Estimation of probe measurements reliability in a supersonic flow of a four-component collisionless plasma

The aim of this work is to estimate the reliability of extracting the plasma electron density and temperature and ionic composition from the current-voltage (I-V) characteristic of an isolated probe system with cylindrical electrodes. An earlier proposed mathematical model of current collection by the probe system at positive bias potentials and an arbitrary ratio of the electrode areas is analyzed. The model is supplemented with a formula that determines, with an accuracy of several percent, the value of the bias potential at which the probe is under the plasma potential and the I-V characteristic splits into a transition and an electronic region. The analytical dependence of the bias potential on the plasma parameters and the ratio of the electrode areas made it possible to formalize the procedures for determining and assessing the reliability of the extracted plasma parameters using the regions of their strongest effect on the collected probe current. Parametric studies of the effect of the plasma parameters on the probe current were carried out for conditions close to measurements in the ionosphere. The paper demonstrates the feasibility of partitioning the sought-for plasma parameters into the regions of their strongest and weakest effect on the probe current in the range of the bias potentials considered. The problem of plasma parameter identification is formulated on the basis of a comparison of the probe current and the measured I-V characteristic in the L2 theoretical approximation. To each parameter there corresponds an objective function of its own, which differs in the domain of definition and the ratio of the electrode areas used in I-V characteristic measurements. Based on this formulation of the inverse problem in L2, estimates of the reliability of identification of the parameters of a plasma with two ion species are obtained depending on the errors of the model and probe measurements. The results obtained may be used in ionospheric plasma diagnostics.

Photoelectrochemical Degradation of Organic Pollutants on a La3+ Doped BiFeO3 Perovskite

Towards nonconventional wastewater treatment methods for the degradation of organic pollutants in wastewater, a perovskite-based photoelectrochemical system was developed. Bismuth ferrite doped with lanthanum (La-BiFeO3, La-BFO) perovskite was synthesised through a hydrothermal method with low calcination temperature for the photoelectrochemical degradation of orange II dye and other cocktails of dyes. Photoanodes were prepared by the deposition of the perovskites on a fluorine-doped tin oxide (FTO) substrate. The photoanodes were characterised using XRD, FESEM, FTIR and UV-vis diffuse reflectance. The photoelectrochemical properties of the synthesised photoanodes were investigated with chronoamperometry and electrochemical impedance spectroscopy (including Mott–Schottky analysis). The results show that all La3+-doped BFO photoanodes exhibited a higher absorption edge in the visible light region than the undoped BFO. The photocurrent response of 10% La-BFO (the best performing electrode) exhibited a three times higher current response than the pure BFO. In addition, the electrode exhibited a good degradation efficiency of 84.2% within 120 min with applied bias potential of 2 V at a pH of 7. EIS studies showed a significant enhancement of the interfacial electron transfer of the charge carriers. The enhancements in electrode performances were attributed to the synergistic effect of the applied bias potential and the introduction of La3+ into the BFO matrix. This study therefore shows that the photoelectrocatalytic performance of BFO for water treatment can be improved by the introduction of perovskites-doping ions such as La3+.

A Model for Bias Potential Effects on the Effective Langmuir Adsorption–Desorption Processes

We discuss the foundations of a model based on an extension of the Langmuir approximation for the adsorption–desorption phenomena, in which the phenomenological coefficients depend on the bias potential, in addition to their dependence on the adsorption energy. The theoretical analysis focuses on the effect of these effective coefficients on the electrical response of an electrolytic cell to an external electric field, as predicted by the Poisson–Nernst–Planck model. Kinetic balance equations govern the current densities on the electrodes when the adsorption phenomenon occurs in the presence of an electric bias. The influence of the phenomenological parameters entering the model, as well as of the symmetry of the cell on the cyclic voltammetry, is investigated.

Influence of Bias Potential Magnitude on Structural Engineering of ZrN-Based Vacuum-Arc Coatings

The creation of the scientific foundations for the structural engineering of ultrathin nanolayers in multilayer nanocomposites is the basis of modern technologies for the formation of materials with unique functional properties. It is shown that an increase in the negative bias potential (from -70 to -220 V) during the formation of vacuum-arc nanocomposites based on ZrN makes it possible not only to control the preferred orientation of crystallites and substructural characteristics but also changes the conditions for conjugation of crystal lattices in ultrafine (about 8 nm) nanolayers.

An angular motion of a conserved four-helix bundle facilitates alternating access transport in the TtNapA and EcNhaA transporters

There is ongoing debate regarding the mechanism through which cation/proton antiporters (CPAs), like Thermus thermophilus NapA (TtNapA) and Escherichia coli NapA (EcNhaA), alternate between their outward- and inward-facing conformations in the membrane. CPAs comprise two domains, and it is unclear whether the transition is driven by their rocking-bundle or elevator motion with respect to each other. Here we address this question using metadynamics simulations of TtNapA, where we bias conformational sampling along two axes characterizing the two proposed mechanisms: angular and translational motions, respectively. By applying the bias potential for the two axes simultaneously, as well as to the angular, but not the translational, axis alone, we manage to reproduce each of the two known states of TtNapA when starting from the opposite state, in support of the rocking-bundle mechanism as the driver of conformational change. Next, starting from the inward-facing conformation of EcNhaA, we sample what could be its long-sought-after outward-facing conformation and verify it using cross-linking experiments.