Changes in the Spatial Allocation of Cropland in the Ft. Cobb Watershed as a Result of Environmental Restrictions

Pollution runoff estimates from SWAT are used in a mathematical programming model to optimally model site-specific crop and conservation practices for pollution abatement in the Ft. Cobb watershed in Southwestern Oklahoma. Results indicate the tradeoffs between producer income, sediment and nutrient runoff and the spatial allocation of crops in the watershed.Environmental Economics and Policy,

Evolved stars in the Local Group galaxies. I. AGB evolution and dust production in IC 1613

We used models of thermally-pulsing asymptotic giant branch (AGB) stars, that also describe the dust-formation process in the wind, to interpret the combination of near- and mid-infrared photometric data of the dwarf galaxy IC 1613. This is the first time that this approach is extended to an environment different from the Milky Way and the Magellanic Clouds (MCs). Our analysis, based on synthetic population techniques, shows a nice agreement between the observations and the expected distribution of stars in the colour-magnitude diagrams obtained with JHK and Spitzer bands. This allows a characterization of the individual stars in the AGB sample in terms of mass, chemical composition, and formation epoch of the progenitors. We identify the stars exhibiting the largest degree of obscuration as carbon stars evolving through the final AGB phases, descending from 1-1.25Msun objects of metallicity Z=0.001 and from 1.5-2.5Msun stars with Z=0.002. Oxygen-rich stars constitute the majority of the sample (65%), mainly low mass stars (<2Msun) that produce a negligible amount of dust (<10^{-7}Msun/yr). We predict the overall dust-production rate from IC 1613, mostly determined by carbon stars, to be 6x10^{-7}Msun/yr with an uncertainty of 30%. The capability of the current generation of models to interpret the AGB population in an environment different from the MCs opens the possibility to extend this kind of analysis to other Local Group galaxies.Comment: 14 pages, 6 figures, accepted for publication on MNRA

Integrated Reservoir Management under Stochastic Conditions

Economic optimization, Lake levels, Marketed and non-marketed water uses, Non-linear programming, Recreational benefits, Reservoir management, Stochastic inflows, Value of a visitor day, Environmental Economics and Policy, International Development, Land Economics/Use, Production Economics, Productivity Analysis, Public Economics, Resource /Energy Economics and Policy, Risk and Uncertainty,

Optimal Allocation of Reservoir Water

The purpose of this paper is to determine the optimal allocation of reservoir water among consumptive and non-consumptive uses. A non-linear mathematical programming model is developed to optimally allocate Lake Tenkiller water among competing uses that maximize the net social benefit. A mass balance is used to determine the level and volume of water in the lake. This paper examines the effect of water management on lake resources when recreational values are and are not included as control variables in the optimization process. Results show that maintaining the lake level to the ‘normal lake level’ of 632 feet during the summer months generates more recreational benefit rather than reducing the lake level by releasing water for hydro power generation.consumptive and non-consumptive use, mass balance equation, non-linear mathematical programming, optimization, recreational uses, water allocation, Resource /Energy Economics and Policy,

On the nature of the most obscured C-rich AGB stars in the Magellanic Clouds

The stars in the Magellanic Clouds with the largest degree of obscuration are used to probe the highly uncertain physics of stars in the asymptotic giant branch (AGB) phase of evolution. Carbon stars in particular, provide key information on the amount of third dredge-up (TDU) and mass loss. We use two independent stellar evolution codes to test how a different treatment of the physics affects the evolution on the AGB. The output from the two codes are used to determine the rates of dust formation in the circumstellar envelope, where the method used to determine the dust is the same for each case. The stars with the largest degree of obscuration in the LMC and SMC are identified as the progeny of objects of initial mass $2.5-3~M_{\odot}$ and $\sim 1.5~M_{\odot}$, respectively. This difference in mass is motivated by the difference in the star formation histories of the two galaxies, and offers a simple explanation of the redder infrared colours of C-stars in the LMC compared to their counterparts in the SMC. The comparison with the Spitzer colours of C-rich AGB stars in the SMC shows that a minimum surface carbon mass fraction $X(C) \sim 5\times 10^{-3}$ must have been reached by stars of initial mass around $1.5~M_{\odot}$. Our results confirm the necessity of adopting low-temperature opacities in stellar evolutionary models of AGB stars. These opacities allow the stars to obtain mass-loss rates high enough ($\gtrsim 10^{-4}M_{\odot}/yr$) to produce the amount of dust needed to reproduce the Spitzer coloursComment: 14 pages, 5 figures, 1 table; accepted for publication in MNRAS Main Journa