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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, Jun 16: Jet fuel or ATF price on Tuesday was hiked by 16.3 per cent while petrol price was increased by 47 paise per litre and that of diesel by a record 93 paise on the back of firming international oil rates.

Aviation turbine fuel (ATF) price was hiked by ₹5,494.5 per kilolitre (kl), or 16.3 per cent, to ₹39,069.87 per kl in the national capital, according to a price notification by state-owned oil marketing companies.

This is the second straight increase in ATF price this month. Rates were hiked by a record 56.5 per cent (₹12,126.75 per kl) on June 1.

Simultaneously, petrol and diesel prices were hiked for the 10th day in a row.

Petrol price in Delhi was hiked to ₹76.73 per litre from ₹76.26, while diesel rates were increased to ₹75.19 a litre from ₹74.26, the price notification said.

In 10 hikes, petrol price has gone up by ₹5.47 per litre and diesel by Rs 5.8 a litre.

Rates have been increased across the country and vary from state to state depending on the incidence of local sales tax or VAT.

The hike in diesel rates is the highest daily increase since the state-owned fuel retailers started daily revision in rates in May 2017.

Hike for 10th consecutive day

Tuesday’s increase in petrol and diesel price marks the 10th straight day of rise in rates since oil companies on June 7 restarted revising prices in line with costs, after ending an 82-day hiatus.

The freeze in rates was imposed in mid-March soon after the government hiked excise duty on petrol and diesel to shore up additional finances.

Oil PSUs Indian Oil Corp (IOC), Bharat Petroleum Corp Ltd (BPCL) and Hindustan Petroleum Corp Ltd (HPCL) instead of passing on the excise duty hikes to customers adjusted them against the fall in the retail rates that was warranted because of fall in international oil prices.

The June 1 hike in jet fuel price had come after seven consecutive reductions in rates since February. ATF price in Delhi before the reduction cycle began in February was ₹64,323.76 per kilolitre, which got reduced to ₹21,448.62 last month.

Industry officials said the hike was necessitated because benchmark international rates have bounced back from a two-decade low.

While ATF prices are revised on 1st and 16th of every month, petrol and diesel prices are revised on a daily basis.

Oil companies used to revise ATF prices on the first of every month, but adopted fortnightly revisions on March 21 to pass on the benefit of falling international oil prices to airlines.