Upwinding constant

Second method consists of a straightforward discretization method first order (Euler) explicit in time and finite differences in space. Both the time step and the grid size are kept constant and satisfying the Courant Friedrichs Lewy (CFL) condition to ensure the stability of the calculations. To deal with the transport part we have considered the minmod slope limiting method based on the first order upwind flux and the higher order Richtmyer scheme (see, e.g. Quarteroni and Valli, 1994, Chapter 14). We call this method SlopeLimit. 

As might be expected, various types of ripples are formed depending upon the availability of transportable sands upwind. Nor can we overlook the fact that fluctuations in wind intensity can alter from moment to moment the character of the ripple formed. The end result is not necessarily something developed in an incrementally constant manner. There may be periods when the ripple is more extensive and higher, or composed of particles of much different size range than those found after the wind has ceased blowing. 

Concentrations of pollutants remain rather low until we reach the Mississippi River, as there are few strong sources to the southwest until Texas. The rise of concentrations is so fast that predicted levels of sulfate and Se are only about 30-40% low at the west site. However, the predicted concentrations rise so high as we move up the Valley that they greatly exceed the nearly constant observed concentrations. The S/Se ratio rises to about 3500 as we move away from SO2 sources in Texas, because the SO2 is mostly converted to sulfate. This is about the expected value for an area downwind from, but outside of areas of high SO2 emissions (4). As expected, the ratio drops sharply when we encounter heavy emissions of SO2 just upwind of the west station. There are large emissions of Se, but the new sulfur is still mostly in the gas phase. Perhaps fortuitously, the predicted S/Se ratios at the three sites are in fairly good agreement with the experimental data. 

It can be noted that at least the explicit upwind method for the constant equation model gives the exact answer for CFL = 1, whereas the implicit upwind differencing method never does. The numerical viscosity of the implicit... 

Upwind differencing is equivalent to adding additional numerical diffusion, or artificial diffusion, to obtain an effective diffusion constant... 

Y-tube olfactometers (Figure 6.4) are generally used to measure the level of attraction or repulsion of host-seeking mosquitoes to volatile stimuli in choice experiments. " Clean and conditioned air constantly runs through the tube system to the end of the base leg, where mosquitoes are connected. During stimulus application, mosquitoes are allowed to fly upwind into a decision chamber to choose between a test cage that holds the test stimulus and a control cage with clean air. 

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