PURPOSE OF THE MODEL

The role of the supply chain design model is to answer the following 

Where should intermediate and final products be produced  

What interplant shipments of intermediate products should occur  

Where should these DCs be located, and what should be the planned 

Which DC should supply a specific customer zone  

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Define the process flow sheet to be modeled and the purpose of the model. 

Focus For the purposes of this discussion, a model is a mathematical representation of the unit. The purpose of the model is to tie operating specifications and unit input to the products. A model can be used for troubleshooting, fault detection, control, and design. Development and refinement of the unit model is one of the principal results of analysis of plant performance. There are two broad model classifications. 

The mathematical model can only be an approximation of real-life processes, which are often extremely complex and often only partially understood. Thus models are themselves neither good nor bad but, as pointed out by Kapur, will either give a good fit or a bad fit to actual process behaviour. Similarly, it is possible to develop several different models for the same process, and these will all differ in some respect in the nature of their predictions. Indeed it is often desirable to try to approach the solution of a given problem from as many different directions as possible, in order to obtain an overall improved description. The purpose of the model also needs to be very clearly defined, since different models of a process, each of which has been developed with a particular purpose in mind, may not satisfy a different aim for which the model was not specifically constructed. 

The purpose of the model is to represent both the terms used in the business and the rules and procedures it follows. Reduce business rules to invariants, generalized effect invariants, action specs, and timing constraints. 

Figure 6.5 defines for the purposes of the model the distances at which the porosity and coverage with laterals change. It is assumed that, because of the changes in wall permeability along the root, nutrients are only absorbed by the primary root in the zones beyond the laterals (riat < r < rmax) and by the laterals. This is also the surface across which O2 leaks. 

Thus it seems that the type of comparison that should be made depends on the purpose of the model. For design of mixing vessels the tracer curves should be matched, and for reactor design conversions should be matched. Unfortunately, this means that a general approach is not possible for all cases. However, the various criteria of correspondence approach each other with approach to plug flow or... 

The purpose of the Model I ANOVA is to decompose each result as yij=iu+aj+eij where // is the population mean, aj the effect of group j and eij the randomly distributed error or residual. Significance in a fixed effect... 

The answer depends on the purpose of the model. To illustrate this point, we consider a model capable of assessing the fate of phenanthrene in Lake Y (Fig. 21.16). 

Bearing in mind that phenomena occurring in nature are too complex to be completely described by mathematical equations, the required details to be described by the model must be goal-driven, i.e. the complexity of the model, and the related results, must be strictly connected to the main goal of the analysis itself. When, for example, the main purpose of the model is to provide the fuel cell performance, in order to analyze the whole system in which it is embedded, the spatial variation in the physical and chemical variables (such as gas concentration, temperature, pressure and current density, for example) are not relevant however the performances, in terms of efficiency, electrical and thermal power and input requirements are important [1-4],... 

Kouvelis et al. (2004) present a relatively simple multi-period MILP plant location model for global production network design with investment decisions only allowed in the first period. The production system consists of component-dedicated manufacturing sites and final assembly sites. It is limited to two production levels and one final product. The objective function maximizes the NPV of the production network. The main purpose of the model is to analyze the effects financing subsidies, tax regimes, tariff structures and local content requirements have on optimal network design. The analysis is based on theoretical considerations and a numerical example. More complex aspects of international trade such as duty drawbacks are not considered. 

The purpose of the model is not to simulate chemical transport in a given field situation, but rather to estimate how a pesticide will move under a given set of imposed circumstances or to evaluate the susceptibility of a chemical to a given loss pathway and to classify chemicals into groups. 

Depending on the purpose of the model and the status of the molecular knowledge of the network, either simplified kinetic core models or kinetic detailed models can be constructed. Core models are most useful for showing principles of regulation or dynamics [5, 37, 41, 63-66] or to study a network in more phenomenological terms when it is poorly characterized [67-70]. In what follows we only consider detailed kinetic models. 

