Subject validating

For each model that abstracts from the real system, there is the concern whether the model s behavior is a reasonable approximation of the real behavior (Huselius et al., 2006). This concern is addressed by model validation, which can be defined as the "substantiation that a computerized model within its domain of applicability possesses a satisfactory range of accuracy consistent with the intended application of the model" (Schlesinger et al., 1979). Software simulation models can be validated by comparing trace data of the real system versus the model (cf. Figure 4). There are many possible approaches, including statistical and subjective validation techniques (Balci, 1990). Kraft describes a five-step validation process that combines both subjective and statistical comparisons of tracing data (Kraft, 2010, chapter 8). 

Fisher DA and Oddie TM. 1969. Thyroid iodine content and turnover in euthyroid subjects. Validity of estimation of thyroid iodine accumulation from short tern clearance studies. Journal of Clinical Endocrinology, 29, 721. 

The raw data collected during the experiment are then analyzed. Frequently the data must be reduced or transformed to a more readily analyzable form. A statistical treatment of the data is used to evaluate the accuracy and precision of the analysis and to validate the procedure. These results are compared with the criteria established during the design of the experiment, and then the design is reconsidered, additional experimental trials are run, or a solution to the problem is proposed. When a solution is proposed, the results are subject to an external evaluation that may result in a new problem and the beginning of a new analytical cycle. 

A new edition of any book presents an opportunity which an author welcomes for several reasons. It is a chance to respond to constructive criticisms of the previous edition which he thinks are valid. New material can be introduced which may be useful to teachers and students in the light of the way the subject, and the teaching of the subject, has developed in the intervening years. Last, and certainly not least, there is an opportunity to correct any errors which had escaped the author s notice. 

Because experimental measurements are subject to systematic error, sets of values of In y and In yg determined by experiment may not satisfy, that is, may not be consistent with, the Gibbs/Duhem equation. Thus, Eq. (4-289) applied to sets of experimental values becomes a test of the thermodynamic consistency of the data, rather than a valid general relationship. 

These materials are now widely used for coating both steel and concrete surfaces that are subject to a particularly aggressive environment (e.g. North Sea oil platforms). There is less validity for their use under normal atmospheric conditions since they are relatively expensive and tend to chalk on exposure to sunlight. However, their use as zinc phosphate, pretreatment or blast primers for blast-cleaned steel which is subsequently overcoated by any other paint system is an extremely valuable contribution to the painting of new steel work. 

There has been some controversy as to whether s.c.c. occurs by active path corrosion or by hydrogen embrittlement. Lack of space does not permit a full treatment of this subject here. References 14 and 15 are recent reviews on the s.c.c. of high strength steels and deal with the mechanism of cracking (see also Section 8.4). It is appropriate to discuss briefly some of the latest work which appears to provide pertinent information on the cracking mechanism. It should be noted, however, that cracking in all alloy systems may not be by the same mechanism, and that evidence from one alloy system need not constitute valid support for the same cracking mechanism in another. 

Linear viscoelasticity Linear viscoelastic theory and its application to static stress analysis is now developed. According to this theory, material is linearly viscoelastic if, when it is stressed below some limiting stress (about half the short-time yield stress), small strains are at any time almost linearly proportional to the imposed stresses. Portions of the creep data typify such behavior and furnish the basis for fairly accurate predictions concerning the deformation of plastics when subjected to loads over long periods of time. It should be noted that linear behavior, as defined, does not always persist throughout the time span over which the data are acquired i.e., the theory is not valid in nonlinear regions and other prediction methods must be used in such cases. 

The rationale for these simple approaches to water treatment is the argument that these kinds of systems have minimal requirements for MU water and are therefore subject to a reduced level of risk. In practice, the validity of this argument is suspect but is difficult to prove because totalizing water meters are seldom installed on the MU water line. 

This particular scheme has been the subject of many, many publications. Some deal with the rigorous solutions, but more treat various approximate solutions such as the steady-state and prior equilibrium approximations. Several assumptions, valid much of the time, convert the full expressions into more tractable forms. They are the subject of the next two sections. 

Many reports on the hydrolysis of Pu(IV) and polymerization (aggregation) of the primary hydrolysis products exist in one form or another. The validity of some of the earlier data may be subject to question because the experimental conditions were not properly controlled. Therefore, these systems deserve further consideration for the sake of refinements. Nevertheless, the major area of interest for the future will remain with interactions between Pu(IV) hydrolysis products and other reactive species present in the solution. There is not only considerable promise of elucidating novel chemical interactions, but there is also a great practical need to fully understand the extent of these interactions in order to ensure the most complete control of plutonium in reprocessing operations. 

Pu(IV) to Pu(III). The general conclusion is still valid that under these conditions the effect of radiation is to reduce the Pu. It is apparent that steady radiolysis experiments in the near neutral pH regime are subject to the same type of problems of interpretation as are those studies carried out in strong acid. 

The approach taken above estimates the effect of the metal by simply considering its electrostatic effect (subjected, of course, to the correct steric constraint as dictated by the metal van der Waals parameters). To examine the validity of this approach for other systems let s consider the reaction of the enzyme carbonic anhydrase, whose active site is shown in Fig. 8.6. The reaction of this enzyme involves the hydration of C02, which can be described as (Ref. 5)... 

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