Modeling of transpiration reduction in van Genuchten-Mualem type soils

We derive an analytic expression for the matric flux potential (M) for van Genuchten-Mualem (VGM) type soils which can also be written in terms of a converging infinite series. Considering the first four terms of this series, the accuracy of the approximation was verified by comparing it to values of M estimated by numerical finite difference integration. Using values of the parameters for three soils from different texture classes, the proposed four-term approximation showed an almost perfect match with the numerical solution, except for effective saturations higher than 0.9. Including more terms reduced the discrepancy but also increased the complexity of the equation. The four-term equation can be used for most applications. Cases with special interest in nearly saturated soils should include more terms from the infinite series. A transpiration reduction function for use with the VGM equations is derived by combining the derived expression for M with a root water extraction model. The shape of the resulting reduction function and its dependency on the derivative of the soil hydraulic diffusivity D with respect to the soil water content theta is discussed. Positive and negative values of dD/d theta yield concave and convex or S-shaped reduction functions, respectively. On the basis of three data sets, the hydraulic properties of virtually all soils yield concave reduction curves. Such curves based solely on soil hydraulic properties do not account for the complex interactions between shoot growth, root growth, and water availabilit

God as First Known: The Common Ground of Philosophy and Theology in Bonaventure s Thought

Goris, W. [Promotor

Ontwikkelingen in poeder- en keramische technologie

A review with 35 refs. is given of developments and trends in powder prepn. methods and shaping techniques. [on SciFinder (R)

Nieuwe inzichten in het sinterproces

A survey is given of developments in the last decennium, which have contributed to a better insight in the sintering process. The influence of sinter additives and the problems related to the sintering of inhomogeneous systems are also discussed

Het gebruik van thermodynamische beschouwingen voor de beschrijving van keramische processen

A review and discussion with 6 refs. In many cases, the no. of expts. necessary for optimization of a process can be reduced by simple thermodn. predictions. Some examples are discussed for nonoxide ceramic materials