What's the Atkinson cycle in a hybrid powertrain?

[auto123.com]

Aiming for superior fuel economy, a number of hybrid vehicles use an "Atkinson-cycle" engine, in reference to James Atkinson's thermodynamic cycle. A thermodynamic cycle is a mathematical tool illustrating how any engine works. The "Otto" cycle, for instance, is the cycle for a four-stroke gasoline engine.
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[midtoad]

Atkinson-cycle engines are about 10% more efficient than Otto-cyle engines (source: http://www.hybrid-vehicle.org/hybrid-vehicle-ice.html). So, you can get 10% better fuel economy at the price of 20% less power. When crude is at $150/bbl, that seems like a good trade-off. At