Analysis of the electrostatic field distribution in the hemispherical internal cell of radon monitors to estimate the collection efficiency of Po-218

The collection efficiency of the hemispherical internal cell of radon monitors depends on many factors, with the distribution of the electric field and the relative humidity of the air being particularly important. COMSOL is used to simulate an internal cell with a plastic upper surface. Simulation results show a relatively uniform gradient of the electric field. Assuming that the electric field felt by the positively charged Po-218 ions in the internal cell is a linear function of its radial coordinate, a mathematical model of the collection efficiency is proposed. From this model, we obtained the following: 1) under the same neutralization rate and potential, the electric field gradient has little effect on the collection efficiency; 2) under the same neutralization rate, the collection efficiency increases with the potential on the cell wall. If the neutralization rate is small, then the potential value for the maximum collection efficiency is also small. At a relative humidity of 6%–10%, the collection efficiency saturates for values of the electric potential on the cell wall larger than 5 kV; 3) under the same potential, a large neutralization rate corresponds to reduced collection efficiency. At high potential, the collection efficiency is relatively less affected by the neutralization rate. Higher collection efficiency can be achieved under high potential and low humidity conditions. This study provides a theoretical foundation to design the internal cell of radon monitor for improving the collection efficiency of Po-218.

Dynamics of neutralizing antibody responses to SARS-CoV-2 in patients with COVID-19: an observational study

Our understanding of the protective immunity, particularly the long-term dynamics of neutralizing antibody (NAbs) response to SARS-CoV-2, is currently limited. We enrolled a cohort of 545 COVID-19 patients from Hubei, China, who were followed up up to 7 months, and determined the dynamics of NAbs to SARS-CoV-2 by using a surrogate virus neutralization test (sVNT). In our validation study, sVNT IC50 titers and the neutralization rate measured at a single dilution (1:20) were well correlated with FRNT titers (r = 0.85 and 0.84, respectively). The median time to seroconversion of NAbs was 5.5 days post onset of symptoms. The rate of positive sVNT was 52% in the first week, reached 100% in the third week, and remained above 97% till 6 months post onset. Quantitatively, NAbs peaked in the fourth week and only a quarter of patients had an estimated peak titer of >1000. NAbs declined with a half-time of 61 days (95% CI: 49–80 days) within the first two months, and the decay deaccelerated to a half-time of 104 days (95% CI: 86–130 days) afterward. The peak levels of NAbs were positively associated with severity of COVID-19 and age, while negatively associated with serum albumin levels. The observation that the low-moderate peak neutralizing activity and fast decay of NAbs in most naturally infected individuals called for caution in evaluating the feasibility of antibody-based therapy and vaccine durability. NAbs response positively correlated with disease severity, warning for the possibility of repeat infection in patients with mild COVID-19.

Fast cascade neutralization of an oxidized sensitizer by an in situ-generated ionic layer of I− species on a nanocrystalline TiO2 electrode

A novel coadsorbent including three terminal double bonds reacted with I2 and generated ionic complexes on the surface of TiO2. The in situ-generated ionic layer accelerated the neutralization rate of dye+ and decreased the recombination reactions with dye+ and I3− due to coadsorbent effects, resulting in 22% higher power conversion efficiency, even at 15% low dye loading, compared to the conventional device.

On the influence of fuel sulfur induced stable negative ion formation on the total concentration of ions emitted by an aircraft gas turbine engine: comparison of model and experiment

A model which considers the formation and evolution of combustion ions in a combustor of an aircraft engine in dependence on the electron detachment efficiency from negative ions is presented. It is a further development of the model reported by (Sorokin et al., 2003). The model allows to consider the effect of the transformation of primary negative ions to more stable secondary negative ions with a much higher electron affinity and as a consequence a greater stability with respect to electron thermal detachment. The formed stable negative ions most probably are sulfur-bearing ions. This effect slows down the charged particle neutralization rate leading to an increase of the concentration of positive and negative ions at the combustor exit. The results of the simulation and their comparison with the ground-based experimental data obtained within the framework of the project PartEmis (Particle emission, measurements and predictions of emission of aerosols and gaseous precursors from gas turbine engines; coordinator: C. Wilson) at the QinetiQ test facility at Pyestock, UK (Wilson et al., 2003) support the above hypothesis, i.e. the increase of the fuel sulfur content leads to an increase of the ion concentration at the combustor exit.

Article

We have used stopped-flow kinetic studies to conduct an investigation into the acid neutralization reaction between overbased detergent additives and aqueous acid dispersed as w/o microemulsion droplets. Water-soluble pH indicators have been used to monitor the change in pH during the reaction. The acid neutralization rate was found to be dependent on the concentration of overbased additive, the temperature of the system, and the hydrocarbon chain length of the solvent. The systems are of importance in relation to the mechanism of acid neutralization by engine lubricants.Key words: overbased detergent additive, acid neutralization, pH indicator, stopped flow.