arXiv subjects

Vimal Kishore

Publications and source records attributed to Vimal Kishore.

9 recordsLinked to original sources

arXiv2026

Coalescence of Polymer Droplets Moving on a Surface with Stiffness Gradient

Here, we study the coalescence of two droplets that are moving in the same direction on a soft surface; the motion of the droplets is caused by a gradient in the surface stiffness. As reference, stationary coalescence of the same droplets is also studied on the corresponding uniform surfaces for different stiffness values. To describe the coalescence phenomenon on a surface with stiffness gradient, a relevant range of velocity ratios of the leading and the trailing droplet was considered to elucidate the effect of this parameter on coalescence. Moreover, to analyze the dynamics of the process, the temporal growth of the bridge height $(h)$ was investigated, which follows a power law $(h \sim t^{\alpha})$, before eventually attaining a constant value. The obtained values of $\alpha$ show a transition from a higher to a lower value as a function of time, pointing to the presence of two distinct power-law growth regimes, where the transition signifies the crossover from the capillarity-dominated regime to the viscoelasticty-dominated regime of coalescence. In addition, varying attractive strengths for droplet--droplet and intra-droplet interactions were considered. The results indicate that both the dynamics and the degree of the coalescence strongly depend on these interaction parameters. Thus, we anticipate that our results will shed more light on the durotaxis-driven coalescence of polymeric droplets for various relevant system parameters, which will have practical implications for applications ranging from microfluidics to ink-jet printing, where substrate properties may vary. In addition, results may add to the fundamental understanding of the interactions among multicellular aggregates moving on biological surfaces.

cond-mat.soft↗

arXiv2025

Bunching of extreme events on complex network

Extreme events such as earthquakes, floods, and power blackouts often display burst phenomena where multiple extreme events occur in quick succession or in bunches. This study examines bunching of extreme events on a complex network using a random walk transport model. We find that in a modular network, a small cluster sparsely connected with the rest, shows bunching and correlations among extreme events. The bunching and correlations emerge naturally in our system. We use several characterization techniques, namely the recurrence time distribution, autocorrelation function, bursty trains, burstiness parameter and memory coefficient to quantify the bunching and correlations of extreme events. Our study shows that the network structure plays a significant role in the bunching of extreme events.

physics.soc-ph↗

arXiv2025

Approach to network failure due to intrinsic fluctuations

A networked system can fail when most of its components are unable to support flux through the nodes and edges. As studied earlier this scenario can be triggered by an external perturbation such as an intentional attack on nodes or for internal reasons such as due to malfunction of nodes. In either case, the asymptotic failure of the network is preceded by a cascade of nodal failures. In this work, we focus on the nodal failure arising from the intrinsic fluctuations in the flux passing through the nodes. By modeling these as extreme events, it is shown that three distinct nodal failure regimes can be identified before a complete network failure takes place. Further, the approach to network failure through the three regimes is shown to be qualitatively similar on a square lattice, all-to-all, scale free, and Erdos-Renyi networks. We obtain approximate analytical description of the approach to failure for an all-to-all network. This is also demonstrated numerically for real transportation network of flights.

cond-mat.stat-mech↗

arXiv2022

Order and Information in the Patterns of Spinning Magnetic Micro-disks at the Air-water Interface

The application of the Shannon entropy to study the relationship between information and structures has yielded insights into molecular and material systems. However, the difficulty in directly observing and manipulating atoms and molecules hampers the ability of these systems to serve as model systems for further exploring the links between information and structures. Here, we use, as a model experimental system, hundreds of spinning magnetic micro-disks self-organizing at the air-water interface to generate various spatiotemporal patterns with varying degrees of orders. Using the neighbor distance as the information-bearing variable, we demonstrate the links among information, structure, and interactions. Most importantly, we establish a direct link between information and structure without using explicit knowledge of interactions. Finally, we show that the Shannon entropy by neighbor distances is a powerful observable in characterizing structural changes. Our findings are relevant for analyzing natural self-organizing systems and for designing collective robots.

cond-mat.soft↗

arXiv2021

Biocompatible carbon nitride-based light-driven microswimmer propulsion in biological and ionic media with responsive on-demand drug delivery

