Ahead of 2+2 dialogue, US official says no change in H-1B visa policy

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.

Jan 23: Hundreds of Central Americans trying to reach the United States were stuck at the Mexico-Guatemala border on Wednesday after the Mexican government beefed up security to meet US demands to contain migrant flows.

Under sustained pressure from President Donald Trump, Mexico's government has adopted tougher measures to reduce the number of people heading towards the U.S. border.

Migrants in Tecun Uman, on the Guatemalan side of the border, were taken by surprise.

"We thought we'd be allowed through just like with the October caravan when they reached Tijuana," said Honduran migrant Ritzy Anabel, who did not give her surname.

"People from Mexico and Guatemala treated them well. But now it's changed because Mexicans don't want (us) to enter."

Many Central Americans migrants heading north are fleeing economic hardship and violence at home. A large caravan of migrants crossed into Mexico and went north in October 2018. Migrants crossing into Mexico earlier this week faced tear gas from security forces, who delivered a firmer response than in previous mass movements at the border.

Even so, about 1,000 migrants, most of them from Honduras, managed to reach Mexican soil on Tuesday. Mexican Foreign Minister Marcelo Ebrard said several hundred of the new arrivals were immediately deported on planes and buses.

On Wednesday, Mexican authorities said that 460 Honduran migrants were deported throughout the day. Other migrants from the group, including families traveling with children, were pondering their next moves.

Honduran Carlos Amador said that while some of his compatriots were returning home, others were hoping for positive news.

Trump has repeatedly threatened to punish Mexico and Central American countries if they fail to clamp down on the migrant flows. That has resulted in a series of agreements aimed at delivering on Trump's campaign promises to curb immigration.

Department of Homeland Security Acting Secretary Chad Wolf called the measures put in place by the Mexican National Guard "effective", adding that dozens of his personnel was on the ground in Central America assisting local immigration and security officials. Trump tweeted: "Sorry, if you come you will be immediately sent back!"