Thermal fluctuations of total and free electrode charges

Using the Nyquist fluctuation-dissipation theorem, the analysis of thermal fluctuations in a complex electrochemical system is carried out for the case of slow discharge accompanied by surfactant adsorption. It is shown that the dispersion of thermal fluctuations of the total and free charges of a reversible electrode obey an equation general for both Gibbs and Einstein-Landau approaches to the theory of thermal fluctuations of extensive values and also the noise approach based on the Nyquist fluctuation-dissipation theorem. Thus, in contrast to the higher correlations of the fluctuating electrode charge, the Gibbs theory of squared correlations is in complete agreement with the Nyquist fluctuation-dissipation theorem.     

Electrochemical symmetric stochastic diffusion

Symmetric stochastic diffusion in an equilibrium electrochemical ac circuit is studied theoretically. The electrochemical circuit included double layer capacitance and slow discharge resistance. Electrochemical analog of the stochastic Einstein formula is found. An equation is obtained for the excess of electrochemical stochastic diffusion. It is shown that an excess of electrochemical stochastic diffusion increases at high relaxation times in proportion to the observation time. It is found that excess is related to correlation between the phenomenon of electrochemical stochastic diffusion and the central limiting theorem.     

Chemical Composition and Anti-Urolithiatic Activity of Extracts from Argania spinosa (L.) Skeels Press-Cake and Acacia senegal (L.) Willd

Ethnobotanical studies have reported the traditional medicinal uses of Acacia senegal (L.) Willd. and Argania spinosa (L.) Skeels against kidney stone formation and other chronic kidney diseases. The present work is undertaken to study the litholytic activity and the inhibiting activity of calcium oxalate crystallization by bioactive compounds identified in Argania spinosa (L.) Skeels press-cake (residue of Argan oil) and in Acacia senegal (L.) Willd. The litholytic activity was studied in vitro on cystine and uric acid stones using a porous bag and an Erlenmeyer glass. The study of the inhibiting activity of calcium oxalate crystallization, was based on temporal measurements of the optical density, registered at a 620 nm wavelength for 30 min using an ultraviolet–visible spectrophotometer. The silylation method was performed to identify phytochemicals, followed by gas chromatography coupled with mass spectrophotometry (GC/MS) analysis. The results show significant litholytic activity of Argania Spinosa press-cake hydro-ethanolic extract on uric acid and cystine stones, respectively, with dissolution rates (DR) of 86.38% and 60.42% versus 3.23% and 9.48% for the hydro-ethanolic extract of Acacia senegal exudate. Furthermore, the percentages of nucleation inhibition are 83.78% and 43.77% (p ˂ 0.05) for Argania spinosa and Acacia senegal, respectively. The results point to the detection of 17 phytochemicals in Argania spinosa press-cake extract, the majority of which are phenolic acids and have potent anti-urolithiatic action.     

Revaz Romanovich Dogonadze

Russian Journal of Electrochemistry -     

Langevin's Linear Equations for Non-Gaussian Equilibrium Noise

The existence of Langevin's universal linear equations interrelating non-Gaussian fluctuations of current and emf in nonlinear equilibrium systems with distributed parameters is proved.     

Alexander Georgievich Pshenichnikov

Russian Journal of Electrochemistry -     

The fractal theory of electrochemical diffusion noise: Correlations of the third and fourth order

Based on the Langevin linear stochastic equation, the correlations of the 3rd and 4th order for thermal fluctuations of the electrode potential are studied in an electrochemical ac circuit involving an electric double layer capacitance, a resistance of steady-state diffusion, and a Warburg impedance. The presence of the noisy Warburg impedance in the ac circuit makes the Langevin linear stochastic equation fractal. The analogy with the steady-state diffusion noise and with the noise of the barrierless-activationless slow discharge is used. Equations for bispectrum and trispectrum of electrode-potential activation are shown. It is demonstrated that the intensity of bispectrum and trispectrum is determined exclusively by the noise of the steady-state diffusion resistance if one of frequency arguments in the polyspectrum is zero. It is found that in an electrochemical ac circuit containing the noisy Warburg impedance, the asymptotics of establishment of equilibrium values of asymmetry and excess of electrode-potential fluctuations (thermalization) obeys the power law rather than the exponential law. Furthermore, the excess thermalization proceeds faster as compared with asymmetry thermalization. The performed theoretical analysis of correlations of the 3rd and 4th order of the fractal noise of electrochemical diffusion is of practical interest. For instance, the concepts of the fractal electrochemical noise can be used in the noise diagnostics of devices of electrochemical power engineering and in the noise methods for studying corrosion systems.