Non-Equilibrium Phase Transitions

非平衡相的研究越来越受到人们的关注 我们对它们的理解还远未完成。 拟议的研究将探索远离平衡的过渡 在几个特定的系统中：流体侵入、磁畴壁 运动、流体扩散、摩擦和固体剪切， 流体. 除了允许洞察的基本特征， 非平衡过渡，这项工作将解决系统的 技术重要性。 前三个过程是 通过无序介质的界面运动的典型例子。 无序阻碍界面运动，需要有限的力来 启动流动。 两种类型的临界现象已经被 在运动开始时识别：去钉扎和渗透。 一 这项研究的目标将是一个完整的表征这些 针对特定型号的过渡。 脱钉的变化 力、临界指数和界面形态， 无序的空间维度、性质和强度 被探索。 不同普适性之间的相变 班级也将学习。 摩擦和剪切的研究 系统将探讨内部自由度的作用， 产生不连续的相变。 一个重点将是 胶体悬浮液中的剪切诱导熔融转变。 这 这项工作还将提供有关固体流动的信息，在高 剪应力 第二个焦点是粘滑摩擦力 在两个表面之间交替粘附和滑动。 粘滑 运动导致铰链发出吱吱声并导致运动部件磨损。 的 拟议的研究将扩展最近的研究，这些研究表明， 粘滑摩擦是由周期性非平衡相引起的 过渡。

There has been growing interest in non-equilibrium phase transitions, yet our understanding of them is far from complete. The proposed research will explore transitions far from equilibrium in several specific systems: fluid invasion, magnetic domain wall motion, fluid spreading, friction, and shearing of solids and fluids. In addition to allowing insight into basic features of non-equilibrium transitions, the work will address systems of technological importance. The first three processes are prototypical examples of interface motion through disordered media. Disorder impedes interface motion and a finite force is needed to initiate flow. Two types of critical phenomena have been identified at the onset of motion: depinning and percolation. One goal of the research will be a complete characterization of these transitions for specific models. The variation of the depinning force, the critical exponents, and the interface morphology with the spatial dimension and nature and strength of the disorder will be explored. Phase transitions between different universality classes will also be studied. Studies of friction and sheared systems will explore the role of internal degrees of freedom in producing discontinuous phase transitions. One focus will be the shear-induced melting transition in colloidal suspensions. This work will also provide information about flow of solids under high shear stresses. A second focus will be stick-slip friction - alternate sticking and sliding between two surfaces. Stick-slip motion leads to squeaks in hinges and to wear of moving parts. The proposed research will extend recent studies which indicate that stick-slip friction is caused by periodic non-equilibrium phase transitions.