It's the way to store energy in a place that protects it, packs it away, and keeps it for pregnancy and for nursing the baby, so it's very important from a reproductive point of view.

这样把能量储存在一个地方,保护起来,为怀孕和养育孩子备用,从生殖观点来看这是很重要的

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选

er is a vector at each point of length one pointing radially away from the center.

r 是一个模长恒为 1 的矢量,方向沿半径向外

耶鲁公开课 - 基础物理课程节选