Noise-Induced Fluctuations in Nonequilibrium Systems

非平衡系统中噪声引起的波动

• 批准号: 0099484
• 负责人: Robert Maier
• 金额: $ 26.1万
• 依托单位: University of Arizona
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-08-15 至 2005-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0099484&HistoricalAwards=false
• 关键词: Noise; Induced; Fluctuations; Nonequilibrium; Systems

Maier Small random fluctuations, which are often of thermal origin, are the cause of many important and interesting physical phenomena. These include chemical reactions, the nucleation phenomenon in phase transitions (i.e., the formation of a droplet of one phase within another phase), and the formation of unusual spatially localized states in liquid crystals. In all of these, `noise', i.e., random fluctuations, eventually drives a physical system over a barrier, and moves it from one stable state to another. Several special cases of this phenomenon were treated by Kramers in 1940,and for several decades thereafter, theoretical and experimental physicists relied heavily on his work. However, his formulas, and modified versions which other researchers later derived, apply only if the physical system is capable of coming to equilibrium, in a thermodynamic sense. Many physical systems are inherently out of equilibrium, either because of the unusual nature of their microscopic dynamics or random fluctuations, or because they are driven by external forces (for example, periodically).This research will study, both theoretically and experimentally, several nonequilibrium systems, and will extend the range of theoretical techniques that can be applied to them. Systems to be investigated include systems where the barrier to be crossed oscillates periodically, on account of externally applied periodic driving. A system that exemplifies this is a mesoscopic particle confined to a periodically modulated dual optical trap, and subject to small thermal fluctuations. Also to be investigated are multistable systems with spatial extent. In systems with spatial extent, the state of the system is infinite-dimensional: it comprises much more information than the position of a single particle. An example is a thin layer of a nematic liquid crystal, driven by weak spatiotemporal noise. Among other projects, this research will attempt to extend the Kramers approach to systems with spatial extent.

小的随机涨落，通常是热的起源，是许多重要和有趣的物理现象的原因。 这些包括化学反应，相变中的成核现象（即，在另一相中形成一相的液滴），以及在液晶中形成不寻常的空间局域态。 在所有这些，“噪音”，即，随机波动，最终驱动物理系统越过障碍，并将其从一个稳定状态移动到另一个。Kramers在1940年处理了这种现象的几个特殊情况，在此后的几十年里，理论和实验物理学家都非常依赖他的工作。 然而，他的公式，以及后来其他研究人员推导出的修改版本，只有在物理系统能够达到热力学意义上的平衡时才适用。 许多物理系统本质上是不平衡的，要么是因为它们的微观动力学或随机波动的不寻常性质，要么是因为它们受到外力的驱动（例如，周期性的）。本研究将从理论和实验两方面研究几个非平衡系统，并将扩展可应用于它们的理论技术的范围。 要研究的系统包括系统中的障碍要跨越周期性振荡，在外部施加的周期性驱动的帐户。 一个系统，证明这是一个介观粒子限制在一个周期性调制的双光阱，并受到小的热波动。 还将研究具有空间范围的多稳定系统。 在具有空间范围的系统中，系统的状态是无限维的：它包含的信息比单个粒子的位置多得多。 一个例子是一层薄的液晶，由弱时空噪声驱动。 在其他项目中，这项研究将试图将Kramers方法扩展到具有空间范围的系统。