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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.

Washington, Jul 9: The United States recorded 55,000 new coronavirus cases in 24 hours on Wednesday (Thursday in Malaysia), a tally by Johns Hopkins University showed, bringing its total to 3,046,351 recorded infections since the pandemic began.

The country, the hardest-hit in the world, had earlier on Wednesday passed the grim milestone of three million infections. The actual number is likely far higher due to issues over getting tested in March and April.

The US also added an additional 833 virus deaths, bringing the death toll to 132,195, the Baltimore-based institution showed at 8.30pm (0030 GMT Thursday).

US President Donald Trump regularly downplays the numbers, attributing them to an increase in testing capacity during the month of June.

Coronavirus cases are surging in several southern hotspots including Texas, Florida, Louisiana and Arizona, but the pandemic has almost entirely receded from its former epicentre in New York and the north-east.

Several states have been forced to suspend their reopening processes or even reverse course, with some ordering bars to close again.

On Wednesday morning, Trump called on schools throughout the country to reopen in the fall, lashing out at his own top health agency to ease health and safety requirements aimed at slowing the spread of the virus, such as social distancing.

The Japan government on Monday decided to lift the state of emergency for COVID-19 in Tokyo and four other prefectures of the country, the only places where the measure implemented to curb the pandemic had remained in force.

The lifting of the alert was backed by the coronavirus advisory panel and will be formally approved by the government later day, the economic revitalization minister and head of the working group to coordinate Japan's fight against COVID-19, Yasutoshi Nishimura, said.

The Japanese authorities made the decision after taking into account the number of infections and the situation of the health system in Tokyo, the three neighbouring prefectures of Chiba, Kanagawa and Saitama and the northern Hokkaido, the only ones where the state of emergency declared more than a month ago to control the pandemic remained in effect, reports Efe news.

The health alert was initially declared in Tokyo and six other prefectures on April 17 and subsequently extended across the country.

It allowed local authorities to ban large-scale public events and close bars and restaurants at night, among other measures, while the government has launched a campaign to encourage teleworking and staying at home.

The government resorted to this measure for the first time in the country's recent history to contain the spread of the virus and is now withdrawing it after a sustained slowdown in infections throughout the archipelago, where around 16,600 confirmed COVID-19 cases and 839 deaths have been recorded, according to the latest data.

The group of experts advising the government appreciated the efforts made by citizens to comply with the recommendations to achieve the target of reducing interpersonal contact by 80 percent, top government spokesperson Yoshihide Suga said at a press conference on Monday.

The recommendation for citizens to avoid unnecessary trips outside and the request for non-essential businesses to close were not mandatory nor accompanied by fines or other penalties for non-compliance, unlike the stricter containment measures implemented in other countries.

The government plans to formally approve the lifting of the state of emergency on Monday after consulting with other political parties in parliament and another meeting with the advisory panel, following which Japanese Prime Minister Shinzo Abe will hold a press conference.

The government had already decided to lift the emergency in 39 prefectures on May 14 after they reported a marked decrease in the number of infections, leaving out the more populated regions such as Tokyo and Osaka.

To avoid new outbreaks of the virus, Abe has urged people to become accustomed to a "new lifestyle" that includes maintaining social distancing, the use of masks outside as well as a series of guidelines for the reopening of shops, restaurants and public facilities.