Session VM09: Mini-Conference on Plasma Applications to Ameliorate Covid-19 II

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Droplet generation and transport during coughing and sneezing has been studied for decades to characterize disease transmission by symptomatic individuals. Nevertheless, reports document that asymptomatic and presymptomatic individuals contribute to the spread of COVID-19, e.g. during social interactions. Droplet emission occurs during speech, yet there are few quantitative studies of the flows that provide the transport mechanism. We analyze flows during breathing and speaking, including linguistic features, using order-of-magnitudes estimates, numerical simulations, and laboratory experiments. We show how plosive sounds like `P' are associated with vortical structures, producing transport over half a meter in a split second. When produced individually, puffs decay over a meter, traveling in time $t$ a distance $L\sim t^{1/4}$, and mix with the slower environmental circulation. In contrast, material exhaled over time scales longer than a few seconds, characteristic of speech, which is effectively a train of puffs, forms a conical turbulent jet with a scaling law $L\sim t^{1/2}$. This work will inform thinking about aerosol transport in disease transmission for humans and animals, and offer understanding of linguistic aerodynamics.   

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The history of research on the virus spread by sneezing started in the middle of last century. A lot of experimental and theoretical studies determined the spread of droplets using assumptions standard for the description of the turbulent submerged jet. In these studies, it was shown that the effects of the environment (either indoors or outdoors, humidity, etc.) need to be taken into account. These studies provide grounds for recommendations for the safe distance. Penetrations of droplets through the masks will be also reviewed. Poor ventilation systems can significantly contribute to infection spread. Closed HVAC (Heating Ventilation and Air Conditioning) systems can conserve contamination inside the buildings and multiply it over time. Models of contamination spread in the building with force air HVAC systems were created for various purposes and provide guidance for establishing healthier indoor environments. A retrofit air-exchange system can be added to supply fresh air inside the building, while maintaining the system efficiency through heat exchange between incoming from outside and outgoing inside air. These systems were introduced several decades ago and are now mandated by the code in the new buildings in many states. Retrofit UV lamps installed inside the ventilation system can be much less expensive to manufacture and install than the air-exchange units, because they would not have any moving parts and would not require additional ductwork.   

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The widespread use of UV disinfection technology for air and water is currently based on a drastic increase in the power and lifetime of UV lamps with electric discharge in mixtures of argon-neon and mercury vapor at low pressure. The improvement of lamps occurred after studies of in electric discharge effect on the electrodes and quartz walls. Increasing the power of UV lamps to 300-350 W with an efficiency of 254 nm UV line generation of about 35% made it possible to create equipment for water disinfection. Increasing the power of UV lamps to 600-1000 W made it possible to create the plant for wastewater disinfection in Moscow with a record consumption of 4.2 million cubic meters daily. Disinfection of air and surfaces has become increasingly important recently, as the number of infected patients inside hospitals is constantly increasing. To disinfect air and surfaces, special high-power UV lamps were created for open irradiators, closed irradiators (recirculators) and for air conditioning and ventilation systems. Since the recommended UV doses for covid 19 are several times higher than for Staphylococcus aureus, for which they were designed, not all equipment can be used effectively now. Individual small-sized devices with a low-power UV lamp of several Watts are needed to dis   

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The information on typical values of ion energy and angular distributions (IEADs) on surfaces delivered by plasma jets and dielectric barrier discharges (DBDs) is equally important for the plasma processing and plasma medicine. The therapeutic effects of application of DBDs and jets in plasma medicine are partially attributed to energetic ions impinging on surfaces. In this paper, we report on results from a computational investigation of the IEADs for atmospheric pressure plasmas. The two-dimensional nonPDPSIM modeling platform is used in which IEADs are computed using Monte Carlo techniques. We compare two plasma sources - DBDs and plasma jets - and show that (i) when using a DBDs source, ions with high energies can be delivered to surfaces, (ii) while IEADs produced by plasma jets are characterized by much smaller energies. In particular, we demonstrate that ionization wave (IW) in plasma jets of positive cycle or pulse produce ion energies of a few eV while for the negative IW the ions are almost thermalized. The dependence of IEADs on the underlying material is also discussed.   

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Dourbal Electric, Inc. developed~ a pulsed arc system for production of plasma-activated water with silver nanoparticles~for biological applications. The system uses a specially designed voltage pulser that allows for robust control of arc in water.~ An electrode is made of silver that is ablated by the arc, which produces silver nanoparticles of the size of tens of nanometers. It is well known that such nanoparticles have strong antibacterial and antiviral~effects.~ In addition to production of nanoparticles, the arc discharge produces very long living (on order of weeks) active radical species which further contribute to destruction of pathogens, including viruses and bacteria, without harming live tissues.~ The water has been tested for biological effects against various medical conditions such as psoriasis on skin, fungal and stomach infections. Routine use of water as a nasal spray to wash nasal~passages reduces nasal congestion and seems to ameliorate spread of infections; though all studies were conducted on volunteers without a large statistical sample.~   

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Cleaning and disinfection of environmental rooms and surfaces are an essential part of control infections. Plasma-based systems might be capable of rapidly disinfecting rooms and surfaces. Compared to current disinfection methods based on wet chemistry, the plasma-based technique would be much more effective. The efficiency of the plasma disinfection systems is determined by the fact that the plasma is capable of acting on COVID-19 viruses by the electric field and active radicals produced by the plasma. To date, no effective plasma systems have been created. A device for the aerosol spray of radicals and excited states of molecules and atoms produces the volume disinfection contains a nozzle for spraying liquid, placed on the flow path a ring electrode with symmetrically located six tips, oriented so that the flow passes through the ring without touching it. High voltage is applied to the sprayed liquid, and the ring, characterized in that between the ring electrode and the flow of sprayed liquid, a volumetric electric discharge with liquid electrodes is generated, described in that chemically active free radicals. Compounds are sprayed with the useful liquid chemical components into the room. 1. Son E. Plasma spray discharge to kill viruses in the volume. Patent Application, Russia, June 2020. 2. Gulyaev Yu.V., Cherepenin V.A. On the possibility of using powerful electromagnetic pulses to disinfect bacteriologically contaminated objects. J. Radio Electronics. 2020. No.4. http://jre.cplire.ru/jre/apr20/13/text.pdf.\textunderscore DOI 10.30898 / 1684-1719.2020.4.13   

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We review all major components of pandemic spread: current epidemiology models, models of virus spread in air and through masks, issues with ventilation systems and possible amelioration~strategies.~ The virus can remain active on surfaces without treatment for a very long time. The chemical treatment uses a lot of chemicals and contributes to significant deleterious environmental effects. To avoid this, we propose wider~use of UVc radiation for deactivation of viruses. These systems are cheap, allow for fast processing of surfaces, but require~strict safety protocol. Recent studies suggest that even soft UV from sunlight can deactivate the viruses indicating the need to gather outside and use fresh outside air in ventilation as opposed to closed systems typical for modern buildings.~ ~   

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While the development of vaccines to inoculate the population against the SARS-Cov-2 virus is underway, and various promising treatments to improve outcomes have been identified, the primary mitigation effort to combat the spread of the virus has so far been the implementation of non-pharmaceutical interventions (NPIs). These NPIs include shelter-in-place orders, work-from-home and telecommute policies, and school closures. To determine the impact of these different NPI policies on infection within select regional populations, we deploy statistical inference tools to study the forecasts made by an agent-based model for viral spread. The basic concepts of the model will be discussed, as well as how tools regularly employed for uncertainty quantification in plasma modeling are used for calibration, sensitivity analysis, and uncertainty propagation, in order to inform intervention strategies.