Sources of variation

Chemical Reaction Measurements. Experimental studies of incineration kinetics have been described (37—39), where the waste species is generally introduced as a gas in a large excess of oxidant so that the oxidant concentration is constant, and the heat of reaction is negligible compared to the heat flux required to maintain the reacting mixture at temperature. The reaction is conducted in an externally heated reactor so that the temperature can be controlled to a known value and both oxidant concentration and temperature can be easily varied. The experimental reactor is generally a long tube of small diameter so that the residence time is well defined and axial dispersion may be neglected as a source of variation. Off-gas analysis is used to track both the disappearance of the feed material and the appearance and disappearance of any products of incomplete combustion. 

The average value of the rephcates is reported along with the standard deviation, which reflects the variabihty in the measurement. Large standard deviations relative to the average measurement indicate the need for an action plan to improve measurement precision. This can be accomphshed through more rephcate measurements or the elimination of the source of variation, such as the imprecision of an instmment or poor temperature control during the measurement. 

Mean bed particle size (thus, the in-bed heat-transfer coefficient) may vary for external reasons such as a change of feedstock supply or a deterioration in crusher performance. This potential source of variation should be considered before any decision to resurface is made. 

The purpose of the control plan is to ensure that all process outputs will be in a state of control by providing process monitoring and control methods to control product and process characteristics. The control plan is covered in section 6 of the APQP manual. It consists of forms containing data for identifying process characteristics and helps to identify sources of variation in the inputs that cause product characteristics to vary. The APQP manual provides excellent guidance on the compilation and use of the control plan so no further guidance is given here. 

A technique for improving the quality of both processes and products by effectively investigating several sources of variation at the same time using statistically planned experiments. 

There are conflicting generalizations in the heterocyclic literature as to the relative reactivity of a- and y-positions in azines toward nucleophiles. Variations in the relative reactivity are attributed in this and subsequent sections to specific factors operating in addition to activation by azine-nitrogen. Another possible source of variation may be a decrease in selectivity with increasing reactivity of one or both reagents, an effect established in electrophilic aromatic... 

The source of variation occurring in the product may be difficult to locate. 

As Equations 10-1 and 10-2 show, the variance (s2) can lay claim to being a more fundamental variable than the standard deviation. In any event, when s2 significantly exceeds sc2, there may be several important sources of variation. It is then advisable to discover what these sources are. Because analysis of variance is a systematic procedure for making this discovery, it is expedient to use it, and to stop thinking exclusively in terms of the standard deviation. 

In analysis of variance, the variance due to each source of variation is systematically isolated. A test of significance, the E-test, is then applied to establish roughly how seriously one must regard each source of variation. The interested reader is urged to consult books on statistics14 for discussions of this valuable statistical method. 

The last column of Table 10-5 shows (1) that the long-term source of variation clearly overshadows the short-term, the ratio of variances exceeding 70 and (2) that the short-term variance is comparable with Arx, which is, of course, the standard counting error squared (Equation 10-8). 

Polymer stereochemistry, sometimes referred to as tacticity, is not the only source of variation in polymer configuration. For the monosubstituted butadiene isoprene, the structures shown in Figure 3.2 are possible. 

The major sources of variation in 8 C are the two C4 plants, maize and sugar cane. Most other foods are C3 and animals used for food were mainly feeding on C3 plants. Maize and sugar cane (in the form of molasses) are found... 

Capreolus capreolus dwelling in a forest 35 km south-west of Paris have negative 6 N values, ranging from -2.8 to -0.4%o, probably because of local acidic soil conditions and the very territorial habits of this deer species (Rodiere et al. 1996). Such differences between habitats should be confirmed by further studies in modem imdisturbed ecosystems. This would provide a very useful framework for understanding sources of variation in Pleistocene species. 

G.D. Farquhar, unpublished), tomato (Martin Thorstenson, 1988) and cotton (Hubick Farquhar, 1987). The sources of variations in A (and W) were both environmental and genetic in these experiments. An example is given in Fig. 5. 

In the described MC simulation, the action of several simultaneous sources of variation is considered. The explanation of the different time courses of parameter influence on volume size between sensitivity and MCCC analyses lies in the fact that classic sensitivity analysis considers variations in model output due exclusively to the variation of one parameter component at a time, all else being equal. In these conditions, the regression coefficient between model output and parameter component value, in a small interval around the considered parameter, is approximately equal to the partial derivative of the model output with respect to the parameter component. 

Schneider, A. J. Willis, H. J. Sources of variation in a standardized and semi-micro procedure for serum glutamic oxalacetic transaminase. Clin. Chem. (1958), 4, 392-408. Atwood, J. G. DiCesare, J. L. Making enzymatic methods optimum for measuring compounds with a kinetic analyzer. Clin. Chem. (1975), n, 1263-1269. 

Albert-Gonzalez, R, Identification of sources of variation affecting food behaviour pilot study assessing variations in lycopene content during tomato ketchup production, MSc thesis, Wageningen University, Wageningen, 2004. 

The attempt to classify biological activities upon the basis of their velocities as affected by temperature involves for a number of cases the adjustment of curves to data inevitably subject to several sources of variation. One of these arises from the fact that the measurements may be secured with different individuals at each of several temperatures. The latitude of variation in series of data obtained in this way may be large, and unless great numbers of observations are available interpretation may be difficult. Indication already obtained as to the theoretical significance of the exact quantitative relationship between velocity of a vital process and temperatme make it desirable to demonstrate the limits of variation in material which is as nearly as possible biologically homogeneous. 

Even If the cost of estimation error cannot be quantified as this model requires, effective allocation of resources may be possible when detailed knowledge of sources of variation Is available. In this case, a replication strategy can be based on variance component and cost Information. For example, consider the problem of deciding how many samples to collect and how many analyses to perform on each sample Let... 

A slight modification of the pilot study is a double-sampling plan for estimation (9,10). Double-sampling plans were developed to provide estimates with a fixed precision using as few observations as possible. If the sources of variation and variance components are known prior to the study, then a fixed sample size plan is the best... 

Determine the components of variance that should be built Into the statistical design Proper stratification of the study area will allow Identification and quantification of several sources of variation. The sources of variation that can be controlled by the sampling are determined by the particular sampling design and by the pattern of sample collection superimposed over the area. An analysis of variance of the data provides estimates of the components of variance ... 

The modem HPLC system is a very powerful analytical tool that can provide very accurate and precise analytical results. The sample injection volume tends to be a minor source of variation, although fixed-loop detectors must be flushed with many times their volume in sample to attain high precision. Assuming adequate peak resolution, fluorimetric, electrochemical, and UV detectors make it possible to detect impurities to parts per billion and to quantitate impurities to parts per thousand or, in favorable cases, to parts per million. The major sources of error in quantitation are sample collection and preparation. Detector response and details of the choice of chromatographic method may also be sources of error. 

Another important advance has been the application of PyMS with ANNs to discriminate between methicillin-resistant and methicillin-sensitive Staphylococcus aureusIn this study DFA and HCA showed that the major source of variation between the pyrolysis mass spectra of 15 methicillin-resistant (MRSA) and 22 methicillin-sensitive Staphylococcus aureus (MSSA) strains resulted from the phage group of the bacteria, rather than from their resistance or sensitivity to methicillin. By contrast, ANNs could recognize those aspects of the pyrolysis mass spectra that differentiated MRSA and MSSA strains. These results gave the first demonstration that the combination of PyMS with ANNs could provide a rapid and accurate antibiotic-susceptibility testing technique. 

Source of variation Sum of squares Degrees of freedom Variance F-test... 

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