arXiv subjects

Hongyi Bian

Publications and source records attributed to Hongyi Bian.

8 recordsLinked to original sources

arXiv2026

Hydrated porous substrates modulate the spatiotemporal dynamics of bacterial turbulence

Boundary conditions strongly influence bacterial turbulence, motivating the question of how hydrated porous substrates affect near-interface collective motion. We characterize the spatiotemporal dynamics of dilute and dense Escherichia coli suspensions above agar substrates of varying concentrations, with glass serving as a nonporous reference. In dense suspensions shortly after loading, collective in-plane kinetic energy varies nonmonotonically with agar concentration, while individual swimming energy and characteristic spatial scales show comparatively little variation. Over five minutes above agar, the collective flow attenuates strongly, accompanied by shorter spatial correlations, longer temporal correlations, and a greater relative spectral weight at higher wavenumbers. To explore how the porous boundary may contribute to these changes, we extend mean-field kinetic theory (MFKT) to incorporate normal seepage and tangential slip at the interface. Linear stability analysis distinguishes near-interface collective modes from those in the bulk and identifies how fluid-layer thickness and permeability-dependent slip length modify the instability cutoff. The predicted reduction in the associated length scale provides a qualitative interpretation of the smaller flow structures observed over time and at higher agar concentrations. These findings reveal distinct substrate-dependent changes in the intensity, persistence, and spatial organization of near-interface bacterial turbulence.

cond-mat.soft↗

arXiv2026

Rheologically tuned diffusion modulates quorum sensing in Vibrio fischeri

Understanding how the physical properties of a fluid influence bacterial behavior is essential for explaining how microorganisms interact with their environment and with animal hosts. Here, we examine how changes in fluid viscosity and rheological properties affect the locomotion of the marine bacterium Vibrio fischeri and its ability to produce luminescence through cell--cell communication. We track the three-dimensional motion of single cells in well-defined fluids with different physical properties and measure the luminescence emitted by cell populations. We find that fluids with higher viscosity cause V. fischeri to spend more time in a slower, turning-focused swimming mode, which reduces how effectively cells spread out and encounter the chemical signals required to activate luminescence. As a result, luminescence first increases and then decreases in Newtonian fluids, but decreases monotonically in fluids that exhibit non-Newtonian rheological behavior. Computer simulations based on our measurements confirm that the ability of cells to explore their surroundings plays a central role in determining when and how strongly they communicate. These findings reveal a direct link between the physical environment, bacterial movement, and collective behavior, and offer insight into how microorganisms adapt to complex fluid habitats, including those found inside animal hosts.

cond-mat.soft↗

arXiv2026

Directed swimming of Chlamydomonas reinhardtii near complex microstructures

The locomotion of microorganisms near solid-liquid interfaces is of significant scientific interest due to its relevance in various natural and industrial contexts, including biofilm formation and marine biofouling. In this study, we investigate the swimming behavior of C. reinhardtii near a sinusoidal wave-like microstructure. Using fluorescence microscopy and a three-dimensional tracking technique, we observe that the swimming direction of C. reinhardtii is strongly influenced by the geometric constraints imposed by the microstructure. Our results reveal that cells preferentially accumulate at the valley of the microstructure rather than the peak and exhibit a directional swimming tendency in the vicinity of the microstructure. We attribute this behavior to a combination of the "memory effect" and hydrodynamic attraction. By modifying the geometry of the microstructure, we successfully achieve directed guidance of cell swimming, which demonstrates potential applications in micro and nanorobotics and antifouling technologies. This work provides alternative insights into the locomotion mechanisms of microorganisms near solid-liquid interfaces and underscores the potential for manipulating their behavior through microstructure design.

cond-mat.soft↗

arXiv2026

Active turbulence in shear-thinning fluid

The study of active matter system has critical importance in revealing the physical essence of biological collective behavior. Dense bacterial suspension-a typical biological active matter, exhibits a wide range of phenomenona, among which bacterial turbulence has received extensive interest in recent years. This seemingly chaotic motion is widely studied in Newtonian fluid. However, studies based on complex fluids have predominantly focused on viscoelastic effects, leaving the role of shear-thinning viscosity largely unexplored despite its prevalence in natural bacterial environments like mucus and gastric fluids. Here, we experimentally employed Ficoll and Methocel polymers to study the impacts of various viscosities by Newtonian fluid and shear-thinning effects by non-Newtonian fluids on bacterial turbulence. We analyzed various physical properties, including energy, enstrophy, etc., and observed that the shear-thinning effect is significantly suppressed in high-concentration bacterial suspensions. While the ordered arrangement of polymer chains under shear flow leads to the microscopic anisotropic viscosity, the suppression is largely attributed to the disruption of polymer chains caused by strong interbacterial interactions in dense suspensions. To validate this hypothesis, we conducted experiments at a lower bacterial concentration and verified the findings using theoretical calculations based on the modified resistive force theory.

