Characterization quantitative assessments

A particularly insidious failure mechanism that is commonly found in carbon-steel tubing is under-deposit corrosion. In many cases, corrosion products fomi a scab that can mask the presence of the pitting, making it difficult to quantitatively assess using conventional NDT methods. However, by combining proper cleaning procedures with laser-based inspection methods, the internal surface of the tubing can be accurately characterized and the presence of under-deposit corrosion can be confirmed and quantified. 

Usually, some lines of evidence will not be suitable for direct incorporation into quantitative analysis. Semiquantitative or qualitative methods will then be needed to weigh the different lines of evidence, including the quantitative assessment, and integrate them for decision making. Methods for assessing weight of evidence were outside the scope of the workshop that developed this book but are discussed by Suter et al. (2000) and were recently the focus of another workshop (Chapman et al. 2002). Whatever method is used for weighing different lines of evidence, it will be important to characterize uncertainties in each line of evidence and show their effect on the overall assessment outcome. 

Data used to describe variation are ideally representative of some population of risk assessment interest. Representativeness was a focus of an earlier workshop on selection of distributions (USEPA 1998). The role of problem formulation is emphasized. In case of representativeness issues, some adjustment of the data may be possible, perhaps based on a mechanistic or statistical model. Statistical random-effects models may be useful in situations where the model includes distributions among as well as within populations. However, simple approaches may be adequate, depending on the assessment tier, such as an attempt to characterize quantitatively the consequences of assuming the data to be representative. 

Life-cycle impact assessment Technical, quantitative, and/or quaUtative process to characterize and assess die effect of die environmental loading identified in die inventory component. 

Our data demonstrate that the accumulation of contaminants in phytoplankton deviates significantly from this classical pattern and instead shows an S-shaped or sigmoidal pattern of accumulation. This sigmoidal pattern is characterized by an initial instantaneous accumulation based on the time resolution attainable in laboratory experiments, followed by a lag period of approximately 1 day and then a slower but sustained period of accumulation. Although clear deviations from the classical model can be detected in some cases from a qualitative examination of the data, Brisbin et al. (30) reported a quantitative assessment in which the statistical significance of the sigmoidal nature of a data set is determined. 

Toxicity assessment is the determination of the potential of any substance to act as a poison, the conditions under which this potential will be realized, and the characterization of its action. Risk assessment, however, is a quantitative assessment of the probability of deleterious effects under given exposure conditions. Both are involved in the regulation of toxic chemicals. Regulation is the control, by statute, of the manufacture, transportation, sale, or disposal of chemicals deemed to be toxic after testing procedures or according to criteria laid down in applicable laws. 

The estimated upper bound on risk obtained by combining default constants provides no indication of the relative likelihood or frequency of that risk or any other risk between zero and the exaggerated upper bound. On the other hand, the risk characterization obtained by using probability distributions and probabilistic techniques provides a quantitative assessment of the relative likelihood of each of the different possible values for the risk. 

The first plant bioassay [Avena sativa L (oat) coleoptile test] was employed by F.W. Went in the 1920 s to demonstrate the existence of and to quantitatively assess the first growth-modifying substance [indole-3-acetic acid (IAA)] isolated from plants.122 Plant bioassays have been extremely useful and intimately linked to the discovery and characterization of the major classes of plant hormones. In fact, many of the bioassays used now were developed for PGRs. Bioassays have been used to screen, evaluate phytotoxicity or plant growth promotion, study mode... 

Quantitative assessment of these key parameters could require the development of new analytical methods compared to the relatively well established methods currently in use for characterization of stand alone medical devices and biologies. 

The integration step of the evaluation is conducted in three stages. In the first stage, the evaluators examine the data for relevance to potential human toxicity. Then, if the data are determined to be relevant to human exposures, a quantitative assessment is conducted. Finally, the concluding step of the evaluative process is the integration of toxicity and exposure information to characterize the risk of potential reproductive and developmental toxicity. 

That no indication of the significant influence of particle shape on FFF elution behavior has been published until recently may be attributed to the fact that the majority of the approximately 500 papers so far published have reported on spherical or nearly spherical samples, and that the studies on the non-spherical samples focused only on sample fractionation rather than on a quantitative assessment of physicochemical quantities. This problem can be solved if fractions from FFF are further characterized, for example, by dynamic fight scattering or if an independent detector for diffusion coefficients is available. 

Accuracy by Comparison. For drug substance, the only possibility of a quantitative assessment of accuracy is the comparison to the results of another analytical procedure or to a reference (if established with other procedures and/or additional characterization). This can be performed statistically with a r-test (see statistical textbooks or corresponding software). However, the shortcomings of these statistical tests (or better the justification of their use) are especially important here. It must be taken into consideration that two independent analytical procedures most probably differ in their specificity. This may lead to a systematic influence on the results (Table 2). If the effect can be quantified, the means should be corrected before performing the statistical comparison. If a... 

Diene Polymers. It has been known for many years that anionic polymerization of conjugated dienes can give rise to highly stereoregular products. Quantitative assessment of the microstructure of polymers and the characterization of the active centres in propagations are both difficult and have made a full understanding difficult to achieve. 

Characterization of Photooxidation Products Formed in Isooctane. Among the lodometncally titratable species formed in the photooxidation of isooctane, a substance, developed in appreciable amounts, was observed which was easily distinguishable from ordinary alkyl-hydroperoxides. This substance is, at room temperature, readily destroyed by addition of olefins to the reaction medium. This is a reaction which is typical and specific for peracids (10) and can be employed for quantitative assessment of peracids in the presence of alkylhydroperoxides. In contrast to alkylhydroperoxides, peracids react with olefins forming the corresponding epoxide, according to the equation... 

The epimerizalion of the 7a-hydroxyl group can occur either by intra- or interspecies mechanisms [16]. However, it is difficult to quantitatively assess the degree of 7-hydroxy epimerization in vivo because this transformation competes with the irreversible 7-dehydroxylation of bile acids (Section VI). 7a-HSDH activity has been reported in several genera of intestinal bacteria however, the most complete characterization of this enzyme has been carried out with the enzyme isolated from Escherichia coli [37] and Bacteroides sp. [29,38,39] (Table 2). Both enzymes used both free and conjugated bile acids as substrates, showed alkaline pH optima and lower values for dihydroxy than for trihydroxy bile acids. However, cell extracts prepared from Bacteriodes sp. contained both NAD- and NADP-depen-dent 7 -HSDH activities whereas, extracts from E. coli contained only an NAD-de-pendent enzyme activity. Additional studies showed that the two 7a-HSDH activities detected in Bacteriodes sp. differed in molecular weight, differential heat inactivation and Mn " requirement, suggesting the presence of two distinct enzymes [29]. 

The advantages of the piPlug method are the rapid identification of the chemotactic response to a molecule and the ability to compare the responses of two different bacteria using differential labeling (i.e., one strain expresses GFP while the other expresses RFP). In Fig. 4a and b, the RFP-labeled cells were killed by exposure to a lethal dose of kanamycin to provide a nonrespon-sive control to monitor bulk flow, which was negligible. However, this method does not lend itself to quantitative assessment of migration. To obtain a more quantitative characterization of chemotaxis, the flow-based microfluidic device described in the following section was developed. 

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