In 2008, Forbes named Indianapolis as one of its “Ten Best Cities for Jobs,” and CNBC called Indiana the “most improved state for business.” Detroit, by contrast, has continued its decline. It has one of the highest foreclosure rates in the country; swaths of abandoned buildings illustrate the metaphor of a broken city. Although New Orleans and Camden, N.J., bumped Detroit from first place to third in a 2008 list of the most-dangerous cities in America, Detroit is still invoked as a preternatural example of urban blight...

http://americancity.org/daily/entry/1425/
向量张量纯量喜欢加乘不喜欢减除
ReplyDelete功能原理.移項法則->W(力場作正功)=deltaEk(動能之增加)=-ΔU(位能之減少)
機械能守衡.加減法原理->deltaEk+deltaUs.deltaUg=0彈.重力場
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