The purpose of the modeling was to examine the influence of the solution environment on the extent of dissociation of an organic acid. A series of studies was performed initially to establish the validity of the model in preparation for later work. An initial test of the model was to vary the PD value and monitor the concentration of products. As expected, an increase in the PD rule produced an increase in the calculated acid dissociation constant K. A second study examined the influence of acid concentration on the observed properties. As expected, the KA was approximately constant over a modest concentration range. A third study considered the effect of water temperature on the acid dissociation. As the modeled water temperature was increased by increasing the Pb(W) value, the value of the KA decreased, in agreement with a common, but not universal, observation of the effect of temperature on acid dissociation. These three preliminary studies thus revealed emerging attributes consistent with experimental observations. 

In this part of the chapter, a model of acid-mediated styrene polymerization will be developed and discussed. The purpose of the modeling work was twofold ... 

The paradigm of Occam s razor, stating that the theory with fewest unknown parameters is to be preferred, is not suitable for the development of theoretical models for liquids, since without conceptual simplicity and concrete reference to microscopic processes, the whole purpose of the modeling is spoiled. 

An important issue not addressed herein concerns the availability of reliable measurements. Also, note that the intended purpose of the models presented here is optimization and not prediction of the system behavior. 

Any model has its own inherent utilities and limitations. Determination of what model to use should be dependent on the purpose. The purpose of the models used in these two cases was to determine the exposure that was associated with DLT or severe lesions in the discovery and early development phase when the exposure-based prediction needs to be made as reliably as possible in a short time. Although nonspecific measurements (e.g., DLT or lesion scores) do not scale easily across species, this exposure-based approach should still be better in terms of accuracy of prediction than the conventional dose (mg/m2)-only based predictions, such as LD10 in rodents.39... 

The applicability of different urban wind-flow and meteorological models for UAC emergency modelling depends on types of the risk sources and releases, the scale of the dangers, and purposes of the model use (i.e. for emergency forecasting or risk assessments). 

The main purpose of the model was to relate the ion concentration and the local electrostatic parameters. The first step towards this relation was to assume that thermodynamic equilibrium was achieved between the water pools of the reversed micelles and the excess aqueous phase. This hypothesis differs from classical thermodynamics in that the equilibrium does not take place between two macroscopic phases. Biais et already suggested in a microemulsion pseudophase model (60) that, due to the low interfacial tension, chemical potentials of any constituents depend on the composition, even in microscopic domains, but not on the geometric parameters of the structure. 

It is necessary to decide the appropriate number of components to use in a model. The appropriate dimensionality of a model may even change depending on what the specified purpose of the model is. Hence, appropriate dimensionality of, e.g., a PARAFAC model, is not necessarily identical to the three-way pseudo-rank of the data array. Appropriate model dimensionality is not only a function of the data but also a function of the context and aim of the analysis. Hence, a suitable PARAFAC model for exploring a data set may have a rank different from a PARAFAC model where the scores are used for a subsequent regression model. 

For ecological applications like pesticide risk assessment, we have to find ways to avoid ad hoc choices of model types and ad hoc design of the models themselves. As for the choice of model type, it is important that managers understand the strength and weaknesses of different model types so that they formulate the purpose of the model as precisely and detailed as possible. Part of the specification of the model s purpose is also a detailed specification of the acceptance criteria of the model (Bart 1995) What kind of evidence is required to show that a model has been verified and validated ... 

The purpose of the model is to quantify population effects and recovery after pesticide exposure. 

The predictions for total hemoglobin and hemoglobin concentration from the modified model in response to continuous stimulation at 510, 440, and 360 mm Hg total pressure are shown in Figures 4, 5, and 6, respectively. The parameter values used in the simulation are shown in Table I. Although predictions are used to appraise the models validity, it should be remembered that the purpose of the model is not to produce an optimal fit between experimental data and model output but to help understand the behavior and interaction of the components and subsystems. 

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