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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.

Nakhon Ratchasima, Feb 9: The Thai soldier who killed at least 20 people and holed up in a mall overnight was shot dead Sunday morning by commandos, ending a near-17-hour ordeal which left dozens wounded and stunned the country.

It was unclear how many people remained trapped inside the Terminal 21 mall in Nakhon Ratchasima -- also known as Korat -- where the gunman held out through the night, armed with assault weapons stolen from his barracks.

Volleys of gunfire rang out as the siege ran into dawn, hours after Thai security services stormed the ground floor and freed scores of stunned, terrified shoppers from a bloody rampage that the gunman -- a junior army officer identified as Sergeant-Major Jakrapanth Thomma -- had relayed via Facebook posts.

"He was shot dead thirty minutes ago" (0200 GMT), chief of the Crime Suppression Division Jirabhob Bhuridej told AFP.

Commandos from elite Thai police units killed the gunman, a police spokesman added, after an operation involving hundreds of security personnel.

"The official death toll is 20 and wounded 42... nine are in surgery," Narinrat Pitchayakamin, a Korat doctor told reporters, revising down an initial death toll of 21.

But it was unclear if there were more victims inside the multi-level complex which was packed with Saturday shoppers when the gunman stormed in.

A fleet of ambulances left the front of the complex and forensic police poured into the grim crime scene, shortly before the gunman's death was confirmed.

The night was peppered with heavy exchanges of gunfire and sporadic evacuations.

A police officer who took part in a raid to flush out the gunman died, according to deputy prime minister Anutin Charnvirakul. "He had been hit and unfortunately, he couldn't make it," said Anutin.

Shocked evacuees recounted how an ordinary Saturday shopping day at the busy mall descended into horror as the gunman entered.

"It was like a dream... I'm grateful I survived," Sottiyanee Unchalee, 48, told AFP, explaining she hid in the toilet of a gym inside the mall as she heard the gunfire.

"I'm so sorry for those who died... (and) the people still trapped inside."

Stolen weapons

Jakrapanth relayed his shooting spree through Facebook posts which charted the attack from the army barracks in the city to the mall, where an unknown number of shoppers remained trapped.

A volunteer rescue worker recounted a bloody scene of horror after his team carried four corpses to the hospital.

"I've never seen anything like this," Peerapong Chatadee told AFP.

"I just feel so sad. He is a soldier, he should not have fired at unarmed people."

The bloodshed began Saturday afternoon when Jakrapanth shot three people -- among them at least one soldier -- at a senior officer's house and then at the nearby army barracks, before driving an army vehicle to the town centre.

There the gunman used weapons stolen from the military arsenal to unleash carnage in the town centre.

He "used a machine gun and shot innocent victims resulting in many injured and dead", said police spokesman Krissana Pattanacharoen.

Throughout the day, Jakrapanth posted images of himself and wrote several posts on his Facebook page as the attack unfolded.

In one Facebook video -- since deleted -- the assailant, wearing an army helmet, filmed from an open-top jeep, saying, "I'm tired... I can't pull my finger anymore" as he made a trigger symbol with his hand.

There were also photos of a man in a ski mask holding up a pistol.

A Facebook spokesperson said: "We have removed the gunman's accounts from our services and will work around the clock to remove any violating content related to this attack as soon as we become aware of it."

The city is home to one of the largest barracks in Thailand, a country where the military is enmeshed in politics and society.

The nation also has one of the highest rates of gun ownership in the world, and several shootings at courthouses last year renewed concern about gun violence.

Houston, Jul 22: China said on Wednesday that the US has ordered it to close its consulate in Houston in what an official called an outrageous and unjustified move that will sabotage China-US relations.

Foreign ministry spokesperson Wang Wenbin condemned the action, which comes as tensions rise between the world's two largest economies. He warned of firm countermeasures if the US does not reverse its decision.

The unilateral closure of China's consulate general in Houston within a short period of time is an unprecedented escalation of its recent actions against China, Wang said at a daily news briefing.

There was no immediate confirmation or explanation from the U.S. side.

Media reports in Houston said that authorities had responded to reports of a fire at the consulate. Witnesses said that people were burning paper in what appeared to be trash cans, the Houston Chronicle reported, citing police.