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Wednesday, 03 April 2024
Time Speaker Title Resources
09:30 to 09:40 Abhishek Dhar (ICTS-TIFR, India) Welcome Remarks
09:40 to 09:50 Ambarish Kunwar (IIT Bombay, India) Study of Transport by Motor Proteins using Optical Tweezers

In this talk I will talk about some of the recent work from my lab in the area of intra-cellular transport where we have used optical trapping extensively.

09:50 to 10:00 Rupak Bag (RRI, India) Transport of photons in structure waveguide QED systems

I will discuss special features of quantum light-matter interactions inside structured waveguides due to their finite bandwidth, band edges, and nontrivial topological properties. For linear waveguides with infinite bandwidth, the transmission and reflection coefficients of a side-coupled two-level emitter (2LE) are the same as the reflection and transmission coefficients of a direct-coupled 2LE. I'll show how this transport analogy breaks down for structured waveguides due to the appearance of Lamb shift only for the direct-coupled 2LE.

Ref: Quantum light-matter interactions in structured waveguides, Rupak Bag and Dibyendu Roy, Phys. Rev. A 108, 053717

10:00 to 10:10 Saikat Santra (ICTS, India) Tracer Dynamics in Active Random Average Process

We investigate the dynamics of tracer particles in the random average process (RAP), a single-file system in one dimension. In addition to the position, every particle possesses an internal spin variable $\sigma (t)$ that can alternate between two values, $\pm 1$, at a constant rate $\gamma$. Physically, the value of $\sigma (t)$ dictates the direction of motion of the corresponding particle and for finite $\gamma$, every particle performs a non-Markovian active dynamics. Herein, we study the effect of this non-Markovianity in the fluctuations and correlations of the positions of tracer particles. We analytically show that the variance of the position of a tagged particle grows sub-diffusively as $\sim \zeta_{\text{q}} \sqrt{t}$ at large times for the quenched uniform initial condition. While this sub-diffusive growth is identical to that of the Markovian/non-persistent RAP, the coefficient $\zeta_{\text{q}} $ is rather different and bears the signature of the persistent motion of active particles through higher point correlations (unlike in the Markovian case). Similarly, for the annealed (steady state) initial condition, we find that the variance scales as $\sim \zeta_{\text{a}} \sqrt{t}$ at large times with coefficient $\zeta_{\text{a}} $ once again different from the non-persistent case. Although $\zeta_{\text{q}}$ and $\zeta_{\text{a}} $ both individually depart from their Markov counterparts, their ratio $\zeta_{\text{a}} / \zeta_{\text{q}}$ is still equal to $\sqrt{2}$, a condition observed for other diffusive single-file systems. This condition turns out to be true even in the strongly active regimes as corroborated by extensive simulations and calculations.

10:10 to 10:20 Dipankar Roy (ICTS, India) Universality in coupled stochastic Burgers systems with degenerate flux Jacobian

We study 1D stochastic models with two conservation laws. One of the models is the coupled continuum stochastic Burgers equation, for which each current is a sum of quadratic non-linearities, linear diffusion, and spacetime white noise. The second model is a two-lane stochastic lattice gas. As distinct from previous studies, the two conserved densities are tuned such that the flux Jacobian, a 2 × 2 matrix, has coinciding eigenvalues. In the steady state, we investigate spacetime correlations of the conserved fields and the time-integrated currents at the origin. For a particular choice of couplings the dynamical exponent 3/2 is confirmed. Furthermore, at these couplings, continuum stochastic Burgers equation and lattice gas are demonstrated to be in the same universality class. (This is based on the work reported in arXiv:2401.06399.)

10:20 to 10:30 Sahil Kumar Singh (ICTS, India) Thermalization and hydrodynamics in an interacting integrable system: the case of hard rods

A classical Hamiltonian many-body system will generally thermalize to Gibbs Ensemble(GE) if left alone for a long time. However, there may exist systems that do not thermalize to GE, because of the existence of extra conservation laws which restrict their motion in the phase space. Thus, dynamical many-body systems can be thought of as constituting a spectrum, with systems having only Hamiltonian as the conserved quantity at one end of the spectrum, and systems having infinitely many conservation laws at the other end. The latter end consists of integrable many-body systems, which are believed to thermalize to the Generalized Gibbs Ensemble (GGE). They have a number of conservation laws equal to the number of degrees of freedom, and thus an infinity of them in the thermodynamic limit. Their non-equilibrium states close to local GGE is described by generalised hydrodynamics (GHD). In this poster, we will study thermalization to GGE of an interacting integrable system, which is that of hard rods, starting from an initial non-equilibrium state. We will also solve the GHD equations at the Euler level exactly by mapping it to a free particle Euler equation. We will also include the Navier-Stokes corrections to the GHD equations and solve it exactly for certain non-equilibrium initial conditions. We will compare our analytical results with those of molecular dynamics simulations, thus providing a verification of GHD. This talk will be based on [1]
[1] S. K. Singh, A. Dhar, H. Spohn, and A. Kundu, arXiv:2310.18684.

10:30 to 10:40 Anurag Upadhyaya (IISc, India) Protein Sequencing Through Nanopore: A Molecular Dynamics Simulation Study

"Over the past several decades, nanopore technology has risen as a highly promising approach for biomolecule sequencing. Solid-state nanopores have emerged as one of the most versatile tools for single biomolecule detection and characterization [1]. Nanopore sensing is based on the measurement of variations in ionic current as biomolecules translocate through nanometer-sized channels, in response to an external voltage applied across the membrane. The passage of a biomolecule through a pore yields information about its structure and chemical properties[2].

In our investigation, we employed comprehensive all-atom Molecular Dynamics (MD) simulations to explore the electric field-driven translocation of a homopeptide sequence through double-layer graphene nanopores. Application of an external electric field facilitated the observation of ionic current (blockade current) generated by ion passage through the graphene nanopore, alongside the assessment of residence time (dwell time) for individual amino acids during the peptide translocation process.
Our findings suggest that dwell time may offer a more nuanced perspective compared to blockade current. Our analytical approach revealed a discernible influence of amino acid charges on the translocation of homopeptides. Furthermore, our study successfully identified post-translational modifications at the single-molecule level within homopeptide sequences as they traversed the sensing region of the nanopore.
This capability allowed us to discriminate between distinct peptide sequences based on the specific charges present within the peptides.
Reference:
1. Wang, Y., Zhao, Y., Bollas, A. et al. Nanopore sequencing technology, bioinformatics and applications. Nat Biotechnol 39, 1348–1365 (2021)
2. Aksimentiev A, Schulten K. Imaging alpha-hemolysin with molecular dynamics: ionic conductance, osmotic permeability, and the electrostatic potential map. Biophys J. Jun; 88(6), 3745-61 (2005)"

10:40 to 10:50 Amit Amal Ghosal (IISER Kolkata, India) Statics and dynamics of two-dimensional melting in a disordered environment

We will present the results from our study of melting in a two-dimensional system of classical particles with Gaussian-core interactions in disordered environments. The clean system validates the conventional two-step melting with a hexatic phase intervening between the solid and the liquid. This picture gets significantly modified in disordered environments. Disorder, in the form of a random distribution of pinning centers, forces a hexatic-like low-temperature phase that transits into a liquid at a single melting temperature T_RP. In contrast, pinning centers located at randomly chosen sites of a perfect crystal anchor a solid at low temperatures which undergoes a direct transition to the liquid at T_CP. Thus, the two-step melting is lost in either case of disorder. We will discuss the characteristics of melting depending on the nature of the impurities. The intriguing dynamical signatures of the system across melting, both in the presence and absence of impurities will also be discussed.

