Realizations

We studied the behavior of a mix of active and passive particles by simulating active particles with elastic disc interactions on a landscape that consisted of a half space filled with obstacles and another half space free of obstacles. We found an emergent behavior of the system where the active particles prefer to stay in the half-plane with the obstacles and gradually shepherd the passive particles out from among them into the open obstacle-free region. We studied this new phenomenon we call shepherding as a function of particle density and active motor force. We published our results in the article: Phys. Rev. E 104, 044613 (2021).
We introduced an SIR model into our active matter model to understand failures of the mixing assumption,important for designing effective disease mitigation approaches. Working in the motility-induced phase separation regime both with and without quenched disorder, we found two epidemic regimes. For low transmissibility, quenched disorder lowers the frequency of epidemics and increases their average duration. For high transmissibility, the epidemic spreads as a front and the epidemic curves are less sensitive to quenched disorder; however, within this regime it is possible for quenched disorder to enhance the contagion by creating regions of higher particle densities. We discussed how this system could be realized experimentally. We published our results in the article: Scientific Reports 12, 11229 (2022).
The Susceptible-Infected (SI) and Susceptible-Infected-Recovered (SIR) models provide two distinct representations of epidemic evolution, distinguished by the lack of spontaneous recovery in the SI model. Here we introduce a new active matter epidemic model that can transition between these two asymptotic behaviors, as it only allows recovery in the presence of caretakers administering treatment, so we can have a transition both as a function of the caretaker fraction of the population and the effectiveness of the treatment. Ourt results are applicable for diseases such as HIV. We published our results in the article: Phys. Rev. E 107, 024604 (2023).
We studied a system of active particles that are below the density where a spontaneous large cluster would form (the so called MIPS or Motility Induced Phase Separation). We added am epidemiological layer with a one-way transition from living or moving to dead or nonmotile due to lack of fuel, infection, or poisoning. This precipitates a MIPS phase, a wetting phase and a fragmented state formation, in this order. Our results are published in the article: Communications Physics 6, 294 (2023).
We studied a system of an active substrate that is modified by the particles that are moving above it. The particles consume the substrate grid points they cover at a given rate and move towards the direction of the substrate gradient, and the substrate recovers at a fixed rate. The system exhibits interesting collective behaviors depending on the consumption and recovery rates as well as the particle density. We published our results in the article: Phys. Rev. Research 4, 013061 (2022).
We studied in detail the active substrate system that we introduced in the previous paper and showed a rich variety of pattern-forming phases along with directed motion or flocking as a function of the relative rates of resource absorption and consumption as well as the active to passive particle ratio. These include partial phase separation into rivers of active particles flowing through passive clusters, strongly phase separated states where the active particles induce crystallization of the passive particles, mixed jammed states, and fluctuating mixed fluid phases. We published our results in the article: Phys. Rev. E 106, 064602 (2022).
We contributed to an outlook paper, where we discussed the possibility and the advantages of such individual and collectively interacting active matter particles coupled to periodic substrates, where new types of commensuration effects, directional locking, and active phases can occur. Further directions for exploration that we indicated include locking effects, the realization of active solitons or active defects in incommensurate phases, active Mott phases, active artificial spin ice, active doping transitions, active floating phases, active surface physics, active matter time crystals, and active tribology. We published our results in the article: Europhysics Letters 139, 27001 (2022).
We studied a system of elongated particles driven over randomly placed pinning sites. For varied pinning site density, external drive magnitude, and particle elongation, we found a wide variety of dynamic phases, including random structures, stripe phases with nematic order, and clogged states. The optimal nematic ordering occurs when a enough particles can be pinned, generating a local shear and leading to what we call a combing effect. We published our results in the article: Soft Matter 19, 7937 (2023).
We studied a system of active matter swarmalators. These active matter particles have an additional interaction that was inspired by swarm robotics, an interaction that is dependent on their internal parameter and a coupling constant. They also act on modifying this internal parameter of their neighbors via a separate interaction. We found a very rich phase diagram with multiple interesting regimes in this system. We submitted our findings to Phys. Rev. E, with the preprint available here: manuscript submitted
We examined a system of run-and-tumble disks in two-dimensions where the particles also have a Magnus component to their dynamics. For increased activity, we find that the system forms a motility-induced phase-separated (MIPS) state with chiral edge flow around the clusters. We found that smaller amplitude Magnus forces stabilize the clusters, while large Magnus forces break it up into a gel-like state. In the presence of quenched disorder and a uniform drive, and find that the bulk flow exhibits a drive-dependent Hall angle explained with a side-step inside the pinning sites. We submitted our fidings to Phys. Rev. E, with the preprint available here: manuscript submitted
We constructed a robot prototype. We designed a four-layer printed circuit board that holds the main microcontroller and all the peripherical chips and that allows the robot to communicate via wireless and bluetooth, signal the camera with RGB LEDs, drive two wheels, light up the array of IR LEDs on its perimeter for both distance measurement as well as inter-robot communication and also read the IR signal in multiple places around its perimeter. The robot also has sensors mounted underneath that can observe the pattern and gradients it is moving over. The designed allows for the possibility of being extended with a shield for future modularity. We wrote the SDK and tested most of the robot functions, the robot can sense its surroundings and differentiate between a passive obstacle and another robot and in the case they are close to each other can read the other robot's code via the IR signals. We also designed and built the TV surface on which the robots move, including equipping the laboratory with blinds to set the desired amount of ambient light for our experiments, and set up the camera and the robot tracking algorithm. We made the first batches of robots and currently have about 20 robots that are functional and can perform experiments with more being assembled gradually, up to 50+ robots for the creation of swarms. We presented our robot at Lakeside Labs in Klagenfurt and started a collaboration on swarm robotics with the group of prof. Christian Bettstetter.
We repeated the experiment with the Quincke rollers that was performed in Northwestern University. We invited the researcher who performed the experiments, dr. Gasper Kokot from the Iozef Stefan Institute in Ljubljana, and we learned the steps involved in preparing the sample with the correct separation between the plates, application of the voltage and observation of the rolling effect. We are working on modifying our setup with a better microscope and a better camera for future experiments.