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.
An experimental arena is composed of three layers of acryl, blue sand (left side), yellow sand with preformed tunnel, and entrance hole (circle on the right). Experimental arena design (a). An example of an arena before (b), and after (c) the experiment. Deposited sand particles in an enlarged view (d). Black arrows in d) indicate deposited sand particles after excavation in the blue sand area
