Institute Seminar Day

IMSc, Chennai, March 11 and 18, 2019

Venue : Ramanujan Auditorium

Schedule for March 11

(Jump to Schedule for March 18)

Time Speaker Title Abstract

Director's remark and opening

R Ganesh

Insulators as messed up metals

I will describe a recent collaboration with experimentalists where shooting ions into a metal turns it into an insulator. This is an example of 'Anderson localization'. Electrons bouncing off defects become spatially localized, incapable of conducting electricity. As a precursor effect, we see an increase in resistivity due to quantum interference -- a macroscopic consequence of quantum mechanics.

Parameswaran Sankaran

Does the size determine the shape?

The question raised in the title is of course absurd for trivial reasons. But, when one considers a restricted class of spaces, the answer is, quite surprisingly, "almost". The talk should be accessible to a wide audience

R. Shankar

Universal properties of supra-glacial debris distributions

I will describe the observations we have been taking from 2014-18 on Satopanth Bamak (glacier), Garhwal Himalaya, Uttarakhand. Based on our data and that of others on the supra-glacial debris thickness distributions, I will present evidence for some universal scaling properties. Finally, I will pose the theoretical question raised by this result.

Chandrasekhar K A

Mean lifetime doesn't mean much

In various dynamical models people make use of mean periods, be it mean period of an infection, mean lifetime of a molecule, mean time spent in a particular state etc. We believe that in many cases this is insufficient information to even capture the qualitative dynamics of a system. I will provide some examples to support this claim.

Sushmita Venugopalan

What is symplectic geometry?

This talk will explain how symplectic geometry is motivated by Hamiltonian mechanics, and go on to introduce Gromov's non-squeezing theorem, a foundational result in the field.
Coffee Break

R Ramanujam

Towards models of collective memory

Social theorists discuss the notion of collective memory as a process by which a shared pool of individual memories transforms into a group memory, thus shaping group identity and group behaviour. Automata theory is the study of memory structures, and it is reasonable to ask whether automata models can be extended to address collective memory notions as well. We have a modest proposal to offer, pointing to difficulties that lie ahead.

Anand Pathak

Design of a human brain: Uncovering the 'block diagram' of human brain circuitry

In order to understand the functioning of a brain, it is essential to consider it as a complex network of a large number of simpler units interacting with each other through synaptic connections. While studying the entire network at a neuronal resolution is neither practical nor informative at the scale of entire brain, it is rather illuminating to look at a more granular picture where the brain network comprises of individual brain regions as nodes and the white matter tracts connecting them as the links. It is conceptually similar to representing a complex electronic circuit as a block diagram. The brain network at this scale, also known as macro-connectome,signifies the basic wiring of the human brain and this wiring is known to be partly predetermined genetically and partly shaped through individual experiences through plasticity and learning. In this study, we do a comparative analysis of the brain networks of a large set of individuals obtained through brain imaging, in order to understand the basic design of the human brain wiring which remains invariant across the individuals. Further, we ask what can we learn from looking at the variations among individual brains.

Devanand T

Membrane-active peptide Nogo66 induces interdigitization in phospholipid membranes

Our molecular dynamics simulations suggest that membrane active protein Nogo66 inducing interdigitation and phase transition in phospholipid membranes. This phase change happens when the temperature is close to the main transition temperature of themembrane (Tm) and only in the presence of the protein. Our results show that even transient and weak protein-membrane interactions can lead to the formation of lipid defects, which in turn spontaneously lead to the formation of interdigitated lipids in order to prevent energetically unfavorable exposure of hydrophobic defects to water. This study underscores the importance of membrane-active proteins and their interactions with membranes leading to phase transitions which would affect other membrane-related processes.

Shakti Menon

Flocking in systems of stochastically interacting agents with a field of view

Flocking is one of the most spectacular instances of emergent phenomena in the natural world. In recent decades, there has been considerable interest in uncovering the dynamical origins of such phenomena through the framework of "active matter". Such systems comprise self-propelled particles that, through a set of rules specific to the given system, make individual decisions regarding their motion. Changes in these rules can significantly impact the collective dynamical properties of the group as a whole. Consequently, stochasticity in individual behaviour plays a critical role in determining the nature of the emergent flock. In this talk, I will outline a model for the flocking dynamics of agents that exhibit velocity-alignment interactions with neighbours that lie within their field of view. This model differs from most previous approaches in that stochasticity in the dynamics arises purely from uncertainties at the level of interactions. Despite the absence of any attractive forces the model gives rise to a wide range of emergent flocking patterns that exhibit long-time spatial cohesion. The results suggest that the choice of field of view is crucial in determining the emergent flocking dynamics of such systems.

