Investigate the Wake Flow on Houseflies with Particle-Tracking-Velocimetry and Schlieren Photography

Utilizing high-speed schlieren photography and particle-tracking-velocimetry,the wake flow of tethered houseflies is investigated.The high-speed schlieren photography is implemented on tethered houseflies inside an air container with a stable vertical temperature gradient to visualize the disturbed wake flow from the insects.The resulting photography images were then processed with the physics based optical flow method to derive the light-path averaged flow velocity.Additionally,the state of the art:Shake-the-Box system is implemented on a tethered housefly to measure the volumetric flow field in the wake of the insect,revealing interesting flow behavior and structures that can also be observed and correlated to the schlieren photography images.Comparing the dimensionless velocity magnitude of the wake flow from the two experiments,a good qualitative agreement is reached,suggesting the viability of high-speed schlieren photography in investigating the wake flow of small insects.Furthermore,the high-speed schlieren photography is successfully applied on a housefly that is taking off from the ground,visualizing the disturbed wake flow on the freely flying insect that is challenging to visualize with other methods.

The Richtmyer–Meshkov instability of a 'V' shaped air/helium interface subjected to a weak shock

The Richtmyer-Meshkov instability ofa ‘V＇ shaped air/helium gaseous interface subjected to a weak shock wave is experimentally studied. A soap film technique is adopted to create a ‘V＇ shaped interface with accurate initial conditions. Five kinds of ‘V＇ shaped interfaces with different vertex angles are formed to highlight the effects of initial conditions on the flow characteristics. The results show that a spike is generated after the shock impact, and grows constantly with time. As the vertex angle increases, vortices generated on the interface become less noticeable, and the spike develops less pronouncedly. The linear growth rate of interface width after compression phase is estimated by a linear model and a revised linear model, and the latter is proven to be more effective for the interface with high initial amplitudes. The linear growth rate of interface width is, for the first time in a heavy/light interface configuration, found to be a non-monotonous function of the initial perturbation amplitude-wavelength ratio.

Fabrication of a High-Performance and Reusable Planar Face Mask in Response to the COVID-19 Pandemic

The coronavirus disease 2019(COVID-19)pandemic has caused a surge in demand for face masks,with the massive consumption of masks leading to an increase in resource-related and environmental con-cerns.In this work,we fabricated meltblown polypropylene(mb-PP)-based high-performance planar face masks and investigated the effects of six commonly used disinfection methods and various mask-wearing periods on the reusability of these masks.The results show that,after three cycles of treatment using hot water at 70℃ for 30 min,which is one of the most scalable,user-friendly methods for viral disinfection,the particle filtration efficiency(PFE)of the mask remained almost unchanged.After mask wearing for 24 h and subsequent disinfection using the same treatment procedures,the PFE decreased to 91.3%;the average number of bacterial and fungal colonies was assessed to be 9.2 and 51.6 colony-forming units per gram(CFU∙g^(-1)),respectively;and coliform and pyogenic bacteria were not detected.Both the PFE and the microbial indicators are well above the standard for reusable masks after disinfection.Schlieren pho-tography was then used to assess the capabilities of used and disinfected masks during use;it showed that the masks exhibit a high performance in suppressing the spread of breathed air.