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Washington, Jan 12: US president Donald Trump said Saturday the United States was monitoring Iranian demonstrations closely, warning against any new “massacre” as protests broke out after Tehran admitted to shooting down a passenger plane.

Iran said earlier it unintentionally downed a Ukrainian jetliner outside Tehran, killing all 176 people aboard, in an abrupt about-turn after initially saying that it had crashed due to mechanical failure. The firing came shortly after Iran launched missiles at bases in Iraq housing American forces.

President Hassan Rouhani said a military probe into the tragedy had found that “missiles fired due to human error” brought down the Boeing 737, calling it an “unforgivable mistake.”

Trump told Iranians -- in tweets in both English and Farsi -- that he stands by them and is monitoring the demonstrations.

“To the brave, long-suffering people of Iran: I've stood with you since the beginning of my Presidency, and my Administration will continue to stand with you,” he tweeted.

“There can not be another massacre of peaceful protesters, nor an internet shutdown. The world is watching,” he added, apparently referring to an Iranian crackdown on street protests that broke out in November.

“We are following your protests closely, and are inspired by your courage," he said.

The new demonstrations follow an Iranian crackdown on street protests that broke out in November. Amnesty International has said it left more than 300 people dead. Internet access was reportedly cut off in multiple Iranian provinces ahead of memorials planned a month after the protests.

On Saturday evening, police dispersed students who had converged on Amir Kabir University in Tehran to pay tribute to the victims, after some among the hundreds gathered shouted "destructive" slogans, Fars news agency said.

State television reported that students shouted "anti-regime" chants, while the news agency Fars reported that posters of Soleimani had been torn down.

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, Jan 3: US President Donald Trump ordered the killing of Iran Revolutionary Guards commander Qasem Soleimani, who died in Baghdad "in a decisive defensive action to protect US personnel abroad," the Pentagon said Thursday.

"General Soleimani was actively developing plans to attack American diplomats and service members in Iraq and throughout the region. General Soleimani and his Quds Force were responsible for the deaths of hundreds of American and coalition service members and the wounding of thousands more," the Department of Defense said.

Following Soleimani's death, Trump tweeted an image of the US flag without any further explanation.

"US' act of international terrorism, assassinating General Soleimani—the most effective force fighting Daesh (ISIS), Al Nusrah,Al Qaeda, is extremely dangerous & foolish escalation. US bears responsibility for all consequences of rogue adventurism." said Iran Foreign Minister Javad Zarif.