arXiv subjects

Baopi Liu

Publications and source records attributed to Baopi Liu.

7 recordsLinked to original sources

arXiv2025

Effects of Near-Field Hydrodynamic Interactions on Bacterial Dynamics Near a Solid Surface

Near-field hydrodynamic interactions between bacteria and no-slip solid surfaces are the main mechanism underlying surface entrapment of bacteria. In this study, we employ a chiral two-body model to simulate bacterial dynamics near the surface. The simulation results show that as bacteria approach the surface, their translational velocities and diffusion coefficients decrease. Under the combination of near-field hydrodynamic interactions and DLVO forces, bacteria reach a stable fixed point in the phase plane and follow circular trajectories at this point. In particular, bacteria with left-handed helical flagella exhibit clockwise circular motion on the surface. During this process, as the stable height increases, the near-field hydrodynamic interactions weaken. Consequently, the translational velocity of the bacteria parallel to the surface increases while the rotational velocity perpendicular to the surface decreases, collectively increasing the radius of curvature. Ultimately, our findings demonstrate that near-field hydrodynamic interactions significantly prolong the surface residence time of bacteria. Additionally, smaller stable heights further amplify this effect, resulting in longer residence times and enhanced surface entrapment.

cond-mat.soft↗

arXiv2025

Simulation of Flagellated Bacteria Near a Solid Surface: Effects of Flagellar Morphology and Ionic Strength

This study systematically investigates the three-stage process of bacterial surface entrapment, characterized by its height and inclination angle. Initially, bacteria swim towards the surface at an approach velocity proportional to motor rotation frequency. Subsequently, the cotangent of the inclination angle decays exponentially with the product of the motor rotation frequency and time during reorientation. Finally, under the combined action of near-field hydrodynamic interactions and DLVO forces, bacteria reach a stable fixed point near the surface. Bacteria with left-handed chiral flagella exhibit a clockwise circular motion on the surface. The stable heights, inclination angles, and radii of curvature of these circular trajectories are collectively determined by the flagellar morphology and ionic strength of the electrolyte solution. Specifically, increasing the contour length of the flagellum reduces the stable inclination angle and increases the radius of curvature. In contrast, decreasing the ionic strength increases the stable height and radius of curvature, while also decreasing the stable inclination angle. Typically, the stable inclination angle falls within $(\pi/2,\pi)$, the stable height ranges from several nanometers to over one hundred nanometers, and the radius of curvature spans several to tens of micrometers. Our work explains the observed dispersion of the stable heights.

cond-mat.soft↗

arXiv2025

Morphological Effects on Bacterial Brownian Motion: Validation of a Chiral Two-Body Model

We systematically investigate how flagellar morphology governs the stability of bacterial Brownian motion, evaluating the effectiveness of a simplified chiral two-body model. This model, which effectively captures the specific bacterial morphology and significantly reduces computational cost, is used for simulating bacterial Brownian motion. Our results demonstrate that the model accurately reproduces the Brownian motion of bacteria for contour lengths $\Lambda\ge5.0$~\si{\mu m}, helix radii $0.2\le R\le 0.5$~\si{\mu m}, and pitch angles $\pi/6\le\theta\le2\pi/9$. We find that the translational and rotational velocities of bacteria depend linearly on the motor rotation rate, independent of dynamic viscosity. Increasing helix radius and contour length leads to more elongated trajectories and enhances their linearity. Furthermore, longer contour lengths improve the stability of the bacterial forward motion. Collectively, these findings demonstrate the essential role of flagella in stabilizing bacterial Brownian motion and confirm the effectiveness of the chiral two-body model for simulating this phenomenon.

physics.flu-dyn↗

arXiv2025

Effects of Flagellar Morphology on Swimming Performance and Directional Control in Microswimmers

