复杂环境中活性粒子的目标搜索
Target search of active particles in complex environments
AI总结：
本文将转移路径理论及转移路径采样算法推广到非平衡活性粒子系统，系统表征了活性布朗粒子的目标搜索路径系综，并推广承诺函数概念，通过樟脑自推进圆盘实验验证了理论。
摘要：
微型游泳体是一类微观活性智能体，能够从周围环境中获取能量并将其转化为自推进与定向运动。这一独特特征使它们成为打破微观可逆性的非平衡系统。在复杂环境中寻找特定目标对于这些智能体至关重要，因为这一能力被用于多种目的，从觅食获取营养到逃避潜在威胁。本文对微型游泳体在复杂环境中探索时的目标搜索过程进行了详细研究。为此，我们将转移路径理论——对转移过程的严格统计力学描述——推广到目标搜索问题。本论文的主要成果之一是将转移路径采样（TPS）算法推广到非平衡系统；该算法最初是为模拟被动系统中的稀有转移而设计的。TPS算法的运行依赖于微观可逆性，因此将其推广到缺乏细致平衡和微观可逆性的非平衡系统一直是一个重大挑战。在这项工作中，我们将TPS算法推广到活性布朗粒子这一微型游泳体的典型模型的情形，并首次深入认识了这些智能体所探索的反直觉目标搜索路径。本论文的第二个成果是对活性粒子在能量景观中探索时的目标搜索路径系综进行了系统表征。本博士论文的第三个也是最后一个原创性贡献是将承诺函数的概念推广到目标搜索问题，并利用樟脑自推进圆盘的实验对我们的理论进行了验证。
英文摘要：
Microswimmers are microscopic active agents capable of harvesting energy from the surrounding environment and converting it into self-propulsion and directed motion. This peculiar feature characterizes them as out-of-equilibrium systems that break microscopic reversibility. The problem of finding a specific target in a complex environment is essential for these agents since it is employed for a variety of purposes, from foraging nourishment to escaping potential threats. Here, we provide a detailed study of the target search process for microswimmers exploring complex environments. To this end, we generalize Transition Path Theory, the rigorous statistical mechanics description of transition processes, to the target-search problem. One of the main results of this thesis is the generalization to non-equilibrium systems of the Transition Path Sampling (TPS) algorithm, which was originally designed to simulate rare transitions in passive systems. The TPS algorithm relies on microscopic reversibility for its functioning, therefore its generalization to out-of-equilibrium systems lacking detailed balance and microscopic reversibility has remained a major challenge. Within this work, we generalize the TPS algorithm to the case of an active Brownian particle, i.e. a paradigmatic model for microswimmers, and we obtain a first insight into the counterintuitive target-search pathways explored by these agents. The second result of this thesis is a systematic characterization of the target-search path ensemble for an active particle exploring an energy landscape. The third and final original contribution of this Ph.D. thesis is the generalization of the concept of the committor function to target-search problems, with a validation of our theory against experiments of a camphor self-propelled disk.
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