What does 中 (zhōng) mean in 我哥哥是我认识的人中最沉着的一个? 我哥哥是我认识的人中最沉着的一个. I can understand the phrase but I don't see the meaning of 中 in the example. I have consulted in several places without success. Thanks
"中" is a shorter form of "之中" (within; among) 


  "我哥哥是我认识的人(中)最沉着的一个" = "我哥哥是我认识的人(之中)最沉着的一个"


我哥哥 = my brother

是 = is

我认识的人(之中) = (among) the people I know

最沉着的一个 = the calmest one