Linear and Nonlinear Spin Transport in Random Porous Media

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9501171 Candela Nuclear magnetic resonance (NMR) and other techniques will be used to study the propagation of diffusing and dispersing particle and waves in three types of system. The first consists of spin-polarized quantum fluids in random porous media. For example, pure 3He liquid and 3He-4He mixtures in the pores of bead packs and silica aerogel will be polarized by an 8 - 10 T magnetic files and cooled below 10 mK to study the mixture phase diagram, quantum localization effect, and interference and localization of spin waves. The second system is fluids in porous media at room temperature. Pulsed-field-gradient NMR will be used to study the geometric structure of the pore space, and to study trace dispersion in an applied flow over a wide range of Peclet numbers. Finally, nonlinear waves will be studied both in polarized quantum fluids and in a room-temperature water-wave experiment to test the applicability of the inverse spectral transform to physical systems. %%% The objective of this project is to better understand the propagation of particles and waves in complex physical systems that have a random structure. Nuclear magnetic resonance (NMR) will be used to study the motions of molecules in fluids filling the pores of materials like fine powders, silica gels, and natural rock. The studies will take place both at very low temperature, where quantum effects will dominate, and at room temperature, where classical behavior is found. The low temperature studies will test theories relevant to the propagation of electrons in metals and semiconductors. The room temperature work will develop new methods for studying the structure of porous materials, and will test theories concerning the dispersion of tracers by fluid flow. Nonlinear waves will also be studied in a sub-project geared toward engaging undergraduate students in resear ch. ***