Nyquist sequences

The Nyquist frequency is the maximum frequency that can be present in the continuous sequence h(t), if h(t) is to be perfectly represented by the sampled... 

Figure 3.5. Overall impedance response of a proton exchange membrane (PEM) fuel cell for different cell temperatures, depicted as corresponding values of the real and imaginary parts of the complex impedance (sometimes denoted a Nyquist plot). Each sequence of points represents frequencies ranging from 10 to 10 Hz, with the highest values corresponding to the leftmost points. From M. Ciureanu, S. Mik-hailenko, S. Kaliaguine (2003). PEM fuel cells as membrane reactors kinetic cinalysis by impedance spectroscopy. Catalysis Today 82, 195-206. Used with permission from Elsevier).

Very recently Chen and coworkers [56] demonstrated the use of ElS for label-free electrochemical detection of DNA sequences relevant to anthrax lethal factor on gallium nitride (GaN) nanowires. The GaN nanowires were grown on a silicon substrate coated with Au catalyst using Ga as the source material and NH3 as the reactant gas in a tubular furnace via air pressure chemical vapor deposition. ElS measurements of the "as grown" GaN nanowires, observed in the Nyquist plot in Fig. 14.12A, exhibited a semicircle and a straight vertical line, indicative of finite impedance at the GaN/electrol3Ae... 

Halides exert an essential influence on the adsorption of polyethers. It is particularly remarkable that this effect is quite different for copper and tin electrodes. Significant enhancement of adsorption resulting in the inhibition of Cu(II) reduction is observed in the Cu Cu(II) system, whereas diminished polymer adsorption was found to occur in the case of tin electrode. This can be seen from the example shown in Figure 9.29. In the case of copper system, Nyquist plots take the shape of arcs centered below the abscissa axis. An addition of Cl ions gives rise to a decrease in impedance as compared to that obtained for halide-free solution (dashed lines in Figure 9.29). This result is in accordance with voltammetric data [75] chloride diminishes the polarization of Cu(II) reduction. However, the rest halides (Br and I ) increase the impedance over an entire range of the frequencies applied. An opposite effect can be seen in the case of tin system (lower part of Figure 9.29). Both enhancement and suppression effects intensify in the sequence Cl < Br" < I . 

The make-chord program has two new pieces of information in it scale and sim. The former is used to scale down the amplitudes of each note by 70 per cent and sim is a construct that tells Nyquist to produce the three events simultaneously. In a similar way to sim, Nyquist provides another important construct called secj, which tells Nyquist to play events in sequence ... 

We are now in a position to illustrate one of the most powerful features of Nyquist the ability to apply transformations to functions as if these transformations were additional parameters. There are a number transformations available in Nyquist and they are intelligent in the sense that they were programmed with default values that often perform their tasks without the need for major adjustments. As an example of this, suppose we wish to transpose the chord sequence produced by make-sequence five semitones higher. In order to do this we can simply apply the transformation transpose to the make-sequence function as follows (the parameter 5 after transpose indicates the number of semitones for the transposition) ... 

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