Active systems are driven out of equilibrium by exchanging energy and momentum with their environment. This endows them with anomalous mechanical properties that are reviewed in this Colloquium. The case of dry scalar active matter is considered, which encompasses systems whose large-scale behaviors are entirely captured by their density—a scalar field. Arguably the simplest of active-matter systems, they have attracted considerable attention due to their unusual properties when put in contact with boundaries, inclusions, tracers, or disordered potentials. Indeed, studies of the mechanical pressure of active fluids and of the dynamics of passive tracers have shown that active systems impact their environment in nontrivial ways, for example, by propelling and rotating anisotropic inclusions. Conversely, the long-range density and current modulations induced by localized obstacles show how the environment can have a far-reaching impact on active fluids. This is best exemplified by the propensity of bulk and boundary disorder to destroy bulk phase separation in active matter, thereby showing active systems to be much more sensitive to their surroundings than passive ones. This Colloquium aims to provide a unifying perspective on the rich interplay between active systems and their environments.

中文翻译：

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专题讨论会：标量活性物质中的包含物、边界和无序


主动系统通过与环境交换能量和动量而失去平衡。这赋予了它们异常的机械性质，这些性质将在本次研讨会中进行回顾。考虑了干标量活性物质的情况，它包括其大规模行为完全由其密度（标量场）捕获的系统。可以说是最简单的活性物质系统，由于它们在与边界、内含物、示踪剂或无序电位接触时具有不寻常的特性，因此引起了相当大的关注。事实上，对主动流体的机械压力和被动示踪剂动力学的研究表明，主动系统以非微不足道的方式影响其环境，例如，通过推动和旋转各向异性内含物。相反，局部障碍物引起的长距离密度和电流调制表明环境如何对活性流体产生深远影响。体和边界无序破坏活性物质中体相分离的倾向就是最好的例证，从而表明主动系统比被动系统对周围环境更敏感。本次研讨会旨在为主动系统与其环境之间的丰富相互作用提供一个统一的视角。