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London, May 20: The current physical distancing guidelines of 6 feet may be insufficient to prevent COVID-19 transmission, according to a study which says a mild cough in low wind speeds can propel saliva droplets by as much as 18 feet.

Researchers, including those from the University of Nicosia in Cyprus, said a good baseline for studying the airborne transmission of viruses, like the one behind the COVID-19 pandemic, is a deeper understanding of how particles travel through the air when people cough.

In the study, published in the journal Physics of Fluids, they said even with a slight breeze of about four kilometres per hour (kph), saliva travels 18 feet in 5 seconds.

"The droplet cloud will affect both adults and children of different heights," said study co-author Dimitris Drikakis from the University of Nicosia.

According to the scientists, shorter adults and children could be at higher risk if they are located within the trajectory of the saliva droplets.

They said saliva is a complex fluid, which travels suspended in a bulk of surrounding air released by a cough, adding that many factors affect how saliva droplets travel in the air.

These factors, the study noted, include the size and number of droplets, how they interact with one another and the surrounding air as they disperse and evaporate, how heat and mass are transferred, and the humidity and temperature of the surrounding air.

In the study, the scientists created a computer simulation to examine the state of every saliva droplet moving through the air in front of a coughing person.

The model considered the effects of humidity, dispersion force, interactions of molecules of saliva and air, and how the droplets change from liquid to vapour and evaporate, along with a grid representing the space in front of a coughing person.

Each grid, the scientists said, holds information about variables like pressure, fluid velocity, temperature, droplet mass, and droplet position.

The study analysed the fates of nearly 1,008 simulated saliva droplets, and solved as many as 3.7 million equations.

"The purpose of the mathematical modelling and simulation is to take into account all the real coupling or interaction mechanisms that may take place between the main bulk fluid flow and the saliva droplets, and between the saliva droplets themselves," explained Talib Dbouk, another co-author of the study.

However, the researchers added that further studies are needed to determine the effect of ground surface temperature on the behaviour of saliva in air.

They also believe that indoor environments, especially ones with air conditioning, may significantly affect the particle movement through air.

This work is important since it concerns safety distance guidelines, and advances the understanding of the transmission of airborne diseases, Drikakis said.

New Delhi, Mar 16: Due to the coronavirus pandemic, most airlines in the world will be bankrupt by the end of May and only a coordinated government and industry action right now can avoid the catastrophe, said global aviation consultancy firm CAPA in a note on Monday.

"As the impact of the coronavirus and multiple government travel reactions sweep through our world, many airlines have probably already been driven into technical bankruptcy, or are at least substantially in breach of debt covenants," it stated.

Across the world, airlines have announced drastic reduction in their operations in the wake of the coronavirus outbreak. For example, Atlanta-based Delta Air Lines stated on Sunday that it would be grounding 300 aircraft in its fleet and reduce flights by 40 per cent.

The US has suspended all tourist visas for people belonging to the European Union, the UK and Ireland. Similarly, the Indian government has suspended all tourist visas and e-visas granted on or before March 11.

CAPA, in its note on Monday, said, "By the end of May-2020, most airlines in the world will be bankrupt. Coordinated government and industry action is needed - now - if catastrophe is to be avoided."

Cash reserves are running down quickly as fleets are grounded and "what flights there are operate much less than half full", it added.

"Forward bookings are far outweighed by cancellations and each time there is a new government recommendation it is to discourage flying. Demand is drying up in ways that are completely unprecedented. Normality is not yet on the horizon," it said.

India's largest airline IndiGo -- which has around 260 planes in its fleet -- said on Thursday that it has seen a decline of 15-20 per cent in daily bookings in the last few days.

The low-cost carrier had stated that it expects its quarterly earnings to be materially impacted due to such decline.

CAPA said the failure to coordinate the future will result in protectionism and much less competition.

"The alternative does not bear thinking about. An unstructured and nationalistic outcome will not be survival of the fittest.

"It will mostly consist of airlines that are the biggest and the best-supported by their governments. The system will reek of nationalism. And it will not serve the needs of the 21st century world. That is not a prospect that any responsible government should be prepared to contemplate," the consultancy firm said.