N95 respirators comprise a critical part of the personal protective equipment used by frontline health-care workers and are typically meant for one-time usage. However, the recent COVID-19 pandemic has resulted in a serious shortage of these masks leading to a worldwide effort to develop decontamination and re-use procedures. A major factor contributing to the filtration efficiency of N95 masks is the presence of an intermediate layer of charged polypropylene electret fibers that trap particles through electrostatic or electrophoretic effects. This charge can degrade when the mask is used. Moreover, simple decontamination procedures (e.g., use of alcohol) can degrade any remaining charge from the polypropylene, thus severely impacting the filtration efficiency post-decontamination. In this report, we summarize our results on the development of a simple laboratory setup allowing measurement of charge and filtration efficiency in N95 masks. In particular, we propose and show that it is possible to recharge the masks post-decontamination and recover filtration efficiency.
Batchwise heterogeneous photocatalytic oxidation of model wastewater (solutions of the azo dye "Acid Orange 7" in tap water) has been performed in a laboratory-scale stirred vessel reactor with non-submerged UV-A lamps using titanium dioxide "P25" as photocatalyst. Comparison to results of solar pilot-scale Plexiglass double-skin sheet reactor (DSSR) experiments indicates that the lab-scale method may predict area demand for technical-scale DSSR design. Characteristic UV-A fluences leading to TOC or COD reduction to e(-1) of the initial concentrations were determined in lab-scale stirred vessel experiments for treated effluents of seven different industrial branches, secondary municipal effluent and biologically treated greywater. Predicted areas for solar photocatalytic oxidation of these effluents in DSSRs yielding mineralization of 95% of organics in 100 m3 of the respective effluents for a TiO2 concentration of 2 g l(-1) and a sky and solar radiation of 3.9kWh m(-2) d(-1) within one day greatly varied from below 6,000 m2 (biologically treated lubricating oil refinery effluent) to more than 100,000 m2 (highly saline biologically treated effluent of chemical industry). Especially municipal and refinery effluents (except oil reclaiming) have been identified as promising candidates for reuse after solar photocatalytic oxidation. Mineralization efficiency was decreasing with increasing alkalinity of effluents. This was interpreted by competition of hydrogen carbonate anions with organics for binding sites on photocatalyst surface and by OH radical scavenging by hydrogen carbonate. Dependence on alkalinity was superimposed by salinity influence as some effluents with high alkalinity also exhibited high salt concentrations (especially chloride).
It is of interest to fabricate curved surfaces in three dimensions from easily available homogeneous material in the form of flat sheets. The aim is not just to obtain a surface M in R 3 which has a desired intrinsic Riemannian metric, but to get the desired embedding M ⊂ R 3 up to translations and rotations (the Riemannian metric alone need not uniquely determine this). In this paper we demonstrate three generic methods of molding a flat sheet of thermo-responsive plastic by selective contraction induced by targeted heating. These methods do not involve any cutting and gluing, which is a property they share with origami. The first method is inspired by tailoring, which is the usual method for making garments out of plain pieces of cloth. Unlike usual tailoring, this method produces the desired embedding in R 3 , and in particular, we get the desired intrinsic Riemannian metric. The second method just aims to bring about the desired new Riemannian metric via an appropriate pattern of local contractions, without directly controlling the embedding. The third method is based on triangulation, and seeks to induce the desired local distances. This results in getting the desired embedding in R 3 , in particular, it also gives us the target Riemannian metric. The second and the third methods, and also the first method for the special case of surfaces of revolution, are algorithmic in nature. We give a theoretical account of these methods, followed by illustrated examples of different shapes that were physically molded by these methods.arXiv:1809.05659v3 [cond-mat.soft]
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