活性凝胶中的非局域涨落关联
Non-local fluctuation correlations in active gels
摘要：
许多活性物质和生物系统被嵌入的试剂驱动远离平衡，这些试剂自发地产生力并扭曲周围的材料。探测和表征这些非热涨落对于理解此类系统的性质和行为至关重要。在这里，我们提出了一个数学程序来估计力产生剂的局部行动所观察到的波动位移场。活性剂被建模为定向力偶极或各向同性压缩焦点，并且它们所作用的基质被假定为可压缩弹性连续体或耦合网络-溶剂系统。在一个单一的点和点之间的任意距离分离得到的相关性，给出了三个独立的波动模式，可以测试与微观流变学实验。由于定向偶极子和各向同性压缩焦点给这些波动模式不同的贡献，比率分析使我们能够表征力发生器。我们还预测和实验发现一个高频率的弹道制度，所产生的个别力产生的事件的形式缓慢建立的应力，然后快速但有限的衰减。最后，我们提供了一个定量的统计模型来估计平均丝张力从这些非热的波动，这导致主动网络的硬化。
英文摘要：
Many active materials and biological systems are driven far from equilibrium by embedded agents that spontaneously generate forces and distort the surrounding material. Probing and characterizing these athermal fluctuations is essential for understanding the properties and behaviors of such systems. Here we present a mathematical procedure to estimate the local action of force-generating agents from the observed fluctuating displacement fields. The active agents are modeled as oriented force dipoles or isotropic compression foci, and the matrix on which they act is assumed to be either a compressible elastic continuum or a coupled network-solvent system. Correlations at a single point and between points separated by an arbitrary distance are obtained, giving a total of three independent fluctuation modes that can be tested with microrheology experiments. Since oriented dipoles and isotropic compression foci give different contributions to these fluctuation modes, ratiometric analysis allows us characterize the force generators. We also predict and experimentally find a high-frequency ballistic regime, arising from individual force generating events in the form of the slow build-up of stress followed by rapid but finite decay. Finally, we provide a quantitative statistical model to estimate the mean filament tension from these athermal fluctuations, which leads to stiffening of active networks.
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