Rheology and microrheology of homogeneously driven granular matter

我们提出了在致密颗粒系统中的缓慢的非平衡动力学的调查。为了克服颗粒之间碰撞引起的耗散，颗粒状颗粒应被均匀地驱动。在这样的系统中观察到的动力学的一些功能让人想起从平衡系统已知的玻璃态动力学。首先，这种稳定状态的特点，在理论，计算机模拟和实验。第二，在驱动稳态内的单个粒子将被额外的外力拉动。与热系统相反，振动的颗粒物质在稳定状态下已经失去平衡。此外，虽然低力的响应机制可能被认为等同于经典的线性响应机制，但在颗粒的情况下，低力已经探测到非平衡动力学。我们希望得到有效的波动耗散关系的线性政权和扩大调查的非线性政权具有较高的拉力。实验实现计划为一个二维系统的振动台上的探针粒子可以被拉与恒定的速度和恒定的力。应使用适用于颗粒碰撞的事件驱动算法进行计算机模拟。理论描述将依赖于投影算子技术和颗粒动力学理论的结合。

We propose the investigation of the slow off-equilibrium dynamics in dense granular systems. To overcome the dissipation caused by the collisions among the particles, the granular particles shall be driven homogeneously. Some features of the dynamics observed in such systems are reminiscent of glassy dynamics known from equilibrium systems. First, this steady state shall be characterized in theory, computer simulation, and experiment. Second, a single particle within the driven steady state shall be pulled by an additional external force. In contrast to thermal systems, vibrated granular matter is out-of-equilibrium already in the steady state. Also, while the response regime of low forces might be considered equivalent to the classical linear response regime, in the granular case low forces already probe non-equilibrium dynamics. We want to derive effective fluctuation-dissipation relations in the linear regime and extend the investigation to the nonlinear regime with higher pulling forces. The experimental realization is planned for a two-dimensional system on a vibrating table where the probe particle can be pulled both with constant velocity and constant force. The computer simulations shall be done using event-driven algorithms adapted for granular collisions. The theoretical description will rest on a combination of projection operator techniques and granular kinetic theory.