Episode Titles: Fluctuation

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  The Electric Can Opener Fluctuation
  Season 3, Episode 1 - Aired September 21, 2009

  After the gang return from their Arctic expedition, Sheldon is stunned to learn that the guys manipulated his data and invalidated his research. Fearing his scientific reputation has been ruined, Sheldon retreats to his mother's house in Texas. Meanwhile, Leonard catches up with Penny after his summer away, but just as it seems like a relationship is about to start, Leonard must fly to Texas to bring Sheldon home.
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  The Good Guy Fluctuation
  Season 5, Episode 7 - Aired October 27, 2011

  Leonard and Priya's long-distance relationship is put to the test when Leonard meets a cute comic book artist and finds himself drawn to her. Meanwhile, Sheldon tries to get revenge on the guys after they pull a Halloween prank on him.
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  The Decoupling Fluctuation
  Season 6, Episode 2 - Aired October 4, 2012

  When Penny has doubts about her relationship with Leonard, Sheldon comes to his buddy's defense and tries to convince Penny to stay with Leonard. Meanwhile, at the International Space Station, the other astronauts are picking on Howard, and Stuart joins the social group in his absence.
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  The Collaboration Fluctuation
  Season 10, Episode 19 - Aired March 30, 2017

  When Penny and Raj start spending more time together now that Raj has moved into the apartment, Leonard starts to feel like a third wheel.

  Meanwhile, Sheldon's interest in Amy's work leads them to collaborate, but they soon find they can only work well together when they're at each other's throats.