Modeling validation

Iteration of the steps, descriptor selection, model building, and model validation in combination with an optimi ation algorithm allows one to select a descriptor subset having maximum predictivity. 

The abbreviation QSAR stands for quantitative structure-activity relationships. QSPR means quantitative structure-property relationships. As the properties of an organic compound usually cannot be predicted directly from its molecular structure, an indirect approach Is used to overcome this problem. In the first step numerical descriptors encoding information about the molecular structure are calculated for a set of compounds. Secondly, statistical methods and artificial neural network models are used to predict the property or activity of interest, based on these descriptors or a suitable subset. A typical QSAR/QSPR study comprises the following steps structure entry or start from an existing structure database), descriptor calculation, descriptor selection, model building, model validation. 

Model Validity Probabilistic failure models cannot be verified. Physical phenomena are observed in experiments and used in model correlations, but models are, at best, approximations of specific accident conditions. 

Electric Power Research InsHtute, "Preliminary Results from the EPRI Plume Model Validation Project—Plains Site." EPRI EA-1788, RP 1616. Palo Alto, CA. Interim Report. Prepared by TRC Environmental Consultants, 1981. 

IMES was developed to assist in the selection and evaluation of exposure assessment models and to provide model validation and uncertainty information on various models and their applications. IMES is composed of 3 elements 1) Selection - a query system for selecting models in various environmental media, 2) Validation - a database containing validation and other information on applications of models, and 3) Uncertainty - a database demonstrating apfhieatum nl a mode uncertainty protocol. 

Drish, W. F., and Singh, S. (1992). Train Energy Model Validation Using Revenue Service Mixed Intermodal Train Data. Chicago Association of American Railroads. 

The structure and mathematical expressions used in PBPK models significantly simplify the true complexities of biological systems. If the uptake and disposition of the chemical substance(s) is adequately described, however, this simplification is desirable because data are often unavailable for many biological processes. A simplified scheme reduces the magnitude of cumulative uncertainty. The adequacy of the model is, therefore, of great importance, and model validation is essential to the use of PBPK models in risk assessment. 

Considerable numbers of the numerical solutions of full-Hlm EHL for different surface geometries, such as the smooth surfaces, surfaces with single asperity, and sinusoidal waviness, were published over the past years. They provide good reference data for the purpose of model validation. 

The model validation in mixed lubrication should be made under the conditions when asperity contacts coexist with lubrication. Choo et al. [45] measured film thickness on the surface distributed with artificial asperities. The experi-... 

The traditional approach to optimize a process is schematically shown in Figure 2 its principle elements are the development of a model, model validation, definition of an objective function and an optimizing algorithn. The "model" can be (a) theoretical, (b) empirical or (c) a combination of the two. 

The validity of the model is tested against the experiment. A ISOOcc canister, which is produced by UNICK Ltd. in Korea, is used for model validation experiment. In the case of adsorption, 2.4//min butane and 2.4//min N2 as a carrier gas simultaneously enter the canister and 2.1//min air flows into canister with a reverse direction during desorption. These are the same conditions as the products feasibility test of UNICK Ltd. The comparison between the simulation and experiment showed the validity of our model as in Fig. 5. The amount of fuel gas in the canister can be predicted with reasonable accuracy. Thus, the developed model is shown to be effective to simulate the behavior of adsorption/desorption of actual ORVR system. 

QSAR model validation is an essential task in developing a statistically vahd and predictive model, because the real utility of a QSAR model is in its ability to predict accurately the modeled property for new compounds. The following approaches have been used for the vahdation of QSAR Eqs. 1-20 ... 

The PBPK model for a chemical substance is developed in four interconnected steps (1) model representation, (2) model parametrization, (3) model simulation, and (4) model validation (Krishnan and Andersen 1994). In the early 1990s, validated PBPK models were developed for a number of toxicologically important chemical substances, both volatile and nonvolatile (Krishnan and Andersen 1994 Leung 1993). PBPK models for a particular substance require estimates of the chemical substance-specific... 

PARAMETER ESTIMATION AND MODEL VALIDATION 17.4.1 Experimental Data... 

Roy, R. P, R. C. Dykuizen, M. G. Su, and P. Jain, 1988, The Stability Analysis Using Two-Fluid SAT Code for Boiling Flow Systems, Vol 1, Theory Vol. 4, Experiments and Model Validation, EPRI NP-6103-CCM, Palo Alto, CA. (6)... 

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