Evaluating alternative Frequentist inferential approaches for optimal order quantities in the newsvendor model under Exponential demand

Three estimation policies for the optimal order quantity of the classical newsvendor model when the demand is Exponentially distributed are evaluated in this paper. The evaluation is performed analytically for different combinations of sample sizes and values of the requested critical fractile. The statistical measures that have been chosen to perform the evaluation are (a) the actual critical fractile, namely, the actual probability for the estimated order quantities to meet the demand of the period, (b) the mean square error of the estimators for the optimal order quantity, and (c) the range of deviations of estimated order quantities from the optimal order quantity, provided that the probability of taking such a range is the same for the three estimation policies. For small and moderate sample sizes, no estimation policy predominates over the other two approaches, and the choice should be made on a subjective base according to the individual preferences of researchers or practitioners.     

Comparative life cycle assessment of hydrogen and other selected fuels

A streamlined life cycle assessment (LCA) is reported of a nuclear-based copper–chlorine (Cu–Cl) hydrogen production cycle, including estimates of fossil fuel energy use and greenhouse gas (GHG) emissions. Calculations revealed that the process requires 474 kJ of fossil fuel energy per MJ of hydrogen, which is less than for other hydrogen production processes. Moreover, GHG emissions are estimated to be 27 gCO₂e per MJ of hydrogen, which is only slightly higher than the corresponding value for wind-based hydrogen production. A sensitivity analysis demonstrated that the performance of the system could be further improved at higher yields of hydrogen. Although the system significantly outperformed fossil-based gasoline and hydrogen production pathways, the integrated nuclear and thermochemical cycle still requires significant research and development before commercialization is possible.     

Exergy analysis of a hybrid solar hydrogen system with activated carbon storage

A proposed hybrid solar hydrogen system with activated carbon storage for residential power generation is assessed using exergy analysis. Energy and exergy balances are applied to determine exergy flows and efficiencies for individual devices and the overall system. A ‘base case’ analysis considers the proposed system without modification, while a ‘modified case’ extends the base case by considering the possibility of multiple product outputs. It is determined that solar photovoltaic-based sub-systems have the lowest exergy efficiencies (14-18%) and offer the most potential for improvement. A comparison of these two scenarios shows that the additional outputs raise the exergy efficiency of the modified case (11%) relative to the base case (4.0%). An investigation of the energy and exergy efficiencies of separate devices illustrates how energy analyses can be misleading. The hybrid system is expected to have several environmental benefits, which may offset to some degree economic barriers to implementation.