arXiv subjects

Qinghao Mao

Publications and source records attributed to Qinghao Mao.

5 recordsLinked to original sources

arXiv2026

Structure Selection by Non-Conservative 3-Body Acoustic Interactions

Non-conservative multi-body interactions are typically associated with instabilities and activity in driven, field-mediated systems. Here we show that they can also promote stable static structures. Combining experiments and simulations in a minimal, acoustically levitated three-particle system, we tune the relative strength of conservative and non-conservative contributions to the force field. The conservative component favors a symmetric equilibrium configuration, whereas the non-conservative 3-body contribution selects a flattened isosceles triangle. Our results identify non-conservative multi-body forces as a mechanism for static structure selection in driven-dissipative matter in the absence of an effective-energy landscape.

cond-mat.soft↗

arXiv2026

Constraint ratio controls viscosity in shear thickening suspensions

The dramatic viscosity increase observed in dense suspensions under shear poses a major challenge in our understanding of how microscopic contact mechanics translate into macroscopic flow resistance. Here, we introduce a constraint-counting model that incorporates friction and dimensionality naturally without additional assumptions and allows for collapsing of rheological data onto a universal master curve. In this model, we borrow ideas from dry granular jamming physics and classify contacts as either locked or non-locked to define a single state variable, the constraint ratio, which measures the average strength of mechanical constraint per particle. By identifying the constraint ratio as the key control parameter, our framework provides a unifying route toward predictive modeling and rational design of shear-thickening materials.

cond-mat.soft↗

arXiv2025

Non-reciprocity and multibody interactions in acoustically levitated particle systems: A three body problem

In active fluids and active solids the constituents individually generate movement by each extracting energy from their environment or from their own source. Non-reciprocal interactions among these active constituents then enable novel collective behavior that often can be strikingly counterintuitive. However, non-reciprocity in these cases typically requires that the interacting bodies have different physical properties or it needs to be programmed explicitly into all pairwise interactions. Here we show that collective activity in a driven system can emerge spontaneously through multibody nonreciprocal forces, even if all bodies are individually non-active and have identical properties. We demonstrate this with as few as three identical spheres, acoustically levitated in air, which exhibit collective activity as they interact through non-pairwise forces: similar to the classic gravitational three-body problem, the interaction between two spheres depends sensitively on the relative position of the third sphere. Non-reciprocity arises naturally from both near-field sound scattering and microstreaming forces among the spheres. The underdamped dynamics in air furthermore make it possible to go beyond collective center-of-mass propulsion or rotation and observe internal, engine-like reconfigurations that follow limit cycles. These findings open up new possibilities for self-assembly, where now multibody interactions not only determine the resulting structure but also drive the spontaneously emerging dynamics.

cond-mat.soft↗

arXiv2024

Dynamic constraints predict the relaxation of granular materials

Granular materials such as sand, powders, and food grains are ubiquitous in civil engineering, geoscience, agriculture, and medicine. While the influence of friction between the grains on the static structure of these systems is well understood, its impact on the dynamics is an open problem. Here we use particle-based simulations of a granular pack under cyclic shear and discover that the relaxation time of the system is a non-monotonic function of friction. By introducing the concept of dynamic constraints, we reveal that this re-entrant dynamics is due to the competition between increasing frictional coupling and a concurrent change in the structure of the granular pack. Our theoretical approach, which unifies the dynamics of friction-less systems with frictional ones, is applicable to other systems that have a complex free energy landscape and a dynamics which involves time-dependent constraints, thus setting the stage for a description of the dynamic behavior of a large class of complex systems.

cond-mat.soft↗

arXiv2020

Granular Segregation Mechanisms by Cyclic Shear

We present an X-ray tomography study of the segregation mechanisms of tracer particles in a three-dimensional cyclically sheared bi-disperse granular medium. Big tracers are dragged by convection to rise to the top surface and then remain trapped there due to the small downward convection cross-section, which leads to segregation. Additionally, we also find that the local structural up-down asymmetry due to arching effect around big tracers will induce the tracers to have a net upward displacement against its smaller neighbors, which is another mechanism for segregation.

cond-mat.soft↗