The goals of the Workshop are to: (1) Review the existing state of knowledge on (a) physicochemical properties, multi-media transport and fate, exposure mechanisms and (b) release scenarios associated with the production, distribution, and use of ethanol and alkylates in gasoline; (2) Identify key regulatory, environmental, and resource management issues and knowledge gaps associated with anticipated changes in gasoline formulation in California; and (3) Develop a roadmap for addressing issues/knowledge gaps.

Manganese model complexes, relevant to the oxygen-evolving complex (OEC) in photosynthesis, were studied with Mn K-edge X-ray absorption near-edge spectroscopy (XANES), Mn Kb X-ray emission spectroscopy (XES), and vibrational spectroscopy. A more detailed understanding was obtained of the influence of nuclearity, overall structure, oxidation state, and ligand environment of the Mn atoms on the spectra from these methods. This refined understanding is necessary for improving the interpretation of spectra of the OEC. Mn XANES and Kb XES were used to study a di-(mu)-oxo and a mono-(mu)-oxo di-nuclear Mn compound in the (III,III), (III,IV), and (IV,IV) oxidation states. XANES spectra show energy shifts of 0.8 - 2.2 eV for 1-electron oxidation-state changes and 0.4 - 1.8 eV for ligand-environment changes. The shifts observed for Mn XES spectra were approximately 0.21 eV for oxidation state-changes and only approximately 0.04 eV for ligand-environment changes. This indicates that Mn Kb XES i s more sensitive to the oxidation state and less sensitive to the ligand environment of the Mn atoms than XANES. These complimentary methods provide information about the oxidation state and the ligand environment of Mn atoms in model compounds and biological systems. A versatile spectroelectrochemical apparatus was designed to aid the interpretation …

Enhanced water-rock interaction resulting from the emplacement of heat-generating nuclear waste in the potential geologic repository at Yucca Mountain, Nevada, may result in changes to fluid flow (resulting from mineral dissolution and precipitation in condensation and boiling zones, respectively). Studies of water-rock interaction in active and fossil geothermal systems (natural analogs) provide evidence for changes in permeability and porosity resulting from thermal-hydrological-chemical (THC) processes. The objective of this research is to document the effects of coupled THC processes at Yellowstone and then examine how differences in scale could influence the impact that these processes may have on the Yucca Mountain system. Subsurface samples from Yellowstone National Park, one of the largest active geothermal systems in the world, contain some the best examples of hydrothermal self-sealing found in geothermal systems. We selected core samples from two USGS research drill holes from the transition zone between conductive and convective portions of the geothermal system (where sealing was reported to occur). We analyzed the core, measuring the permeability, porosity, and grain density of selected samples to evaluate how lithology, texture, and degree of hydrothermal alteration influence matrix and fracture permeability.

A brief overview of the temperature dependence of yield strength for the different slip systems of MoSi{sub 2} is presented and mechanisms for the yield stress anomaly are discussed. Recent results on the atomistic simulation of the dislocation core structures and mobility are presented next. Finally, we present experimental results on substitutional alloying of polycrystalline MoSi{sub 2} with 1-2 at.% Re, Nb and Al. Re resulted in an order of magnitude increase in compressive strength at 1600 C, Al caused solution softening at near-ambient temperatures, and Nb caused softening at low temperatures and hardening at high temperatures. The quaternary MoSi{sub 2}-Re-Al alloys showed strengthening at elevated temperatures and reduction in flow stress with enhanced plasticity at near-ambient temperatures. The mechanisms of solution hardening and softening are discussed using insight from transmission electron microscopy observations of the dislocation substructures and atomistic simulation results.