Ruggedness coefficient

The isopiestic and manometric methods (units A2j A2.4) for determination of water activity have the limitation of being dependent on fixed laboratory equipment. The electronic-type sensors have advantages of portability, speed, and simplicity of measurement. The characteristics of a sensor depend upon the manufacturer and each instrument must be calibrated separately. The anodized sensors have advantages of ruggedness, small dimensions, and fast response, as well as freedom from large temperature coefficients and less susceptibility to contamination of the lithium chloride conductivity sensors (Smith, 1971). 

To demonstrate the accuracy, two dust and two soil reference materials were analyzed with the described method. The mean value of the correlation coefficients between the certified and the analyzed amounts of the 16 elements in the samples is r = 0.94. By application of factor analysis (see Section 5.4) the square root of the mean value of the communahties of these elements was computed to be approximately 0.84. As frequently happens in the analytical chemistry of dusts several types of distribution occur [KOM-MISSION FUR UMWELTSCHUTZ, 1985] these can change considerably in proportion to the observed sample size. In the example described the major components are distributed normally and most of the trace components are distributed log-normally. The relative ruggedness of multivariate statistical methods against deviations from the normal distribution is known [WEBER, 1986 AHRENS and LAUTER, 1981] and will be tested using this example by application of factor analysis. 

As above represented it is necessary to test the ruggedness of FA against deviations from the normal distribution FA was, therefore, conducted on the basis of the SPEARMAN rank correlation coefficient [WEBER, 1986]. The obtained factor loading matrix... 

From the point of view of lifetime, mechanical ruggedness, and, possibly, ease of manufacture, solid electrolyte systems are very attractive. Two main difficulties are, however, apparent. The first of these is the difficulty in making an intimate high-surface-area soiid-solid interface and maintaining it over a wide temperature range. Even if the electroiyte can be introduced into the pores as a liquid, it may prove difficult to maintain contact on solidification by cooiing or soivent evaporation. The second problem Is that most solid electrolytes are distinctly inferior to liquid electrolytes In terms of their resistivity and the temperature coefficient of that resistivity. 

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