Browsing by Subject "virus"

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    Interactions between Plasma and Liquid Micro-Droplets
    (2021-02) Nayak, Gaurav
    The interaction of plasmas with a liquid phase results into various complex multiphase phenomena that is beneficial for a wide range of applications, such as water treatment, nanoparticle synthesis, material processing, combustion, decontamination, food safety and human health care. These applications have been made possible due to the transferof highly reactive species from the gas phase plasma to the bulk liquid phase. Upon interaction with a liquid phase, atmospheric pressure non-equilibrium plasmas produce numerous chemically reactive species, including ions, radicals, electrons and (V)UV photons. The resulting short-lived highly reactive species can exhibit huge density gradients in the liquid phase as their finite lifetime does not allow them to penetrate into the bulk liquid. This makes the multiphase reactivity transfer highly transport limited. Additionally, the presence of electric field-induced effects, charging, evaporation and heat and mass transfer makes plasma-liquid interaction studies more challenging due to the lack of a detailed understanding of the inter-coupling of these phenomena and their direct impact on the plasma-produced reactive species fluxes to the liquid. To understand and overcome the challenge of transport limitations, a novel plasma-liquid configuration was developed, which involves plasma activation of small dispersed liquid droplets or aerosols. The key advantage of such a configuration is that the large surface-to-volume ratio of these micrometer-sized liquid droplets enhances the reactivity transfer from the gas phase plasma to the liquid phase. Since the droplets are immersed in the plasma, the short-lived reactive species (electrons, ions and radicals) produced in the gas phase plasma due to electron impact processes on average only need to cover smaller length scales to reach and subsequently penetrate the droplet. The foremost goal of the research reported in this thesis is the development of a controlled and well-defined plasma-microdroplet reactor, which is easy to model and experimentally accessible with different diagnostic techniques enabling to obtain quantitative measurements of reactive species densities. Due to the efficient generation of reactive species, a radiofrequency (RF)-driven capacitively coupled diffuse plasma generated in parallel-plate configuration at atmospheric pressure is used in this work. Complete characterization of the RF plasma is helpful for the assessment of the role of different gas-phase reactive species generated by the plasma and their respective fluxes to the liquid microdroplets in transit through the plasma. The reactive species potentially playing a key role in plasma-liquid interactions include electrons, OH radicals, H and O atoms, singlet oxygen, O3, He and Ar metastable atoms and molecules. The absolute densities of electrons and metastable atoms and molecules along with gas and electron temperatures that play a major role in plasma-induced chemistry in He and Ar plasmas were measured using optical emission and broadband absorption spectroscopy. We found that the densities of He and Ar metastables peaked near the sheath edges away from the droplet trajectory, while the densities in the bulk were below their respective detection limits. The Ar and He metastable fluxes to the droplet were found to be 2 orders of magnitude and 5 times smaller than the electron flux to droplet, respectively. Hence, the effect of Ar and He metastable atoms on the droplet chemistry can be considered negligible compared to charged species fluxes. However, these metastable species are an important source of ionization in such low electron density plasmas and play, nonetheless, a major role in the plasma dynamics including ionization processes and the generation of radicals in the gas phase. An understanding of the dynamics of liquid microdroplets in the plasma is important as it not only relays information about the residence time of the droplets in the plasma (i.e. treatment time of the solution by short-lived plasma-produced species) but also droplet charging and the presence of electric fields when entering and exiting the plasma. This residence time dictates the fate of the droplet chemistry and its interactions with the plasma. We characterized the droplet and its trajectory by fast frame imaging in diffuse He glow discharge. From the droplet velocity and acceleration data, the various forces acting on the droplet were evaluated. Using the equilibrium of forces and the droplet charge estimated from an analytical model, the electric field at the plasma edges was determined. We also report on the effect of the initial droplet acceleration during droplet ejection from the piezoelectric nozzle, the plasma composition (He with admixtures of Ar, H2O, H2 and O2), gas flow rate, and the plasma power on the droplet dynamics. Plasmas in or in contact with water have been extensively investigated in the context of plasma-aided decomposition and mineralization of recalcitrant organic pollutants in water for environmental remediation. However, plasma, while being highly effective, sometimes lacks energy efficiency. The water treatment is often due to the transfer of long-lived species into the liquid bulk and secondary reactions. Using the approach of microdroplets treated by plasma, the efficiency of plasma treatment of organics in liquid water microdroplets can be improved by increasing the species fluxes to the droplets. Using detailed plasma diagnostics, droplet characterization and ex situ chemical analysis of the treated droplets, we assessed the relative importance of short-lived radicals, such as O and H atoms, singlet oxygen, solvated electrons and ions, besides OH radicals, responsible for the decomposition of formate, a model organic compound inwater treatment studies, dissolved in droplets. We ascertained the role of OH and O radicals in electronegative plasmas. We also showed for electropositive plasmas that solvated electrons and/or ions injected into the droplet were dominantly responsible for plasma-induced chemistry in the droplet. Results suggested that the charged species lead to the formation of H or OH radicals near the droplet interface via secondary reactions, enabling further decomposition of formate in the droplets. The obtained results allowed us to estimate minimum values of transport properties of O in solution and reaction rates of O radical with formate using a one-dimensional reaction-diffusion model. Gold and silver nanoparticles (AuNP and AgNP) exhibit unique optical, electrical, and thermal properties, and can be synthesized by plasmas in a green and environmentally friendly approach without the use of hazardous chemicals, and without producing harmful byproducts. Previously, researchers have established unprecedented gold ions reduction synthesis rates in liquid droplets treated by an RF plasma to synthesize AuNPs. The reported reduction rates are several orders of magnitude larger than for any other reported electron-initiated methods. The mechanism for the synthesis