Tyler O'Neal, Staff Editor MANUFACTURING

Okinawa Institute of Science and Technology prof uncovers the secrets of COVID-19 transmission in turbulent puffs

Summary

  • Researchers have developed a new model that explains how turbulent puffs, like coughs, behave under different environmental conditions
  • The researchers found that at environmental temperatures 15°C or lower, the puffs behaved with newly observed dynamics, showing more buoyancy and traveling further
  • The researchers verified their models by running simulations through a supercomputer
  • Their findings could help scientists better predict how turbulence and the environment affect the airborne transmission of viruses like SARS-CoV-2

Turbulence is everywhere – in the movement of the wind, the ocean waves, and even magnetic fields in space. It can also be seen in more transient phenomena, like smoke billowing from a chimney, or a cough.

Understanding this latter type of turbulence – called puff turbulence – is important not only for the advancement of fundamental science, but also for practical health and environmental measures, like calculating how far cough droplets will travel, or how pollutants released from a chimney or cigarette might disperse into the surroundings. But creating a complete model of how turbulent puffs of gases and liquids behave has so far proven elusive. Large scale and small scale dynamics of a turbulent puff.

“The very nature of turbulence is chaotic, so it’s hard to predict,” said Professor Marco Edoardo Rosti, who leads the Complex Fluids and Flows Unit at Okinawa Institute of Science and Technology Graduate University (OIST). “Puff turbulence, which occurs when the ejection of a gas or liquid into the environment is disrupted, rather than continuous, has more complicated characteristics, so it’s even more challenging to study. But it’s of vital importance – especially right now for understanding the airborne transmission of viruses like SARS-CoV-2.”

Until now, the most recent theory was developed in the 1970s, and focused on the dynamics of a puff only at the scale of the puff itself, like how fast it moved and how wide it spread.

The new model, developed in a collaboration between Prof. Rosti from OIST, Japan, and Prof. Andrea Mazzino from the University of Genova in Italy, builds on this theory to include how minute fluctuations within the puff behave, and how both large-scale and small-scale dynamics are impacted by changes in temperature and humidity. Their findings were published in Physical Review Letters on August 25th, 2021.

Interestingly, the scientists found that at cooler temperatures (15°C or lower), their model deviated from the classical model for turbulence.

In the classical model, turbulence reigns supreme – determining how all the little swirls and eddies within the flow behave. But once temperatures dipped, buoyancy started to have a greater impact.

“The effect of buoyancy was initially very unexpected. It’s a completely new addition to the theory of turbulent puffs,” said Prof. Rosti.

Buoyancy exerts an effect when the gas or liquid puff is much warmer than the temperature of the immediate surroundings it is released into. Warm gas or fluid is much less dense than the cold gas or fluid of the environment, and therefore the puff rises, allowing it to travel further.

“Buoyancy generates a very different kind of turbulence – not only do you see changes in the large-scale movement of the puff, but also changes in the minute movements within the puff,” said Prof. Rosti.

The scientists used a powerful supercomputer, capable of resolving the behavior of the puff at the large-scale and the small-scale, to run simulations of turbulent puffs, which confirmed their new theory.

The new model could now allow scientists to better predict the movement of droplets in the air that are released when someone coughs or speaks unmasked.

While larger droplets fall quickly to the ground, reaching distances of around one meter, smaller droplets can remain airborne for much longer and travel further.

“How fast the droplets evaporate – and therefore how small they are – depends on turbulence, which in turn is affected by the humidity and temperature of the surroundings,” explained Prof. Rosti. “We can now start to take these differences in environmental conditions, and how they affect turbulence, into consideration when studying airborne viral transmission.”

Next, the researchers plan to study how puffs behave when made of more complicated non-Newtonian fluids, where how easily the fluid flows can change depending on the forces it is under.

“For COVID, this could be useful for studying sneezes, where non-Newtonian fluids like saliva and mucus are forcefully expelled,” said Dr. Rosti.

(ISC)² makes Security Congress 2021 a virtual trade show

Tyler O'Neal, Staff Editor MANUFACTURING

With increasing COVID-19 concerns, an annual security conference to be hosted virtually for the second year

(ISC)2 has announced the decision to change its Security Congress event from a hybrid experience to entirely virtual on the same dates, October 18-20, 2021.

"The health and safety of all attendees, speakers, staff, volunteers, and sponsors is our top priority," said Clar Rosso, CEO, (ISC)2. "With the continued prevalence of COVID-19, we knew this pivot was a possibility. Our team is ready to deliver a dynamic digital experience, building on our 2020 success that drew almost 6,000 online attendees. We look forward to seeing everyone at our world-class, online Security Congress this October."

The online-only Security Congress content – including the number of sessions and CPE opportunities – will not change other than transitioning to a virtual delivery. With more than 125 virtual sessions delivered live, (ISC)² members can earn up to 20 continuing professional education (CPE) credits by attending the event, and even more by accessing the archived content through the end of 2021. This year's event will also feature live Q&A during all keynote sessions and during other sessions.

Additional virtual networking opportunities will be added as the event draws near and the Diversity, Equity, and Inclusion breakfast will now be streamed online.

