Resuspended floor dust constitutes up to sixty percent of the total particulate matter in indoor air. This fraction may also include virus-laden particles that settle on the floor after being emitted by an infected individual. This research focuses on predicting the concentration of influenza A viruses in resuspended dust, generated by people walking in a room, at various heights above the floor. Using a sonic anemometer, we measured the velocity field from floor to ceiling at 10-cm intervals to estimate the magnitude of turbulence generated by walking. The resulting eddy diffusion coefficients varied between 0.06 m2 s-1 and 0.20 m2 s-1 and were maximal at ~0.75-1 m above the floor, approximately the height of the swinging hand. We used these coefficients in an atmospheric transport model to predict virus concentrations as a function of the carrier particle size and height in the room. Results indicate that the concentration of resuspended viruses at 1 m above the floor is about seven times the concentration at 2 m. Thus, shorter people may be exposed to higher concentrations of pathogens in resuspended dust indoors. This study illuminates the possibility that particle resuspension could be a mode of disease transmission. It also emphasizes the importance of considering resuspension of particulate matter when designing ventilation systems and flooring in hospitals and residences. / Master of Science

This study investigates the turbulent mixing characteristics of Peng-hu Channel, South China Sea along 21¢XN and the Kuroshio region by using CTD/LADCP and MicroRider. Dissipation rate of turbulent kinetic energy or thermal variances is estimated primarily by the Thorpe overturn method, and is compared with the microstructure turbulence from direct measurement as well as those estimated from the parameterization method based on shear and strain spectra. Our results indicate that there are different turbulent characteristics and dynamic mechanisms at these three regions. Because of its funnel-shaped topography and strong semi-diurnal tides in the Peng-hu Channel, the turbulent mixing and eddy diffusivity reach a maximum value at the narrowest part of Peng-hu Channel near its sea bottom and show a clear tidal variation. In the main stream of Kuroshio where the current speed is faster than 0.8 m/s, turbulent mixing is not particularly stronger than non-main stream zone. In the Kuroshio frontal zone between the Kuroshio and the coastal waters off east Taiwan coast, strong turbulent mixing in the surface layer can be detected. Island wake which is formed when Kuroshio runs into the Lan-yu Island is a transient feature. Strong mixing in the upper 100 m accompanied with upwelling and vortices were observed during one event. The topography along the latitude of 21¢XN is rugged and rough in the Luzon Strait which consists of several ridges and seamounts. Due to its complicated topography and generation of strong semi-diurnal internal tides, eddy diffusivity as high as 10^(-2)m^2/s was measured in the bottom layer of the Luzon Strait.

This thesis studies the implementation of an Explicit Algebraic Reynolds-Stress Model(EARSM) for Atmospheric Boundary Layer (ABL) in an open source ComputationalFluid Dynamics (CFD) software, OpenFOAM, following the guidance provided by thewind company ENERCON that aims to make use of this novel model to improvesites’ wind-field predictions. After carefully implementing the model in OpenFOAM,the EARSM implementation is verified and validated by testing it with a stratifiedCouette flow case. The former was done by feeding mean flow properties, takenfrom OpenFOAM, in a python tool containing the full EARSM system of equationsand constants, and comparing the resulting flux profiles with the ones extracted bythe OpenFOAM simulations. Subsequently, the latter was done by comparing theprofiles of the two universal functions used by Monin-Obukhov Similarity Theory(MOST) for mean velocity and temperature to the results obtained by Želi et al. intheir study of the EARSM applied to a single column ABL, in “Modelling of stably-stratified, convective and transitional atmospheric boundary layers using the explicitalgebraic Reynolds-stress model” (2021). The verification of the model showed minordifferences between the flux profiles from the python tool and OpenFOAM thus, themodel’s implementation was deemed verified, while the validation step showed nodifference in the unstable and neutral stratification cases, but a significant discrepancyfor stably stratified flow. Nonetheless, the reason behind the inconsistency is believedto be related to the choice of boundary conditions thus, the model’s implementationitself is considered validated. Finally, the comparison between the EARSM and the k − ε model showed thatthe former is able to capture the physics of the flow properties where the latter failsto. In particular, the diagonal momentum fluxes resulting from the EARSM reflectthe observed behaviour of being different from each other, becoming isotropic withaltitude in the case of unstable stratification, and having magnitude u′u′ > v′v′ > w′w′ for stably stratified flows. On the other hand, the eddy viscosity assumption used bythe k − ε model computes the diagonal momentum fluxes as being equal to each other.Moreover, the EARSM captures more than one non-zero heat flux component in theCouette flow case, which has been observed to be the case in literature, while the eddydiffusivity assumption used by the k − ε model only accounts for one non-zero heat fluxcomponent.

À ce jour, les différentes méthodes de reconstruction des mouvements du plasma à la surface du Soleil qui ont été proposées présupposent une MHD idéale (Welsch et al., 2007). Cependant, Chae & Sakurai (2008) ont montré l’existence d’une diffusivité magnétique turbulente à la photosphère. Nous introduisons une généralisation de la méthode du Minimum Energy Fit (MEF ; Longcope, 2004) pour les plasmas résistifs. Le Resistive Minimum Energy Fit (MEF-R ; Tremblay & Vincent, 2014) reconstruit les champs de vitesse du plasma et la diffusivité magnétique turbulente qui satisfont à l’équation d’induction magnétique résistive et qui minimisent une fonctionnelle analogue à l’énergie cinétique totale. Une séquence de magnétogrammes et de Dopplergrammes sur les régions actives AR 9077 et AR 12158 ayant chacune produit une éruption de classe X a été utilisée dans MEF-R pour reconstruire les mouvements du plasma à la surface du Soleil. Les séquences temporelles des vitesses et des diffusivités magnétiques turbulentes calculées par MEF-R sont comparées au flux en rayons X mous enregistré par le satellite GOES-15 avant, pendant et après l’éruption. Pour AR 12158, nous observons une corrélation entre les valeurs significatives de la diffusivité magnétique turbulente et de la vitesse microturbulente pour les champs magnétiques faibles. / To this day, the various methods proposed for the reconstruction of plasma motions at the Sun’s surface are all based on ideal MHD (Welsch et al., 2007). However, Chae & Sakurai (2008) have shown the existence of an eddy magnetic diffusivity at the photosphere. We introduce a generalization of the Minimum Energy Fit (MEF; Longcope, 2004) for resistive plasmas. The Resistive Minimum Energy Fit (MEF-R; Tremblay & Vincent, 2014) infers velocity fields and an eddy magnetic diffusivity which solve the resistive magnetic induction equation and minimize an energy-like functional. A sequence of magnetograms and Dopplergrams documenting the active regions AR 9077 and AR 12158 are used as input in MEF-R to reconstruct plasma motions at the Sun’s surface. Time series of the inferred velocities and eddy magnetic diffusivities are compared to the soft X-ray flux observed by GOES-15. We find a positive correlation between significant eddy magnetic diffusivities and microturbulent velocities for weak magnetic fields in AR 12158.