Tech
Stirling engine generates mechanical power by linking Earth’s warmth to space
Engineers at the University of California, Davis, have invented a device that can generate mechanical power at night by linking the natural warmth around us to the cold depths of space. The invention could be used, for example, to ventilate greenhouses or other buildings. The work is described Nov. 12 in Science Advances.
The invention is a type of machine called a Stirling engine. Other machines such as internal combustion engines generate power from a large heat gradient, said Jeremy Munday, professor of electrical and computer engineering at UC Davis and co-author on the paper. In contrast, a Stirling engine can work based on a small difference in temperature, such as that between a hot cup of coffee and its surroundings.
“These engines are very efficient when only small temperature differences exist, whereas other types of engines work better with larger temperature differences and can produce more power,” Munday said.
Typically, a Stirling engine is directly connected to a heat source on one side and a cooler environment on the other side.
“If you just set it on the table, it’s not going to produce any power on its own because all sides are the same temperature,” Munday said.
One way to generate a temperature difference, of course, is to heat up one side by burning fuel. Munday and graduate student researcher Tristan Deppe wondered if instead they could connect the cold side to something very, very cold but also very far away: deep space.
“It doesn’t actually have to touch space physically, it can just interact radiatively with space,” Munday said. It’s like standing outside on a cold, clear night: Your head will quickly start to feel cold as heat radiates away.
Deppe and Munday’s idea was to take a simple Stirling engine (essentially a piston driving a flywheel), put it on a panel that acts as a heat-radiating antenna and sit the whole thing on the ground outdoors at night. The ground acts as the warm side of the engine and the antenna channels the cold of space.
A year of night time experiments shows that the small device can indeed generate at least 400 milliwatts of mechanical power per square meter. The researchers used the device experimentally to directly power a fan and also coupled it to a small electrical motor to generate current.
The experiments show that it is possible to generate useful amounts of power from the night sky. The potential is greatest in areas where humidity is low and night skies are usually clear, Munday said. The principle could be used, for example, to ventilate greenhouses or residential buildings.
UC Davis has filed a provisional patent related to the work.
More information:
Tristan J. Deppe et al, Mechanical power generation using Earth’s ambient radiation, Science Advances (2025). DOI: 10.1126/sciadv.adw6833
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Stirling engine generates mechanical power by linking Earth’s warmth to space (2025, November 12)
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Tech
The Aventon Soltera 3 Is the Most Bikey Ebike on the Market Right Now
Belt-drive bikes offer some huge upsides. First, they usually require less maintenance, with many belts often lasting twice as long as a typical chain. Second, there’s no grease to speak of, and therefore, no black smudges on your work pants. Third, in the case of the Soltera 3, the belt comes from the Gates brand, whose drivetrain belts are as good as it gets. Belt-drive bikes are silent and often smoother than their chain-driven counterparts.
That said, the inclusion of a low-maintenance element such as a belt drive paired with hydraulic disc brakes, which require bleeding roughly every year, struck me as an odd choice. If Aventon wanted to make the Soltera 3 as hands-off as possible, cable-actuated brakes would have been a more intuitive choice.
The other thing that immediately jumps out about the Soltera 3 is its relatively light weight. At 37 pounds, the Soltera 3 is heavy for an analog bike. But it’s certainly not heavy for an ebike, and it’s nearly as stiff, nimble, and navigable as a conventional bicycle. One issue I’ve always had with ebikes is their heft. Given that they’re often made to replace a car, they’re built with load bearing in mind. Also, ebike batteries are heavy.
Adding to that sense of “this is just like my other bikes,” the Soltera 3 simply looks cool, which is often not the case when it comes to ebikes. The matte black my tester bike arrived in looks cool because matte black almost never doesn’t look cool. (Additionally, the Soltera 3 is available in dark matte blue and a sleek silver.) But beyond the finish, the bike’s geometry; its wide, almost perfectly flat handlebars; and its narrow (by ebike standards) 700 x 36 tires make it feel closer in DNA to a road bike than a traditional ebike.
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Photograph: Michael Venutolo-Mantovani
I’m 6′4′′, and the extra large Soltera 3 that I tested was at a maximum saddle height. It was suitable for me, but I couldn’t recommend anyone bigger than me riding the Soltera 3. That said, with four sizes ranging from small to extra large, the line covers a wide swath of riders, ranging from my height all the way down to 5′ tall.
