Research Projects
Active systems are systems where the microscopic constituents are capable of transducing its internal energy or energy from surrounding to deliberate motion. I have been working on many such systems ranging from Flocking to Naming game, active Brownian systems to modelling bio-mechanical phenomena observed in biological systems. Tissue Folding: 1. During embryonic development of Drosophila, the epithelial tissue has been observed to bend downward from the dorsal side. This has been understood to be due to change in myosin II concentration dependent apical contraction and/or the differential positioning of the adherent junctions. Independent of the chemical cues, we assume the mechanical reason would be the same. We prescribe a physical model of a cellular monolayer using the Phase Field prescription to observe the folding phenomena and to understand the role of different mechanical forces. 2. We further investigate the role of mechanical force generation by microtubule-dynein assembly in maintaining the apical dome shape, helping bear compressive stresses. Also the role of anchoring proteins like patronin seems to be crucial in the control of the cellular shapes within the epithelial tissue during morphogenesis. Collective Cell Migration and Structure Formation: Fascinating structure formation and dynamics in various different cellular aggregates is understood to be triggered by chemical and/or mechanical cues present in the system. We present a detailed understanding of how a collection of mutant Dicty cells, lacking chemotactic activity, behave in a certain way in different density regimes. We propose a physical model using Overdamped Langevin dynamics to understand the roles of different interaction terms in the emergence of the structures. Also we relate the different structures observed in low and high density from the perspective of phase transition. We establish that the structures observed in different densities are nothing but an intermediate phase which instigate the symmetry breaking during the transition to an ordered phase. Active Brownian system: An active Brownian system interacting via a soft core steric repulsion and an nematic alignment shows interesting phenomena as mentioned: 1) Isotropic-Nematic Transition: An isotropic state is where the system is not aligned and the particles are random as a whole. With increasing alignment strength (or with decreasing noise strength) the system reaches a nematic phase where all the particles are aligned nematically. The transition is found out to be a continuous transition showing crossover from a short range order to quasi long range order across the transition. 2) Phase separation: With further increase in noise strength the system shows aggregation to an MIPS phase showing typical features like bimodality in the density and the hexatic order distribution. Local density dependent variation of the local speed verifies a MIPS phase. 3) MIPS to Flocking transition: With increasing activity, the local patches of MIPS starts moving, henceforth breaking the patch to comparatively smaller patches of particles showing flocking behavior. Vicsek-like systems: A system of point-like particles moving under alignment dynamics, familiarly known as Vicsek-like systems, shows interesting features. 1) Density fluctuation driven instabilities: A tunable length dependent binary interaction mechanism incorporated in Vicsek like system gives rise to order-disorder transition, whose nature depends on the density fluctuation embedded by the interaction length-scale. With increasing interaction length-scale, the transition goes to a continuous transition from a discontinuous in the small interaction length limit. 2) Band formation: Band formation has been observed close to the order-disorder transition in most of the flocking models. Here we have probed how an embedded length scale of the system, via a lattice like interaction zone, provides the flexibility of obtaining bands in different directions and with different orientations. An detailed understanding of the formation and structures within the bands and fluctuations within bands is still due. 3) Topological Interaction: A topological interaction model with open boundary conditions ask for some extra constraints for flocking state to emerge. A fixed neighbourhood provides a pathway to flocking in open boundary conditions. It also provides many interesting steady states like cyclic states, rosette like states etc. Naming Games: A naming game is a model to describe how consensus among agents of a community about the name of a particular object can be reached via pairwise interactions. The interactions are in general binary, where an agent, chosen randomly as a ‘speaker’ selects a random name from its vocabulary and compares that with the names present in the vocabulary of another randomly chosen agent, termed as ‘hearer’. The system is fully characterised by two time scales and one length scale, i.e. the time at which the system reaches a state of maximum names, the time scale of reaching a consensus and the maximum size of the vocabulary respectively. 1) Symmetric naming game: A realistic model of the Naming Game, introducing symmetric interaction among agents with the possibility of all possible exchanges in a single time instance, the system reaches consensus faster compared to the original naming game model, with comparatively lower growth exponents for the time scales, but needing larger vocabulary sizes. 2) Limited vocabulary: With restrictions in the cut-off length of the vocabulary sizes of agents, the consensus becomes slower compared to previously observed models of the naming game. A systematic study shows a cross over of the time scale from a smaller value to larger with the variation of the cut-off vocabulary length. |
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Research Scientist,
Laboratory for Physical Biology, RIKEN (BDR), Japan.
Research Interest:
Collective dynamics of active systems:
Effect of confinement;
Motility Induced Phase Separation;
Activity induced melting;
Biological modelling;
Stochastic resetting,
MPCD fluid, Microtubules,
Polymers, Microswimmers etc.