Active matter encompasses systems whose individual consituents dissipate energy to exert propelling forces on their environment. This rapidly developing field harbors a dynamical phenomenology with no counterpart in passive systems. The extent to which this is rooted in the breaking of time-reversibility has recently triggered an important theoretical and experimental activity which is the focus of this review. Building on recent progress in the field, we disentangle the respective roles of the arrow of time and of the non-Boltzmann nature of steady-state fluctuations in single- and many-body active systems. We show that effective time-reversible descriptions of active systems may be found at all scales, and discuss how interactions, either between constituents or with external operators, may reveal the non-equilibrium nature of the microscopic source of energy. At a time when the engineering of active materials appears within our reach, this allows us to discuss to which extent methods stemming from equilibrium statistical mechanics may guide us in their design.
Linking Microscopic Reversibility to Macroscopic Irreversibility, Emphasizing the Role of Deterministic Thermostats and Simple Examples, At and Away From Equilibrium
Microscopic and Macroscopic Rayleigh-Benard Flows : Continuum and Particle Simulations, Turbulence, Fluctuations, Time Reversibility, and Lyapunov Instability
Conditional reversibility in nonequilibrium stochastic systems
对于服从马尔可夫动力学的离散状态随机系统，我们建立了Gallavotti为确定性系统[Ann. de l'Institut Henri Poincaré（A）70，429（1999）]获得的条件可逆性定理的对应定理。我们的结果表明，条件相反的熵产生值的随机轨迹相关的时间反转，在长时间的限制。换句话说，给定具有指定熵产生率$σ$的长轨迹，观察到特定事件序列的概率与给定以相反熵产生$-σ$为条件的轨迹，观察到时间反演的事件序列的概率相同，其中两个轨迹都是从相同的底层马尔可夫过程采样的。为了获得我们的结果，我们使用条件（“微正则”）和偏置（“正则”）合奏的非平衡轨迹之间的等价。我们提供了一个例子来说明我们的研究结果。
Microscopic Reversibility and Emergent Elasticity in Ultrastable Granular Systems
在最近的一篇论文[Phys. Rev. X 12，031021]中，我们报道了在受到小振幅循环剪切的剪切堵塞颗粒系统中的“超稳定”状态的实验观察。在这样的状态下，所有的颗粒位置和接触力在每个剪切循环之后被再现，使得应力和颗粒位置的选通图像看起来是静态的。在目前的工作中，我们报告进一步分析这些实验的数据，以表征全球和本地的超稳态响应在一个剪切周期内，而不仅仅是频闪的动态。我们发现，超稳定状态遵循幂律关系的剪切模量和压力的指数$β\approx 0.5$，让人想起附近的临界标度律堵塞。我们还研究了使用光弹性测量法测量的接触力的演变。我们发现，有两种类型的接触：非持久性接触，可逆地打开和关闭;和持久性接触，从来没有打开\yiqiu{and display no measurable sliding}。我们表明，非持久接触的紧急剪切模量作出不可忽略的贡献。我们还分析了应力张量的空间相关性，并将其与最近的颗粒固体的突发弹性理论，颗粒力学和动力学的矢量电荷理论（VCTG）[Phys. Rev. Lett. 125，118002，arXiv：2204.11811]。我们表明，我们的实验结果可以很好地拟合VCTG，假设单轴对称的接触网络。拟合结果表明，超稳态对外加应力的响应比原始剪切堵塞状态的响应更具有各向同性。我们的研究结果提供了重要的洞察力的机械性能的摩擦颗粒状固体剪切。
Instantaneous equilibrium Transport for Brownian systems under time-dependent temperature and potential variations: Reversibility, Heat and work relations, and Fast Isentropic process
