細菌在固體表面以側鞭毛移動的運動模式稱為蜂擁，蜂擁中的細菌具有集體運動和類流體的行為。而在蜂擁菌群中，擴散是主要傳遞化學和營養物質等被動粒子的途徑。由於蜂擁中的溶藻弧菌具有類似蛇的特殊型態和前後來回的運動，我們在此研究被動粒子在蜂擁溶藻弧菌菌群中的運動。 在此論文中，我們培養出了二維的蜂擁溶藻弧菌，並加入1 微米的聚苯乙烯作為被動粒子。根據聚苯乙烯粒子的運動軌跡，我們計算出方均根位移和在給定時差下位移的機率密度函數。方均根位移和位移的機率密度函數顯示出此蜂擁菌群為被動粒子運動中兩種雜訊的來源。其中一種雜訊對應到粒子的線性運動模式，此模式具有較長的持久長度和較短的相關時間；而另一種雜訊則對應到粒子的擾動模式，此模式則有較短的持久長度和較長的相關時間。我們因此建立了結合兩個 奧恩斯坦-烏倫貝克過程的模型來解釋被動粒子的運動。最後，藉由比較粒子移動方向和粒子相鄰細菌的長軸方向，我們歸納出線性運動發生在當粒子直接被整齊排列的細菌推動時；而粒子的擾動則是由於細菌的隨機排列。;Swarming bacteria, migrating on the solid surface with lateral flagella, show collective motion and fluid-like behavior. In the swarming bacteria motility, diffusion becomes a main process to deliver cargoes like chemicals or nutrients. Here, we investigate the dynamics of passive tracers in the swarming Vibrio alginolyticus bath, because Vibrio alginolyticus has the particular properties such as the snake-like morphology, and forward and backward motion. In this work, we build up a two-dimensional swarming Vibrio alginolyticus bath with 1 μm polystyrene beads. From the trajectories of polystyrene beads, we calculate the mean squared displacement (MSD) and the probability density function (PDF) of the displacement of a single particle at the given time lag. The MSD and PDF reveal that the swarming bath is the source of two noises on passive tracers. One type of the noises, the linear motion, has long persistence length but short correlation time, and the other, the fluctuating motion, has short persistence length but long correlation time. We model this phenomenon as two combined Ornstein-Uhlenbeck process. Finally, by comparing the particle direction to the averaged long-axis direction of neighbor bacteria, we find that the linear motion is resulted from the direct pushing by the spatially well-aligned bacteria and the fluctuating motion is due to the random orientation of bacteria.
