Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Title word co-occurrence network. Nodes are sized relative to the number of times the word occurs (range 5–72). Nodes representing words that occur 15 or more times are colored blue. Edges are sized and colored relative to the number of papers in which the two words co-occur (range 5–51) (color figure online)
