Face Coverings, Aerosol Dispersion and Mitigation of Virus Transmission Risk.

The SARS-CoV-2 virus is primarily transmitted through virus-laden fluid particles ejected from the mouth of infected people. Face covers can mitigate the risk of virus transmission but their outward effectiveness is not fully ascertained. Objective: by using a background oriented schlieren technique, we aim to investigate the air flow ejected by a person while quietly and heavily breathing, while coughing, and with different face covers. Results: we found that all face covers without an outlet valve reduce the front flow through by at least 63% and perhaps as high as 86% if the unfiltered cough jet distance was resolved to the anticipated maximum distance of 2-3 m. However, surgical and handmade masks, and face shields, generate significant leakage jets that may present major hazards. Conclusions: the effectiveness of the masks should mostly be considered based on the generation of secondary jets rather than on the ability to mitigate the front throughflow.

Which factors influence the extent of indoor transmission of SARS-CoV-2? A rapid evidence review.

BACKGROUND: This rapid evidence review identifies and integrates evidence from epidemiology, microbiology and fluid dynamics on the transmission of SARS-CoV-2 in indoor environments. METHODS: Searches were conducted in May 2020 in PubMed, medRxiv, arXiv, Scopus, WHO COVID-19 database, Compendex & Inspec. We included studies reporting data on any indoor setting except schools, any indoor activities and any potential means of transmission. Articles were screened by a single reviewer, with rejections assessed by a second reviewer. We used Joanna Briggs Institute and Critical Appraisal Skills Programme tools for evaluating epidemiological studies and developed bespoke tools for the evaluation of study types not covered by these instruments. Data extraction and quality assessment were conducted by a single reviewer. We conducted a meta-analysis of secondary attack rates in household transmission. Otherwise, data were synthesised narratively. RESULTS: We identified 1573 unique articles. After screening and quality assessment, fifty-eight articles were retained for analysis. Experimental evidence from fluid mechanics and microbiological studies demonstrates that aerosolised transmission is theoretically possible; however, we found no conclusive epidemiological evidence of this occurring. The evidence suggests that ventilation systems have the potential to decrease virus transmission near the source through dilution but to increase transmission further away from the source through dispersal. We found no evidence for faecal-oral transmission. Laboratory studies suggest that the virus survives for longer on smooth surfaces and at lower temperatures. Environmental sampling studies have recovered small amounts of viral RNA from a wide range of frequently touched objects and surfaces; however, epidemiological studies are inconclusive on the extent of fomite transmission. We found many examples of transmission in settings characterised by close and prolonged indoor contact. We estimate a pooled secondary attack rate within households of 11% (95% confidence interval (CI) = 9, 13). There were insufficient data to evaluate the transmission risks associated with specific activities. Workplace challenges related to poverty warrant further investigation as potential risk factors for workplace transmission. Fluid mechanics evidence on the physical properties of droplets generated by coughing, speaking and breathing reinforce the importance of maintaining 2 m social distance to reduce droplet transmission. CONCLUSIONS: This review provides a snap-shot of evidence on the transmission of SARS-CoV-2 in indoor environments from the early months of the pandemic. The overall quality of the evidence was low. As the quality and quantity of available evidence grows, it will be possible to reach firmer conclusions on the risk factors for and mechanisms of indoor transmission.

On the Use of a Single Beam Acoustic Current Profiler for Multi-Point Velocity Measurement in a Wave and Current Basin.

Harnessing the energy of tidal currents has huge potential as a source of clean renewable energy. To do so in a reliable and cost effective way, it is critical to understand the interaction between tidal turbines, waves, and turbulent currents in the ocean. Scaled testing in a tank test provides a controlled, realistic, and highly reproducible down-scaled open ocean environment, and it is a key step in gaining this understanding. Knowledge of the hydrodynamic conditions during tests is critical and measurements at multiple locations are required to accurately characterise spatially varying flow in test tank facilities. The paper presents a laboratory technique using an acoustic velocimetry instrument, the range over-which measurements are acquired being more akin to open water applications. This enables almost simultaneous multi-point measurements of uni-directional velocity along a horizontal profile. Velocity measurements have been obtained from a horizontally mounted Single Beam Acoustic Doppler (SB-ADP) profiler deployed in the FloWave Ocean Energy Research Facility at the University of Edinburgh. These measurements have been statistically compared with point measurements obtained while using a co-located Acoustic Doppler Velocimeter (ADV). Measurements were made with both instruments under flow velocities varying from 0.6 ms-1 to 1.2 ms-1, showing that flow higher than 1 ms-1 was more suitable. Using a SB-ADP has shown the advantage of gaining 54 simultaneous measurement points of uni-directional velocity, covering a significant area with a total distance of 10 m of the test-tank, at a measurement frequency of 16 Hz. Of those measurement points, 41 were compared with co-located ADV measurements covering 8 m of the profile for a tank nominal flow velocity of 0.8 ms-1, and four distributed locations were chosen to to carry out the study at 0.6 ms-1, 1.0 ms-1, and 1.2 ms-1. The comparison with the ADV measurement showed a 2% relative bias on average.

Development of a Sensor to Measure Physician Consultation Times.

The duration of patient-physician contact is an important factor for the optimisation of treatment processes in healthcare systems. Available methods can be labour-intensive and the quality is, in many cases, poor. A part of this research project is to develop a sensor system, which allows the detection of people passing through a door, including the direction. For this purpose, two time of flight sensors are combined with a door sensor and a motion detection sensor (for redundancy) on one single side of the door frame. The period between two single measurements could be reduced to 50 ms, which allows the measurement of walking speed up to 2 ms - 1 . The accuracy of the time stamp for each event is less than one second and ensures a precise documentation of the consultation time. This paper presents the development of the sensor system, the miniaturisation of the installation and first measurement results, as well as the measurement's concept of quality analysis, including multiple door applications. In future steps, the sensor system will be deployed at different medical practices to determine the exact duration of the patient-physician interaction over a longer time period.

Large-scale experiments into the tsunamigenic potential of different iceberg calving mechanisms.

Mass balance analysis of ice sheets is a key component to understand the effects of global warming. A significant component of ice sheet and shelf mass balance is iceberg calving, which can generate large tsunamis endangering human beings and coastal infrastructure. Such iceberg-tsunamis have reached amplitudes of 50 m and destroyed harbours. Calving icebergs interact with the surrounding water through different mechanisms and we investigate five; A: capsizing, B: gravity-dominated fall, C: buoyancy-dominated fall, D: gravity-dominated overturning and E: buoyancy-dominated overturning. Gravity-dominated icebergs essentially fall into the water body whereas buoyancy-dominated icebergs rise to the water surface. We find with unique large-scale laboratory experiments that iceberg-tsunami heights from gravity-dominated mechanisms (B and D) are roughly an order of magnitude larger than from A, C and E. A theoretical model for released iceberg energy supports this finding and the measured wave periods upscaled to Greenlandic outlet glaciers agree with field observations. Whilst existing empirical equations for landslide-tsunamis establish estimates of an upper envelope of the maximum iceberg-tsunami heights, they fail to capture the physics of most iceberg-tsunami mechanisms.