Model tracing

Lee and Bethke (1996) presented an alternative technique, also based on mass balance equations, in which the reaction modeler can segregate minerals from isotopic exchange. By segregating the minerals, the model traces the effects of the isotope fractionation that would result from dissolution and precipitation reactions alone. Not unexpectedly, segregated models differ broadly in their results from reaction models that assume isotopic equilibrium. 

The model traces the reaction path by taking a series of steps along reaction progress, moving forward each step from i to 2- Over a step, the system s isotopic composition can change in two ways reactants can be added or removed, and segregated minerals can dissolve. 

It implies two different IVR processes superimposed on each other (see Fig. 2) and a subsequent VET process. For a realistic comparison of experimental and modeled traces the simulation was convoluted with the cross correlation function of pump and probe pulses. It is... 

Figure 5. Threshold depolarization for generating an action potential as a function of Vm. Threshold voltages were determined from the modified HH model. Trace A V , applied over interval — oo < t < oo . Trace B V , applied over interval 0 < t < 10 ms. Stimulus applied at t = 0.

With these data we can now calculate the distribution of the major species on the surface of goethite in seawater. This approach will form the basis for modeling trace metal adsorption in seawater and determining the competitive effects of the major ions with each other and with trace metals. 

This equation, when applied to melting, is called the equilibrium melting or batch melting equation and, when applied to crystallization, it is called the equilibrium crystallization equation. As emphasized by Langmuir et al. (1992) this equation, and others like it, is enormously powerful and can be applied to model both major elements and trace elements. This approach has received its most widespread use, however, in modeling trace element variations. 

Another attempt at modeling trace metals (copper, nickel, lead, and zinc) in river water is presented by Mouvet and Bourg (1983) for... 

Comparison of native and modelled trace. The first correct structure from Table... 

Luoma, S.N. Davis, J.A., 1983. Requirements for modeling trace metal partioning in oxidized estuarine sediments. Mar. Chem.. 12 159-181. 

More complicated models account for the transport of mass or heat into or out of the system, so that its composition or temperature, or both, vary over the course of the calculation. The system s initial equilibrium state provides the starting point for this class of reaction path models. From this point, the model traces how mass entering and leaving the system, or changes in temperature, affects the system s equilibrium state. 

Modelling trace elemeitt processes in igneous rocks... 

Modelling trace element processes in Igneous rocks... 

Faidt tree models These logical cause-effect models trace the failures of the safety system functions considered in the event-trees back to basic events hke, for instance, the failures of system components. As result, they provide values for the unavailabiUties of the individual functions. 

Following the development of more precise analytical methods for the lanthanides about 20 years ago, a quantitative approach to modelling trace element distribution during crystal-liquid equilibria was developed (see Haskin 1984 and DePaolo 1981b for relevant equations). The distribution coefficient, K, is a measure of the partitioning behaviour of an element between a crystal and a co-existing melt ... 

Many attempts to model trace element abmdance variations in natural systems have employed the so-called Berthelot-Nernst distribution coefficient or distribution coefficients following the Henderson and Kracek treatment (see review of Mclntire, I963). Both Mclntire (1963) and Banno and Matsui (1973) have previously discussed the relative advantages and disadvantages of these distribution coefficients and reference is made to these works for additional discussion. 

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