Biological membranes undergo dramatic shape transformations during vesicle release, organelle division, and intracellular trafficking. At the microscopic level these events require a change in membrane topology: the transformation of one continuous membrane into two separate ones. Such transitions occur on nanometre length scales where lipids must rearrange into highly curved, non-bilayer structures while still preserving the membrane’s barrier function.
In cells, specialized proteins such as dynamin catalyze these topological transitions. In this talk I will show how theoretical modelling and simulations can reveal the mechanisms and the control knobs that make them fast, reliable, and sometimes leaky. Using self-consistent field theory, coarse-grained molecular simulations, and phenomenological models, we map the energy landscapes governing membrane fusion and fission and identify the transient intermediates that dominate them, including hemifusion diaphragms, stalks, rim pores, and worm-like micelles.
A central message is that small changes in membrane composition or membrane–protein interactions can strongly reshape the energy landscape, producing large changes in the free-energy barriers and therefore in the rates and outcomes of membrane division. I will also discuss how multiple-membrane geometries, such as mitochondria and endoplasmic-reticulum contact sites, open additional pathways to membrane fission through transient inter-membrane fusion events.
Coiled coils (CCs) are ubiquitous structural motifs in biological materials, e.g., forming load-bearing elements of cytoskeleton and extracellular matrix proteins. CCs consists of two (or more) α-helices wound around each other in a superhelical fashion. This well-defined geometry, combined with sequence modularity, makes CCs attractive building blocks for bioinspired materials, where engineered CCs can serve as reversible crosslinks. Our key goal is to understand the molecular determinants of CC mechanics and to exploit this knowledge for the design of materials with molecularly encoded dynamic mechanical properties. Using atomic force microscope (AFM)-based single-molecule force spectroscopy, we have shown that the molecular rupture forces of CCs depend on length, helix propensity, hydrophobic core packing and pulling geometry. Based on this knowledge, we have developed a library of CCs with tuneable thermodynamic, kinetic and mechanical properties and synthesized a series of CC-crosslinked poly(ethylene glycol)-based hydrogels. We show that equilibrium thermodynamic and kinetic parameters (as well as network architecture) determine bulk viscoelastic properties in the linear viscoelastic range while molecular rupture forces correlate with bulk material failure. Our modular hydrogel platform thus provides a molecularly controlled extracellular matrix mimic for dissecting how local and global mechanical properties govern cellular mechanosensing.
Flare ribbons are a quintessential part of a flare. They are extensively used to understand the overlying reconnection mechanism and overall flaring process. Further, the reconnection rate is a key parameter in the magnetic reconnection process. But it is difficult to estimate the rate from direct observations at higher heights in the solar atmosphere. However, flare ribbons are believed to be one of the major energy deposition sites and the imprints of reconnection occurring at higher altitudes. Utilizing this advantage to map the reconnection rate at the corona, Qiu et al. (2002, 2006) had provided an approach to estimate the flux and flux rate in a flare.
In the talk, I will discuss about the application of this method to multiple wavelengths in the solar atmosphere using high resolution data from ground-based Multi Application Solar Telescope (MAST)/Udaipur Solar Observatory in Ca II 8542 line, and data in UV and EUV channels from the Atmospheric Imaging Assembly (AIA) and Helioseismic Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). I will highlight the interesting profiles of reconnection flux and associated rates for all the channels in ribbon (sub)structures, along with the probable nature of reconnection occurring there. The work also explains the triggering mechanism behind the reconnection in 3D using the non-force-free-field (NFFF) extrapolation model.
Correlated quantum systems in 1D have a long and impactful history in the study of quantum matter. Many analytical and numerical insights that remain elusive for their higher-dimensional analogues are now available for these systems. Yet, the understanding that these isolated 1D models afford cannot directly be translated to equivalent ones in 2D and 3D. Quasi-1D systems, higher-dimensional systems comprised of many 1D sub-units weakly coupled to one another, offer a way out of this dilemma. This presentation will review our recent results, obtained with several collaborating groups, in using such systems to bootstrap the considerable power of methods originally developed for 1D to key challenges for higher-dimensional models in the domain of correlated quantum matter. Specifically, this talk will show how designing a high-Tc superconducting model material in 3D from microscopic first principles is possible using this approach [1,2], as is the study of induced superconductivity evolving out of non-equilibrium dynamics [3], or the gaining of new insight into Kivelson’s long-standing proposal for reservoir-enhanced superconductivity [4,5]. It will further be shown how quasi-1D systems are ideal proving grounds for powerful new hybrid algorithms to treat correlated quantum matter in 2D and 3D [6,7].
[1] Phys. Rev. X 13, 011039 (2023).
[2] Phys. Rev. B 111, 125141 (2025).
[3] SciPost Phys. 15, 236 (2023).
[4] arXiv:2507.18707 (accepted as Letter in PRB).
[5] arXiv:2602.11153 (in review at PRB)
[6] arXiv:2411.00480.
[7] Phys. Rev. B 112, 205133 (2025).
