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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.

Geneva, May 27: The number of confirmed cases of COVID-19 worldwide has increased by nearly 100,000 over the past 24 hours to surpass 5.4 million, the World Health Organisation (WHO) said.

According to the WHO, the global case tally currently stands at 5,404,512 -- a rise by 99,780 over the past day.

The death count worldwide amounts to 343,514 -- an increase by 1,486.

Most cases of infection are recorded in the Americas -- 2,454,452, with 143,739 deaths.

Pentagon, Jan 25: Thirty-four US troops had been diagnosed with concussions and traumatic brain injury (TBI) as a result of the January 8 Iranian missile attack on two military bases in Iraq housing American soldiers, the Pentagon said.

"Eight service members who were previously transported to Germany have been brought to the US, they would continue to receive treatment in the US either at Walter Reed or their home bases," Pentagon spokesman Jonathan Hoffman told the media on Friday.

Hoffman said that nine service members were still undergoing treatment in Germany, and the rest of the 17 injured troops have already returned to duty in Iraq, reports Xinhua news agency.

Lat week, the US military had said that 11 service members were treated for concussion symptoms due to the missile attacks.

Hoffman noted that the symptoms "are late developing and manifested over a period of time".

In retaliation for the killing of Iranian Major General Qasem Soleimani in an American drone attack on January 3 in Baghdad, Tehran launched over 13 ballistic missiles on the two military bases in Anbar and near the city of Erbil.

US military initially said that no casualty was reported from the Iranian attack. President Donald Trump then downplayed the seriousness of those injures.

"I heard that they had headaches and a couple of other things, but I would say and I can report that it's not very serious," Trump told reporters on Wednesday at a press conference in Davos, Switzerland.

More than 5,000 US troops are deployed in Iraq to support the country's forces in the battle against Islamic State militants.