arXiv subjects

Guo-Jie Jason Gao

Publications and source records attributed to Guo-Jie Jason Gao.

6 recordsLinked to original sources

arXiv2026

Digging through 2D densely-packed coarse granular media as a critical phenomenon

We create a mechanical digger able to move within 2D densely-packed granular media, in a manner intrinsically different from the existing biomimic diggers. The characteristics of our design include that the average grain size is about one tenth as large as the digger, and the area packing density ϕ for testing is between about 0.610 and 0.762. Unlike conventional autonomous diggers that move by fluidizing the surrounding granular media with a much finer grain size, our digger uses a different mobility mechanism as coarse grains with interparticle friction are hard to be fluidized. To cope with high interparticle friction, the digger has a circular shape and singly captures granular particles near the front entrance of the recess formed by the center unit running across its body and then ejects the captured particles backwards. We validate this moving strategy in both experiments using a manual digger and the corresponding numerical simulations, and demonstrate that the moving efficiency can be enhanced by the judgement of the human operator but the effectiveness is not significantly influenced by the shape of granular particles. In addition, localized vibration is needed to degrade friction between interlocked irregular-shaped particles. Our numerical results show that the distribution of both moving distances and time intervals between consecutive ejections follow a power-law. Reducing ϕ shrinks the spatial and temporal spans over which the power laws hold. Further, we experimentally verify this finding by demonstrating that similar power-laws are observed from an automated digger which periodically randomizes its digging direction. Finding these spatio-temporal power laws indicates that digging within a densely-packed granular environment could be a critical phenomenon.

cond-mat.soft↗

arXiv2026

A Dynamical Trap Made of Target-Tracking Chasers

We propose a dynamical trapping system composed of multiple chasers subject to target-tracking forces utilizing the velocity and position information of a single escaping target. To successfully capture the target, dividing chasers into multiple groups while each group approaching its assigned destination in the proper vicinity of the target is essential. Moving direction synchronization between the target and its chasers is crucial to the capturing process, while guiding chasers to the predicted position of the target in future only improves the efficiency of capture but is not indispensable. Potential applications of our trapping system include capturing live animals such as bears invading a human residential area.

cond-mat.soft↗

arXiv2021

Enhanced flow rate by the concentration mechanism of Tetris particles when discharged from a hopper with an obstacle

We apply a holistic 2D Tetris-like model, where particles move based on prescribed rules, to investigate the flow rate enhancement from a hopper. This phenomenon was originally reported in the literature as a feature of placing an obstacle at an optimal location near the exit of a hopper discharging athermal granular particles under gravity. We find that this phenomenon is limited to a system of sufficiently many particles. In addition to the waiting room effect, another mechanism able to explain and create the flow rate enhancement is the concentration mechanism of particles on their way to reaching the hopper exit after passing the obstacle. We elucidate the concentration mechanism by decomposing the flow rate into its constituent variables: the local area packing fraction $ϕ_l^E$ and the averaged particle velocity $v_y^E$ at the hopper exit. In comparison to the case without an obstacle, our results show that an optimally placed obstacle can create a net flow rate enhancement of relatively weakly driven particles, caused by the exit-bottleneck coupling if $ϕ_l^E > ϕ_o^c$, where $ϕ_o^c$ is a characteristic area packing fraction marking a transition from fast to slow flow regimes of Tetris particles. Utilizing the concentration mechanism by artificially guiding particles into the central sparse space under the obstacle or narrowing the hopper exit angle under the obstacle, we can create a man-made flow rate peak of relatively strongly-driven particles that initially exhibit no flow rate peak. Additionally, the enhanced flow rate can be maximized by an optimal obstacle shape, particle acceleration rate towards the hopper exit, or exit geometry of the hopper.

cond-mat.soft↗

arXiv2018

A Tetris-like Model Showing a Universal Enhanced Flow Rate of a Hopper Discharging Hard Discs Through an Adjustable Inclusion

In the literature, placing an inclusion near the orifice of a hopper, containing disc particles, has been experimentally and numerically reported to locally enhance the gravity-driven hopper flow rate. Moreover, the peaked flow rate can happen regardless of the interparticle friction, the inclusion geometry, or the disc dispersity. To reveal the fundamental reason causing this local effect, we propose a Tetris-like model that sequentially moves one disc particle at a time towards the hopper orifice. A Gaussian displacement function that independently controls a disc's movement in the horizontal or vertical direction, and the algorithm of the model accepts a movement as long as it creates no overlap between objects in the system. Our model creates an artificial steady probability-driven hopper flow without knowing the Newtonian dynamics which allows interparticle collaborative motion. Under specific conditions, we reproduce the enhanced flow rate and show that a moderate response time of the system and a flow rate difference between its value around the inclusion and its maximum without an inclusion are sufficient to explain this local effect with no Newton's laws involved.

cond-mat.soft↗

arXiv2017

A vehicle with a two-wheel steering system mobile in shallow dense granular media

We design a vehicle with a steering system made of two independently rotatable wheels on the front. We quantify the effectiveness of the steering system in the mobility and maneuverability of the vehicle running in a box containing a layer ping-pong balls with a packing density 0.8, below the random close packing value 0.84 in 2D. The steering system can reduce the resistance exerted by the jammed balls formed ahead of the fast-moving vehicle. Moreover, if only one of the two steering wheels rotates, the vehicle can turn into the direction opposite to the rotating wheel. The steering system performs more efficiently if the wheels engage the ping-pong balls better by increasing the contact area between the wheels and the balls. We advocate applying our design to machines moving in granular materials with a moderate packing density.

cond-mat.soft↗

arXiv2016

Embryo as an active granular fluid: stress-coordinated cellular constriction chains

Mechanical stress plays an intricate role in gene expression in individual cells and sculpting of developing tissues. However, systematic methods of studying how mechanical stress and feedback help to harmonize cellular activities within a tissue have yet to be developed. Motivated by our observation of the cellular constriction chains (CCCs) during the initial phase of ventral furrow formation in the Drosophila melanogaster embryo, we propose an active granular fluid (AGF) model that provides valuable insights into cellular coordination in the apical constriction process. In our model, cells are treated as circular particles connected by a predefined force network, and they undergo a random constriction process in which the particle constriction probability P is a function of the stress exerted on the particle by its neighbors. We find that when P favors tensile stress, constricted particles tend to form chain-like structures. In contrast, constricted particles tend to form compact clusters when P favors compression. A remarkable similarity of constricted-particle chains and CCCs observed in vivo provides indirect evidence that tensile-stress feedback coordinates the apical constriction activity. We expect that our particle-based AGF model will be useful in analyzing mechanical feedback effects in a wide variety of morphogenesis and organogenesis phenomena.

cond-mat.soft↗