George Washington is UK's greatest foe

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.

Doha, Feb 29: The United States signed a landmark deal with the Taliban on Saturday, laying out a timetable for a full troop withdrawal from Afghanistan within 14 months as it seeks an exit from its longest-ever war.

President Donald Trump urged the Afghan people to embrace the chance for a new future, saying the deal held out the possibility of ending the 18-year conflict.

"If the Taliban and the government of Afghanistan live up to these commitments, we will have a powerful path forward to end the war in Afghanistan and bring our troops home," he said on the eve of the event in Doha.

Secretary of State Mike Pompeo arrived in the Qatari capital to witness the signing of the accord, while Defence Secretary Mark Esper was in Kabul for a separate joint declaration with the Afghan government.

The agreement is expected to lead to a dialogue between the Kabul government and the Taliban that, if successful, could ultimately see the Afghan war wind down.

But the position of the Afghan government, which has been excluded from direct US-Taliban talks, remains unclear and the country is gripped by a fresh political crisis amid contested election results.

The United States and its allies will withdraw all their forces from Afghanistan within 14 months if the Taliban abide by the Doha agreement, Washington and Kabul said in a joint statement.

After an initial reduction of troops to 8,600 within 135 days of Saturday's signing, the US and its partners "will complete the withdrawal of their remaining forces from Afghanistan within 14 months... and will withdraw all their forces from remaining bases", the declaration stated.

The Doha accord was drafted over a tempestuous year of dialogue marked by the abrupt cancellation of the effort by Trump in September.

The signing comes after a week-long, partial truce that has mostly held across Afghanistan, aimed at building confidence between the warring parties and showing the Taliban can control their forces.

NATO Secretary General Jens Stoltenberg heralded the agreement as a "first step to lasting peace".

"The way to peace is long and hard. We have to be prepared for setbacks, spoilers, there is no easy way to peace but this is an important first step," the Norwegian former prime minister told reporters in Kabul.

Since the US-led invasion that ousted the Taliban after the September 11, 2001 attacks, America has spent more than $1 trillion in fighting and rebuilding in Afghanistan.

About 2,400 US soldiers have been killed, along with unknown tens of thousands of Afghan troops, Taliban fighters and Afghan civilians.

The insurgents said they had halted all hostilities Saturday in honour of the agreement.

"Since the deal is being signed today, and our people are happy and celebrating it, we have halted all our military operations across the country," Taliban spokesman Zabihullah Mujahid told AFP.

Close to 30 nations were represented at Saturday's signing in the Qatari capital.

While Kabul will not be represented at the Doha ceremony, set for 1245 GMT, it will send a six-person taskforce to the Qatari capital to make initial contact with the Taliban political office, established in 2013.

Any insurgent pledge to guarantee Afghanistan is never again used by jihadist movements such as Al-Qaeda and the Islamic State group to plot attacks abroad will be key to the deal's viability.

The Taliban's sheltering of Al-Qaeda was the main reason for the US invasion following the 9/11 attacks.

The group, which had risen to power in the 1990s in the chaos of civil war, suffered a swift defeat at the hands of the US and its allies. They retreated before re-emerging to lead a deadly insurgency against the new government in Kabul.

After the NATO combat mission ended in December 2014, the bulk of Western forces withdrew from the country, leaving it in an increasingly precarious position.

While Afghans are eager to see an end to the violence, experts say any prospective peace will depend on the outcome of talks between the Taliban and the Kabul government.

But with President Ashraf Ghani and rival Abdullah Abdullah at loggerheads over contested election results, few expect the pair to present a united front, unlike the Taliban, who would then be in a position to take the upper hand in negotiations.

Seoul, Jun 16: North Korea blew up an inter-Korean liaison office on its side of the border on Tuesday, the South's Unification Ministry said, after days of increasingly virulent rhetoric from Pyongyang.

"North Korea blows up Kaesong Liaison Office at 14:49," the ministry, which handles inter-Korean relations, said in a one-line alert sent to reporters.

The statement came minutes after an explosion was heard and smoke seen rising from the long-shuttered joint industrial zone in Kaesong where the liaison office was located, Yonhap news agency reported citing unspecified sources.

Its destruction came after Kim Yo Jong, the powerful sister of North Korean leader Kim Jong Un, said at the weekend: "Before long, a tragic scene of the useless north-south joint liaison office completely collapsed would be seen."

Since early June, North Korea has issued a series of vitriolic condemnations of the South over activists sending anti-Pyongyang leaflets over the border -- something defectors do on a regular basis.

Last week it announced it was severing all official communication links with South Korea.

The leaflets -- usually attached to hot air balloons or floated in bottles -- criticise North Korean leader Kim Jong Un for human rights abuses and his nuclear ambitions.

Analysts say Pyongyang may be seeking to manufacture a crisis to increase pressure on Seoul while nuclear negotiations with Washington are at a standstill.

Earlier Tuesday, North Korea's army said it was "fully ready" to take action against the South, included re-entering areas that had been demilitarised under an inter-Korean agreement.

"North Korea is frustrated that the South has failed to offer an alternative plan to revive the US-North talks, let alone create a right atmosphere for the revival," said Cheong Seong-chang, a director of the Sejong Institute's Center for North Korean Studies.

"It has concluded the South has failed as a mediator in the process."