At least 24 killed, 42 wounded in Kabul bombing

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.

Feb 4: Americans on Monday kicked off the first vote of the 2020 presidential race as the midwestern state of Iowa began its caucuses, the closely-watched first step in deciding which Democrat will face incumbent Donald Trump in November's election.

The two frontrunners, left-wing Senator Bernie Sanders and former Vice President Joe Biden face a key test in the sparsely populated state, with a handful of others looking to make their mark to give their campaigns momentum.

The Iowa vote is a critical early look at the viability of the 11 Democratic candidates still in the race - even though just 41 Iowa delegates are up for grabs, a fraction of the 1,991 needed to secure the party nomination in July.

Iowa Democrats filed into nearly 1,700 caucus sites - schools, libraries, churches, mosques and meeting halls with Sanders and Biden in the lead in the state, followed by former South Bend, Indiana mayor Pete Buttigieg and Senator Elizabeth Warren, who is also on the left of the party.

But polling has fluctuated and Iowa's quirky caucus system - where voting is not by secret ballot but by public declaration for a candidate - makes the night hard to predict.

Luke Elzinga, a volunteer for Sanders, appeared early at Lincoln High School in Des Moines which was converted into a caucus location.

"I think he really inspires a lot of young people, a lot of disaffected voters who might not otherwise turn out," Elzinga, 28, told AFP news agency shortly before the caucusing began.

"And so I think he's the best candidate to beat Trump."

Three candidates - Sanders, Warren and Amy Klobuchar - have faced the unprecedented scenario of spending much of the past two weeks tethered to Washington for the impeachment trial of Trump instead of on the campaign trail in Iowa.

Even as candidates sought to make 11th-hour impressions on undecided voters, the senators were obligated to return to Washington for the trial's closing arguments on Monday.

Defeating Trump

In a vote scheduled for Wednesday, Trump is almost certain to be acquitted by the Republican-led upper house on charges of abuse of power and obstruction of Congress.

For Democrats, second-tier hopefuls Klobuchar and tech entrepreneur Andrew Yang look to outpace expectations and seize momentum heading into the next contest in New Hampshire on February 11.

Earlier on Monday Biden - who still holds the lead in national polls - brought pizza to a field office in a strip mall near Des Moines to thank volunteers.

"I'm feeling good about today," he said.

Like many candidates, Biden spent the weekend crisscrossing Iowa in a final push to convince undecided voters he is best placed to accomplish Democrats' number one goal: defeating Trump.

The president has not stood idly by. On Sunday he branded Biden "Sleepy Joe" and described Sanders as "a communist," previewing a likely line of attack were Sanders to win the nomination.

Unlike secret ballot voting, caucus-goers publicly declare their presidential choice by standing together with other supporters of a candidate.

Candidates who reach 15 percent support earn delegates for the nomination race while supporters of candidates who fall short can shift their allegiance to others.

Turnout is critical, and candidates and their representatives will seek to persuade voters on issues including healthcare, taxes and ending Washington corruption.

One key candidate who has opted not to contest in Iowa is billionaire businessman Michael Bloomberg, who entered the race in November but has surged into fourth place in RealClearPolitics' national polling average.

The former New York mayor, who has spent more than $300m on advertising, according to Advertising Analytics, is focused on running a national campaign with particular emphasis on states that vote on "Super Tuesday," on March 3.