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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.

Seoul, Jul 26: North Korean authorities have imposed a lockdown on the border city of Kaesong after discovering what they called the country's first suspected case of the novel coronavirus, state media reported Sunday.

Leader Kim Jong Un convened an emergency politburo meeting on Saturday to implement a "maximum emergency system and issue a top-class alert" to contain the virus, official news agency KCNA said.

If confirmed, it would be the first officially recognised COVID-19 case in the North where medical infrastructure is seen as woefully inadequate for dealing with any epidemic.

KCNA said a defector who had left for the South three years ago returned on July 19 after "illegally crossing" the heavily fortified border dividing the countries.

But there have been no reports in the South of anyone leaving through what is one of the world's most secure borders, replete with minefields and guard posts.

Pyongyang has previously insisted not a single case of the coronavirus had been seen in the North despite the illness having swept the globe, and the country's borders remain closed.

The patient was found in Kaesong City, which borders the South, and "was put under strict quarantine", as would anybody who had come in close contact, state media said.

It was a "dangerous situation... that may lead to a deadly and destructive disaster", the media outlet added.

Kim was quoted as saying "the vicious virus could be said to have entered the country", and officials on Friday took the "preemptive measure of totally blocking Kaesong City".

The nuclear-armed North closed its borders in late January as the virus spread in neighbouring China and imposed tough restrictions that put thousands of its people into isolation, but analysts say the North is unlikely to have avoided the contagion.

South Korea is currently recording around 40 to 60 cases a day.

Earlier this month Kim warned against any "hasty" relaxation of anti-coronavirus measures, indicating the country will keep its borders closed for the foreseeable future.

New Delhi, May 11: Former prime minister Manmohan Singh is stable and under observation at the AIIMS here after suffering reaction to a new medication and developing fever, hospital sources said on Monday.

The 87-year-old Congress leader was admitted to the hospital on Sunday evening after he complained of uneasiness. He has now been shifted out of the ICU.

The sources said that Singh had developed a reaction to a new medication and further investigation is being carried on him to rule out other causes of fever.

"Dr Manmohan Singh was admitted for observation and investigation after he developed a febrile reaction to a new medication," the sources said.

"He is being investigated to rule out other causes of fever and is being provided care as needed. He is stable and under care of a team of doctors at the Cardiothoracic Centre of AIIMS," they said.

"All his parameters are fine. He is under observation at the AIIMS," a source close to him has said.

Singh, a senior leader of the opposition Congress, is currently a Member of Rajya Sabha from Rajasthan. He was the prime minister between 2004 and 2014.

In 2009, Singh underwent a successful coronary bypass surgery at the AIIMS. A number of leaders expressed have expressed concern over his health and wished him a speedy recovery.