Dynamics of condensed matter systems

我的研究集中在微观结构的时间演化上。由于微观结构取决于样品的历史，因此需要非平衡热力学才能理解它。材料的微观结构是其大部分物理和机械性能的核心。不仅故障率，而且许多其他重要的性能，包括抗拉强度、化学反应性和磁矫顽力，都关键取决于这种形态。这些结构的典型长度尺度为微米。理解微结构是如何产生的，如何表征它们，以及它们是如何随时间演化的，这是物理学中的一个重要的基本问题。无序和非平衡体系跨越材料的范围，包括二元合金(用于喷气涡轮机的Ni3Al)和定向凝固晶体(雪花)。无序系统中相干性和关联性的性质和作用仍未被完全理解。实时原位X射线测量，使用时间分辨衍射或X射线光子相关光谱，允许在类似于加工材料所用条件的条件下测量微结构。因此，它们非常适合于研究微观结构的时间演化。 我的研究主要有两个方面的发展。第一个是开发更好的仪器和技术，用于现场时间分辨X射线散射，以帮助解决这些问题。我的观点是，物理学最大的影响之一是发展了其他科学所使用的仪器。为了追求这一目标，我参与了SLAC使用最亮的x射线同步加速器源和新的x射线激光器的仪器的设计和建造。第二个重点是通过对微结构起重要作用的材料进行X射线实验来理解上述物理学。

My research concentrates on the time evolution of microstructures. Since the microstructure depends on the history of the sample it requires nonequilibrium thermodynamics for its understanding. The microstructure of a material is central to most of its physical and mechanical properties. Not only failure rates, but many other important properties including tensile strength, chemical reactivity and magnetic coercivity, depend crucially on this morphology. The typical length scales of these structures is micrometers. It is an important fundamental problem in physics to understand how microstructures arise, how to characterize them and how they evolve in time. Disordered and nonequilibrium systems span the range of materials including binary alloys (Ni_3Al used for jet turbines) to directionally solidifying crystals (snowflakes). The nature and role of coherence and correlations in disordered systems is still not fully understood. Real-time in-situ x-ray measurements, using either time resolved diffraction or x-ray photon correlation spectroscopy, allow measurements of the microstructure under conditions similar to the conditions used in processing the materials. They are thus ideally suited to study the time evolution of microstructure. My research has a two main areas of development. The first is to develop better instrumentation and techniques for in-situ time-resolved x-ray scattering to help address these issues. It is my opinion is that one of the largest impacts of physics has been to develop the instrumentation used by the rest of science. In order to pursue this objective, I am involved in designing and building instrumentation to use the brightest x-ray synchrotron sources and the new x-ray laser at SLAC. The second focus is to understand the physics described above by performing x-ray experiments on materials where microstructure plays an important role.