Subhankar Khatua

In how many ways can four vectors be added to zero -- part 2.

Magnetic systems with frustration are known to have large classical degeneracy. Their low energy physics can be understood as dynamics within the space of classical ground states. We explore this idea in a family of clusters where every pair of spins is connected by an XY antiferromagnetic bond. The dimer with two spin-S spins provides the simplest example -- it maps to a quantum particle on a ring (S^1). The trimer is more complex, equivalent to a particle that lives on two disjoint rings (S^1xZ_2). For both the dimer and the trimer, the validity of the effective theory can be seen from a path-integral-based derivation. This approach cannot be extended to the quadrumer which has a non-manifold ground state space, consisting of three tori that touch along lines. In order to understand dynamics on this space, we develop a tight binding model with this connectivity. Remarkably, this successfully reproduces the low energy spectrum of the quadrumer. The non-manifold character of this space leads to a remarkable effect -- at low energies, the system is localized around singular lines in the ground state space. The low energy spectrum consists of an extensive number of bound states, formed around singularities. Physically, this manifests as an order-by-disorder-like preference for collinear ground states. However, unlike order-by-disorder, this `order by singularity' persists even in the classical limit.
Director's Lunch

Mukul Laad

Can one have a Continuous Metal-Insulator quantum phase transition?

Metal-Insulator phase transitions are generally abrupt. An exception is the one driven by disordering a material till electronic conduction becomes impossible. I will try to convince you that this case hides novel physics

G Baskaran

Crowded Protons and Neutrons in Nuclei

Traditionally we discuss nucleus of atoms using shell model, as atomic mass increases. Filling of shells is well known for electrons in atoms, where positively charged nucleus bind together mutually repelling electrons. In nuclei, even in the absence of an attracting center, protons and neutrons hold themselves together using strong-mutual nuclear forces. A consequent revision of shell model has been suggested in some cases. That is, certain nuclei may support novel quantum many body states. Quantum crowd of electrons in some crystalline solids or liquid He3 droplets could help understand this.

Shreyansh S Dave

Effects of magnetic field on plasma evolution in relativistic heavy-ion collisions

Very strong magnetic fields can arise in non-central heavy-ion collisions at ultra-relativistic energies, which may not decay quickly in a conducting plasma. We carry out relativistic magneto-hydrodynamics (RMHD) simulations to study the effects of this magnetic field on the evolution of the plasma and on resulting flow fluctuations in the ideal RMHD limit. Our results show that the magnetic field leads to enhancement in elliptic flow for small impact parameters while it suppresses it for large impact parameters. Interestingly, we find that magnetic field in localized regions can temporarily increase in time as evolving fluid energy density fluctuations lead to reorganization of magnetic flux. This can have important effects on the chiral magnetic effect.

Ria Ghosh

Topological transitions to vortex unbinding in systems of coupled oscillators

Periodic activity is seen in a variety of natural systems spanning several length and time scales. Such systems can be understood by investigating the collective behavior of systems of coupled oscillators under different conditions. Intrinsic heterogeneity or external noise can often induce the spontaneous generation of vortices or spiral waves of reentrant activity in systems of coupled oscillators arranged on a two-dimensional lattice. The phase singularity at the tip of a spiral wave is a topological defect in the phase field (with a topological charge of +1 or -1 depending on the chirality of the spiral). The analogy with similar defects seen in the 2-dimensional XY spin model (with different spin orientations associated with each lattice site, similar to the different phase angles associated with each oscillator) has led us to explore whether a KT-like transition occurs in coupled oscillator systems leading to unbinding of vortex-antivortex pairs at sufficiently high levels of noise. The existence of such a transition can have functional consequences for biological systems that comprise of coupled oscillating elements (such as the gravid uterus).
Coffee Break

