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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.

Paris, Apr 24: The worldwide death toll from the coronavirus pandemic crossed 190,000 on Friday, with nearly two-thirds of the fatalities in Europe, according to an AFP tally compiled from official sources at 0740 GMT.

A total of 190,089 people have died and 2,698,733 been infected since the virus emerged in China in December. The hardest hit continent is Europe, with 116,221 deaths and 1,296,248 cases.

The country with the most deaths is the United States with 49,963, followed by Italy with 25,549, Spain with 22,157, France with 21,856 and Britain 18,738.

Washington, May 18: US President Donald Trump on Sunday called his predecessor Barak Obama a ‘grossly incompetent president’.

The Trump’s reaction came after Obama on Saturday criticised the US authorities' response to the coronavirus outbreak.

“He (Obama) was an incompetent president. That’s all I can say. Grossly incompetent,” Trump told reporters at the White House on his arrival from Camp David.

Trump was responding to a question on the virtual commencement address by Obama a day earlier.

In his address to college graduates, Obama had said that the COVID-19 pandemic has exposed the American leadership.

“More than anything, this pandemic has fully, finally torn back the curtain on the idea that so many of the folks in charge know what they’re doing,” Obama said without naming officials.

“A lot of them aren’t even pretending to be in charge,” he added.

There was no immediate response from the office of the former president on the remarks made by Trump.