10:50 to 11:00 Auditya Sharma (IISER Bhopal, India) Evidence that the AT transition disappears below six dimensions

One of the key predictions of Parisi’s broken replica symmetry theory of spin glasses is the existence of a phase transition in an applied field to a state with broken replica symmetry. This transition takes place at the de Almeida-Thouless (AT) line in the h − T plane. We have studied this line in the power-law diluted Heisenberg spin glass in which the probability that two spins separated by a distance r interact with each other falls as a power-law. Tuning the exponent σ is equivalent to changing the dimension d of the short-range system, with the relation being d = 2/(2σ − 1) for σ < 2/3. We have found by numerical simulations that the AT line does not exist for σ > 2/3 (i.e below 6 dimensions). Therefore, the Parisi scheme is not appropriate for spin glasses in three dimensions.

11:00 to 11:10 Subhra Sen Gupta (‎SNIoE, India) Non-uniform Multifractality in Disordered Spin Chains and Some Special Random Matrix Models
11:30 to 13:00 -- Posters
14:00 to 14:10 Suravi Pal (SNBNCBS, India) Equilibrium and transient behaviour of modulated binary colloid

We explore the phase and dynamical behaviour of a 2D binary mixture of big and small mutually repulsive particles with diameter ratio 2:1. We perform Monte Carlo (MC) simulations to obtain phase separated system in absence of any external modulation. The particles undergo mixing when being applied to a spatially periodic external modulation whose wavelength matches with the diameter of the bigger particles. The demixing to mixing phenomena is accompanied by a first order phase transition. We then study the transient behaviour of the same binary modulated colloidal system going from modulated mixed state to a demixed one using Brownian Dynamics simulation. We characterise the transient structure and its growth as the system gradually reaches equilibrium by means of average cluster size, radius of gyration vs. time. We observe that the cluster size follows a power law dependence with time before the system reaches steady state. We also observe that the ratio of the radii of gyration along the direction of modulation and in the transverse direction gradually reaches unity reflecting compact circular like shape of the clusters. We observe gradual increase of average demixing order parameter as the system reaches the steady state. We explore the dynamical behaviour of both the types of particles by looking into mean square displacement (MSD) with time. We observe that the smaller particles form slowly diffusing clusters in a background of faster diffusing bigger ones.

14:10 to 14:20 Jaya Kumar Alageshan (IISc, India) Neural network assisted electrostatic global gyrokinetic toroidal code using cylindrical coordinates

Several simulation codes, including GTC, GYRO, ORB5, GENE, etc., have been created to investigate microturbulence within the linear and nonlinear domains of tokamak and stellarator cores. These codes employ flux coordinates to simplify computations affected by anisotropy from confinement magnetic fields. However, flux coordinates encounter mathematical singularities at the magnetic separatrix surface. To address this challenge, we developed the Global Gyrokinetic Code using Cylindrical Coordinates (G2C3), assisted by neural networks, for studying electrostatic microturbulence in realistic tokamak geometries. G2C3 utilizes a cylindrical coordinate system for particle dynamics, enabling motion within arbitrarily shaped flux surfaces, including the tokamak's magnetic separatrix. The code employs an efficient particle locating hybrid scheme, utilizing a neural network and iterative local search algorithm for charge deposition and field scattering. G2C3 uses numerically integrated field lines to train the neural network as a universal function approximator, accelerating subroutines related to gathering and scattering operations in self-consistent gyrokinetic simulation. Notably, G2C3 is the sole code integrating a multilayer neural network with field line geometry for self-consistent simulation in the world fusion program. To demonstrate the new code's capabilities, we present results from self-consistent simulations of ion temperature gradient modes in the tokamak's core region.

14:20 to 14:30 Gopal R (SASTRA University, India) Data driven exploration of swarmalators with higher-order harmonics

We explore the dynamics of swarmalator population comprising higher-order harmonics in phase interaction. A key observation in our study is the emergence of the active asynchronous state in swarmalators with higher-order harmonics, mirroring findings in the one-dimensional analogue of the model, accompanied by the formation of clustered states. Particularly, we observe a transition from the static asynchronous state to the active phase wave state via the active asynchronous state. We have successfully delineated and quantified the stability boundary of the active asynchronous state through a completely data-driven method. This was achieved by utilizing the enhanced image processing capabilities of convolutional neural networks, specifically the U-Net architecture. Complementing this data-driven analysis, our study also incorporates an analytical stability of the clustered states, providing a multifaceted perspective on the system’s behavior. Our investigation not only sheds light on the nuanced behavior of swarmalators under higher-order harmonics but also demonstrates the efficacy of convolutional neural networks in analyzing complex dynamical systems. 

1. K. P. O’Keeffe, J. H. Evers, and T. Kolokolnikov, Physical Review E 98, 022203 (2018).
2. R. Senthamizhan, R. Gopal, and V. K. Chandrasekar, Physical Review E (Submitted , 2024).

14:30 to 14:40 Tapan Chandra Adhyapak (NISER Bhubaneswar, India) Physics of active particles: how important is fully resolved hydrodynamics

We present our recent works on model microswimmers under confinements, shear flow, and complex environments. We incorporate detailed hydrodynamic interactions and elastic properties of the flexible parts of the swimmers. Through two different models, suitable, respectively, for resolving the swimmers with remarkable details and at intermediate resolutions, we investigate the role of hydrodynamic flows. We show that fully resolved hydrodynamics and elastic properties are not just details but are crucial to understanding some of the open questions, such as those related to the hydrodynamic trapping of bacterial on a substrate and flagellar polymorphic dynamics of E. coli during its tumbling motion. 

14:40 to 14:50 Prasenjit Das (IISER Mohali, India) Domain Kinetics in Active Binary Mixtures

We study motility-induced phase separation (MIPS) in active AB binary mixtures in $d=2$. We begin with the master equation for the run-and-tumble bacterial model and coarse-grain that to obtain the evolution equations for the density fields $\rho_i(\vec r, t)$. We numerically solve the evolution equations using the Euler discretization technique for a critical (50\%A-50\%B) binary mixture that shows spatio-temporal pattern formation. Next, we characterize the patterns by calculating the equal-time correlation function $C(r, t)$ and the structure factor $S(k, t)$. For $k\rightarrow\infty$, $S(k, t)$ follows Porod's law: $S(k, t)\sim k^{-(d+1)}$. The average domain size $L(t)$ follows the Lifshitz-Slyozov~(LS) law $L(t)\sim t^{1/3}$.

