arXiv subjects

Wei-Chih Li

Publications and source records attributed to Wei-Chih Li.

4 recordsLinked to original sources

arXiv2026

Nonreciprocal interactions drive intermittent melting of Coulomb clusters

Complex systems out of equilibrium often experience intermittent oscillations between quiescent and highly dynamic states. While intermittency is usually driven by stochastic noise or external forcing, energy can also be sourced from field-mediated interactions between particles, which are often nonreciprocal and effectively violate Newton's 3rd law. Here we demonstrate how nonreciprocal interactions produce intermittency in clusters of charged micron-sized particles confined in a plasma sheath. Using three-dimensional particle tracking, we observe that vertical oscillations, induced by a noisy plasma environment, are parametrically coupled to the horizontal vibrational modes. Experiments and simulations show that nonreciprocal interactions strongly amplify this coupling, injecting energy into the system. This mechanism triggers explosive melting transitions from an ordered cluster to an ergodic gas-like state, and leads to intermittent switching between states over long time. Overall, our work identifies nonreciprocal interactions as a key mechanism through which strongly-coupled finite systems transform interaction-mediated activity into dynamical nonequilibrium states.

cond-mat.soft↗

arXiv2024

How soap bubbles change shape while maintaining a fixed volume of air?

We combine experiments and theoretical derivations to study the evolution of a stretched soap bubble and compare it with an open film to highlight the effect of volume conservation. We identify a critical length for both surfaces, beyond which a bottleneck develops in the middle and begins to shrink irreversibly, ultimately pinching off into multiple compartments. Before leaving the equilibrium regime, surface energy minimization governs the shape, which can be addressed theoretically via the variational method. In contrast to open films, soap bubble volume conservation introduces a Lagrange multiplier, analogous to a pressure difference, mediating long-range shape evolution. By examining how boundary constraints influence deformation, we contrast the bubble's convex-to-concave transition with the behavior of soap films under similar conditions. Our analysis of equilibrium and breakup regimes reveals critical differences between bubble and film stability profiles, shedding light on universal behaviors in non-equilibrium fluid mechanics, with implications for biological and material sciences.

physics.flu-dyn↗

arXiv2024

Two types of quaking and shear unjamming: state diagram for soft granular particles under shear

Understanding intermittency, an ubiquitous behavior in flows of packed grains, is pivotal for establishing the rheology of granular matter. A straightforward explanation has been missing despite the long development of theories at various levels of abstraction. Here, we propose the use of a Stribeck-Hertz model that starts with the classic Coulomb friction but takes into account the inter-particle tribology, i.e. the reduction of friction coefficient with sliding speed as is commonly observed. Our numerical experiments reveal a state diagram that covers a wide range of packing fractions and show that incorporating the tribology enables the occurrence of quaking intermittency in the mid-range of a newly established dimensionless shear rate, in consistence with prior experimental observations. Further study of the discontinuities in the evolution of mean contact number leads to our discovery of two types of quaking, that are distinguished by the abrupt increase or decrease of neighboring contacts and reveal different pathways of microstructural change underlying these discrete events. In contrast to the prevailing paradigm in which shear is believed to promote jamming at intermediate densities, our study demonstrates that shear can also unjam a granular system, and this occurrence depends on the shear rate.

cond-mat.soft↗

arXiv2022

Self-similarity with universal property for soap film and bubble in roll-off stage

All children enjoy blowing soap bubbles that also show up in our bath and when we wash dishes. We analyze the thinning and breaking of soap bubble neck when it is stretched. To contrast with the more widely studied film whose boundaries are open, we concentrate on the bubble with a conserved air volume V. Like film (F), non-equilibrium state can be divided into four regimes for bubble (B): (1) roll-off, (2) cusp approach, (3) pinch-off and (4) breakup. We establish the existence of self-similarity in F-1, B-1 and B-3, and universal property in F-1 and B-1 for the profile of soap membrane. The former means that the profile at successive times can be mapped to a master curve after being rescaled by the countdown time τ. Whiles, the latter further requires this master curve to be identical for different ring sizes R for film and different V and R for bubble while keeping V/R^3 fixed. The exhibition of universal property indicates that the process of memory erasing starts earlier than regime 3. We also found that the minimum radius scales as h_{min}~τ^{1/2}, independent of V and pulling speed. Note that the validity of our discussion is limited by the duration of roll-off regime from 10^{-2}~10^{-3} s.

cond-mat.soft↗