Experimental study and mathematical modelling of self-oscillation at the electrode-magnetic fluid interface in an electric field

The article describes a mathematical model of self-oscillation in the form of a boundary value problem for a nonlinear system of partial differential equations, with a numerical solution. The numerical results were compared to the experimental data to confirm the adequacy of the model. The model uses the classical system of differential equations of material balance, Nernst-Planck and Poisson equations without simplifications or fitting parameters. The aim of the article was to study the parameters of concentration self-oscillation in a layer of the dispersed phase particles of magnetic fluid at the interface with an electrode in an electric field. For this purpose, we developed a mathematical model, the consistency of which wasconfirmed by the corresponding physical mechanism.As a result of numerical experiments, we found the critical value of the potential jump after which self-oscillation began. We also determined the oscillation growth period and other characteristics of the process. We developed software called AutoWave01 with an intuitive user interface and advanced functionality for the study of self-oscillation in a thin layer of magnetic colloid.

Traveling-wave tubes on looping waveguides with a potential jump

Using computer simulation, a study of the effect of a potential jump on the interaction processes in O-type traveling-wave tubes has been carried out. In these devices, the interaction of the electron beam with a slowed down electromagnetic wave is carried out. To slow down the electromagnetic wave, various electrodynamics systems are used: spiral, on chains of coupled resonators, etc. In this work, we have chosen a slowing down system in the form of a chain of looping rectangular waveguides. Its advantage is that it has a wide bandwidth and each link in such a chain is coordinated with the adjacent ones. To assess the effect of a potential jump on the interaction processes in O-type traveling-wave tubes, a mathematical model has been developed, which takes into account most fully all the factors influencing the interaction processes. These include: relativistic effects during the motion and interaction of electrons, sagging of fields in the gaps of the waveguide, losses in the walls of the waveguide, taking into account the space charge fields (taking into account the periodization of the fields). Based on the developed model, a program was compiled and calculations of various variants of TWT were carried out for accelerating voltages of 20–500 kV, electron beam currents of 0.3...160 A. When performing calculations, the gap with a potential jump was located in different places of the TWT slow-wave structure and its location was chosen where the maximum effect on the electron bunching processes is manifested. As the calculations have shown, the potential jump makes it possible to increase the output power of the TWT by 15–20 %. It can be noted for comparison that the use of a potential jump in multi-cavity klystrons [1] also leads to an increase in the output power by 15-25 %. This confirms the reliability of the mathematical models used in TWT and klystrons.

Potentiometric Titration of Vanadium (V) with Iron (II) in the Presence of NTA and DTPA Using Dry-Cell Graphite Electrode

A sensitive potentiometric titration for vanadium (V) based effect of ligands such as nitrilotriacetic acid (NTA) and diethylenetriaminepenta-acetic acid (DTPA) are reviewed. The potential iron system decreased the presence of NTA and DTPA. In this case, iron (III) increased with respect to the vanadium (IV) volume. The production of iron (III)-ligand complex has increased. This result suggested that the formation of V(V)-NTA and V(V)-DTPA complexes were less favoured than that of V(IV)-NTA and V(IV)-DTPA complexes. The calculated correlation coefficients (r) conveyed the effectiveness of the graphite electrode as the indicator electrode for the potentiometric titrations. On comparing the potential jump values, the extent of potential caused by DTPA was found to be more than that of NTA. The utilization of graphite electrode has facilitated the potentiometric titration by significantly causing larger potential jump. This method was precise and accurate as no interference of foreign ions was observed. Hence, the approach could be applied to the vanadium (V) of any samples.

