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Flow visualization with a laser sheet reveals the turbulent vortices in the store air currents and their size distribution.
Source publication
We report experimental results on aerosol dispersion in two large German cash-and-carry hardware/DIY stores to better understand the factors contributing to disease transmission by infectious human aerosols in large indoor environments. We examined the transport of aerosols similar in size to human respiratory aerosols (0.3-10 $\mu$m) in representa...
Context in source publication
Context 1
... flow visualization around inlet and outlet vents in Store 1, we used a commercial fogger (Smoke Factory GmbH), and a 5 W continuous wave (CW) frequency-doubled Nd:YAG laser that with a cylindrical lens produced a light sheet of approximately 3mm beam width and opening angel of 90 • . Fig. 3 shows an example of flow visualization with the laser sheet under an exhaust vent, revealing the turbulent structures in the airflow by the concentration fluctuations of the turbulently entrained fog. A thermal imager (VarioCam head from Jenoptik Laser Optik Systeme GmbH, equipped with an IR 1.0/25 LW lens) was also used to measure the ...
Citations
Many countries have manifested COVID-19 trajectories where extended periods of constant and low daily case rate suddenly transition to epidemic waves of considerable severity with no correspondingly drastic relaxation in preventive measures. Such solutions are outside the scope of classical epidemiological models. Here, we construct a deterministic, discrete-time, discrete-population mathematical model called cluster seeding and transmission model, which can explain these non-classical phenomena. Our key hypothesis is that with partial preventive measures in place, viral transmission occurs primarily within small, closed groups of family members and friends, which we label as clusters. Inter-cluster transmission is infrequent compared with intra-cluster transmission but it is the key to determining the course of the epidemic. If inter-cluster transmission is low enough, we see stable plateau solutions. Above a cutoff level, however, such transmission can destabilize a plateau into a huge wave even though its contribution to the population-averaged spreading rate still remains small. We call this the cryptogenic instability. We also find that stochastic effects when case counts are very low may result in a temporary and artificial suppression of an instability; we call this the critical mass effect. Both these phenomena are absent from conventional infectious disease models and militate against the successful management of the epidemic.
