ABSTRACTActive Matter refers to systems whose constituents are continually supplied with free energy which they convert into mechanical work. The idea behind this definition is to bring living materials like cells, tissues and groups of organisms into the fold of condensed matter physics � the study of the macroscopic states of matter. I will talk about our early and recent work on liquid crystalline active matter, to which Aditi Simha made outstanding contributions.
10.10-10.30
R. Rajesh
Levy walking droplets
ABSTRACTForaging and other natural phenomena show super-diffusive transport that are described by Levy walks. In this talk, I will argue that a drop of octanoic acid, when placed in aqueous unsaturated OA solutions, executes a Levy walk, and hence is an easy to set up table-top model system for studying Levy walks in controlled environments
10.30-10.50
Dillip K. Satapathy
Water desorption in confined hydrogels
TEA BREAK
11.10-11.30
Satyavani Vemparala
Aggregation of charged polymers: a coarse grained and atomistic perspective
ABSTRACTIn this talk, I will describe our work on aggregation of charged polymers from both a coarse grained (CG) and all-atom (AA) simulation perspective. The CG simulations on charged polymer systems suggest that the backbone flexibility of the polymers plays a crucial role in the aggregate conformational dynamics. The polymer flexibility introduces additional time scales into the aggregation dynamics in case of flexible polymers and results in a more complex phase diagram as a function of polymer charge density. While the CG simulations give us insights into long time aggregation dynamics, they lack the detail to probe specific effects of nature of counterions on the aggregation dynamics of such charged polymers, which are ubiquitous in biology. We then probe the early stage aggregation dynamics of biologically relevant charged peptides in water via AA simulations. The simulations reveal that the chemical identity and valency of cation in the added salt play a crucial role in aggregate dynamics and morphology of the peptides. The different ways in which the cations effectively renormalize the charges of peptides are suggested to be the cause of the differential effects of salts. These simulations underscore the different roles of CG and AA simulations in probing the nature of counterintuitive aggregation dynamics of similarly charged polymers.
11.30- 11.50
Basudev Roy
Detection of self-generated nanowaves on the interface of an evaporating sessile water droplet
ABSTRACTPEvaporating sessile droplets have been known to exhibit oscillations on the air-liquid interface. These are generally over millimeter scales. Using a novel approach, we are able to measure surface height changes of 500 nm amplitude using optical trapping of a set of microscopic particles at the interface, particularly when the vertical thickness of the droplet reduces to less than 50 ??�m. We find that at the later stages of the droplet evaporation, particularly when the convection currents become large, the top air-water interface starts to spontaneously oscillate vertically as a function of time in consistency with predictions. We also detect travelling wave trains moving in the azimuthal direction of the drop surface which are consistent with hydrothermal waves at a different combination of Reynolds, Prandtl and Evaporation numbers than previously observed. This is the first time that wave-trains have been observed in water, being extremely challenging to detect both interferometrically and with infra-red cameras. We also find that such waves apply a force parallel to the interface along the propagation direction.
11.50- 12.10
Basavaraja Gurappa
Shape anisotropic particles at fluid-fluid interfaces
ABSTRACTParticles positioned at interface between two immiscible liquids provide a platform to study colloids in two dimensions. In this contribution to the symposium in memory of Aditi, work carried out as part of Anjali�s PhD thesis will be discussed. Aditi contributed to this work as a member of doctoral thesis committee. In this talk, fundamental aspects such as when do shape anisotropic particles adsorb at an interface and what orientation (s) they assume at the interface will be discussed. Further, ability to manipulate adsorption and desorption of particles from the interface will be exploited to tailor stability of particle stabilized �Pickering� emulsions.
12.10- 12.30
Ashwin Joy
Friction Scaling Laws for Transport in "living" Turbulence
ABSTRACTUnderstanding the role of frictional drag in diffusive transport is an important problem in the field of �living� or active turbulence. Using a generic continuum model that applies well to living systems, we investigate the role of Ekmann friction on the passive transport of Lagrangian tracers that go with the local flow. We find that the crossover from ballistic to diffusive regime happens at a time scale t c that attains a minimum at zero friction, meaning that both injection and dissipation of energy delay the relaxation of tracers. We explain this by proposing that t_c ~ l* /u rms , where l* is a dominant length scale extracted from energy spectrum peak, and u_rms is a velocity scale that sets the kinetic energy at steady state, both scales monotonically decrease with friction. Finally, we predict friction scaling laws for l*, u rms and the diffusion coefficient D ~ l* u rms /2, that are valid over a wide range of fluid friction. The findings of our report should apply to transport phenomena in dense bacterial suspensions, micro-tubule networks or even artificial swimmers, to name a few.
LUNCH
14.00- 14.30
P. B. Sunil Kumar
Collective dynamics of wet and dry active polymers under confinement
14.30- 14.50
Pritha Dolai
Single file diffusion of active particles.
ABSTRACTWe study single-file dynamics in three classes of interacting active particles: run-and-tumble particles, active Brownian particles and active Ornstein-Uhlenbeck particles. For all three classes, we find that the mean-squared displacement of a tagged particle scales asymptotically as $\sim \sqrt{t}$ and the particles form dynamic clusters at high activity. We show that this mean-squared displacement and the cluster size distribution are scaled functions of the model parameters, with same scaling exponents for the three classes. At high activity, we find that the velocity distribution function of the mobile clusters is non-Gaussian for run-and-tumble particles and active Brownian particles. Concomitantly, we observe that the two point density correlation function displays richer structures, including a second peak reminiscent of particle clustering induced by effective attractive interactions.
14.50- 15.10
Sumesh Thampi
Active nematics in channels
TEA BREAK
15.30- 15.50
Rahul Siddharthan
DNA and chromatin: nuclear soft matter that regulates everything
ABSTRACTI will give a quick overview of how the complexity of DNA packaging in the nucleus is being probed experimentally today, and the role of chromatin organization and remodelling in gene regulation and other cellular processes, with some reference to my current work. I will try to convey why soft matter physicists should be excited by this field.
15.50- 16.10
Manoj Gopalakrishnan
Anomalous diffusion of randomly migrating eukaryotic cells
ABSTRACTChemotaxis is a common mode of motility found in both prokaryotic and eukaryotic cells, by which a cell tries to follow a chemical gradient upstream or downstream. While prokaryotic bacteria like E.coli measure the chemical environment by performing a ``run and tumble" walk, eukaryotic cells ``polarise" when exposed to an external gradient by non-uniform localisation of intracellular signaling molecules. Generation of this internal polarity vector, or ``chemical compass", guides the motion of the cell by its coupling to actin polymerisation. Interestingly, in the absence of a chemo-attractant gradient, many eukaryotic cells have been found to move about randomly in a super-diffusive manner, characterised by long-range correlations in velocity. Using a rather generic model of cell polarisation, we argue that the origins of this super-diffusive motion might lie in the slow, algebraic decay of auto-correlation of the cell polarity, which can be traced to spontaneous density fluctuations in an otherwise uniform chemo-attractant concentration field.
