Gran Sasso Science Institute (GSSI), Via. F. Crispi 7, 67100, L'Aquila, Italy.
Scuola di Scienze e Tecnologie, Università di Camerino - via Madonna delle Carceri, 62032, Camerino, Italy.
Sci Rep. 2019 Feb 4;9(1):1386. doi: 10.1038/s41598-018-36824-z.
We study a system of interacting active particles, propelled by colored noises, characterized by an activity time τ, and confined by a single-well anharmonic potential. We assume pair-wise repulsive forces among particles, modelling the steric interactions among microswimmers. This system has been experimentally studied in the case of a dilute suspension of Janus particles confined through acoustic traps. We observe that already in the dilute regime - when inter-particle interactions are negligible - increasing the persistent time, τ, pushes the particles away from the potential minimum, until a saturation distance is reached. We compute the phase diagram (activity versus interaction length), showing that the interaction does not suppress this delocalization phenomenon but induces a liquid- or solid-like structure in the densest regions. Interestingly a reentrant behavior is observed: a first increase of τ from small values acts as an effective warming, favouring fluidization; at higher values, when the delocalization occurs, a further increase of τ induces freezing inside the densest regions. An approximate analytical scheme gives fair predictions for the density profiles in the weakly interacting case. The analysis of non-equilibrium heat fluxes reveals that in the region of largest particle concentration equilibrium is restored in several aspects.
我们研究了一个由有色噪声驱动的相互作用的活性粒子系统，其特征是活动时间 τ，并受到单阱非谐势的限制。我们假设粒子之间存在相互排斥的力，从而模拟微泳者之间的空间相互作用。在含有声阱限制的 Janus 粒子稀悬浮液的情况下，已经对该系统进行了实验研究。我们观察到，即使在稀相中 - 当粒子间相互作用可以忽略不计 - 增加持续时间 τ 也会将粒子推离势阱最小值，直到达到饱和距离。我们计算了相图（活性与相互作用长度），结果表明相互作用不会抑制这种离域现象，而是在最密集的区域中诱导出液体或固体状结构。有趣的是，观察到了一种再进入行为：从较小值开始增加 τ 会起到有效的升温作用，有利于流化；在更高的值下，当发生离域时，进一步增加 τ 会在最密集的区域中引起冻结。近似分析方案可以对弱相互作用情况下的密度分布进行合理预测。对非平衡热通量的分析表明，在最大粒子浓度区域，从多个方面恢复了平衡。
