Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
Phys Rev E. 2018 May;97(5-1):052613. doi: 10.1103/PhysRevE.97.052613.
We numerically examine ballistic active disks driven through a random obstacle array. Formation of a pinned or clogged state occurs at much lower obstacle densities for the active disks than for passive disks. As a function of obstacle density, we identify several distinct phases including a depinned fluctuating cluster state, a pinned single-cluster or jammed state, a pinned multicluster state, a pinned gel state, and a pinned disordered state. At lower active disk densities, a drifting uniform liquid forms in the absence of obstacles, but when even a small number of obstacles are introduced, the disks organize into a pinned phase-separated cluster state in which clusters nucleate around the obstacles, similar to a wetting phenomenon. We examine how the depinning threshold changes as a function of disk or obstacle density and find a crossover from a collectively pinned cluster state to a disordered plastic depinning transition as a function of increasing obstacle density. We compare this to the behavior of nonballistic active particles and show that as we vary the activity from completely passive to completely ballistic, a clogged phase-separated state appears in both the active and passive limits, while for intermediate activity, a readily flowing liquid state appears and there is an optimal activity level that maximizes the flux through the sample.
我们通过数值方法研究了在随机障碍物阵列中驱动的弹道主动盘。与被动盘相比，主动盘在障碍物密度低得多的情况下会形成钉扎或堵塞状态。作为障碍物密度的函数，我们确定了几个不同的相，包括去钉扎的涨落簇态、钉扎的单簇或堵塞态、钉扎的多簇态、钉扎的凝胶态和钉扎的无序态。在较低的主动盘密度下，在没有障碍物的情况下会形成漂移的均匀液体，但即使引入少量障碍物，盘也会在障碍物周围形成钉扎的相分离簇态，类似于润湿现象。我们研究了去钉扎阈值如何随盘或障碍物密度的变化而变化，并发现随着障碍物密度的增加，从集体钉扎的簇态到无序的塑性去钉扎转变的交叉。我们将这与非弹道主动粒子的行为进行了比较，并表明随着我们从完全被动到完全弹道的活性变化，在主动和被动极限中都会出现堵塞的相分离状态，而对于中间活性，会出现易于流动的液体状态，并且存在最佳的活性水平，可最大限度地提高通过样品的通量。
