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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.

Beijing, Mar 21: China reported no domestically transmitted coronavirus cases for the third consecutive day even as seven more fatalities have been confirmed, taking the death toll in the country to 3255.

No new domestically transmitted cases of COVID-19 were reported on the Chinese mainland for the third day in a row on Friday, China's National Health Commission (NHC) said on Saturday.

The overall confirmed cases on the mainland had reached 81,008 by the end of Friday, which included 3,255 who died, 6,013 patients still undergoing treatment, 71,740 patients who had been discharged after recovery, the NHC said.

The NHC said 41 new confirmed COVID-19 cases were reported on the Chinese mainland on Friday from the people arriving from abroad, taking the total number of imported cases to 269.

Beijing, Feb 9: After making sure everyone's face mask is on and sanitizer is to hand, the Qiao family heads out to Jingshan Park, a former royal sanctuary beside the Forbidden City in China's capital Beijing.

Snow has fallen for a second day, a rare event in the city of 21.5 million that would normally bring hundreds of thousands of people out to take photos and play. But the streets are empty and the parks are so quiet the only sound is of birds chirping.

It's not just Beijing. Shanghai, China's financial hub, and other cities in the world's most populous nation have turned into ghost towns after the government extended a holiday and asked residents not to go out because of the coronavirus.

"We know the situation of the coronavirus is severe. But the epicentre is far away, so we think it should be fine here ... It's a God-given chance to enjoy this family moment with snow and without work," said Mr Qiao, who has an 11-year-old daughter.

The epidemic has killed 722 people and infected nearly 32,000 in China as of February 8. More than three-quarters of the cases are in the central Hubei province where the virus originated - more than 1,000 km (620 miles) from Beijing.

Only a few people are brave enough to come out. A security guard at Jingshan Park said there were less than a third of the number of tourists than usual, even with the rare snowfall.

Even at one of the best spots for snapping photos of snowy Beijing just outside the Forbidden City, there's barely a crowd, while the usual tour buses and groups of people speaking different dialects are nowhere to be seen.

"Last year when it snowed, I took a few hours off work to come down here to take a picture and the crowd was several layers deep," said a man in his 30s who gave his surname as Yang. "But this year, I am not at all worried about finding a space to take a photo. The virus is keeping people indoors."

Security guards along Wangfujing street, a popular pedestrianised shopping area in downtown Beijing, said it was normally so crowded during the holiday period that it was hard to move around.

"Look at it now, there are more security guards and street cleaners than tourists!" said one of the guards.

Businesses, including shops, bars and restaurants, have been severely hit by the epidemic as the government has banned mass gatherings and even group meals in an effort to curb the spread of the coronavirus.

"You would have to wait outside for a table on a normal day," said a waitress at a restaurant with more than 50 tables. Just five were taken at the peak lunch hour.

Only a handful of the more than 100 restaurants along Beijing's famous food street, Guijie, were open, and the remaining outlets were wondering how long they can hold out.