A decomposition approach in multistage stochastic programming

In this contribution we present a time and nodal decomposition approach to solve a rather general multistage stochastic programming problem that can be tackled in the framework of a discrete time optimal control problem. The optimal solution is obtained solving small decomposed subproblems and using a mean valued fixed-point iterative scheme. Moreover to enhance the convergence we propose an optimization step in which the weights are chosen in an optimal way at each iteration

CO2 Thermosiphon for Competitive Geothermal Power Generation

Engineered geothermal systems represent a significant unutilized energy source, with the potential to assist in meeting growing energy demands with clean, renewable energy. Traditional geothermal systems use water as the working fluid. An alternative working fluid is carbon dioxide which offers potential benefits including favorable thermodynamic and transport properties and the potential for sequestration. An important feature is that CO2 does not dissolve mineral salts, and this will serve to reduce fouling and corrosion problems which afflict piping and surface equipment in conventional water cycles. Our modeling shows that a CO2-based power plant has net electricity production comparable to the traditional approach, but with a much simpler design, and demonstrates the comparative efficacy of CO2 as a heat extraction and working fluid. While the economic viability of a CO2-based system remains to be proven, this analysis provides a starting point for more detailed thermodynamic and economic models of engineered geothermal systems power conversion utilizing CO2

Plug-in specimens for measurement of the corrosion rate of Mg alloys

Magnesium alloy corrosion is often nonlinear. The corrosion rate accelerates to steady state after an initial period of low corrosion. Plug-in specimens permit simultaneous measurement of the corrosion rate using hydrogen evolution, P (H), and Tafel extrapolation of cathodic polarization curves, P-i. Moreover, weight loss allows independent verification. P-H is consistently greater than P-i. The data, for short exposure periods up to 10 days, are consistent with the unipositive Mg+ ion being a short-lived intermediate. Tafel extrapolation needs to be used with caution for estimation of Mg corrosion, as the measured corrosion rate can have a significant contribution from crevice corrosion. Furthermore, measurements made at short immersion times may not reflect the steady-state corrosion rate, and the corrosion reaction at the Mg surface may be decoupled from the electrochemical measurement