Reasons for the Formation and Properties of Soliton-Like Charge Waves in Membrane Systems When Using Overlimiting Current Modes

The study of ion transport in membrane systems in overlimiting current modes is an important problem of physical chemistry and has an important application value. The influence of the space charge on the transport of salt ions under overlimiting current modes was first studied in the work of Rubinstein and Shtilman and later in the works of many authors. The purpose of this research is to study, using the method of mathematical modeling, the reasons of formation and properties of the local maximum (minimum) space charge in membrane systems under overlimiting current conditions. It is shown that, in the diffusion layer of the cation-exchange membrane (CEM), the local maximum of the space charge appears due to the limited capacity (exchange capacity) of the membrane at a given potential jump, i.e., the local maximum of space charge appears due to the presence of a local minimum of space charge at the surface of the CEM. The local maximum of the space charge moves as a single soliton-like wave into the depth of the solution. Unlike real solitons, this charged wave changes its size and shape, albeit quite slowly. In the section of the desalination channel, the situation is completely different. First, the space charge of the anion-exchange membrane (AEM) has a negative value, so we should be talking about the local minimum (or the maximum of the absolute value of the charge). However, this is an insignificant clarification. Secondly, the space charge waves of different signs begin to interact, which leads to a new effect, namely the effect of the breakdown of the space charge. The dependence of the local maximum on the input parameters—the cation diffusion coefficient, the growth rate of the potential jump, and the initial and boundary concentrations—is studied.

Aromaticity Driven Electrocatalytic Water Oxidation by a Phosphorus-Nitrogen PN3-Pincer Cobalt Complex

Water oxidation is the primary step in both natural and artificial photosynthesis to convert solar energy in into chemical fuels. Herein, we report the first cobalt-based pincer catalyst for electrolytic water oxidation at neutral pH with high efficiency under electrochemical conditions. Most importantly, ligand (pseudo)aromaticity is identified to play an important role in the electrocatalysis. A significant potential jump (~300 mV) was achieved towards a lower positive value when the aromatized cobalt complex was transformed to a (pseudo)dearomatized cobalt species. This complex catalyzes the water oxidation in its high valent oxidation state at a much lower overpotential (~ 340 mV vs. NHE) based on the onset potential (0.5 mA/cm²) of catalysis at pH 10.5, outperforming all the other literature systems. These observations may provide a new strategy for the design of earth-abundant transition metal-based water oxidation catalysts.

Aromaticity Driven Electrocatalytic Water Oxidation by a Phosphorus-Nitrogen PN3-Pincer Cobalt Complex

Water oxidation is the primary step in both natural and artificial photosynthesis to convert solar energy in into chemical fuels. Herein, we report the first cobalt-based pincer catalyst for electrolytic water oxidation at neutral pH with high efficiency under electrochemical conditions. Most importantly, ligand (pseudo)aromaticity is identified to play an important role in the electrocatalysis. A significant potential jump (~300 mV) was achieved towards a lower positive value when the aromatized cobalt complex was transformed to a (pseudo)dearomatized cobalt species. This complex catalyzes the water oxidation in its high valent oxidation state at a much lower overpotential (~ 340 mV vs. NHE) based on the onset potential (0.5 mA/cm²) of catalysis at pH 10.5, outperforming all the other literature systems. These observations may provide a new strategy for the design of earth-abundant transition metal-based water oxidation catalysts.

Constant Potential, Electrochemically Active Boundary Conditions for Electrochemical Simulation

This manuscript presents a theoretical model for simulating molecular dynamics at electrode-electrolyte interfaces. The novelty of the model is that it combines a method for simulating constant potential electrodes and a method for simulating stochastic interfacial charge transfer. We combine these methods to simulate model electrochemical systems under driven conditions, where charge is flowing across the electrode-electrolyte interface. The manuscript describes the theoretical formalism and applies it to a model battery system. We highlight the ability of the model to support the formation of electrical double-layers and to provide microscopic physical insight the results of potential jump experiments.

Constant Potential, Electrochemically Active Boundary Conditions for Electrochemical Simulation

This manuscript presents a theoretical model for simulating molecular dynamics at electrode-electrolyte interfaces. The novelty of the model is that it combines a method for simulating constant potential electrodes and a method for simulating stochastic interfacial charge transfer. We combine these methods to simulate model electrochemical systems under driven conditions, where charge is flowing across the electrode-electrolyte interface. The manuscript describes the theoretical formalism and applies it to a model battery system. We highlight the ability of the model to support the formation of electrical double-layers and to provide microscopic physical insight the results of potential jump experiments.