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KNOW IT ALL: Tuesday's Top 6 Stories at NBC News

From the fallout over an Oklahoma fraternity's racist chant to a deadly chopper crash in Argentina, see the stories we're following.

Good morning. Here are some of the stories we’re following today:

1. With Oklahoma fraternity in the spotlight, do Greek bans work?

A new wave of crackdowns have grabbed the nation's attention, driven by growing sensitivity to campus violence and discrimination, pressure from authorities on sexual assault, liability issues and the power of social media. The latest example occurred last weekend at Oklahoma University, where officials shut down the Sigma Alpha Epsilon fraternity after members were caught on video chanting a racial slur. The school joins John Hopkins University, MIT, Duke and Texas Tech among many universities that took action in recent months against individual fraternities in response to allegations of rape or hazing. Read more in NEWS.

2. Argentina helicopter collision kills 10, including French Olympians

A trio of French sports stars were among 10 people killed when two helicopters filming a reality show collided in Argentina on Monday, according to officials. Adventure Line Productions confirmed the "terrible" accident, saying the collision took place shortly after takeoff as filming was getting underway on the second season of survival show, "Dropped." Olympic swimming gold medalist Camille Muffat, long-distance sailor Florence Arthaud and boxing champion Alexis Vastine were among those killed. Read more in NEWS.

3. Iran outraged over Republicans’ letter about nuke talks

Iranian Foreign Minister Mohammad Javad Zarif joined the chorus of outrage Monday, including the White House and Democrats, over the Senate Republicans' letter to the Tehran government about nuclear negotiations. Zarif said he was astonished that "some members of the U.S. Congress find it appropriate to write to leaders of another country against their own president and administration." The 47 Republican senators who signed the letter suggested to Iran that they can undo whatever President Barack Obama's administration agrees to in regards to a nuclear deal with the government. Read more in NEWS.

4. Poll: Nearly 60 percent looking for change in 2016

More Americans are clamoring for change in the upcoming 2016 presidential election than they were in the "Hope and Change" year of 2008, according to a new NBC News/Wall Street Journal poll. That desire for change is a potential roadblock for two of the leading frontrunners — Democrat Hillary Clinton and Republican Jeb Bush. But it might be a more significant challenge for Bush, the former governor of Florida, given that fewer than half of Republican primary voters believe he would provide new ideas and a vision for the future, versus nearly three-quarters of Democrats who think the same of Clinton. Read more in POLITICS.

5. Ferguson judge named in DOJ report resigns

A Ferguson municipal court judge — named in a scathing Justice Department report that showed a pattern of bias in the city's police force and courts — was replaced Monday by a state judge. Judge Ronald Brockmeyer informed the mayor and the city of Ferguson that he was resigning following the report's release, and the Supreme Court of Missouri announced it was transferring Judge Roy Richter to the St. Louis County Circuit Court instead. Richter will hear all of Ferguson's pending and future municipal division cases, officials said. Read more in NEWS.

6. 'Simpsons' co-creator Sam Simon dies after cancer battle

Simon, the co-creator of the long-running animated series, died following a battle with colorectal cancer, according to a statement released by his foundation Monday. He was 59. "It is with much sadness that we must let you know that Sam Simon has passed over," said a post on the Sam Simon Foundation Facebook page. "We take comfort in knowing how many greetings he is receiving across that Rainbow Bridge. We love you Sam!" Read more in POP CULTURE.

And now this ...

A plane has begun a trip to become the first round-the-world flight powered by nothing but the sun.