The temperature of Earth’s surface is generally pretty stable, but it has to let heat off somehow. When heat waves rise off a sidewalk, for example, they dissipate into cooler air. That cooling process eventually reaches the upper atmosphere and then the cold, lifeless environs of space, in a process called radiative sky cooling. Scientists want to use the principles behind radiative sky cooling to create a low-cost energy source that could help people all over the world who lack stable electricity.

“This effect occurs naturally all the time, especially on clear nights,” says study author Aaswath Raman, an assistant professor of materials science and engineering at the UCLA Samueli School of Engineering, in a press statement. “The result is that the object ejecting the heat, whether it’s a car, the ground or a building, will be slightly cooler than the ambient temperature.”

Radiative sky cooling occurs wherever there’s a ground and a sky. A surface facing the sky will eventually eject some of its heat, and that rejection takes the form of thermal radiation.

The air of Earth’s atmosphere doesn’t have as stable a temperature as the ground. The UCLA team’s technology uses those temperatures differences to their advantage. It captures some of the heat from the surrounding air that would otherwise rise into the sky. That heat is then converted it into electricity.

Facebook has updated its “Portal” range of video chat devices, including a new version that plugs directly into a TV.

Portal TV, available in the US from November, sits on top of – or at the bottom of – the screen and, like other Portal devices, features tracking technology to follow people around the room.

But the company also revealed it had resumed the use of human contractors to review and transcribe audio clips gathered through its Portal devices.

Data collection and storage was suspended last month following controversy over the practice, which some argued was not properly disclosed to users.

But. as of Wednesday, clips gathered through the use of Portal’s voice assistant would again be heard and analysed by humans, unless users choose to opt out. Human review of audio captured by Facebook’s Messenger mobile app was still “paused”, the firm said.

“The new settings begin to roll out tomorrow on existing Portal devices,” a spokeswoman said.

“Everyone will get a notification that explains how your ‘Hey Portal’ voice interactions are used and directs you to settings if you want to turn off storage.”

The audio does not include the content of calls made on the device, Facebook added.

Gatwick has become the UK’s first airport to confirm it will use facial-recognition cameras on a permanent basis for ID checks before passengers board planes.

It follows a self-boarding trial carried out in partnership with EasyJet last year.

The London airport said the technology should reduce queuing times but travellers would still need to carry passports.

Privacy campaigners are concerned.

On Tuesday, a spokeswoman for Gatwick told BBC News it had taken the decision, first reported by the Telegraph newspaper, after reviewing feedback from passengers in the earlier test.

“More than 90% of those interviewed said they found the technology extremely easy to use and the trial demonstrated faster boarding of the aircraft for the airline and a significant reduction in queue time for passengers,” she said.

“Gatwick [is now planning] a second trial in the next six months and then rolling out auto-boarding technology on eight departure gates in the North Terminal when it opens a new extension to its Pier 6 departure facility in 2022.”

She added passengers would still need to pass through the bag-check security zone, at which point they would need to present a boarding pass.

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In addition, they would need to scan their passport at the departure gate for the system to be able to match the photo inside to their actual face.

The process is similar to that already used at the ePassport arrival gates at some UK airports. But it differs from Gatwick’s original test, where travellers scanned their faces at the luggage drop-off zone.

Consent concerns

That decision will limit Gatwick’s ability to use facial recognition for other services.

China’s Chengdu Shuangliu airport, for example, recently installed a system that automatically presents travellers with up-to-date information about their flights when they walk up to a screen. This is made possible because visitors have to present their passports at an earlier stage

Even so, one civil liberties group is worried travellers might not realise they can opt out.

“Our main concern… would be the issue of proper consent,” said Ioannis Kouvakas, from Privacy International.

“Placing general or vague signs that merely let individuals know that this technology is being deployed, once individuals are already inside the check-in area, is inadequate, in our view, to satisfy the strict transparency and consent requirements imposed by data-protection laws.

“If this would apply to child travellers… it raises even more concerns, considering the special protection afforded to children’s privacy and the risks associated with having their biometrics taken by the airport private entities.”

A spokeswoman for Gatwick said it had designed its use of the technology to be “compliant with all data protection law” and passengers would be able to choose to have their passports checked by human staff.

“Our next passenger trial will take place in the next six months and no data will be stored – instead it will be held momentarily while the identity check takes place, only a matter of seconds,” she said.

Children under a certain age would need parental or guardian consent, she added, although Gatwick had still to determine what the cut-off point would be.