Janaki R

Lateral inhibition as a mechanism for pattern formation

The collective dynamics seen in a wide variety of chemical, biological and ecological systems involve interactions between relaxation oscillators that typically involve fast activation process coupled with a slower inactivation. In this talk, I will explain how systems of such oscillators having distinct kinetics governing local dynamical behavior and whose interactions are described by different connection topologies, can exhibit strikingly similar spatiotemporal patterns when diffusively coupled via their inactivation component. I will also highlight the apparent universality of this global behavior by showing that relaxation oscillators interacting via lateral inhibition will generally yield two basic classes of patterns, viz., one comprising one or more clusters of synchronized oscillators while the other is a time-invariant spatially inhomogeneous state resulting from oscillation death. All observed collective states can be interpreted either as specific instances of these fundamental patterns or as resulting from their competition.

R. Janani

Network science perspective on a chemical space harmful to humankind

Humankind is exposed to several chemicals in their daily environment which can affect our well-being. Endocrine Disrupting Chemicals (EDCs) is a group of chemicals that can cause adverse health effects related to reproduction, development, metabolism, immune and nervous system. We have developed a detailed pipeline and identified 686 EDCs with experimental evidence specific to human or rodents from published literature. We have classified these 686 EDCs into 7 broad categories and 48 sub-categories based on their environmental source or product use. Importantly, we have documented the specific endocrine-mediated perturbations along with the dosage range for individual EDCs at which endocrine disruption was observed in mammalian experiments. Based on our resource, we have constructed two networks, namely, the chemical similarity network and the chemical-target network. Subsequently, we have analyzed these networks to investigate relationships between chemical structure and biological function of EDCs. Our resource will aid academia, industry and regulatory agencies to deliver safer consumer products in future. This work is in collaboration with Bagavathy Shanmugam Karthikeyan, Karthikeyan Mohanraj, R.P. Vivek-Ananth and Areejit Samal.

Sanjukta Roy

Manipulating Tournaments: How to make your favourite player win?

A very common type of tournament is the so-called knockout tournament where no ties are allowed i.e., every match produces a winner. Moreover, once a player loses a match, s/he is eliminated from the competition. Thus the winner of a knockout tournament has won all of her/his matches. In this talk we will see if one can affect the outcome of the competition by changing the structure of the tournament. We will also point out the computational aspect of this problem.

Sitabhra Sinha

How representative is our democracy? Using open data on the Web to relate wealth and electoral performance in recent Indian general elections

Using open databases (publicly available on the Web) of assets declarations made by candidates contesting in the Indian general elections held over the last decade, we show that the distribution of their wealth follows a universal scaling form which is independent of the year, as well as, states and, most surprisingly, even the parties to which the candidates belong. We also observe that the set of winners, as well as, that of the “serious candidates” (contenders) have asset distributions which deviate significantly from those of the remaining candidates. This is a worrying aspect given the supposedly representative nature of electoral democracies, particularly in light of the recent worldwide rise to power of xenophobic populism.
End Of Day One

Schedule for March 18

Time Speaker Title Abstract


Gautam Menon

How is the cell nucleus organized?

A central problem in biophysics is to understand how the contents of the cell nucleus, mainly chromosomes, are organized inside iit. This seems like an unimaginably complex and intractable problem. However, addressing this question using a simplified model that emphasizes the role of non-equilibrium physics has enabled some surprising progress towards this end. I will try to describe these ideas at a qualitative level.


Rakesh Netha

The role of chromatin in TF binding

It is well known that differential gene expression gives rise to different cell types. Various factors such as genome organization, binding of transcription factors(TFs) on the genome etc. contribute to this differential gene expression. It is also shown co-operative binding or combinatorial binding of TFs at a given region of genome is one of mechanism that contributes to the differential gene expression. In our study, we are exploring binding patterns of different TFs on genome regions which are sequentially far apart, but spatial proximal due to 3D chromatin organization. We are also exploring functional roles of such binding patterns.


Pallavi Jain

Committee Selection in Social Choice: Why and How?

Selecting a non-controversial committee of size k is an important question in social choice theory and voting theory. A committee is weakly Gehrlein stable if each committee member is preferred to each non-member by at least half of the voters. In this talk, we will see how hard it is to choose a weakly Gehrlein stable committee of size k.