We propose two-dimensional organic poly(heptazine imide) (PHI) carbon nitride microparticles as light-driven microswimmers in various ionic and biological media. Their demonstrated high-speed (15-23 $μ$m/s) swimming in multi-component ionic solutions with concentrations up to 1 M and without dedicated fuels is unprecedented, overcoming one of the bottlenecks of previous light-driven microswimmers. Such high ion tolerance is attributed to a favorable interplay between the particle's textural and structural nanoporosity and optoionic properties, facilitating ionic interactions in solutions with high salinity. Biocompatibility of the microswimmers is validated by cell viability tests with three different cell types and primary cells. The nanopores of the swimmers are loaded with a model cancer drug, doxorubicin (DOX), in high (185%) loading efficiency without passive release. Controlled drug release is reported in different pH conditions and can be triggered on-demand also by illumination. Light-triggered, boosted release of DOX and its active degradation products is demonstrated in oxygen-poor conditions using the intrinsic, environmentally sensitive and light-induced charge storage properties of PHI, which could enable future theranostic applications in oxygen-deprived tumor regions. These organic PHI microswimmers simultaneously solve the current light-driven microswimmer challenges of high ion tolerance, fuel-free high-speed propulsion in biological media, biocompatibility and controlled on-demand cargo release towards their biomedical, environmental and other potential future applications.

cond-mat.soft↗

arXiv2013

Manipulation of extreme events on scale-free networks

Extreme events taking place on networks are not uncommon. We show that it is possible to manipulate the extreme events occurrence probabilities and its distribution over the nodes on scale-free networks by tuning the nodal capacity. This can be used to reduce the number of extreme events occurrences on a network. However monotonic nodal capacity enhancements, beyond a point, do not lead to any substantial reduction in the number of extreme events. We point out the practical implication of this result for network design in the context of reducing extreme events occurrences.

cond-mat.stat-mech↗

arXiv2012

Extreme events and event size fluctuations in biased random walks on networks

Random walk on discrete lattice models is important to understand various types of transport processes. The extreme events, defined as exceedences of the flux of walkers above a prescribed threshold, have been studied recently in the context of complex networks. This was motivated by the occurrence of rare events such as traffic jams, floods, and power black-outs which take place on networks. In this work, we study extreme events in a generalized random walk model in which the walk is preferentially biased by the network topology. The walkers preferentially choose to hop toward the hubs or small degree nodes. In this setting, we show that extremely large fluctuations in event-sizes are possible on small degree nodes when the walkers are biased toward the hubs. In particular, we obtain the distribution of event-sizes on the network. Further, the probability for the occurrence of extreme events on any node in the network depends on its 'generalized strength', a measure of the ability of a node to attract walkers. The 'generalized strength' is a function of the degree of the node and that of its nearest neighbors. We obtain analytical and simulation results for the probability of occurrence of extreme events on the nodes of a network using a generalized random walk model. The result reveals that the nodes with a larger value of 'generalized strength', on average, display lower probability for the occurrence of extreme events compared to the nodes with lower values of 'generalized strength'.

cond-mat.stat-mech↗

arXiv2011

Extreme events on complex networks

We study the extreme events taking place on complex networks. The transport on networks is modelled using random walks and we compute the probability for the occurance and recurrence of extreme events on the network. We show that the nodes with smaller number of links are more prone to extreme events than the ones with larger number of links. We obtain analytical estimates and verify them with numerical simulations. They are shown to be robust even when random walkers follow shortest path on the network. The results suggest a revision of design principles and can be used as an input for designing the nodes of a network so as to smoothly handle an extreme event.

cond-mat.stat-mech↗

arXiv2005

Self-Organized Dynamical Equilibrium in the Corrosion of Random Solids

Self-organized criticality is characterized by power law correlations in the non-equilibrium steady state of externally driven systems. A dynamical system proposed here self-organizes itself to a critical state with no characteristic size at ``dynamical equilibrium''. The system is a random solid in contact with an aqueous solution and the dynamics is the chemical reaction of corrosion or dissolution of the solid in the solution. The initial difference in chemical potential at the solid-liquid interface provides the driving force. During time evolution, the system undergoes two transitions, roughening and anti-percolation. Finally, the system evolves to a dynamical equilibrium state characterized by constant chemical potential and average cluster size. The cluster size distribution exhibits power law at the final equilibrium state.

cond-mat.soft↗