International Centre for Theoretical Sciences, Tata Institute of Fundamental Research

报告摘要：

Active turbulence --- the spatio-temporally complex motion of a dense suspension of microorganisms such as bacteria --- has gathered great traction recently as an intriguing class of emergent, complex flows, occurring in several living systems at the mesoscale, whose understanding lies at the interface of non-equilibrium physics and biology. However, are these low Reynolds number living flows really turbulent or just chaotic with structural, or even superficial, similarities with high Reynolds number (classical) inanimate turbulence? This is a vital question as the fingerprints of classical turbulence —-- universality, intermittency and chaos —-- makes it unique amongst the many different driven-dissipative systems. In this talk we address these questions with a focus on the issues of (approximate) scale-invariance, intermittency and maximally chaotic states and how they lead to anomalous diffusion in bacterial suspensions. In particular, we show the existing of a  critical level of activity beyond which the physics of bacterial flows become  universal, accompanied by maximally chaotic states which allow for efficient,  Levy-walk mediated foraging strategies.

Refs:

1. Intermittency, fluctuations and maximal chaos in an emergent universal state of active turbulence,  S. Mukherjee, R. K. Singh, M. James and Samriddhi Sankar Ray. Nature Physics 19, 891 (2023)

2. Lagrangian Manifestations of Anomalies in Active Turbulence, R. K. Singh, S. Mukherjee and Samriddhi Sankar Ray.  Physical Review Fluids 7, 033101 (2022)

3. Anomalous Diffusion and Levy Walks Distinguish Active Turbulence from Inertial Turbulence, S. Mukherjee,  R. K. Singh, M. James and Samriddhi Sankar Ray. Physical Review Letters 127, 118001 (2021)

报告人简介：

Samriddhi Sankar Ray is an Associate Professor at the International Centre for Theoretical Sciences of the Tata Institute of Fundamental Research (ICTS-TIFR) in Bangalore, India. Prior to this Samriddhi obtained his PhD in Physics from the Indian Institute of Science (IISc), Bangalore and then a short post-doctoral stint at Observatoire de la Cote d'Azur in Nice, France. His research interests, lying at the interface of statistical physics, applied mathematics and computational fluid dynamics, focusses on high Reynolds number fully-developed turbulence and turbulent transport. He has also worked extensively on problems of thermalisation of finite-dimensional ideal hydrodynamics as well as, most recently, low Reynolds number bacterial suspensions.

邀请人：彭毅