Amritanshu Prasad

Canonical constructions of polyhedra

The symmetry group of the dedecahedron, icoasahedron, and football are all the same - the alternating group on five letters. Is it possible to start with a set of five elements and construct these polyhedra in such a way that this symmetry emerges naturally? I will describe such constructions which I developed with the help of Abhinav Kumar. They also reflect the duality between the dodecahedron and icosahedron.


Prashanth Raman

Stokes Polytopes and Scattering amplitudes

In this talk, we begin by showing the one to one correspondence between dissections of polygons and tree graphs. We describe the associahedron which is a famous polytope associated with dissection of a polygon into triangles known since the 60's. We then describe a recently discovered polytope called the Stokes polytope for more general dissections of polygons. Finally, we briefly present a new reformulation of scattering amplitudes as the volume of some of these polytopes.
Coffee Break


Shrihari Gopalakrishna

Higgs Vacuum Stability

The recently determined Higgs mass indicates that the Higgs vacuum state we find ourselves in is meta-stable and may decay to a new vacuum state in which the particle masses will be very different from what they are now. I will discuss the Higgs vacuum stability issue and how this is affected by new physics beyond the standard model of particle physics.


Ria Sain

Optimal Observable technique

There are several low energy observables which can be measured with very good accuracy in different experiments. The interesting scenarios are the ones where the Standard Model (SM) of particle physics predictions for one or more observables significantly deviate from their respective measured values. If we understand very well the SM calculations along with their respective errors, then we can suspect that the observed discrepancies are due to some Beyond Standard Model (BSM) physics. There could be various New Physics (NP) explanations of an observed excess, although it is not necessary for an observable to show equal sensitivity to all the different types of NP. In these contexts, the question that inevitably arises is: How an observable can be optimized to get maximal sensitivity to a specific NP coupling? In search of the answer to this question, Optimal Observable technique is used. With this technique, one can systematically estimate the statistical uncertainty of the measurable parameters while extracting them from some observable. This, in turn, will help us to check the sensitivity of that observable to a particular type of NP structure.


Srimoy Bhattacharya

Survival for the fittest (No Talk)

Flavor physics anomalies are basically based on the mismatch among data and theory. Here as a standard theory, we consider "The Standard Model". Nowadays, there are a plethora of new physics models, that are available to explain the observed anomalies ( the mismatch in the experimental outcome and the standard model prediction for flavor observables). Hence it is very useful to identify among all these which type of new physics model can best explain the current data. In this talk, I will try to emphasize on the information-theoretic approaches, especially of `Second-order Akaike Information Criterion' (AICc) for the aforementioned model selection procedure.


Anantha Padmanabha

What someone knows and what everyone knows?

Suppose everyone knows that raining makes the ground wet and someone knows that it is raining, then we should be able to conclude that someone knows that the ground is wet. In our institute, while applying for contingency grant, we know that somebody knows the procedure to process the application (though we might not know who exactly it is) and on the other hand, everybody knows that the money will be deposited within a month. As an other example, we can say that somebody knows the proof of Fermat's last theorem without knowing who Andrew Wiles is. Associating knowledge with a particular "agent" without knowing the identity (name of the agent) is quite common. Such scenarios include games with large number of players (like voting), social media, security protocols etc where the anonymity is often crucial. In this talk we shall discuss how to model such scenarios using formal logic.


M Ashraf

Network Representation of Sequences

We show using simple examples of how sequences of symbols can be graphically represented as networks. The properties of networks generated from randomized sequences (i.e., those generated by considering a probability distribution of occurrence of a finite set of symbols, i.e., the ``alphabet'') are analyzed using network metrics such as average path length and clustering coefficient. Against these, we compare the properties of networks generated from empirically obtained sequences, viz., extracts of texts written in known languages. We show that the latter is characterized by path lengths shorter than that in corresponding randomized networks, and are also much less clustered. Consequently, we have termed them as infra-small-world networks.


