Testing the Significance of Influencing Factors

In analytical chemistry, the optimality criterion is frequently the relative increase of that share of the analytical gross signal that is caused by the analyte itself, namely Saa a/Ja- According to Eq. (3.16a)  

On the other hand, Eqs. (3.16a) and (5.1), respectively, can also be interpreted as being composed of the analyte signal and diverse (more or less) anonymous deviations enej or eAij, respectively, see Eq. (3.16b,c)  

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Physical factors can play a major role in service, and each investigator should be alert to the significance of these factors. Included here are such factors as the volume of scale to the volume of substrate from which it is produced, the so-called Pilling-Bedworth ratio [72], the coefficient of expansion differences between the scale and substrate, the effect of the relative scale thicknesses, scale transformation stresses, thermal stresses, imposed stresses, plasticity of the scale, and the physical condition of the scale (porosity, presence md nature of any cracking, decohesion, and number of layers). Specimen size and shape can influence test results. Edges md comers behave differently than planar smfaces. 

Potential factors that affect a given objective function are best selected by the domain expert in a particular analytical field. The test for significance of the factors influence should be performed on the basis of a simple experimental design, a screening design, by means of statistical tests. Factors should not be kept or eliminated solely for subjective reasons. 

The F-test indicated that, at a significance level of p=0.05, the critical factors for As(III) determination were the deposition time, the length of the reactor R2 and the binary interactions flow rate-deposition time and flow rate-reaction coil length. The significance of the binary interactions is a consequence of the influence of both factors in the correct mixture of the sample solution and the electrolyte support solution. On the other hand, for total As determination, the variable with major contribution was the flow rate. 

The biodegradation of surfactants is studied by means of many different tests and sometimes under different conditions. Some factors with significant influence on the results are uncontrollable factors and in other cases are not controllable. This causes a dispersion in biodegradability data that makes comparisons difficult. For this reason only general conclusions can be obtained from the data available. Swisher carried out an exhaustive collection of available data in his complete study on surfactant biodegradation [385]. Some basic and significant features of biodegradation of alcohol and alcohol ether sulfates are discussed below. 

The influence of compressibility was assessed by varying the Mach number in the range 0 < Ma < 0.38, while Kn and ks/H were kept low. Friction factor data were reported only with Ma < 1 at the exit, to ensure the flow rate was controlled by viscous forces alone. A mild increase in the friction factor (8%) was observed as Ma approached 0.38. This effect was verified independently by numerical analysis for the same conditions as in the experiment. The range of relative surface roughness tested was 0.001 < ka/H < 0.06, yet there was no significant influence on the friction factor for laminar gas flow. 

Once the model was complete, it was adjusted to a steady state condition and tested using historic carbon isotope data from the atmosphere, oceans and polar ice. Several important parameters were calculated and chosen at this stage. Sensitivity analysis indicated that results dispersal of the missing carbon - were significantly influenced by the size of the vegetation carbon pool, its assimilation rate, the concentration of preindustrial atmospheric carbon used, and the CO2 fertilization factor. The model was also sensitive to several factors related to fluxes between ocean reservoirs. 

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