of nanoparticles using this approach is still largely unknown. Using the known gas-phase plasma properties, absorption spectroscopy, and transmission electron microscopy (TEM), we identified the role of hydrogen peroxide in the reduction of gold ions. On the other hand, the reported results for AgNP formation from Ag ions in the same reactor, suggested that the effect of solvated electrons and H radicals were dominant for the reduction of silver ions. We also demonstrate the possibility to use plasma-droplet interactions for the synthesis of surfactant-free, spherical and crystalline Au and AgNPs without the use of any stabilizer(s) within a few milliseconds. In view of the recent COVID-19 pandemic caused by the airborne transmission of SARS-CoV-2 virus aerosols, many excellent surveillance and control measures are being implemented in conned spaces, where the effect of the virus transmission is the highest. The application of plasma-aided virus disinfection is quite nascent, and the interaction of plasma with the virus aerosols in air streams has not been dealt with in detail. The actual mechanism for the virus inactivation is often ascribed to ozone, however, in short time scales of milliseconds, more reactive species might be needed to obtain an effective inactivation. We report on the use of a dielectric barrier discharge (DBD) for in-flight inactivation of airborne aerosolized porcine reproductive and respiratory syndrome (PRRS) virus. The measurements were performed in a laboratory-scale wind test tunnel. Using infectivity tests and reverse transcriptase quantitative polymerase chain reaction (RT-qPCR), we showed a 3.5 log10 reduction in the viable virus titer during in-flight treatment by the DBD within a few milliseconds. We identified both short-lived species such as OH radicals and singlet oxygen and peroxynitrous acid chemistry at low pH in the virus-laden droplets responsible for the observed inactivation of virus aerosols by plasma. The fundamental understanding of the interactions of plasma and liquid microdroplets, gained in this work, have the potential to increase significantly the efficacy of plasma processes. There is no doubt that improved reactor design and plasma generation informed by our findings will further advance the development of such unique interactions for the novel applications of water treatment, nanoparticle synthesis and virus aerosol inactivation.
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    The use of movement data and network models to measure the effectiveness of control strategies for foot-and-mouth disease in swine
    (2018-11) Kinsley, Amy
    Foot-and-mouth disease has been considered a significant epidemic threat to livestock since the sixteenth century, hindering animal health and leading to direct and indirect economic losses through treatment, decreased productivity, trade restrictions, and disease control programs. The disease is caused by infection with foot-and-mouth disease virus (FMDV), which belongs to the Aphthovirus genus and the family Picornavirdae. There are several main serotypes circulating throughout the world, with numerous subtypes creating challenges for global eradication. In the event of a of foot-and-mouth disease (FMD) incursion into an FMD-free country, response strategies are required to control, contain and eradicate the pathogen as efficiently as possible. Simulation models have often been used to test the effectiveness and efficiency of alternative control strategies to mitigate the spread of infectious animal diseases and have contributed greatly to advancements in our understanding of disease transmission. However, quantitative values on the duration of the stages of FMD infection, within-farm transmission dynamics, and understanding between-farm movement patterns are all essential components in using simulation models in livestock populations. In this thesis, we quantified values associated with the duration of the stages of FMD infection (latent period, subclinical period, incubation period, and duration of infection), probability of transmission (within-herd and between-herd via spatial spread), and time to the diagnosis of a vesicular disease within a herd using a meta-analysis of peer-reviewed literature and expert opinion. We then assessed the impact of farm structure (different barns or rooms for breeding and gestation, farrowing, nursery, and finishing) and demography (piglet births and deaths, and animal movement within and off of the farm) by testing the impact of assuming a homogeneous mixing/closed population, a common assumption for within-farm models of highly contagious diseases of swine, such as foot-and-mouth disease (FMD), on predictions about disease spread. Looking beyond within-farm dynamics, we described the annual movement patterns between swine farms in three production systems of the United States and identified farms that may be targeted to increase the efficacy of infectious disease control strategies. We then used the results from the within-farm model and analysis of movement patterns to understand the impact of using empirical movement data compared to simulated movement data and compared targeted control strategies using metrics of the movement data to control strategies that are based on geographical factors such as zones and rings. The results worth highlighting from of our investigations include the following: Chapter 2: When quantifying the duration of the stages of FMD infection in swine, we found that the latent period and the incubation period ranged from 1 to 7 days and 1 to 9 days, respectively. Furthermore, we found that distribution of those values is dependent on the strain of FMDV, in which some strains have a shorter latent period and incubation period than others, which should be considered when modeling FMD transmission. Chapter 3: In this chapter, we incorporated farm structure and demography in to the within-herd model and observed transmission dynamics that differed in the latter portion of an outbreak in certain conditions. Specifically, we observed that farm structure and demography, which were included in the farrow to finish and farrow to wean farms, resulted in FMD virus persistence within the population, which can have significant impacts on between-farm spread. Chapter 4: Through our analysis of empirical movement data, we showed that targeting farms based on a metric that captured the temporal sequence of movements (mean infection potential), substantially reduced the potential for transmission of an infectious pathogen in the contact network and performed consistently well across production systems. This result highlights the importance of detailed movement data in understanding potential disease spread within production systems. Chapter 5: In this chapter we modeled the impact of alternative control strategies on between-farm transmission of FMD, we saw that control strategies, which preemptively targeted specific farms based on their spatial network, reduced the number of infected farms, duration of the epidemic, number of vaccinated farms, and the number of culled farms when compared to reactive scenarios that used the formation of rings and zones around infected-detected farms.