Tier 1-3 methods

The critical use of extrapolation methods implies consideration of the issue of validation. It has been remarked that validation of an extrapolation method should be considered in view of the target of an assessment, so that 1 approach can be sufficient for 1 target (e.g., setting quality criteria) but not for others (precise quantification of risk at contaminated sites). Higher tier methods can be used to address the degree of validity of lower tier methods, especially in the case of the higher tier physical models of reality. 

Validation by practical use occurs frequently, especially for the lower tier methods scientific validation is less well developed and one extrapolation approach can be considered valid for 1 assessment type, but not for the other. 

Higher-tier assessments do not require the quantification of every uncertainty. Therefore, a tiered approach is proposed where each individual source of uncertainty in an assessment may be treated at one of three tiers, beginning with qualitative approaches (Tier 1) and progressing to deterministic (Tier 2) or probabilistic approaches (Tier 3) when appropriate. Within a single uncertainty assessment, different sources of uncertainty may be treated at different tiers. Higher-tier methods are targeted on those uncertainties that have most influence on the assessment outcome. It is never practical to treat all uncertainties probabilistically therefore, even in a very refined assessment, some uncertainties will still be treated at the lower tiers. 

Another feature of the two-tier method is the use of special iteration variables for improved convergence stability. The equilibrium stage model is formulated as follows, beginning by writing the component material balances and equilibrium relations in terms of component molar flow rates instead of mole fractions ... 

Several algorithms have been proposed to solve the model equations with chemical reactions (Holland, 1981 Saito et al., 1971 Tierney et al., 1982). Venkataraman et al. (1990) applied the two-tier method for this purpose. 

Protein Risk Assessment The first step is to identify the source of the extract and the amount of protein it contains. The total protein content is needed to estimate potential exposure upon the use of the product containing the extract. A tiered approach can be followed to determine the level of protein in the botanical extract. The complexity and cost of the method used increase with the tier. Therefore only lower tier methods are usually sufficient for botanicals and naturals used at very low levels in the cosmetic product. For those botanicals or natural extracts for which there is a relatively high prevalence of sensitization, highest tier methods are recommended. 

If actual fuel consumption data are not available, a standardised tiered method shall be used to estimate fuel consumption data based on best available information. 

Separation method selection is governed by a two-tier set of rules for selecting among potential operations. The first tier involves the selection between strategic and opportunistic operations. Strategic separations are favored, as these are known to be required in the flow sheet at some point, as are separations which directly reach a desired product composition. The rules in the first tier state that once all the potential opportunistic and strategic operations have been identified for the current stream, the next step is to determine the order in which these operations should be tried. The foUowing... 

Research is needed on developing the triggers to move from one hazard tier to the next and on risk assessment methods. 

Methode de financement par laquelle une compagnie (le preneur) peut louer du materiel appartenant a un tiers (le bailleur) en utilisant pour le paiement le flux de tresorerie obtenu grace k ce materiel. 

The application of NMR spectroscopy to tacticity determination of synthetic polymers was pioneered by Bovey and Tiers.9 NMR spectroscopy is the most used method and often the only technique available for directly assessing tacticity of polymer chains. "2 7 8 0JI The chemical shift of a given nucleus in or attached to the chain may be sensitive to the configuration of centers three or more monomer units removed. Other forms of spectroscopy (e.g. TR spectroscopy l2 lJ) are useful with some polymers and various physical properties (e.g. the Kerr effect14) may also be correlated with tacticity. 

In our view, architecture is not only about Gothic-scale structures but is also about all structures and relationships used down to the level of code.1 The decision to use a four-tier structure, with a thin client, a Web server, a business application server, and a database, is architectural. But, in the extreme, we consider a consistent use of getXQ and setX(x) methods also to be part of the (detailed) architecture. This view leads to a somewhat less formal definition of architecture. 

Web server This tier forwards appropriate requests to a servelet, a request handler that uses a standard API to plug in to the Web server. It translates CGI-encoded requests into proper method calls using distributed object invocations on an enterprise component. Then it formats and returns the results to the client. 

Gad, S.C. (1989b). A tier testing strategy incorporating in vitro testing methods for pharmaceutical safety assessment. Flumane Innovations and Alternatives in Animal Experimentation 3 75-79. 

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