Developing Conceptual Models

Conceptual models link anthropogenic activities with stressors and evaluate the relationships among exposure pathways, ecological effects, and ecological receptors. The models also may describe natural processes that influence these relationships. Conceptual models include a set of risk hypotheses that describe predicted relationships between stressor, exposure, and assessment end point response, along with the rationale for their selection. Risk hypotheses are hypotheses in the broad scientific sense they do not necessarily involve statistical testing of null and alternative hypotheses or any particular analytical approach. Risk hypotheses may predict the effects of a stressor, or they may postulate what stressors may have caused observed ecological effects. 

Diagrams can be used to illustrate the relationships described by the conceptual model and risk hypotheses. Conceptual model diagrams are useful tools for communicating important pathways and for identifying major sources of uncertainty. These diagrams and risk hypotheses can be used to identify the most important pathways and relationships to consider in the analysis phase. The hypotheses considered most likely to contribute to risk are identified for subsequent evaluation in the risk assessment. 

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Soil formation, or pedogenesis, is a major activity for pedologists. The origins of soil attributes, distinctive horizons, and profiles must be understood to develop conceptual models for soil evolution over both long and short time periods (e.g., Smeck, Runge, and MacKintosh 1983). Such models have intuitive, predictive power in the forensic comparison of soils. 

Such enhanced understanding will be incorporated into a developing conceptual model (Whipple etal. 2005a), and also into an ecosystem... 

Progress has been made in a complementary way by those who have tried to answer the fundamental questions concerning the exact definition of a chemical bond, those who have translated the basic physics into efficient and computer friendly algorithms and those who have developed conceptual models and presented them in a way which could be used and adapted by experimental chemists. The subsequent chapters in this series of volumes of Structure and... 

During process development, a model can be developed as soon as a conceptual flow sheet has been formulated. This model can be updated as more information about the process is obtained. Even at an early stage in the project, the model can be used to assess the preliminary economics of the process and the effect of technological changes on these economics. The model can aid in interpreting pilot-plant data and allows the study of many process alternatives. 

Upon completion of both the preliminary and detailed site investigation, a conceptual model can be prepared. A conceptual model is essentially a site model which includes all of the information that has been acquired for the site from both preliminary and detailed investigations, as well as other investigations not directly related to the site. The conceptual model can be anything from simple diagrams to detailed computer simulations, depending ujran the complexity of the site. The model must be continually updated to include new information as it is developed. 

Once the conceptual model is operating, it can be utilized to help develop a technically sound, cost-effective recovery and treatment system. Potential uses for a conceptual model include provision of continual upniates of project developments, provision of a yardstick to measure what has been done and what needs to be done, and helping prioritize areas for Corrective Action. Ultimately, the principal use for a conceptual model is to help determine what Corrective Actions or alternatives are applicable to the site. 

Although it is probably not possible at present to develop a completely satisfactory quantitative model, a conceptual model that identifies the critical processes can be developed. First, it is apparent that before significant chemical reaction can occur substantial modification must be induced by the shock-compression process. With present knowledge, the problem is one of mechanical deformation, rather than one of chemistry. The materials studies... 

Conceptual model of conventional Cl combustion characterized by a sequence of processes occurring in a fully developed reacting jet. (From Dec, A Conceptual Model of DI Diesel Combustion Based on Laser Sheet Imaging, SAE, 970873,1997. With permission.)... 

Stochastic or probabilistic techniques can be applied to either the moisture module, or the solution of equation (3) — or for example the models of Schwartz Crowe (13) and Tang et al. (16), or can lead to new conceptual model developments as for example the work of Jury (17). Stochastic or probabilistic modeling is mainly aimed at describing breakthrough times of overall concentration threshold levels, rather than individual processes or concentrations in individual soil compartments. Coefficients or response functions and these models have to be calibrated to field data since major processes are studied via a black-box or response function approach and not individually. Other modeling concepts may be related to soil models for solid waste sites and specialized pollutant leachate issues (18). 

Figure 13.4 illustrates some of the factors known to be involved in the development of AD many of the known and putative links between factors are also shown. It should also be noted that the patterns of inter-factor modulation may be either positive or negative. However, it is clear that no single factor or combination of factors can explain all AD cases. It is best to conceptually model AD as a broad end point that can be reached in numerous ways. Similar multi-factorial models have been proposed for schizophrenia and depression (Chapters 11 and 12) and almost certainly underlie every other complex psychobiological concept. 

At the time of the submission of this extended abstract the background research on arsenic mobility is complete and the acquisition of the hydrogeological and geochemical datasets as well as the development of the preliminary conceptual model and hydrogeological framework is... 

General Observations About x. its Relationship to the Overall Partitioning Coefficient and to the Concept of Surface-Site Heterogeneity. One approach to metal/particle surface interactions which has been developed, historically, in a variety of forms, is a conceptual model that assumes only two conditions for surface sites occupied by an adsorbate or unoccupied. In applying this approach to the solid/aqueous solution interface, the adsorption... 

The student should be aware that a pathway is essentially a conceptual model developed by biochemists in order to represent the flow of compounds and energy through metabolism. Such models are simply ways of trying to explain experimental data. A potential problem in representing metabolic pathways as in Figure 1.1 is that there is an implication that they are physically and/or topographically organized sequences. This is not necessarily true. With some exceptions (described in Section 1.3), most enzymes are likely to be found free within the cytosol or a compartment of a cell where reactions occur when an enzyme and its substrate meet as a result of their own random motion. Clearly this would be very inefficient were it not for the fact that cells contain many copies of each enzyme and many molecules of each type of substrate. 

Appendix B consists of a systematic classification and review of conceptual models (physical models) in the context of PBC technology and the three-step model. The overall aim is to present a systematic overview of the complex and the interdisciplinary physical models in the field of PBC. A second objective is to point out the practicability of developing an all-round bed model or CFSD (computational fluid-solid dynamics) code that can simulate thermochemical conversion process of an arbitrary conversion system. The idea of a CFSD code is analogue to the user-friendly CFD (computational fluid dynamics) codes on the market, which are very all-round and successful in simulating different kinds of fluid mechanic processes. A third objective of this appendix is to present interesting research topics in the field of packed-bed combustion in general and thermochemical conversion of biofuels in particular. 

Investigators can systematically analyze data from past incidents to identify lessons learned and develop incident stereotypes. This makes it possible to develop a model displaying the anatomy of a process-related incident using a conceptual framework. Figure 3-1 provides a tool to help us understand incident causation. 

The US Environmental Protection Agency (USEPA 1998) describes problem formulation as an iterative process with 4 main components integration of available information, definition of assessment endpoints, definition of conceptual model, and development of an analysis plan. These 4 components apply also to probabilistic assessments. In addition, it is useful to emphasize the importance of a 5th component dehnition of the assessment scenarios. The relationships between all 5 components are depicted in Figure 2.1. Note that the bidirectional arrows represent the interdependency of the different components and imply that they may need to be revised iteratively as the formulation of the problem is rehned. 

That conceptual models be developed in a modular way, standard modules being developed to represent states and processes that occur repeatedly in many assessments... 

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