publications

2024

1. Buckling instability in a chain of sticky bubbles

   Carmen L. Lee, and Kari Dalnoki-Veress

   Phys. Rev. Res., Jun 2024

   Publisher: American Physical Society

   Abs

   A slender object undergoing an axial compression will buckle to alleviate the stress. Typically the morphology of the deformed object depends on the bending stiffness for solids, or the viscoelastic properties for liquid threads. We study a chain of uniform sticky air bubbles that rise due to buoyancy through an aqueous bath. A buckling instability of the bubble chain with a characteristic wavelength is observed. If a chain of bubbles is produced faster than it is able to rise, the dominance of viscous drag over buoyancy results in a compressive stress that is alleviated by buckling the bubble chain. Using low Reynolds-number hydrodynamics, we predict the critical buckling speed, the terminal speed of a buckled chain, and the geometry of the buckles.

2. Particle scale anisotropy controls bulk properties in sheared granular materials

   Carmen L. Lee, Ephraim Bililign, Emilien Azéma , and 1 more author

   May 2024

   arXiv:2405.00653 [cond-mat]

   Abs

   The bulk dynamics of dense granular materials arise through a combination of particle-scale and mesoscale effects. Theoretical and numerical studies have shown that collective effects are created by particle-scale anisotropic structures such as grain connectivity (fabric), force transmission, and frictional mobilization, all of which influence bulk properties like bulk friction and the stress tensor through the Stress-Force-Fabric (SFF) relationship. To date, establishing the relevance of these effects to laboratory systems has remained elusive due to the challenge of measuring both normal and frictional contact forces at the particle scale. In this study, we perform experiments on a sheared photoelastic granular system in an quasi-2D annular (Couette) cell. During these experiments, we measure particle locations, contacts, and normal and frictional forces vectors during loading. We reconstruct the angular distributions of the contact and force vectors, and extract the corresponding emergent anisotropies for each of these metrics. Finally, we show that the SFF relation quantitatively predicts the relationship between particle scale anisotropies, the stress tensor components, and the bulk friction coefficient, capturing even transient behaviors. As such, this method shows promise for application to other dense particulate systems where fabric anisotropy can provide a useful measure of bulk friction.

2023

1. Synchronized locomotion can improve spatial accessibility inside ant colonies

   Grant Navid Doering, Carmen L. Lee, and Kari Dalnoki-Veress

   Proc. R. Soc. B., Nov 2023

   Abs

   Synchronization is a conspicuous form of collective behaviour that is of crucial importance in numerous biological systems. Ant colonies from the genera Leptothorax and Temnothorax form small colonies, typically made up of only a few hundred workers, and exhibit a form of synchronized behaviour where workers inside colonies’ nests become active together in rhythmic cycles that have a period of approximately 20–200 min. However, it is not currently known if these synchronized rhythms of locomotion confer any functional benefit to colonies. By using a combination of multiple image analysis techniques, we show that inactive Leptothorax ants can act as immobile obstacles to moving ants, and that synchronized activity has the potential to reduce the likelihood that individual ants will encounter regions of immobile obstacles that impede access to portions of the nest. We demonstrate qualitatively similar findings using a computational model of confined active particles with oscillating activity.

2022

1. Noise resistant synchronization and collective rhythm switching in a model of animal group locomotion

   Grant Navid Doering, Brian Drawert, Carmen Lee , and 3 more authors

   R. Soc. open sci., Mar 2022

   Abs

   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.

2. Multiple droplets on a conical fiber: formation, motion, and droplet mergers

   Carmen L. Lee, Tak Shing Chan, Andreas Carlson , and 1 more author

   Soft Matter, Mar 2022

   Publisher: Royal Society of Chemistry

2021

1. Film coating by directional droplet spreading on fibers

   Tak Shing Chan, Carmen L. Lee, Christian Pedersen , and 2 more authors

   Phys. Rev. Fluids, Jan 2021

   Publisher: American Physical Society

   Abs

   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 characterize 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 fibers 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.

2. Droplet migration on conical fibers

   Clementine Fournier, Carmen L. Lee, Rafael D. Schulman , and 2 more authors

   Eur. Phys. J. E, Feb 2021

   Number: 2 Publisher: Springer Berlin Heidelberg

   Abs

   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.

3. Capillary levelling of immiscible bilayer films

   Vincent Bertin, Carmen L. Lee, Thomas Salez , and 2 more authors

   Journal of Fluid Mechanics, Mar 2021

   Abs

   , 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.