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.
Spectral analysis of Twitter activity (amplitude of the Fourier transform) of major urban areas (more cities in the electronic supplementary material). The dashed lines indicate (from left to right) the frequencies (q) corresponding to the periods of 24, 12 and 8 h respectively.
