The movement of fluids in a fractured, porous medium has been the subject of considerable study. This paper presents a continuum model that may be used to evaluate the isothermal movement of water in an unsaturated, fractured, porous medium under slowly changing conditions. This continuum model was developed for use in evaluating the unsaturated zone at the Yucca Mountain site as a potential repository for high‐level nuclear waste. Thus its development has been influenced by the conditions thought to be present at Yucca Mountain. A macroscopic approach and a microscopic approach are used to develop a continuum model to evaluate water movement in a fractured rock mass. Both approaches assume that the pressure head in the fractures and the matrix are identical in a plane perpendicular to flow. Both approaches lead to a single‐flow equation for a fractured rock mass. The two approaches are used to calculate unsaturated hydrologic properties, i.e., relative permeability and saturation as a function of pressure head, for several types of tuff underlying Yucca Mountain, using the best available hydrologic data for the matrix and the fractures. Rock mass properties calculated by both approaches are similar.

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Metal Clusters may be synthesized in the interior of surfactant aggregates called inverse micelles. These nanosize chemical reactors permit the controlled growth of several types of metal clusters. We describe this process for the formation of Au, Ag, Pd, Pt and Ir clusters and cluster alloys. Two size-control strategies are described: 1)variation of micelle size by alteration of the surfacant and/or solvent combination used, and 2) judicious use of micelle interactions or phase behavior. Using these two methods size control in the range of 1-100 nm is possible. The optical properties of metal clusters of gold, silver, and gold/silver alloys are described and the surface plasmon resonances are shown to have dramatic blue shifts and extensive line broadening with decreasing size in the range of 10-1 nm. In the case of gold clusters, the distinct resonancein the visible disappears for sizes less than 2.0 nm and new features appear in the UV. The optical spectra of alloys of gold and silver are shown to differ dramatically from their homoatomic counterparts of the same average size. We use electron and X-ray diffraction to determine the phase structure of the metal clusters and small angle X-ray scattering, neutron scattering, light scattering and TEM to characterize the average size and size distributions of these clusters. Finally, we describe measurements of the catalytic activity of Pd clusters and demonstrate a dramatic increase in hydrogenation activity on the size range of 2-10 nm.

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