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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.

Wuhan, Jan 31: The World Health Organization declared a global emergency over the new coronavirus, as China reported Friday the death toll had climbed to 213 with nearly 10,000 infections.

The UN health agency based in Geneva had initially downplayed the threat posed by the disease, but revised its risk assessment after crisis talks.

suspended or reduced service to China include British Airways, German flag carrier Lufthansa, American Airlines, KLM and United.

Chinese efforts to halt the virus have included the suspension of classes nationwide and an extension of the Lunar New Year holiday.

All football matches across the country also will be postponed, the Chinese Football Association said on Thursday, including games in the top-tier Chinese Super League.

World stock markets tumbled again Thursday on fears that trouble in the "world's factory" would upset global supply chains and dent profits.

Toyota, IKEA, Starbucks, Tesla, McDonald's and tech giant Foxconn were among the corporate giants temporarily freezing production or closing large numbers of outlets in China.

Volkswagen announced Thursday its China joint-venture plants would not start production again before February 9.

US Federal Reserve Chairman Jerome Powell said the coronavirus posed a fresh risk to the world economy.

Throughout China, signs of paranoia multiplied, with residents of some Beijing residential compounds erecting makeshift barriers to their premises.

In one of many similar photos posted online, a man wearing a surgical mask and brandishing a traditional martial arts weapon squatted on a barricade outside a Chinese village, near a sign saying: "Outsiders forbidden from entering".

The crisis has caused food prices to spike, and the central government on Thursday blamed this partly on overzealous preventive measures, issuing a directive banning any roadblocks or other hindrances to food shipments.

Washington, Mar 27: The United States has seen a record 18,000 new confirmed coronavirus cases and 345 deaths over the past 24 hours, according to a Johns Hopkins University tracker.

There are now 97,028 declared virus cases in the country and there have been 1,475 deaths, Johns Hopkins said.