TikTok's For You Page (FYP) is the default home screen for users of the video-sharing platform. It's a personalized, algorithmically driven content feed, but the approach differs from other social media in that TikTok's algorithm relies heavily on implicit signals—such as how long users watch particular videos—as well as explicit signals such as likes or follows. And generally, that algorithm does remarkably well at predicting which videos will interest particular users.

But some users have voiced concerns that TikTok's almighty algorithm doesn't seem to incorporate negative feedback very well. Even when they don't watch a suggested video or click the "not interested" feature, they keep seeing those videos on their FYP. Northeastern University computer scientists put those suspicions to the test. According to their recent paper, the engagement signals do have an effect, but only temporarily. Then the algorithm gradually relapses unless a user consistently gives the same feedback over and over again.

The research group specializes in "algorithm audits," co-author Piotr Sapiezynski told Ars, to better understand online platforms: "how they work, how they fail, when they fail, how they harm individuals and societies." In this case, he and his co-authors wanted to take a closer look at user agency after hearing multiple anecdotal reports from TikTok users that their negative feedback—responding to prompts by indicating they aren't interested or want to see less of a certain kind of video—doesn't seem to remove those posts from their FYP. "On the other hand, it's unclear why the platforms would offer it, if it doesn't work," said Sapiezynski.

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The proliferation of nuclear power in space got a little more real Tuesday with the launch of a small satellite developed by a Florida-based company specializing in nuclear micro-power technology.

It's a long way from launching a bona fide nuclear reactor, a breakthrough that could help power a permanent Moon base and efficiently drive rockets throughout the Solar System. But you have to start somewhere.

The satellite from Miami-based City Labs is named BOHR, short for Betavoltaic Orbital High-Reliability, and it launched on a SpaceX rideshare mission Tuesday alongside 80 other payloads. SpaceX's Falcon 9 rocket released the BOHR satellite into an orbit between 350 and 400 miles (nearly 600 km) in altitude.

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One of the central features of plate tectonics is the formation of new crust at mid-ocean ridges. Part of the spreading process that drives continents apart, it was arguably the discovery of these ridges that drove widespread acceptance of plate tectonics as a theory. Thanks to decades of exploration, we now have a good picture of what the crust that forms at the site of spreading looks like. But we still have an incomplete idea of how its features are actually produced.

In other words, we have a good idea of the outcome of the process, but not a detailed picture of the process itself.

That is starting to change. In 2024, a team of French scientists was able to remotely monitor a major event on the border between the Australian and Antarctic plates, only two months after they installed equipment on the ocean floor. Their data shows that most of the spreading occurred in a relatively short time window, and some key events happened without any obvious seismic activity.

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US rare earths produced by Washington-backed companies are flowing to Japan and South Korea, as American demand has yet to materialize despite the Trump administration’s push to develop a national supply chain.

Rare earths products produced by MP Materials, Energy Fuels and Phoenix Tailings—which together have won billions of dollars in US government support—are being sold to companies in Asia, where the scale of magnet manufacturing remains larger than the nascent production in the US.

China’s lock on global supplies of rare earths and critical minerals has become a national security concern in the US and other Western nations, since Beijing started restricting access to them. The metals are crucial to 21st-century technology and are used in the manufacturing of everything from weapons guidance systems to electric vehicle batteries.

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