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When people think of particle accelerators, they tend to think of giant structures: tunnels many miles long that electrons and protons race through at tremendous speeds, packing enormous energy.

But scientists in California think small is beautiful. They want to build an accelerator on semiconductor chips. An accelerator built that way won't achieve the energy of its much larger cousins, but it could accelerate material research and revolutionize medical therapy.

First of all, what is an accelerator?

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AILSA CHANG, HOST:

The Trump administration faces the same challenge as its predecessors: how to ensure the tens of thousands of unauthorized immigrant families who are apprehended each year show up for their immigration hearings. Trump wants to lock more of them up. Immigrant advocates want him to expand alternatives to detention, which are already widely in use.

Former White House press secretary Sean Spicer has words of praise for Sarah Sanders, his successor on the podium, and says she has figured out how to please President Trump in the job in a way he struggled to do.

"I think Sarah has done a great job of making sure that she understands what the president wants," Spicer told NPR's Mary Louise Kelly in an interview on Wednesday in advance of next week's release of his book The Briefing: Politics, the Press and the President.

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