In-person registration will be automatically converted to a virtual registration, and those attendees will receive a credit of the price difference back to their original form of payment.

All speakers, attendees, and those considering attending this year's event are encouraged to join the next Inside (ISC)² webinar on Tuesday, August 31 at 1:00 pm EDT for additional information on this year's Security Congress, as well as future plans for (ISC)² events. CEO Clar Rosso and Director of Events Megan Gavin will host the live webinar, which will conclude with an audience Q&A.

For more information and to register to attend virtually, please visit: https://congress.isc2.org

Chilean researchers aim to optimize disease prevention in prison populations with rapid testing

Tyler O'Neal, Staff Editor MANUFACTURING

The use of rapid tests to screen for diseases in prisons could enable the diagnosis of asymptomatic individuals and reduce the spread of infection. Victor Riquelme, Pedro Gajardo, and Diego Vicencio (all from the Universidad Técnica Federico Santa María in Chile) recently explored how to optimally control a communicable disease inside a prison population using inexpensive, low-complexity rapid tests that personnel can administer with only basic training. Their results appear in a paper publishing today in the SIAM Journal on Control and Optimization.

Certain diseases are much more prevalent in prisons than in the general population. Overcrowding, high-risk behavior, a higher probability of disease risk factors like depression and drug use, and deficiencies in prison health care systems all contribute to this problem. “This is a general social problem and not only a penitentiary concern,” Riquelme said. “Prisons act as reservoirs of diseases, which are subsequently transmitted to the community when inmates are released, or when they are in contact with the outside population like visitors or prison workers.”

The current standard for disease detection in prisons is passive and based purely on obvious outward symptoms. A more active application of rapid tests could increase the access of diagnoses for asymptomatic patients, thereby preventing long-term complications and interrupting the chain of disease transmission. But despite these obvious benefits, there is little research on the use of these types of technologies in prison contexts.

Gajardo first became interested in this issue during a collaboration with the Center for Epidemiology and Public Health Policy Studies at the Universidad del Desarrollo in Chile that focused on finding the most cost-effective strategy for the detection of syphilis in prisons. One of the best-evaluated policies involved screening the new inmate population with rapid tests upon prison entry, a topic that Riquelme, Gajardo, and Vicencio’s recent paper further explores. “We set ourselves the problem of determining the best way to apply this policy,” Gajardo said.

The study utilized a simple epidemiological model that represents diseases that people can still catch even if they have already had them before, like meningitis or gonorrhea. “Although this [model] may seem unrealistic for many diseases, it allows us to obtain valuable insights into the structure of the optimal strategy and its dependence in terms of the problem data,” Vicencio said. While more realistic models would be necessary to ultimately design real-life policies, this preliminary approach allowed the researchers to identify useful information about the optimal strategy’s general properties and how different qualities of a prison environment might impact the strategy.

The authors incorporated this basic epidemiological model into their own model of a prison that screens a certain proportion of new inmates at the entrance. They hoped to find the optimal strategy for rapid testing at the prison’s entry point based on both infection reduction and cost-effectiveness. “The decision we aim to optimize is the percentage of new inmates to be screened at each period of time,” Gajardo said. “Our objective is to minimize the total costs of this procedure, along with the maintenance cost of infected people inside the prison.” Minimized costs could be a powerful draw for prison administrations, making them more likely to adopt the proposed testing strategy.

The model assumes that the size of the prison population does not change, an assumption that can be explained by prison overcrowding — as soon as a space becomes vacant, it is filled by a new inmate. The screening test has a certain true positive rate, and anyone who tests positive receive immediate treatment for the identified disease. However, a certain proportion of infected individuals do still enter the prison: those for whom treatment did not work, those who received a false-negative test result, and those who were not tested.

According to this simplified model, the optimal strategy is to switch between applying a screening at maximum capacity at the prison’s entry and not screening at all; it is never best to operate at a partial testing capacity. “To apply the rapid test to an intermediary percentage, say 60 percent, is never optimal,” Riquelme said. “This is a bang-bang strategy, a strategy that only considers possible extreme values.”

The question then becomes when to switch from full testing to no testing and vice versa. “Surprisingly to us, we found that there are situations—depending on the problem data—where it is not optimal to start screening at maximum capacity,” Riquelme said. “It is better to wait a bit and then apply the maximum screening capacity.” Many different parameters impact the decision of when and how frequently to test prison entrants, including contagion and recovery rates; test sensitivity; the rate at which inmates enter and exit the prison; and the costs of screening, treating, and holding infected individuals within the prison.

Further research could build upon these preliminary results to define more elaborate testing strategies while also accounting for some additional specifics of the prison environment. “Our work may help to design the application schedule of rapid tests at the entrance,” Gajardo said. “Nevertheless, for a real application, more complex models that are tailored to the diseases in question should be considered. Our results can help these studies, providing the general structure of the strategies that should be tested.” Ultimately, this study indicates that rapid testing is a worthwhile method for facilitating access to disease diagnosis and treatment in prisons; future efforts could put it into practice.