14:50 to 15:00 Sivasurender Chandran (IIT Kanpur, India) Harnessing Activity to Control the Microscopic Dynamics underlying Bacterial Turbulence.

Dense bacterial suspensions display collective motion exhibiting coherent flow structures reminiscent of turbulent flows. However, understanding the microscopic dynamics of bacterial fluid elements undergoing such turbulent motion is in its incipient stages. In this talk, I will discuss our experiments revealing correlations between microscopic dynamics and the emergence of collective motion in bacterial suspensions. Our detailed analysis of the trajectories of the passive tracers and the velocity field of the bacterial suspensions allowed us to systematically correlate the Lagrangian and the Eulerian perspectives. Bacteria within the collective dynamics followed initial ballistic dynamics followed by intermittent Lévy walk before the eventual decay to random Gaussian fluctuations. Intriguingly, the fluid correlation time decreased linearly with an increase in the effective activity, while the flow correlation length did not vary. The fluid correlation time defined the transition from Lévy to Gaussian fluctuations demonstrating the microscopic reason underlying the observation. Our results reveal transitions in microscopic dynamics underlying the bacterial turbulence and provide a lever to control the transitions between the microscopic regimes.

15:00 to 15:10 Jitendra Kethepalli (ICTS, India) Full Counting statistics for the short-range Riesz gas

We investigate the Full counting statistics (FCS) of a harmonically confined 1d Riesz gas consisting of $N$ particles in equilibrium at finite temperature. The particles interact with each other through a repulsive power-law interaction with an exponent $-k$. We examine the probability distribution of the number of particles in the semi-infinite domain $(-\infty, W]$, called "index" represented by $\mathcal{I}(W, N)$. Statistical properties of the Index were known only for some values of $k<1$, in particular Dyson's log gas ($k\to 0$) and one-dimensional 1dOCP ($k=-1$). This study aims to fill the gap in our understanding of the FCS of $\mathcal{I}(W, N)$ for the short-range Riesz gas, i.e., $k>1$. We analyze the probability distributions of $\mathcal{I}(W, N)$ and show that it exhibits large deviation forms for large $N$ characterised by a speed $N^{\frac{3k+2}{k+2}}$ and by a function of the fraction $c$ of the particles inside the domain and $W$. We derive analytical expressions for the large deviation functions. The saddle point densities that create the large deviations display interesting shape transitions which are manifested by a third-order phase transition exhibited by the large deviation functions through discontinuous third derivatives. Our Monte-Carlo (MC) simulations show good agreement with the expression for saddle point density profiles. Typical fluctuations of $\mathcal{I}(W, N)$ around their mean are Gaussian distributed with a variance that scales as $N^{\nu_k}$, with $\nu_k = (2-k)/(2+k)$. We furthermore compute the thermodynamic pressure and bulk modulus using the LDF for index distribution. Our approach is shown to be adaptable beyond harmonic confinement.

15:10 to 15:20 Indranil Mukherjee (IISER Kolkata, India) Hidden superuniversality in systems with continuous variation of critical exponents

Re-normalization group theory allows continuous variation of critical exponents along a marginal direction (when there is one), keeping the scaling relations invariant. We propose a super-universality hypothesis (SUH) suggesting that, up to constant scale factors, the scaling functions along the critical line must be identical to that of the base universality class even when all the critical exponents vary continuously. We demonstrate this in the Ashkin-Teller (AT) model on a two-dimensional square lattice where two different phase transitions occur across the self-dual critical line: while magnetic transition obeys the weak-universality hypothesis where exponent ratios remain fixed, the polarization exhibits a continuous variation of all critical exponents. The SUH not only explains both kinds of variations observed in the AT model, it also provides a unified picture of continuous variation of critical exponents observed in several other contexts.

15:20 to 15:30 Jasna C K (CUSAT, India) Percolation of aligned and overlapping shape anisotropic objects on lattices

In this work, we investigate the percolation properties of a system of aligned, overlapping and shape anisotropic objects on lattices. We study a system of overlapping and aligned rectangles on 2D square lattices using Monte Carlo simulation as well as lattice version of excluded volume theory. Recently proposed lattice version of excluded volume theory enables us to evaluate percolation threshold for various objects on lattices to higher accuracy. Quantity of interest in our problem is the percolation threshold. We compare variation of percolation threshold with length of the percolating units. Theory predicts a monotonic dependence of threshold on length of the rectangles chosen. We kept width of the rectangle a constant and increased its length alone. Variation of the percolation threshold with length of the rectangle is studied for various widths. Specifically, we obtain a monotonic decrease of threshold with stick length for rectangles of width unity(sticks) and monotonic increase of threshold with length for rectangles of width greater than two. For width two, threshold is found to be independent of length for rectangles on 2D square lattices. Length independence of threshold is an interesting result which can be extended to higher dimensions as well. Results from excluded volume theory adapted to a lattice setting is found to be in good agreement with results from simulations especially for larger rectangles. Finiteness of limiting threshold value is also evident from the theory. Shape anisotropy influences the percolation threshold to a greater extent. We evaluate percolation thresholds of system for two directions, specifically, check for a spanning cluster in the orthogonal direction to alignment and in the direction of alignment. Both yield same threshold in the infinite system size limit. This peculiar behaviour is observed only for percolation of shape anisotropic objects.

16:00 to 16:10 Daniya Davis (VIT, India) Phase Separation of Fluids in Confined Geometry : Partial and Complete Wetting

Exploring the intricate dynamics of phase separation in a confined cylindrical pore with wetting influence, this work delves into the fascinating phenomenon of binary fluid phase separation and its implications for various industrial and scientific applications. Unlike existing studies that suggested complete phase separation is unattainable within cylindrical porous media, our realistic model incorporates fluid-wall particle interactions. By implementing our model, we successfully achieved complete phase separation, presenting a significant advancement in understanding this phenomenon. Our numerical analysis explores the phase separation process under varying wetting strengths, pinpointing the critical threshold where partial wetting transitions to complete wetting. Predominantly we investigate the growth of the domain length scale and determine the growth exponent for all the cases, shedding light on the underlying dynamics of this intriguing phenomenon, which shows different behavior with different strength of interactions. Distinct growth exponents are exhibited by various particle types once transitioned to complete wetting regime. To provide further justification and explanation for these findings, we employ the structure factor, leveraging the Porod law and Super-universality principle.
Ref: D. Davis and B.S. Gupta, Phys. Rev. E, 108, 064607 (2023)

16:10 to 16:20 Arvind Ayyer (IISc, India) The inhomogeneous multispecies PushTASEP

We introduce and study a natural multispecies variant of the inhomogeneous PushTASEP with site-dependent rates on the finite ring. We derive the stationary distribution explicitly by constructing a multiline process which projects to the multispecies PushTASEP, and identifying its stationary distribution using time-reversal arguments. We also study symmetry properties of the process under interchange of the rates associated to the sites. These results hold not just for events depending on the configuration at a single time in equilibrium, but also for systems out of equilibrium and for events depending on the path of the process over time. Lastly, we give explicit formulas for nearest-neighbour two-point correlations in terms of Schur functions. This is joint work with James Martin (Oxford).

