Jaming and Geometry of Two-Dimensional Foams

Foam in a two-dimensional Couette shear: a local measurement of bubble deformation

We re-analyse experiments on a foam sheared in a two-dimensional Couette geometry [Debregeas <i>et al.</i>, Phys. Rev. Lett. <b>87</b>, 178305 (2001)]. We characterise the bubble deformation by a texture tensor. Our measurements are local in time: they show two regimes, one transient and one stationary. They provide both the average and fluctuations of the anisotropy. Measurements are also local in space: they show that both the deformation and the elastic contribution to the stress field do not localise, varying smoothly across the shear gap. We can thus describe the foam as a continuous medi…

Growth laws and self-similar growth regimes of coarsening two-dimensional foams: Transition from dry to wet limits

We study the topology and geometry of two dimensional coarsening foams with arbitrary liquid fraction. To interpolate between the dry limit described by von Neumann's law, and the wet limit described by Marqusee equation, the relevant bubble characteristics are the Plateau border radius and a new variable, the effective number of sides. We propose an equation for the individual bubble growth rate as the weighted sum of the growth through bubble-bubble interfaces and through bubble-Plateau borders interfaces. The resulting prediction is successfully tested, without adjustable parameter, using e…

Aqueous foams in microgravity, measuring bubble sizes

The paper describes a study of wet foams in microgravity whose bubble size distribution evolves due to diffusive gas exchange. We focus on the comparison between the size of bubbles determined from images of the foam surface and the size of bubbles in the bulk foam, determined from Diffuse Transmission Spectroscopy (DTS). Extracting the bubble size distribution from images of a foam surface is difficult so we have used three different procedures : manual analysis, automatic analysis with a customized Python script and machine learning analysis. Once various pitfalls were identified and taken i…

Local description of the two-dimensional flow of foam through a contraction

The 2D flow of a foam confined in a Hele-Shaw cell through a contraction is investigated. Its rheological features are quantified using image analysis, with measurements of the elastic stress, rate of plasticity, and velocity. The behavior of the velocity strongly differs at the contraction entrance, where the flow is purely convergent, and at the contraction exit, where a velocity undershoot and a re-focussing of the streamlines are unraveled. The yielded region, characterized by a significant rate of plasticity and a maximal stress amplitude, is concentrated close to the contraction. These q…

Flow in linearly sheared two dimensional foams: from bubble to bulk scale

We probe the flow of two dimensional foams, consisting of a monolayer of bubbles sandwiched between a liquid bath and glass plate, as a function of driving rate, packing fraction and degree of disorder. First, we find that bidisperse, disordered foams exhibit strongly rate dependent and inhomogeneous (shear banded) velocity profiles, while monodisperse, ordered foams are also shear banded, but essentially rate independent. Second, we introduce a simple model based on balancing the averaged drag forces between the bubbles and the top plate and the averaged bubble-bubble drag forces. This model …

三维基于细胞的顶点模型的平均场弹性模量

Mean field elastic moduli of a three-dimensional cell-based vertex model

本研究采用平均场方法，针对基于截角八面体的三维细胞顶点模型，分析了形状指数调节引发的刚性转变，揭示了形状参数化和变形方案对弹性模量的非平凡影响。

Jamming of Soft Particles: Geometry, Mechanics, Scaling and Isostaticity

Amorphous materials as diverse as foams, emulsions, colloidal suspensions and granular media can jam into a rigid, disordered state where they withstand finite shear stresses before yielding. Here we review the current understanding of the transition to jamming and the nature of the jammed state for disordered packings of particles that act through repulsive contact interactions and are at zero temperature and zero shear stress. We first discuss the breakdown of affine assumptions that underlies the rich mechanics near jamming. We then extensively discuss jamming of frictionless soft spheres. …

糖蛋白pherophorin II的时空分布揭示了团藻（Volvox carteri）生长中细胞外基质（ECM）的随机几何特征

Spatiotemporal distribution of the glycoprotein pherophorin II reveals stochastic geometry of the growing ECM of $Volvox~carteri$

本研究以团藻Volvox carteri为模式生物，通过融合yfp与pherophorin II基因并结合共聚焦显微镜观察，揭示其生长中ECM的随机几何特征，为理解多细胞生物ECM形成与扩展提供定量基准。

二维刚性圆盘系统中玻璃转变与摩擦性阻塞的几何学

The Geometry behind the Glass Transition and Frictional Jamming in Systems of Two-Dimensional Hard Disks

研究通过几何学揭示了二维刚性圆盘系统中玻璃转变与摩擦性阻塞的内在机制，指出动态转变由全等五边形铺砌引发，其影响延伸至三维结构。