Model refinements

The effects that changes in vegetation have on soil carbon pools and nutrient availability are also difficult to evaluate. However, several models have been successful in predicting vegetation-soil nutrient relationships because they assume that such changes occur as a result of different rates of decomposition and nutrient release from leaf litter of different taxa 50, 60), Such predictions could be tested and the models refined or parameterized for new taxa by measuring soil nutrient availability and respiration in stands of different species on the same soil type. For example, fifty years ago the U.S. Civilian Conservation Corps (CCC) established such stands as species trial plots measurements in some indicate large differences in soil nutrient availability (48), Further measurements in these stands would now occur at the same time-scale at which we expect the feedback between species replacement and soil processes to occur. 

PBPK/PD models refine our understanding of complex quantitative dose behaviors by helping to delineate and characterize the relationships between (1) the external/exposure concentration and target tissue dose of the toxic moiety, and (2) the target tissue dose and observed responses (Andersen et al. 1987 Andersen and Krishnan 1994). These models are biologically and mechanistically based and can be used to extrapolate the pharmacokinetic behavior of chemical substances from high to low dose, from route to route, between species, and between subpopulations within a species. The biological basis of... 

Turkevich who established the first reproducible standard procedure for the preparation of metal colloids [44] also proposed a mechanism for the stepwise formation of nanoclusters based on nucleation, growth, and agglomeration [45,46]. This model, refined by data from modern analydical techniques and results from thermodynamic and kinetic studies, is in essence stiU valid today (Figure 2) [82]. 

In the following chapter model refinements are described and compared with the setup used by Gughelmo (2008). The focus is given on the represention of marine organic matter. In a sensitivity study the impact of organic matter on long-range transport is explored. Additionally, a study is included that clarifies the relative importance of sea surface temperature, wind speed, and pollutant concentration for volatilisation of DDT from the ocean. 

We have seen how to draw and write these abstract descriptions, but how can you be sure they accurately represent the code The concepts of abstraction and refinement capture the essential relationship between these descriptions. This chapter is about different forms of abstraction and refinement, and it explains the rules for showing that a more detailed model refines (or conforms to) a more abstract one. 

Model refinement, then, means to establish the relationship between the more abstract model used to define postconditions and the more complex practical implementation. Retrieve functions translate from the refined model attributes to the abstract ones. 

Model refinement has the second longest history, dating back to VDM and Z in the 1970s. 

If we can write the whole thing, spec and all, in code, we can also show both the abstract model and the more detailed design in one picture—see Figure 6.22 on page 245. The C etind Sum refinements are only model refinements, because the abstraction did not promise any behavior requirements on those types. 

Action Conformance and Layered Design Action Refinement Brings Model Refinement... 

Action refinement is nearly always associated with model refinement. To represent the intermediate states, the more detailed model needs more information. 

The implementation s vocabulary should be translated to the specification s by using retrieve functions as in Section 6.4, Spreadsheet Model Refinement. 

The finer actions refine the abstract one, and the relationship is documented as an action refinement consisting of a model refinement and an action refinement sequence. Many refinements of one action may be possible. 

Table 4. Results of the multipole model refinement of germanium (single crystal) with electron diffraction data...

Difficulties in obtaining good quantitative agreement between predicted and measured distribution results are indicative that model refinements as well as an improved property database will be needed before accurate quantitative predictions of not only overall polarization curve but also detailed distributions within a DMFC may be obtained. 

Conclusions. The objectives cited earlier were met. Solid trends do exist in this series can be documented, and can be used to chart new work. Significant trends in residuals encountered after the first phase of the study provided the basis for model refinement. Good support exists for the premise that we have thoroughly traversed the most attractive areas of structure/activity space in this series. 

The use of cross-validation should be widely recommended for crystallographic model refinement. Its simplicity to understand for the nonexpert and its power in discriminating models that are consistent with the experimental data make it indispensable. However, in modern crystallography model refinement is often falsely seen as the... 

Skubak, R, Murshudov, G.N. and Pannu, N.S. (2004) Direct incorporation of experimental phase information in model refinement. Acta Crystallogr. D60,2196-2201. 

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