Development of a Combined Quantity and Quality Model for Optimal Management of Unsteady Groundwater Flow Fields

Presented are alternative techniques for including conservative solute transport within computer models for optimizing groundwater extraction rates. Unsteady two-dimensional flow and dispersed conservative solute transport are assumed. Comparisons are made of the practicality of including modified forms of implicit and explicit finite difference solute transport equations within optimization models. These equations can be calibrated and subsequently used within a MODCON procedure. The MODCON modelling procedure consists of an integrated series of five optimization or simulation modules. The procedure is applicable for either an entire aquifer system or for a subsystem of a larger system. The first module, A, computes physically feasible recharge rates across the boundaries of the modelled subsystem. Module B computes optimal extraction rates without considering groundwater quality. Module C uses method of characteristics simulation to compute solute transport that would result from implementing the pumping strategy of model B. Module D uses linear goal programming and nonlinear solute transport equations to calibrate linear coefficients. It attempts to duplicate the solute transport predicted by module C. Calibration is performed because coarsely discretized implicit or explicit solute transport equations may not be as accurate as the method of characteristics. Module E includes appropriate calibrated equations of module D as well as the flow equations of module B. It computes an optimal pumping (extraction or recharge) strategy that can satisfy future groundwater contaminant concentration criteria. Testing of the validity of this optimal pumping strategy is subsequently accomplished using module C. If necessary, one may cycle through modules C, D and E until convergence is obtained--until concentrations resulting from implementing the strategy of E are demonstrated to be acceptable

Magnetic Exchange Couplings from Noncollinear Spin Density Functional Perturbation Theory

We propose a method for the evaluation of magnetic exchange couplings based on noncollinear spin-density functional calculations. The method employs the second derivative of the total Kohn-Sham energy of a single reference state, in contrast to approximations based on Kohn-Sham total energy differences. The advantage of our approach is twofold: It provides a physically motivated picture of the transition from a low-spin to a high-spin state, and it utilizes a perturbation scheme for the evaluation of magnetic exchange couplings. The latter simplifies the way these parameters are predicted using first-principles: It avoids the non-trivial search for different spin-states that needs to be carried out in energy difference methods and it opens the possibility of "black-boxifying" the extraction of exchange couplings from density functional theory calculations. We present proof of concept calculations of magnetic exchange couplings in the H--He--H model system and in an oxovanadium bimetallic complex where the results can be intuitively rationalized.Comment: J.Chem. Phys. (accepted

The effect of manganese oxide on the sinterability of hydroxyapatite

The sinterability of manganese oxide (MnO2) doped hydroxyapatite (HA) ranging from 0.05 to 1 wt% was investigated. Green samples were prepared and sintered in air at temperatures ranging from 1000 to 1400 °C. Sintered bodies were characterized to determine the phase stability, grain size, bulk density, hardness, fracture toughness and Young's modulus. XRD analysis revealed that the HA phase stability was not disrupted throughout the sintering regime employed. In general, samples containing less than 0.5 wt% MnO2 and when sintered at lower temperatures exhibited higher mechanical properties than the undoped HA. The study revealed that all the MnO2-doped HA achieved >99% relative density when sintered at 1100–1250 °C as compared to the undoped HA which could only attained highest value of 98.9% at 1150 °C. The addition of 0.05 wt% MnO2 was found to be most beneficial as the samples exhibited the highest hardness of 7.58 GPa and fracture toughness of 1.65 MPam1/2 as compared to 5.72 GPa and 1.22 MPam1/2 for the undoped HA when sintered at 1000 °C. Additionally, it was found that the MnO2-doped samples attained E values above 110 GPa when sintered at temperature as low as 1000 °C if compared to 1050 °C for the undoped HA

Development of a Combined Quanity and Quality Model for Optimal Groundwater Management

Presented is a procedure for incorporating solute transport as linear constraints within computer models for optimizing regional groundwater extraction strategies. The MODCON modelling procedure uses linear goal programming, embedded linearized equations for flow and solute transport and a MOC simulation model. Assumed is 2D flow and solute transport and a dispersed conservative contaminant. The MODCON procedure develops steady groundwater extraction strategies that will satisfy future groundwater quality constraints while simultaneously causing future piezometric heads to be as close to current heads as possible. The procedure is applied to a 160 square mile area in southeastern Arkansas

South polar dynamics of the Venusian atmosphere from VIRTIS/Venus Express mapping in the thermal range

We report on measurements of Venus cloud velocities from VIRTIS/Venus Express observations of the south polar region of Venus. Cloud tracking has been performed using a method of automated digital correlation. Tracking has been performed on pairs of monochromatic VIRTIS images selected mainly in the 5 μm window, but also at 1.74, 2.3, 3.93 micrometers. Wind measurements from vector retrievals based on automated feature tracking show high variability, indicating the presence of important transient motions. The time-averaged zonal winds indicate different day and night side regimes. On the day side both the zonal wind component (u) and the meridional one (v) are approximately uniform between 84S and 76S, with u ∼ −40 m/s and v ∼ −10 m/s. On the night side the zonal wind decreases poleward, from a maximum at 76S. The meridional wind is smaller than on the day side and appears to change sign from poleward to equatorward at 76S. The cold collar boundary appears to be a transition region not only for the temperature, but for the winds as well. In this region wave motions are also apparent, with amplitudes on the order of 40 m/s for u′ and 10 m/s for v′