cond-mat.soft↗

arXiv2026

DRL-Based Secure Transmission for Rotatable Antenna-Enabled Low-Altitude ISAC Systems

The development of the low-altitude economy has driven innovation in intelligent antenna systems within ISAC systems. In this paper, we investigate a Rotatable Antenna (RA)-enabled low-altitude integrated sensing and communication (ISAC) system. In practical terms, the RA array can flexibly adjust the three-dimensional (3D) beam direction of each antenna to enhance array directional gain, thereby improving the communication security of legitimate mobile users against potential eavesdropping risks from the unmanned aerial vehicle (UAV). Our objective is to maximize the minimum secrecy rate (SR) by jointly optimizing transmit beamforming matrix, transmit and receive RAs' pointing matrices. To this end, an multi-agent proximal policy optimization with three improvement mechanisms (MAPPO-T) algorithm is proposed to cope with the issue of complex multi-agent collaborative decision-making problem. Simulation results show that the introduction of RAs can effectively improve SR performance compared to the traditional fixed orientation antenna (FOA)-based system. In addition, the proposed MAPPO-T algorithm validate the superiority compared to the standard MAPPO algorithm.

eess.SP↗

arXiv2025

Boundaries Program Deformation in Isolated Active Networks

Cellular structures must organize themselves within strict physical constraints, operating with finite resources and well-defined boundaries. Classical systems demonstrate only passive responses to boundaries, from surface energy minimization in soap films to strain distributions in elastic networks. Active matter fundamentally alters this paradigm - internally generated stresses create a bidirectional coupling between boundary geometry and mass conservation that enables dynamic control over network organization. Here we demonstrate boundary geometry actively directs network deformation in reconstituted microtubule-kinesin systems, revealing a programmable regime of shape transformation through controlled boundary manipulation. A coarse-grained theoretical framework reveals how boundary geometry couples to internal stress fields via mass conservation, producing distinct dynamical modes that enable engineered deformations. The emergence of shape-preserving and shape-changing regimes, predicted by theory and confirmed through experiments, establishes boundary geometry as a fundamental control parameter for active materials. The control principle based on boundaries advances both the understanding of biological organization and enables design of synthetic active matter devices with programmable deformation.

cond-mat.soft↗

arXiv2024

Hydrodynamic interaction leads to the accumulation of Chlamydomonas reinhardtii near a solid-liquid interface

The physical mechanism of microbial motion near solid-liquid interfaces is crucial for understanding various biological phenomena and developing ecological applications. However, limited works have been conducted on the swimming behavior of C. reinhardtii, a typical "puller" type cell, near solid surfaces, particularly with varying and conflicting experimental observations. Here, we investigate the swimming behavior of C.reinhardtii using a three-dimensional real-time tracking microscopy system both near a solid-liquid interface and in the fluid bulk region. We explore the relationships between the cell density, swimming speed and orientation with respect to the distance from the solid-liquid interface, confirming the phenomenon of C. reinhardtii accumulation near the solid-liquid interface. Based on the traditional definitions of "pusher" and "puller" cells, we propose a simplified model consisting of two pairs of mutually perpendicular force dipoles for C. reinhardtii. This model is employed to analyze the complex hydrodynamic interactions between C. reinhardtii and the solid surface, providing a potential theoretical explanation for the observed accumulation phenomenon at the solid-liquid interface.

physics.bio-ph↗

arXiv2024

Propulsion Contribution from Individual Filament in Flagellar Bundle

Flagellated microorganisms overcome the low-Reynolds-number time reversibility by rotating helical flagella. For peritrichous bacteria, such as Escherichia coli, the randomly distributed flagellar filaments align along the same direction to form a bundle, facilitating complex locomotive strategies. To understand the process of flagella bundling, especially the propulsion force, we develop a multi-functional macroscopic experimental system and employ advanced numerical simulations for verification. Flagella arrangements and phase differences between helices are investigated, revealing the variation in propulsion contribution from the individual helix. Numerically, we build a time-dependent model to match the bundling process and study the influence of hydrodynamic interactions. Surprisingly, it is found that the total propulsion generated by a bundle of two filaments is constant at various phase differences between the helices. However, the difference between the propulsion from each helix is significantly affected by the phase difference, and only one of the helices is responsible for the total propulsion at a phase difference equals to pi. Through our experimental and computational results, we provide a new model considering the propulsion contribution of each filament to better understand microbial locomotion mechanisms, especially on the wobbling behavior of the cell. Our work also sheds light on the design and control of artificial microswimmers.

cond-mat.soft↗