Noise spectrography

ABSTRACT The principle of electrical spectrography and its measurement system is discussed. The phenomenon of noise in electrolytes and interfaces receives attention. Noise spectrography is found to have applications in some biomolecular systems, viz., DNA helix-to-coil transition, thermal transconformation, and salt-free premelting effects. Noise conductivity emission spectra of collagen solutions gave information on permanent dipole fluctuations and hydrodynamic properties of the system. 

For KCl and NaQ (concentration < 10 mol/liter), the mean mobilities < > evaluated by noise spectrography are identical with those obtained by conventional bridge methods. 

DNA solutions in aqueous NaCl are employed as the dielectric of a cylindrical capacitor with gold electrodes the voltage fluctuations are then studied as described above by noise spectrography. We report here some original results obtained in our laboratory. 

This fact gives a possible explanation for the high value of the permittivity 6 observed in the low-frequency domain, where conventional dielectric measurement are carried on. Nevertheless, if this model introduces a possible dispersion phenomenon in the absence of an externally applied electric field E (due to the various K fluctuation modes of the counterions), this effect is too small to be observable by noise spectrography. 

Actually, by noise spectrography measurements, electrode polarization effects are considerably eliminated and there is not an induced moment due to an external applied field. 

Noise spectrography is an efficient technique allowing observation of electrical phenomena in systems which are liable to be perturbed by the application of an external electric field. As a consequence, noise measurements are convenient for the study of electrochemical or bioelec-trochemical systems such as electrolytes, biopolyelectrolytes, electrolyte-membrane interfaces, etc. 

For DNA solutions, the role of the counterionic atmosphere around the negative phosphate sites is critical. The general behavior of this ionic atmosphere may be readily studied by noise spectrography, and we have shown that... 

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