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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.

May 12: Gunmen stormed a hospital on Tuesday in an ongoing attack in the Afghan capital Kabul, as a suicide blast killed 15 people at a funeral in the country's restive east.

Special forces rescued 80 people including mothers and babies from the Kabul hospital after three gunmen launched a morning assault, killing at least four people, the interior ministry said in a statement.

Heavily armed forces were seen carrying babies wrapped in blankets away from the scene, as the clearance operation continued.

The facility, which has a large maternity ward, is located in the west of the city, home to the capital's minority Shiite Hazara community -- a frequent target of Sunni militants from the Islamic State group.

The flare-up in violence comes as Afghanistan grapples with myriad crises including a rise in militant operations across the country and a surge in coronavirus infections.

A paediatrician who fled the hospital told AFP he heard a loud explosion at the entrance of the building.

"The hospital was full of patients and doctors, there was total panic inside," he said, asking not to be named.

The maternity services at the hospital are supported by humanitarian organisation Doctors Without Borders (MSF).

"Hospitals and health workers must not be attacked. We call on all sides to stop attacking hospitals and health workers," said deputy health minister in the city, Waheed Majroh.

Around an hour later, a suicide bomber killed at least 15 people at the funeral of a local police commander in the country's eastern Nangarhar province, according to provincial spokesman Ataullah Khogyani.

The attacker detonated his explosives in the middle of the ceremony.

Zaher Adel, spokesman for the government hospital in Jalalabad, earlier said 12 bodies had arrived from the blast site and more than 50 people were being treated for injuries.

Amir Mohammad, who was wounded in the blast, said thousands of people had gathered for the funeral, an event which often draws huge crowds in Afghanistan.

The violence comes just a day after four roadside bombs exploded in a northern district of Kabul, wounding four civilians including a child.

The bombings were later claimed by the Islamic State group, according to the SITE intelligence group.

They were just the latest in a string of IS attacks on the capital.

In March, at least 25 people were killed by a gunman at a Sikh temple in Kabul, which was later claimed by the group.

IS is also responsible for an infamous attack in March 2017 on one of the country's largest hospitals, when gunmen disguised as doctors stormed the Kabul building and killed dozens.

In recent months, the jihadist group has suffered mounting setbacks after being hunted by US and Afghan forces as well as Taliban offensives targeting their fighters, but it still retains the ability to launch major assaults on urban centres.

The Taliban have largely refrained from launching large attacks on Afghan cities since February when they signed a landmark withdrawal deal with the US meant to pave the way for peace talks with the Kabul government.

Under the agreement, the Taliban promised not to target forces from the US-led coalition, but made no such pledge toward Afghan troops and have stepped up attacks in the provinces.

The Taliban have denied involvement in both of Tuesday's attacks.

Mexico City, Jun 13: The number of people, who have died of COVID-19 in Mexico, has risen by 544 to 16,448 within the past 24 hours, Jose Luis Alomia, the director of epidemiology at the Health Ministry, said.

He also said on late Friday that the number of confirmed coronavirus cases had increased by 5,222 to 139,196 within the same period of time.

A day earlier, the Latin American nation has recorded 4,790 new confirmed cases of the coronavirus, with 587 fatalities.

The World Health Organization declared the COVID-19 outbreak a pandemic on March 11. To date, more than 7.6 million people have been infected with the coronavirus worldwide, with over 425,000 fatalities, according to Johns Hopkins University.