Impedance variables influencing

Since hydration of the skin has been shown to be the primary variable influencing the skin s impedance [7,10,11,18], one can speculate that the time variation in the skin s impedance may be a strong function of the time variation of the skin s hydration. The reason for the skin s profound dependence on hydration results from the skin s hydroscopic nature [15] coupled with water s significant impact on the skin s dielectric constant [12]. The skin s hydroscopic characteristic is speculated to be in part due to the presence of amino acids in the skin [15]. Hydration probably influences the skin s dielectric constant because the following components are sensitive to an electric field [7] (a) The keratin protein chains contained in the stratum comeum have a dipole moment. Thus, as the stratum comeum becomes more hydrated, the keratin becomes more flexible and responsive to an applied electric field, (b) As the stratum comeum becomes more hydrated, the ions in the stratum comeum become freer to move and thus more responsive to an applied electric field. 

The ability to change and control the composition of the nutrient solution and the relatively small size of the microcosms used enables manipulation of environmental variables and time-course studies of rhizodeposition to be made relatively easily. The influence of nutrient availability, mechanical impedance, pH, water availability, temperature, anoxia, light intensity, CO2 concentration, and microorganisms have all been examined within a range of plant species (9). A few examples to illustrate the continued interest in examining the effect of such variables on rhizodeposition in nutrient culture are given in Table 1. 

Impedance spectroscopy is one of the most informative methods in electrochemistry research [1,2], The essence of the method consists in investigating the response of a target taking place in stationary conditions to weak influences of a variable voltage or to an electric current in a wide range of frequencies. It is possible... 

A working understanding of complex variables is essential for the analysis of experiments conducted in the frequency domain, such as impedance spectroscopy. The objective of this chapter is to introduce the subject of complex variables at a level sufficient to understand the development of interpretation models in the frequency domain. Complex variables represent an exciting and important field in applied mathematics, and textbooks dedicated to complex variables can extend the introduction provided here. The overview presented in this chapter is strongly influenced by the compact treatment presented by Fong et al. ... 

Remember 14.4 Transfer functions serve to isolate the influence of specific independent variables that contribute to the electrochemical impedance response of a system. 

In experiments, there may be other observable variables than the experimental factors, which have an influence on the dependent variable. This variable may be continuous, and therefore problematic to add as a factor in the design. In this case, the variable can be added as a covariate in the design. Let us use the example of measuring impedance in solutions during different chemical reactions. The temperature changes may be unknown... 

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