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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.

Beijing, Feb 18: Police in China have arrested a prominent activist who had been a fugitive for weeks and criticised President Xi Jinping's handling of the coronavirus epidemic while in hiding, a rights group said Tuesday.

Anti-corruption activist Xu Zhiyong was arrested on Saturday after being on the run since December, according to Amnesty International.

China's ruling Communist Party has severely curtailed civil liberties since Xi took power in 2012, rounding up rights lawyers, labour activists and even Marxist students.

The death this month of a whistleblowing doctor who was reprimanded by police for raising the alarm about the deadly new virus before dying of it himself triggered rare calls for political reform and freedom of speech.

The "Chinese government's battle against the coronavirus has in no way diverted it from its ongoing general campaign to crush all dissenting voices," said Patrick Poon, China researcher at Amnesty International, in an emailed statement.

Another source, who spoke to news agency on the condition of anonymity, said Xu had been arrested in the southern city of Guangzhou.

Guangzhou police did not respond to requests for comment.

Xu went into hiding after authorities broke up a December gathering of intellectuals discussing political reform in the eastern coastal city of Xiamen in Fujian province, prior to the coronavirus crisis.

Over a dozen lawyers and activists were detained or disappeared after the Xiamen gathering, according to rights groups -- and Xu's detention appears linked to his presence at the meeting, explained Poon.

But while on the run, Xu continued to post information on Twitter about rights issues.

On February 4 Xu released an article calling on Xi to step down and criticised his leadership across a range of issues including the US-China trade war, Hong Kong's pro-democracy protests and the coronavirus epidemic, which has now killed nearly 1,900 people.

"Medical supplies are tight, hospitals are filled with patients, and a large number of infected people have no way to be diagnosed," he wrote. "It's a mess."

"The coronavirus outbreak shows just how important values like freedom of expression and transparency are -- the exact values that Xu has long advocated," Yaqiu Wang, China researcher at Human Rights Watch, told news agency.

But the disappearance of Xu illustrates how the Chinese state "persists in its old ways" by "silencing its critics", she said.

Xu -- who founded a movement calling for greater transparency among high-ranking officials -- previously served a four-year prison sentence from 2013 to 2017 for organising an "illegal gathering".

"That he was a fugitive for so many days while continuing to speak out, that in itself was... a kind of challenge to (Chinese authorities)," said Hua Ze, a long-time friend of Xu who told AFP she lost contact with the Chinese activist on Saturday morning.

London, May 12: British Prime Minister Boris Johnson has warned that a mass vaccine for the novel coronavirus may be over a year away and, in the worst-case scenario, may in fact never be found.

In his foreword to the government’s new 50-page guidance on a step by step easing of the lockdown measures in place to control the spread of the deadly virus, the UK prime minister lays out plans for businesses to gradually start reopening with “COVID-19 Secure” measures of social distancing and for the public to use “good solid British common sense” as the economy is unlocked.

“A mass vaccine or treatment may be more than a year away,” said Johnson, highlighting the work being done in the UK by scientists at Oxford University and Imperial College London towards this mission.

“Indeed, in a worst-case scenario, we may never find a vaccine. So our plan must countenance a situation where we are in this, together, for the long haul, even while doing all we can to avoid that outcome,” he said.

Admitting that a vaccine or drug-based treatment is the only “feasible long-term solution”, he said the UK has accelerated this with “promising” vaccine development programmes and a collaboration between Oxford University and pharma major AstraZeneca was a vital step that could help rapidly advance the manufacture of a Covid-19 vaccine when it is ready.

As part of global efforts, he flagged the GBP 388 million in aid funding for research into vaccines, tests and treatment, including GBP 250m to the Coalition for Epidemic Preparedness Innovations.

“But while we hope for a breakthrough, hope is not a plan,” he said, as he unveiled his plan for starting to lift lockdown restrictions from this week in phases.

Following a televised address to the nation on Sunday night and a statement in Parliament on Monday, the guidance comes into effect in public life across England from Wednesday when people will be allowed one-to-one contact with people other than those they live with, as long as they remain outside and two metres apart.

They are allowed to play sport with a friend or family member from outside their household or socialise with them in the open air for the first time in more than six weeks since the lockdown was imposed.

People are still advised to work from home where possible but start heading into work where necessary, in sectors such as construction and manufacturing, keeping the social distancing norms in place.

Under the step by step plan, by the start of next month non-essential shops will also reopen, with some hairdressers, pubs and cinemas to follow from July. However, as part of a Covid-19 Alert System, if infection rates are seen to be rising again, restrictions would be tightened “possibly at short notice”.

Fines for breaching the new rules will also be increased to GBP 100 and will double for each repeat offence, up to a maximum of GBP 3,200.

Johnson said: "I must ask the country to be patient with a continued disruption to our normal way of life, but to be relentless in pursuing our mission to build the systems we need. The worst possible outcome would be a return to the virus being out of control – with the cost to human life, and – through the inevitable re-imposition of severe restrictions – the cost to the economy. We must stay alert, control the virus, and in doing so, save lives.

“Then, as vaccines and treatment become available, we will move to another new phase, where we will learn to live with Covid-19 for the longer term without it dominating our lives.”

The devolved administrations of Scotland and Wales are putting their own measures in place and keeping the “stay at home” message in place, rather than switch to the new “stay alert” message.

The UK government’s latest messaging has come under attack from the Opposition and other sections of society over a feared lack of clarity for the general public.