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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.

Shanghai, Jun 13: Authorities in Beijing have temporarily shut a major wholesale agricultural market following a rise in locally transmitted novel coronavirus infections in China's capital city over the past two days.

The closure of the Xinfadi wholesale market at 3 a.m. local time on Saturday (1900 GMT on Friday), came after two men working at a meat research centre who had recently visited the market were reported on Friday as having been infected by the novel coronavirus. It was not immediately clear how the men had been infected.

Concern is growing of a second wave of the new virus, even in many countries that seemed to have curbed its spread. It was first reported at a seafood market in Wuhan, the capital of central China's Hubei province, in December.

Beijing authorities had earlier halted beef and mutton trading at the Xinfadi market, alongside closures at other wholesale markets around the city.

Reflecting concerns over the risk of further spread of the virus, major supermarkets in Beijing removed salmon from their shelves overnight after the virus causing COVID-19 was discovered on chopping boards used for imported salmon at the market, the state-owned Beijing Youth Daily reported.

Beijing authorities said more than 10,000 people at the market will take nucleic acid tests to detect coronavirus infections. The city government also said it had dropped plans to reopen schools on Monday for students in grades one through three because of the new cases.

Health authorities visited the home of a Reuters reporter in Beijing's Dongcheng district on Saturday to ask whether she had visited the Xinfadi market, which is 15 km (9 miles) away. They said the visit was part of patrols Dongcheng was conducting.

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China reported 11 new COVID-19 cases and seven asymptomatic cases for Friday, the national health authority said on Saturday. And all six locally transmitted cases were confirmed in Beijing.

Washington, Jul 21: Democrat Joe Biden urged Muslim Americans on Monday to join him in the fight to defeat President Donald Trump as he addressed an online summit hosted by the advocacy organisation Emgage Action to mobilise Muslim voters ahead of the presidential election.

I want to earn your vote not just because he's not worthy of being president, the presumptive presidential nominee told participants.

I want to work in partnership with you, make sure your voices are included in the decision-making process as we work to rebuild our nation.

Biden also reiterated a pledge to overturn a Trump administration ban on travelers from several predominantly Muslim countries, calling it vile.

Wa'el Alzayat, CEO of Emgage Action, said by email that the organisation was seeking to maximise Muslim American turnout in key battleground states.

In Michigan alone one of the states where the organisation has chapters and where Trump won in 2016 by fewer than 11,000 votes he said he believed there are more than 150,000 registered Muslim voters.

Several prominent Muslim American elected officials endorsed Biden for president in a letter organised by Emgage Action ahead of the summit.

Among those who signed the letter are Minnesota Rep. Ilhan Omar, Minnesota Attorney General Keith Ellison and Indiana Rep. Andre Carson, all Democrats.

Omar, one of the first Muslim women elected to Congress, served as a high-profile surrogate for Bernie Sanders before he exited the presidential race in April making her support for Biden potentially helpful as the former vice president seeks to mobilise Muslim voters this fall.

Muslim American voices matter to our communities, to our country, Biden said.

But we all know that your voice hasn't always gotten recognised or represented.

Emgage Action has titled the event Million Muslim Votes, underscoring its emphasis on boosting Muslim turnout in November.

Joe Biden's presence serves not only to galvanise Muslim Americans to cast their ballots, but to usher in an era of engaging with Muslim American communities under a Biden administration, Alzayat said by email before the summit.

The pro-Biden letter from Muslim American elected officials decried a number of Trump's domestic and international policies, including his administration's travel ban and his pullout from the Iran nuclear deal.

A Biden administration will move the nation forward on many of the issues we care about, the letter said, citing racial justice, affordable health care, climate change and immigration.

The Muslim American officials also praised Biden's agenda for their communities.

Among other goals, Biden has vowed to rescind the travel ban affecting Muslims on Day One if he's elected.

In his address, he pledged to include Muslim American voices in his administration, if elected, and to speak out against human rights abuses against Muslim minorities around the world.

I'll continue to champion the rights of Palestinians and Israelis to have a state of their own as I have for decades, each of them a state of their own, he said.

Other state- and local-level Muslim American officials signing onto the pro-Biden letter hail from several states, including Michigan.