Self-organized Models of Selectivity in Ca and Na Channels

A simple pillbox model with two adjustable parameters accounts for the selectivity of both DEEA Ca channels and DEKA Na channels in many ionic solutions of different composition and concentration. Only the side chains are different in the model of the Ca and Na channels. Parameters are the same for both channels in all solutions. 'Pauling' radii are used for ions. No information from crystal structures is used in the model. Side chains are grossly approximated as spheres. The predicted properties of the Na and Ca channels are very different. How can such a simple model give such powerful results when chemical intuition says that selectivity depends on the precise relation of ions and side chains? We use Monte Carlo simulations of this model that determine the most stable-lowest free energy-structure of the ions and side chains. Structure is the computed consequence of the forces in this model. The relationship of ions and side chains vary with ionic solution and are very different in simulations of the Na and Ca channels. Selectivity is a consequence of the 'induced fit' of side chains to ions and depends on the flexibility (entropy) of the side chains as well as their location. The model captures the relation of side chains and ions well enough to account for selectivity of both Na channels and Ca channels in the wide range of conditions measured in experiments. Evidently, the structures in the real Na and Ca channels responsible for selectivity are self-organized, at their free energy minimum. Oversimplified models are enough to account for selectivity if the models calculate the 'most stable' structure as it changes from solution to solution, and mutation to mutation.Comment: Version of http://www.ima.umn.edu/2008-2009/W12.8-12.08/abstracts.html, talk given at the Institute for Mathematics and its Applications, University of Minnesota, November 19, 2008. Abstract published in Biophysical Journal, Volume 96, Issue 3, 253

On Sylvia Bowerbank, Green Literary Scholar

To accompany the posthumous publication of Sylvia Bowerbank’s personal essay “Sitting in the Bush, Or Deliberate Idleness,” eight scholars introduce her ecocritical thought and practice to a new generation of ecocritics by reflecting on the ways Sylvia herself or her writing or teaching influenced them. Their tributes to this trailblazing ecocritic emphasize her passionate commitment to radical green change within the world, within the university, and within the self

Policy Options for Water Management in the Verde Valley, Arizona (Executive Summary)

The water of the Verde Valley, both in the ground and flowing at the surface, is a natural resource that is critical to the regional economy, environmental sustainability, and quality of life -- but the Verde River faces unprecedented threats from over-allocation, development, and lack of cohesive water management. This report presents the results of three related initiatives designed to examine possible futures for the Verde and provides information for stakeholders and decision makers regarding the Verde Valley's water resources, its economic value, and possible tools for sustainable water management.Our analysis included modeling the effects of growth on river flows and on the regional economy. Population growth and development in the basin, if not mitigated, are likely to cause further decrease in the summer base flow in the Verde River. Decreases in the Verde River's flow have already been observed, and further reductions could have harmful side effects on the region's economy and could lead to federal intervention in local water management to maintain habitat for endangered species

Lithological and facies analysis of the Roseneath and Murteree shales, Cooper Basin, Australia

Unconventional shale plays have received marked attention over the last five years because of their economic potential for hydrocarbon generation, and yet they are amongst the least understood of all clastic sedimentary rock systems. The Cooper Basin is one of the largest Gondwana intracratonic basins in Australia, extending from northern South Australia into south-western Queensland and covering approximately 130,000 km2. The basin is may be prospective for shale gas, particularly within the lacustrine shales of the Permian Murteree and Roseneath formations. This study investigates lithological characteristics of these two units in relation to reservoir evaluation. Core samples representing the Dirkala-02 and Moomba-46 wells were used for petrographic analysis. A combination of wireline log analysis, thin section petrography, X-ray diffraction and pyrolysis analysis was used to define and characterize four distinct lithofacies facies within the Roseneath and Murteree shales: siliceous mudstone, organic siliceous mudstone, calcareous siliceous mudstone, and silty siliceous mudstone. The siliceous mudstone and organic siliceous mudstone are the most common. Diagenetic siderite occurs in all four lithofacies. A conceptual depositional model is developed for deposition of the Roseneath and Murteree shales. Wireline-log cross plots were interpreted and utilized in the construction of electrofacies. The study was concentrated on the northern portion of the basin between the Nappameri and Patchawarra Troughs in order to understand the nature of lithofacies and variability in reservoir architecture, which was controlled by relative lake level fluctuation. The results of this study will aid in the evaluation of shale gas potential for this portion of the basin, as well as a better understanding of shale gas opportunities in the Cooper Basin more generally