Models single-source

U.S. Environmental Protection Agency, "User s Manual for the Single Source (CRSTER) Model," EPA-450/2-77-013. Research Triangle Park, NC, 1977. 

The work in this group has focussed mainly in antimony and bismuth because of the thermoelectric properties of the chalcogenides186 and as low temperature single-source precursors to related semiconductor materials.187 The use of bismuth compounds in the treatment of gastrointestinal disorders has lead to the study of several thiolate compounds as models to understand the bioactivity. 

Because of the dominance of distributed sources over local single sources in the production of photochemical oxidants, point-source models are not discussed here. Related research regarding the measurement of diffusion or the development of atmospheric chemical submodels are not emphasized. Giapter 2 is devoted to the chemical processes that govern atmospheric transformation and removal, and this aspect of the models is not repeated here. 

Single-sourcing restrictions can be employed between different echelons of a supply chain. Their objective often is to reduce the complexity of the supply network. For example, in a production-distribution model a restriction might be included to ensure that each customer is only served by one distribution center (e.g., Tsiakis et al. 2001, p. 3590 Geoffrion and Graves 1974, p. 823). 

Restrictions (3.42) to (3.46) implement the single-sourcing restrictions discussed in Chapter 3.3.6. The allocation of a dedicated intermediate source for every site using internally produced intermediates is achieved via equations (3.42) to (3.44).While the intention of this restriction is to ensure a homogenous quality of intermediates supplied, it is also exploited in the import duty calculations. Restriction (3.45) covers the case where for certain customers supply from a pre-specified site is to be ensured. Generally, dedicated plant-market allocations are not required in specialty chemicals but a model formulation analogous to the one for intermediates could be employed if required. Finally, restriction (3.46) blocks site-market allocations that are not permitted, e.g., because of trade restrictions. 

It should be noted that the structure chosen here to model tariffs is based on assumptions specific to the problem instances analyzed (especially by exploiting the single sourcing assumption). Modifications might be required for example in order to allow drawbacks across a higher number of... 

To enforce the single sourcing restriction assumed for intermediates equation (3.94) sets the decision variable indicating that an intermediate is sourced from a certain vendor to 1 if a material flow between a vendor and a site exists for this material. Equation (3.44) from the basic model has to be modified to include the choice between internal and external sources for those intermediates where make or buy options exist. Flow constraint (3.20) has to be modified to ascertain that secondary demand is met either from internal or external sources. 

At the allocation level product-plant and plant-market allocation decisions can be evaluated. In many cases these decisions take the form of regular single-sourcing restrictions. Alternatively, it might be desired to asses the impact of producing certain products only at a single site that is to be selected by the model or pre-determined by the user to reduce the complexity of the network. As discussed in the context of the numerical performance analysis, the latter type of restriction has to be handled with care because of the strong increase in calculation time that was observed. 

The most important assessment is the comparison with the company s present level of cost of capital, as measured by the CAPM for a single source, or the WACC for capital derived from several sources. As interest rates have fallen quite considerably, it is likely that these models, being historical, are higher than would be the case for capital raised now. However, to set either of these as the target rate would probably be safe, were it not for the risks involved in any new project. 

Using both a hybrid receptor model, developed by Lewis and Stevens ( 2) and modified by Gordon and Olmez (3), and a simple model of emission from the Ohio River Valley, we compare the results of the College Park (CP) samples as well as those of another continuous set of samples taken from July 3-29, 1983 at Wallops Island, VA (WI), to predicted results. Single-source differential equations (2) are used to describe the time-varying concentrations of SO2, SO and a particulate element characteristic of coal-fired power plant emissions (chosen here as Se). An additional equation (3) can be added to describe the concentration variation of B(0H)3 The following rate constants apply to the concentrations of the four species in question ... 

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