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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 7: No country in the world says everybody is welcome, External Affairs Minister S Jaishankar said on Saturday, hitting out at those criticising India over the Citizenship (Amendment) Act.

Jaishankar criticised the United Nations Human Rights Council (UNHRC) for its criticism on the situation in Jammu and Kashmir, saying its director had been wrong previously too and one should look at the UN body's past record on handling the Kashmir issue.

"We have tried to reduce the number of stateless people through this legislation. That should be appreciated," he said when asked about the CAA at the ET Global Business Summit. "We have done it in a way that we do not create a bigger problem for ourselves."

"Everybody, when they look at citizenship, have a context and has a criterion. Show me a country in the world which says everybody in the world is welcome. Nobody says that," the minister said.

The external affairs minister said moving out of the Regional Comprehensive Economic Partnership (RCEP) was in the interest of India's business.

Asked about the UNHRC director not agreeing with India on the Kashmir issue, Jaishankar said: "UNHRC director has been wrong before.

"UNHRC skirts around cross-border terrorism as if it has nothing to do with country next door. Please understand where they are coming from; look at UNHRC's record how they handled Kashmir issue in past," he added.

New Delhi, Mar 27: Prime Minister Narendra Modi on Friday described British premier Boris Johnson as a "fighter" and hoped he recovers from coronavirus infection.

"Dear PM @BorisJohnson, you're a fighter and you will overcome this challenge as well," Modi tweeted.

He said he prays for his good health and extends best wishes in ensuring a healthy UK.

Johnson said on Friday that he has tested positive for coronavirus after experiencing mild symptoms and is now self-isolating at 10 Downing Street in line with the medical advice.

"I am now self-isolating, but I will continue to lead the government's response via video-conference as we fight this virus," he said.