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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.

New Delhi, Feb 10: A 44-year-old man allegedly killed his daughter and son before ending his life by jumping in front of a Delhi metro train at Haiderpur Badli Mor station on Sunday, police said.

No suicide note has been recovered, but police claimed that the man, Madhur Malani, was depressed since his sandpaper-manufacturing factory was closed some six months ago due to financial crunch leaving him jobless. Madhur's parents had been supporting his family financially since then.

He used to stay with his wife Rupali, daughter Samiksha (14) and six-year-old son Shraiyans at a rented house in northwest Delhi's Shalimar Bagh area, they said.

Rupali was not at home when Madhur strangled their children. He might have also smothered their daughter but the exact cause of death would be ascertained only after the post-mortem reports arrive, a police official said.

After killing his two children, he jumped in front of an approaching train at Haiderpur Badli Mor Metro station following which he was rushed to a hospital where doctors declared him 'brought dead', the official said.

Metro services on the Yellow Line were briefly delayed due to the incident.

"Delay in services from Samaypur Badli to GTB Nagar due to a passenger on track at Haiderpur Badli Mor," the Delhi Metro Rail Corporation (DMRC) tweeted.

After about 15 minutes, it again tweeted that normal services have been restored. The Delhi Metro's Yellow Line connects Samaypur Badli in Delhi to HUDA City Centre in Gurgaon.

The suicide was reported to the police around 5.40 pm while the Shalimar Bagh Police station received a call about the killings around 6.50 pm.

On reaching the house, police found bodies of the children lying in beds in two rooms. During enquiry, it was learnt that their father has left the house, a senior police officer said.

While police were trying to trace Madhur, they learnt about a suicide at the metro station. On verifying the details, it surfaced that Madhur committed suicide after killing his children, the officer said.

Rupali told police that she had gone to a nearby market around 3 pm and on returning home she found the bodies of her children while her husband was missing.

A case under relevant sections of the IPC has been registered and investigation was underway, Deputy Commissioner of Police (Northwest) Vijayanta Arya said.