Density fluctuations and energy spectra of 3D bacterial suspensions
Density fluctuations and energy spectra of 3D bacterial suspensions
复制标题
3D 细菌悬浮液的密度波动和能谱
DOI：
10.1039/d1sm01183a
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发表时间：
2021
期刊：
影响因子：
3.4
通讯作者：
Cheng, Xiang
中科院分区：
文献类型：
--
作者：
Liu, Zhengyang;Zeng, Wei;Ma, Xiaolei;Cheng, Xiang
巨大的数字波动通常被认为是活跃流体出现的非平衡动力学的标志。然而，迄今为止，这些异常密度波动仅在二维干活性系统中进行了实验报道。在这里，我们研究了散装大肠杆菌悬浮液的密度波动，这是三维（3D）湿活性流体的范例。我们的实验证明了 3D 细菌悬浮液中巨大数量波动的存在并量化了比例关系。令人惊讶的是，在过渡到主动湍流之前，低浓度悬浮液中的反常结垢在小尺度上持续存在，反映了 3D 湿活性流体的流体动力相互作用的长程性质。为了说明密度波动的起源，我们测量了悬浮液流的能谱，并探索了主动湍流的稳态和瞬态中的密度-能量耦合。在广泛的长度尺度上发现了密度涨落和能谱之间的尺度不变、密度无关的相关性。此外，我们的实验表明，细菌湍流的能谱表现出 3D 活性向列流体的缩放，挑战了将致密细菌悬浮液视为活性极性流体的普遍观点。
Giant number fluctuations are often considered as a hallmark of the emergent nonequilibrium dynamics of active fluids. However, these anomalous density fluctuations have only been reported experimentally in two-dimensional dry active systems heretofore. Here, we investigate density fluctuations of bulk Escherichia coli suspensions, a paradigm of three-dimensional (3D) wet active fluids. Our experiments demonstrate the existence and quantify the scaling relation of giant number fluctuations in 3D bacterial suspensions. Surprisingly, the anomalous scaling persists at small scales in low-concentration suspensions well before the transition to active turbulence, reflecting the long-range nature of hydrodynamic interactions of 3D wet active fluids. To illustrate the origin of the density fluctuations, we measure the energy spectra of suspension flows and explore the density–energy coupling in both the steady and transient states of active turbulence. A scale-invariant density-independent correlation between density fluctuations and energy spectra is uncovered across a wide range of length scales. In addition, our experiments show that the energy spectra of bacterial turbulence exhibit the scaling of 3D active nematic fluids, challenging the common view of dense bacterial suspensions as active polar fluids.