Sibasish Ghosh

Quantum precision thermometry with weak measurement

As the miniaturization of electronic devices, which are sensitive to temperature, grows apace, sensing of temperature with ever smaller probes is more important than ever. Genuinely quantum mechanical schemes of thermometry are thus expected to be crucial to future technological progress. We propose a new method to measure the temperature of a bath using the weak measurement scheme with a finite dimensional probe. The precision order of the temperature measurement by the present scheme not only shows similar qualitative features as the usual Quantum Fisher Information based thermometric protocols, but also allows for flexibility over setting the optimal thermometric window through judicious choice of post selection measurements. [In collaboration with Arun K. Pati, Chiranjib Mukhopadhyay, and Sagnik Chakraborty; arXiv:1901.07415 (quant-ph)]


Vinay V

Coupling of heat and mass transport in liquids

Maintaining the two ends of a matter at different temperatures i.e., imposing a temperature gradient results in heat flow. A liquid mixture under such thermal gradient has an additional response of mass flow leading to compositional inhomogeneity. Understanding this phenomenon which is popularly known as thermophoresis or Ludwig-Soret effect, is crucial in the context of volcanic-eruption, metallic alloys, mixture fractionation etc. In this talk, I will discuss the Soret effect in glass-forming liquid mixtures.


Kamal Tripathi

Conformations of confined/crowded polymers near attractive curved surfaces

Adsorption of polymers onto surfaces has relevance in applications such as the coating of surfaces, aspects of Interfacial macromolecular recognition, adhesion, wetting etc. Polymers are also an integral part of novel biological applications such as bioadhesive drug delivery systems and understanding the conformations they take at different surfaces is relevant in such applications. We perform extensive molecular dynamics simulations of a single long neutral polymer confined in a spherical volume, in both good and poor solvent conditions, to understand the role of specific interactions of polymers with the crowder particles and with the confining wall.


Snehajit Misra

Nef cone and pseudoeffective cone of product of projective bundles over a curve

Nef cone and pseudoeffective cone are fundamental invariants of a smooth projective complex variety and an active area of research in Algebraic Geometry. In this talk, we will discuss about the nef cones and pseudoeffective cones of product of projective bundles over a smooth irreducible curve C. We will explore these cones in different cases, depending on the vector bundles defining the projective bundles. This is a joint work with Rupam Karmakar and Nabanita Ray and has appeared in Bull. Sci. Math, 151,(2019) 1-12.
Coffee Break


K Srinivas

On Euclidean domains

One of the classical problems in number theory is to determine which Integral-domains are Euclidean. We shall discuss this topic in this talk.


Shraddha Srivastava

Koszul duality

A class of multilinear operations like tensor powers, symmetric powers, and exterior powers can be formalized as modules for the Schur algebra S(n,d). These modules can also be viewed as representations of general linear group GL(n). Classical Schur-Weyl duality relates these modules with representations of the symmetric group S_d. Representations of S_d are parametrized by Young diagrams of size d. Multiplication by the sign character of S_d sends a Young diagram to its transpose. Under Schur-Weyl duality, this operation becomes the Koszul duality functor discovered by Krause. We discuss a surprising relationship between Koszul duality and the Schur algebra associated with the alternating group. This gives a new approach to understanding Koszul duality. Based on joint work with T. Geetha and A. Prasad.


Lawqueen Kanesh

Representative sets

We will see an algorithmic tool via a combinatorial identity.


Harish K

The shape of complex networks

Topological Data Analysis (TDA) is emerging as a powerful tool to analyze the structure and the 'shape' of real-world data. This has resulted in wide-spread applications of TDA by both the industrial and scientific communities. A survey of existing literature concerning the study of persistent homology of complex networks revealed a need for a more systematic procedure to study the persistent homology of unweighted networks. In this joint work with Areejit Samal and Indrava Roy, we present a new method based on discrete Morse theory to study the topological properties of unweighted and undirected networks using persistent homology. We have employed our methods to explore the persistent homology of several unweighted model and real-world networks. In particular, we find that the corresponding persistence diagrams can distinguish between the 'shape' of different types of model networks, thereby increasing the applicability of persistent homology to investigate the inherent topological features of unweighted complex networks.


Roohani Sharma

Surgical Preprocessing

Preprocessing is ubiquitous when it comes to solving a difficult problem. Given a large instance of a difficult problem, the goal of pre-processing is to typically reduce the problem size into a ``manageable" chunk. We will talk about a kind of pre-processing, which we call surgical pre-processing, for problems modelled on graphs, and its connection with the ``language" used to express the problem.
High Tea

Last modified: Mon Mar 18 11:34:50 IST 2019