把函数$f\left(x\right)=\sin 2x$的图象向左平移$\frac{\pi }{4}$个单位，所得图像的解析式是（   ）

    I was playing in my kitchen. My mom stood in front of me, hardly keeping the tears from spilling over. She told me that my little cousin had cancer. Hearing this, I went completely numb. How could this be happening? I had just seen her, and she was fine.

    These things didn't happen to our family, that's what my uncle said. It seemed like the world turned upside down; just last week my grandmother had passed away. I felt like I couldn't get my feet on solid ground.

    That's when my sister, Ella, came down the stairs with her long brown hair freshly washed. She sat next to me and smiled. Despite what was happening, everything would work out, her smile seemed to say.

    “Mom, do you think I could get my hair cut tomorrow?” Ella asked.

    “Sure,” Mom said, starting to wash the dishes.

    “I want to donate it to Locks of Love” Ella smiled.

    My mom stopped washing and turned to look at her. “Are you sure?” I noticed that Mom was holding back tears. This was a sacrifice(牺牲) for Ella. Her long hair was an important part of her.

    “Yeah, it's just hair. Eventually it will grow back.” She said.

    “All right,” Mom said quietly, smiling again.

    Ella gave up a part of herself for a while. She let a piece of herself go to someone else, someone she didn't know. That day she became my hero too.

结合整段文字，以“曲率驱动”为开头，给“曲率驱动”下个定义，须包含概念产生和“曲率驱动”的原理、优点，不超过80个字。

曲率驱动是一个由于科幻电影《星际迷航》而变得流行一时的概念。一艘太空飞船，如果能够利用某种方式把它后面一部分空间烫平，以减小其曲率，那么飞船就会被前方曲率更大的空间拉过去。这样的飞船，其动力可以看成是由曲率提供的，这种驱动方式可以使飞船实现10倍光速飞行。

为什么飞船会被曲率更大的空间拉过去？这就像一条小船，在平坦的（即曲率为零）河流上航行，不会自动加速。但如果前方有一道瀑布（即曲率无穷大），则小船会很快加速。

1994年墨西哥物理学家明戈·阿尔库贝利提出了曲率驱动的概念。他设计了一个环状结构，可以让飞船四周的时空发生弯曲，前方空间曲率加大，后方空间变为平坦。然而计算显示这种装置需要无法达到的极高能量才能实现。