The effect of partial charge transfer on the electrochemical turbulent noise

Theoretical analysis of the effect of electrode potential on the spectral density of random alternating current emerged in electrochemical cell under the action of turbulent pulsations of the electrolyte solution velocity is carried out. An impedance model of metal electrode dissolution reaction, including two adsorption stages, is suggested, with allowance for the oxidized ion diffusion in electrolyte solution. It is known that in terms of the Ershler-Randles model, at low frequencies the experimentally measured slope of bilogarithmic frequency dependence of spectral density equals 3, which is characteristic of the diffusion control; at high frequencies the slope equals 4, which is characteristic of the kinetic control. It is shown that for the model of impedance of the two-stage adsorption oxidation process, in the middle segment of the spectrum the local slope must decrease down to 2, provided the first oxidation stage, which proceeds within the inner electrical double layer, is slow; the local slope must increase up to 6 (or 5, for diffusion control), provided the second oxidation stage (the partially oxidized ion desorption to solution) is slow. The “height” and “width” of the slope local changes appeared explicitly depending on the parameters of the partial charge transfer. This makes the turbulent noise method somewhat superior to the impedance method in the studying of the above-specified reaction type.     

Interpretation of the impedance comprising negative capacitance and constant phase elements on iron electrode in weakly acidic media

The negative low-frequency capacitance that appears in interpretations of impedance of the iron electrode in weakly acidic solutions is shown to arise in the case of interaction of two consecutive nonequilibrium flows that constitute a two-stage anodic faradaic process of intermediate adsorption in the prepassivation potential range. The low-frequency capacitance is negative throughout a potential range where the logarithm of rate constant vs. potential (logk vs. E) dependence has the higher slope for the limiting stage. The low-frequency capacitance becomes positive at higher anodic potentials and for the other limiting stage.     

Poincaré-Chetaev bifurcation diagrams in the problem of motion of an inhomogeneous dynamically and geometrically symmetric ellipsoid on a smooth plane

The existence, stability, and bifurcation of steady motions of an inhomogeneous dynamically and geometrically symmetric ellipsoid is considered. The mass center of the ellipsoid is shifted and located on its symmetry axis. The ellipsoid moves on a perfectly smooth horizontal plane.     

Total reflection X-ray fluorescence and archaeometry: Application in the Argentinean cultural heritage

Archaeometry is an interdisciplinary research area involved in the development and use of scientific methods in order to answer questions concerned with the human history. In this way the knowledge of archaeological objects through advanced chemical and physical analyses permits a better preservation and conservation of the cultural heritage and also reveals materials and technologies used in the past. In this sense, analytical techniques play an important role in order to provide chemical information about cultural objects. Considering the non destructive characteristic of this study, analytical techniques must be adequate in order to prevent any alteration or damage and in addition to allow the conservation of their integrity. Taking into account the irreplaceable character of the archaeological and artistic materials considered in this study, analytical techniques must be adequate in order to prevent any alteration or damage and in addition to allow the conservation of their integrity.     

On the Circumference of 2-Connected $$\mathcal{P}_{3}$$-Dominated Graphs

Let G be a connected graph. For at distance 2, we define , and , if then . G is quasi-claw-free if it satisfies , and G is P ₃-dominated() if it satisfies , for every pair (x, y) of vertices at distance 2. Certainly contains as a subclass. In this paper, we prove that the circumference of a 2-connected P ₃-dominated graph G on n vertices is at least min or , moreover if then G is hamiltonian or , where is a class of 2-connected nonhamiltonian graphs.     

Kinetics of isotope exchange of dioxygen with a powdered high-temperature superconducting material Ba2YCu3O7?x

It has been found that the rate of isotope exchange in Ba₂YCu₃O_7–x–O₂ system is high. Its kinetics is exponential, first order with respect to dioxygen and the exchange is of the mixed first/third type.

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Ba₂YCu₃O_7–x–O₂ . -, -, - .

     

Analysis of Turbulent Noise Spectra of Electrochemical Reactions in Different Experimental Conditions

The Ershler–Randles impedance model is used to analyze the physical foundations of potentiostatic and galvanostatic spectra of turbulent noise of electrochemical redox reactions as a function of the frequency range of measurements and the electrode potential. On the whole, the theoretically calculated and experimentally measured spectra are in satisfactory agreement. A computer simulation of the dependence of characteristic frequencies on the electrode potential, reaction parameters, and experimental conditions is realized. The approach allows one to tentatively estimate the in-principle possibility of experimental realization of spectrum sections, which are located in different frequency ranges and contain information on the characteristic frequencies and kinetic parameters of the reaction under study, and to formulate conditions required for performing an experiment and extracting data on the process kinetics.     

DFT Calculation of the Structure of the Coordination Unit of Chlrophyll-Containing Proteins

In a DFT/B3LYP study (6-31G(d) basis set), the structure, IR spectra, and thermodynamic parameters of Mg-porphin-imidazole and Mg-khlorin-imidazole complexes, serving as models of the coordination unit of chlorophyll in proteins, have been calculated. When an axial ligand is added, the Mg atom goes out of the plane of the tetrapyrrole macrocycle, the deviation being 0.34 Å. The frequency of the out-of-plane vibrations of Mg in the complexes increased by 50 cm⁻¹, and the frequencies of the two in-plane vibrations decreased by 25 cm^{− 1}–30 cm⁻¹. IR vibrational spectra have been simulated.Original Russian Text Copyright © 2004 by M. D. Elkin, O. D. Ziganshina, K. V. Berezin, and V. V. Nechaev__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 1132–1135, November–December, 2004.