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We present a nonequilibrium reaction rate model of the ionic transition through an open ion channel, taking account of the interaction between an ion at the entrance of the channel and an ion at the binding site in a self-consistent way. The electrostatic potential is calculated by solution of the Poisson equation for a channel modeled as a cylindrical tube. The transition rate, and the binding site occupancy as a function of the left bulk concentration are compared to 1D Brownian dynamics simulations. The analysis is performed for a single binding site of high-affinity, with the exit rate influenced by barrier fluctuations at the channel exit. The results are compared with experimental data for the permeation of the Na⁺ ion through the Gramicidin A channel, with which they are shown to be in good agreement.

Nd₂CuO${}_{4\pm \delta }$ is known to possess either oxygen vacancies or interstitial oxygen defects, depending on the synthesis route, as well as may exhibit the A-site deficiency. In this work, insight into physicochemical properties of Nd₂CuO${}_{4\pm \delta }$ and Nd${}_{1.9}$CuO${}_{4\pm \delta }$ layered oxides is given, focusing on the crystal structure, electrical conductivity, and oxygen permeation, as well as on numerical density functional theory (DFT) simulations concerning ionic defects formation and their possible movement in the crystal structure. The results indicate that in oxidizing conditions at low temperatures, interstitial oxygen defects are stable, but with the increase of temperature, the release of oxygen is observed, leading to formation of the oxygen vacancies. Both materials are stable at elevated temperatures in air and Ar. Larger oxygen nonstoichiometry and improved electrical conductivity at high temperatures for Nd${}_{1.9}$CuO${}_{4\pm \delta }$ compound are accompanied by the recorded oxygen flux of ca. 0.2mLcm${}^{-2}$min${}^{-1}$ at 880^∘C for 0.8mm thick ceramic membrane.

New technologies deeply depend on the ability of chemists to synthesize new functional materials. However, this synthetic step requires great efforts. Moreover, it is very likely that the ensuing compound does not fit the expected properties. With the advent of simulation, associated with the increase in computer performance and efficiency of codes, a screening of the best potential candidates to be synthesized becomes available. Accordingly, getting a polymer with a specific permeability, and also understanding the molecular reasons underlying this process, are some of the assets of molecular simulation. Nevertheless, representation of a material from a molecular perspective is not straightforward. A specific protocol must be established. It takes into account the fact that calculations are carried out on very tiny systems. An accurate depiction and perpetual validations confronting simulated results with experimental data make the protocol relevant. The computation of the penetrants’ diffusion coefficient and solubility is then introduced, in order to reveal the simulation of the permeation of a small molecule through an amorphous polymer system. The paper concludes with the most recent studies on the subject.

Permeation is a technique for realising a primary measurement standard for gas composition. A permeation tube is suspended in a permeation chamber and emits a constant mass flow of the nominally pure substance contained in it. This flow is combined with a flow of a carrier gas to obtain a calibration gas mixture with known composition. We used an automated weighing system to monitor the mass loss of the tube, and prepared mixtures of ammonia (NH3) in nitrogen. The advantage of such dynamic gas standards is that unlike static standards they do not have stability issues and the composition of the calibration gas mixture can be chosen more rapidly than with static mixtures.

We revisited and extended existing measurement models describing the standard. We show how dependencies between the input quantities in the extended model can be taken into account. We describe the effect of temperature fluctuations on the permeation rate, temperature and pressure effects on the dispersion of the weighing data. For evaluating the linearity of the balance, a simple Bayesian model was established that takes into account the repeatability and resolution of the balance. We also show that the use of ordinary least squares regression to obtain the permeation rate is justified.

We present a nonequilibrium reaction rate model of the ionic transition through an open ion channel, taking account of the interaction between an ion at the entrance of the channel and an ion at the binding site in a self-consistent way. The electrostatic potential is calculated by solution of the Poisson equation for a channel modeled as a cylindrical tube. The transition rate, and the binding site occupancy as a function of the left bulk concentration are compared to 1D Brownian dynamics simulations. The analysis is performed for a single binding site of high-affinity, with the exit rate influenced by barrier fluctuations at the channel exit. The results are compared with experimental data for the permeation of the Na⁺ ion through the Gramicidin A channel, with which they are shown to be in good agreement.