@article{lee_chan_carlson_dalnoki-veress_2022, title={Multiple droplets on a conical fiber: formation, motion, and droplet mergers}, volume={18}, url={http://dx.doi.org/10.1039/d1sm01462e}, DOI={10.1039/d1sm01462e}, abstractNote={Small droplets on slender conical fibers spontaneously move along the fiber due to capillary action. The droplet motion depends on the geometry of the cone, the surface wettability, the surface tension, the viscosity, and the droplet size. Here we study with experiments and numerical simulations, the formation, spontaneous motion, and the eventual merger, of multiple droplets on slender conical fibers as they interact with each other. The droplet size and their spacing on the fibre is controlled by the Plateau-Rayleigh instability after dip-coating the conical fiber. Once these droplets are formed on the fiber, they spontaneously start to move. Since droplets of different size move with different speeds, they effectively coarsen the droplet patterning by merging on the fiber. The droplet merging process affects locally the droplet speed and alters the spatiotemporal film deposition on the fiber.}, number={7}, journal={Soft Matter}, publisher={Royal Society of Chemistry (RSC)}, author={Lee, Carmen L. and Chan, Tak Shing and Carlson, Andreas and Dalnoki-Veress, Kari}, year={2022}, pages={1364–1370} }
 @article{doering_drawert_lee_pruitt_petzold_dalnoki-veress_2022, title={Noise resistant synchronization and collective rhythm switching in a model of animal group locomotion}, volume={9}, url={http://dx.doi.org/10.1098/rsos.211908}, DOI={10.1098/rsos.211908}, abstractNote={Biology is suffused with rhythmic behaviour, and interacting biological oscillators often synchronize their rhythms with one another. Colonies of some ant species are able to synchronize their activity to fall into coherent bursts, but models of this phenomenon have neglected the potential effects of intrinsic noise and interspecific differences in individual-level behaviour. We investigated the individual and collective activity patterns of two Leptothorax ant species. We show that in one species (Leptothorax sp. W), ants converge onto rhythmic cycles of synchronized collective activity with a period of about 20 min. A second species (Leptothorax crassipilis) exhibits more complex collective dynamics, where dominant collective cycle periods range from 16 min to 2.8 h. Recordings that last 35 h reveal that, in both species, the same colony can exhibit multiple oscillation frequencies. We observe that workers of both species can be stimulated by nest-mates to become active after a refractory resting period, but the durations of refractory periods differ between the species and can be highly variable. We model the emergence of synchronized rhythms using an agent-based model informed by our empirical data. This simple model successfully generates synchronized group oscillations despite the addition of noise to ants' refractory periods. We also find that adding noise reduces the likelihood that the model will spontaneously switch between distinct collective cycle frequencies.}, number={3}, journal={Royal Society Open Science}, publisher={The Royal Society}, author={Doering, Grant Navid and Drawert, Brian and Lee, Carmen and Pruitt, Jonathan and Petzold, Linda R. and Dalnoki-Veress, Kari}, year={2022}, month={Mar} }
 @article{bertin_lee_salez_raphaël_dalnoki-veress_2021, title={Capillary levelling of immiscible bilayer films}, url={https://doi.org/10.1017/jfm.2020.1045}, DOI={10.1017/jfm.2020.1045}, abstractNote={Abstract Flow in thin films is highly dependent on the boundary conditions. Here, we study the capillary levelling of thin bilayer films composed of two immiscible liquids. Specifically, a stepped polymer layer is placed atop another, flat polymer layer. The Laplace pressure gradient resulting from the curvature of the step induces flow in both layers, which dissipates the excess capillary energy stored in the stepped interface. The effect of different viscosity ratios between the bottom and top layers is investigated. We invoke a long-wave expansion of the low-Reynolds-number hydrodynamics to model the energy dissipation due to the coupled viscous flows in the two layers. Good agreement is found between the experiments and the model. Analysis of the latter further reveals an interesting double cross-over in time, from Poiseuille flow, to plug flow and finally to Couette flow. The cross-over time scales depend on the viscosity ratio between the two liquids, allowing for the dissipation mechanisms to be selected and finely tuned by varying this ratio.}, journal={Journal of Fluid Mechanics}, author={Bertin, Vincent and Lee, Carmen L. and Salez, Thomas and Raphaël, Elie and Dalnoki-Veress, Kari}, year={2021}, month={Mar} }
 @article{fournier_lee_schulman_raphaël_dalnoki-veress_2021, title={Droplet migration on conical fibers}, volume={44}, url={http://dx.doi.org/10.1140/epje/s10189-021-00014-z}, DOI={10.1140/epje/s10189-021-00014-z}, abstractNote={The spontaneous migration of droplets on conical fibers is studied experimentally by depositing silicone oil droplets onto conical glass fibers. Their motion is recorded using optical microscopy and analyzed to extract the relevant geometrical parameters of the system. The speed of the droplet can be predicted as a function of geometry and the fluid properties using a simple theoretical model, which balances viscous dissipation against the surface tension driving force. The experimental data are found to be in good agreement with the model.}, number={2}, journal={The European Physical Journal E}, publisher={Springer Science and Business Media LLC}, author={Fournier, Clementine and Lee, Carmen L. and Schulman, Rafael D. and Raphaël, Élie and Dalnoki-Veress, Kari}, year={2021}, month={Feb} }
 @article{chan_lee_pedersen_dalnoki-veress_carlson_2021, title={Film coating by directional droplet spreading on fibers}, volume={6}, url={https://doi.org/10.1103/PhysRevFluids.6.014004}, DOI={10.1103/PhysRevFluids.6.014004}, abstractNote={Plants and insects use slender conical structures to transport and collect small droplets, which are propelled along the conical structures due to capillary action. These droplets can deposit a fluid film during their motion, but despite its importance to many biological systems and industrial applications the properties of the deposited film are unknown. We characterise the film deposition by developing an asymptotic analysis together with experimental measurements and numerical simulations based on the lubrication equation. We show that the deposited film thickness depends significantly on both the fiber radius and the droplet size, highlighting that the coating is affected by finite size effects relevant to film deposition on fibres of any slender geometry. We demonstrate that by changing the droplet size, while the mean fiber radius and the Capillary number are fixed, the thickness of the deposited film can change by an order of magnitude or more. We show that self-propelled droplets have significant potential to create passively coated structures.}, number={1}, journal={Physical Review Fluids}, publisher={American Physical Society (APS)}, author={Chan, Tak Shing and Lee, Carmen L. and Pedersen, Christian and Dalnoki-Veress, Kari and Carlson, Andreas}, year={2021}, month={Jan} }