Forty years ago Tuesday, President Richard Nixon became the first U.S. president to visit China. Renee Montagne looks back on that day in 1972.

Rhythm in music is about timing — when notes start and stop. And now scientists say they've found a curious pattern that's common to musical rhythm. It's a pattern also found in nature.

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Some new research throws into question things we say all the time about the Internet. The research focuses on Twitter, the service that lets many millions of people send short messages to each other from computers or cell phones. It's commonly said that social networking like this is revolutionary, that it's created new communities, even that it's obliterated geography. You can connect with people who share common interests, not just people who happen to live nearby. NPR's Shankar Vedantam is here to explode all that. Hi, Shankar.

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RENEE MONTAGNE, HOST:

This is MORNING EDITION, from NPR News. I'm Renee Montagne.

STEVE INSKEEP, HOST:

And I'm Steve Inskeep. Good morning.

One more Arab nation is changing a longtime leader. Yemen's president for 33 years was Ali Abdullah Saleh. Today, millions of Yemenis vote. And they're being asked to ratify a plan under which Saleh's vice president will replace him. NPR's Kelly McEvers is in Yemen's capital Sana'a.

And, Kelly, where exactly are you in the capital city?

The March issue of the medical journal Pediatrics features an editorial looking at gender identity disorder in children. Pediatricians apparently are seeing more young patients who express an interest in changing their gender.

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(SOUNDBITE OF SONG, "SWING LOW, SWEET CHARIOT")(Singing) Swing low, sweet chariot, coming for to carry me home. Swing low...) Transcript provided by NPR, Copyright National Public Radio.

Tension has been high in the Maldives after Mohamed Nasheed resigned as president earlier this month. He later claimed that he was the victim of a coup, but his successor denies this. Nasheed talks to Renee Montagne about his situation, and what it means for the Indian Ocean islands.

The film Saving Face is nominated for an Oscar. It chronicles the lives of acid-attack survivors in Pakistan. Filmmaker Sharmeen Obaid Chinoy talks to Renee Montagne about what happens to some of the victims.

Steve Inskeep has the Last Word in business.