Thermodynamics of Microscopic Systems far from Equilibrium

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My PhD will consist of a number of projects themed around the study of microscopic far-from-equilibrium systems. As highlighted in the EPSRC's physical sciences strategy, interest in the physics of emergent phenomena and non-equilibrium thermodynamics has grown dramatically in recent decades. Whilst great advances have been made in our understanding of large, complex systems, certain fundamental questions about the underlying microscopic physics remain unanswered. One objective of my research is to better understand the relationship between the level of detail at which a system is described and the thermodynamic properties of that system. Certain non-equilibrium systems appear "equilibrium-like" when parts of their evolution are hidden. This is a practical as well as a theoretical concern; observers rarely have access to every microscopic detail of experimental systems. In my research I seek to quantify the entropy production rate, a measure of distance from equilibrium, of a simple system under conditions of complete and partial knowledge. Whereas previous research has sought to place general bounds on the entropy production in these partially hidden systems, we employ a perturbative approach to quantify the entropy production rate more precisely. It is hoped that this work will have be of practical importance to experimental scientists seeking to quantify the energetics of cells, bacteria and other forms of life. In parallel to this, I am interested in the extraction of useful energy from swimming microorganisms. The prospect of building an, "active engine," powered by microscopic bacteria has gathered interest in recent years. Myself and collaborators within Imperial College have placed theoretical bounds on the maximum amount of work that could hypothetically be extracted from a single stochastically self-propelling cell, under the realistic constraint that its self-propulsion cannot be directly measured. The potential impact of this work is evident; it's hoped that active engines could provide a flexible, endlessly sustainable source of energy. They have even been proposed as a possible power source for spacecraft and satellites.This work aligns closely with the EPSRC strategic theme of, "Emergence and physics far from equilibrium". I study the microscopic, far-from-equilibrium physical systems which constitute the building blocks of the emergent phenomena which arise in the study of active matter, such as flocking and motility-induced phase separation. Through this bottom-up approach, I hope to offer a contribution to our understanding and ability to model realistic non-equilibrium systems.