Infosys-ICTS Chandrasekhar Lectures
Ajay Sood (Indian Institute of Science, Bangalore)
Date & Time
09 August 2017, 16:00 to 17:00
Ramanujan Lecture Hall, ICTS Bangalore

Lecture 1: 7 August 2017, 16:00 to 17:00

Title: Microscopic Stochastic Heat Engines Using Nonequilibrium Bacterial Reservoirs.
Abstract: The conventional macroscopic heat engine, a device to convert thermal energy to mechanical energy, is a triumph of the understanding of classical thermodynamics over the last three centuries. In recent years, taking the heat engine concepts to microscopic scale, necessarily dominated by fluctuations, has led to the development of stochastic thermodynamics. The first experimental realization of microscopic heat engine was demonstrated by replacing piston-cylinder of a conventional engine by a time dependent optical laser trapping a colloidal particle in a thermal reservoir cycled between high and low temperatures[1]. The talk will discuss the recent experiments[2] on microscopic heat engines where the thermal reservoirs are replaced by out of equilibrium non-thermal reservoirs of varying activities (different non-Gausian noise statistics). Remarkably even for engines with the same energy input, differences in non-Gaussianity of reservoir noise results in distinct performances. The experiments bring out a message towards the fundamental insights into the functioning of engines operating out of equilibrium. These ongoing experiments will be presented related to coupled microscopic heat engines[3].

  1. V. Blickle and C. Bechinger, Realization of micrometer sized stochastic heat engine, Nat. Phys. 8, 143 (2012)
  2. Sudeesh Krishnamurthy, Subho Ghosh, Dipankar Chatterji, Rajesh Ganapathy and A.K. Sood, A Micrometer-sized Heat Engine Operating Between Bacterial Reservoirs. Nature Physics 2, 1134 (2016)
  3. Sudeesh Krishnamurthy, R. Ganapathy and A.K. Sood (2017).


Lecture 2: 8 August 2017, 16:00 to 17:00

Title: Single particle and collective behavior of self-propelled active particles: Fluctuation relation, Flocking and Sorting.
Abstract: This talk will discuss the experiments over the last few years using geometrically polar granular rods confined in 2D geometry, subjected to sinusoidal vertical oscillations which undergo noisy self-propulsion in a direction determined by their polarity. When surrounded by a medium of spherical beads, the active particle displays substantial negative fluctuations in its velocity. The speaker will discuss the nature of the large deviation function (LDF) for the velocity and the nonequilibrium fluctuation relation[1], including the recently probed isometric fluctuation-relation[2]. When a sufficient number of these active particles are put amidst the medium of spherical beads, a spectular emergent order called flocking is seen. Here a collective self-organized motion of the active particles in a single direction emerges without any central coordination, similar to what is seen in many living objects like ants, fishes, locusts, birds etc[3]. Even at very low coverage by the active particles, a sufficient concentration of the non-motile spherical beads leads to an emergence of flocking order. More recent results on the trapping of these active particles, leading to sorting of different types of active particles based on their dynamics will be presented[4].

  1. Nitin Kumar, S. Ramaswamy and A.K. Sood, Symmetry properties of the large deviation function of the velocity of a self-propelled polar particle, Phys. Rev. Lett. 106, 118001 (2011)
  2. N. Kumar, H. Soni, S. Ramaswamy and A.K. Sood, Anisotropic Isometric Fluctuations in experiment and theory on a self-propelled rod, Phys. Rev. E (Rap. Comm) 91, 030102 (R) (2015).
  3. Nitin Kumar, Harsh Soni, S. Ramaswamy and A.K. Sood, Flocking at a distance in active granular matter, Nature Communications, 5:4688/DOI:10.1038/ncomms5688 (3 September, 2014)
  4. Nitin Kumar, Harsh Soni, Rahul Kumar Gupta, Sriram Ramaswamy and A.K. Sood, Sorting motile rods by activity; Cond-mat. arXiv 1603.08535 (2016)


Lecture 3: 9 August 2017, 16:00 to 17:00

Title: Driven Soft Matter.
Abstract: Soft matter such as colloidal suspensions, gels and crystals under shear provides a rich playground for studying nonequilibrium physics. The talk will cover experimental work in this area, with an objective to bring out new phenomena. The speaker will present the shear driven crystallization above equilibrium freezing temperature[1], crystallization of defects in a novel random mesh phase[2] and directional grain growth in polycrystals[3]. The second part will cover yielding and mechanical memory in an amorphous phase. The signatures of nonequillibrium phase transitions at the yield point are seen in diverging time scales and onset of irreversibility, similar to the absorbing phase transition[4]. Recent work related to mechanical memory in amorphous films studied experimentally using varying strain oscillatory shear will be discussed[5].

  1. Vikram Rathee, Rema Krishnaswamy, Antara Pal, V.A Raghunathan, Marianne Imperor, Brigitte Pansu and A.K. Sood, A reversible shear-induced crystallization above equilibrium freezing temperature in a   lyotropic surfactant system, Proceedings of National Acad. Sciences (USA) 110, 14849-14854 (2013).
  2. Pradip Bera, Rema Krishnaswamy and A.K. Sood (2017)
  3. Shreyas Gokhale, K. Hima Nagamanasa, V. Santhosh, A.K. Sood and R. Ganapathy, Directional grain growth from shear-induced anisotropic kinetic roughening of grain boundaries, Proc. Nat. Acad. Sc. (USA) 109, 20314-20319 (2012).
  4. K. Hima Nagamanasa, S. Gokhale, A.K. Sood and R. Ganapathy, Experimental signatures of a non-equilibrium phase transition governing yielding of a soft glass, Phys. Rev. E 89, 062308 (2014); Pradip Bera,  A.K. Kandar, R. Krishnaswamy and A.K. Sood(2017).
  5. Srimayee Mukherji, N. Kandula, A.K. Sood and R. Ganapathy (2017).


This lecture series is part of Stochastic Thermodynamics, Active Matter and Driven Systems