theoretical work leads the research work in this field. In our research, we use surface swarming bacteria as the active-material to study the emerging behavior of active nematics in two-dimension system. Vibrio alginolyticus is a marine bacterium with dual flagellar motor systems. This system is composed by a ?? + driven polar flagellum and several H + lateral flagella. The lateral flagella will only express in the environment with high viscosity, for example, the surface, and become the main source of swarming motility on the viscous surface. In our experiment, we use a mutant strain YM19 which have lateral flagella only to be the experimental material of self-propelled rods on 2D surface. Inoculating 0.5μl’s bacteria suspension on the 1% thin VC agar plate, YM19 will then spread out in 3~4 hours to form a 2D colony with mono-layer area where the jamming state will be formed later.
By custom-wrote image processing and particle tracking software, we are able to trace each single bacterium in this 2D jamming state. Our analysis is divided into three parts, global motion of jamming state, local motion of jamming state and global motion of jamming process. 1. Global motion of jamming state: The jamming state have several unique and special characteristics. Here, we calculate some global features such as velocity, density, trajectory, length and cluster pattern to represent the property of jamming state. 2. Local motion of jamming state: Although the jamming state looks generally caged, various local dynamics can be observed in the active jamming system. Here, we separated the local area into three types, dynamic area, restricted area and caged area. We chose two bacteria in a region once and calculate their MSD, relationship between body angle and velocity correlation. The results not only show the essential differences between these three areas but also reveal the effect of different rearrangement ability. 3. Global motion of jamming process: Besides knowing the detail of the jamming state bacteria, we are also curious about the origin of it. The time-lapse experiment in the same region was done for understanding the transition from unjammed to jammed state. As the agent density increase, the overall order increase while the average velocity drops. The local arrangement of order structures enhances the jamming condition. | en_US |