Ni : Average population density in area i. To simplify the analysis, Earth’s surface is divided into a grid of squares i, and the distribution is assumed to be uniform in each.

Ni：指i区的平均人口密度，为了简化分析，地球表面被按照网格分成多个i区，每个区的分布假定是统一的。

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LIPA's grid operator, National Grid, has assumed communications responsibilities from LIPA, following harsh critiques of LIPA by New York state and residents for the utility's communications during Sandy.

WSJ: Officials Urge Caution as Snow Starts Falling