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Theoretical physicists working at a blackboard collaboration pod in the Beecroft building.
Credit: Jack Hobhouse

Prof Ramin Golestanian

Professor of Theoretical Condensed Matter Physics

Sub department

  • Rudolf Peierls Centre for Theoretical Physics

Research groups

  • Condensed Matter Theory
Ramin.Golestanian@physics.ox.ac.uk
Telephone: 01865 273974
Rudolf Peierls Centre for Theoretical Physics, room 70.28
Max Planck Institute for Dynamics and Self-Organization
Oxford Podcast (2014): Living Matter & Theo Phys
Oxford Podcast (2017): The bacterial Viewpoint
  • About
  • Teaching
  • Publications

Entropy production and thermodynamic inference for stochastic microswimmers

ArXiv 2310.15311 (2023)

Authors:

Michalis Chatzittofi, Jaime Agudo-Canalejo, Ramin Golestanian
Details from ArXiV

A DNA turbine powered by a transmembrane potential across a nanopore.

Nature nanotechnology (2023)

Authors:

Xin Shi, Anna-Katharina Pumm, Christopher Maffeo, Fabian Kohler, Elija Feigl, Wenxuan Zhao, Daniel Verschueren, Ramin Golestanian, Aleksei Aksimentiev, Hendrik Dietz, Cees Dekker

Abstract:

Rotary motors play key roles in energy transduction, from macroscale windmills to nanoscale turbines such as ATP synthase in cells. Despite our abilities to construct engines at many scales, developing functional synthetic turbines at the nanoscale has remained challenging. Here, we experimentally demonstrate rationally designed nanoscale DNA origami turbines with three chiral blades. These DNA nanoturbines are 24-27 nm in height and diameter and can utilize transmembrane electrochemical potentials across nanopores to drive DNA bundles into sustained unidirectional rotations of up to 10 revolutions s-1. The rotation direction is set by the designed chirality of the turbine. All-atom molecular dynamics simulations show how hydrodynamic flows drive this turbine. At high salt concentrations, the rotation direction of turbines with the same chirality is reversed, which is explained by a change in the anisotropy of the electrophoretic mobility. Our artificial turbines operate autonomously in physiological conditions, converting energy from naturally abundant electrochemical potentials into mechanical work. The results open new possibilities for engineering active robotics at the nanoscale.
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Dynamical Pattern Formation without Self-Attraction in Quorum-Sensing Active Matter: The Interplay between Nonreciprocity and Motility.

Physical review letters 131:14 (2023) 148301

Authors:

Yu Duan, Jaime Agudo-Canalejo, Ramin Golestanian, Benoît Mahault

Abstract:

We study a minimal model involving two species of particles interacting via quorum-sensing rules. Combining simulations of the microscopic model and linear stability analysis of the associated coarse-grained field theory, we identify a mechanism for dynamical pattern formation that does not rely on the standard route of intraspecies effective attractive interactions. Instead, our results reveal a highly dynamical phase of chasing bands induced only by the combined effects of self-propulsion and nonreciprocity in the interspecies couplings. Turning on self-attraction, we find that the system may phase separate into a macroscopic domain of such chaotic chasing bands coexisting with a dilute gas. We show that the chaotic dynamics of bands at the interfaces of this phase-separated phase results in anomalously slow coarsening.
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Lorentz Reciprocal Theorem in Fluids with Odd Viscosity.

Physical review letters 131:17 (2023) 178303

Authors:

Yuto Hosaka, Ramin Golestanian, Andrej Vilfan

Abstract:

The Lorentz reciprocal theorem-that is used to study various transport phenomena in hydrodynamics-is violated in chiral active fluids that feature odd viscosity with broken time-reversal and parity symmetries. Here, we show that the theorem can be generalized to fluids with odd viscosity by choosing an auxiliary problem with the opposite sign of the odd viscosity. We demonstrate the application of the theorem to two categories of microswimmers. Swimmers with prescribed surface velocity are not affected by odd viscosity, while those with prescribed active forces are. In particular, a torque dipole can lead to directed motion.
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Nonreciprocal interactions give rise to fast cilium synchronization in finite systems.

Proceedings of the National Academy of Sciences of the United States of America 120:40 (2023) e2307279120

Authors:

David J Hickey, Ramin Golestanian, Andrej Vilfan

Abstract:

Motile cilia beat in an asymmetric fashion in order to propel the surrounding fluid. When many cilia are located on a surface, their beating can synchronize such that their phases form metachronal waves. Here, we computationally study a model where each cilium is represented as a spherical particle, moving along a tilted trajectory with a position-dependent active driving force and a position-dependent internal drag coefficient. The model thus takes into account all the essential broken symmetries of the ciliary beat. We show that taking into account the near-field hydrodynamic interactions, the effective coupling between cilia even over an entire beating cycle can become nonreciprocal: The phase of a cilium is more strongly affected by an adjacent cilium on one side than by a cilium at the same distance in the opposite direction. As a result, synchronization starts from a seed at the edge of a group of cilia and propagates rapidly across the system, leading to a synchronization time that scales proportionally to the linear dimension of the system. We show that a ciliary carpet is characterized by three different velocities: the velocity of fluid transport, the phase velocity of metachronal waves, and the group velocity of order propagation. Unlike in systems with reciprocal coupling, boundary effects are not detrimental for synchronization, but rather enable the formation of the initial seed.
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