Contact and inhalation of virions-carrying human aerosols represent the primary transmission pathway for airborne diseases including the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Relative to sneezing and coughing, non-symptomatic aerosol-producing activities such as speaking are highly understudied. The dispersions of aerosols from vocalization by a human subject are hereby quantified using high-speed particle image velocimetry. Syllables of different aerosol production rates were tested and compared to coughing. Results indicate aerosol productions and penetrations are not correlated. E.g. ‘ti’ and ‘ma’ have similar production rates but only ‘ti’ penetrated as far as coughs. All cases exhibited a rapidly penetrating “jet phase” followed by a slow “puff phase.” Immediate dilution of aerosols was prevented by vortex ring flow structures that concentrated particles toward the plume-front. A high-fidelity assessment of risks to exposure must account for aerosol production rate, penetration, plume direction and the prevailing air current.
Plenoptic particle image velocimetry (PPIV) has been demonstrated in the past as a viable single-/dual-camera technique for 3D flow measurements. Compared to established fourcamera tomographic-PIV and 3D-PTV, PPIV has the advantages of lower cost, a simpler setup with a smaller footprint, a deeper depth-of-field for a given aperture and potential for access to otherwise optically restricted facilities. However, because camera bodies must be significantly modified to accommodate an embedded plenoptic microlens array (MLA), past PPIV implementations have been limited to <5 Hz low-speed Imperx cameras. The mitigation of this shortcoming through the development of a modular plenoptic adaptor is hereby presented. The developed adaptor, which consists of an externally mounted MLA and a pair of relay lenses, attaches to and enables plenoptic capability in unmodified off-the-shelf imaging devices, including kHz-rate high-speed cameras and intensifiers. Imaging performance is found to be comparable to embedded-MLA designs, and results from the PPIV measurement of 4D flows around a ctenophore Mnemiopsis ('comb jelly') using the high-speed system is hereby presented.
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