A friend’s call for help led Mykhailo Rudominski into defense work. His company, Himera, makes electronic warfare-resistant radios.

“Frankly, we wouldn’t be able to afford 420,000 square feet in downtown San Francisco,” said Keith Miao, the founder of Birdstop, a drone start-up in Detroit.

A tour of the Geothermal House of the CERAWeek energy conference in Houston this week. Geothermal energy is emerging as one of the big green winners of the current era.

The West Lake in Hangzhou, China. The city has become a hub for artificial intelligence start-ups, helped along by government subsidies and tax breaks.

Group14 Technologies, a start-up, slowed the construction of a battery materials factory in Moses Lake, Wash., after its customers in China balked at paying higher tariffs.

A screenshot of a recent TikTok from the dancer Melissa Becraft which used A.I to digitally superimpose a poster for Bubly, the sparkling water brand owned by PepsiCo, onto the wall of her apartment.

The new talks between Sam Altman and OpenAI’s board were the latest twist in a fast-moving drama at what is perhaps the world’s highest-profile artificial intelligence company.

The senior executives of OpenAI in March. From left, Mira Murati, now the company’s interim chief executive; Sam Altman, the ousted chief executive; Greg Brockman, OpenAI’s president who quit on Friday night; and Ilya Sutskever, a member of the company’s board.

A visualization of the rapidly-changing frequencies of the Himera military radio, which features signal-hopping technology that makes it difficult to jam.