i and j are unit vectors in the x and y directions.

和 j 分别是 x 和 y 方向上的单位矢量

耶鲁公开课 - 基础物理课程节选

Unit vector i points away from the origin in the x direction.

单位矢量 i 从原点指向 x 轴正方向

耶鲁公开课 - 基础物理课程节选

At Llanidloes, the LHB plans to cut 18 beds, close an X-ray unit, a birthing centre and outpatient services.

BBC: NEWS | UK | Wales | Mid Wales | Town fights hospital service cuts

Two years later they lobbied the state legislature to allow them to add a recovery ward, X-ray unit and kitchen to convert the surgery center into a hospital.

FORBES: Magazine Article

One of the ships the Anastasis, is 522 feet long and has three operating theatres, a dental clinic and an X-ray unit and it has a ward with 38 beds.

BBC: NEWS | Health | ''Floating hospitals' mercy missions'