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.
Overlay visualization: (a) keywords based on their occurrences and average publication per year scores; (b) Cluster 1 with 31 keywords; (c) Cluster 24 with three items; (d) Cluster 5 with 14 items. Individual circle sizes indicate the relative frequency of occurrence of each keyword.
