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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, Jun 17: Beijing's airports cancelled more than 1,200 flights and schools in the Chinese capital were closed again on Wednesday as authorities rushed to contain a new coronavirus outbreak linked to a wholesale food market.

The city reported 31 new cases on Wednesday while officials urged residents not to leave Beijing, with fears growing about a second wave of infections in China, which had largely brought its outbreak under control.

Tens of thousands of people linked to the new Beijing virus cluster -- believed to have started in the sprawling Xinfadi wholesale food market -- are being tested, with almost 30 residential compounds in the city now under lockdown.

At least 1,255 scheduled flights were cancelled Wednesday morning, state-run People's Daily reported, nearly 70 percent of all trips to and from Beijing's main airports.

The outbreak had already forced authorities to announce a travel ban for residents of "medium- or high-risk" areas of the city, while requiring other residents to take nucleic acid tests in order to leave Beijing.

Meanwhile, several provinces were quarantining travellers from Beijing, where all schools -- which had mostly reopened -- have been ordered to close again and return to online classes.

"The epidemic situation in the capital is extremely severe," Beijing city spokesman Xu Hejian warned Tuesday.

Mass testing under way

Officials have closed 11 markets and disinfected thousands of food and beverage businesses in Beijing after the outbreak was detected.

The city has now reported 137 infections over the last six days, with six new asymptomatic cases and three suspected cases on Wednesday, according to the municipal health commission.

An additional two domestic cases, one in neighbouring Hebei province and another in Zhejiang, were reported by national authorities on Wednesday, while there were 11 imported cases.

Authorities have so far banned group sports, ordered people to wear masks in crowded enclosed spaces, and suspended inter-provincial group tours in response to the outbreak.

Officials said that since May 30, more than 200,000 people had visited Xinfadi market, which supplies more than 70 percent of Beijing's fruit and vegetables.

More than 8,000 workers there were tested and quarantined.

Until the new outbreak, most of China's recent cases were nationals returning from abroad as COVID-19 spread globally, and the government had all but declared victory against the disease.

China's Center for Disease Control and Prevention said Monday that the virus type found in the Beijing outbreak was a "major epidemic strain" in Europe.

Apr 12: India and other South Asian countries are likely to record their worst growth performance in four decades this year due to the coronavirus outbreak, the World Bank said on Sunday.

The South Asian region, comprising eight countries, is likely to show economic growth of 1.8 per cent to 2.8 per cent this year, the World Bank said in its South Asia Economic Focus report, well down from the 6.3 per cent it projected six months ago.

India's economy, the region's biggest, is expected to grow 1.5 per cent to 2.8 per cent in the fiscal year that started on April 1. The World Bank has estimated it will grow 4.8 per cent to 5 per cent in the fiscal year that ended on March 31.

"The green shoots of a rebound that were observable at the end of 2019 have been overtaken by the negative impacts of the global crisis," the World Bank report said.

Other than India, the World Bank forecast that Sri Lanka, Nepal, Bhutan and Bangladesh will also see sharp falls in economic growth.

Three other countries - Pakistan, Afghanistan and the Maldives - are expected to fall into recession, the World Bank said in the report, which was based on country-level data available as of April 7.

Measures taken to counter the coronavirus have disrupted supply chains across South Asia, which has recorded more than 13,000 cases so far - still lower than many parts of the world.

India's lockdown of 1.3 billion people has also left millions out of work, disrupted big and small businesses and forced an exodus of migrant workers from the cities to their homes in villages.

In the event of prolonged and broad national lockdowns, the report warned of a worst-case scenario in which the entire region would experience an economic contraction this year.

To minimize short-term economic pain, the Bank called for countries in the region to announce more fiscal and monetary steps to support unemployed migrant workers, as well as debt relief for businesses and individuals.

India has so far unveiled a $23 billion economic plan to offer direct cash transfers to millions of poor people hit by its lockdown. In neighbouring Pakistan, the government has announced a $6 billion plan to support the economy.

"The priority for all South Asian governments is to contain the virus spread and protect their people, especially the poorest who face considerable worse health and economic outcomes," said senior World Bank official Hartwig Schafer.