AZO-Based ZnO Nanosheet MEMS Sensor with Different Al Concentrations for Enhanced H2S Gas Sensing

The properties of H2S gas sensing were investigated using a ZnO nanostructure prepared with AZO (zinc oxide with aluminium) and Al surfaces which were developed on a MEMS (Micro Electromechanical System) device. Hydrothermal synthesis was implemented for the deposition of the ZnO nanostructure. To find the optimal conditions for H2S gas sensing, different ZnO growth times and different temperatures were considered and tested, and the results were analysed. At 250 °C and 90 min growth time, a ZnO sensor prepared with AZO and 40 nm Al recorded an 8.5% H2S gas-sensing response at a 200 ppb gas concentration and a 14% sensing response at a gas concentration of 1000 ppb. The dominant sensing response provided the optimal conditions for the ZnO sensor, which were 250 °C temperature and 90 min growth time. Gas sensor selectivity was tested with five different gases (CO, SO2, NO2, NH3 and H2S) and the sensor showed great selectivity towards H2S gas.

Numerical Modelling of Positive Surface Discharges in C-C4F8/CF3I/N2 Gas Mixture under Non-Uniform Field

As an environmentally friendly gas with good insulation and stable chemical properties, CF3I gas mixture is considered as a potential alternative to SF6 gas to compensate for the shortcomings of SF6 gas as a greenhouse gas. This article attempts to study the CF3I ternary gas mixtures with c-C4F8 and N2 by considering the process of streamer development in surface discharge. The model of surface discharge in CF3I gas mixture under DC voltage was established by COMSOL, and the drift-diffusion equations of particles was solved to show the discharge process, and the changes of electric field and particle concentration, etc. during the development of streamer were obtained, which provides the theoretical basis for the reliable diagnosis of partial discharge. On this basis, the model is compared with models for two other different gases (SF6/N2, artificial air) in terms of particle characteristics, streamer characteristics and streamer branches characteristics. Finally, it is concluded that under this model, although the insulation characteristics in CF3I gas mixture are weaker than those in SF6, the difference is not large and both are much better than those in artificial air, so c-C4F8/CF3I can be considered as a potential substitute for SF6.

Plasma and photon technologies against bio-factors, dangerous to human being

Possible plasma and photonic methods and devices for monitoring and preventing dangerous infections and human diseases are presented. In experiments with different types of atmospheric pressure discharges in different gases, the significant bactericidal effect was found. The prototype of device based on the method of absorption spectroscopy for detecting human diseases by biomarkers in the exhaled air has been proposed and tested. The importance of the plasma technology of deposition of coatings by magnetron sputtering for the creation of anti-covid masks and high-quality optics (mirrors) for photon monitoring devices is emphasized.

Émile Zola and the Literary Language of Climate Change

On 7 February 1861, John Tyndall, professor of natural philosophy, delivered a historical lecture: he could prove that different gases absorb heat to a very different degree, which implies that the temperate conditions provided for by the Earth's atmosphere are dependent on its particular composition of gases. The theoretical foundation of climate science was laid. Ten years later, on the other side of the Channel, a young and ambitious author was working on a comprehensive literary analysis of the French era under the Second Empire. Émile Zola had probably not heard or read of Tyndall's discovery. However, the article makes the case for reading Zola's Rougon-Macquart as an extensive story of climate change. Zola's literary attempts to capture the defining characteristic of the Second Empire led him to the insight that its various milieus were all part of the same ‘climate’: that of an all-encompassing warming. Zola suggests that this climate is man-made: the economic success of the Second Empire is based on heating, in a literal and metaphorical sense, as well as on stoking the steam-engines and creating the hypertrophic atmosphere of the hothouse that enhances life and maximises turnover and profit. In contrast to Tyndall and his audience, Zola sensed the catastrophic consequences of this warming: the Second Empire was inevitably moving towards a final débâcle, i.e. it was doomed to perish in local and ‘global’ climate catastrophes. The article foregrounds the supplementary status of Tyndall's physical and Zola's literary knowledge. As Zola's striking intuition demonstrates, literature appears to have a privileged approach to the phenomenon of man-induced climate change.

Modification and optical degradation of thin multilayers under VUV/UV radiation from compressed plasma flows

Coaxial plasma accelerators are under consideration for generation of compressed plasma flows which are suitable for emitting of powerful broadband radiation (including the VUV/UV ranges). The using of different gases in a chamber allows to control the spectrum. For inert gases the upper value of energy is limited by its first ionization potential (for neon ≈ 21.55 eV). For air the maximum energy is limited by ≈ 6 eV. Such technical systems are suitable for studying of optical properties stability for thin multilayers and the other coatings. Such tests were fulfilled for bilayers based on HfO2/SiO2 pair on silica substrates which is stable for laser radiation in the visible and IR ranges. It was found that a single exposure of the radiation (for neon and air) caused a relative decline of the radiation durability in ≈ 1.03…1.14 times. Spectral measuring demonstrated that the maximum decline of transmission (up to of ≈ 3…4%) was detected for exposures in neon in the range of 320…450 nm.

Recommendation System to Predict Missing Adsorption Properties of Nanoporous Materials

Nanoporous materials (NPMs) selectively adsorb and concentrate gases into their pores, and thus could be used to store, capture, and sense many different gases. Modularly synthesized classes of NPMs, such as covalent organic frameworks (COFs), offer a large number of candidate structures for each adsorption task. A complete NPM-property table, containing measurements of the relevant adsorption properties in the candidate NPMs, would enable the matching of NPMs with adsorption tasks. However, in practice the NPM-property matrix is only partially observed (incomplete); (i) many properties of any given NPM have not been measured and (ii) any given property has not been measured for all NPMs.<br /><br />The idea in this work is to leverage the observed (NPM, property) values to impute the missing ones. Similarly, commercial recommendation systems impute missing entries in an incomplete item-customer ratings matrix to recommend items to customers. We demonstrate a COF recommendation system to match COFs with adsorption tasks by training a low rank model of an incomplete COF--adsorption-property matrix. A low rank model, trained on the observed (COF, adsorption property) values, provides (i) predictions of the missing (COF, adsorption property) values and (ii) a "map" of COFs, represented as points, wherein COFs with similar (dissimilar) adsorption properties congregate (separate). We find the performance of the COF recommendation system varies for different adsorption tasks and diminishes precipitously when the fraction of missing entries exceeds 60%. The concepts in our COF recommendation system can be applied broadly to many different materials and properties. <br />

Sensing Performance of Thermal Electronic Noses: A Comparison between ZnO and SnO2 Nanowires

In recent times, an increasing number of applications in different fields need gas sensors that are miniaturized but also capable of distinguishing different gases and volatiles. Thermal electronic noses are new devices that meet this need, but their performance is still under study. In this work, we compare the performance of two thermal electronic noses based on SnO2 and ZnO nanowires. Using five different target gases (acetone, ammonia, ethanol, hydrogen and nitrogen dioxide), we investigated the ability of the systems to distinguish individual gases and estimate their concentration. SnO2 nanowires proved to be more suitable for this purpose with a detection limit of 32 parts per billion, an always correct classification (100%) and a mean absolute error of 7 parts per million.

Estimation of the turbulent Schmidt number in a model gas turbine combustor

This article presents the estimation of turbulent Schmidt number in a model gas turbine combustor. Different gases are used as the model fuel while maintaining the mass flow rate. The simplest closure models for Reynolds stress and turbulent flux are considered. The anisotropy of turbulent viscosity is demonstrated.