Google is rolling out a second-generation Nexus 7 tablet designed for improved performance and portability, featuring the company's just-announced mobile operating system, Android Jelly Bean 4.3. The device offers numerous enhancements over the original Nexus 7 tablet that Google released last year. It is also the first device to ship with Android Jelly Bean 4.3, the latest version of Google's mobile OS, the company announced Wednesday.