16:20 to 16:30 Hitesh Garg (IMSc, India) Bridging induced coil-to-globule transitions in polymers

Macromolecules or polymers are generally found in crowded environments. The interior of a cell has a high concentration of macromolecules, typically constituting 20-30% of the total volume of a cell. Crowders play an important role in what is known as the coil-to-globule (C-G) transition of macromolecules, which is crucial for the functioning of biomacromolecules such as RNA, DNA, and proteins. The C-G transition can occur due to various reasons and phenomena, including solvent quality, co-non-solvency, temperature-mediated changes, depletion effect, etc. In this work, we studied the C-G transition occurring due to bridging interactions, where crowders act as bridges or glues between monomers to induce collapse. We performed extensive coarse-grained molecular dynamics simulations to investigate the phase diagram of both neutral and charged polymers in the presence of attractive crowders. We also shed light on the effects of crowder-crowder interactions, density, valency of counterions, and the size of crowders on such transitions.

16:30 to 16:40 Akshit Goyal (ICTS, India) Linear response theory of ecosystems to environmental perturbations
16:40 to 16:50 Pinaki Chaudhuri (IMSc, India) Creep response of amorphous solids

We study the response of model amorphous solids to applied shear stress, and analyse the role of thermal fluctuations in determining the observed macro behaviour.

16:50 to 17:00 Rajiv G Pereira (TIFR Hyderabad, India) Distribution of spins in random field XY models

In this talk we shall consider XY models with quenched disorder and explore the nature of the ordered state. The focus will be on the patterns of spin distribution in typical configurations of quenched disorder, which are not visible in methods of study where we average over different configurations of disorder. The patterns remain robust for large system sizes.

In particular, we shall investigate the zero- and low-temperature arrangements of spins in:
1) Infinite-range XY model with random field (RFXY)
2) Infinite-range XY model with random crystal field (RCXY).
At 0-temperature, for the RFXY model, there is a first order phase transition as the strength of the random field is varied across the critical value. The spins are distributed within a cone in the ordered phase and over a circle in the disordered phase. Whereas in the case of the RCXY, where there is no phase transition, the spins are distributed within a cone which widens with the strength of the crystal field.

Study of low temperature dynamics in both models show that randomly distributed spins first form a cone in a short timescale. In a longer timescale the cone rotates and eventually orient in the right direction, corresponding to the equilibrium.

17:00 to 17:10 Suman Dutta (NCBS, India) Entropic Timescales of Dynamic Heterogeneity in Supercooled Liquid

Non-Gaussian displacement distributions are universal predictors of dynamic heterogeneity in slowly varying environments. Here, we explore heterogeneous dynamics in supercooled liquid using molecular dynamics simulations and show the efficiency of the information-theoretic measure in quantifying dynamic heterogeneity over the widely used moment-based quantifications of non-Gaussianity. Our analysis shows that the heterogeneity quantified by the negentropy is significantly different from the one obtained using the conventional approach that considers deviation from Gaussianity up to lower-order moments. Further, we extract the timescales of dynamic heterogeneity using the two methods and show that the differential changes diverge as the system experiences strong intermittency near the glass transition.

17:10 to 17:20 Shovan Dutta (RRI, India) Global heating from local cooling (and vice versa)

I will discuss a generic setup where an interacting quantum system (spin chain) coupled to a zero-temperature bath at the boundary can heat up to a highly excited state provided it conserves a U(1) charge (total Sz) that is broken by the coupling. This counterintuitive result highlights the importance of symmetry and the nature of system-bath coupling in thermalization (or lack thereof).

17:20 to 17:30 Sankaran Nampoothiri (GITAM, India) Brownian non-Gaussian diffusion

The familiar image of the diffusion process can be characterized by the mean square displacement (MSD) growing linearly in time and a Gaussian probability distribution function (PDF) for the position. However, the fascinating aspect is that nature often springs surprises, and the same holds true for diffusion. There are situations in which the simple, familiar diffusion picture does not hold. For example, have you ever wondered about the diffusion of particles in a liquid with enormous density fluctuations? Or have you envisioned the diffusive dynamics of a polymer chain's center of mass (CM) with the number of monomers in the chain fluctuating? This talk shows some familiar images of diffusion breaks in the scenarios described. Instead, new insights and ideas emerge. Specifically, diffusive processes can be characterized in these situations by the MSD growing linearly in time, like in the standard Brownian diffusion, but with a non-Gaussian probability distribution function (PDF) for the position. In the end, the talk briefly delves into the implications of this novel non-Gaussian feature in diffusive processes on the first-passage statistics.

Thursday, 04 April 2024
Time Speaker Title Resources
09:30 to 09:40 R. Rajesh (IMSc, India) Mpemba effect: An anomalous relaxation phenomenon

The entropy of the fully packed limit of the covering of a lattice using rigid rods that cannot overlap is determined using upper and lower bounds.

09:40 to 09:50 Aravinda (IIT Tirupati, India) Ergodic and mixing quantum channels: From two-qubit to many-body quantum systems

The development of classical ergodic theory has had a significant impact in the areas of mathematics, physics, and, in general, applied sciences. The quantum ergodic theory of Hamiltonian dynamics has its motivations to understand thermodynamics and statistical mechanics and is still debated a lot. Quantum channel, a completely positive trace-preserving map, represents a most general representation of quantum dynamics and is an essential aspect of quantum information theory and quantum computation. In this work, we study the ergodic theory of quantum channels by characterizing different levels of ergodic hierarchy from integrable to mixing. The quantum channels on single systems are constructed from the unitary operators acting on bipartite states and tracing out the environment. The interaction strength of these unitary operators measured in terms of operator entanglement provides sufficient conditions for the channel to be mixing. By using block diagonal unitary operators, we construct a set of non-ergodic channels. From integrable to mixing is characterized explicitly in the case of the two-qubit unitary operator. Moreover, we also study interacting many-body quantum systems that include the famous Sachdev-Ye-Kitaev (SYK) model and show that they display mixing within the framework of the quantum channel.

09:50 to 10:00 Sujit Sarkar (PPISR, India) A conformal field theory study for Quantum Ising Model with Longer Range Interaction

We study and present the results of central charge for quantum Ising model with longer range interaction in presence and absence of transverse field. This model Hamiltonian system has different gapped phase with different topological index and also different quantum critical depending on the transverse field. We also present the conformal field theory (cft) study for this model Hamiltonian system and present the central charge for the different regimes of the parameter space. We show explicitly non-universal, i.e, for the same value of central charge behaviour of topological states are different. We show explicitly on the interplay of criticality, topology and central charge in presence and absence of transverse field. We also show how the Lifshitz transition occurs in presence of transverse field. We also present the effect of transverse field on the quantum critical line and also for the evaluation of central charge. We show explicitly that the minimal model which
describe the cft behavior of quantum Ising model is not sufficient to describe the behaviour of quantum Ising model with long range interaction. We show explicitly the existence of CFT criticality and non-CFT criticality in the different region of parameter space. This work will provide a new perspective in conformal field theory.

