Orientational dynamics of bacterial active fluids

The dynamics of bacterial active matter have caught wide attention due to their rich phenomenon in non-equilibrium physics as well as their biological importance. While theoretical models such as polar fluid model describe certain dynamics of bacterial active fluid well, an essential, yet not fully investigated problem is how single cell orientation, the direction of active energy input, distributes and interacts with flow in dense bacterial collective motion, typically induced by viscoelasticity. We build a variable-step multichannel imaging setup for the observation of fluorescent cell body, stained flagellar and phase contrast. We analyze orientation statistics such as polar order and nematic order in bacterial turbulence and channel flow. Our results reveal the intrinsic relation between cell orientation and collective flow and give insights on the viability of potential models.