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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.

Meerut, Jan 8: Hangman Pawan Jallad, who officials say is being considered to carry out the execution of the four Nirbhaya gangrape case convicts, on Tuesday said he is ready for the job which will send out a strong message in the society.

He said executing those who were involved in the horrific crime will bring "great relief" to him, Nirbhaya's parents and everybody else.

Earlier in the day, a Delhi court issued death warrants against all the four convicts in the Nirbhaya gangrape-murder case and ordered that they are hanged on January 22 at 7 am in Tihar jail.

The death warrant, also known as a black warrant, addressed to the office of the Tihar jail chief, was issued by Additional Sessions Judge Satish Kumar Arora against Mukesh (32), Pawan Gupta (25), Vinay Sharma (26) and Akshay Kumar Singh (31).

"I do not have any information regarding the execution, nobody has spoken to me yet. If anyone approaches me, I am ready to do the job. Earlier, I was asked to be ready for the execution on December 16," Pawan Jallad told reporters here.

"Those who were involved in this brutal incident must be hanged, which will send out a strong message in the society," he said.

"Hanging the Nirbhaya gangrape case convicts will certainly bring great relief to me, her parents and everybody else," he added.

Nirbhaya, a 23-year-old paramedic student, was gang-raped and brutalised on the intervening night of December 16-17, 2012, inside a moving bus in south Delhi by the four men, along with two others, before being dumped on the road.

She died on December 29, 2012, at Mount Elizabeth Hospital in Singapore.

Of the six persons convicted, one allegedly committed suicide in jail and another, a juvenile, was released from a reformation home after serving a three-year term.

When contacted, Jail Superintendent of Meerut prison V P Pandey said he has not yet received any letter from Tihar authorities.

"Last month, we had received a letter asking us to keep Pawan Jallad ready but there is no fresh communication. The Delhi court warrants were issued this evening, maybe we will get the letter for sending him by tomorrow (Wednesday)," he said.

The gangrape of 23-year-old, who came to be known as 'Nirbhaya', the fearless one, sparked outrage across the country. Repulsed, people took to the streets across the country, demanding justice for her and better safety measures for women.

The case led to toughening of India's rape laws.