Abstract: Particulate flows like dust-storms and snow avalanches are impossible to solve exactly for, and so we need to develop analytical and numerical techniques to obtain an understanding of them. I will discuss why this is a hard problem, and discuss a few simplified problems.

References:

1. Sedimentation dynamics of bodies with two planes of symmetry. Harshit Joshi & Rama Govindarajan. Physical Review Letters, 134, 014002, 2025.
2. Explicit Runge-Kutta algorithm to solve non-local equations with memory effects: case of the Maxey-Riley-Gatignol equation. Divya Jaganathan, Rama Govindarajan, Vishal Vasan, arXiv: 2308.09714. Quarterly of Applied Mathematics, LXXXIII, 1, 135–158, https://doi.org/10.1090/qam/1693, 2025.
3. Mechanism of instability in non-uniform dusty channel flow. Anup Kumar & Rama Govindarajan, Journal of Fluid Mechanics, 997, A77, 2024.
4. Trapping and extreme clustering of finitely dense inertial particles near a rotating vortex pair. Saumav Kapoor, Divya Jaganathan and Rama Govindarajan, Journal of Fluid Mechanics, 996, A44, 2024.

Dr. Tapomoy Bhattacharjee

Title: Physical confinement selectively favours bacterial growth based on cell shape

Abstract: How are bacterial communities altered by changes in their microenvironment? Evidence from homogeneous liquid or flat plate cultures implicates biochemical cues — such as variation in nutrient composition, response to chemoattractants and toxins, and inter-species signaling — as the primary modes of bacterial interaction with their microenvironment. However, these systems fail to capture the effect of physical confinement on bacteria in their natural habitats. Bacterial niches like the pores of soil, mucus, and infected tissues are disordered microenvironments with material properties defined by their internal pore sizes and shear moduli. Here, using three-dimensional matrices that match the viscoelastic properties of gut mucus, we test how altering the physical properties of their microenvironment influences bacterial growth under confinement. We find that low aspect-ratio bacteria form compact, spherical colonies under confinement while high aspect-ratio bacteria push their progenies further outwards to create elongated colonies with a higher surface area, enabling increased access to nutrients. As a result, the population level growth of high aspect-ratio bacteria is more robust to increased physical confinement compared to that of low aspect-ratio bacteria. Thus, our results capture the first experimental evidence that physical constraints play a selective role in bacterial growth based on cell shape.

References

1. Gupta R, Adhikary S, Dhalpatraj N, Laxman S. Nature Communications. 2024, Volume 15, article number 7254.
2. Ahmad M. S. et al under preparation 2025

Prof. K. Ganapathy Ayappa

Title: Molecular understanding of oxidized membrane sterols on the loss of GPCR signalling in aged cells

Abstract: G-protein coupled receptors (GPCRs) are transmembrane proteins used for communicating extracellular signals into the cell, responsible for a wide variety of cellular functions. Signal transduction occurs with the binding of a extracellular ligand or signalling molecule which translates into a cascade of intracellular events involved in sensation, cellular growth, inflammation and communication with the immune system. So ubiquitous is the role of GPCRs that they form about 30 – 40 % of existing drug targets.

Ageing has been associated with the onset of senescence wherein cells undergo divisional arrest and resist clearance by the immune system. This senescent state, linked to enhanced inflammatory response, has been associated with enhanced levels of oxysterols in the cellular membrane due to elevated oxidative stress. This disrupts CXCR4 signalling a GPCR that plays a crucial role in modulating immune response and inflammation. In collaboration with the laboratory of Deepak Saini at IISc, we examine the reasons for this disruption using a combination of experiments and molecular dynamics simulations. We report elevated oxysterol levels in senescent cells, which altered classical CXCL12-mediated CXCR4 signalling. Tail-oxidized sterols disrupted signalling more than ring-oxidized counterparts. Molecular dynamics simulations revealed that 27-hydroxycholesterol displaces cholesterol (required for efficient signalling) and binds strongly to alter the conformation of critical signalling residues to modify the sterol-CXCR4 interaction landscape. Our study provides a molecular view of the observed mitigated GPCR signalling in the presence of oxysterols. Overall, we present an altered paradigm of GPCR signalling where cholesterol oxidation alters the signalling outcome in aged cells.

Prof. Raj Ganesh S. Pala

Title: Catalysing Nuclear Reactions & Channelizing its energy

Abstract: The distinguished electrochemist, Martin Fleischmann along with Stanley Pons, announced (in March 1989) that nuclear fusion can be implemented in a table-top electrochemical cell. “Cold fusion” with its glamorous introduction (via a press conference!), uncertain scientific foundations, and formidable issues of reproducibility, rapidly became associated with pathological science (~July 1989). History of science typically relies on one set of scientists establishing empirical facts and another proposing an underlying theory. Unfortunately, Fleischmann-Pons not only burgeoned the experimental results but also proposed a rather untenable theory, which proved to be a straw man, vitiating the usual cycles of evolution of a scientific field in peer-reviewed literature. Being outliers of the mainstream, a band of scientists continued to pursue the work courageously developing their sub-culture.

This seminar is aimed at a general scientific audience and not necessarily at expert nuclear scientists. We will first unfold the field historically, then present the efforts led by Google, the US-DOE, the European Union and the Japanese government-industry consortium to buttress the fact-finding aspirations and pollution-free energy generation. Following this, we will present the results from the “Electrochemically-Activated-Nuclear-Reactions” group at IIT-Kanpur, wherein the focus has been on heavy element nuclear transmutations and signatures of nuclear reactions. Finally, the wanderings in this less chartered territory will include the possibilities at the frontiers of science and consequential engineering.

Prof. M. Eswaramoorthy

Title: Adaptive Pores: Gating of ion transport in mesoporous silica through reversible pore engineering

Abstract: Non-covalent and dynamic covalent methods were used to reversibly modify the pore size and philicity of mesoporous silica. In the non-covalent approach, the strong, charge-transfer interactions between pyranine and viologen moieties were used for reversible pore engineering.The fast binding of donors enabled quick and facile functionalization at room temperature. The viologen based charge transfer modules were employed in electrostatic gating of ion transport through the nanochannels (<10 nm) in mesoporous silica. The polarity of ion transport was switched from anion selective to cation selective through ambipolar stage by controlling the extent of pyranine bound to the viologen. The modularity of the approach enables modification of nanopores with custom designed compositions, components and functions.

References:

1.  B. V. V. S. Pavan Kumar, K. V. Rao, T. Soumya, S. J. George and M. Eswaramoorthy, , J. Am. Chem. Soc., 135, 10902 – 10905 (2013)
2. B. V. V. S. Pavan Kumar, K. Venkata Rao, S. Sampath, S. J. George and M. Eswaramoorthy, Angew. Chem. Int. Ed., 53, 13073-13077 (2014).
3. B. V. V. S. Pavan Kumar, K. P Sonu, K. V Rao, S Sampath, S. J George, M. Eswaramoorthy, ACS Applied Materials & Interfaces 10 (28), 23458-23465 (2018)