In a fluid environment, flagellated microswimmers propel themselves by rotating their flagella. The morphology of these flagella significantly influences forward speed, swimming efficiency, and directional stability, which are critical for their survival. This study begins by simulating the three-dimensional motion trajectories of microswimmers to analyze their kinematic characteristics. The simulation results demonstrate that microswimmers can actively adjust their forward direction by modifying the orientation of their flagella. We subsequently perform numerical simulations to visualize the flow fields generated by a microswimmer and examine the hydrodynamic interactions between the cell body and the flagella, focusing on their impacts on forward speed and swimming efficiency. We conclude that forward speed and swimming efficiency are closely related to the filament radius, pitch angle, and contour length of the flagella, while the yaw angle of locomotion is determined by the helix radius and contour length of the flagella. We conclude that the pitch angle for maximum forward speed is slightly smaller than that for maximum swimming efficiency, which suggests that microswimmers can effectively alternate between states of maximum forward speed and maximum swimming efficiency by fine-tuning their pitch angle and adapting to varying ecological conditions. These morphological characteristics of microswimmers may result from species competition and natural selection. This research establishes an optimized model for microswimmers, providing valuable insights for the design of enhanced microrobots tailored to specific applications.

physics.flu-dyn↗

arXiv2025

Effective and efficient modeling of the hydrodynamics for bacterial flagella

The hydrodynamic interactions among bacterial cell bodies, flagella, and surrounding boundaries are essential for understanding bacterial motility in complex environments. In this study, we demonstrate that each slender flagellum can be modeled as a series of spheres, and that the interactions between these spheres can be accurately characterized using a resistance matrix. This approach allows us to effectively and efficiently evaluate the propulsive effects of the flagella. Notably, our investigation into bacterial motility near a colloidal sphere reveals significant discrepancies between results derived from the twin multipole moment and those obtained through resistive force theory. Consequently, neglecting the hydrodynamic interactions among cell bodies, flagella, and colloidal spheres may lead to substantial inaccuracies. Our model simplifies bacteria into a series of spheres, making it well-suited for examining bacterial motility near spherical boundaries, as well as the nonlinear deformation dynamics of elastic flagella.

cond-mat.soft↗

arXiv2024

Phase behaviors and dynamics of active particle systems in double-well potential

In this study, we investigate the behaviors and dynamics of self-propelled particles with active reorientation (AR) in a double-well potential. We explore the competition between AR and external potentials, revealing that self-propelled particles exhibit flocking and clustering behaviors in an asymmetric potential trap. Through molecular dynamics simulations, we obtain a phase diagram that illustrates flocking behavior as a function of active reorientation and potential asymmetry. We compare the responses of inactive and active particles to the potential, finding that active reorientation significantly increases aggregation on one side of the asymmetric potential well. Additionally, by calculating the mean squared displacement and scaling exponent, we identify distinct diffusion regimes. Our findings demonstrate that active particles with active reorientation are more sensitive to variations in double-well potentials.

cond-mat.soft↗

arXiv2020

Spherical-harmonic Expansion of the Modified Diffusion Equation for Wormlike Chain in Curvilinear Coordinates

We investigate the wormlike polymer chains using self-consistent field theory and take into account the Onsager excluded-volume interaction between polymer segments. The propagator of polymer chain is one of the essential physical quantities used to study the conformation of polymers, which satisfies the modified diffusion equation (MDE) for wormlike chain. The propagator of wormlike chain is not only dependent on the spatial variables, but also on the orientation. We separate the variables of propagator by using spherical-harmonic series and then simplify the MDE to a coupled set of equations only depends on spatial variables in this paper. We expand the MDE by spherical-harmonic functions in cylindrical coordinates and spherical coordinates, respectively. We find that there are three ways to set the orientation, no matter in cylindrical coordinates or spherical coordinates. But for the convenience of calculation, we compare these three forms and choose the simplest one to simplify the MDE. And we get a coupled set of equations only depends on spatial variables.

cond-mat.soft↗