10:00 to 10:10 Mamata Sahoo (Univ. of Kerala, India) Transition from random self-propulsion to rotational motion in a non-Markovian microswimmer

We study the motion of an inertial microswimmer in a non-Newtonian environment with a finite memory and present the theoretical realization of an unexpected transition from its random self-propulsion to rotational (circular or elliptical) motion. Further, the rotational motion of the swimmer is followed by spontaneous local direction reversals yet with a steady state angular diffusion. Moreover, the advent of this behaviour is observed in the oscillatory regime of the inertia-memory parameter space of the dynamics. We quantify this unconventional rotational motion of microswimmer by measuring the time evolution of direction of its instantaneous velocity or orientation. By solving the generalized Langevin model of non-Markovian dynamics of an inertial active Ornstein-Uhlenbeck particle, we show that the emergence of the rotational (circular or elliptical) trajectory is due to the presence of inertia and memory in the environment or medium.

10:10 to 10:20 Ashwin S.S (GITAM, India) Rouse Polymer in Random Media: Some Exact Results

We calculate the eigenvalues of a class of random matrices, namely the randomly segmented tridiagonal quasi-Toeplitz (rstq-T) matrix, in exact closed-form. The contexts under which these matrices arise are ubiquitous in physics. In our case, they arise when studying the dynamics of a Rouse polymer embedded in random environments. Unlike in the case of Rouse polymers in homogeneous environments, where the dynamics give rise to a circulant matrix and the diagonalization is achieved easily via a Fourier transform, analytical diagonalization of the rstq-T matrix has remained unsolved thus far. We analytically calculate the spectral distribution of the rstq-T matrix, which is able to capture the effect of disorder on the modes.

10:20 to 10:30 Sanjib Sabhapandit (RRI, India) Noninteracting particles in a harmonic trap with a stochastically driven

We study a system of $N$ noninteracting particles on a line in the presence of a harmonic trap, where the trap center undergoes a bounded stochastic modulation. We show that this stochastic modulation drives the system into a nonequilibrium stationary state, where the joint distribution of the positions of the particles is not factorizable. This indicates strong correlations between the positions of the particles that are not inbuilt, but rather get generated by the dynamics itself. Moreover, we show that the stationary joint distribution can be fully characterized and has a special conditionally independent and identically distributed (CIID) structure. This special structure allows us to compute several observables analytically even in such a strongly correlated system, for an arbitrary bounded drive. These observables include the average density profile, the correlations between particle positions, the order and gap statistics, as well as the full counting statistics. We then apply our general results to two specific examples where (i) the drive represents a dichotomous telegraphic noise, and (ii) the drive represents an Ornstein-Uhlenbeck process. Our analytical predictions are verified in numerical simulations, finding excellent agreement.

10:30 to 10:40 Rahul Pandit (IISc, India) Machine-learning-based estimation of critical exponents: Ising, Blume-Capel, and Antiferromagnetic-Ising Models

I will provide a brief overview of recent work, done with Vasanth Kumar Babu, in which we train convolutional neural networks (CNNs) with Ising-model Monte Carlo spin configurations, both above and below the critical temperature, and then use the CNNs, along with finite-size scaling, to obtain critical exponents for the ferromagnetic-Ising, Blume-Capel, and antiferromagnetic-Ising Models.

10:40 to 10:50 Vaibhav H Wasnik (IIT Goa, India) Revisiting multiple thermal reservoir stochastic thermodynamics

In this talk starting from a simple proof showing that for a Markovian system connected to two thermal reservoirs with temperatures T1 and T2, the transition rate between two energy states labelled by m and m′, W_{m,m′} cannot be written as W1_{m,m′}+W2_{m,m′}, where W1_{m,m′}, W2_{m,m′} are the transition rates between energy states for systems connected to the corresponding thermal reservoirs, we go on to show that the evolution of a system as a whole connected to two thermal reservoirs is non-Markovian by considering an example of a system made up of two points at different temperatures, each following a Markovian evolution.

10:50 to 11:00 Subhro Bhattacharjee (ICTS, India) Deconfined quantum phase transition in non-collinear magnets
11:00 to 11:10 Brato Chakrabarti (ICTS, India) Active Carpet Model for Intracellular Flows
11:30 to 13:00 -- Posters
14:00 to 14:10 Jaydeb Chakrabart (SNBNCBS, India) Model studies on motion of respiratory droplets driven through a face mask

Face masks are used to intercept respiratory droplets to prevent spreading of air- borne diseases. Designing face masks with better efficiency needs microscopic understanding on how respiratory droplets move through a mask. Here we study a simple model on the interception of droplets by a face mask. The mask is treated as a polymeric network in an asymmetric confinement, while the droplet is taken as a micrometer-sized tracer colloidal particle, subject to driving force that mimics the breathing. We study numerically, using the Langevin dynamics, the tracer particle permeation through the polymeric network. We show that the permeation is an activated process following an Arrhenius dependence on temperature. The potential energy profile responsible for the activation process increases with tracer size, tracer bead interaction, network rigidity and decreases with the driving force and confinement length. A deeper energy barrier led to better efficiency to intercept the tracer particles of a given size in the presence of driving force at room temperature. Our studies may help to design masks with better efficiency.

14:30 to 14:40 Sudipto Muhuri (Savitribai Phule Pune University, India) Theoretical analysis of cargo transport by catch bonded motors in optical trapping assays

In-vitro experiments performed using micro-patterned one dimensional substrate has allowed for quantitative study of the collective manifestation of cell motility and cell-cell interactions in confined 1D channels. Motivated by these experiment, we study the clustering characteristics of cells within the ambit of an Active spin model which incorporates the motility behaviour of individual cells, their mutual interaction between cells within a channel and their interactions across neighbouring channels.

14:40 to 14:50 Abhishek Chaudhuri (IISER Mohali, India) Chirality in active matter

In this talk, I will be discussing about some of our recent results on exact moment calculations of a chiral active brownian particle.

14:50 to 15:00 Syed Mohammad Kamil (SNU, India) Temperature-dependent anomalous viscosity of aqueous solutions of imidazolium-based ionic liquids.

Ionic liquids (ILs) are organic salts with a low melting point compared to inorganic salts. Room temperature ILs are of great importance for their widespread potential industrial applications. The viscosity of aqueous solutions of two imidazolium-based ILs, investigated in the present study, exhibits an anomalous temperature variation. Unlike conventional molecular fluids, the viscosity of 1-methyl-3-octyl imidazolium chloride [OMIM Cl] and 1-methyl-3-decyl imidazolium chloride [DMIM Cl] solutions is found to increase with temperature and then depress. The Small Angle X-ray Scattering (SAXS) data suggest that the lattice parameter of the body-centered cubic lattice formed by the spherical micelles of these ILs, and the morphology of the micelles remain intact over the measured temperature range. The molecular dynamics simulation shows the micelles to be more refined with their integrated structure on increasing the temperature. On further increase of the temperature, the structure is found to be loosened, which is corroborated by the simulation work. The ionic conductivity of these IL solutions shows a trend that is opposite to that of the viscosity. The observed anomalous nature of the viscosity is attributed to the trapped dissociated ions in the network of the micellar aggregates.