Tech
Tin Can Is a Dumb Phone for Kids. Can Someone Teach Them How to Use It?
Chet Kittleson, 38, is the cofounder of Tin Can and a father of three kids, 10, 8, and 5. I suspect he wouldn’t much like my description of the product’s function as “spying” (keeping watch over one’s kids is part of a parent’s job) or the product itself as a “toy.” He thinks of it, instead, as a utility: a way for kids to talk to Grandma or make plans with friends and to be “part of the same world that grown-ups are a part of.” When he was a kid, he says, the landline was “arguably the most successful social network of all time.” Every house had one. Then came cell phones and smartphones. Direct lines to the internet. “And somewhere along the way we decided the landline was obsolete,” Kittleson says. “In doing that, we overlooked a group that was a major beneficiary of it: kids.”
I’m talking to him over Zoom one afternoon from my home in Los Angeles and his office in Seattle. When I tell him that Amos and Clara had called me more than two dozen times, he doesn’t seem particularly surprised. At first there’s a burst of activity, he says, and then over the course of a few weeks, the kids mature. “They’re like, oh, OK, I see that I can actually do things with this that are important,” he says.
Kittleson, who guesses that most Tin Can users are between the ages of 5 and 13, says he wants to help create a “better childhood” or, as he puts it, “giving kids back a sense of independence and confidence.” (Mike Duboe, a partner at Greylock Ventures, which led a round that invested $12 million in the company in October, says something similar.) One parent, describing their kid’s Tin Can use on X, wrote that it “felt like the old days.”
Amos and Clara weren’t the only ones who, over the holidays, got the gift of gab. In late December, frustrated parents flooded the company’s feedback forms and posted on Reddit that their Tin Cans weren’t working. Though the Tin Can engineers had anticipated a surge in usage around the holidays, the hundredfold increase in call volume took them by surprise.
When I ask Kittleson about the holiday meltdown, he winces. “It was a stressful Christmas,” he concedes. (A message on the Tin Can homepage said, “We’re investigating an issue impacting the network.”) He says that future shipments of the product will be staggered.
And the product’s far from perfect: There can be echoes, unstable sound quality, and long pauses. The buttons on the device are hard to press, which can be challenging to little fingers like Amos’. His mother, Rebecca, sometimes has to help him make calls. “It takes a little bit out of the independence of it,” she says.
My first phone, like that of other kids in my generation, was my family’s, a mustard yellow piece of hard plastic that sat on the mottled brown linoleum counter adjacent to the kitchen. It held a special place in my imagination—an object full of potential—but like most phones back then it was shared within a family and maybe even overheard or monitored. It was also tethered to a wall, making it difficult to multitask or move around while on a call. Kittleson, in fact, says that one inspiration for Tin Can was his frustration when he called his mother on her cell phone. She was, he says, “the worst”: the sort of person who ran around the house while on the call, doing laundry or whatnot. Difficult to hear. Easily distracted.
Tech
The Newest Google Pixel Phone Comes With a $100 Gift Card (for Now)
The Google Pixel 10a comes out on March 5, and right now, Amazon and Best Buy are both offering free $100 gift cards when you preorder. The phone’s price is $499, but the gift card sweetens the deal. It’ll be automatically added to your cart.
Amazon’s gift card is a physical one that ships with the phone; Best Buy’s is a digital gift card that will be sent to your email after your preorder is fulfilled. At Amazon, instead of the gift card, you also have the option of choosing a free pair of Pixel Buds 2a when you preorder. They are our favorite earbuds, but you probably don’t need them if you already have decent headphones.
The Google Pixel 10a isn’t super impressive compared to previous A-series smartphones. In fact, the Pixel 9a is still our favorite Android phone. The two phones are largely similar, even rocking the same chipset. The Pixel 10a does come in some new colors, though, like Fog and Lavender, and the phone is slightly thinner, with a less noticeable camera bump. The screen is a little brighter and a little more scratch-resistant, and the device is made with more recycled materials.
However, there are some software changes in the 10a compared to the 9a. The Pixel 10a is getting some of the same AI features as you’d find in the Pixel 10, plus support for AirDrop as well. The battery lasts up to 30 hours on a single charge, and the phone will have seven years of software and security updates. We can help you decide which Google Pixel to order, and if you decide on the 10a, these gift card deals are definitely worth it (especially if you were already planning on spending money at Amazon or Best Buy anyway).
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