This award supports theoretical research and education at the interface of statistical mechanics and biology. The fundamental understanding of nonequilibrium systems will be advanced thorough the identification and study of a real world biological example that is accessible to experiment. The research contributes to the development and extension of theories of equilibrium statistical mechanics to produce a theoretical structure that both matches experiment and maintains the fundamental correctness required for physics laws.
The model system for which theory will be developed and applied is an active suspension of swimming bacteria. The dynamical study includes as an essential aspect the response of the statistical distribution of the bacteria to stimuli and determines their evolution with time in collective fashion.
The model active system, a bacterial bath, consists of a population of rod-like motile or self-propelled bacteria suspended in a fluid environment. This is a non-equilibrium version of lyotropic liquid crystals with the generalization of driven diffusive dynamics. The dynamics of a bacterial bath is studied using coarse-grained effective descriptions, such as phenomenological hydrodynamic equations, with appropriate modifications to the equations of its equilibrium counterpart - a lyotropic crystal. Theory development includes (i) formulating the two-fluid hydrodynamical equations for lyotropic liquid crystals to describe the microrheology of the liquid crystal and the effects of state-dependent dissipative coefficient on the pretransitional dynamics and (ii) deriving hydrodynamic equations for an active bacterial bath by generalizing the equilibrium counterpart. Combined with the theoretical framework for the microrheology of active systems, to which the PI is the principal contributor, it is proposed to explain experimental measured quantities, such as the stress-fluctuation spectrum observed in microrheology experiments on bacterial baths. Theoretical development are directly related to far-from-equilibrium issues, such as (i) the non-equilibrium analogs of the depletion interaction, (ii) the validity of the Fluctuation Theorem in an active system, (iii) derivations of hydrodynamic equations from a mesoscopic description of interacting bacteria, and (iv) a substantiation of the hydrodynamic equations with computational models, in order to address nonlinear regimes.
The research includes synergistic applications of theoretical concepts and techniques, that are derived from statistical physics and stochastic processes, to real experimental situations. The projects are theoretically important for providing a more accurate and complete description of active systems. The involvement of students in the research advances their education and forms the basis for dissertation research.
NON-TECHNICAL SUMMARY:
This award supports theoretical research and education at the interface of statistical mechanics and biology. The research focuses on the study of a real biological system to advance fundamental understanding of systems that are not in equilibrium. The PI seeks to develop a general theoretical framework that extends our comparatively well-developed theory of unchanging equilibrium systems to describe systems that are out of equilibrium, like living things.
The model system for which theory will be developed and applied is an active suspension of swimming bacteria. The dynamical study includes as an essential aspect the response of the bacteria to stimuli and how the billions of individuals that make up the system evolve with time in a collective manner.
The model active system, a bacterial bath, consists of a population of rod-like self-propelled bacteria suspended in a fluid. The dynamics of a bacterial bath is studied theoretically using descriptions that do not attempt to represent each individual component but instead characterize properties of regions and then identify regional interaction that lead to equation similar to those encountered in the theory of flow of fluids. The component particle, bacteria, being themselves moving are more complex than the component atoms and molecules of a normal fluid, so the theoretical development of this new fluid flow model must identify appropriate modifications to the equations.
The research includes synergistic applications of theoretical concepts and techniques, that are derived from statistical physics and random processes, to real experimental situations. The projects are theoretically important for providing a more accurate and complete description of systems with self actuated component parts. The involvement of students in the research advances their education and forms the basis for dissertation research.
This is fundamental research that contributes to developing general principles that can be applied to understand aspects of seemingly diverse systems that are out of equilibrium, from the molecular processes that form the basis of life to granular matter to the weather to the structure of the universe. It also contributes to the understanding of the physical basis of life with potential consequences for future medicine.