15:00 to 15:10 Kavita Jain (JNCASR, India) Run-and-tumble particle with bounded rates
15:20 to 15:30 Sayantan Majumdar (RRI, India) Memory formation in shear jammed dense suspensions

Under rapid perturbation, the viscosity of many dense particulate suspensions increases dramatically, an effect known as shear-thickening. In some cases, the suspension can even become jammed solid-like. interestingly, once the perturbation is removed the jammed solid-like state rapidly relaxes to the initial liquid-like state. This indicates that shear-jamming in dense suspension is a reversible phenomenon. In this talk, I'll argue in light of our recent experiments that although the stress response shows reversibility, the structural memory persists. This results in an evolution of the mechanical properties of the shear-jammed state.

16:00 to 16:10 Udaysinh T. Bhosale (VNIT, India) Exactly solvable dynamics and signatures of integrability in an infinite-range many-body Floquet spin system

We study N qubits having infinite-range Ising interaction and subjected to a periodic pulse of an external magnetic field. We analytically solve the cases of N = 5 to 11 qubits, finding its eigensystem, the dynamics of the entanglement for various initial states, and the unitary evolution operator. These quantities shows signatures of quantum integrability. For the general case of N > 11 qubits, we provide a conjecture on quantum integrability based on the numerical evidence such as degenerate spectrum, and the exact periodic nature of the time-evolved unitary evolution operator and the entanglement dynamics. Using linear entropy, we show that for the class of initial unentangled state, the entanglement periodically displays maximum and zero values.

16:10 to 16:20 Sumilan Banerjee (IISc, India) Information scrambling and butterfly velocity in quantum spin glass chains

In a generic quantum many-body system, quantum information encoded in local degrees of freedom in the initial state scrambles to spread globally over the entire system due to its time evolution. For systems with many metastable configurations, information scrambling via quantum dynamics may become enhanced when the dynamics samples these multitude of configurations, leading to extreme sensitivity to initial conditions in the classical limit. Glasses are among the most prominent examples of such systems. I will discuss lattice generalizations of two well-known zero dimensional models of quantum spin glass, Sachdev-Ye (SY) and spherical quantum p-spin glass model, to one dimension for studying crossovers in non-local information scrambling dynamics due to glass transition, complex dynamics, and quantum and thermal fluctuations in paramagnetic and replica-symmetry broken spin glass phases.

16:20 to 16:30 Muktish Acharyya (Presidency University, India) Nonequilibrium tricritical behaviour in anisotropic XY ferromagnet

The thermodynamical behaviour of a three dimensional anisotropic XY ferromagnet driven by elliptically polarized propagating magnetic field wave has been studied by Monte Carlo simulation. Bilinear exchange and single site anisotropies are considered here. The time average magnetisation component was found to show a nonequilibrium phase transition. The order of the phase transition has been found to depend on the amplitude of the propagating polarized field wave and the strength of the anisotropy. The comprehensive phase diagram is drawn. The tricritical line, separating the regions of second order and first order transitions, is also shown.

16:30 to 16:40 Aritra Ghosh (IIT Bhubaneswar, India) Energetics of Quantum Brownian Oscillators

In this talk, I will describe the energetics of a quantum Brownian oscillator, in strong coupling with the heat bath. It is shown that the thermally-averaged kinetic and potential energies of the oscillator are unequal for strong system-bath coupling; this leads to a novel form of the virial theorem. I will describe two unequal perceptions of energy, namely, the mean energy and the internal energy, briefly comparing the two. The talk will be concluded with a discussion on the weak-coupling limit, in which all our results reduce to the familiar ones for a quantum harmonic oscillator in the canonical ensemble.

16:40 to 16:50 Punyabrata Pradhan (SNBNCBS, India) Collective diffusion in hardcore run-and-tumble particles

We characterize collective diffusion in hardcore run-and-tumble particles (RTPs) by calculating the bulk-diffusion coefficient for arbitrary density and tumbling rate. We study two minimal models of RTPs: Model I is a standard version of hardcore RTPs, whereas model II is a long-ranged lattice gas (LLG) with hardcore exclusion - an analytically tractable variant of model I. We calculate the bulk-diffusion coefficient analytically for model II and numerically for model I through an efficient Monte Carlo algorithm; notably, both models have qualitatively similar features. In the strong-persistence regime, the fascinating interplay between persistence and interaction is quantified in terms of two length scales: Persistence length and a “mean free path”, which is simply a measure of the average gap (empty stretch) size in the hopping direction. Notably, for finite density and tumbling rate, we do not find any diffusive instability in the systems, implying that motility-induced phase separation (MIPS) is not possible in the conventional models of RTPs.

16:50 to 17:00 Sreedhar Dutta (IISER Tirupati, India) Periodically driven Langevin systems with vanishingly small viscous drives

Periodically driven Langevin systems support stable non-equilibrium states called oscillating states, whose properties are drastically different from those at equilibrium. They exhibit even more exotic features for low viscous drives, which is a regime that is hard to probe due to the singular behavior of Langevin dynamics near vanishing viscosity. We propose a method, based on singular perturbation and Floquet theories, that allows us to obtain oscillating states and analyze their thermodynamic properties.

17:00 to 17:10 Tridib Sadhu (TIFR Mumbai, India) Dynamical phase transitions in certain non-ergodic stochastic processes

Dynamical phase transitions are singular changes in the distribution of dynamical observables and reflect as a non-analyticity in their large deviation functions. I shall present a class of stochastic processes where the distribution of time-integrated (empirical) observables is singular and it relates to phase transitions of dynamical trajectories. These illustrative simple examples include Brownian motion on a sticky surface or in the presence of an absorbing wall where we consider a set of empirical observables like the local time, average velocity, and area. I shall show how to obtain the large deviation function of these observables using a backward Fokker-Planck approach, in which singularities emerge from a competition between survival and diffusion. I shall also discuss an equivalent scenario of these dynamical phase transitions in terms of tilted operators, which is analogous to the familiar mechanism of phase transitions in terms of the degeneracy of the transfer matrix in the Ising model. At the singular point, effective dynamics undergo an abrupt transition. Extending on the tilted operator approach, I shall show that similar phase transitions may generically arise in non-ergodic Markov chains. This scenario is robust and generalizable for non-Markov processes and for many-body systems, which can even lead to a sequence of such dynamical transitions.

