Experimental Stream (IMAGE) University of Pennsylvania Caption An experimental 'stream' -- a circular channel with varying sizes of particles and fluid embedded with fluorescent dye -- enabled the Penn team to examine the forces influencing the sorting of rocks in a riverbed. Credit University of Pennsylvania Usage Restrictions In context of reporting License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.