SFI Talks
Why Don't Glasses Flow?
Date and Time: Friday, July 8, 12:15 p.m. Location: Medium C.R. Speaker: Jean-Philippe Bouchaud Affiliation: Science & Finance, Capital Fund Management and SPEC, Commissariat a l'Energie Atomique
Glasses are liquids that do not flow. They look like liquids but behave like solids. A very important experimental observation is that the viscosity of glasses (a dynamical property) seems highly correlated to its entropy, i.e., the number of microscopic configurations in which the glass can get stuck. The smaller this number, the larger the viscosity. The striking observation that makes the `problem of glasses' interesting is that very many, totally different materials, exhibit the same properties, pointing to the exitence of a somewhat universal mechanism: glassy dynamics is physics more than chemistry. An idea is that of "cooperatively rearranging regions" of increasing length. The dynamics becomes sluggish because larger and larger regions of the material have to move simultaneously to allow for a substantial motion of individual particles. Although this idea seems most reasonable, its reality has remained elusive until recently: the difficulty is that, contrarily to better understood systems where this length corresponds to the size over which the system has ordered, glasses do not `order' in any obvious way. This cooperative length is purely dynamical and hence more more difficult to measure. Is it because this length can become large that all glassy materials behave in the same way, because microscopic details become irrelevant?
Spatiotemporal Intermittency and its Application to Problem of Memory and Learning
Tuesday, April 19, 2005 • 12:15 PM • Robert N. Noyce Conference Room
Yuzuru Sato / Santa Fe Institute
This is a review talk. Spatiotemporal intermittency is observed in many physical and biological systems and has been studied as a problem in high-dimensional nonlinear dynamics. I will explain this phenomenon including Arnold diffusion and chaotic itinerancy and describe possible mechanisms for them. The application to dynamic memory in rodent's odor sensing will be briefly discussed.