17:10 to 17:20 Satya Majumdar Universal distribution of the number of minima for random walks and Levy flights
Friday, 05 April 2024
Time Speaker Title Resources
09:30 to 09:40 Deepak Gupta (IIT Indore, India) Efficient control protocols for an active Ornstein-Uhlenbeck particle
09:40 to 09:50 Anirban Ghosh (RRI, India) Stochastic search processes under Resetting:: Cover time

Stochastic search processes are ubiquitous in nature. Animals searching food, Proteins searching for specific DNA sequences to bind, Sperm cells searching for an oocyte to fertilize are very important examples related to search processes. Cover time is the minimum time needed by a random walk to visit all sites at least once of a confined domain. We have studied how the statistics of cover time evolves under resetting. We have also shown that cover time decreases due to resetting, consequently the search process becomes more efficient.

09:50 to 10:00 T R Vishnu (RRI, India) Heat transport through an open coupled scalar field theory hosting stability-to-instability transition

We investigate heat transport through a one-dimensional open coupled scalar field theory, depicted as a network of harmonic oscillators connected to thermal baths at the boundaries. The non-Hermitian dynamical matrix of the network undergoes a stability-to-instability transition at the exceptional points as the coupling strength between the scalar fields increases. The open network in the unstable regime, marked by the emergence of inverted oscillator modes, does not acquire a steady state, and the heat conduction is then unbounded for general bath couplings. In this work, we engineer a unique bath coupling where a single bath is connected to two fields at each edge with the same strength. This configuration leads to a finite steady-state heat conduction in the network, even in the unstable regime. We also study general bath couplings, e.g., connecting two fields to two separate baths at each boundary, which shows an exciting signature of approaching the unstable regime for massive fields. We derive analytical expressions for high-temperature classical heat current through the network for different bath couplings at the edges and compare them. Furthermore, we determine the temperature dependence of low-temperature quantum heat current in different cases. Our study will help to probe topological phases and phase transitions in various quadratic Hermitian bosonic models whose dynamical matrices resemble non-Hermitian Hamiltonians, hosting exciting topological phases.

10:00 to 10:10 Nivedita Deo (University of Delhi, India) Multiplex Networks of Protein Families

The Beta-lactamase protein family is vital in countering Beta-lactam antibiotics, a widely used antimicrobial. To enhance our understanding of this family, we adopted a novel approach employing a multiplex network representation of its multiple sequence alignment. Each network layer, derived from the physiochemical properties of amino acids, unveils distinct insights into the intricate interactions among nodes, thereby enabling the identification of key motifs. Nodes with identical property signs tend to aggregate, providing evidence of the presence of consequential functional and evolutionary constraints shaping the Beta-lactamase family. We further investigate the distribution of evolutionary links across various layers. We observe that polarity manifests the highest number of unique links at lower thresholds, followed by hydrophobicity and polarizability, wherein hydrophobicity exerts dominance at higher thresholds. Further, the combinations of polarizability and volume, exhibit multiple simultaneous connections at all thresholds. The combination of hydrophobicity, polarizability, and volume uncovers shared links exclusive to these layers, implying substantial evolutionary impacts that may have functional or structural implications. By assessing the multi-degree of nodes, we unveil the hierarchical influence of properties at each position, identifying crucial properties responsible for the protein’s functionality and providing valuable insights into potential targets for modulating enzymatic activity.

10:10 to 10:20 Prabal Kumar Maiti (IISc, India) Decoding Mpemba effect using MD simulations

The statement that warm water freezes faster than cold water is commonly known as the Mpemba effect. Named after Erasto Mpemba, he showed in 1969 [1], that for liquid water, two systems similar in every way except their initial temperature, when quenched into a sub-freezing temperature, will show that the system which was initially warmer, undergoes the freezing process faster. In this study, using classical MD simulations of TIP4P/ice water, the process of freezing from liquid water to ice was observed through the direct coexistence method, and for various starting temperatures of liquid water, the time for complete freezing was compared for these temperatures. The comparisons resulted in the observation that the liquid water that was initially hotter took less time to fully freeze as compared to the liquid water that was colder. To obtain a molecular level understanding of the underlying mechanism, two possibilities were considered: that the difference between liquids at high versus low temperatures is either structural or dynamical. We calculate several autocorrelation functions and other structural quantities to get a microscopic origin of the Mpemba effect.
References:
1. E. B. Mpemba and D. G. Osborne, Cool?, Physics Education 4, 172 (1969).

10:20 to 10:30 Subir Kumar Das (JNCASR, India) Metastability in Freezing: Simulations of Mpemba effect in WATER and comparison with certain simpler systems

Universality of exponents dictated by the division between short- and long-range interactions is well studied in the context of equilibrium critical phenomena. In this talk I will discuss analogous picture for kinetics of corresponding phase transitions. Analyses of results, obtained from Monte Carlo simulations of the Ising model, show interesting deviation, even at the qualitative level, from the equilibrium scenario, in terms of the above mentioned division as well as universality. Some of these results are in agreement with the predictions by A.J. Bray.

10:30 to 10:40 Abhishek Dhar (ICTS, India) Page curve entanglement dynamics of free fermions: results from numerics and hydrodynamics

We consider a gas of non-interacting fermions that is released from a box into the vacuum. This provides a simple analytically tractable model that reproduces many features of the Page curve characterizing the evolution of entanglement entropy during evaporation of a black hole. Apart from the entropy we consider several other physical observables and show that generalized hydrodynamics provides a rather surprisingly accurate description of the quantum dynamics.
[Joint work with Madhumita Saha and Manas Kulkarni]

10:40 to 10:50 Aashna (IIT Delhi, India) Geometry-induced friction at a soft interface

During my talk, I will be discussing the role of geometry on friction at a soft interface that moves with a small relative velocity. We conducted experiments using a novel experimental setup to study the friction between a thin polymer sheet and a hydrogel substrate. Our findings indicate that the friction between the two surfaces greatly relies on their relative geometry. Specifically, we found that a flat sheet experiences significantly higher friction on the spherical substrate compared to the cylindrical or planar substrate. We believe that the stress developed in the sheet due to the incompatible confinement of the sheet over the spherical surface is responsible for the increased friction.

10:50 to 11:00 Manas Kulkarni (ICTS, India) Generating Entanglement by Quantum Resetting

We consider a closed quantum system subjected to stochastic Poissonian resetting. Resetting drives the system to a nonequilibrium stationary state (NESS) with a mixed density matrix which has both classical and quantum correlations. We provide a general framework to study these NESS correlations for a closed quantum system with a general Hamiltonian. We then apply this framework to a simple model of a pair of ferromagnetically coupled spins. We compute exactly the NESS density matrix of the full system. This then provides access to three basic observables, namely, (i) the von Neumann entropy of a subsystem, (ii) the fidelity between the NESS and the initial density matrix, and (iii) the concurrence in the NESS (that provides a measure of the quantum entanglement in a mixed state), as a function of the two parameters: the resetting rate and the interaction strength. One of our main conclusions is that a nonzero resetting rate and a nonzero interaction strength generate quantum entanglement in the NESS (quantified by a nonzero concurrence) and moreover this concurrence can be maximized by appropriately choosing the two parameters. Our results show that quantum resetting provides a simple and effective mechanism to enhance entanglement between two parts of an interacting quantum system.

11:00 to 11:10 Kabir Ramola (TIFR Hyderabad, India) Green's Functions For Random Resistor Networks

The conductivity of disordered random media is a problem of fundamental interest in a variety of condensed matter contexts, including in transport measurements and critical phenomena. Simple tractable models that are often used for modeling such phenomena are electrical networks, most often constituting resistor elements, studied either in the steady-state or as a dynamical system. In this context, we analyzed random resistor networks through a study of lattice Green’s functions in arbitrary dimensions. I will discuss a systematic disorder perturbation expansion to describe the weak disorder regime of such a system. We have used this formulation to compute ensemble averaged nodal voltages and bond currents in a hierarchical fashion. Additionally, we have constructed a formalism to recursively obtain the exact Green’s functions for finitely many disordered bonds.

11:30 to 11:40 Sanjay Puri (JNU, India) Active Matter with Quenched Disorder

We will discuss some recent results obtained for the Vicsek model with randomly placed obtsacles.

11:40 to 11:50 Urna Basu (SNBNCBS, India) Hamonically trapped inertial Run-and-Tumble Particle in one dimension

We study the behaviour of a one-dimensional inertial run-and-tumble particle (RTP) trapped in a harmonic potential. We find that the presence of inertia leads to two distinct dynamical regimes, namely, overdamped and underdamped regimes, which are characterized by distinct behaviour of position and velocity fluctuations. In particular, the underdamped regime, in the strongly active limit, shows several novel features like multi-peaked position and velocity distributions, which we characterize analytically using an effective model. We also show that, both the position and velocity distributions show shape transitions as the activity is changed.

11:50 to 12:00 Ranjini Bandyopadhyay (RRI, India) The effect of controlled physical aging on the onset of desiccation cracks in aqueous clay suspensions

Accumulation of drying-induced stresses in a colloidal suspension causes the formation of desiccation cracks. When clay, a constituent of natural soil, is mixed with water, it transforms spontaneously from a viscoelastic liquid to a viscoelastic solid over time. This property, popularly referred to as physical aging, occurs due to the spontaneous and gradual build-up of electrostatic interparticle interactions during the swelling and breakup of clay particle stacks. We prepared and dried aqueous Laponite clay suspensions of various particle and added salt concentrations. We determined the time corresponding to the appearance of the first crack via digital image analysis and performed micro-indentation measurements using an atomic force microscope to extract the elasticity of the partially dried sample. We see that increase in the strength of interparticle attraction results in early crack formation, with the crack onset time scaling with the inverse of the square root of the suspension elasticity. We combine a poroelastic model with the Griffith's criterion for crack formation to model our data. We estimate a fracture energy of ~ 1000J/m$^2$, a value that agrees well with data reported for other colloidal and polymeric gels.

12:00 to 12:10 Sriram Ramaswamy (IISc Bangalore, India) The anomalous long-ranged influence of an inclusion in a viscous active fluid

This work was done with T A de Pirey and Y Kafri, see arXiv:2402.12996. We examine theoretically the flow and concentration fields created by an inclusion in an momentum-conserving active suspension. An inclusion of polar shape is of particular interest, as it is motile in an active medium and needs to be held still by an external force. Advection by the resulting Stokeslet flow proves to be marginal, in the renormalization-group sense, and competes delicately with diffusion. The outcome is an active-particle concentration whose power-law decay with distance from the inclusion is governed by an anomalous exponent determined by the symmetry of the inclusion and varying continuously with the dimensionless advection strength, which also governs the angular dependence of the profile. A pair of pinned inclusions interact non-reciprocally at long distances.

12:10 to 12:20 Anupam Kundu (ICTS, India) Generalised hydrodynamic approach to Generalized Gibbs equilibrium in a harmonic chain

I will talk about our recent results on MSD and certain correlations of tracer particles in passive and active single file motion.

12:20 to 12:30 Varsha Banerjee (IIT Delhi, India) Phase separation of a magnetic fluid: Asymptotic states and non-equilibrium kinetics

Furukawa predicted that at late times, the domain growth in binary fluids scales as $\ell(t)\sim t^{2/3}$, and the growth is driven by fluid inertia. The {\it inertial growth regime} has been highly elusive in molecular dynamics (MD) simulations. We perform coarsening studies of the Stockmayer (SM) model comprising of magnetic dipoles that interact via long-range dipolar interactions as well as the usual Lennard-Jones (LJ) potential. This fascinating polar fluid exhibits a gas-liquid phase coexistence, and magnetic order even in the absence of an external field. From comprehensive MD simulations, we observe the inertial scaling [$\ell(t)\sim t^{2/3}$] in the SM fluid for an extended time window. The equilibrium morphologies have density dependent shapes which are robust and non-volatile, and exhibit characteristic magnetic properties that have versatile applications.

12:30 to 12:40 Rajeev Kapri (IISER Mohali, India) Unzipping a DNA hairpin in Active Environment

We study the unzipping of a DNA hairpin in a bath of self-propelled particles (SPPs) using Langevin dynamics simulations. We found that the DNA can be unzipped from a hairpin (zipped) conformation to a completely open single-stranded (unzipped) conformation when the magnitude of the self-propelling force, $F^a$, acting on each particle of the bath exceeds a critical value $F^a_c$. We found that below $F^a_c$ the DNA remains in the hairpin conformation, and above it, the DNA is in an unzipped conformation. Our analysis suggests that this unzipping of a DNA hairpin in an active bath is a first-order phase transition.

12:40 to 12:50 Samriddhi Sankar Ray (ICTS, India) Spectral scaling in bacterial turbulence

We discuss new results on the scaling of the energy spectrum in active turbulence and its consequences.

12:50 to 13:00 Srikanth Sastry (JNCASR, India) Stochastic process model of fatigue failure in glasses
13:00 to 13:10 Vijaykumar Krishnamurthy (ICTS, India) Hydrodynamic model for size & shape control in growing tissues

Morphogenetic patterns result from a tight coupling between genetic programs, active mechanochemical processes, and the geometry of shape. While much is known about genetic circuits underlying many biophysical processes, the mechanisms by which this information controls the dynamical evolution of geometrical shapes during development driven by active mechanics is far less explored. We will discuss a hydrodynamic model for describing evolving shapes of tissues wherein the dynamics of the geometry is controlled by active stresses (arising from cell proliferation and topological rearrangements) within the changing geometry. Our results in 1D reveal two distinct ``phases'' with controlled and uncontrolled growth of the tissue size. In 2D, the same framework leads to the emergence of non-trivial shapes.

13:10 to 13:20 Sthitadhi Roy (ICTS, India) Spectral Multifractality and Emergent Energyscales at the Many-Body Localisation Transition

In this talk, I will show that analysing the multifractal properties of the spectral decompositions of eigenstates at different energyscales can help us identify emergent energyscales which may show universal scaling behaviour near the many-body localisation transition.